A method for designing a diffraction grating lens of the present invention is a method for designing a diffraction grating lens having a diffraction grating composed of a plurality of diffraction zones, the method including the steps of: (a) determining widths of the plurality of diffraction zones; and (b) determining an aspherical coefficient of a diffraction surface on which the diffraction grating is provided while the determined widths of the plurality of diffraction zones are fixed, after the step (a).

It is widely known that a diffraction grating lens whose surface has a pattern of diffraction zones is superior in correcting lens aberrations, such as field curvature and chromatic aberration (misalignment of convergence points between different wavelengths). This is because a diffraction grating has peculiar characteristics, such as inverse dispersiveness and abnormal dispersiveness, providing a significant chromatic aberration correcting capability. In a case where a diffraction grating is used in an image pickup optical system, as compared to an image pickup optical system formed only by an aspherical lens, it is possible to reduce the number of lenses for the same performance. Therefore, it is possible to reduce the manufacturing cost and to shorten the optical length, thus allowing for reduction in height.
FIG. 30 shows a method for deriving a diffraction grating surface shape of a diffraction grating lens. Note that a diffraction grating lens is designed primarily by the phase function method or the high refractive index method. While the phase function method will be discussed herein, the same results are obtained eventually also when the design is done by a high refractive index method. A diffraction grating lens is formed by an aspherical shape (FIG. 30(a)), which is the base shape, and a diffraction grating shape determined by the phase function (FIG. 30(b)). The phase function is represented by Exp. 1 below.
                                                                                ϕ                                            (                r                )                                      =                                                            2                                    π                                                  λ                  0                                                                          ψ                                                  (                  r                  )                                                                                ψ                                            (                r                )                                      =                                                            a                  1                                                r                            +                                                a                  2                                                                  r                  2                                            +                                                a                  3                                                                  r                  3                                            +                                                a                  4                                                                  r                  4                                            +                                                a                  5                                                                  r                  5                                            +                                                a                  6                                                                  r                  6                                            +              …              +                                                a                  i                                                                                r                    i                                                                                (                                                            r                      2                                        =                                                                  x                        2                                            +                                              y                        2                                                                              )                                                                                [                  Exp          .                                                    1                ]
In Exp. 1, φ is the phase function, Ψ is the optical path difference function, r is the distance in the radial direction from the optical axis, λ0 is the design wavelength, and a1, a2, a3, a4, a5, a6, . . . ai are coefficients.
In the case of a diffraction grating utilizing first-order diffraction light, one diffraction zone is arranged each time the phase is equal to 2π in the phase function φ(r), as shown in FIG. 30(b). The diffraction grating surface shape is determined as shown in FIG. 30(c) by adding the phase shape which has been cut into pieces arranged every 2π, to the aspherical shape of FIG. 30(a). Specifically, the value of the phase function of FIG. 30(b) is converted so that the step height 241 of the diffraction zone forming portion satisfies Exp. 2 below, and is added to the aspherical shape of FIG. 30(a).
                    d        =                                            m              0                        ·            λ                                                              n                1                                                          (                λ                )                                      -            1                                              [                  Exp          .                                                    2                ]
Herein, mo is the design order (mo=1 for first-order diffraction light), λ is the working wavelength, d is the step height of the diffraction grating, and ni(λ) is the refractive index of the lens base at the working wavelength λ and is a function of the wavelength. With such a diffraction grating that satisfies Exp. 2, the phase difference is 2π between the base and the tip of the diffraction step portion, and the diffraction efficiency of first-order diffraction light for single-wavelength light (hereinafter referred to as the "first-order diffraction efficiency") can be substantially 100%.
In accordance with Exp. 2, the value d changes, for which the diffraction efficiency becomes 100% as the wavelength λ varies. That is, if the value d is fixed, the diffraction efficiency does not become 100% at wavelengths other than the wavelength λ which satisfies Exp. 2. However, where a diffraction grating lens is used in a general photograph-taking application, it is necessary to diffract light over a wide wavelength range (e.g., the visible light range from a wavelength of about 400 nm to about 700 nm, etc.). Therefore, there occurs diffraction light 256 of an unnecessary order (hereinafter referred to also as the "unnecessary-order diffraction light") in addition to the main, first-order diffraction light 255, as shown in FIG. 31. For example, if the wavelength with which the step height d is determined is set to the green wavelength (e.g., 540 nm), although the first-order diffraction efficiency at the green wavelength is 100% and there occurs no unnecessary-order diffraction light 256 of the green wavelength, the first-order diffraction efficiency is not 100% at the red wavelength (e.g., 640 nm) or the blue wavelength (e.g., 440 nm) and there occurs zero-order diffraction light of red or second-order diffraction light of blue. The zero-order diffraction light of red or the second-order diffraction light of blue is the unnecessary-order diffraction light 256, which may spread across the image surface in the form of a flare or a ghost to deteriorate the image or may lower the MTF (Modulation Transfer Function) characteristics. Only second-order diffraction light is shown in FIG. 31 as the unnecessary-order diffraction light 256.
It is possible to suppress the occurrence of the unnecessary-order diffraction light 256 by applying or attaching, as an optical adjustment film 261, an optical material having a different refractive index and a different refractive index dispersion from a lens base 251 onto the surface on which a diffraction grating 252 has been formed, as shown in FIG. 32. Patent Document No. 1 discloses an example in which the wavelength dependency of the diffraction efficiency is reduced by setting the refractive index of the base material on which the diffraction grating 252 has been formed and the refractive index of the optical adjustment film 261 formed to cover the diffraction grating 252 so as to satisfy a particular condition. Then, it is possible to eliminate the flare due to the unnecessary-order diffraction light 256 as shown in FIG. 31.
Patent Document No. 2 discloses providing a light-absorbing portion in the vicinity of the base portion of the slope surface of a diffraction zone, thereby blocking the reflected light from the step surface by the light-absorbing portion, in order to prevent the reflected light at a step surface 262 of the diffraction grating 252 from passing through the blazed surface and becoming flare light.
When designing a diffraction grating lens, it is common to vary and optimize simultaneously the phase function of the diffraction grating surface and the aspherical shape thereof as parameters. This is because the optical performance of the diffraction grating lens as a whole is not determined by adding together the phase function and the aspherical shape as separate parameters, but is determined as a result of these parameters influencing each other in a complicated manner. Thus, designing a lens while simultaneously optimizing the phase function and the aspherical shape is expected to improve the image-capturing performance as compared with a case where the phase function and the aspherical shape are individually optimized one after another.

Method for designing and method for manufacturing diffraction-grating lens

Panasonic Intellectual Property Management Co., Ltd.


Adhesive compositions suitable for use as tie-layer adhesives in multi-layer films and sheets are provided. The adhesive compositions contain an olefin polymer base resin, a modified polyolefin and a paraffinic liquid hydrocarbon.

Multilayer film structures containing barrier films are frequently used in the food packaging industry for products such as snack foods, meats and cheeses. In these applications, it is desirable for the multilayer structure to demonstrate good adhesion characteristics and clarity. Inferior adhesion properties can result in de-lamination of the film layers in the manufacturing process or in the end-use product. Clarity is an important aesthetic property having direct influence on consumers. Tie layers are often incorporated in multilayer film structures to adhere dissimilar layers which cannot be bonded directly, however, conventional efforts to improve adhesion provided by the tie layer, such as by increasing the level of grafted material in the tie layer composition, can result in a corresponding deterioration in clarity. This unfortunate result can sometimes occur in applications using an ethyl vinyl (ethylenevinyl or ethylene-vinyl) alcohol copolymer ("EVOH") barrier layer, where undesirable chemical interaction between the maleic anhydride functionality of the tie layer resin and the EVOH functionality of the barrier layer result in a distorted appearance in the product film, typically described as "orange peel" or "grainy." Clarity can also be affected in the process by which film layers are coextruded, when differences in the viscosities of the molten resins making up adjacent layers cause stress at the layer interface, leading to weavy-type flow instability.
Various adhesive mixtures have been described in U.S. Pat. Nos. 4,087,587; 4,298,712; 4,487,885; 4,774,144, 5,367,022, 5,439,974, 5,525,672, 5,597,865, 6,716,928, 6,838,520, 7,125,929 and Pat. Appl. Pub. Nos. 2007/0054142, 2008/0032148 and 2008/0163978. Nevertheless, a continuing need exists for tie layer adhesive compositions in multilayer film applications that provide improved adhesion, while minimizing deterioration in, or improving, film clarity. It has unexpectedly been found that mixtures of an olefin polymer base resin, modified polyolefin and a paraffinic liquid hydrocarbon provide a superior balance of adhesion and clarity in tie layer compositions.

This patent is subject to a terminal disclaimer.


An article of footwear includes a footwear upper and a sole assembly secured to the footwear upper. The sole assembly has a heelward portion and a toeward portion, and includes a deck assembly disposed substantially in the heelward portion of the sole assembly. The deck assembly includes an upper deck portion, a lower deck portion spaced from the upper deck portion, and right and left supports attached to respective right and left portions of the upper and lower deck portions substantially near respective right and left lateral edges of the upper and lower deck portions. The deck assembly defines a cavity between the upper and lower decks. The deck assembly directs translation of ground contact forces incurred by the heelward portion of the sole assembly at least partially laterally outwardly.

In general, shoes, a type of articles of footwear, include an upper portion and a sole. When the upper portion is secured to the sole, the upper portion and the sole together define a void that is configured to securely and comfortably hold a human foot. Often, the upper portion and/or sole are/is formed from multiple layers that can be stitched or adhesively bonded together. For example, the upper portion can be made of a combination of leather and fabric, or foam and fabric, and the sole can be formed from at least one layer of natural rubber. Often materials are chosen for functional reasons, e.g., water-resistance, durability, abrasion-resistance, and breathability, while shape, texture, and color are used to promote the aesthetic qualities of the shoe.


An aqueous non-melt processible polytetrafluoroethylene dispersion having non-melt processible polytetrafluoroethylene particles in an amount of 30 to 70% by weight and an amount of non-ionic surfactant between 2 and 15% by weight based on the weight of polytetrafluoroethylene solids. The dispersion is free of fluorinated surfactant or contains fluorinated surfactant in amounts of not more than 200 ppm based on the amount of polytetrafluoroethylene solids. At least part of the non-melt processible polytetrafluoroethylene particles comprise an effective amount of ionic end groups in the polytetrafluoroethylene polymer chains.

Fluoropolymers, i.e. polymers having a fluorinated backbone, have been long known and have been used in a variety of applications because of several desirable properties such as heat resistance, chemical resistance, weatherability, UV-stability etc. The various fluoropolymers are for example described in "Modern Fluoropolymers", edited by John Scheirs, Wiley Science 1997. The fluoropolymers may have a partially fluorinated backbone, generally at least 40% by weight fluorinated, or a fully fluorinated backbone. Particular examples of fluoropolymers include polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) (FEP polymers), perfluoroalkoxy copolymers (PFA), ethylene-tetrafluoroethylene (ETFE) copolymers, terpolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV) and polyvinylidene fluoride polymers (PVDF).
In particular PTFE dispersions have found wide applications because of the unique and desirable chemical and physical properties of PTFE. For example, PTFE dispersions are frequently used in preparing coating compositions for coating metal substrates such as cookware because of the high temperature resistance of PTFE and anti-stick properties. The chemical resistance and corrosion resistance of PTFE have been exploited in industrial applications such as in chemical manufacturing plants. Because of its unrivalled weathering stability, PTFE has further been used for coating woven glass cloth for architectural fabrics. Details on fabrication and processing of PTFE-dispersions can be found in Fluoroplastics, Vol. 1, "Non-melt processible fluoroplastics", p. 168-184, Sina Ebnesajjad, Plastics Design Library, Norwich, N.Y. 13815, publ. 2000.
Aqueous dispersions of PTFE are typically obtained by aqueous emulsion polymerization. The aqueous emulsion polymerization is typically carried out in the presence of a non-telogenic fluorinated surfactant. Frequently used fluorinated surfactants include perfluorooctanoic acids and salts thereof, in particular ammonium perfluorooctanoic acid. Further fluorinated surfactants used include perfluoropolyether surfactants such as disclosed in EP 1059342, EP 712882, EP 752432, EP 816397, U.S. Pat No. 6,025,307, U.S. Pat. No. 6,103,843 and U.S. Pat. No. 6,126,849. Still further surfactants that have been used are disclosed in U.S. Pat. No. 5,229,480, U.S. Pat. No. 5,763,552, U.S. Pat. No. 5,688,884, U.S. Pat. No. 5,700,859, U.S. Pat. No. 5,804,650, U.S. Pat No. 5,895,799, WO 00/22002 and WO 00/71590. The aqueous emulsion polymerization method to produce PTFE is well known and is described in for example U.S. Pat. No. 2,434,058, U.S. Pat. No. 2,965,595, DE 25 23 570 and EP 030 663.
Aqueous emulsion polymerization of TFE is also used at industrial scale for making fine resin powders, so called paste ware. For making fine resin powders, core-shell polymerization is widely used to achieve certain properties of the resin powders and end-use properties of articles made thereof. Generally speaking, core-shell polymerization produces very high molecular weight polymer in the shell and significantly lower molecular weights in the core of the resin powder particles.
Core-shell polymerization of PTFE has also been described to improve certain properties of PTFE. For example, core-shell polymerization of PTFE is described in U.S. Pat. No. 2,965,595, U.S. Pat. No. 3,142,665 and EP 525 660. EP 481 509 discloses a core shell polymerization to obtain PTFE that has good blending and dispersing properties in a resin, an elastomer or a paint. It is taught in this patent that the shell of the PTFE particles should have a molecular weight of about 10,000 to 800,000 g/mol. A chain transfer agent is typically used to achieve the low molecular weight in the shell of the core shell particles.
WO 02/072653 teaches core shell PTFE dispersions that contain at least 1.5% by weight of rod-shaped PTFE particles that have a length to diameter ratio of at least 5. The majority of PTFE particles in the dispersion are cylindrical, i.e., having a length to diameter ratio of 1.5 or more. It is taught that such dispersions have an enhanced shear stability combined with a high critical cracking thickness. However, to produce non-spherical particles the polymerization conditions need to be carefully controlled. Moreover, WO 02/072653 teaches the use of a telogenic agent during the last stage of the polymerization, which will result in producing a substantial amount of very low molecular weight PTFE and which might potentially compromise the desirable properties of PTFE.
Following the aqueous emulsion polymerization, the obtained dispersion is generally further upconcentrated to yield the desired fluoropolymer solids, which is typically between 40 and 70% by weight. Methods of upconcentration include for example thermal upconcentration, ultrafiltration as disclosed in U.S. Pat. No.4,369,266 and decantation as disclosed in U.S. Pat. No. 2,037,953. Generally, the dispersions are upconcentrated in the presence of a stabilizing surfactant such as a non-ionic surfactant.
Because of some environmental concerns that have been raised against the presence of the fluorinated surfactants typically used in the aqueous emulsion polymerization and because such surfactants are fairly expensive, methods have been developed to remove and recover the fluorinated surfactant from aqueous fluoropolymer dispersions, including PTFE dispersions. A particularly effective method for recovering fluorinated surfactants from a PTFE dispersion has been disclosed in WO 00/35971. This method involves contacting the fluoropolymer dispersion with an anion exchanger whereby the fluorinated surfactant binds to the anion exchange resin and is thus effectively removed from the aqueous dispersion. The fluorinated surfactant will generally bond to the anion exchange resin as a result of physical adsorption and to the ion exchange sites where it will replace the anions of the resin. Typically, this method achieves a residual amount of fluorinated surfactant of not more than 100 ppm and frequently not more than 50 ppm of fluorinated surfactant based on the weight of fluoropolymer solids.
In many applications, the PTFE dispersion resulting after polymerization and upconcentration are combined with further additives or components to produce a final composition. For example, in metal coating, in particular for coating cookware, the final composition may be obtained by further blending heat resistant polymers such as polyamide imide, polyimide or polyarylen sulphide with the PTFE dispersion. Still further ingredients such as pigments and mica particles may be added as well to obtain the final coating composition for coating metal. Such additional components are typically dispersed in organic solvents such as toluene, xylene or N-methylpyrrolidone. The fluoropolymer dispersions typically represent about 10 to 80% by weight of the final composition. Coating compositions for metal coatings and components used therein have been described in e.g. WO 02/78862, WO 94/14904, EP 22257 and U.S. Pat. No. 3,489,595.
It has now been found that when PTFE dispersions having no or little fluorinated surfactant, are used to prepare final coating compositions as for example described above, coagulation may occur during preparation of the final coating composition, in particular when the level of fluorinated surfactant is very low. Also, problems may arise in the application of the final coating composition to a substrate such as for example a metal substrate for cookware. For example, when spraying such a coating die clogging occurred after some time. Furthermore, coagulation occurred in the pumping system, pumping the dispersion to a coating station for coating for example glass fabrics. Still further, coagulation in the dispersion may occur when excess coating composition is removed by doctor blades.
Thus, notwithstanding the excellent storage stability of aqueous PTFE dispersions from which the fluorinated surfactant has been removed, such dispersions present coagulation problems in the preparation and/or application of the final coating compositions in which they are combined with further coating ingredients.
Accordingly, it is desirable to overcome or at least to reduce the aforementioned problems. Desirably, the aforementioned problems are reduced or resolved without impairing or substantially impairing the good mechanical and physical properties of PTFE and coatings produced therewith. Preferably the solution should be easy and convenient and should be cost effective and environmentally friendly.
Disclosure
In accordance with the present invention there is provided an aqueous non-melt processible polytetrafluoroethylene dispersion comprising non-melt processible polytetrafluoroethylene particles in an amount of 30 to 70% by weight and an amount of non-ionic surfactant between 2 and 15% by weight, preferably 3 to 12% by weight based on the weight of polytetrafluoroethylene solids, wherein the dispersion is free of fluorinated surfactant or contains fluorinated surfactant in amounts of not more than 200 ppm based on the amount of polytetrafluoroethylene solids. At least part of the non-melt processible polytetrafluoroethylene particles comprise an effective amount of ionic end groups in the polytetrafluoroethylene polymer chains such that an aqueous dispersion thereof having the following composition:    58% by weight of the non-melt processible polytetrafluoroethylene particles having said effective amount of ionic end groups;    an amount of 5% by weight based on the total weight of solids of non-ionic surfactant consisting of polyethylene glycol mono [4-(1,1,3,3-tetramethylbutyl)phenyl] ether having an average of 9-10 ethylene oxide groups (available as TRITON™ X-100);    less than 100 ppm of fluorinated surfactant;    and having a conductivity of at least 500 μS/cm;has a shear stability of at least 3 minutes, preferably at least 4 minutes when the average particle diameter of the polytetrafluoroethylene particles is 150 nm or more, or a shear stability of at least 4 minutes, preferably at least 5 minutes when the particle size is less than 150 nm and wherein the shear stability is measured by stirring 150 g of the aqueous dispersion with 2 g of xylol at a temperature of 20° C. and a stirring rate of 8000 rpm.
By the term "non-melt processible polytetrafluoroethylene" is meant that the melt viscosity of the polytetrafluoroethylene is so high that conventional melt processing equipment cannot be used to process the polytetrafluoroethylene. This means in general that the melt viscosity is >1010 Pa·s. The aqueous dispersions according to the invention can offer such advantages as being more environmentally friendly because of a low amount of fluorinated surfactant combined with less problems of coagulation during preparation and/or application of a final coating composition in which the dispersions are combined with further components and in particular organic solvents. The dispersions may be conveniently and cost effectively produced.
Thus, the present invention in a further aspect provides a method of making an aqueous dispersion of non-melt processible polytetrafluoroethylene, the method comprising:
(a) an aqueous emulsion polymerization of an amount of tetrafluoroethylene to produce a final amount of polytetrafluoroethylene solids and optionally up to 1% by weight based on the amount of tetrafluoroethylene of a perfluorinated comonomer, wherein said aqueous emulsion polymerization is initiated with a free radical initiator and the polymerization is carried out in the presence of a fluorinated surfactant, and wherein before completing the feeding of said amount of tetrafluoroethylene but after feeding at least 80% by weight of said amount of tetrafluoroethylene, free radicals capable of introducing ionic end groups or precursors thereof in the polytetrafluoroethylene polymer are caused to be formed at a rate that without counter measures would cause an increase in the polymerization rate of at least 20%;
(b) reducing the amount of fluorinated surfactant in the thus obtained aqueous dispersion to an amount of not more than 200 ppm, preferably not more than 100 ppm and more preferably not more than 50 ppm based on the amount of polytetrafluoroethylene solids.
Polymerization Process
The aqueous dispersions of PTFE are produced using an aqueous emulsion polymerization of TFE. PTFE produced in accordance with the present invention includes modified PTFE and accordingly, the polymerization may optionally involve the use of a perfluorinated comonomer such as, for example, a perfluorinated vinyl ether or a perfluorinated C3-C8 olefin such as for example hexafluoropropylene. The term 'perfluorinated monomer' as used in connection with the present invention not only includes monomers consisting of carbon and fluorine atoms but also includes monomers in which some of the fluorine atoms are replaced by chlorine or bromine such as for example in chlorotrifluoroethylene. Nevertheless, a perfluorinated monomer in connection with the invention should not have hydrogen atoms in the molecule. The amount of such optional comonomer(s) should generally not exceed 1% by weight of the total amount of monomer feed. If the amount would be more than 1%, the resulting PTFE will likely be melt-processible and would no longer conform to the ISO 12086 standard defining non-melt processible PTFE.
The aqueous emulsion polymerization is carried out in the presence of a fluorinated surfactant. An effective amount of fluorinated surfactant should typically be used to sufficiently stabilize the PTFE particles and to obtain a desired particle size of the PTFE particles. The amount of fluorinated surfactant is generally between 0.03 and 1%, preferably between 0.08 and 0.5% by weight relative to the amount of water used in the aqueous emulsion polymerization.
Any of the fluorinated surfactants known or suitable for use in aqueous emulsion polymerization of fluorinated monomers can be used. Particularly suitable fluorinated surfactants are typically anionic fluorinated surfactants that are non-telogenic and include those that correspond to the formula:Q-Rf-Z-Ma  (I)wherein Q represents hydrogen, Cl or F whereby Q may be present in terminal position or not; Rf represents a linear or branched perfluorinated alkylene having 4 to 15 carbon atoms; Z represents COO31  or S03−, Ma represents a cation including an alkali metal ion or an ammonium ion.
Representative examples of emulsifiers according to above formula (I) are perfluoroalkanoic acids and salts thereof such as perfluorooctanoic acid and its salts in particular ammonium salts.
Further fluorinated surfactants that may be used include perfluoropolyether surfactants such as disclosed in EP 1059342, EP 712882, EP 752432, EP 816397, U.S. Pat. No. 6,025,307, U.S. Pat. No. 6,103,843 and U.S. Pat. No. 6,126,849. Still further surfactants that have been used are disclosed in U.S. Pat. No. 5,229,480, U.S. Pat. No. 5,763,552, U.S. Pat. No. 5,688,884, U.S. Pat. No. 5,700,859, U.S. Pat. No. 5,804,650, U.S. Pat. No. 5,895,799, WO 00/22002 and WO 00/71590.
The aqueous emulsion polymerization of TFE is initiated with a free radical initiator. Any of the known or suitable initiators for initiating an aqueous emulsion polymerization of TFE can be used. Suitable initiators include organic as well as inorganic initiators although the latter are generally preferred. Examples of inorganic initiators that can be used include for example ammonium-, alkali-, or earth alkali salts of persulfates, permanganic or manganic acid or manganic acids. A persulfate initiator, e.g. ammonium persulfate (APS), can be used on its own or may be used in combination with a reducing agent. Suitable reducing agents include bisulfites such as for example ammonium bisulfite or sodium metabisulfite, thiosulfates such as for example ammonium, potassium or sodium thiosulfate, hydrazines, azodicarboxylates and azodicarboxyldiamide (ADA). Further reducing agents that may be used include sodium formaldehyde sulfoxylate (available as Rongalite® from BASF Co., Ludwigshafen, Germany) or fluoroalkyl sulfinates as disclosed in U.S. Pat. No. 5,285,002. The reducing agent typically reduces the half-life time of the persulfate initiator. Additionally, a metal salt catalyst such as for example copper, iron or silver salts may be added. Generally, when manganic or permanganic based initiators are used, the manganic ions may be removed subsequent to the polymerization by contacting the resulting dispersion with a cation exchange resin.
The polymerization will typically be conducted at a temperature of 10 to 100° C., preferably between 20° C. and 90° C. and at a pressure of 4 to 30 bar, preferably 10 to 25 bar. The aqueous emulsion polymerization system may further comprise auxiliaries, such as buffers, complex-formers and gas carriers. The polymerization of TFE is strongly mass transfer controlled and accordingly, the polymerization rate strongly depends on agitation conditions. TFE is quicker consumed via polymerization than it is replenished in the aqueous phase from the gaseous phase (head-space). To mitigate this difficulty, the polymerization may be carried out in presence of a gas carrier. This is typically an organic liquid immiscible with water that has a substantially higher solubility for TFE in comparison with water. Suitable gas carriers are e.g. paraffin wax that is liquid under the polymerization conditions as described e.g., WO 02/072653 A2 or a Freon such as R113. The amount of the gas carrier is typically about 10% by volume of the aqueous phase.
In a particular embodiment, a seeded polymerization may be used. That is, the polymerization is initiated in the presence of small particles of fluoropolymer, typically small PTFE particles having a volume average diameter of between 50 and 100 nm. Such seed particles are produced in a separate aqueous emulsion polymerization and may be used in an amount of 20 to 50% by weight based on the weight of water in the aqueous emulsion polymerization. The use of seed particles allows better control over the PTFE particle size that is desired and avoids formation of coagulum during polymerization, which could cause explosion during the polymerization. Also, it is generally preferred that the polymerization conditions are elected such that the particles produced are generally spherical, that is the ratio of the largest to the smallest of two principal orthogonal dimensions of the particles is less than 1.5 and preferably is between 1 and 1.3. Accordingly, the polymerization should be carried out without taking special measures, e.g. as disclosed in WO 02/072653, to cause non-spherical particles such as rods or cylindrical particles to form and thus at least 90% by weight and more preferably at least 99% by weight of the PTFE particles produced will be spherical. Spherical particles can conveniently be obtained by starting the polymerization in presence of small amounts of HFP or perfluoro alkyl vinylethers.
The amount of polymer solids that can be obtained at the end of the polymerization is typically between 10% and 35% by weight, preferably between 20% and 30% by weight and the average particle size (volume average diameter) of the resulting fluoropolymer is typically between 50 nm and 350 nm, for example between 100 and 300 nm. PTFE dispersions of small particles generally provide more stable dispersions, have lower settling rates and generally may provide better film forming properties.
In accordance with the present invention, at the final stage of the emulsion polymerization, free radicals capable of introducing ionic end groups or precursors thereof in the polytetrafluoroethylene polymer are caused to be formed at a rate that without counter measures would cause an increase in the polymerization rate of at least 20%, preferably at least 25%, more preferably at least 35% and most preferably at least 40%. Without intending to be bound by any theory, it is believed that an increased amount (relative to an unmodified polymerization run) of ionic end groups and/or precursors thereof is formed in the PTFE polymer. It is believed that these ionic groups (and precursors thereof when converted to the corresponding ionic group) are substantially present at the surface of the PTFE particles and even after reducing the level of fluorinated surfactant of the dispersion later on, continue to stabilize the particles such that a high shear stability is achieved when such dispersion is blended with further components to produce a final coating composition as described above.
By 'final polymerization stage' is meant the stage at which at least 80%, preferably at least 85% and more preferably at least 90% by weight of the total amount of TFE to produce a final amount of PTFE, has been fed to the polymerization. By 'final amount of PTFE' is meant the amount of PTFE solids obtained at the end of the polymerization. When a seeded polymerization using PTFE particles is used, the final polymerization stage is determined relative to the total amount of TFE fed to the seeded polymerization without accounting for the amount of TFE used to produce the seed particles. Generally, the shorter the final polymerization stage, the lower the amount of lower molecular weight PTFE that may form will be. But, generally when the final polymerization stage is shorter, it may be desirable to use a larger increase in the polymerization rate to achieve an effective amount of ionic end groups. Thus, when the final polymerization stage starts when at least 90% by weight of the total amount of TFE has been fed to the polymerization, it will then generally be preferred to effect a polymerization rate increase (absent counter measures) of at least 35%, preferably at least 40% whereas with the final polymerization stage starting at 80% by weight of the total amount of TFE having been fed to the polymerization, the polymerization rate increase may not need to be more than 20 or 25%.
By the increase in polymerization rate absent counter measures is meant the polymerization rate increase determined from the relative increase in the polymerization rate between the average polymerization rate in the polymerization stage during which 10% by weight of the total amount of TFE is being converted and which immediately precedes the final polymerization stage and the average polymerization rate during the final polymerization stage where no counter measure has been taken to avoid the polymerization rate increase to occur in the final polymerization stage. Thus, if the final polymerization stage is started at 80%, the polymerization rate increase is determined between the average polymerization rate between the points of 70 and 80% of total addition of TFE and the average polymerization rate in the final stage, i.e., between 80 and 100% of the amount of TFE having been added.
The free radicals capable of introducing ionic end groups or precursors thereof in the polymer PTFE (hereinafter for sake of abbreviation referred to as 'ionic free radicals'), are formed in an amount such that without counter measures, the polymerization rate would increase by at least 20%. While it will generally be preferred to take suitable counter measures to avoid an increase or a too high increase in the polymerization rate, it is contemplated in the present invention to actually allow the polymerization rate to increase, i.e., not taking counter measures that would cause an increase in the polymerization. Counter measures that may be taken to mitigate or completely compensate the increase of the polymerization increase include for example a lowering of the pressure at which TFE is fed to the polymerization or the addition of a perfluorinated comonomer. Suitable perfluorinated comonomers that may be co-fed during the final stage of the polymerization to moderate the otherwise increase in the polymerization rate include perfluorinated vinyl ethers, for example those of the formula:CF2═CF—O—Rf  (II)wherein Rf represents a perfluorinated aliphatic group that may contain one or more oxygen atoms. Specific examples include perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether (PMVE), perfluoroethyl vinyl ether and perfluoro n-propyl vinyl ether (PPVE-1), perfluoro-2-propoxypropylvinyl ether (PPVE-2), perfluoro-3-methoxy-n-propylvinyl ether and perfluoro-2-methoxy-ethylvinyl ether. Preferred perfluoro alkyl vinylethers are gaseous or have a vapor pressure of at least 10 kPa at polymerization temperature. Further examples of suitable perfluorinated comonomers include perfluorinated allyl ethers and perfluorinated olefins having 3 to 8 carbons such as for example hexafluoropropylene. The co-feeding ratio of the perfluorinated comonomer to TFE will generally be selected so as to adjust the polymerization rate to the rate desired. Typically, the co-feeding ratio will be at least 0.015, typically between 0.015 and 0.07 on a molar basis. The co-feeding ratio is defined by the ratio of moles comonomer added to moles of TFE present in the head-space at the start of the final polymerization stage. The perfluorinated monomer may be co-fed continuously or batch-wise. It is generally also possible to counter the polymerization rate increase by adding a chain transfer agent in the final stage of the polymerization. This will however generally not be preferred as a chain transfer agent further lowers the molecular weight of the PTFE in the final polymerization stage without forming ionic end groups or precursors thereof, which is generally undesired. The use of the aforementioned perfluorinated comonomers to counter an increase in the polymerization is most preferred, as it has been found that such perfluorinated comonomer further enhances the shear stability of the dispersion when blended with further components to produce a final coating composition.
According to a particular embodiment of the present invention, a perfluorinated co-monomer used in the final polymerization stage may include one or more ionic groups or precursors thereof. Such co-monomers may offer the advantage of substantially further enhancing the stability of the dispersion as they may introduce further ionic groups on the surface of the PTFE particles. Examples of ionic groups in the ionic comonomer include acid groups or salts thereof such as carboxylic acid, sulfonic acid, phosphoric or phosphonic acid and salts thereof. Precursor groups of ionic groups include groups that upon hydrolysis yield an ionic group such as for example esters, which upon hydrolysis yield a carboxylic acid group or a salt thereof, and SO2F groups that upon hydrolysis yield sulfonic acid groups or salts thereof. Preferably, the ionic comonomer is a perfluorinated monomer including for example a perfluorinated allyl or vinyl ether having one or more ionic groups or precursors thereof.
According to a particular embodiment, the ionic comonomer corresponds to the general formula:CF2═CF—(—CFX)s—(OCF2CFY)t(O)h—(CFY′)u-Awherein s is 0 or 1, t is 0 to 3; h is 0 to 1; u is 0 to 12; X represents —F, —Cl or —CF3; Y and Y′ independently represent —F or a C1-10 perfluoralkyl group; A represents an ionic group or a precursor thereof —CN, —COF, —COOH, —COOR, —COOM, or —COONRR′, —SO2F, —SO3M, —SO3H, —PO3H2, —PO3RR′, —PO3M2; M represents an alkali metal ion or a quarternary ammonium group; R and R′ represent a hydrocarbon group such as e.g. a C1-10 alkyl group and R and R′ may be the same or different.
According to a further embodiment, the ionic comonomer corresponds to the general formula:CF2═CF—O—Rf-Zwherein Rf represents a perfluoroalkylene group optionally interrupted by one or more oxygen atoms and Z represents a carboxylic acid group, a salt thereof or a precursor thereof such as an ester of the formula COOR wherein R represents a hydrocarbon group such as an alkyl group or an aryl group, or a sulfonic acid group, a salt thereof or a precursor thereof such as SO2F. In one embodiment, Rf represents a perfluoroalkylene group having between 2 and 8 carbon atoms. Alternatively, Rf may be a perfluoroether group e.g. corresponding to the formula A or B:—(CF2)n(O(CF2)x)m(CF2)k—  (A)wherein n is an integer of 1 to 6, x is an integer of 1 to 5, m is an integer of 1 to 4 and k is an integer of 0 to 6;—[CF2CF(CF3)O]p—(CF2)q—wherein p is in an integer of 1 to 3 and q is an integer of 2 to 4.
Specific examples of ionic comonomers include:CF2═CF—O—(CF2)2—SO2FCF2═CF—O—(CF2)3—SO2FCF2═CF—O—(CF2)3—COOCH3CF2═CF—O—CF2CF(CF3)—O—(CF2)2—COOCH3CF2═CF—O—CF2CF(CF3)—O—(CF2)3—COOCH3CF2═CF—O—[CF2CF(CF3)—O]2—(CF2)2—COOCH3CF2═CF—O—CF2CF(CF3)—O—(CF2)2—SO2FCF2═CF—O—[CF2CF(CF3)—O]2—(CF2)2—SO2F
The ionic free radicals in the final polymerization stage may be formed from any suitable source capable of forming radicals that form ionic end groups or precursors thereof in the PTFE polymer. Preferably, the ionic end groups are groups that are strongly acidic, preferably those that have a pKa of not more than 3. Examples of such end groups include sulfonic and carboxylic acid groups including salts thereof. These groups have a pKa of 2 or less. Conveniently, the ionic free radicals are formed from an inorganic initiator or initiator system as described above. For example, free radicals obtained from the thermal decomposition of a persulfate, typically ammonium persulfate (APS), will introduce carboxylic acid groups (—CF2—COOH) and/or salts thereof in the PTFE polymer. When bisulfite as a reducing agent is used, —CF2—SO3H and/or salts thereof are introduced as end groups. The effective amount of ionic end groups needed in accordance with the present invention is so low that the precise amount thereof cannot be reliably quantified by known analytical methods such as infrared analysis or end-group titration. Nevertheless, the effective amount can be indirectly determined by the test method set forth above and illustrated in the examples. In addition to the ionic end groups, also other end groups that may be converted into ionic end groups may form. For example, —COF and —CONH2 end groups may form that can be converted into carboxylic acid end groups or salts thereof through hydrolysis, for example at a basic pH of the dispersion. Such end groups thus represent examples of suitable precursors for ionic end groups.
The ionic free radicals need to be formed in an effective amount in the final stage of the polymerization to cause an increase in polymerization rate by at least 20%, preferably at least 25%, more preferably at least 35% and most preferably at least 40% when no counter measures would be taken to reduce the polymerization rate. The necessary or effective amount of ionic free radicals can be caused in a variety of ways. For example, when an inorganic initiator has been used to initiate the polymerization of PTFE, the rate of decomposition of the inorganic initiator may be increased in the final stage of polymerization by adding a further amount of inorganic initiator, by increasing the polymerization temperature, by adding a reducing agent in case of a redox initiator system such as for example in case of APS by adding a reducing agent such as bisulfite or ADA, by adding a catalyst or by a combination of any of these measures.
The extent to which the temperature needs to be raised or to which extent further initiator amounts or amounts of components that accelerate the decomposition of an inorganic initiator (e.g. reducing agent or catalyst) need to be added to the final stage of the polymerization to achieve an increase of the polymerization rate of at least 20% (absent counter measures) will depend on such factors as the particular polymerization conditions at the point when the measure is taken. Generally, the extent of the measure to be taken to cause the effective amount of ionic free radicals to be formed can be estimated on the basis of the radical flux ratio F defined according to the following equation:F=Rf/Ri  (eq. 1)wherein Ri is the rate at which free radicals initiating polymerization are generated at the point just before the start of the final polymerization stage (i.e. before the measure is taken) and Rf is the rate at which ionic free radicals are generated in the final polymerization stage (i.e. after the measure has been taken).
When the initiator system used has a long half lifetime that is at least about twice the polymerization time, i.e. time needed to carry out the complete polymerization, F can be calculated or estimated in accordance with one of the following equations if the increase in polymerization rate will be caused by adding further initiator or components thereof:F=mIs/mIk  (eq. 2)F=(mOS*mRS)/(mOK*mRK)  (eq. 3)F=(mOS*mRS*mCS)/(mOK*mRK*mCK)  (eq. 4)
In the above equations, m represents the amount of the respective compound indicated by the index character, the first index character indicates the nature of the compound with I representing a single initiator component that decomposes on its own without the addition of other components (e.g. thermally decomposing APS in absence of catalyst or reducing agent), O represents the oxidizing component of a redox system, R represents the reducing agent of a redox system and C represents a catalyst, of the second index character S represents the total amount added during the complete polymerization and K represents the amount added during the final stage of the polymerization. The above equations are valid if a same or similar inorganic initiator system is used in all stages of the polymerization. Equation 2 can be used if the polymerization is carried out using a single initiator component, equation 3 applies if a redox system is used and equation 4 applies if a catalyst is also used. For example, equation 2 can be used when APS is used in all stages of the polymerization and equation 4 may be used with a system comprising APS, bisulfite and a metal catalyst such as copper.
For initiator systems that have a very short half life time such as for example in case of permanganate as the initiator or an initiator system based on APS, ADA and catalysed with cupper ions, it will generally not be possible to calculate the aforementioned radical flux ratio F. In such case, the radical flux ratio F can be estimated as follows. Assuming that with such systems, the initiator or one component thereof, is entirely consumed, the flux ratio is close to the ratio of the consumption of the initiator per kg TFE polymerized before the final polymerization stage to the consumption of initiator or one component thereof per kg TFE polymerized in the final polymerization stage.
With regard to a copper catalyzed APS/ADA initiator system, the radical flux ratio F (eq. (1)) thus can be estimated by modifying eq. (4) toF=(mADA,O/Mp,O+mADA,fin/Mp,fin)/(mADA,O/Mp,O)  eq. (5)provided that APS is stoichiometrically in excess. In the above equation mADA,O and mADA,fin represent respectively the amount of ADA added prior to the final polymerization stage and at the final polymerization stage. The amount of polymer produced before the final polymerization stage is Mp,O and at the final polymerization stage is Mp,fin. The degree of conversion at the start of the final polymerization stage is defined by Mp,O/(Mp,O+Mp,fin).
The radical flux ratio may alternatively be determined empirically by measuring Ri and Rf independent of the polymerization but using conditions similar to those existing during the polymerization. Such empirical determination is generally needed if the polymerization rate increase is wholly or partially caused by an increase in polymerization temperature.
The optimal radical flux ratio F to obtain an effective amount of ionic end groups in the PTFE particles generally depends on when the final polymerization stage starts. The later the final polymerization stage starts, and thus the shorter that stage will be, the higher the value F should typically be to obtain an effective amount of ionic end groups. Generally, F should be at least 2, preferably at least 4 when the final polymerization starts at 80% of the amount of TFE having been fed, and at least 3, preferably at least 10 when the final polymerization stage starts at 95%.
Reduction of the Amount of Fluorinated Surfactants
The amount of fluorinated surfactant in an aqueous dispersion of PTFE may be reduced in a number of ways. Generally such methods will require the addition of a stabilizing (non fluorinated) surfactant. This stabilizing non-fluorinated surfactant is typically a non-ionic surfactant although other stabilizing surfactants may be suitable as well depending on the technique used to remove the fluorinated surfactant. Examples of useful non-ionic surfactants include those according to the formula:R1—O—[CH2CH2O]n—[R2O]m—R3  (III)wherein R1 represents an aromatic or aliphatic hydrocarbon group having at least 8 carbon atoms, R2 represents an alkylene having 3 carbon atoms, R3 represents hydrogen or a C1-C3 alkyl group, n has a value of 0 to 40, m has a value of 0 to 40 and the sum of n+m being at least 2. It will be understood that in the above formula (III), the units indexed by n and m may appear as blocks or they may be present in an alternating or random configuration. Examples of non-ionic surfactants according to formula (III) above include alkylphenol oxy ethylates such as ethoxylated p-isooctylphenol commercially available under the brand name TRITON™ such as for example TRITON™ X 100 wherein the number of ethoxy units is about 10 or TRITON™ X 114 wherein the number of ethoxy units is about 7 to 8. Still further examples include those in which R1 in the above formula (III) represents an alkyl group of 4 to 20 carbon atoms, m is 0 and R3 is hydrogen. An example thereof includes isotridecanol ethoxylated with about 8 ethoxy groups and which is commercially available as GENAPOL®X 080 from Clariant GmbH. Non-ionic surfactants according to formula (III) in which the hydrophilic part comprises a block-copolymer of ethoxy groups and propoxy groups may be used and well. Such non-ionic surfactants are commercially available from Clariant GmbH under the trade designation GENAPOL® PF 40 and GENAPOL® PF 80.
According to one embodiment to reduce the amount of fluorinated surfactant, a non-ionic surfactant, e.g. as disclosed above is added to the fluoropolymer dispersion and the fluoropolymer dispersion is then contacted with an anion exchanger. Such a method is disclosed in detail in WO 00/35971.
The anion exchange process is preferably carried out in essentially basic conditions. Accordingly, the ion exchange resin will preferably be in the OH−form although anions like fluoride or sulfate may be used as well. The specific basicity of the ion exchange resin is not very critical. Strongly basic resins are preferred because of their higher efficiency in removing the low molecular weight fluorinated surfactant. The process may be carried out by feeding the fluoropolymer dispersion through a column that contains the ion exchange resin or alternatively, the fluoropolymer dispersion may be stirred with the ion exchange resin and the fluoropolymer dispersion may thereafter be isolated by filtration. With this method, the amount of low molecular weight fluorinated surfactant can be reduced to levels below 150 ppm or even below 10 ppm. Accordingly, dispersions substantially free of fluorinated surfactant may thereby be obtained.
In case the fluorinated surfactant is in its free acid form is steam-volatile, the following method may alternatively be used to reduce the amount of fluorinated surfactant. A steam-volatile fluorinated surfactant in its free acid form may be removed from aqueous fluoropolymer dispersions, by adding a nonionic surfactant to the aqueous fluoropolymer dispersion and, at a pH-value of the aqueous fluoropolymer dispersion below 5, removing the steam-volatile fluorinated surfactant by distillation until the concentration of steam-volatile fluorinated surfactant in the dispersion reaches the desired value as disclosed in DE 100 18 853. Fluorinated surfactants that can be removed with this process include for example the surfactants according to formula (I) above.
Still further, the amount of fluorinated surfactant may be reduced to the desired level through the use of ultrafiltration as disclosed in U.S. Pat. No. 4,369,266. Generally, this method will simultaneously also increase the solids amount of the dispersion and thus may be used to simultaneously remove the fluorinated surfactant and upconcentrate the dispersion.
Upconcentration
Generally subsequent to reducing the level of fluorinated surfactant the aqueous dispersion may be upconcentrated if the resulting PTFE solids are lower than desired. It is however also possible to reduce the amount of fluorinated surfactant in an upconcentrated dispersion or simultaneously with the upconcentration as described above. To increase the amount of fluoropolymer solids, any suitable or known upconcentration technique may be used. These upconcentration techniques are typically carried out in the presence of a non-ionic surfactant which is added to stabilize the dispersion in the upconcentration process. The amount of non-ionic surfactant that should generally be present in the dispersion for upconcentration is typically between 2% by weight and 15% by weight, preferably between 3% by weight and 10% by weight. Suitable methods for upconcentration include ultrafiltration, thermal upconcentration, thermal decantation and electrodecantation as disclosed in GB 642,025.
The method of ultrafiltration comprises the steps of (a) adding non-ionic surfactant to a dispersion that desirably is to be upconcentrated and (b) circulating the dispersion over a semi-permeable ultra-filtration membrane to separate the dispersion into a fluorinated polymer dispersion concentrate and an aqueous permeate. The circulation is typically at a conveying rate of 2 to 7 meters per second and affected by pumps, which keep the fluorinated polymer free from contact with components, which cause frictional forces.
To increase the fluoropolymer solids in the aqueous dispersion, thermal decantation may also be employed. In this method, a non-ionic surfactant is added to the fluoropolymer dispersion that is desirably upconcentrated and the dispersion is then heated so as to form a supernatant layer that can be decanted and that typically contains water and some non-ionic surfactant while the other layer will contain the concentrated dispersion. This method is for example disclosed in U.S. Pat. No. 3,037,953 and EP 818506.
Thermal upconcentration involves heating of the dispersion and removal of water under a reduced pressure until the desired concentration is obtained.
Aqueous PTFE Dispersion
The method of the invention will typically result in an aqueous PTFE dispersion that is free of fluorinated surfactant or contains the latter in an amount of not more than 200 ppm, preferably not more than 100 ppm, more preferably not more than 50 ppm and most preferably not more than 20 ppm based on the PTFE solids in the dispersion. The dispersion will typically also contain a non-ionic surfactant. The amount thereof should generally be between 2 and 15% by weight based on the weight of PTFE solids, preferably between 3 and 12% by weight. The amount of non-ionic surfactant may result from the amount of stabilizing surfactant used during the removal of the fluorinated surfactant and/or during the optional upconcentration of the dispersion. But the amount of non-ionic surfactant may be adjusted by adding further non-ionic surfactant to achieve a desired level of non-ionic surfactant within the aforementioned range in the dispersion. The dispersion should typically have a amount of PTFE solids in the range of 30 to 70% by weight, preferably between 40 and 65% by weight so as to make the dispersion most suitable for combination with further components to produce a final coating composition for coating substrates such as for example metal.
The PTFE particles resulting from the method of the invention have an effective amount of ionic end groups such that a dispersion having a composition and conductivity as described above and tested under the conditions as described above has a shear stability of at least 3 minutes when the average particle diameter of the particles is 150 nm or more and at least 4 minutes when the average particle diameter is less than 150 nm. It has been found that PTFE dispersion of which at least part of the PTFE particles meet this requirement, can be used to formulate final coating compositions that can be used in existing coating equipment without the risk or with a reduced risk for clogging of spray heads or without the risk or with a reduced risk of coagulation in pumping systems used. Generally the risk of coagulation is reduced sufficiently such that coagulation in a practical application would not occur or not impair the coating process. Preferably at least 30% by weight of the total amount of PTFE particles, more preferably at least 50% by weight and most preferably at least 80% by weight or all of the PTFE particles are PTFE particles having the effective amount of end groups.
The PTFE dispersion may contain a mixture of PTFE particles of different average particle size, i.e., the particle size distribution of the PTFE particles can be bimodal or multi-modal as disclosed in e.g. U.S. Pat. No. 5,576,381 and EP 969 055. Multi-modal PTFE particle dispersions may present advantageous properties. For example, the PTFE dispersion may comprise a mixture of first PTFE particles having an average particle size of at least 180 nm in combination with second PTFE particles that have an average particle size volume average particle diameter) of not more than 0.7 times the average particle size of the first PTFE particles as disclosed in U.S. Pat. No. 5,576,381. Bimodal or multi-modal PTFE dispersions can be conveniently obtained by blending the aqueous PTFE dispersion of different PTFE particle size together in the desired amounts. It will generally be preferred that the individual PTFE dispersion used to obtain a multi-modal or bimodal PTFE dispersion have been prepared according to the aqueous emulsion polymerization process described above. In particular at least the small PTFE particles, having for example an volume average particle diameter of 50 to 200 nm, in a bimodal or multi-modal dispersion should be prepared according to the aqueous emulsion polymerization process described above as it has been found that these particles have the largest impact on the problems encountered during preparation and use of a final coating composition. Preferably the individual dispersions already are free of fluorinated surfactant or contain a reduced amount thereof. It is however also possible to reduce the amount of fluorinated surfactant subsequent to mixing the dispersions together.
Additionally, the PTFE dispersion may be mixed with aqueous dispersions of other fluoropolymers, in particular melt-processible fluoropolymers. Suitable dispersion of melt-processible fluoropolymers that can be mixed with the PTFE dispersion include dispersions of the following fluoropolymers: copolymers of TFE and a perfluorinated vinyl ether (PFA) and copolymers of TFE and HFP (FEP). Such dispersions may be monomodal, bi-modal or multimodal as disclosed in e.g. EP 990 009.
The PTFE dispersion preferably has a conductivity of at least 500 μS, typically between 500 μS and 1500 μS. When the conductivity is too low, the shear stability may be reduced. The desired level of conductivity of the dispersion may be adjusted by adding a salt thereto such as for example a simple inorganic salt such as sodium chloride or ammonium chloride and the like. Also, the level of conductivity may be adjusted by adding an anionic non-fluorinated surfactant to the dispersion as disclosed in WO 03/020836.
Generally preferred anionic non-fluorinated surfactants are surfactants that have an acid group that has a pKa of not more than 4, preferably not more than 3. It was found that such anionic surfactants in addition to controlling the viscosity are generally also capable of increasing the stability of the fluoropolymer dispersion. Examples of non-fluorinated anionic surfactants include surfactants that have one or more anionic groups. Anionic non-fluorinated surfactants may include in addition to one or more anionic groups also other hydrophilic groups such as polyoxyalkylene groups having 2 to 4 carbons in the oxyalkylene group, such as polyoxyethylene groups, or groups such as such as an amino groups. Nevertheless, when amino groups are contained in the surfactant, the pH of the dispersion should be such that the amino groups are not in their protonated form. Typical non-fluorinated surfactants include anionic hydrocarbon surfactants. The term "anionic hydrocarbon surfactants" as used herein comprises surfactants that comprise one or more hydrocarbon moieties in the molecule and one or more anionic groups, in particular acid groups such as sulphonic, sulfuric, phosphoric and carboxylic acid groups and salts thereof. Examples of hydrocarbon moieties of the anionic hydrocarbon surfactants include saturated and unsaturated aliphatic groups having for example 6 to 40 carbon atoms, preferably 8 to 20 carbon atoms. Such aliphatic groups may be linear or branched and may contain cyclic structures. The hydrocarbon moiety may also be aromatic or contain aromatic groups. Additionally, the hydrocarbon moiety may contain one or more hetero atoms such as, for example, oxygen, nitrogen and sulfur.
Particular examples of anionic hydrocarbon surfactants for use in this invention include alkyl sulfonates such as lauryl sulfonate, alkyl sulfates such as lauryl sulfate, alkylarylsulfonates and alkylarylsulfates, fatty (carboxylic) acids and salts thereof such as lauric acids and salts thereof and phosphoric acid alkyl or alkylaryl esters and salts thereof. Commercially available anionic hydrocarbon surfactants that can be used include Emulsogen™ LS (sodium lauryl sulfate) and Emulsogen™ EPA 1954 (mixture of C12 to C14 sodium alkyl sulfates) available from Clariant GmbH and TRITON™ X-200 (sodium alkylsulfonate) available from Union Carbide. Preferred are anionic hydrocarbon surfactants having a sulfonate group.
Further optional components that may be present in the aqueous PTFE dispersion include buffering agents and oxidizing agents like KClO3 as required or desired for the various applications.
The PTFE dispersions of the present invention can be used to produce final coating compositions for coating various substrates such as metal substrates, e.g. cookware, fabrics such as glass fiber based fabrics, which may be used as architectural fabrics. Generally, the PTFE dispersions will be blended with further components typically used to produce a final coating composition. Such further components may be dissolved or dispersed in an organic solvent such as toluene, xylene and the like. Typical components that are used in a final coating composition include heat resistant polymers such as polyamide imide, polyimide or polyarylen sulphide. Still further ingredients such as pigments and mica particles may be added as well to obtain the final coating composition. The PTFE dispersions typically represent about 10 to 80% by weight of the final composition. Details on coating compositions for metal coatings and components used therein have been described in e.g. WO 02/78862, WO 94/14904, EP 22257 and U.S. Pat. No. 3,489,595.

Aqueous dispersions of polytetrafluoroethylene having a low amount of fluorinated surfactant


The present invention relates generally to the use of genetic engineering to induce developmental regulation in anther tissue of plants, and more particularly to induce nuclear male sterility, and to genetic sequences useful for same. More particularly, the present invention relates to the identification of a genomic clone and promoter capable of tissue- and development-specific expression which provides a means of tissue and developmental regulation in plants and more specifically a means of producing nuclear male sterile plants. Even more particularly, the present invention provides a genomic clone having a nucleotide sequence as set forth in SEQ ID NO. 1 or homologous sequences thereof such as the nucleotide sequence as set forth in SEQ ID NO. 3.

The present invention relates generally to the use of genetic engineering to induce developmental regulation in anther tissue of plants, and more particularly to induce nuclear male sterility, and to genetic sequences useful for same.
Nucleotide and amino acid sequences are referred to herein by sequence identity numbers (SEQ ID NOs) which are defined after the bibliography. A general summary of the SEQ ID NOs is provided before the examples.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.
Anther-specific genes are those genes that are expressed exclusively in the male reproductive tissues, rather than xe2x80x9chouse-keepingxe2x80x9d genes which are active in all plant cells. Anther-specific genes play an important role in pollen development and, hence, in the control of seed production.
Differentiation and development of the male gametophyte of angiosperms, the pollen grain, depends partly upon transcription of the haploid genome following meiosis (Mascarenhas, 1988). The study of these coordinated events at the molecular level has been considered important in order to understand the developmentally specific regulation and functions of pollen-expressed genes. In this regard, Theerakulpisut et al (1991) studied gene expression in pollen of Brassica campestris. By differential screening of a mature B. campestris pollen cDNA library, an anther-specific clone, designated Bcp1, was isolated.
In work leading up to the present invention, the inventors undertook a detailed investigation of Bcp1 expression with the aim of isolating a genomic clone and to sub-clone and characterise the 5xe2x80x2 upstream regulatory regions of the genomic clone. It has been surprisingly discovered that the genomic clone of Bcp1, i.e. Bgp1, is tissue and developmentally specific thereby providing a means to enable tissue and developmental regulation in plants and in particular to produce nuclear male sterile plants. It has further been discovered that the Bgp1 gene from B. campestris represents a family of homologous genes from a diverse range of plants. By way of shorthand notation, a genomic clone is referred to herein by the genus and/or species of the plant from which it is isolated followed by the term xe2x80x9cBgp1xe2x80x9d. A cDNA clone is referred to in similar fashion except using the term xe2x80x9cBcp1xe2x80x9d.
Accordingly, one aspect of the present invention contemplates a genomic DNA isolate comprising:
(i) all or part of a gene or related genetic sequence preferentially expressed in anther tissue of a plant and substantially not expressed in non-anther tissue; and
(ii) an open reading frame having a nucleotide sequence as set forth in SEQ ID NO. 1:
or having at least 20% similarity to all or part thereof.
The deduced amino acid sequence to the open reading frame defined in SEQ ID NO. 1 is shown in SEQ ID NO. 2.
The expression xe2x80x9cgene or related genetic sequencexe2x80x9d is used in is broadest sense and includes any contiguous series of nucleotides constituting an open reading frame. Generally, an open reading frame comprises at least 48 contiguous nucleotides arranged into triplets without interuption by a stop codon.
A nucleotide sequence having at least 20% similarity to all or a portion of SEQ ID NO. 1 is referred to herein as a xe2x80x9chomologous genexe2x80x9d. Preferably, there is at least 20% similarity to the entire SEQ ID NO. 1 sequence. Even :more preferably, there is at least 30% similarity, still more preferably at least 45% similarity, even still more preferably at least 55-60% similarity, yet even still more preferably at least 75-95% similarity to all or part of SEQ ID NO. 1. A xe2x80x9cpartxe2x80x9d in this context is a contiguous series of at least 20 nucleotides in SEQ ID NO. 1.
Preferably, the genomic DNA isolate is a dicotyledonous plant such as tomato, corn, rice, wheat, raddish, tobacco and oil seed rapes. Particularly preferred plants are Brassica species, Arabidopsis species and Nicotiana species.
In a most preferred embodiment, the plant is Brassica campestris and the genomic DNA isolate has an open reading frame with a sequence as set forth in SEQ ID NO. 1. A preferred homologous gene having at least 20% nucleotide similarity to SEQ ID NO. 1 is from Arabidopsis thaliana comprising an open reading frame with a nucleotide sequence as set forth in SEQ ID NO. 3:
The deduced amino acid sequence of SEQ ID NO. 3 is defined in SEQ ID NO. 4.
Another aspect of the present invention provides a genomic DNA isolate as defined above and further comprising a promoter region 5xe2x80x2 to the open reading frame, wherein said promoter region:
(i) is capable of directing expression in taptum and/or pollen tissue; and
(ii) comprises a nucleotide sequence as set forth in,SEQ ID NO. 5:
or having at least 20% similarity to all or part thereof.
Preferred promoters comprise the promoter defined in SEQ ID NO. 5 and the promoter defined in SEQ D NO. 6 which has the following nucleotide sequence:
Yet another aspect of the present invention relates to a genomic DNA isolate comprising:
(i) all or part of a gene or related genetic sequence preferentially expressed in anther tissue of a plant and substantially not expressed in non-anther tissue;
(ii) a promoter region capable of directing expression in tapetum and/or pollen tissue;
(iii) a nucleotide sequence substantially as set forth in SEQ ID NO. 7:
or having at least 20% similarity to all or part thereof.
In a preferred embodiment, the above genomic DNA isolate further comprises:
(iv) a nucleotide sequence which is capable of hybridising under low stringency conditions to all or part of a nucleotide sequence substantially complementary to SEQ ID NO. 7.
Most preferred genomic DNA isolates comprise SEQ ID NO. 7 and SEQ ID NO. 8, the latter which has the following nucleotide sequence:
Still yet another aspect of the present invention contemplates an isolated nucleic acid molecule which is capable of hybridising under low stringency conditions to the genomic DNA isolates defined above. Preferred nucleic acid molecules comprise a complementary strand of all or part of SEQ ID NO. 1 or SEQ ID NO. 3. A xe2x80x9cpartxe2x80x9d in this context includes an oligonucleotide.
A further aspect of the present invention provides a genetic construct comprising:
(i) a promoter region capable of directing expression of a nucleotide sequence when operably linked downstream thereof in tapetum and/or pollen tissue; and
(ii) said promoter being capable of hybridising under low stringency conditions to a complementary strand of SEQ ID NO. 5.
For the purposes of defining the level of stringency, reference can conveniently be made to Sambrook et al., Supra at pp 387-389 which is herein incorporated by reference where the washing step at paragraph 11 is considered high stringency. A low stringency is defined herein as being in 0.1-0.5% w/v SDS at 37-45xc2x0 C. for 2-3 hours. Depending on the source and concentration of nucleic acid involved in the hybridisation, alternative conditions of stringency may be employed such as medium stringent conditions which are considered herein to be 0.25%-0.5% w/v SDS at xe2x89xa745xc2x0 C. for 2-3 hours or high stringent conditions as disclosed by Sambrook et al., Supra.
In a further related embodiment, there is provided a nucleic acid isolate having a sequence of nucleotides comprising or a complementary sequence of nucleotides comprising SEQ ID NO. 5 or a promoter functional derivative, fragment, part, homologue or analogue thereof. The latter functional derivative and like molecules comprise at least 20% nucleotide sequence similarity to SEQ ID NO. 5. An example of a promoter having at least 20% nucleotide similarity to SEQ ID NO. 5 is the promoter from A. thaliana Bgp1 having the sequence set forth in SEQ ID NO. 6.
In accordance with these and other aspects of the present invention, the term xe2x80x9cpromoterxe2x80x9d is used in its most general sense and refers to any nucleotide sequence which binds RNA polymerase and directs same to a transcriptional start site whereupon a gene or other nucleotide sequence downstream of said promoter is transcribed. A nucleotide sequence xe2x80x9cdownstreamxe2x80x9d of the promoter is also said to be xe2x80x9crelativexe2x80x9d the promoter.
The term xe2x80x9cgenetic constructxe2x80x9d is used in its most broadest sense to include an isolated nucleic acid molecule comprising a sequence of nucleotides.
Preferably, the promoter is from a Brassica species such as B. compestris or from an Arabidopsis species such as A. thaliana. Preferably, the genetic construct is transformable and operable in dicotyledon plants and in particular a Brassica species, Arabidopsis species or a Nicotiana species.
The genetic construct may be conveniently engineered so as to place an endonuclease restriction site in a region 3xe2x80x2 of the promoter to thereby readily enable the insertion of nucleotide sequences downstream of the promoter for their transcription. Generally, the inserted restriction site is unique to the genetic construct or may be represented twice but separated by a length of nucleic acid to be deleted upon restriction digestion of the genetic construct and followed by insertion of the required nucleotide sequence to be transcribed.
The genetic construct of the present invention may comprise solely the promoter and optionally a nucleotide sequence downstream thereof or, alternatively, may comprise additional nucleotide sequences constituting promoter regulatory region(s), transcribed sequence regulatory regions, a marker (eg. antibiotic resistance, chemical compound resistance or enzyme), autonomous replication region and/or genome integration sequence. The promoter may be the naturally occurring promoter or may be an active fragment or part thereof or a derivative, analogue or homologue of the promoter.
By xe2x80x9cderivativexe2x80x9d is meant to include any single or multiple nucleotide deletion, insertion and/or substitution to the promoter nucleotide sequence, provided said derivative is still active in tapetum and/or pollen tissue. Manipulation of the nucleotide sequence at known predetermined sites or random mutagenesis are conveniently accomplished by any number of techniques including M13, transposon and/or oligonucleotide mutagenesis. Various techniques are described by Maniatis et al (1989).
Homologues and analogues of the promoter include promoters having a nucleotide sequence having at least 20%, preferably at least 30% similarity, more preferably at least 45% similarity, still more preferably at least 55-60% similarity and even more preferably at least 75-95% similarity to the first mentioned promoter and which function in anther tissue.
Most preferred promoters comprise the sequence SEQ ID NO. 5 or SEQ ID NO. 6.
The promoter of the present invention is tissue specific for anther tissue. More particularly, the promoter is specific for tapetum and/or pollen tissue. However, this is not intended to exclude genetic constructs based on the promoter of the present invention but modified to be capable of expression in non-anther tissues.
The nucleotide sequence down stream of the promoter might give rise to antisense RNA or may encode specific traits such as a xe2x80x9clethal genexe2x80x9d or a xe2x80x9cMiller genexe2x80x9d to specifically render a pollen grain infertile or incapable of maturation. The nucleotide sequence may also encode a trait, for example, which renders the pollen grain more resistant to predator or pathogen attack. In one particular embodiment, the nucleotide sequence downstream of the promoter is a ribozyme capable of targetting a mRNA transcript corresponding to SEQ ID NO. 1 or SEQ ID NO. 3 or a homologous genetic sequence thereof.
According to this latter embodiment, there is provided a ribozyme which comprises a hybridising region and a catalytic region wherein the hybridising region is capable of hybridising to at least part of a target mRNA sequence transcribed from a genomic Bgp1 gene as hereinbefore defined wherein the catalytic region is capable of cleaving said target mRNA thereby substantially down regulating expression of said genomic DNA isolate. A ribozyme according to this aspect of the invention may also be a polyribozyme.
Methods for the construction of ribozyme are conveniently disclosed in Haseloff and Gerlach (1988) and in International Patent Application No. WO89/05852. Preferably, the ribozyme is under the control of a Bgp1 promoter as hereinbefore described.
The present invention further extends to a hybrid genetic sequence comprising a ribozyme as hereinbefore described fused, linked or otherwise chemically bonded to one or more sequence of nucleotides which is/are substantially antisense to all or part of SEQ ID NO. 1 or a homologous sequence (e.g. antisense to all or part of SEQ ID NO. 3).
The antisense sequence may flank both sides of a ribozyme or may be located to one end of said ribozyme. Reference to a ribozyme in this context includes reference to a polyribozyme. A xe2x80x9csubstantially antisensexe2x80x9d molecule is a molecule capable of hybridising under physiological conditions to the reference sequence (e.g. SEQ ID NO. 1 or SEQ ID NO. 3) to a sufficient extent to reduce translation of said target sequence into functional protein or which results in male sterility.
The present invention is particularly exemplified using the promoter isolated from a genomic clone of Bcp1, the genomic clone being designated herein xe2x80x9cBgp1xe2x80x9d, from Brassica species or non-Brassica species with similar acting promoters. Such other promoters are referred to herein as xe2x80x9chomologous promotersxe2x80x9d and include the promoter from the homologous gene A. thaliana Bgp1 defined by SEQ ID NO. 6. Most of the Bgp1 promoter is required for pollen expression and in particular nucleotide regions xe2x88x92580 to xe2x88x92767, xe2x88x92322 to xe2x88x92580 and xe2x88x92116 to xe2x88x92168 whereas the nucleotide region up to xe2x88x92116 is only required for tapetum expression.
According to a preferred embodiment, the present invention provides an isolated nucleic acid molecule carrying a promoter capable of directing expression in tapetum and pollen tissue and comprising the following nucleotide sequence identified as SEQ ID NO. 5, including functional derivatives or homologue having at least 20% nucleotide similarity to all or a part thereof and/or which are capable of hybridising to a complementary strand thereof under at least low stringency conditions.
According to another embodiment, there is provided an isolated nucleic acid molecule carrying a promoter capable of directing expression in pollen tissue but not tapetum, said nucleic acid molecule comprising the following nucleotide sequence identified as SEQ ID NO. 9:
including functional derivatives or homologues having at least 20% nucleotide similarity to all or a part thereof and/or which are capable of hybridising to a complementary strand thereof under at least low stringency conditions.
A particularly important homologue is SEQ ID NO. 6 from A. thaliana.
Preferably, the nucleotide sequence of SEQ ID NO. 5, SEQ ID NO. 9 or SEQ ID NO. 6 is modified by the introduction of a restriction endonuclease cleavage site to facilitate the insertion of an operably linked second nucleotide sequence downstream of the promoter.
Preferably, the nucleotide sequence of the present invention form part of a vector.
The identification of a tissue and developmentally dependent promoter enables the production of genetic constructs which can be used to generate transgenic plants having certain traits expressed or down regulated. For example, the function of the Bgp1 gene can be conveniently disrupted using antisense RNA or a ribozyme. Conveniently, the cDNA clone Bcp1 is inserted in the reverse orientation relative the Bgp1 promoter. This construct, when introduced into a suitable host, produces antisense RNA which disrupts expression of the Bgp1 gene. Although not intending to limit the present invention to any one theory of mode of action, it is possible the antisense RNA forms a duplex with Bgp1 RNA to thereby prevent its translation. Transgenic plants carrying the particular construct are generally male sterile but female fertile.
According to this aspect of the present invention there is provided an antisense construct:
(i) which comprises a nucleic acid molecule comprising at least eight contiguous nucleotides;
(ii) which is capable of hybridising under physiological conditions to all or part of SEQ ID NO. 1 or a homologous.-sequence thereof; and
(iii) which, in use, is capable of down regulating expression of a plant Bgp1 gene.
In this context, a xe2x80x9chomologousxe2x80x9d sequence comprises a nucleotide sequence having at least 20% similarity to all or part of SEQ ID NO. 1 and which is a Bgp1 gene.
Preferably, the antisense construct is at least 20 nucleotides long. More preferably, the antisense construct is at least 50-100 nucleotides long. Even more preferably, the antisense construct is all or part of a plant Bcp1 or Bgp1 in reverse orientation relative a promoter.
The term xe2x80x9cdown regulatesxe2x80x9d or similar expressions such as xe2x80x9cdown regulatingxe2x80x9d means a reduction in the amount of full length Bgp1 mRNA as determined by hybridisation or extent of translation into a Bgp1 product or, most conveniently, generation of substantially male sterile plants.
Yet another aspect of the present invention contemplates a method for generating male sterile plants, said method comprising transforming a cell or group of cells of said plant with a genetic construct capable of directing expression of a nucleotide sequence having a deleterious effect on tapetum and/or pollen tissue, regenerating a transgenic plant from said transformed cells and growing and/or maintaining said transgenic plant under conditions to thereby having a deleterious effect on said tapetum and/or pollen tissue resulting in said plant being substantially male sterile.
In an alternative embodiment, there is provided a method for generating male sterile plants, said method comprising introducing into a cell or group of cells of said plant, a genetic construct comprising all or part of a Bgp1, said Bgp1 having a nucleotide sequence substantially similar to an endogenous Bgp1 of the plant and then regenerating a plant from said cells. This method is term xe2x80x9cco-suppressionxe2x80x9d. The introduced Bgp1 may be with or without a promoter. By xe2x80x9csubstantiallyxe2x80x9d similar is meant an exogenous Bgp1 comprising 85-100% nucleotide sequence similarity to an endogenous Bgp1.
Still yet another aspect of the present invention provides a transgenic male sterile plants such as those made by the above method.

Developmental regulation in anther tissue of plants


The present invention pertains to novel antibodies capable of binding to CD26, as well as to their use as a medicament. Moreover, the present invention provides antibodies for use in treating and/or preventing Graft-versus-Host Disease (GvHD), for use in treating Aplastic Anemia and/or for use in promoting engraftment after haematopoietic stem cell transplantation. Furthermore, the present invention provides pharmaceutical compositions comprising at least one antibody of the present invention, as well as provides a kit of parts.

CD26 is a widely distributed 110 kDa cell surface glycoprotein, initially defined as a T-cell activation antigen (Fox et al. (1984) J. Immunol. 133, 1250-1256, Fleischer (1987) J. Immunol. 138, 1346-1350, and Morimoto et al. (1989) J. Immunol. 143, 3430-3439). This molecule has been shown to have dipeptidyl peptidase IV (DPPIV; EC184.108.40.206) activity in its extracellular domain, and wide tissue distribution (Hegen et al. (1990) J. Immunol. 144, 2908-2914 and Ulmer et al. (1990) J. Immunol. 31, 429-435; WO 2007/014169 A2). CD26 has multiple functions in human T-cell physiology. For instance, evidence suggests that CD26 can deliver a costimulatory signal for T-cell activation (Morimoto et al. (1994) Immunologist 2: 4-7 and Fleischer (1994) Immunol. Today 15:180-184). Further, CD26 has been identified as the ADA binding protein, and the CD26/ADA complex may play a key role in regulating immune system function (Dong et al. (1996) J Immunol. 156(4):1349-55, Kameoka et al. (1993) Science. 261(5120):466-9, and Morrison et al. (1993) J Exp Med. 177(4):1135-43). A functional association between CD26 and the cellular protein topoisomerase II a has also been reported (Aytac et al. (2003) British Journal of Cancer 88:455-462). Anti-CD26 antibodies are e.g. known from WO 2007/014169 A2.
Haematopoietic stem cell transplantation (HSCT) represents an important therapy for many haematological and numerous epithelial malignancies, as well as for a considerable number of non-malignant diseases (Ferrara et al., 2009, Lancet.; 373: 1550-1561; Sun et al., 2007, Transl. Res.; 150: 197-214). Graft-versus-host disease (GvHD) is a major complication of allogeneic haematopoietic stem cell transplantation (HSCT), and therefore limits the use of these important therapies.
There are two major types of haematopoietic cell transplantation: autologous and allogeneic. Autologous transplantation involves isolation of haematopoietic stem cells (HSC) from a patient, storage of the stem cells, medical treatment of the patient that destroys stem cells remaining in the body, and return of the patient's own stored stem cells to his body. Autologous transplants have the advantage of a lower risk of graft rejection, infection and other correlated diseases. Allogeneic transplantation involves two persons: one is the healthy donor and one is the patient or recipient. Allogeneic HSC donors must have a tissue (HLA human leukocyte antigens) type that matches the recipient and, in addition, the recipient requires immunosuppressive medications. There are three possible sources of haematopoietic stem cells for transplantation: the Bone Marrow (BM), the Peripheral Blood (PB) and the Umbilical Cord Blood (UCB).
The development of novel strategies has helped to expand the indications for allogeneic HSCT over the last several years (Sun et al., 2007, supra). Improvements in infectious prophylaxis, immunosuppressive medications, supportive care and DNA-based tissue typing have also contributed to improved outcomes after allogeneic HSCT (Ferrara et al., 2009, supra). For these reasons, the number of allogeneic haematopoietic cell transplantations continues to increase. However, graft-versus-host disease (GvHD) remains a major complication of allogeneic HSCT.
GvHD occurs when donor T cells identify genetically defined proteins on host cells as not-self and mount an immune response in order to destroy them (Ferrara et al., 2009, supra). Depending on the time at which it occurs after HSCT, GvHD can be either acute or chronic. Acute GvHD (aGvHD) is responsible for 15% to 40% of mortality and is the major cause of morbidity after allogeneic HCT, while chronic GvHD (cGvHD) occurs up to 50% of patients who survive three months after HCT (Sun et al., 2007, Transl. Res.; 150: 197-214).
Acute Graft-versus-Host Disease generally occurs after allogeneic HSCT as reaction of donor immune cells against host tissues. The three main tissues affected by acute GvHD are the skin, liver, and gastrointestinal tract. Clinically, the diagnosis is suspected when a recipient of HSCT develops any or all of the following signs or symptoms: dermatitis (skin rash), cutaneous blisters, crampy abdominal pain with or without diarrhoea, persistent nausea and vomiting, hepatitis (with elevation of bilirubin and/or liver enzymes). Symptoms most frequently start with donor engraftment, before day 100 after the HSCT, but may also occur late. Acute GvHD is a clinical diagnosis confirmed by histological evidences.
Acute GvHD can be staged by the number and extent of organ involvement. The current staging system is derived from Glucksberg first aGvHD classification in 1974 (Glucksberg et al., 1974, Transplantation; 18:4 295-304). Recent data support the use of the grading system, since it is able to subdivide patients into risk categories for complications and mortality. In this system, patients are divided into one of four grades (I-IV) depending on the degree or stage of involvement in three organs. The skin is staged with percent body surface involved, the liver is staged with degree of bilirubin elevation, and the gastrointestinal tract is staged with amount of diarrhoea. Using these criteria, a single grade is assigned to each patient (Jacobsohn et al., 2007, Orphanet J. of Rare Diseases; 2:35).
Various clinical manifestations of GvHD are known. The earliest and most common manifestation is skin GvHD. This is essentially a maculopapular rash that can begin anywhere in the body but often start with palm and sole involvement. The patient may complain of pruritus or tenderness in affected areas. In severe cases, blisters may occur. The gastrointestinal manifestations include diarrhoea, which may become bloody, cramping, nausea, vomiting and failure to thrive. Furthermore, jaundice from hyperbilirubinemia is the hallmark of liver GvHD (Jacobsohn et al., 2007, supra), although a hepatitic variant of GvHD with a rise in liver enzymes like an acute viral hepatitis, has been recognized (Akpek et al., 2002, Blood; 100: 3903-3907). Even if methylprednisolone is not registered in any European Countries for this indication, it is considered current standard of care in first line treatment of acute GvHD.
First line treatment of acute GvHD, with methylprednisolone 2 mg/kg/day is effective in over 50% of patients, but produces durable responses only in ⅓ of the patients. Non responders are offered second line therapy, which is based on combinations of immunosuppressive agents not registered in this indication. Second line therapy is largely unsatisfactory with one year survival of 30% in most large clinical trials. None of these strategies has achieved the level of success required to become standard of care. After 30 years of transplant experience steroid refractory acute GvHD (aGvHD), remains largely an untreatable disease. It has to be emphasized that aGvHD patients resistant to steroid therapy have very limited therapeutic options and that there are no currently authorized treatments for this clinical situation. This condition is life-threatening in particular due to the increased mortality in this patient population, particularly secondary to infection.
Any clinically relevant result in this patient population would be of significant benefit as it would offer a clinically relevant advantage for steroid resistant aGvHD patients.
Moreover, approaches for facilitating engraftment after haematopoietic stem cell transplantation, will be useful. Engraftment is the process in which the transplanted stem cells find their way to the bone marrow spaces in the centre of the large bones of the body. Only then can the transplanted stem cells begin to produce new blood cells. Experts are not completely certain how this process happens but it is generally acknowledged that this is a long process: it takes approximately two to four weeks after the bone marrow is infused for engraftment to occur. Until the blood stem cells engraft, the patient will be at risk of developing an infection. This is because the transplanted patient has been normally subjected to radiation and/or chemotherapy, whose result is the destruction of the white blood cells in the patient's body. While waiting for the engraftment, a transplanted patient could suffer of serious complication due to an infection (caused by bacteria, virus or fungus), which is one of the main cause of transplant related mortality after Bone Marrow Transplantation (BMT). Accordingly, there is a need in the art for an agent able to improve engraftment. Such an agent will be of significant value for BM transplanted patients. If homing and engraftment can be enhanced, the time to recovery of hematopoietic lineages can be reduced resulting in less engraftment failures and better overall survival, especially in UCB transplantation (Broxmeyer, H. E. (2006). Umbilical Cord Blood Stem Cells: Collection, Processing, and Transplantation. Blood Banking and Transfusion Medicine: Basic Principles and Practice. C. D. Hillyer et al., Churchill Livingston, an imprint of Elsevier, Inc.: 823-832; Lewis, 2002, Intern Med J 32(12): 601-9).
Aplastic anemia is a type of anemia, wherein bone marrow fails to produce sufficient amounts of blood cells for replenishing blood cells. In particular, a congenital and an acquired form of aplastic anemia may exist. Acquired aplastic anemia (AA) is a rare bone marrow failure state characterized by marrow hypocellularity and low peripheral blood cell counts [Young N S, Maciejewski J P. The pathophysiology of acquired aplastic anemia. N Eng J Med 1997, 336:1365-1372]. The evidence of an autoimmune pathogenesis is mostly indirect and the characterization of the underlying immune response is incomplete mainly due to technical difficulties resulting from the disease-specific hypocellularity. Acquired Aplastic anemia is thought to be an immunomediated disease, and current standard non transplant therapy is anti-thymocyte globulin (ATG) plus cyclosporin A (CsA). Failures include patients not responding to first line (30%) and patients relapsing after a first response (30%), such that event free survival does not exceed 30-40% (Bacigalupo A., Passweg J., 2009, Hematol Oncol Clin North Am. 23: 159-70).
Untreated aplastic anemia may lead to death, in some cases even within a short period of merely several months. Current treatments of aplastic anemia encompass for example bone marrow transplantation or immunosuppressive drug therapies. Immunosuppressive drug therapies fail however in a significant number of cases and bone marrow transplantation is not possible in absence of an appropriate donor. Thus, there is also a need in the art to provide alternative agent(s) for treating aplastic anemia, which preferably may be effective for treating patients which are non-responsive to at least one other therapy.