Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-08-27
2002-03-26
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C523S346000, C523S351000
Reexamination Certificate
active
06362271
ABSTRACT:
BACKGROUND OF INVENTION
The invention relates to miscible polymer blends comprising polyvinylidene fluoride (“PVDF”) and its copolymers, and polyalkyl methacrylates having a molecular weight from about 25,000 grams per mole to about 200,000 grams per mole, including polymethyl methacrylate (“PMMA”). The terms polyvinylidene fluoride and polyalkyl methacrylate as used herein are meant to encompass polymers comprising these materials, including homopolymers of these materials and copolymers comprising these materials. Miscible polymer blends can be generally described as polymer blends that are homogeneous down to the molecular level associated with a negative value of the free energy of mixing. The invention provides miscible polymer blends with superior and unexpected physical characteristics, including solvent resistance, gloss retention and adhesion after weathering.
Polyvinylidene fluoride, in particular, PVDF is a very important raw material for architectural coatings based largely on ultraviolet (“UV”) light transparency. PVDF, for example, provides long term protection for metal surfaces against exterior exposure, much better than other known coating materials. In order to balance the performance of polyvinylidene fluoride coatings, such as PVDF coatings, a secondary resin normally is needed to provide good adhesion to substrate, to reduce the shrinkage of the polyvinylidene fluoride due to excess crystallization, to increase the dispersability of a pigment in a coating and to obtain good optical properties. The selection of the secondary resin is based largely on the miscibility of the resin with polyvinylidene fluoride polymers.
Blending polymers has been an important industrial approach towards development of polymeric coating materials, however much of the development work has been based on compatibility of polymers. PVDF is compatible with a few industrial polymers, including polymers of alkyl methacrylate and alkyl acrylates with carbon content on alkyl groups of less than 3. The polymers miscible with PVDF, as well as other polymers comprising polyvinylidene fluoride, have the common characteristic of high concentrations of C═O groups, particularly on side chains of the carbon polymer.
PVDF is thermodynamically miscible with polymers of alkyl methacrylate and it is discovered by the inventors that PVDF is thermodynamically miscible with polymethyl methacrylate having a molecular weight of from about 25,000 grams per mole to about 250,000 grams per mole which, as a miscible polymer blend, unexpectedly results in a blend having superior physical characteristics favorable for weather resistant coating materials.
U.S. Pat. Nos. 4,770,939 and 5,030,394 to Sietses et al. (“Sietses”) describe a process for preparing blends comprising PVDF having molecular weight of between about 10,000 and 70,000 with thermoplastic PMMA. According to Sietses, coating materials made with the process of that invention with PVDF having molecular weights above 70,000 are said to be unacceptable because the coating material remains too viscous when treated with heat during application on a substrate. The blends in Sietses are cryogenically ground to a powder and require the use of a flow promoter. Powder coating requires a low melt viscosity. Therefore, high molecular weight polymers are not suitable for such application. This is different from dispersion coating such as that of the invention, which allows the use of polymers having from low to high molecular weight. The Sietses patent concerns the use of low molecular weight polymers for processibility rather than the optimization of coating performance.
For comparison, Sietses prepared a dispersion coating comprising PVDF with a molecular weight of about 350,000 and viscosity of about 31,000 poise and an unspecified thermoplastic methyl methacrylate polymer. Because of the lack of optimization it has only 85% gloss retention after 2,000 hours. The current invention exhibited the optimized polymethyl methacrylate structure, that is a molecular weight of between about 25,000 grams per mole and about 200,000 grams per mole to provide 100% of gloss retention after 5,000 hours of QUV exposure as illustrated in FIG.
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U.S. Pat. No. 3,324,069 to Koblitz et al. discusses dispersions of PVDF and acrylate polymer. The disclosure of this patent does not address miscibility of the polymer and characterizes the compositions as alloys. This patent indicates that addition of more than 25% acrylate polymer is unfavorable as it causes a significant reduction in the properties of the PVDF.
U.S. Pat. No. 5,082,616 to White (“White”) describes a method for preparing biaxially oriented PVDF/PMMA films comprising blends of PVDF with a molecular weight of about 330,000 to about 390,000 and PMMA with a molecular weight of about 110,000 to about 125,000. The amount PMMA in the film, or other polymers, is from about 10% to about 30% of the film, and it is said in White that addition of more than about 30% other polymer detrimentally affects the physical properties of the film. The biaxially oriented film is made by a double bubble process.
The properties and characteristics of PVDF and PMMA blends can be fashioned to achieve purposes of a particular application. In White, for example, PVDF/PMMA blends are formulated to obtain films and not coating compositions. An aspect of the invention in White is retarding the crystallization of PVDF during the double bubble processing method used to obtain the film.
Thus, the film obtained by the method in White comprises PVDF with a lower crystallinity than the PVDF in blends of the invention. With respect to the coating compositions of the invention described herein, it is desired to maintain the crystalline structure of the vinylidene fluoride as this results, in part, in the unexpected properties of the weather resistance and solvent resistance of the coating compositions. The coating composition maintains crystallinity of the vinylidene fluoride polymer by employing a solvent preparation method. The polymers are blended in a latent solvent and then a pigment is added. The solvated blend is then heated to remove the solvent thus forming the coating composition. The coating composition of the invention has highly crystalline polyvinylidene fluoride and the retardation of crystallization of the polymer during coating formation.
The invention described herein is a coating used on substrates. White describes PVDF films capable of exhibiting desirable piezoelectric properties and, thus, White does not describe weather coating compositions, and characteristics such as gloss retention and solvent resistance are not important or characteristics of the piezoelectric films of White. It is not uncommon for polymers with similar content to be different and exhibit different characteristics based on internal or molecular structural differences. White, for example, concerns a biaxially oriented film with PVDF having retarded crystallinization as contrasted with the coating preparation of the invention. The invention exhibits superior qualities such as gloss retention and solvent resistance after QUV exposure. This is achieved, in part, by the crystalline structure of the polyvinylidene fluoride, such as PVDF, which remains significantly unaffected during blending of the vinylidene fluoride polymer with other polymers.
U.S. Pat. No. 3,607,754 to Asahina concerns the use of PVDF/PMMA blends for their piezoelectric properties and concerns blends with very high molecular weight PMMA, that is about 1,000,000 grams per mole, for use as electrets. U.S. Pat. No. 4,822,122 to Yamamato concerns PVDF/PMMA blends used as optical transmission media. These patents provide further examples of the use of vinylidene fluoride polymer and polyalkyl methacrylate blends formulated to achieve desired properties and characteristics for particular applications.
The present invention utilizes miscible blends comprising polyalkyl methacrylates such as PMMA, within a certain molecular weight range and vinylidene fluoride polymers, such as PVDF for coatings
Argasinski Karol
Kamsler Craig
Lin Shiow-Ching
Ausimont USA, Inc.
Cain Edward J.
Norris & McLaughlin & Marcus
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