Patent Application
20060210715
This invention relates to compositions of matter classified in the art of chemistry as fluoropolymers, more specifically to copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) and still more specifically to such copolymers having very low or no crystallinity, to processes for their use and the products produced by such use processes. The copolymers at all levels of HFP content remain highly flexible, thermoplastic copolymers which show low surface tack even at high HFP levels and thereby permit use of such copolymers in unique applications for which polyvinylidene fluoride homo- and copolymers previously known were not considered suitable, or were considered suitable only when combined with other polymers or other materials such as primers and the like.
Fluoropolymers and copolymers of VDF, collectively VDF-based polymers wherein the VDF portion is greater than the total molecular percent of comonomers, are well known and widely used. Among the variety of fluoropolymers based upon tetrafluoroethylene, chlorotrifluoroethylene, and other specialty fluorine-containing monomers, the VDF polymers are unique offering the widest possible range of processing options to obtain articles having the beneficial attributes associated with improved chemical resistance and surface properties associated with the high concentration of carbon fluorine bonds. Thus, among the wide spectrum of fluoropolymers, the VDF polymers may be melted in typical processing equipment for thermoplastic resin for extrusion or molding or combinations such as extrusion-blown film and molding tanks.
This versatility in processing options is related to the linear polymer chain structure and the presence of the highly polar-CF2-groups alternating along the VDF polymer chain. The microstructure of the polymer chain and morphology of these polymers reflects these two factors in many interesting ways as described in Polymeric Materials Encyclopedia, 1996, Vol. II, CRC Press; Vinylidene Fluoride-Based Thermoplastics (Overview and Commercial Aspects), J. S. Humphrey, pp. 8585 to 8588; Vinylidene Fluoride-Based Thermoplastics (applications), J. S. Humphrey and E. J. Bartoszek, pp. 8588-8591; Vinylidene Fluoride-Based Thermoplastics (Blends with Other Polymers), J. S. Humphrey and X. Drujon, pp. 8591-8593; Vinylidene Fluoride-Based Thermoplastics (Homopolymerization and Copolymerization), J. S. Humphrey and X. Drujon, pp. 8593-8596.
Low crystallinity fluorinated polymers are highly useful, particularly as coating and encapsulants, because of their low surface energy, low refractive index, good chemical resistance, and the relative ease of coating or encapsulating objects with such inert polymers. The balance between amorphous and crystalline regions, the nature and extent of the crystalline regions, and the interphase between these regions affects the processability options to obtain articles having the beneficial attributes and hence, the ultimate applications for a given resin composition.
Copolymers of VDF and HFP vary in their properties. At one end of the spectrum there are totally amorphous thermoplastic polymers and at the other extreme the highly crystalline polymers. The microstructure of the polymer chain determines the flexibility (or alternately the stiffness) at a given temperature. This mechanical behavior is controlled by the type and amount of the crystalline phase (if any) and the dynamics of the molecular motion along the chain such that at some temperature the polymer undergoes a second order change in response to applied stresses, the so-called glass transition temperature (Tg). Above the Tg the polymer chain has molecular motions which are free to rotate, stretch, etc. and thereby absorb the energy input. Below the Tg the molecular motions are frozen and the stresses may lead to brittle fracture or glass-like behavior.
The immediate invention is concerned more with the morphology and crystalline/amorphous ratio of the VDF polymers and the ultimate end uses. It is therefore important to understand the background of the present invention in the context of the teaching how crystalline and amorphous content fit into the range of polymers which are classed as thermoplastic engineering resins or thermoplastic elastomeric resins. In this particular invention, the key attribute is related to highly flexible resins related to both categories. This invention employs a variety of VDF-HFP resins, which are to the low level of crystallinity compared to resins of the otherwise same nominal monomer ratio composition produced by standard teachings. Thus, the present invention relates to a novel fluoro-thermoplastic having a unique combination of properties including excellent flexibility, low temperature processability, high clarity, solution stability and room temperature film forming capability from aqueous dispersion and which, as stated above, enables them to be used in unique ways.
U.S. Pat. No. 3,051,677 describes batch emulsion and continuous emulsion processes for copolymerization of vinylidene fluoride and hexafluoropropylene (HFP) in the range of 30 to 70 weight percent of hexafluoropropylene monomer and 70 to 30 weight percent vinylidene fluoride monomer. The copolymers described in this reference have relatively high crystallinity as is confirmed by the properties described in the document for the products exemplified. Analogous materials from a batch process are described by Moggi, et al., in Polymer Bulletin, Vol. 7 pp. 115-122 (1982).
U.S. Pat. No. 3,178,399 describes both batch and semi-continuous emulsion processes for preparing HFP-VDF copolymers having between 85 and 99 mole percent VDF and 1 and 15 mole percent HFP (approximately 2 to 30 weight percent HFP and 70 to 98 weight percent VDF). Once again, the copolymers produced having relatively high internal crystallinity and this fact is evidenced by the physical data provided for those copolymers actually exemplified. This patent discloses that Tensile X Reversible Elongation was increased as the overall HFP proportion decreased in the copolymer. This implies that crystallinity increases as HFP content decreases.
U.S. Pat. No. 5,093,427 describes HFP-VDF copolymers, with the other extreme crystalline melting behavior, containing from about 1 to 20 weight percent HFP wherein, based on the synthetic method described, a polymer containing significant portions having a high proportion of HFP in the copolymer results. Thus, compositions of the copolymers described in this reference are intended to be highly crystalline which in turn are significantly different from the copolymers contemplated by the present invention.
Indonesian Patent Application W-980105, published Nov. 26, 1998 as number 020.295A equivalent to WO 98/38242 and to U.S. patent application Ser. No. 09/031,014, the contents of which have been included in CIP application Ser. No. 09/641,015 discloses an emulsion process for producing HFP-VDF copolymers having more homogenous distribution of the comonomers from to chain than polymers of the prior art thereby having reduced extractable content and improved solution clarity over HFP-VDF copolymers prepared according to the techniques of the preceding references. These materials differ from the copolymers of the present invention because the products of the present invention have crystallinity level well below of those of corresponding polymers of W-9809105.
In Polymer, Vol. 27, pp. 905 (1986) and Vol. 28, pp. 224 (1987), Moggi, et al., report synthesis of HFP-VDF copolymers and studies of various physical properties and how these may be correlated to certain internal structural features such as crystallinity, monomer sequencing in individual molecules and the like. The limited synthesis information indicates that the polymers formed were analogous to those prepared according to the previous references except for U.S. patent application Ser. No. 09/031,014 and the limited physical data provided is consistent with this interpretation and that the polymers described had a high degree of crystallinity.
Although it is well established in the prior art to reduce crystallinity by means of adding higher amounts of HFP to the copolymer, there is no prior art suggesting how to produce as low crystallinity as is provided by the present invention at any given nominal proportion of HFP. Thus, the copolymers employed herein have measurably lower crystallinity at any given HFP level than copolymers with the same nominal HFP content produced in accordance with processes enabled by any of the above listed references and, thus have use properties completely unpredictable from the properties of previously known VDF/HFP copolymers.
U.S. Pat. No. 4,618,641 discloses treatment of fabric with concentrated dispersions of vinylidene fluoride copolymers stabilized with nonhalogenated carboxylic acid surfactants. High solids concentrations are required and the fabric treatments must be heat set. The present invention using the copolymers described herein are able to accomplish the same or better treatment results using lower solids concentrations, while avoiding the need for a specific class of detergents.
U.S. Pat. Nos. 4,983,459 and 4,997,684 disclose methods of treatment and the dirt, stain repellant and non wetting surfaced articles treated with a mixture of a perfluoroalkyl silane and a fluorinated olefin telomer. The surfaces treated are stated to be glass compositions, or other inorganic surfaces such as ceramics, enamels, metal or metal oxide films. The formula given for the fluorinated telomer excludes the copolymer of this invention and the present invention provides an adherent coating on glass, metal and other mineral, ceramic and the like surfaces without the need of any silane additive primer coat.
Chem. Abstracts: CAN 70:79210, abstracting Mekh. Polim (1968) 4(6), 1065-70 summarizes the effect on the adhesive properties due to treatment of a film of semicrystalline VDF/HFP copolymers on steel, and window glass. The steel and glass coated with the film were subjected to treatment at 200 to 280° for 1 to 120 minutes. Treatment of the film coated steel at 280° C. for 2 hours greatly improved adhesion of the film and resistance to boiling water due to formation of Fe2O3 under the coating. HCl and HNO3 introduced at the interface between the film and either glass or steel reduced adhesion. While the abstract concludes that adhesion is possible at temperatures below the melting point of the film no actual values are provided. Given the fact that later literature indicates that satisfactory adhesion of VDF homo-and copolymers including these with HFP known prior to the copolymer used in the present application required alloying with nonfluoropolymers at least the use of primer coats for satisfactory adhesion to substrates such as glass and steel, this abstract provides no information which would lead one having knowledge in the art to discover the unique use properties applicants have found for the VDF/HFP copolymers described and used herein.
U.S. Pat. No. 4,347,268 discloses coatings made from metallic oxide free solvent solutions of elastomeric copolymers of HFP and VDF in the VDF/HFP concentration ranges of U.S. Pat. No. 3,051,677 and a vinyl copolymer by applying the solution to a surface and evaporating the solvent. Suitable substances for coating are stated to be aluminum, steel, glass, EPDM and nitrile rubber.
U.S. Pat. No. 4,764,431, corresponding to EP 0192 494 B1 discloses the use of solvent solutions of copolymers of VDF and HFP in the VDF/HFP concentration ranges of U.S. Pat. No. 3,051,677 for applying coatings for protecting and consolidating stone materials.
EP 0481 283 B1 corresponding to U.S. Pat. Nos. 5,219,661 and 5,270,115 discloses solvent based reversible polymer gels for treating and consolidating stone materials and impregnating various fabrics including glass cloth. One essential material is an elastomeric VDF/HFP copolymer in the VDF/HFP concentration ranges of U.S. Pat. No. 3,051,677 and a second essential component is a polymer selected from non elastomeric vinylidene fluoride polymer or copolymer, a vinyl fluoride polymer or a (meth)acrylate polymer or copolymer.
U.S. Pat. No. 4,141,873 describes an aqueous based vinylidene fluoride polymer film forming suspension for coating various substrates which also contains a suspension of a (meth)acrylate polymer and a water dispersible latent solvent for the two polymers.
U.S. Pat. No. 4,985,282 corresponding to EP 0374 803 B1 discloses the protection of surfaces of stony materials, tiles, cement conglomerates and relevant manufactured articles by applying a mixture of an aqueous dispersion of a VDF/HFP elastomer in the VDF/HFP concentration ranges of U.S. Pat. No. 3,051,677 and an aqueous emulsion or microemulsion of a perfluoropolyether by conventional methods to such surfaces.
U.S. Pat. No. 5,212,016 corresponding to EP 0479 240 B1 describes consolidating of and protection of surfaces of stone, marble, sandstone, bricks concrete and articles manufactured therefrom by applying solvent solution of an mixture of a then known nonelastomeric polyvinylidene fluoride homo- or copolymer or a polyalkyl methacrylate and an elastomeric copolymer of VDF and HFP in the VDF/HFP concentration range of U.S. Pat. No. 3,051,677.
U.S. Pat. No. 4,125,673 teaches rendering the surfaces of inorganic materials olephobic and hydrophobic by applying to their surfaces a solution or dispersion of a fluorine containing organic polymer or a solution of a water soluble polymer of an unsaturated carboxylic acid and solution of an organosilicon compound.
EP 0739 869 A1 teaches improving the reinforcing power and protective effectiveness of the separate components by combining in an aqueous composition an inorganic silicate or colloidal silica and a fluoroelastomer based on VDF and HFP in the VDF/HFP concentration range of U.S. Pat. No. 3,051,677 optionally containing other comonomers.
Applicants are unaware of any art related to forming stable, self-supporting open celled foam (reinforced or unreinforced) from any polymer simply by freezing a latex or suspension of such polymer and allowing the aqueous phase to drain after allowing the aqueous phase to thaw.
The copolymers of VDF and HFP employed in the processes of the present invention are more fully described in copending application PCT/US00/30449.
By a vinylidene fluoride hexafluoropropylene copolymer having from about 1 to 66 weight percent hexafluoropropylene content having low crystallinity is meant that such copolymers have measurably lower crystallinity than copolymers produced according to the prior art references, which provide sufficient details for a reproductive synthesis of the materials described therein. Thus, the copolymers having 36% by weight or greater HFP content have the heats of fusion calculated from any endotherms detected in a differential scanning calorimeter (DSC) scan (described below), of about 0 J/g and for copolymers having less than 36 weight percent HFP content any endotherm detected in a DSC scan as described below is at least about 1.5 J/g less than the endotherm detected for copolymers of substantially (±1.00 weight percent) similar HFP content for copolymers produced according to the prior art listed above. Thus, the copolymers having from greater than 0 to 28.5 weight percent HFP content have an endotherm of melting on the second heating cycle which is defined by the relationship:
ΔH=56.49−1.854 (HFP wt %)
and the copolymers having from greater than 28.5 up to less than 36 weight percent HFP content have an endotherm of melting on the first heating cycle which is defined by the relationship:
ΔH=54.81−1.53 (HFP weight percent).
In addition, the copolymers of from greater than 0 to 30 weight percent HFP also have lower DSC melting points at a given HFP content than any of the copolymers of the same HFP content described in any of the references cited above and the melting point for a copolymer having a particular HFP content in the greater than 0 to 30 weight percent HFP range is defined by the relationship:
Melt Temp. (° C.)=162.16−3.192 (HFP weight percent).
Copolymers having greater than 30 weight percent HFP produced according to such prior art all exhibit exotherms in their DSC scans run as described below significantly greater than O/J/g. Those having lower than 30% HFP content all have high crystallinity as defined by higher ΔH of melting determined by DSC than those of this invention.
The DSC scan measuring the crystalline content is performed according to ASTM D 451-97 using a Perkin Elmer 7 DSC apparatus with an Intercooler II attachment. The instrument is equipped with a dry box with an N2 purge through the dry box. Specimens of 9 to 10 mg are used and crimped in aluminum pans.
For samples with a low degree of crystallinity, the DSC run is begun at −50° C. followed by a 110° C./min ramp to 180° C.
For samples with an HFP content lower than 30 weight percent and, thus, a higher degree of crystallinity, the DSC run is performed in a three step cycle. The cycle is begun at −50° C. followed by a 10° C./min ramp to 180° C. with a 10 minute hold. The sample is then cooled at a rate of 10° C./min to −50° C. and then reheated at the 10° C./min rate to 180° C.
In comparison with other previously known copolymers of VF2/HFP produced by the above cited references, the reduced crystalline content of VF2/HFP at a given HFP level provides a unique combination of properties among which are those offering the following advantages:
The low crystallinity polymers described herein are useful in a wide range of applications, many of which are related to the fact that the polymers are readily used as emulsions; therefore, there is no need for isolation, drying of the polymer. So the polymers of this invention are readily useable in latex form to produce films, coating and encapsulants. Films and coatings may be particularly useful because of the inherent properties of the polymer, such as lack of crystallinity (or haze), low surface energy (water repellency) low index of refraction, low coefficient of friction, etc.
One of unusual properties of the VDF and HFP copolymers used in the present invention is, as the crystallinity of the HFP copolymers decreases, it has been found that the Tg increases and still more surprisingly, it has been found that when blended with acrylic polymers, for the copolymers of the present invention, the Tg for the mixture actually increases with decrease of crystallinity at a given composition. This is highly unexpected because normally a homogeneous mixture of polymers shows an approximate value inversely proportional to the weight of each pure component times their respected 1/Tg (R. Amin-Sanayei, Macromolecules, Vol. 24, pp. 4479, (1991)).
For example, two copolymers of the present invention were mixed in equal parts by weight with three different polyacrylate esters and the Tg values for each mixture determined and compared with the Tg values for each identically proportioned mixture of a standard commercially available VDF/HFP copolymer which had a ΔH of melting of 372 (KYNAR® Flex 2750, available from ATOFINA Chemicals, Inc., Philadelphia, Pa. which contains about 15.5 weight percent HFP). All three copolymers had a Tg of about −25±2° C.
Copolymer sample 1 (sample 1) of the present invention had about 16.5 weight percent HFP content and a ΔH of melting of 30.4 while copolymer sample 2 (sample 2) of the present invention had about 14.1 weight percent HFP content and a ΔH of melting of 26.7.
A blend of 50 weight percent polymethylmethacrylate with the KYNAR Flex had, as expected, a Tg of 24.2° C., while the analogous mixture with sample 1 had Tg of 34.3° C. and the analogous mixture with sample 2 had Tg of 40.8° C.
A blend of 50 weight percent polyethylmethacrylate with the KYNAR Flex had, as expected, a Tg of 17.8°, while the analogous mixture with sample 1 had Tg of 26.3° C. and the analogous mixture with sample 2 had Tg of 30° C.
A blend of 50 weight percent polybutylmethacrylate with the KYNAR Flex had, as expected a Tg of 11.7° C., while the analogous blend with sample 1 had Tg of 18.6° C. and the analogous blend with sample 2 had Tg of 23.1° C.
HFP content was alternatively determined by 19F NMR using the following methods.
In preparation for the NMR analysis, VDF/HFP copolymer samples were dissolved in a 5 mm diameter NMR tube. Samples of less than 10 weight percent HFP were dissolved in acetone-d6 at 50° C. An amount of copolymer, 2 to 4 mg, was placed in a tube and enough solvent was added to fill the tube to 5.5 cm (about 0.75 ml of solvent). A heating block was used to bring the samples to temperature. The samples were heated for at least one hour, until the solid was dissolved and there was no gel present, but in the case of DMSO-d6, for a time no longer than 8 hours in order to avoid degradation. Tubes were inverted to check for gel.
Spectra were acquired on either a Bruker DMX or a Varian Mercury 300 spectometer operated at 80° C. in the case of DSMO-d6 solvent or at 50° C. in the case of acetone-d6 solvent.
Specific parameters for the instruments were as follows:
*No fluorine background observed on this instrument.
**This will be instrument dependent, depending on severity of background.
***This is inverse gated decoupling on the Bruker to improve resolution.
Spectra were analyzed according to the signal assignments described in Pianca et al., Polymer, Vol. 28, 224-230 (February 1987). As a check on the accuracy of the NMR acquisitions, the integrals of the CF3's and the CF's were compared to see if they were in a ratio of 3 to 1.
The synthetic technique described herein also provides a method for preparing a high solids small particle size latex of the copolymers of the invention.
This high solids small particle latex which because of its low crystallinity offers the following applied use properties in addition to those mentioned above:
Copolymers produced according to the prior art are those produced by the methods enabled by those references listed above and are the copolymers employed in the references cited above disclosing various uses of those copolymers.
The invention provides in a first process aspect, a process for the manufacture of a three dimensional open celled foam based on a polymer having low internal crystallinity and a Tg less and minimium film forming temperature than the freezing point of the aqueous phase of a latex or suspension containing such polymer in a dispersed phase which comprises:
Special mention is made of processes of the first process aspect of the invention wherein the polymer in the disperse phase in a vinylidene fluoride, hexafluoropropylene copolymer having from about 1 to about 66 weight percent hexafluoropropylene content and having low crystallinity.
Special mention is particularly made of processes where the vinylidene fluoride, hexafluoropropylene copolymer has greater than 30 weight percent hexafluoropropylene content.
Special mention is also particularly made of aspects of the process where the vinylidene fluoride, hexafluoropropylene copolymer has greater than 36% by weight hexafluoropropylene content.
Special mention is also made of aspects of the first process aspect of the invention where in the polymer in the disperse phase is in the presence of reinforcing fibers in said disperse phase or in a second disperse phase.
The invention provides in a first composition aspect, a three dimensional, self-supporting open cell foam prepared by the first process aspect of the invention.
The invention provides in a second process aspect, a process for the application of a self adherent polyvinylidene fluoride based polymer film coating on a substrate which comprises
The coated surfaces provided by the second process aspect of the invention are moisture and oil resistant, as well as fire retardant while retaining the original feel and look of the surface on which the coating was applied.
In an equivalent variation of the second process aspect of the invention, the vinylidene fluoride, hexafluoropropylene copolymer having low crystallinity may be applied to the surface as a suspension in water or an organic solvent or solvents or as solution in an organic solvent or solvents and the water or organic solvent or solvents evaporated to leave a coating on said surface.
Particular mention is made that the surfaces to be coated may be natural and or artificial materials either in fiber form or on the surface of larger flat or three dimensional objects which may be natural stone such as marble, limestone, granite, man made building material such as bricks, mortar, cementitious materials such as hardened Portland cement and concrete, as well as glass, metal objects such as iron, steel, aluminum, carbon and such fibers as glass fibers, carbon fibers and fibers from natural and synthetic polymers such as cotton, wool, linen, cellulose, rayon, nylons, aramids, polyolefins and the like.
The invention provides in a second composition aspect, an article of manufacture coated on at least one surface thereof with a vinylidene fluoride, hexafluoropropylene copolymer having low crystallinity.
Special mention is made of aspects of the second process and composition aspects of the invention wherein the VDF/HFP copolymer contains from about 1 to about 66 weight percent HFP, more particularly where it contains greater than 20 weight percent HFP and still more particularly where it contains greater than 36 weight percent HFP.
Special mention is also made of aspects of the invention wherein glass fibers either reinforcing the foam aspect of the invention or coated to form the second composition aspect of the invention are either coated with the conventional phenolic coating employed in the manufacture of glass fiber or are uncoated with such phenolic coating prior to coating with the vinylidene fluoride, hexafluoropropylene copolymers contemplated for use in the invention.
The manner of practicing the process of the invention and of making and using the embodiments of the invention will now be illustrated with reference to specific embodiments thereof.
The vinylidene fluoride, hexafluoropropylene copolymers employed by the invention are conveniently made by an emulsion polymerization process, but suspension and solution processes may also be used. In an emulsion polymerization process, a reactor is charged with deionized water, water soluble surfactant capable of emulsifying the reactor mass during polymerization and the reactor and its contents are deoxygenated while stirring. The reactor and contents are heated to the desired temperature and vinylidene fluoride, hexafluoropropylene and, optionally, chain transfer agent to control copolymer molecular weight are added. When the desired reaction pressure is reached, initiator to start and maintain the reaction is added. To obtain the VDF/HFP copolymer used in the present invention, the initial charge of VDF and HFP monomers is such that the weight ratio of HFP to VDF is an exact first ratio which is from three to five times the weight ratio of HFP to VDF to be fed during the reaction. HFP and VDF are fed during the reaction in a proportion such that the total amount of HFP added over the entire course of the reaction is approximately equal to the proportionate amount of HFP desired in the final copolymer. The VDF/HFP ratios, are thus, different in the initial charge and in the continuous feed. The process uses total amounts of VDF and HFP, monomers such that the amount of HFP incorporated in the total copolymer is up to about 66 wt. % of the combined total weight of the monomers.
To determine the exact first ratio for a particular reaction to provide the optimum low crystallinity at any desired HFP ratio at a desired reaction temperature and pressure, one of skill in the art will understand how to perform a few pilot scale runs varying the initial HFP concentration in the desired range to select the proper exact ratio while keeping other reaction conditions constant.
The reactor is a pressurized polymerization reactor preferably a horizontal polymerization reaction equipped with a stirrer and heat control means. The temperature of the polymerization can vary depending on the characteristics of the initiator used, but it is typically between 30° and 130° C., and most conveniently it is between 50° and 120° C. The temperature is not limited to this range, however, and might be higher or lower if a high-temperature or low-temperature initiator is used. The pressure of the polymerization is typically between 20 and 80 bar, but it can be higher if the equipment permits operation at higher pressure. The pressure is most conveniently between 40 and 60 bar.
Surfactants used in the polymerization are water-soluble, halogenated surfactants, especially fluorinated surfactants such as the ammonium, substituted ammonium, quaternary ammonium, or alkali metal salts of perfluorinated or partially fluorinated alkyl carboxylates, the perfluorinated or partially fluorinated or partially fluorinated monoalkyl phosphate esters, the perfluorinated or partially fluorinated monoalkyl phosphate esters, the polyether carboxylates, the perfluorinated or partially fluorinated alkyl sulfates. Some specific, but not limiting examples are the salts of the acids described in U.S. Pat. No. 2,559,752 of the formula X(CF2)nCOOM, wherein X is hydrogen or fluorine, M is an alkali metal, ammonium, substituted ammonium (e.g., alkylamine of 1 to 4 carbon atoms), or quaternary ammonium ion, and n is an integer from 6 to 20; sulfuric acid esters polyfluoroalkanols of the formula X(CF2)nCH2OSO3M, where X and M are as above; and salts of M are as above; n is an integer from 3 to 7, and m is an integer from 0 to 2, such as in potassium perfluorooctyl sulfonate. The surfactant charge is from 0.05% to 2% by weight on the total monomer weight used, and most preferably the surfactant charge is from 0.1% to 1.0% by weight.
A paraffin antifoulant may be employed, if desired, although it is not preferred, and any long-chain, saturated, hydrocarbon wax or oil may be used. Reactor loadings of the paraffin may be from 0.01% to 0.3% by weight on the total monomer weight used.
After the reactor has been charged with deionized water, surfactant, and any optional paraffin antifoulant, the reactor is either purged with nitrogen or evacuated to remove oxygen. The reactor is brought to temperature, and chain-transfer agent may optionally be added. The reactor is then pressurized with a mixture of vinylidene fluoride and hexafluoropropylene.
Chain-transfer agents which may be used are well-known in the polymerization of fluorinated monomers. Alcohols, carbonate esters, ketones, carboxylate esters, and ethers are oxygenated compounds which serve as chain-transfer agents. Specific, but not limiting examples, are isopropyl alcohol, such as described in U.S. Pat. No. 4,360,652, acetone, such as described in U.S. Pat. No. 3,857,827, and ethyl acetate, as described in the published Unexamined Application (Kokai) JP 58065711. Other classes of compounds which serve as chain-transfer agents in the polymerization of fluorinated monomers as halocarbons and hydrohalocarbons such as chlorocarbons, hydrochlorocarbons, chlorofluorocarbons, and hydrochlorofluorocarbons all having 1 to 6 carbon atoms; specific, but not limiting examples are trichlorofluoromethane, such as described in U.S. Pat. No. 4,569,978, and 1,1-dichloro-2,2,2-trifluoroethane. Chain-transfer agents may be added all at once at the beginning of the reaction, in portions throughout the reaction, or continuously as the reaction progresses. The amount of chain-transfer agent and mode of addition which is used depends on the activity of the agent and the desired molecular weight characteristics of the product. The amount of chain-transfer agent used is from 0.05% to 5% by weight on the total monomer weight used, and preferably it is from 0.1 to 2% by weight.
The reactor is pressurized by adding vinylidene fluoride and hexafluoropropylene in a definite ratio (exact first ratio) such that the hexafluoropropylene ratio in the VDF/HFP mixture initially charged ranges from about 3 to 5 times the ratio of hexafluoropropylene fed into the reactor during the reaction. The exact ratio can be selected by a series of controlled laboratory runs as described above.
The reaction can be started and maintained by the addition of any suitable initiator known for the polymerization of fluorinated monomers including inorganic peroxides, “redox” combinations of oxidizing and reducing agents, and organic peroxides. Examples of typical inorganic peroxides are the ammonium or alkali metal salts of persulfates, which have useful activity in the 65° C. to 105° C. temperature range. “Redox” systems can operate at even lower temperatures and examples include combinations of oxidants such as hydrogen peroxide, t-butyl hydroperoxide, cumene hydroperoxide, or persulfate, and reductants such as reduced metal salts, iron(II) salts being a particular example, optionally combined with activators such as sodium formaldehyde sulfoxylate or ascorbic acid. Among the organic peroxides which can be used for the polymerization are the classes of dialkyl peroxides, peroxyesters, and peroxydicarbonates. Exemplary of dialkyl peroxides is di-t-butyl peroxide, of peroxyesters are t-butyl peroxypivalate and t-amyl peroxypivalate, and of peroxydicarbonates are di-n-propyl) peroxydicarbonate, diisopropyl peroxydicarbonate, di(sec-butyl) peroxydicarbonate, and di(2-ethylhexyl) peroxydicarbonate. The use of diisopropyl peroxydicarbonate for vinylidene fluoride polymerization and copolymerization with other fluorinated monomers is taught in U.S. Pat. No. 3,475,396, and its use in making vinylidene fluoride/hexafluoropropylene copolymers is further illustrated in U.S. Pat. No. 4,360,652. The use of di(n-propyl) peroxydicarbonate in vinylidene fluoride polymerizations is described in the Published Unexamined Application (Kokai) JP 58065711. The quantity of an initiator required for a polymerization is related to its activity and the temperature used for the polymerization. The total amount of initiator used is generally between 0.05% to 2.5% by weight on the total monomer weight used. Typically, sufficient initiator is added at the beginning to start the reaction and then additional initiator may be optionally added to maintain the polymerization at a convenient rate. The initiator may be added in pure form, in solution, in suspension, or in emulsion, depending upon the initiator chosen. As a particular example, peroxydicarbonates are conveniently added in the form of an aqueous dispersion.
As the reaction progresses, a mixture of vinylidene fluoride and hexafluoropropylene monomers is fed in a definite ratio (second effective ratio) so as to maintain reaction pressure. The proportion of hexafluoropropylene in the second effective ratio used corresponds to the monomer unit ratio desired in the final composition of the copolymer, and it can range up to 66% of the combined weight of the monomers being fed continuously throughout the reaction. The feed of vinylidene fluoride, hexafluoropropylene, and optionally initiator and chain-transfer agent is continued until the desired solid content is obtained.
Upon reaching the desired solids level in the reactor, the feed of monomers is discontinued, but the feed of initiator is continued to consume residual monomers. To minimize compositional drift at this stage, after the reactor pressure drops by 10 to 20 bar from the continuous reaction pressure, a portion of VDF is added to bring the reactor pressure back up to the initial set point and initiator feed continues until the reactor pressure falls about 15 to 25 bar. After a delay time of about 10 to 20 minutes the reactor is cooled as quickly as possible. After reaching ambient temperatures (20° to 35° C.), the unreacted monomers are vented and the latex produced by the reaction is drained into a suitable receiving vessel. To obtain dry resin, the latex is coagulated by conventional methods, the coagulum is separated and the separated coagulum may be washed. To provide powder, the coagulum is dried.
For the coagulation step, several well-known methods can be used including freezing, the addition of acids or salts, or mechanical shear with optional heating. The powder, if desired, can be further processed into pellets or other convenient resin forms.
One of skill in the art will recognize that small quantities of a third monomer known to be copolymerizable with VDF (up to about 10% by weight of the HFP level) may also be included in the above described synthesis to provide VDF based terpolymers also having low crystallinity. Such known copolymerizable monomers may, for example, be selected from among C(2-8) alkenes containing at least one fluorine atom besides HFP, an alkyl vinyl ether containing at least one fluorine atom, an aliphatic or cyclic C(3-6) ketone containing fluorinated α-α′ positions and non-fluorinated C(2-4) unsaturated hydrocarbons, C(3-6) alkyl vinyl ethers or C(4-6) vinyl esters.
The techniques of practicing the processes of the invention and making the compositions produced by such processes are conventional and are not considered by of the invention per se, although it is considered surprising that in contrast to previously known VDF/HFP copolymers, these techniques can be employed without the mandatory use of alloying polymers, or primer coatings required by such previously known copolymers to attain adhesion and that simple freezing of a latex of the polymers, including particularly the low crystallinity VDF/HFP copolymers, contemplated by the invention is capable of forming a self supporting open cell foam.
To practice the first process aspect of the invention and prepare the first composition aspect of the invention, a latex of the VDF/HFP copolymers having low crystallinity, prepared as described above, is simply placed into a closed mold having a internal shape which is a mirror image of the desired outer shape of the final foam and the mold and contents chilled by any convenient means to a temperature below the freezing point of the aqueous phase and above the glass transition temperature (Tg) of the polymer. Preferably the copolymer may contain from about 30 to 99% by weight vinylidene fluoride with the balance being hexafluoropropylene.
The substitution of tetrafluoroethylene (TFE) and/or chlorotrifluoroethylene (CTFE) for some or all of the hexafluoropropylene in the above described synthetic procedure to make VDF copolymers also having low crystallinity and having equivalent properties in the processes of the invention and, thus, providing equivalent foams or coated materials is contemplated by the invention. Also contemplated as equivalents by the invention in use in the first process aspect of the invention to form shaped foams are any other low crystallinity or amorphous polymer prepared by suspension or emulsion polymerization having Tg below the freezing point of the aqueous phase of the latex emulsion or suspension and a softening point above the thaw point of the frozen aqueous phase. Such polymers are well known to skilled polymer chemists and readily identified in the art.
For the coating processes contemplated by, the invention, the latex of formation of the VDF/HFP copolymers having low crystallinity or their equivalent TFE and/or CTFE containing analogs prepared by the processes described above may be used as obtained from the reaction mixture or preferably diluted for coating fibers, woven and non-woven fabrics and for impregnating the various natural and artificial stony and cementitious construction materials contemplated by the invention or the polymer may be isolated from the latex and suspended in aqueous or nonaqueous solvents, or dissolved in suitable solvents and applied to the substrate to be treated. Suitable concentration ranges for a particular treatment on a particular substrate may readily be determined by one of skill in the art with a few well-chosen pilot treatments to optimize the coating desired.
For treatment on solid glass and metal objects, it has been found that use of the latex as obtained from the synthesis preferably with the addition of the aid of a film forming solvent and evaporation of the volatile material at elevated temperature preferably at about 110° C. or higher provides excellent, contiguous, adherent coatings.
For foam formation it has been found helpful for the VDF/HFP copolymers in the range of HFP concentration where a small degree of internal crystallinity exists (30 weight percent HFP or lower) to add a small amount of swelling solvent such as ethyl acetate or acetone to the latex prior to placing it in the mold and freezing it.
The following examples further illustrate the best mode contemplated by the inventors for the practice of their invention and should be considered as illustrative and not in limitation thereof.
Vinylidene fluoride, hexafluoropropylene copolymers having low crystallinity having varying HFP levels were dissolved in a convenient solvent (triethylphosphate) (TEP) which was diluted with deionized (Dl) water to the desired final polymer concentration in solution with the optional addition of a surfactant, such as Surflon s-111, or Pluronic L92 where necessary to stabilize the emulsion formed. The required amount of TEP required to obtain clear films is shown in Table I for the different HFP levels in the copolymers. Optionally, a convention wetting agent such as BYK-346 and/or thickener, such as T-615 may be added to the latex. For comparison purposes a sample of a commercially available VDF/HFP copolymer in aqueous emulsion was also compared. The copolymer was KYNAR®2750 available from ATOFINA Chemicals, Inc.
The above emulsions are then coated on degreased glass or aluminum panels using a conventional draw bar and allowed to dry in air at room temperature. To insure complete removal of solvent, the coated substrates may be heated at 110° C. for a minimum of one hour.
1-A—Formulation for High HFP Content.
The following three solutions or dispersions were prepared:
Emulsions of VDF/HFP copolymers having HFP content ranging from 25 to 66 weight having about 40% by weight solids content were diluted to the concentrations shown in Tables II A, B, and C using DI water. Solutions in acetone or ethyl acetate were prepared by dissolution of isolated resin in the solvent. Substrates (paper, cloth and leather) were coated by these solutions or emulsions using a disposable pipette. In order to ensure that the coatings were free of solvent, the treated substrates were placed in a conventional oven at 85° C. for at least 10 minutes prior to making the surface energy measurements.
Surface energy measurements were conducted by using a G10 KRUSS angle contact angle measuring instrument where the surface energies were calculated using the KRUSS software using the Owens-Wendt model. The four solvents used to determine the surface energy of the coated substrates were water, ethylene glycol, tetradecane and formamide. At least four drops of each solvent were place on the dried, treated surface by a micro-syringe and the average of the observed contact angles was used by the computer to back calculate the surface energy of the treated substrate.
The results are tabulated in Tables II A, II B and II C.
Setting rates of emulsions of the VDF/HFP copolymers having low crystallinity, VDF/HFP copolymers of high HFP content made according to the prior art known synthetic techniques, an emulsion of a commercially available, thermoplastic VDF/HFP copolymer and application of these emulsions on several stone types.
It is particularly required for use in preserving antique stone structures, monuments and the like that the consolidating/protecting material must:
References on materials which have been used to consolidate and protect stony materials are contained in the book by Amoroso and Fassina, “Stony Decay and Conservation”, Elsevier El, Amsterdam (1983).
A material satisfying the above criteria will, obviously, also be suitable for use in preserving other stone and masonry structures in addition to antiquities monuments and the like constructed from various stone materials such as sandstone, granite, slate, marble, ceramic and other types of tile, cement, mortar, cement conglomerates and the like.
VDF/HFP Copolymers Used for the Treatments Illustrated in this Example
Copolymers made according to the synthesis procedure for low crystallinity copolymer described hereinabove were prepared using an initial HFP content in the synthesis of 66.7 weight percent and a steady state HFP feed ratio of 35.8 weight percent (Sample 3.1), an initial HFP ratio of 66.8 weight percent and a steady state HFP feed ratio of 45.5 weight percent (Sample 3.2) and an initial HFP ratio of 75.1 weight percent and a steady state feed HFP ratio of 45.9 weight percent (Sample 3.3).
VDF/HFP copolymers were prepared according to the method of U.S. Pat. No. 3,051,677 using an initial HFP ratio of 56.6 weight percent and a steady state HFP feed ratio of 38.3 weight percent (Comparative Sample 3.1), an initial HFP ratio of 50.0 weight percent and a steady state HFP feed ratio of 36.3 weight percent (Comparative Sample 3.2) and an initial HFP ratio of 50.0 weight percent and a steady state HFP feed ratio of 45.0 weight percent (Comparative Sample 3.3).
VDF/HFP copolymers were prepared according to the method of U.S. Pat. No. 3,178,399 using an initial HFP ratio of 39.4 weight percent and a steady state HFP feed ratio of 38.1 weight percent (Comparative Sample 3.4) and using an initial HFP ratio of 49.8 weight percent and a steady state HFP feed ratio of 45.8 weight percent (Comparative Sample 3.5).
For comparison of setting time of emulsions of the various copolymers an emulsion of commercially available thermoplastic VDF/HFP copolymer (KYNAR FLEX®2750) was employed.
Spray application of Low crystallinity VDF/HFP copolymers emulsions of the type of similar to Samples 3.1, 3.2 and 3.3 on stone.
Three samples of two different lithotypes were treated by spraying a 2.5% aqueous dispersion of the VDF/HFP copolymer having 40 weight percent of HFP. The lithotypes tested were a very porous Italian limestone (Pietra di Lecce, total porosity: 32±2%, saturation index: 65±5%) and Carrara marble (total porosity: 3.8±0.2%, saturation index: 7.4±0.6%). The reduction of water absorption was determined over a time of 20 minutes according to NORMAL 11/85(EP %).
The change in color of the treated material was measured according to CIEBLAB 1976, observing angle 10°, source D65 and expressed in ΔE units. Also measured according NORMAL 11/85 was the slope of the curve obtained by drawing a graph of water quantity absorbed per square dm vs. the square root of time (Absorption Coefficient, AC g cm−2 s−1/2) that is related to the protection obtained. The reduction in water vapor transmission (Rp %) was measured according to NORMAL 21/85 at 30±0.5° C. and 30±1% relative.
Brush Application of Emulsions VDF/HFP Copolymers of Low Crystallinity on Stone
Surfaces of three different lithotypes were treated with VDF/HFP copolymers of low crystallinity prepared as described hereinabove. The HFP content ranged from 25 to 40% by weight HFP. The lithotypes tested and the results are shown in table 3.3.
As a comparison three samples of Pietra di Lecce were treated by brushing a 2.5% by weight aqueous dispersion of the low crystallinity VDF/HFP copolymer having 40% by weight HFP and two emulsions of the KYNAR/FLEX emulsions contained 1:1 and 4:1 by weight of triethylphosphate (TEP) calculated on resin content to aid in film formation. The reduction in water absorption was determined and the results are shown in Table 3.4.
The protective efficiency of the low crystallinity VDF/HFP copolymer in contrast to that of the KYNAR FLEX is clearly shown.
In the absence of TEP KYNAR FLEX has no effect on the stone and a white deposit was observed on samples treated with KYNAR FLEX.
The general procedure for the production of foams from the lattices of formation of the VDF/HFP copolymers having low crystallinity described hereinabove is as follows:
A latex as placed in an appropriate closed mold of the described shape, the mold and its latex contents are cooled below the freezing point of the aqueous phase of the latex. The frozen latex is then removed from the mold, its temperature is allowed to use above the melting point of the aqueous phase and the thawed aqueous phase allowed to drain from the foam which is then dried. One of the skill in the art will recognize that this process is applicable for producing an open celled polymer foam from any polymer latex or suspension which does not coagulate on freezing, where the polymer has a Tg and minimium film formation temperature below the freezing point of the aqueous phase and where the polymer particles are able to adhere to one another while being compressed together during the expansion of the aqueous phase while freezing and remain sufficiently adherent on thawing and up to any higher intended use temperature to provide a self supporting solid foam after the aqueous phase is drained away. The range of applicable polymers can be expanded by introduction of small quantities of known swelling solvents for a particular polymer into the latex is quantities sufficient to soften the polymer particles but not sufficient to begin their actual dissolution.
The addition of solvents also permits one to adjust the solids content of the foam in a way which permits lower density foams to be prepared as will be more specifically illustrated below in connection with specific examples of foam prepared from the VDF/HFP copolymers having low crystallinity.
The following formulations were prepared:
The three formulations were placed in closed molds, conveniently 2 oz polyethylene bottles chilled to −25° C. until frozen, then the bottles are cut open, the frozen foam removed and placed on a drying rack to allow drainage of the aqueous phase as it thaws. A self supporting foam remains.
The foams are subjected to the following physical tests.
Apparent Density:
The volume is measured and the sample weighed. Density is the standard weight/volume measurements. The measurement gives an apparent density because any skin is not removed during measurement. The standard procedure is ASTM D1621-94 for this and compression testing.
Compression testing is run according to the above general procedure using an INSTRON with head speed at 0.5 in/min over 3 runs using 1.5 inch tall cylinders stress and strain at given times are measured.
Compression Set is determined according to ASTM D3573-93 but for 70 hours rather than 22
The apparent densities determined for foam from formulations 4.1, 4.2 and 4.3 are:
This is in contrast to the solid polymer which has a density of about 1.8 g/ml.
Examination of a cross section of the foam under magnification reveals that in unlike the uniform curved surface of the cells of blown foam, the cells of foam formed in this manner have angular surfaces which, without being bound to any particular theory, are the mirror images of the ice crystals of the frozen aqueous phase formed during foam formation.
Reinforced Foams
Following the same above general procedure formulations analogous to formulation 4.2 but using low crystallinity VDF/HFP of 31 weight percent HFP are combined by stirring with varying amounts (0 to 4 g) of degreased fiber glass wool and the mixtures are then formed into foam.
Foam containing no glass fiber had an apparent density of 0.5 and a compression modules of about 0.15 whereas foam containing 4.6% by weight glass fiber had an apparent density of 0.30 and a compression modules of about 0.53.
Compression set is also reduced by the presence of the glass fibers. The coated materials and foams exhibit the inherent applied use properties of enhanced corrosion resistance, enhanced flame and heat resistance as well as lower smoke emissions.
This application claims priority from provisional application 60/268,843 filed Feb. 15, 2001.
| Number | Date | Country | |
|---|---|---|---|
| 60268843 | Feb 2001 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10134262 | Apr 2002 | US |
| Child | 11438775 | May 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US02/03559 | Feb 2002 | US |
| Child | 10134262 | Apr 2002 | US |
