WO2010084089A1

WO2010084089A1 - Mixtures of pvdf, n-alkyllactams and organic carbonate and their applications

Info

Publication number: WO2010084089A1
Application number: PCT/EP2010/050492
Authority: WO
Inventors: Yoshihisa Fujii; Kanno Hiroyasu
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2009-01-22
Filing date: 2010-01-18
Publication date: 2010-07-29
Anticipated expiration: 2011-07-22

Abstract

The present invention relates to mixtures with an improved color quality comprising poly(vinylidenefluoride) (PVDF), an N-alkyllactam and one or more organic carbonates wherein the molar ratio of N-alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 and the content of PVDF is 1 to 95 percent by weight based on the combined weight of N alkyllactam and organic carbonate and the use of said mixtures in the processing of PVDF, e.g in electronic applications, especially the production of lithium batteries. The present invention also relates to a process of preparing a solution comprising PVDF with improved color quality.

Description

Mixtures of PVDF, N-alkyllactams and organic carbonate and their applications

Specification

The present invention relates to mixtures with an improved color quality comprising poly(vinylidene fluoride) (PVDF), N-alkyllactam (NAL) and organic carbonate and a method for their production. The present invention also relates to the use of said mixtures in processing PVDF for applications in which improved color is a quality requirement.

Poly(vinylidene fluoride) (PVDF) is the addition polymer of 1 ,1-difluoroethene, also known as vinylidene fluoride.

PVDF is a semi crystalline polymer which is usually polymerized in emulsion or suspension using free-radical initiators. PVDF combines the characteristic resistance of fluoropolymers to harsh chemical, thermal, ultraviolet, weathering and oxidizing environments with other unique properties such as a high polarity, a high dielectric constant as well as an excellent piezoelectric and pyroelectric activity. Because of these properties PVDF is used in many applications, e.g. in wire and cable products, electronic devices, as a weather resistant binder for exterior architectural finishes.

The polymer is readily melt processed using conventional moulding or extrusion equipment or cast from solutions to form membranes and films. Finishes are deposited from dispersions using specific solvents. When processing PVDF from or in solution usually a solvent with a high polarity is selected. For many applications, either N-alkyllactams (NAL), such as N-Methyl- pyrrolidone (NMP), or organic carbonates, such as propylene carbonate or ethylene carbonate, formamides, such as dimethyl formamide of sulfoxides, such as dimethyl sulfoxide, among others have been suggested. The use of N-alkyllactams as a processing solvent for PVDF has a decisive setback. JP-A1 -10310795 discloses that solutions of PVDF in N-alkyllactams tend to discolor after a short while due to a small amount of impurities contained in NALs making these solutions unsuitable for use in high end applications, such as electronics or coatings. To avoid these problems, JP-A1 -10310795 teaches a method for dissolving or washing PVDF with an NAL-compound which has been brought into contact with a solid acid substance, e.g. an ion exchange resin, or a mineral acid prior to distillation. The method disclosed in JP-A1 -10310795 requires an additional processing step to purify the respective N-alkyllactams. This makes additional equipment and handling necessary.

Organic carbonates have the disadvantage that they have a low solvency for PVDF. Therefore organic carbonates are not well suited to prepare PVDF-solutions having the required concentrations needed for practical and industrial applications. The object of the present invention was to provide a mixture of PVDF with commercially available solvents which does not require elaborate cleaning procedures to ensure a high color quality and which allows the preparation of solutions having PVDF- concentrations needed for practical and industrial applications. It is a further object of the present invention to provide a mixture of PVDF and solvents which is economically viable, easy to produce and which shows an improved color quality, i.e. reduction in the discoloration and/or improvement in the color stability, especially in the course of storage.

Therefore, in the frame of the present invention mixtures with an improved color quality comprising PVDF, an N-alkyllactam and one or more organic carbonates wherein the molar ratio of N-alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 and the content of PVDF is 1 to 95 percent by weight based on the combined weight of N- alkyllactam and organic carbonate were developed.

It was totally unexpected that solutions of improved color and color stability and sufficient concentration could be achieved by combining NALs with organic carbonates in a certain ratio, instead of using the respective solvents alone.

The mixtures of the present invention comprise PVDF.

PVDF is commercially available, e.g. as Kynar® from Arkema, Dyneon® from Dyneon, Solet ® from Solvay S.A., and KF-Polymer® from Kureha.

Methods of preparation of PVDF are disclosed for instance in Kirk-Othmer Encyclopedia of Chemical Technology (Kirk-Othmer Encyclopedia of Chemical Technology, "Fluorine-Containing Polymers, Poly(vinylidene fluoride), Electronic Edition, Last updated: 17 Oct 2008, John Wiley & Sons, Inc.).

The mixture of the present invention also comprises one or more organic carbonates.

Organic carbonates can be cyclic carbonates or acyclic carbonates.

Preferably, the organic carbonate is a cyclic carbonate.

Preferred cyclic carbonates are propylene carbonate, ethylene carbonate, trimethylene carbonate, butylene carbonate, and pentylene carbonate. Especially preferred cyclic carbonates are propylene carbonate and ethylene carbonate. The most preferred cyclic carbonate is propylene carbonate.

The organic carbonate can also be an acyclic carbonate.

Preferred acyclic carbonates are dimethyl carbonate, diethyl carbonate, dipropyl car- bonate, dibutyl carbonate, dihexyl carbonate, methyl ethyl carbonate, methyl butyl carbonate, diphenyl carbonate and methyl phenyl carbonate. Acyclic and cyclic carbonates are commercially available.

Propylene carbonate can for example be obtained as a byproduct of the synthesis of polypropylene carbonate from propylene oxide and carbon dioxide. It can be also synthesized from urea and propylene glycol over a catalyst, for example a zinc-iron double oxide catalyst.

Ethylene carbonate is usually obtained by the reaction of ethylene oxide and carbon dioxide.

The mixture also comprises an N alkyllactam. The N-alkyllactam is preferably an N-alkyllactam of the general formula I

in which R is a linear or branched, saturated aliphatic radical, preferably Ci-12-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, sec-pentyl, neo-pentyl, 1 ,2-dimethylpropyl, n-hexyl, isohexyl, sec-hexyl, cyclopentylmethyl, n-heptyl, isoheptyl, cyclohexylmethyl, n-octyl, 2-ethylhexyl, n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, n-dodecyl, isododecyl, more preferably Ci-s-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-octyl and 2-ethylhexyl, most preferably Ci-4-alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl,

or a

saturated cycloaliphatic radical having from 3 to 12 carbon atoms, preferably C_4-8- cycloalkyl, such as cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl, more preferably cyclopentyl and cyclohexyl,

and n is an integer from 1 to 5 and where the carbon atoms of the heteroorganic ring of the N-substituted lactam may bear from one to two substituents inert under the conditions, for example alkyl radicals, e.g. Ci-s-alkyl radicals, which are each independently preferably a Ci-s-alkyl radical, particularly a Ci-4-alkyl radical.

Examples of Ci-8-alkyl radicals which may bear the carbon atoms of the heteroorganic ring of the N-substituted lactam are: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl and 2-ethylhexyl, for example in 1 ,5-dimethyl-2-pyrrolidone and 1-ethyl-5-methyl-2-pyriOlidone.

In the mixture according to the invention, particular preference is given to using N-alkyllactams of the formula I

in which R is Ci-4-alkyl as described above and n is 1 , 2 or 3, and where the carbon atoms of the heteroorganic ring of the N-substituted lactam may bear a Ci-4-alkyl radical, particularly methyl or ethyl radical.

Most preferred N-alkyllactams are N-Methyl-2-pyrrolidone (NMP) and N-Ethyl-2- pyrrolidone (NEP).

The N-alkyllactams used may have a purity of > 90% by weight, preferably > 95% by weight, more preferably > 99% by weight.

The preparation of N-alkyllactams is known. N-alkyllactams can be effected, for example, by reacting gamma-butyrolactone (γ-BL) with monoalkylamines to release one equivalent of water, for example analogously to Ullmann^'s Encyclopedia of

Industrial Chemistry, volume A22, 5th ed., p. 459 (1993) or analogously to DE-A-19 626 123 (BASF AG). N-alkyllactams can likewise be prepared from maleic anhydride or other dicarboxylic acid derivatives and monoethylamines in the presence of hydrogen and a hydrogenation catalyst, for example according to EP-A-745 598 (Bayer AG) or WO-A-02/102773 (BASF AG). NMP and NEP are commercially available, for example from BASF SE.

The molar ratio of N-alkyllactams of formula I and organic carbonates is in the range between 0.2:1 and 20:1 , preferably 0.4:1 to 10:1 , most preferably 0.5:1 to 4:1 , in par- ticularly 0.8:1 to 3:1.

The content of PVDF in the mixtures according to the invention is between 1 and 95% by weight based on the combined weight of N-alkyllactams and organic carbonates, preferably between 1 and 80% by weight, most preferably between 1 and 60% by weight, in particularly between 1 and 50% by weight based on the combined weight of N-alkyllactams and organic carbonates.

In a further preferred embodiment the content of PVDF is between 3 and 40% and preferably between 5 and 30% by weight based on the combined weight of N-alkyllactams and organic carbonates. The mixtures may be prepared by bringing PVDF, N-alkyllactam and the organic carbonates into contact, most preferably by stirring the mixture e.g. in a stirred tank reactor. Suitable stirrers, e.g. planetary stirrers, and vessels for preparing the mixtures according to the invention are known to a person skilled in the arts.

The temperature range at which the components of the mixture are brought into contact is in the usually in the range of 0 to 200⁰C, preferably at 5 to 150⁰C and most preferably at 10 to 100°C and most preferably at 10° to 50⁰C, in particularly at ambient temperatures.

The duration of mixing the components to obtain a homogeneous solution depends on the concentration of PVDF and the temperature. Usually the duration of mixing is between 1 minutes and 24 hours, preferably between 5 minutes and 12 hours, most preferably between 10 minutes and 6 hours and in particularly between 15 minutes and 2 hours.

The components of the mixture can be brought into contact under atmospheric conditions or under inert conditions, e.g. under a nitrogen atmosphere. Most preferably the mixture is mixed under inert conditions.

In a preferred embodiment the mixtures are prepared by bringing into contact PVDF, an N alkyllactams and one or more organic carbonates, wherein the molar ratio of N alkyllactams of formula I to organic carbonates is in the range of 0.2:1 to 20:1 and the content of PVDF is between 1 and 95% by weight based on the combined weight of N alkyllactams and organic carbonates.

In a particular embodiment the mixtures are prepared by bringing into contact PVDF, an N-alkyllactams of formula I and one or more organic carbonate at a temperature of 10 to 100⁰C for a duration of 15 minutes to 2 hours under a nitrogen atmosphere, wherein the molar ratio of N-alkyllactams of formula I to organic carbonates is in the range of 0.8:1 to 3:1 and the content of PVDF is between 5 and 50% by weight based on the combined weight of N-alkyllactams and organic carbonates.

The mixtures of the present invention may also contain other components, such as co- solvents, fillers, processing aids, other polymers, salts, which may be required for the specific application.

The mixtures can be processed directly after mixing or they can be stored. Preferably the mixtures are stored at ambient temperatures or slightly elevated temperatures under an inert atmosphere.

Most preferred mixtures contain PVDF, N-Methyl-pyrrolidone (NMP) and propylene carbonate (PC) wherein the molar ratio of NMP to PC is in the range of 0.8:1 to 3:1 and the content of PVDF is 1 to 50 percent by weight based on the combined weight of N- alkyllactam and organic carbonate.

The Iodine color numbers determined according to DIN EN ISO 6261 of the mixtures of the present invention are preferably less than 1000, more preferably less than 500, even more preferably less than 100 and in particularly less than 50.

The mixtures according to the invention have an improved color quality and show a high solvency for PVDF. In contrast to mixtures in which N-Alkyllactams or organic carbonates are not used in combination, the mixtures according to the invention do not turn brown or black but keep a light clear color.

The present invention therefore also relates to the use of a mixture comprising an N- alkyllactam and one or more organic carbonates wherein the molar ratio of N- alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 for preparing solutions of PVDF with improved color quality, especially solutions having an iodine number of less than 1000, more preferably less than 500, even more preferably less than 100 and in particularly less than 50.

The mixtures of the present invention can be used in processing PVDF, especially for applications in which improved color is a quality requirement.

In particularly this invention also relates to the use of a mixture with an improved color quality comprising an N-alkyllactam and one or more organic carbonate wherein the molar ratio of N-alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 for processing PVDF. Most preferred mixtures comprise NMP or NEP as N-alkyllactam and ethylene carbonate or propylene carbonate as organic carbonates. Especially most preferred mixtures comprise NMP and propylene carbonate.

The mixtures of the present invention can be used in processing PVDF for applications in which improved color is a quality requirement.

In particularly the mixtures according to the invention can be used for making PVDF- films and/or membranes which show an improved color quality, especially for electronic applications, in particularly lithium batteries.

Preferably, the mixtures according to the invention are also used for the production of battery binder and sheets for solar panel.

The present invention therefore also relates to a method of processing PVDF by using the mixtures according to the present invention. In a preferred embodiment PVDF is processed using a mixture comprising N-Methyl- pyrrolidone and propylene carbonate wherein the molar ratio of N-Methyl-pyrrolidone to propylene carbonate is in the range of 0.2:1 to 20:1.

Membranes of improved color quality may be prepared according to the method disclosed by Grandine et al. (US 4,203,847) or Benzinger (US 4,384,047), which are herein incorporated by reference, using the mixtures of the present invention during processing instead of the solvents disclosed within these references. Such membranes and films are required in the fabrication of light emitting diodes, fuel cells and in particularly lithium batteries for the preparation of the electrode material or as a solid electrolyte. Methods for preparing electrode material and electrolytes based on PVDF are disclosed for example in W0-A1 -01/65616, EP-A1 -0567015, US 5,900,183, US 5,962,167 EP-A1 -0793286, WO-A1-01/82403 and US-B1 -6,510,042.

The advantage of the present invention is that a mixture has been found which is suitable for the processing of PVDF for applications in which an improved color is of importance. This mixture is easily obtainable and does not require elaborate cleaning and washing procedures. Furthermore, the mixtures have a good solvency for PVDF making it possible to prepare solutions having a PVDF concentration needed for practical and industrial applications. These mixtures may be used for the fabrication of membranes and films used in electronic applications, in which color quality is of high importance and the impurities associated with discoloration are undesirable.

The application is illustrated in the following examples:

Example 1 :

NMP (origin BASF) was heated up to 100⁰C first and then cooled down. Then 8 weight-

% PVDF (Kureha KF W1 100) were added to NMP at room temperature under a blanket of nitrogen. The mixture was stirred while the temperature was slowly increased to

80⁰C until the polymer dissolved.

After the polymer was solved, the temperature was reduced to room temperature and the iodine color number of the PVDF-solution was measured. The iodine color number was determined to be 1 100.

Example 2:

NMP (origin BASF) was mixed with PC (origin BASF) with the ratio of 7:3 (V/V).The mixture was heated up to 100°C first and then cooled down. Then 8 weight-% PVDF (Kureha KF W1 100) were added to this solvent mixture at room temperature under a blanket of nitrogen. The mixture was stirred while the temperature was slowly increased to 80⁰C until the polymer dissolved. After the polymer was solved, the temperature was reduced to room temperature and the iodine color number of the PVDF-solution was measured. The iodine color number was determined to be 700.

Example 3:

NMP (origin BASF) was mixed with PC (origin BASF) with the ratio of 6:4 (V: V). The mixture was heated up to 100⁰C first and then cooled down. Then 8 weight-% PVDF (Kureha KF W1 100) were added to this solvent mixture at room temperature under a blanket of nitrogen. The mixture was stirred while the temperature was slowly increased to 80⁰C until the polymer dissolved.

After the polymer was solved, the temperature was reduced to room temperature and the iodine color number of the PVDF-solution was measured. The iodine color number was determined to be 100.

Example 4:

NMP (origin BASF) was mixed with PC (origin BASF) with the ratio of 1 :1 (V: V). The mixture was heated up to 100°C first and then cooled down. Then 8 weight-% PVDF (Kureha KF W1 100) were added to this solvent mixture at room temperature under a blanket of nitrogen. The mixture was stirred while the temperature was slowly increased to 80⁰C until the polymer dissolved.

After the polymer was solved, the temperature was reduced to room temperature and the iodine color number of the PVDF-solution was measured. The iodine color number was determined to be 1.

The thus obtained solutions were stored at room temperature for 2 months. After 2 months no change in the iodine color number could be observed.

Claims

Claims:

1. Mixtures with an improved color quality comprising poly(vinylidenefluoride) (PVDF), an N-alkyllactam and one or more organic carbonates wherein the molar ratio of N- alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 and the content of

PVDF is 1 to 95 percent by weight based on the combined weight of N alkyllactam and organic carbonate.

2. Mixture according to claim 1 , wherein the ratio of N-alkyllactam to organic carbon- ate is in the range of 0.8:1 to 3:1.

3. Mixture according to one of the preceding claims, wherein the content of PVDF is 1 to 50 percent by weight based on the combined weight of N alkyllactam and organic carbonate.

4. Mixture according to one of the preceding claims, wherein the N-alkyllactam is N- Methyl-pyrrolidone (NMP) and/or N-Ethyl-pyrrolidone (NEP).

5. Mixture according to one of the preceding claims, wherein the organic carbonate is a cyclic carbonate.

6. Mixture according to one of the preceding claims, wherein the organic carbonate is propylene carbonate.

7. Process for preparing a solution comprising PVDF with improved color quality by bringing into contact PVDF, an N-alkyllactams and one or more organic carbonates, wherein the molar ratio of N-alkyllactams of formula I to organic carbonates is in the range of 0.2:1 to 20:1 and the content of PVDF is between 1 and 95% by weight based on the combined weight of N-alkyllactams and organic carbonates.

8. Mixture obtainable by a process according to claim 7.

9. Use of mixtures according to any of claims 1 to 6 or obtainable according to claim 8 in the processing of PVDF.

10. Use of mixtures according to any of claims 1 to 6 or obtainable according to claim 8 for the production of films, membranes and coatings of improved color quality.

1 1. Use of mixtures according to any of claims 1 to 6 or obtainable according to claim 8 for the production of films and membranes of improved color quality for electronic applications.

12. Use of mixtures according to any of claims 1 to 6 or obtainable according to claim 8 for the production of films, membranes of improved color quality for lithium batteries.

13. Use of a mixture comprising an N-alkyllactam and one or more organic carbonates wherein the molar ratio of N-alkyllactam to organic carbonate is in the range of 0.2:1 to 20:1 for preparing solutions of PVDF having an iodine color number of less than 1000.

14. Use of a mixture comprising N-Methyl-pyrrolidone and propylene carbonate wherein the molar ratio of N-Methyl-pyrrolidone to propylene carbonate is in the range of 0.8:1 to 3:1 for preparing solutions of PVDF having an iodine color number of less than 100.

15. Method of processing PVDF using mixtures according to any of claims 1 to 6 or obtainable according to claim 8.