REINFORCED FLUOROPOLYMER

Abstract

A curable fluoropolymer composition includes a crosslinkable fluorine-containing polymer, and a filler selected from surface-reacted calcium carbonate, ultrafine calcium carbonate, or a mixture thereof, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source. Furthermore, the disclosure relates to a cured fluoropolymer product formed from said composition, an article including the cured fluoropolymer product, a method of producing a cured fluoropolymer product, and use of said filler for reinforcing a cured fluoropolymer product.

Claims

1. A curable fluoropolymer composition comprising a crosslinkable fluorine-containing polymer, and a filler selected from surface-reacted calcium carbonate, ultrafine calcium carbonate, or a mixture thereof, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source.

2. The curable fluoropolymer composition of claim 1, wherein the crosslinkable fluorine-containing polymer is a copolymer of vinylidene fluoride and at least one monomer selected from the group comprising hexafluoropropylene, tetrafluoroethylene, fluorinated vinyl ether, perfluoroalkylvinylether, chlorotrifluoro-ethylene, propylene, ethylene, bromine- or iodine-containing fluoroolefins, and mixtures thereof.

3. The curable fluoropolymer composition of claim claim 1, wherein the crosslinkable fluorine-containing polymer has a specific gravity from 0.5 to 5, measured according to ASTM D297, and/or the crosslinkable fluorine-containing polymer has a fluorine content from 53 to 71 wt.-%, based on the total weight of the crosslinkable fluorine-containing polymer.

4. The curable fluoropolymer composition of claim 1, wherein the filler is present in an amount from 1 to 80 wt.-%, based on the total weight of the curable fluoropolymer composition.

5. The curable fluoropolymer composition of claim 1, wherein the surface-reacted calcium carbonate has a volume median particle size d.sub.50 from 0.1 to 75 μm, and/or a volume top cut particle size d.sub.98 from 0.2 to 150 μm, and/or a specific surface area of from 15 m.sup.2/g to 200 m.sup.2/g, measured using nitrogen and the BET method.

6. The curable fluoropolymer composition of claim 1, wherein the ultrafine calcium carbonate has a volume median particle size d.sub.50 from 0.05 to 1 μm, and/or a weight top cut particle size d.sub.98 from 0.2 to 10 μm, and/or a specific surface area of from 1 m.sup.2/g to 100 m.sup.2/g, measured using nitrogen and the BET method.

7. The curable fluoropolymer composition of claim 1, wherein the natural ground calcium carbonate is selected from the group consisting of marble, chalk, limestone, and mixtures thereof, or the precipitated calcium carbonate is selected from the group consisting of precipitated calcium carbonates having an aragonitic, vateritic or calcitic crystal form, and mixtures thereof.

8. The curable fluoropolymer composition of claim 1, wherein the at least one H.sub.3O.sup.+ ion donor is selected from the group consisting of hydrochloric acid, sulphuric acid, sulphurous acid, phosphoric acid, citric acid, oxalic acid, an acidic salt, acetic acid, formic acid, and mixtures thereof.

9. The curable fluoropolymer composition of claim 1, wherein the ultrafine calcium carbonate is selected from the group consisting of ultrafine ground calcium carbonate, ultrafine precipitated calcium carbonate, ultrafine dolomite, and mixtures thereof.

10. The curable fluoropolymer composition of claim 1, wherein the filler comprises a surface-treatment layer on at least a part of the filler surface, wherein the surface-treatment layer is formed by contacting the filler with at least one surface-treatment agent in an amount from 0.07 to 9 mg/m.sup.2 of the filler surface, and wherein the at least one surface treatment agent is selected from the group consisting of mono- or di-substituted succinic anhydride containing compounds, mono- or di-substituted succinic acid containing compounds, mono- or di-substituted succinic acid salts containing compounds, saturated or unsaturated fatty acids, salts of saturated or unsaturated fatty acids; unsaturated esters of phosphoric acid, salts of unsaturated phosphoric acid esters, functionalized poly- and/or perfluorinated alkyl compounds, abietic acid, salts of abietic acid, and mixtures thereof and reaction products thereof.

11. The curable fluoropolymer composition of claim 1, wherein the curable fluoropolymer composition comprises a crosslinking agent.

12. The curable fluoropolymer composition of claim 1, wherein the polymer composition further comprises acid acceptor, accelerator, colouring pigment, dyes, wax, lubricant, oxidative- and/or UV-stabilizer, antioxidant, additional filler, processing aid, plasticizer, additional polymer, and mixtures thereof.

13. A cured fluoropolymer product formed from the curable fluoropolymer composition according to claim 1.

14. An article comprising the cured fluoropolymer product according to claim 13, wherein the article is selected from the group comprising o-ring seals, shaft seals, gaskets, tubing, valve stem seals, fuel hose, tank seals, diaphragms, flexi liners for pumps, mechanical seals, pipe coupling, valve lines, military flare blinders, electrical connectors, fuel joints, roll covers, firewall seals, and clips for jet engines.

15. A method of producing a cured fluoropolymer product, comprising the steps of i) providing a crosslinkable fluorine-containing polymer, ii) providing a filler selected from surface-reacted calcium carbonate, ultrafine calcium carbonate, or a mixture thereof, wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source, iii) combining the crosslinkable fluorine-containing polymer of step i) and the filler of step ii) to form a curable fluoropolymer composition, and iv) curing the curable fluoropolymer composition of step iii).

16. The method of claim 15, wherein the curing step iv) is carried out by adding a crosslinking agent, heat treatment, ultraviolet light radiation, electron-beam radiation and/or nuclear radiation.

17. A method comprising providing a filler for reinforcing a cured fluoropolymer product, wherein the filler is selected from surface-reacted calcium carbonate, ultrafine calcium carbonate, or a mixture thereof, and wherein the surface-reacted calcium carbonate is a reaction product of natural ground calcium carbonate or precipitated calcium carbonate with carbon dioxide and one or more H.sub.3O.sup.+ ion donors, wherein the carbon dioxide is formed in situ by the H.sub.3O.sup.+ ion donors treatment and/or is supplied from an external source.

18. The method of claim 17, wherein the tear resistance and/or the elongation at break of the cured fluoropolymer product is increased compared to a cured fluoropolymer product containing an equivalent volume of carbon black N550 as filler.

Description

EXAMPLES

1. Methods

[0295] Molecular Weight

[0296] The number-average molecular weight M.sub.n is measured by gel permeation chromatography, according to ISO 16014-1:2019 and ISO 16014-2/2019.

[0297] Acid Number

[0298] The acid number is measured according to ASTM D974-14.

[0299] Specific Surface Area (BET)

[0300] The specific surface area (in m.sup.2/g) is determined using the BET method (using nitrogen as adsorbing gas), which is well known to the skilled man (ISO 9277:2010). The total surface area (in m.sup.2) of the filler material is then obtained by multiplication of the specific surface area and the mass (in g) of the corresponding sample.

[0301] Iodine Number

[0302] The iodine number is measured according to DIN 53241/1.

[0303] Particle Size

[0304] Volume median particle size d.sub.50(vol) and volume top cut particle size d.sub.98(vol) are evaluated using a Malvern Mastersizer 3000 Laser Diffraction System. The d.sub.50 or d.sub.98 value, measured using a Malvern Mastersizer 3000 Laser Diffraction System, indicates a diameter value such that 50% or 98% by volume, respectively, of the particles have a diameter of less than this value. The raw data obtained by the measurement are analysed using the Mie theory, with a particle refractive index of 1.57 and an absorption index of 0.005.

[0305] The weight median particle size d.sub.50(wt) and weight top cut particle size d.sub.98(wt) is determined by the sedimentation method, which is an analysis of sedimentation behaviour in a gravimetric field. The measurement is made with a Sedigraph™ 5100 or 5120, Micromeritics Instrument Corporation. The method and the instrument are known to the skilled person and are commonly used to determine grain size of fillers and pigments. The measurement is carried out in an aqueous solution of 0.1 wt.-% Na.sub.4P.sub.2O.sub.7. The samples were dispersed using a high speed stirrer and sonicated.

[0306] The processes and instruments are known to the skilled person and are commonly used to determine the particle size of fillers and pigments.

[0307] Analysis on Cured Fluoropolymer Product Samples

[0308] For all tests on the cured fluoropolymer product samples, a minimum period of 16 h was kept between molding and testing of the rubber samples. The samples were kept in a controlled environment (temperature: 23±2° C., relative humidity: 50±5%).

[0309] Tensile Strength and Elongation at Break:

[0310] Tensile strength was measured according to NF ISO 37 on a Zwick Z100 or Zwick Z005 device using the parameters outlined in Table 1 below.

TABLE-US-00001 TABLE 1 Tensile strength measurement parameters. Standard NF ISO 37 Type of test piece Type H2 Preparation of test piece: Samples were cut from sheets of 2 ± 0.2 mm thickness Cutting direction Parallel of calendering direction State Initial Temperature 23 ± 2° C. Relative humidity 50 ± 5% Number of test pieces used 3 Units MPa for strength % for elongation Test specimen conditioning Minimum 16 h at 23° C. and before test 50% relative humidity Conditioning after ageing in air None Conditioning after immersion None Rate of grip separation 500 mm/min

[0311] Tear Resistance

[0312] Tear resistance (DELFT) was measured according to NF ISO 34-2 on a Zwick Z100 or Zwick Z005 device using the parameters outlined in Table 2.

TABLE-US-00002 Table 2: Tear resistance (DELFT) measurement parameters. Standard NF ISO 34-2 Type of test piece Delft Preparation of test piece Samples were cut from sheets of 2 ± 0.2 mm thickness Cutting direction perpendicular to calendering direction State Initial Temperature 23 ± 2° C. Relative humidity 50 ± 5% Number of test pieces used 3 Test specimen conditioning Minimum 16 h at 23° C. and before test 50% relative humidity Rate of grip separation 500 mm/min

2. Materials

[0313] Treatment A

[0314] Treatment A is a low molecular weight maleinized polybutadiene (M.sub.n: 3100 Da, Brookfield viscosity: 6500 cps+/−3500 at 25° C., acid number: 40.1-51.5 meq KOH/g, total acid amount: 7-9 wt.-%, based on total weight of treatment composition; microstructure (molar % of butadiene): 20-35% 1,2-vinyl functional groups.

[0315] Treatment B

[0316] Treatment B is a poly(hexafluoropropylene oxide) functionalized with a carboxylic group situated on the terminal fluoromethylene group (molecular weight: ca. 2500 Da, viscosity (cSt, 40° C.): 99.4-149, TAN-E (mg KOH/g): 23-27, density (g/mL, −9° C.): 1.91). It is commercially available from Chemours Company under tradename Krytox 157FS(L).

[0317] Treatment C

[0318] Treatment C is a fatty acid mixture, which consists of a 1:1 mixture of stearic acid and palmitic acid.

[0319] Powder 1

[0320] Powder 1 is a modified calcium carbonate composed of 80 wt.-% hydroxyapatite and 20 wt.-% calcite (BET=85 m.sup.2/g, d.sub.50(vol)=6.1 μm, d.sub.98(vol)=13.8 μm), prepared by the following method:

[0321] In a mixing vessel, 350 liters of an aqueous suspension of natural ground calcium carbonate was prepared by adjusting the solids content of a ground marble calcium carbonate from Hustadmarmor, Norway, with a particle size distribution of 90 wt.-% less than 2 μm, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained. Whilst mixing the suspension, 62 kg of a 30% concentrated phosphoric acid was added to said suspension over a period of 10 minutes at a temperature of 70° C. Finally, after the addition of the phosphoric acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying it.

[0322] Powder 2

[0323] Powder 2 was obtained by preparing 350 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground marble calcium carbonate from Omya Spa, Carrara, Italy, having a mass based median particle size of 1.7 μm, as determined by sedimentation, such that a solids content of 15 wt.-%, based on the total weight of the aqueous suspension, was obtained. Whilst mixing the slurry, 33 kg of a 30% concentrated phosphoric acid was added to said suspension over a period of 20 minutes at a temperature of 70° C. After the addition of the acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying it using a jet-dryer.

[0324] The surface-reacted calcium carbonate thus obtained had a d.sub.50(vol) of 6.2 μm, a d.sub.98(vol) of 15.1 μm, and specific surface area of 30 m.sup.2/g.

[0325] Powder 3

[0326] Powder 3 was obtained by preparing 350 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground limestone calcium carbonate from Omya SAS, Orgon, France, having a mass based median particle size of 1.3 μm, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained. Whilst mixing the slurry, 37 kg of a 30% concentrated phosphoric acid was added to said suspension over a period of 20 minutes at a temperature of 70° C. After the addition of the acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying it using a jet-dryer.

[0327] The surface-reacted calcium carbonate thus obtained had a d.sub.50(vol) of 6.6 μm, a d.sub.98(vol) of 18.4 μm, and specific surface area of 53.1 m.sup.2/g.

[0328] Powder 4

[0329] Powder 4 was obtained by preparing 2500 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground limestone calcium carbonate from Omya SAS, Orgon, France, having a mass based median particle size of 0.6 μm, as determined by sedimentation, such that a solids content of 10 wt.-%, based on the total weight of the aqueous suspension, was obtained. Whilst mixing the slurry, 445 kg of a 30% concentrated phosphoric acid was added to said suspension over a period of 45 minutes at a temperature of 70° C. After the addition of the acid, the slurry was stirred for additional 5 minutes, before removing it from the vessel and drying it using a jet-dryer.

[0330] The surface-reacted calcium carbonate thus obtained had a d.sub.50(vol) of 7.5 μm, a d.sub.98(vol) of 19.3 μm, and specific surface area of 83.8 m.sup.2g.sup.−1.

[0331] Powder 5

[0332] Powder 5 has been prepared by surface-treating powder 1 with 5 wt.-% of treatment A, based on the total weight of powder 1. To carry out the treatment, the treatment agent (45 g) was first dispersed in 300 mL of deionized water, heated to 60° C. and neutralized to pH 10 with NaOH solution.

[0333] A suspension of powder 1 (900 g in 8 L deionized water) was prepared and heated to 80° C. The pH was adjusted to 10 with Ca(OH).sub.2 and the neutralized treatment agent was then added under vigorous stirring. Mixing was continued at 85° C. for 45 minutes, and the suspension was then filtered on a Büchner funnel and dried overnight in an oven (110° C.). The dried filter cake was then deagglomerated using a SR300 rotor beater mill (Retsch GmbH, Germany).

[0334] Powder 6

[0335] Powder 6 has been prepared by surface-treating powder 1 with 5 wt.-% of treatment B, based on the total weight of powder 1. Treatment was performed in a 10 L batch reactor, under vigorous stirring, by first dispersing 500 g of powder 1 in deionized water (5 L) and heating to 85-90° C. The pH was then adjusted to 10 with Ca(OH).sub.2, and treatment agent B was then added (25 g), and the resulting suspension was stirred at 85° C. for 45 minutes. After that time the filler was filtered on a Büchner funnel and dried overnight in an oven (110° C.). The dried filter cake was then deagglomerated using a SR300 rotor beater mill (Retsch GmbH, Germany).

[0336] Powder 7

[0337] Powder 7 was obtained by preparing 8 litres of an aqueous suspension of ground calcium carbonate in a mixing vessel by adjusting the solids content of a ground marble calcium carbonate from Omya Spa, Carrara, Italy, having a mass based median particle size of 7.9 μm, as determined by sedimentation, such that a solids content of 20 wt.-%, based on the total weight of the aqueous suspension, was obtained. Whilst mixing the slurry at room temperature, 215 g of an 85% concentrated phosphoric acid was added rapidly to said suspension. After mixing for 30 minutes the resulting product was ground in circulation for 3 h using a Dynomill KDL horizontal mill (Willy A. Bachofen AG, Muttenz, Switzerland) with a 600 ml chamber and 0.6-1.0 mm grinding media.

[0338] Powder 7 is a modified calcium carbonate composed of 83 wt.-% calcite and 17 wt.-% hydroxyapatite (specific surface area=67 m.sup.2/g, d.sub.50(vol)=1.2 μm, d.sub.98(vol)=9.7 μm).

[0339] Powder 8

[0340] Powder 8 has been prepared by surface-treating an ultrafine ground calcium carbonate from Norway (specific surface area=13 m.sup.2/g, d.sub.50(vol)=0.3 μm, d.sub.98(vol)<2 μm). For that purpose, the calcium carbonate powder was treated in a high speed mixer (120° C., 1000 rpm, 15 minutes) with 0.6 wt.-% treatment C, 1 wt.-% treatment A, and 2.5 wt.-% treatment B, based on the total weight of calcium carbonate.

[0341] Powder CE1 (Comparative)

[0342] Powder CE1 is a N550 carbon black filler, commercially available from Orion engineered Carbons GmbH (Purex® HS 45, iodine number: 43±5 mg/g; STSA surface area (according to ASTM D 6556): 39±5 m.sup.2/g).

[0343] Powder CE2 (Comparative)

[0344] Powder CE2 is a natural barium sulfate, commercially available from Deutsche Baryt-Industrie Dr. Rudolf Alberti GmbH &Co KG (d.sub.50(vol)=5.2 μm, d.sub.98(vol)=20 μm).

[0345] Powder CE3 (Comparative)

[0346] Powder CE3 was obtained from HPF Minerals LTD (Tremin® 283-600, d.sub.50(vol): 3.5 μm, d.sub.98(vol): 16 μm, specific surface area=4 m.sup.2/g).

[0347] Further Components [0348] Viton GBL-200S: Copolymer of hexafluoropropylene, vinylidene fluoride, and tetrafluoroethylene with a cure site monomer (Chemours Company). [0349] Elastomag 170: Magnesium oxide (BET: 165 m.sup.2/g), vulcanizer, activator, and acid acceptor for halogenated elastomers (Akrochem Corporation). [0350] Rhenofit CF: Calcium hydroxide, cross-linking activator (RheinChemie Additives). [0351] Luperox 101XL: 2,5-Dimethyl 2,5-di(tert-butylperoxy) hexane, organic peroxide (Arkema Inc.). [0352] Diak 7: triallyl isocyanurate, co-agent for peroxide vulcanization (Chemours Company).

3. Examples

[0353] Cured fluoropolymer products were prepared as described in the following, wherein the compositions of the prepared cured fluoropolymer products are compiled in Table 5 below.

[0354] Step 1: Mixing

[0355] Mixing of ingredients was performed in an open mill cylinder mixer (150×350 mm). Composition of the curable fluoropolymer compositions is described in Table 3.

TABLE-US-00003 TABLE 3 Curable fluoropolymer composition. Component Part by weight Viton GLB200S 100 Filler (comparative or inventive) 20 N550 (powder CE1) 2 Elastomag 170 (MgO) 3 Rhenofit CF 6 Luperox 101XL 3 Diak 7 3

[0356] All the samples produced were mixed with the same times, cylinder speeds, and cylinder spacing as to not influence in the rheological properties comparison. The cooling system was set to 25° C. and the metal guides were set as to allow the curable fluoropolymer composition to occupy 70% of the cylinder surface. In between two accelerations the cylinders were cleaned and let cool. The detail proceedings for this process are described in Table 4 below.

TABLE-US-00004 TABLE 4 External mixing procedure. (min) Operation Cylinder Spacing (mm) t = 0 Introduction of elastomer 1 t = 1 Insertion of fillers 1 t = 5-8 Insertion of curing system 1 t = 5-8 5 thin passings 0.6 Calendering sheet, thickness 2 mm 2

[0357] Step 2: Molding

[0358] Cured fluoropolymer products were then produced by compression molding at 160 or 180° C. and 100 kgf/cm pressure. This way, small 150×150×2 mm sheets were prepared. The curing time, which determines the molding time, was determined through a rheological MDR test.

TABLE-US-00005 TABLE 5 Composition of cured fluoropolymer products. Example Filler Description CE-1 Powder CE1 N550 CE-2 Powder CE2 Barium sulfate CE-3 Powder CE3 Wollastonite E-1 Powder 1 Surface-reacted calcium carbonate E-2 Powder 2 Surface-reacted calcium carbonate E-3 Powder 3 Surface-reacted calcium carbonate E-4 Powder 4 Surface-reacted calcium carbonate E-5 Powder 5 Surface-reacted calcium carbonate, treatment A E-6 Powder 6 Surface-reacted calcium carbonate, treatment B E-7 Powder 7 Surface-reacted calcium carbonate E-8 Powder 8 Ultrafine calcium carbonate, treatment A, B, and C

[0359] The obtained cured fluoropolymer products were subjected to DELFT tear resistance and elongation at break tests. The results are compiled in Table 6 below and in FIGS. 1 and 2.

TABLE-US-00006 TABLE 6 Results of DELFT and elongation at break measurements. DELFT 23° C. Elongation Example (MPa) at break (%) CE-1 28.9 187 CE-2 22.6 305 CE-3 22.1 369 E-1 40.6 222 E-2 24.1 388 E-3 27.3 404 E-4 28.5 408 E-5 40.2 206 E-6 37.3 214 E-7 26.1 385 E-8 31.2 294

[0360] The DELFT tear resistance measurements show that Examples E1, E5, E6 and E8 outperform all comparative Examples CE-1 to CE-3. More importantly, one can note that all but E2, E3 and E7 inventive samples outperform carbon black, which is the only reinforcing filler reference (wollastonite and barium sulfate are usually not considered highly reinforcing fillers).

[0361] The tensile tests reveal that all inventive examples outperform the comparative example CE-1 in terms of elongation at break, which is the only reinforcing filler (wollastonite and barium sulfate are not considered reinforcing fillers).