CURABLE FLUOROELASTOMER COMPOSITION

Abstract

The invention pertains to certain fluoroelastomer compositions comprising an iodine-containing (per)fluoroelastomer of low molecular weight and certain organic peroxides, possessing outstanding cross-linking behaviour at limited temperatures, and yielding resulting final parts exhibiting good mechanical and sealing properties, while avoiding discoloring/degradation phenomena, and enabling easy colour match in a wide range of colours.

Claims

1. A fluoroelastomer composition comprising: a (per)fluoroelastomer [fluoroelastomer (A)] having a number-averaged molecular weight of 10 000 to 30 000, said (per)fluoroelastomer comprising iodine atoms in an amount of 0.5 to 10.0% wt with respect to the total weight of fluoroelastomer (A); at least one organic peroxide (O) selected from the group consisting of di(3-carboxypropionyl) peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoylperoxy) hexane, dibenzoyl peroxide, t-amylperoxy 2-ethylhexanoate, t-butylperoxy 2-ethylhexanoate, t-butyl peroxyisobutyrate, t-butyl peroxy-(cis-3-carboxy)propenoate, and 1,1-di(t-amylperoxy)cyclohexane, said peroxide (O) being present in the fluoroelastomer composition in an amount of at least 1.8 phr and at most 5.0 phr.

2. The fluoroelastomer composition of claim 1, wherein the peroxide (O) is dibenzoyl peroxide.

3. The fluoroelastomer composition of claim 1, wherein fluoroelastomer (A) is selected from the group consisting of: (1) VDF-based copolymers, wherein VDF is copolymerized with at least one comonomer selected from the group consisting of: (a) C.sub.2-C.sub.8 perfluoroolefins; (b) hydrogen-containing C.sub.2-C.sub.8 olefins; (c) C.sub.2-C.sub.8 fluoroolefins comprising at least one of iodine, chlorine and bromine; (d) (per)fluoroalkylvinylethers (PAVE) of formula CF.sub.2CFOR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 (per)fluoroalkyl group; (e) (per)fluoro-oxy-alkylvinylethers of formula CF.sub.2CFOX, wherein X is a C.sub.1-C.sub.12 ((per)fluoro)-oxyalkyl comprising catenary oxygen atoms; (f) (per)fluorodioxoles having formula: ##STR00008## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal to or different from each other, is independently selected from the group consisting of fluorine atom and C.sub.1-C.sub.6 (per)fluoroalkyl groups, optionally comprising one or more than one oxygen atom; (g) (per)fluoro-methoxy-vinylethers having formula:
CF.sub.2CFOCF.sub.2OR.sub.f2 wherein R.sub.f2 is selected from the group consisting of C.sub.1-C.sub.6 (per)fluoroalkyls; C.sub.5-C.sub.6 cyclic (per)fluoroalkyls; and C.sub.2-C.sub.6 (per)fluorooxyalkyls, comprising at least one catenary oxygen atom; (h) C.sub.2-C.sub.8 non-fluorinated olefins (Ol); and (i) ethylenically unsaturated compounds comprising nitrile (CN) groups, optionally (per)fluorinated; and (2) TFE-based copolymers, wherein TFE is copolymerized with at least one comonomer selected from the group consisting of (c), (d), (e), (g), (h) and (i) as above detailed.

4. The fluoroelastomer composition of claim 1, wherein fluoroelastomer (A) has a number-averaged molecular weight of at least 11 000 and/or at most 25 000.

5. The fluoroelastomer composition of claim 1, further comprising at least one of the following: (a) at least one curing coagent, in amount between 0.5 to 10 phr relative to fluoroelastomer (A); (b) at least one metallic compound, in amount between 1 and 15 phr relative to fluoroelastomer (A), selected from the group consisting of oxides and hydroxides of divalent metals, optionally combined with a salt of a weak acid; (c) at least one acid acceptor different from metal oxides.

6. The fluoroelastomer composition according to of claim 1, wherein said composition comprises at least one colorant selected from pigments and dyes, in an amount of 0.1 to 10 phr.

7. A method for fabricating shaped articles, the method comprising shaping a fluoroelastomer composition according to claim 1.

8. A method of fabricating a shaped article, said method comprising: simultaneously moulding and curing the composition according to claim 1 at a temperature of at most 130 C., de moulding the composition so as to obtain a pre-formed article; and post-curing the pre-formed article in an oven at a temperature of at most 170 C.

9. The method of claim 8, wherein said shaped article is a jewelry item.

10. A Cured article obtained by moulding and curing the fluoroelastomer composition according to claim 1.

11. A method for processing the fluoroelastomer composition according to claim 1, the method comprising liquid injection moulding, screen printing, form-in-place or combinations thereof.

12. The fluoroelastomer composition of claim 3, wherein fluoroelastomer (A) is selected from the group consisting of: (1) VDF-based copolymers, wherein VDF is copolymerized with at least one comonomer selected from the group consisting of: (a) tetrafluoroethylene (TFE), hexafluoropropylene (HFP); (b) vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl ethylenes of formula CH.sub.2CHR.sub.f, wherein R.sub.f is a C.sub.1-C.sub.6 perfluoroalkyl group; (c) chlorotrifluoroethylene (CTFE); (d) (per)fluoroalkylvinylethers (PAVE) of formula CF.sub.2CFOR.sub.f, wherein R.sub.f is CF.sub.3, C.sub.2F.sub.5, or C.sub.3F.sub.7; (e) (per)fluoro-oxy-alkylvinylethers of formula CF.sub.2CFOX, wherein X is perfluoro-2-propoxypropyl; (f) (per)fluorodioxoles having formula: ##STR00009## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal to or different from each other, is independently selected from the group consisting of CF.sub.3, C.sub.2F.sub.5, C.sub.3F.sub.7, OCF.sub.3, and OCF.sub.2CF.sub.2OCF.sub.3; (g) (per)fluoro-methoxy-vinylethers having formula:
CF.sub.2CFOCF.sub.2OR.sub.f2 wherein R.sub.f2 is selected from the group consisting of CF.sub.2CF.sub.3, CF.sub.2CF.sub.2OCF.sub.3 and CF.sub.3; (h) ethylene and propylene; and (2) TFE-based copolymers, wherein TFE is copolymerized with at least one comonomer selected from the group consisting of (c), (d), (e), (g) and (h) as above detailed.

13. The fluoroelastomer composition of claim 4, wherein fluoroelastomer (A) has a number-averaged molecular weight of at least 12 000, and/or at most 20 000.

14. The fluoroelastomer composition of claim 5, wherein the curing coagent is selected from the group consisting of triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N diallylacrylamide; N,N,N,N-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltri siloxane; and bis-olefins (OF) of formula: ##STR00010## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6, equal or different from each other, are H or C.sub.1-C.sub.5 alkyl; Z is a linear or branched C.sub.1-C.sub.18 hydrocarbon radical, optionally containing oxygen atoms and optionally at least partially fluorinated, or a (per)fluoropolyoxyalkyl ene radical.

15. The fluoroelastomer composition of claim 5, wherein the metallic compound is present in amount between 2 and 10 phr relative to fluoroelastomer (A).

16. The fluoroelastomer composition of claim 5, wherein the metallic compound is selected from the group consisting of oxides and hydroxides of Mg, Zn, Ca or Pb, optionally combined with a salt of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites.

17. The fluoroelastomer composition of claim 5, wherein the salt of a weak acid is selected from the group consisting of stearates, benzoates, carbonates, oxalates and phosphites of Ba, Na, K, Pb, and Ca.

18. The fluoroelastomer composition of claim 5, wherein the acid acceptor different from metal oxides is 1,8-bis(dimethylamino)naphthalene or octadecylamine.

19. The fluoroelastomer composition of claim 5, wherein: (a) the curing coagent is selected from the group consisting of triallyl cyanurate; triallyl isocyanurate (TAIC); tris(diallylamine)-s-triazine; triallyl phosphite; N,N diallylacrylamide; N,N,N,N-tetraallylmalonamide; trivinyl isocyanurate; 2,4,6-trivinyl methyltrisiloxane; and bis-olefins (OF) of formula: ##STR00011## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6, equal or different from each other, are H or C.sub.1-C.sub.5 alkyl; Z is a linear or branched C.sub.1-C.sub.18 hydrocarbon radical, optionally containing oxygen atoms and optionally at least partially fluorinated, or a (per)fluoropolyoxyalkylene radical; (b) the metallic compound is present in amount between 2 and 10 phr relative to fluoroelastomer (A) and is selected from the group consisting of oxides and hydroxides of Mg, Zn, Ca or Pb, optionally combined with a salt of a weak acid, for instance Ba, Na, K, Pb, Ca stearates, benzoates, carbonates, oxalates or phosphites; the salt of a weak acid is selected from the group consisting of stearates, benzoates, carbonates, oxalates and phosphites of Ba, Na, K, Pb, and Ca; and (c) the acid acceptor different from metal oxides is 1,8-bis(dimethylamino)naphthalene or octadecylamine.

20. The method of claim 9, wherein the jewelry item is a bracelet, a wrist bands for a watch, or a packing for outer cladding components of a clock or watch.

Description

EXAMPLES

Preparative Example 1Manufacture of a Fluoroelastomer of Low Mn

[0106] In a 10 liters reactor equipped with a mechanical stirrer operating at 545 rpm, 5.4 l of demineralized water and 40 ml of a microemulsion, previously obtained by mixing 8.8 ml of a perfluoropolyoxyalkylene having acidic end groups of formula: CF.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.2COOH, wherein n/m=10, having average molecular weight of 600, 5.6 ml of a 30% v/v NH.sub.4OH aqueous solution, 20.0 ml of demineralized water and 5.5 ml of GALDEN D02 perfluoropolyether of formula: CF.sub.3O(CF.sub.2CF(CF.sub.3)O).sub.n(CF.sub.2O).sub.mCF.sub.3 with n/m=20, having average molecular weight of 450, were introduced. The reactor was heated and maintained at a set-point temperature of 80 C. A mixture of tetrafluoroethylene (TFE) (11% moles), vinylidene fluoride (VDF) (70% moles) and hexafluoropropylene (HFP) (19% moles) was then added to reach a final pressure of 30 bar (3.0 MPa). 54 ml of 1,4-diiodoperfluorobutane (C.sub.4F.sub.8I.sub.2) as chain transfer agent and 1.8 g of ammonium persulfate (APS) as initiator were then introduced. Pressure was maintained at set-point of 30 bar by continuous feeding of a gaseous mixture of TFE (11% moles), VDF (70% moles) and HFP (19% moles) up to a total of 3150 g. Then the reactor was cooled, vented and the latex recovered. The latex was coagulated by freezing and subsequent thawing, the polymer separated from the aqueous phase, washed with demineralised water and dried in a convection oven at 100 C. for 16 hours.

[0107] A fluoroelastomer was so recovered having the following molar composition: TFE: 11% moles; VDF: 70% moles; HFP: 19% moles, comprising 2.3% wt of iodine. This fluoroelastomer, when analyzed by GPC, by dissolving a sample thereof at about 0.5% wt/vol concentration in tetrahydrofurane for 6 hours under magnetic stirring at room temperature; the solution so obtained was filtered over a PTFE filter having 0.45 m pore size and the filtered solution was injected in the GPC system; details of the GPC conditions are listed hereinafter:

[0108] Mobile phase Tetrahydrofuran; Flow rate 1.0 mL/min; Temperature 35 C.; Injection system Autosampler model 717 plus; Injection volume 200 l; Pump Isocratic Pump model 515; Column set Precolumn+4 Waters Styragel HR: 10.sup.6, 10.sup.5, 10.sup.4 and 10.sup.3 ; DetectorWaters Refractive Index model 2414; Software for data acquisition and processing: Waters Empower 3. The fluoroelastomer was found to possess a M.sub.n of 12 398, a M.sub.w of 23 355, and a polydispersity index of 1.9; substantially no fraction was found having a molecular weight of below 1 000.

[0109] The Mooney Viscosity measured at 200 C. (1+10 min) according to ASTM D1646 provided non-measurable values, more precisely values below the detection limit of the instrument, demonstrating the very low viscosity as related to the molecular weight.

[0110] Fluoroelastomer of Preparative Example 1 was compounded with the additives, as specified in Table below, in a Speedmixer. Plaques were cured in a pressed mould and then post-treated in an air circulating oven in conditions (time, temperature) below specified.

[0111] Cure behaviour was characterized by Moving Die Rheometer (MDR), in the conditions specified in the Table below, by determining the following properties:

[0112] M.sub.L=Minimum torque (lbin)

[0113] M.sub.H=Maximum torque (lbin)

[0114] t.sub.S2=Scorch time, time for two units rise from M.sub.L (sec);

[0115] t.sub.02=Time to 2% state of cure (sec);

[0116] t.sub.50=Time to 50% state of cure (sec);

[0117] t.sub.90=Time to 90% state of cure (sec).

[0118] The tensile properties have been determined on specimens punched out from the plaques, according to the DIN 53504 S2 Standard, wherein:

[0119] M50 is the tensile strength in MPa at an elongation of 100%;

[0120] M100 is the tensile strength in MPa at an elongation of 100%;

[0121] TS is the tensile strength in MPa;

[0122] EB is the elongation at break in %.

[0123] The Shore A hardness (3) (HDS) has been determined on 3 pieces of plaque piled according to the ASTM D 2240 method. Compression set values have been determined on 3 disks punched out from the plaques piled according to the ASTM D 395-B method.

[0124] Yellow Index has been determined according to the ASTM E313 method.

[0125] Curing recipe and conditions and properties of cured sample are summarized in Table 1.

TABLE-US-00001 TABLE 2 Recipe title Ex. 2C Ex. 3 Ex. 4 Polymer from Ex.1 (wt parts) 100.00 100.00 100.00 Taicros-Degussa.sup.({circumflex over ()}) (phr) 2.50 2.50 2.50 Luperox A70S- (phr) 1.80 3.60 Sigma Aldrich (*) Trigonox 101-Akzo (phr) 1.50 Nobel.sup.(#) MDR @ 120 C. 36 min @ 12 min @ 12 min @ 120 C. 120 C. 120 C. M.sub.L lb*in 0.0 0.0 M.sub.H lb*in 7.1 6.9 t.sub.S2 S do not cure 97 69 t.sub.02 S 62 47 t.sub.50 S 152 95 t.sub.90 S 590 338 MDR 12 min @ 170 C. M.sub.L lb*in 0.0 M.sub.H lb*in 6.2 t.sub.S2 S 66 t.sub.02 S 41 t.sub.50 S 111 t.sub.90 S 581 Molding-duration = t.sub.90 t.sub.90 @ t.sub.90 @ t.sub.90 @ 170 C. 120 C. 120 C. No Postcure Mechanical Properties 23 C. DIN 53504 S2 TS MPa 2.1 2.8 1.8 M50 MPa 0.9 1.0 1.0 M1000 MPa 1.1 1.3 1.3 EB % 156 137 109 Hardness Shore A 50 53 54 Post-cure 4 h @ 150 C. Mechanical Properties, 23 C. DIN 53504 S2 Tensile Strength MPa 2.8 2.5 2.6 50% Modulus MPa 0.8 1.0 1.0 100% Modulus MPa 1.1 1.3 1.4 Elongation @ Break % 198 143 133 Hardness Shore A 52 54 55 Post-cure 4 h @ 190 C. Mechanical Properties, 23 C. DIN 53504 S2 Tensile Strength MPa 2.9 2.5 2.7 50% Modulus MPa 0.8 1.0 1.0 100% Modulus MPa 1.1 1.3 1.4 Elongation @ Break % 201 150 134 Hardness Shore A 51 54 55 Post-cure 4 h @ 230 C. Mechanical Properties, 23 C. DIN 53504 S2 Tensile Strength MPa 3.1 3.2 2.9 50% Modulus MPa 0.9 1.0 1.0 100% Modulus MPa 1.1 1.3 1.3 Elongation @ Break % 201 163 145 Hardness Shore A 51 53 55 Yellow index E313 No postcure YI 34.6 13.8 20.6 Postcure 4 h @ 150 C. YI 62.2 30.7 49.9 Postcure 4 h @ 170 C. YI 91.7 45.8 65.9 Postcure 4 h @ 190 C. YI 98.6 55.5 76.8 Postcure 4 h @ 230 C. YI 112.6 123.0 137.2 .sup.({circumflex over ()})Taicros is neat triallylisocyanurate; .sup.(*)Luperox A705 is a mixture of benzoyl peroxide (70%) and water; the amount listed above in phr wrt fluoroelastomer are referred to neat benzoyl peroxide; .sup.(#)Trigonox is neat 2,5-dimethyl-2,5-di(ter-butylperoxy)hexane.