Fluoroelastomer curable composition

Abstract

The invention pertains to UV-curable compositions comprising a iodine-containing (per)fluoroelastomer, and well-defined amount of certain combinations of given photoinitiators and crosslinking which are particularly effective in delivering through low temperature UV curing crosslinked parts possessing outstanding mechanical properties.

Claims

1. A composition (C) comprising: at least one fluroelastomer (A), wherein fluoroelastomer (A) is a (per)fluoroelastomer comprising iodine cure sites in an amount such that iodine content is in a range from 0.04 to 10.0% wt, with respect to the total weight of fluoroelastomer (A); at least one initiator (P), wherein initiator (P) is a photoinitiator of formula: ##STR00012## wherein: each of R.sup.1.sub.H, equal to or different from each other, is a C.sub.1-C.sub.12 hydrocarbon group, optionally containing one or more than one heteroatom, selected from the group consisting of oxygen, nitrogen, and sulfur; j is zero; R.sup.2.sub.H is a phenyl, a methyl group or an ethyl group; R.sup.3.sub.H is selected from a methyl group and an ethyl group; said initiator (P) being present in an amount of 4.0 to 15.0 phr, based on fluoroelastomer (A); and at least one compound (U), wherein compound (U) is a polyunsaturated compound selected from: (U-1) tri-substituted isocyanurate compounds of general formula: ##STR00013## wherein each of R.sub.isocy, equal to or different from each other and at each occurrence, is independently selected from H or a group R.sub.risocy or OR.sub.risocy, with R.sub.risocy being C.sub.1-C.sub.5 alkyl, optionally comprising halogen(s), and each of J.sub.isocy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms, and (U-2) tri-substituted cyanurate compounds of general formula: ##STR00014## wherein each of R.sub.cy, equal to or different from each other and at each occurrence, is independently selected from H or a group R.sub.rcy or OR.sub.rcy, with R.sub.rcy being C.sub.1-C.sub.5 alkyl, optionally comprising halogen(s), and each of J.sub.cy, equal to or different from each other and at each occurrence, is independently selected from a bond or a divalent hydrocarbon group, optionally comprising heteroatoms; said compound (U) being present in an amount of 2.5 to 15.0 phr, based on fluoroelastomer (A).

2. The composition (C) of claim 1 wherein said at least one photoinitiator (P) is at least one initiator (P-1), wherein initiator (P-1) is a photoinitiator of formula: ##STR00015## wherein: R.sup.1.sub.H and R.sup.2.sub.H, equal to or different from each other, are independently a methyl group or an ethyl group; each of R.sup.3.sub.H, equal to or different from each other, is a C.sub.1-C.sub.12 hydrocarbon group, optionally containing one or more than one heteroatom selected from the group consisting of oxygen, nitrogen, and sulfur; and j is zero or is an integer of 1 to 3, said initiator (P-1) being present in an amount of 4.0 to 15.0 phr, based on fluoroelastomer (A).

3. The composition (C) of claim 2, wherein R.sup.1.sub.H and R.sup.2.sub.H are each a methyl group; and j is zero.

4. The composition (C) of claim 1, wherein said fluoroelastomer (A) comprises recurring units derived from at least one (per)fluorinated monomer, wherein said (per)fluorinated monomer is selected from the group consisting of: C.sub.2-C.sub.8 fluoro- and/or perfluoroolefins; C.sub.2-C.sub.8 hydrogenated monofluoroolefins; 1,2-difluoroethylene, vinylidene fluoride (VDF) and trifluoroethylene (TrFE); (per)fluoroalkylethylenes complying with formula CH.sub.2CHR.sub.f0, in which R.sub.f0 is a C.sub.1-C.sub.6 (per)fluoroalkyl or a C.sub.1-C.sub.6 (per)fluorooxyalkyl having one or more ether groups; chloro- and/or bromo- and/or iodo-C.sub.2-C.sub.6 fluoroolefins; fluoroalkylvinylethers complying with formula CF.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl; hydrofluoroalkylvinylethers complying with formula CH.sub.2CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6 fluoro- or perfluoroalkyl; fluoro-oxyalkylvinylethers complying with formula CF.sub.2CFOX.sub.0, in which X.sub.0 is a C.sub.1-C.sub.12 oxyalkyl, or a C.sub.1-C.sub.12 (per)fluorooxyalkyl having one or more ether groups; functional fluoro-alkylvinylethers complying with formula CF.sub.2CFOY.sub.0, in which Y.sub.0 is a C.sub.1-C.sub.12 alkyl or (per)fluoroalkyl, a C.sub.1-C.sub.12 oxyalkyl or a C.sub.1-C.sub.12 (per)fluorooxyalkyl, said Y.sub.0 group comprising a carboxylic or sulfonic acid group, in its acid, acid halide or salt form; (per)fluorodioxoles, of formula: ##STR00016## wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6, equal to or different from each other, is independently a fluorine atom, a C.sub.1-C.sub.6 fluoro- or per(halo)fluoroalkyl, optionally comprising one or more oxygen atom.

5. The composition (C) of claim 4, wherein said fluoroelastomer (A) is selected from: (1) VDF-based copolymers, in which VDF is copolymerized with at least one additional comonomer selected from the group consisting of: (a) C.sub.2-C.sub.8 perfluoroolefins; (b) hydrogen-containing C.sub.2-C.sub.8 fluorinated 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: ##STR00017## 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 (2) TFE-based copolymers, in which TFE is copolymerized with at least one additional comonomer selected from the group consisting of (c), (d), (e), (g), (h) and (i) as above detailed.

6. The composition (C) according to claim 1, wherein compound (U) is selected from the group consisting of triallyl isocyanurate and trivinyl isocyanurate.

7. The composition according to claim 1, wherein the amount of the compound (U) ranges from 0.1 to 20 weight parts per 100 parts by weight (phr) of fluoroelastomer (A).

8. The composition according to claim 7, wherein the amount of the compound (U) ranges from 1 to 15 weight parts per 100 parts by weight of fluoroelastomer (A).

9. The composition according to claim 8, wherein the amount of the compound (U) ranges from 1 to 10 weight parts per 100 parts by weight of fluoroelastomer (A).

10. The composition (C) according to claim 1, said composition additionally comprising at least one organic solvent.

11. The composition (C) according to claim 10, wherein the at least one organic solvent is selected from the group consisting of ketonic solvents, polar solvents, esters, ethers and mixtures thereof.

12. The composition (C) according to claim 1, wherein the composition (C) includes at least one plasticizer (P).

13. The composition (C) according to claim 12, wherein the at least one plasticizer (P) comprises one or more ester-based plasticizers, wherein the one or more ester-based plasticizers is selected from the group consisting of glutarates, adipates, maleates, azelates, sebacates, trimellitates, citrates, phosphate esters, and mixtures thereof.

14. A method for fabricating shaped articles comprising curing the composition (C), according to claim 1.

Description

EXAMPLES

(1) Raw Materials

(2) TPO-L is ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate, commercially supplied as OMNIRAD TPO-L from IGM Resins, and used as received.

(3) D-1173 is 2-hydroxy-2-methyl-1-phenyl-propan-1-one, which was supplied from Aldrich and used as received.

(4) D-MBF is phenyl glyoxylic acid methyl ester (otherwise referred to as methyl benzoyl formate), which was supplied from Sigma Aldrich and used as received.

(5) TAIC is triallylisocyanurate, commercially available as TAICROS from Degussa and used as received.

(6) Iodine-containing peroxide curable fluoroelastomer commercially available as TECNOFLON P 457 from Solvay Specialty Polymers Italy S.p.A. was used; it will be referred to as (A-2), hereunder.

EXAMPLES

Preparative Example 1Manufacture of Fluoroelastomer (A-1)

(7) 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 polymer was recovered drying the latex in a rotatory evaporator under vacuum until complete removal of the liquid phase.

(8) A fluoroelastomer was so recovered having the following molar composition: TFE: 12.0% moles; VDF: 70.5% moles; HFP: 17.5% 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:

(9) 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.

(10) The Mooney Viscosity measured at 121 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.

(11) Compounding and Crosslinking Procedure

(12) Fluoroelastomer of Preparative Example 1 was compounded with the additives, as specified in Tables below, according to the procedure below detailed.

(13) General procedure of final sheet preparation for characterization includes: mixing of polymer with curing agent and initiator of curing till full homogenization. Mixing was performed by manula mixing, or in a speedmixer or in a stirred receptacle in a solvent.

(14) In particular, when the composition comprised a solvent, in 100 ml glass Becker, equipped with magnetic stirrer, the ingredients were introduced according to the following procedure: the fluoroelastomer was dissolved in the solvent at 40 C., and stirred at 600 rpm until complete dissolution of fluoroelastomer; multifunctional compound and photoinitiator were then added and homogenization of the blend was pursued during 5 minutes. The composition was then poured on a petri dish and dried in static oven at 40 C. in order for removing solvent. Dried compound was then cured by ultraviolet irradiation.

(15) When the composition did not comprise any solvent, SpeedMixer bladeless centrifugal mixer equipment, model DAC400 FVZ, purchased from company FlackTek Inc was used. All ingredients of the composition (fluoroelastomer; multifunctional compound and photoinitiator) were introduced in a 300 ml polypropylene jar and mixed by SpeedMixer device till full homogenization. Then composition was poured on a petri dish and cured by ultraviolet irradiation.

(16) Ultraviolet Irradiation Conditions

(17) UV curing was carried-out in UV curing device, called Curing test of Helios Italquartz S.r.l. Curing test equipped with UV lamp HMPL. HMPL is MEDIUM PRESSURE MERCURY VAPOUR LAMP which emits across the entire spectrum of ultraviolet light (UVA, UVB and UVC) with peak emission in the UVA range at 366 nm.

(18) In order to cure the compound, the specimen was placed inside of Curing test and exposed to irradiation in nitrogen environment. N.sub.2 was feeded at constant flux at 0.5 bar. Irradiation cycle lasted 9 minutes. The sample temperature was controlled to avoid heating beyond 50 C. The device was employed at 100% of power irradiation (800 Watt).

(19) After UV irradiation, cured sample could be post-cured (PC). PC for the samples cured by UV included thermal treatment in static for 48 hours at 50 C.

(20) In tables below, amounts of ingredients are provided as weight parts, on the basis of 100 weight parts of fluororubber base.

(21) Mechanical Properties Determination on Cured Samples

(22) The tensile properties have been determined on specimens punched out from the piled films, according to the ASTM D638 Type V Standard.

(23) M.sub.100 is the tensile strength in MPa at an elongation of 100%;

(24) TS is the tensile strength in MPa;

(25) EB is the elongation at break in %.

(26) The Shore A hardness (3) (HDS) has been determined on 3 pieces of plaque piled according to the ASTM D 2240 method.

(27) Crosslinking Efficiency Assessment

(28) The specimen is immersed into MEK in a closed glass vessel (ratio 1 g of polymer in 50 mL of MEK), at room temperature for 16 hours (overnight) without stirring. Suitable polymer amount for test is 2 g.

(29) After the immersion the sample is dried in an oven at 110 C. for 4 hours under vacuum. The drying process is needed to evaporate the absorbed liquid and to determine if a partial dissolution of the sample has occurred. Crosslinking efficiency is then determined as insoluble percentage of the specimen as percent weight ratio between final weight and initial weight of specimen.

(30) TABLE-US-00001 TABLE 1 Composition Ex. 1C Ex. 2C Ex. 3 Ex. 4 Ex. 5 Ex. 6C Ex. 7 (A-1) 100 100 100 100 100 100 (A-2) 100 D-1173 9 9 9 9 9 18 9 TAIC 0.7 1.1 3.0 7.5 9 18 9 Solvent Ethyl acetate.sup.1 EFX.sup.2 Characterizations XL after UV (%) 0% 56% 86% 88% 91% 86%* 91% XL after PC (%) 73% 87% 93% 96% n.d. TS (MPa) n.d. - 3.3 5 5.8 5.3 7.1 5.6 M.sub.100 (MPa) not cured 4 4 5 5 9 EB (%) 603 269 158 143 74 Hardness (Shore 38 50 n.d. 53 n.d. 42 A) *very dark cured specimen, mechanical properties not suitable for use as fluororubber; .sup.1composition prepared via solution method using ethyl acetate as solvent; .sup.2composition prepared via solution method using EFX solvent.

(31) TABLE-US-00002 TABLE 2 Composition Ex. 8 Ex. 9C Ex. 10C Ex. 11C Ex. 12C Ex. 13 (A-1) 100 100 100 100 100 100 D-1173 6.5 3.1 1.1 2.5 D-MBF 9.0 TPO-L 9.0 TAIC 9.0 9.0 9.0 2.5 9.0 9.0 Solvent Ethyl acetate.sup.1 Characterizations XL after UV (%) 87% 84% n.d. 81% No cure 85% XL after PC (%) 95% 90% n.d. 84% 85% TS (MPa) 6.4 4.1 3.9 2.4 8.3 M.sub.100 (MPa) 5 4 3 2 5 EB (%) 150 135 162 226 170 Hardness 60 47 46 39 n.d. (Shore A) .sup.1composition prepared via solution method using ethyl acetate as solvent

(32) As comparison, a cured specimen was prepared by standard compounding (see Ex. 14C) using same fluoroelastomer raw gum, but adding traditional peroxide curing ingredients and molding for 10 minutes at 170 C., followed by post-curing 4 h at 230 C.; results shown below demonstrate that low temperature UV curing of composition of the invention leads to substantially similar product performances.

(33) TABLE-US-00003 TABLE 3 Composition Ex. 14C.sup.1 Ex. 15.sup.3 (A-1) 100 100 D-1173 9.0 Peroxide.sup.2 4.05 TAIC 9.0 9.0 XL after UV (%) n.a. 86% XL after PC (%) 98% n.d. TS (MPa) 6.5 n.d. M.sub.100 (MPa) 6 n.d. EB (%) 118 117 Hardness 58 43 (Shore A) .sup.1composition prepared in the absence of solvent in SpeedMixer; .sup.2Luperox 101, 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane; .sup.3composition prepared by mixing manually, in the absence of solvent, and UV cured and post-cured according to the procedure described above.