IMPROVED SCORCH SAFETY OF CURABLE FLUOROELASTOMER COMPOSITIONS

Abstract: This invention provides a curable fluoroelastomer composition comprising: (A) a fluorine-containing polymer or a blend of fluorine-containing polymers each comprising interpolymerized units derived from one or more fluorine-containing ethylenically unsaturated monomers; (B) an aromatic polyhydroxy crosslinking agent; (C) at least one organo-onium compound; and (D) a monohydroxyfunctional phenol. The compositions provide for a method of improving scorch safety of curable fluoroelastomer compositions.

Description: Improved Scorch Safety of Curable Fluoroelastomer Compositions FIELD OF THE INVENTION This invention relates to fluorocarbon elastomers and their curing. In another aspect it relates to improved scorch safety of curable fluoroelastomers. BACKGROUND OF THE INVENTION Fluorocarbon elastomers are synthetic elastomeric polymers with a high fluorine content — see, for example, W. M. Grootaert., G.H. Millet, & A.T. Worm. Fluorocarbon Elastomers, 8 Kirk-Othmer Encyclopedia Of Chemical Technology 990-1005 (4th ed. 1993). Fluorocarbon elastomers, particularly the copolymers of vinylidene fluoride with other ethylenically unsaturated halogenated monomers such as hexafluoropropene (C 3 Fβ) have become the polymers of choice for high temperature applications, such as seals, gaskets, and linings. These polymers exhibit favorable properties against the exposure to aggressive environments such as solvents, lubricants, and oxidizing or reducing agents. Additionally, these polymers can be compounded and cured to have high tensile strength, good tear resistance, and low compression set. Presently used curing agents for fluoroelastomers include aromatic polyhydroxy crosslinking agents, such as polyphenols, used in combination with certain organo-onium vulcanization accelerators. U.S. Pat. Nos. 4,882,390 (Grootaert et al.), 4,912,171 (Grootaert et al.) and 5,086,123 (Guenthner et al.), for example, describe these compounds. In accordance with conventional curing processes, desired amounts of compounding ingredients and other conventional adjuvants or ingredients are added to the unvulcanized fluorocarbon elastomer stock and intimately admixed or compounded therewith by employing any ofthe usual rubber mixing devices such as Banbury mixers, roll mills, or any other convenient mixing device. The temperature ofthe ingredients during mixing typically will not rise above 120 °C. During mixing, the components and adjuvants are distributed throughout the fluorocarbon gum. The curing process typically comprises either extrusion ofthe compounded mixture into a mold (injection molding) or pressing ofthe compounded mixture in a mold (press cure), e.g. a cavity or a transfer mold, followed subsequently by oven- curing (post cure). Injection molding ofthe compounded mixture is usually conducted in two temperature ranges. The compounded mixture is first introduced into an injection barrel whose orifice is typically operated at about 70 °C to 90 °C. The mixture is then forced down the extruder barrel with the aid ofa mechanical screw. The mold into which the mixture is extruded is typically operated at about 180 °C to 200 °C. The resulting molded articles are also typically ultimately subjected to a post-cure at elevated temperatures for an extended period of time, e.g. at temperatures above 200 °C for 16 to 24 hours. A drawback to the production of many of these conventional fluoroelastomers is their tendency towards "scorching," i.e., the premature or excessively rapid cure ofthe compounded composition when exposed to elevated temperatures or high shear conditions that produce a high temperature environment. This scorching behavior is particularly troublesome for injection-molded fluoroelastomers, wherein scorching is characterized by a premature cure initiation occurring prior to and during injection ofthe compounded composition into a mold. The point of cure initiation for injection-molded fluoroelastomers may be defined as the time after which the compounded fluoroelastomer is subjected to injection molding temperature conditions (i.e., upon introduction into an injection barrel at a temperature above approximately 70 °C) when the curing compound begins to gel or harden. Such a change in physical properties, particularly the corresponding viscosity increase, can greatly reduce processing efficiency by hindering the ability to inject the compounded mixture into a mold. The point of cure initiation may be manipulated in a conventional bisphenol curing system by varying the concentration of crosslinking agent present in the compounded composition for otherwise identical formulations. An increase in the concentration ofthe crosslinking agent in the compounded composition is observed to delay the post-compounding cure initiation. Because ofthe resulting higher crosslink density, however, the resulting physical properties ofthe cured product under this scheme are also significantly altered. Reducing the amount of accelerator or accelerators in the system also will affect the final physical properties ofthe cured composition and will alter cure rates in an undesirable manner. Generally, increases in crosslinking agent concentration will raise the maximum torque obtained by an oscillating disk rheometer (ODR) test proportionally and will give the cured end product the characteristics of higher crosslink density fluoroelastomers, e.g. increased hardness, lower compression set, and lower elongation. Specifically, the decrease in elongation at break makes it difficult to demold the cured article from a hot mold cavity without tearing the article. It is desirable to develop a curable fluoroelastomer composition possessing a delayed post-compounding cure initiation and a reduced tendency toward scorching behavior without significantly altering the physical characteristics ofthe cured end product. SUMMARY OF THE INVENTION Briefly, in one aspect, this invention provides a curable fluoroelastomer composition comprising: (A) a fluorine-containing polymer or a blend of fluorine- containing polymers each comprising interpolymerized units derived from one or more fluorine-containing ethylenically unsaturated monomers; (B) an aromatic polyhydroxy crosslinking agent; (C) at least one organo-onium compound; and (D) a monohydroxyfunctional phenol. In another aspect, the present invention provides a method of improving scorch safety of curable fluoroelastomer compositions comprising curing the aforementioned composition. The combination of an organo-onium compound and a monohydroxyfunctional phenol as incorporated into a curable fluoroelastomer composition in accordance with the present invention provides improved scorch safety of curable fluoroelastomers by providing a delay in post-compounding cure initiation at operating temperatures without significantly affecting the resulting physical properties ofthe cured product. For lower crosslink density fluoroelastomer compositions, little or no change in resulting properties is observed with the addition ofa monofunctional phenol according to this invention. DETAILED DESCRIPTION OF THE INVENTION The addition ofa desired monohydroxyfunctional phenol to a curable fluoroelastomer composition acts to delay the post-compounding cure initiation over any given range of crosslink densities without significantly affecting the rheological profile ofthe composition or its resulting physical characteristics when cured. For the purposes of this invention, a delay in cure initiation of 30 seconds or more over an identical fluoroelastomer composition not containing a monohydroxyfunctional phenol is deemed significant, although cure delays of more than several minutes are achieved. Among the polymers which may be compounded in accordance with this invention are the elastomeric polymers whose interpolymerized units are derived from one or more ofthe following fluoromonomers: vinylidene fluoride, hexafluoropropene, chlorotrifluoroethylene, 2-chloropentafluoropropene, perfluoromethyl vinyl ether, tetrafluoroethylene, 1-hydropentafluoropropene, dichlorodifluoroethylene, trifluoroethylene, 1,1-chlorofluoroethylene, and mixtures thereof. Other terminally ethylenically-unsaturated fluoromonomers are also considered useful provided they contain at least one fluorine atom substituent on each double-bonded carbon atom, each carbon atom of said fluoromonomer being substituted only with fluorine and optionally with chlorine, hydrogen, a lower fluoroalkyl radical, or a lower fluoroalkoxy radical. These fluoromonomers may also be copolymerized with other compounds such as non-fluorinated alpha-olefin co-monomers, e.g. ethylene or propylene. A preferred class of elastomers are copolymers of vinylidene fluoride and at least one terminally ethylenically- unsaturated fluoromonomer containing at least one fluorine atom substituent on each double-bonded carbon atom, each carbon atom of said fluoromonomer being substituted only with fluorine and optionally with chlorine, hydrogen, a lower fluoroalkyl radical, or a lower fluoroalkoxy radical. Particularly preferred are the elastomers produced by copolymerizing vinylidene fluoride with hexafluoropropene. Fluoroelastomer copolymers according to the type described above are commercially available as incorporated cure copolymer gumstock that include the curable fluoroelastomer, a suitable crosslinking agent, and certain vulcanization accelerators together in one product. These commercial compositions are sold, for example, under the "Fluorel" trademark by the 3M Company, Saint Paul, Minnesota. Suitable products ofthe "Fluorel" line include Fluorel™ FC-2174 Fluoroelastomer (Fluorel™ Fluoroelastomers, product bulletin 98-0211-2133-4, issued 7/85, available from 3M Co., St. Paul, Minn.). Other commercially available products include fluoroelastomers sold under the "Fluorel II," "Niton," "Diael," and "Tecnoflon" trademarks. A common crosslinking agent for a fluorocarbon elastomer gum is a polyhydroxy compound. The polyhydroxy compound used in its free or non-salt form and as the anionic portion ofthe onium salt complex can be any of those polyhydroxy compounds that function as a crosslinking agent or co-curative for fluoroelastomers, such as those polyhydroxy compounds disclosed in U.S. Pat. Νos. 3,876,654 (Pattison), and 4,233,421 (Worm). Representative aromatic polyhydroxy compounds include any one ofthe following: di-, tri-, and tetrahydroxybenzenes, naphthalenes, and anthracenes, and bisphenols ofthe following formula: ( I ) wherein A is a difunctional aliphatic, cycloaliphatic, or aromatic radical of 1 to 13 carbon atoms, or a thio, oxy, carbonyl, sulfonyl, or sulfonyl radical, A is optionally substituted with at least one chlorine or fluorine atom, x is 0 or 1, n is 1 or 2, and any aromatic ring ofthe polyhydroxy compound is optionally substituted with at least one atom of chlorine, fluorine, bromine, or with a carboxyl or an acyl radical (e.g. — COR, where R is H or a Ci to Cg alkyl, aryl, or cycloalkyl group) or alkyl radical with, for example, 1 to 8 carbon atoms. It will be understood from the above bisphenol formula that the — OH groups can be attached in any position (other than number one) in either ring. Blends of two or more of these compounds may also be used. One ofthe most useful and commonly employed aromatic polyhydroxy compounds is 2,2-bis(4-hydroxyphenyl)hexafluoro-propane, known more commonly as bisphenol AF. The compounds 4,4'-dihydroxydiphenyl sulfone (Bisphenol S) and 2,2-bis(4-hydroxyphenyl)propane (bisphenol A) are also considered useful in the present invention. Other useful aromatic polyhydroxy compounds include hydroquinone and dihydroxybenzenes such as, resorcinol, 2- methyl resorcinol, 5-methyl resorcinol, 2-methyl hydroquinone, 2,5-dimethyl hydroquinone, and 2-t-butyl hydroquinone, 1,5-dihydroxynaphthalene and 9,10- dihydroxyanthracene. Still other suitable crosslinking compounds are known in the art and described, for example, in U.S. Pat. Nos. 4,912,171 (Grootaert et al.) and 5,262,490 (Kolb et al.) whose descriptions are incorporated herein by reference. Many ofthe organo-onium compounds which are admixed with the fluorine- containing polymer are capable of functioning as a vulcanization accelerator. As is known in the art, an organo-onium is the conjugate acid ofa Lewis base (e.g., phosphine, amine, ether, and sulfide) and can be formed by reacting said Lewis base with a suitable alkylating agent (e.g., an alkyl halide or acyl halide) resulting in an expansion ofthe valence ofthe electron donating atom ofthe Lewis base and in a positive charge on the organo-onium compound. Many ofthe organo-onium compounds useful in the present invention contain at least one heteroatom, i.e., a non-carbon atom such as N, P, S, O, bonded to organic or inorganic moieties. One class of quaternary organo-onium compounds particularly useful in the present invention broadly comprises relatively positive and relatively negative ions wherein a phosphorus, arsenic, antimony or nitrogen generally comprises the central atom of the positive ion, and the negative ion may be an organic or inorganic anion (e.g. halide, sulfate, acetate, phosphate, phosphonate, hydoxide, alkoxide, phenoxide, bisphenoxide, etc.). The organo-onium compounds useful in this invention are described and known in the art. See, for example, U.S. Pat. Nos. 4,912,171 (Grootaert et al.), 5,086, 123 (Guenthner et al.), and 5,262,490 (Kolb et al.) whose descriptions are herein incorporated by reference. Specific representative examples include the following individually listed compounds and mixtures thereof: triphenylbenzyl phosphonium chloride tributylallyl phosphonium chloride tributyl-(2-methoxypropyl)phosphonium chloride tributylbenzyl ammonium chloride tetrabutyl ammonium bromide triaryl sulfonium chloride tritolyl sulfonium chloride 8-benzyl-l,8-diazabicyclo [5,4,0]-7-undecenium chloride benzyl tris(dimethylamino) phosphonium chloride benzyl(diethylamino)diphenylphosphonium chloride The monohydroxyfunctional phenols admixed with the above described compositions act to delay the fluoroelastomer cure at process operating temperatures. These mono- or multi-substituted phenols can be represented by the following general formula: ( π ) wherein R is a halogen atom or an acyl, aryl, polyaryl (fused to or separated from the aromatic ring) or alkyl radical substituent (or any combination thereof), the latter three of which may be straight-chained, branched, cyclic, or halogenated. When R is a halogen atom, x may be between 1 and 5, otherwise, x may be between 1 and 3. Additionally, the — R group may optionally contain one or more caternary heteroatoms, i.e. a non-carbon atom such as nitrogen or oxygen. However, where x is one and where the single — R group is a carboxylic acid group and the resulting compound is classifiable as a benzoic acid, (e.g. where R is — COOH), the carboxylic acid substituent must be placed in either the meta or para position on the ring relative to the hydroxyl group. It will be understood from the above formula that the constituent — R group can otherwise be attached in any position in the ring relative to the hydroxy functional group. Preferably, however, to avoid possible steric hindrance ofthe — OH functionality, said — R group is configured in either the meta ox para position relative to the hydroxyl group where said — R group contains more than two carbon atoms. The constituent — R group may contain a phenol where the resulting compound, classifiable as a polyphenol, is monohydroxy functionally hindered by steric effects on one ofthe hydroxyl groups (i.e. there are one or more substituent groups that contain more than 2 carbon atoms in the meta or para position relative to that hindered hydroxyl group). Such a monohydroxyfunctionally hindered polyphenol will act for the purposes ofthe present invention as a monophenol, such as, for example, where — R is 2,6-di t- butyl 4-hexafluoropropyl phenol. The ability of any particular monohydroxyfunctional phenol such as described above to act as a cure initiation inhibitor is believed to be in part a function ofthe relative acidity of that monohydroxyfunctional phenol with respect to the crosslinking agent used in the fluoroelastomer composition. Accordingly, the particular monohydroxyfunctional phenol chosen for use in a given curable fluoroelastomer composition preferably is more acidic than the crosslinking agent used. For the common, and preferred, example where 2,2-bis(4- hydroxyphenyl)hexafluoro-propane (Bisphenol AF) is chosen as the crosslinking agent, a useful monohydroxyfunctional phenol preferably has a Pk_ less than that of Bisphenol AF in the environment ofthe fluoroelastomer composition. Especially preferred — R groups are those with strong electron withdrawing capacities such as where R is a cyanide ( — CN) or a nitro ( — NO 2 ) substituent. Additionally, in accordance with well-known principles governing relative electron withdrawing capacities, these preferred groups are preferentially placed in the para position on the phenyl ring relative to the hydroxyl group, unless R is a halogen atom, in which case it is preferentially placed in the meta position on the phenyl ring relative to the hydroxyl group. Preferred halogenated monophenols include 2,6- dibromophenol and 3,5-dichlorophenol. Pentafluorophenol and pentachlorophenol are also considered useful for the purposes of this invention. Representative individual constituent — R groups according to the above- described formula I useful in the present invention include the following: — CN, — NO 2 , — COCβHs, — COCHzCeHj, — COCH 3 , — COOCH 3 , — CF 3 , — NHCH 2 COOH, —COOH, — C 6 H 5 , — CH 2 OH. The concentration ofthe monohydroxyfunctional phenol present in the curable fluoroelastomer composition may be chosen to effect the desired cure delay under processing conditions. The minimum concentration ofthe monophenol present in the compounded fluoroelastomer mixture to effect a cure delay of 30 seconds over an identically formulated mixture without the monophenol depends on the relative concentration ofthe polyphenol crosslinking agent. Compositions containing 1 part of crosslinking agent per 100 parts of incoφorated cure copolymer gumstock (low crosslink density formulations) require a minimum molar monophenol concentration of one-half the concentration of crosslinking agent to a affect a 30 second cure delay. Compositions containing 2 parts of crosslinking agent per 100 parts of incoφorated cure copolymer gumstock (high crosslink density formulations) require a minimum molar monophenol concentration of only one- fourth the concentration of crosslinking agent to effect a 30 second cure delay. Above this minimum concentration, a very nearly linear relationship exists between the increase in concentration ofthe monophenol and the resulting relative cure delay for all crosslink density ranges of interest. For high crosslink density fluoroelastomer formulations, increases in monophenol concentration is seen to produce a slight rise in compression set for the cured end product over all measured monofunctional phenol concentration ranges. The addition ofa monohydroxyfunctional phenol is not, however, seen to significantly alter other physical properties ofthe cured end product, such as tensile strength, elongation at break, and modulus at 100 percent elongation, for either the low or high crosslink density formulations. The following examples are offered to aid in a better understanding ofthe present invention. These examples present and evaluate a number of monohydroxyfunctional phenols. This list is not to be unnecessarily construed as an exhaustive compilation of all monophenols useful in the present invention and the examples are not to be unnecessarily construed as limiting the scope of this invention. EXAMPLES A plurality of curable fluorine-containing copolymers of this invention were prepared by mixing the previously described compounds. Observations were made ofthe cure characteristics and rheological properties ofthe uncured compositions using ASTM D 2084-93 with a Monsanto Oscillating Disk Rheometer Model 100S, using a small disk (AR177, available from Monsanto, Inc.) with the following conditions: no preheat, oscillator frequency of 100 cpm and a 3° arc, at 177°C. Specifically, the samples were evaluated for Minimum Torque (ML), Maximum Torque (MH) (or the highest torque attained during a specified period of time where no plateau or maximum torque is obtained), time t s 2, representing the time to a 2 inch-lb (2.26 dN-meter) rise in viscosity, reported in minutes. The times t'50 and t'90, respectively, represent the time necessary to reach the torque 50% ofthe distance between the minimum torque and the maximum torque and the torque 90% ofthe distance between the minimum torque and the maximum torque, also reported in minutes. Mooney Scorch characteristics were determined in accordance with ASTM D 1646-94 using a Monsanto Mooney Viscometer (Model 2000) with a 1 minute preheat and a small rotor at a temperature of 121°C. The results are reported as Mooney Minimum Viscosity, reported in Mooney units, and Mooney Scorch (t 10 ), reported in minutes. The Mooney minimum viscosity is the mimmum, or lowest, viscosity recorded during the test. Mooney Scorch represents the time required to increase viscosity 10 Mooney units from the minimum viscosity. Compression set, reported as a percent, was determined in accordance with ASTM D 395-89 (method B) using O-rings with a 3.5 mm cross-section at 200°C for 70 hours. Tensile strength, elongation at break and modulus at 100 percent elongation were measured in accordance with ASTM D 412-92 , using Die D. Hardness was measured in accordance with ASTM D 2240-91, using Durometer A and taking readings 2 seconds after the presser foot came into contact with the specimen. All composition percentages are given in weight percent unless otherwise noted. Example 1 Example 1, an example ofthe invention, was prepared by compounding the following ingredients in a conventional manner on a two-roll mill: 100 g of a fluorine-containing copolymer of 60 wt% vinylidene fluoride (VF 2 )and 40 wt% hexafluoropropene (HFP) with a Mooney viscosity of about 37, available from 3M Co. as Fluorel™ Fluoroelastomer FC-2230, 0.35 g (0.0009 moles) triphenylbenzylphosphonium chloride, 1.0 g (0.003 moles) 4,4'- (hexafluoroisopropylidene)diphenol (Bisphenol AF), 6 g of Ca(OH)2, 3 g of MgO, 30 g of Thermax™ carbon black N-990, and 0.595 g (0.003 moles) of 4-hydroxy benzophenone, a monohydroxyfunctional phenol as shown in Table 1. The cure characteristics and rheological properties ofthe uncured compositions were determined and are reported in Table 2. Press-cured sheets, 150 mm x 150 mm x 2 mm, were formed from the curable fluorine-containing copolymer mixture by pressing in a mold at about 6.9 MPa for 15 minutes at 177°C. The sheets were removed from the press and placed in a circulating oven set at 230°C for 16 hours. Physical properties were then measured on the post-cured sheet and are reported in Table 3. Comparative Example Cl For Comparative Example Cl, a sample was prepared and evaluated as in Example 1 except the substituted monohydroxyfunctional phenol, 4-hydroxy benzophenone, was omitted. The cure characteristics and rheological properties of the uncured composition are reported in Table 1, and the physical properties of their post-cured sheets are reported in Table 3. Examples 2-8 For Examples 2-8, a series of substituted monohydroxyfunctional phenols of the formula R-C6H4-OH ( I ) were evaluated. The substituent R was varied as listed in Table 1, along with the location of R in relation to -OH. All materials were obtained from Aldrich Chemical Co., Inc. unless otherwise indicated. The cure characteristics and rheological properties ofthe uncured compositions are reported in Table 2, and the physical properties of their post-cured sheets are reported in Table 3. Table 1 Example R Location of M R" 1 C6H5CO- para 2 C6H5CH2CO- para 3 CN- para 4 CN- ortho 5 CH3CO- para 6 O2N- para 7 O2N- ortho 8 O2N- meta Table 2 Example TMAX TMIN *,2 t'50 t'90 Mooney Ho (MH) (ML) (min.) (min.) (min.) minimum (min.) 1 57.5 10 2.5 3.6 4.4 39.0 104.9 2 60 9.7 3.4 4.7 6.1 36.5 3 54 8 2.7 3.8 4.1 36.4 96.9 4 61 12 2.2 3.3 4.9 39.3 69.1 5 58 9.6 2.5 3.6 4.7 36.8 94.6 6 57 11 4.2 5.7 7.2 41.5 >180 7 59 11 2.0 3.4 5.7 44.4 58.2 8 56 10 2.5 3.5 4.7 40.8 103.9 Cl 38 12 1.3 1.9 3.4 35.8 28.4 The results in Table 2 show the examples ofthe invention exhibit the desired delay in the cure curve. Values of t s 2, t 50 and 1 90 for the examples ofthe invention are longer than the comparable values for Comparative Example Cl. Also, the times available for processing, as shown by Mooney Scorch, t 10 , are all longer for Examples 1-8 when compared to Comparative Example Cl. The results of testing post cured sheets for certain physical properties on are shown in Table 3. Table 3 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) at break (%) (MPa) (%) 1 13.8 310 3.2 73 31.5 2 13.4 243 4.0 76 37.4 3 14.4 316 2.8 73 26.4 4 14.7 319 3.0 73 26.4 5 13.4 308 3.0 74 28.5 6 12.7 291 2.8 73 28.3 7 13.4 314 2.8 72 30.9 8 13.1 310 3.0 73 24.4 Cl 9.3 380 2.2 72 41.0 The data of Table 3 show no substantial loss in physical properties in the samples ofthe invention, that show a delayed cure, as compared to Comparative Example Cl. Examples 9-20 For Examples 9-20, samples ofthe invention were made as in Example 1 except the "R" group ofthe monohydroxyfunctional phenols of Formula I were varied as shown in Table 4. All materials were obtained from Aldrich Chemical Co., Inc. unless otherwise indicated. Comparative Examples C2 and C3 For Comparative Examples C2 and C3, samples were made as in Example 1 except that the "R" group of each was selected, as shown in Table 4, to be a group that was more electron donating instead of electron withdrawing, as in the examples ofthe invention. The cure characteristics and rheological properties ofthe uncured compositions of these examples are reported in Table 5, and the physical properties of their post-cured sheets and are reported in Table 6. Table 4 Example "R M Location of M R" 9 CH3O2C- para 10 F 3 C- para 11 F- 3,4 - difluoro 12 Cl- para 13 Br- para 14 HO 2 CCH 2 HN- para 15 HOOC- para 16 HOOC- meta 17 C6H5- para 18 HOCH2- para 19 CH3CONH- ortho 20 CH3CONH- para C2 (CH3)2NCH2- para C3 CH3O- para Cure characteristics and rheological data were measured as in Example 1 and the results are reported in Table 5. Values for Comparative Example Cl are included for reference. Table 5 Example (MH) (ML) t,2 t 50 t 90 Mooney tio (min.) (min.) (min.) minimum (min.) 9 59.5 10.5 2.1 2.9 3.9 36.8 98.3 10 43.0 7.5 1.7 2.6 5.0 11 58.0 10.5 1.3 1.8 2.7 12 56.0 10.0 1.8 2.7 3.5 . 13 54.0 9.0 1.8 2.5 3.4 14 47.0 11.0 1.9 2.9 4.3 37.4 76.0 15 51.0 10.5 2.2 3.5 5.3 37.2 100.3 16 48.0 10.6 2.2 3.5 5.6 37.4 98.2 17 57.0 11.0 2.1 3.1 3.8 35.4 102.3 18 46.0 10.4 2.1 3.4 5.3 39.1 95.6 19 55.0 9.0 1.9 2.8 4.2 38.4 74.9 20 55.0 10.0 2.0 3.0 3.9 36.9 72.6 C2 47.5 10.6 1.3 2.0 2.6 36.2 32.5 C3 51.0 10.2 1.5 2.3 3.1 35.2 59.6 Cl 38.0 12.0 1.3 1.9 3.4 35.8 28.4 The results in Table 5 indicate a delay in the cure in the examples ofthe invention that contain either a halogen atom or a strong electron withdrawing substituent as compared to the Comparative Examples Cl, C2, and C3. This is demonstrated by the longer times for t s 2, t 50 and 19Q for the examples ofthe invention. Although Example 11 shows no delay in this data, when the monohydroxyfunctional phenol used in Example 11 is tested at a higher concentration (0.009 moles) in the Mooney Scorch test, run at 122°C, a minor delay effect is noted. Examples 14 and Examples 17-20 show a slight delay effect even though the "R" groups are not strongly electron-withdrawing. This may be due to other factors governing the mechamsm ofthe bisphenol cure system including relative solubilities ofthe phenols in the fluoroelastomer gum system. Table 6 presents the physical properties ofthe post-cured sheets of some of the above examples. Again, the data of Comparative Example Cl is included for reference. Table 6 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) at break (%) (MPa) (%) 9 13.7 312 3.0 74 28.9 14 11.0 294 2.9 73 34.5 15 12.7 324 2.8 72 35.5 16 12.9 328 2.7 72 34.2 17 12.7 333 2.8 73 35.3 18 12.0 340 2.7 73 34.0 19 12.3 253 3.4 72 37.7 20 11.5 248 3.6 75 33.5 C2 12.8 306 3.0 72 48.6 C3 11.6 312 2.6 72 39.0 Cl 9.3 380 2.2 72 41.0 The results of Table 6 further demonstrate that the addition ofa monohydroxyfunctional phenol in accordance with the present invention does not significantly effect the resulting physical properties ofthe cured fluoroelastomer. Comparative Example C4 For Comparative Example C4, a composition was made in a manner similar to Example 1 except 2,6-di-t-butylphenol was used instead of 4-hydroxy benzophenone. Examples 21-22 For Examples 21-22, curable fluoroelastomer compositions ofthe invention were made and evaluated as in Example 1 except that the monohydroxyfunctional phenol was varied as listed in Table 7. All materials were obtained from Aldrich Chemical Co., Inc. Table 7 Example Monohydroxyfunctional Phenol C4 2,6-di-t-butylphenol 21 3 , 5 -dichlorophenol 22 2,6-dibromophenol Cure characteristics and rheological data were measured as in Example 1 and the results are listed in Table 8. Table 8 Example (MH) (ML) t,2 t ' 50 90 Mooney tio (min.) (min.) (min.) minimum (min.) 21 62 10 2.9 3.9 4.8 22 61 11 2.3 4.2 11.8 43.0 79.6 C4 46 10.8 1.5 2.3 3.5 35.9 49.3 The results in Table 8 indicate that although Comparative Example C4 is technically a monophenol, it does not act like the other monohydroxyfunctional phenols, i.e., it does not show the delay of cure initiation. This may be because the -OH group may be sterically hindered by the two nearby tertiary-butyl groups. Physical properties were measured on post-cured sheets ofthe above examples as in Example 1 and the results are shown in Table 9. Table 9 Example Tensile Elongation Modules Hardness Comp. Set (MPa) (%) (MPa) (%) 21 12.1 311 2.8 72 32.4 22 13.9 313 3.1 73 29.6 C4 11.7 331 2.9 74 36.2 The results of Table 9 further demonstrate that the addition ofa monohydroxyfunctional phenol in accordance with the present invention does not significantly effect the resulting physical properties ofthe cured fluoroelastomer. Examples 23-32 For Examples 23-32, curable fluoroelastomer compositions ofthe invention were made and evaluated in a manner similar to Example 1 in which the concentration ofthe monohydroxyfunctional phenol and the crosslinking agent, Bisphenol AF, were varied. For Example 23, the composition included only 0.0015 moles of 3,5,dichlorophenol, a monohydroxyfunctional phenol as described above in Table 7 and 1.0 g (0.003 moles) Bisphenol AF. For Examples 24-32, samples were made in a manner similar to Example 23 except the monohydroxyfunctional phenol concentration and/or crosslinking agent concentration were varied as shown in Table 10. For examples 23-27, the concentration of triphenylbenzylphosphonium chloride used was 0.0009 mol. For examples 28-32 where the concentration of bisphenol AF was increased to 0.006 mol., the concentration of triphenylbenzylphosphonium chloride used was 0.0013 mol. Comparative Examples Cl and C5 The composition of Comparative Example Cl, presented earlier, is similar to the composition of Example 23 without the monohydroxyfunctional phenol. Comparative Example C5 was made in a similar manner to Examples 28 except that no monohydroxyfunctional phenol was added. Table 10 Example Bisphenol AF Mono-phenol Concentration Concentration (moles) (moles) Cl 0.003 0.0 23 0.003 0.0015 24 0.003 0.003 25 0.003 0.006 26 0.003 0.009 27 0.003 0.012 C5 0.006 0.0 28 0.006 0.0015 29 0.006 0.003 30 0.006 0.006 31 0.006 0.009 32 0.006 0.012 The above examples were evaluated as in Example 1 and the cure and rheological properties are reported in Table 11. Table 11 The results in Table 11 indicate that the cure delay effects are present when the monohydroxyfunctional phenol is present in concentrations as little as 0.0015 moles for formulations high in Bisphenol AF concentration (high crosslink density), and as little as 0.0015 for formulations low in Bisphenol AF concentrations (low crosslink density). Cure delay effects can be influenced by varying the concentration of cross-linkers, such as polyhydroxy compounds, but this may also change other physical properties, such as MH or elongation as shown below in Table 12. Physical properties were measured on post-cured sheets as in Example 1 and the results are shown in Table 12. Table 12 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) (%) (MPa) (%) Cl 9.3 380 2.2 72 41.0 23 11.4 342 2.6 72 41.6 24 12.1 311 2.8 72 32.4 25 14.0 294 3.0 72 32.9 26 13.0 248 3.1 72 32.4 27 14.1 255 3.2 72 36.1 C5 14.3 6.9 80 14.5 28 13.8 167 7.3 81 15.8 29 13.3 161 6.8 81 17.4 30 14.6 176 7.1 80 18.1 31 14.8 153 8.0 80 21.4 32 14.1 153 8.2 80 22.7 The results in Table 12 indicate significant changes in physical properties occur when the cross-linker concentration is increased giving, in general, higher tensiles, lower elongations higher modulus and hardness and lower compression set as shown by comparing Comparative Examples Cl and C5. The addition ofthe monohydroxyfunctional phenol does not substantially alter this relationship. Example 33 For Example 33, a sample ofthe invention was prepared and evaluated in a manner similar to Example 1 except that triarylsulfonium chloride, as made according to the method described in U.S. Pat. No. 4,233,421 (Worm) Example 1, was used instead of triphenylbenzylphosphonium chloride and para-nitrophenol was substituted for 4-hydroxy benzophenone on an equal molar basis. Comparative Example C6 For Comparative Example C6, a sample was made and evaluated as in Example 33 except that the para-nitrophenol was omitted. Example 34 Example 34, a sample ofthe invention, was prepared and evaluated in a manner similar to Example 1 except that tributylbenzylammonium chloride was substituted for triphenylbenzylphosphonium chloride and para-nitrophenol was substituted for 4-hydroxy benzophenone, both substitutions made on an equal molar basis. Comparative Example C7 For Comparative Example C7, a sample was made and evaluated as in Example 34 except the para-nitrophenol was omitted. Example 35 For Example 35, a sample ofthe invention was prepared and evaluated in a manner similar to Example 1 except that tributylmethoxypropylphosphonium chloride was substituted for triphenylbenzylphosphonium chloride and para- nitrophenol was substituted for 4-hydroxy benzophenone, both substitutions made on an equal molar basis. Comparative Example C8 For Comparative Example C8, a sample was made and evaluated as in Example 35 except that the para-nitrophenol was omitted. The cure and rheological properties and the post-cured physical properties ofthe above examples are presented in Tables 13 and 14 respectively. Table 13 Example (MH) (ML) *,2 t 50 t 90 Mooney *ιo (min.) (min.) (min.) minimum (min.) 33 29.5 9.5 11.7 14.8 17.6 37.2 90+ C6 25.0 10 3.0 3.8 4.9 37.7 90+ 34 56.0 10 3.6 4.9 5.9 36.6 90+ C7 49.5 12 .95 1.6 2.0 37.1 31.2 35 62.0 10 2.4 3.5 4.3 36.5 74.5 C8 57.0 12 0.9 1.3 1.7 36.4 16.3 The results in Table 13 indicate each example ofthe invention exhibits the desired cure delay when compared to a similar sample without a monohydroxyfunctional phenol. The tio values of 90+ indicate the test was run for 90 minutes and the viscosity had not yet reached a 10 point viscosity increase, at which point the test was stopped. Physical properties were measured on post-cured sheets as in Example 1 and the results are shown in Table 14. Table 14 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) (%) (MPa) (%) 33 1234 436 317 72 48.1 C6 868 730 273 68 75.5 34 1919 284 451 73 30.4 C7 1763 358 390 72 39.0 35 1805 237 478 73 24.2 C8 1859 289 443 72 27.6 The results of both Tables 13 and 14 indicate similar effects in cure delay and post-cure physical properties in the examples ofthe invention with various oniums when compared to similar compositions without a monohydroxyfunctional phenol. Example 36 For Example 36, a sample ofthe invention was made and evaluated in a manner similar to Example 35 except that the gum used was a fluorine-containing teφolymer of 45 wt% VF 2 , 23 wt% TFE and 32 wt% HFP, available from 3M Co. as Fluorel™ Fluoroelastomer FT-2481. Comparative Example C9 For Comparative Example C9, a sample was made and evaluated as in Example 36 except that the para-nitrophenol was omitted. Example 37 For Example 37, a sample ofthe invention was made and evaluated in a manner similar to Example 36 except that the concentration of tributylmethoxypropylphosphonium chloride was increased to 0.0024 mol. and the gum used was a fluorine-containing teφolymer of 30 wt% VF 2 , 55 wt% TFE and 15 wt% propylene, available from 3M Co. as Fluorel™ Fluoroelastomer FX-11705. Comparative Example CIO For Comparative Example CIO, a sample was made and evaluated as in Example 36 except that the para-nitrophenol was omitted. The above examples were evaluated as in Example 1 and the cure and rheological properties are reported in Table 15. The tio values of 90+ indicate the test was run for 90 minutes and the tio value had not yet reached a 10 point viscosity increase. Table 15 Example (MH) (ML) t,2 t 50 t 90 Mooney tio (min.) (min.) (min.) minimum (min.) 36 52.0 21.0 4.2 5.5 6.8 66.3 90+ C9 55.0 25.8 1.2 1.9 2.8 66.2 28.1 37 48.0 14.0 5.9 8.2 10.7 38.3 90+ CIO 46.0 14.0 2.5 4.0 6.6 34.4 35.0 The results in Table 15 show a delay before the onset of cure in each example ofthe invention when compared to the sample without the monohydroxyfunctional phenol. Physical properties ofthe above examples were measured on post-cured sheets as in Example 1 and the results are shown in Table 16. Table 16 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) (%) (MPa) (%) 36 13.7 310 2.9 73 41.9 C9 12.3 341 3.0 73 50.2 37 12.8 199 4.9 75 52.9 CIO 12.2 275 3.7 74 60.7 The results in Table 16 indicate useful properties are obtained with the addition ofthe monohydroxyfunctional phenol. Examples 38-41 For Example 38, a curable fluoroelastomer composition ofthe invention was made and evaluated in a manner similar to Example 6 except the cross-linker, Bisphenol AF, was replaced with 0.006 moles of 4,4'-sulfonyldiphenol, available from Aldrich Chemical Company, Inc., and the triphenylbenzylphosphonium chloride was used at the 0.0013 molar level. For Example 39, a curable fluoroelastomer composition ofthe invention was made and evaluated in a manner similar to Example 38 except the cross-linker used was 0.006 moles of 4,4'-isopropylidenediphenol (commonly known as bisphenol A), available from Aldrich Chemical Company, Inc. For Example 40, a curable fluoroelastomer composition ofthe invention was made and evaluated in a manner similar to Example 38 except the cross-linker used was 0.006 moles of 4,4'-dihydroxybenzophenone, available from Aldrich Chemical Company, Inc. For Example 41, a curable fluoroelastomer composition ofthe invention was made and evaluated in a manner similar to Example 38 except that amount of Ca(OH) 2 used was 2.0 g, the amount of MgO used was 4.0 g, and the cross-linker used was 0.006 moles ofa fluorinated diol made as described in Example 1 of U.S. Pat. No. 5,266,650 (Guerra et al.) with a molecular weight of 1250 instead of 1500, and with an average hydroxyl functionality of 1.7 instead of 1.8. Comparative Examples Cl 1-C14 For Comparative Examples Cl 1-C14, samples were made and evaluated as in Examples 38-41 respectively, except the monohydroxyfunctional phenol, para- nitrophenol, was omitted in each case. The test results for above examples for the cure and rheological properties are reported in Table 17 and the physical properties are reported in Table 18 Table 17 Example (MH) (ML) t,2 t * 50 t 90 Mooney tio (min.) (min.) (min.) minimum (min.) 38 49.0 9.5 6.0 7.9 10.1 37.6 90+ Cll 41.0 11.0 2.8 4.8 8.3 39.4 79.8 39 92.0 10.0 2.7 3.6 4.7 38.8 55.2 C12 69.0 11.0 2.0 3.5 4.2 35.2 37.6 40 66.0 8.0 3.8 5.3 7.9 36.4 90+ C13 52.0 10.5 2.7 4.4 7.1 36.2 73.3 41 68.0 7.5 1.8 3.2 5.5 26.9 33.3 C14 46.0 7.0 1.9 4.7 8.9 22.1 10.9 The results in Table 17 indicate a delay in cure initiation in each example of the invention when compared to its comparative example without the monohydroxyfunctional phenol when using the Mooney Scorch values. Physical properties were measured on post-cured sheets as in Example 1 and the results are shown in Table 18. Table 18 Example Tensile Elongation Modulus Hardness Comp. Set (MPa) (%) (MPa) (%) 38 11 282 3.0 76 26.3 Cll 10.6 361 2.9 76 40.1 39 12.8 182 5.5 81 28.2 C12 12.0 256 4.0 78 28.4 40 12.6 232 4.0 78 20.0 C13 11.9 305 3.2 76 26.4 41 12.8 281 2.6 65 18.9 C14 11.8 313 2.3 64 23.3 The results in Table 18 indicate useful properties are obtained with the addition ofthe monohydroxyfunctional phenol. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit ofthe present invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth hereinabove.

Claims: Claims We claim: 1. A curable fluoroelastomer composition comprising: (a) a fluorine-containing polymer or blend of fluorine-containing polymers each comprising inteφolymerized units derived from one or more fluorine- containing ethylenically unsaturated monomers; (b) a aromatic polyhydroxy crosslinking agent; (c) at least one organo-onium compound; and (d) a monohydroxyfunctional phenol. 2. A curable fluoroelastomer composition comprising: (a) a fluorine-containing polymer or blend of fluorine-containing polymers each comprising inteφolymerized units derived from one or more fluorine- containing ethylenically unsaturated monomers; (b) a aromatic polyhydroxy crosslinking agent; (c) at least one organo-onium compound; and (d) a monohydroxyfunctional phenol having the general formula wherein R may be placed on any position relative to the aromatic ring and is a halogen atom or an acyl, aryl, polyaryl, or alkyl radical substituent, the latter three of which may be straight-chained, branched, cyclic, or halogenated, and wherein R may optionally contain one or more caternary heteroatoms; and x may be between 1 and 5 inclusive when R is a halogen, otherwise, x may be between 1 and 3 inclusive. 3. The composition of claim 1 or 2 wherein the monohydroxyfunctional phenol is selected from the group consisting of /Miitrophenol, j-cyanophenol, and 4- hydroxy benzophenone. 4. The composition of claim 1 or 2 wherein the aromatic polyhydroxy crosslinking agent is 2,2-bis(4-hydroxyphenyl)hexafluoro-propane. 5. The composition of claim 1 or 2 wherein one or more ofthe organo-onium compounds are selected from the group consisting of triphenylbenzylphosphonium chloride, triarylsulfonium chloride, tributylbenzylamonium chloride, and tributylmethoxypropylphosphonium chloride. 6. The composition of claim 1 or 2 wherein one or more ofthe fluorine-containing polymers comprise a copolymer of vinylidene fluoride and at least one terminally ethylenically-unsaturated fluoromonomer. 7. The composition of claim 1 or 2 wherein one or more ofthe fluorine-containing polymers comprise a copolymer of vinylidene fluoride, hexafluoropropene, and tetrafluoroethylene. 8. A method of making a shaped elastomeric article comprising curing the composition of claim 1 or 2 to form the article. 9. The method of claim 8 wherein the curing comprises injection molding. 10. A cured fluoroelastomer article comprising the composition of claim 1 or 2.

Inventors: JING NAIYONG, KOLB ROBERT E, JING, NAIYONG, KOLB, ROBERT, E.
Applicants: MINNESOTA MINING & MFG, MINNESOTA MINING AND MANUFACTURING COMPANY
Application year: 1996
Main classification: C08K5
IPC codes: C08K5, C08L27