EP0739378A1

EP0739378A1 - A vulcanizable fluoroelastomer composition

Info

Publication number: EP0739378A1
Application number: EP95904057A
Authority: EP
Inventors: Keiichi Toda; Hiroshi Saito
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1993-12-02
Filing date: 1994-12-01
Publication date: 1996-10-30
Also published as: JPH07196881A; WO1995015359A1

Abstract

A vulcanizable fluoroelastomer composition having excellent extrusion properties is provided which comprises (A) a bromine-containing fluoroelastomer having a multi-modal molecular weight distribution, an intrinsic viscosity of 40 to 200 mL/g, and an Mw/Mn ratio of 3-25 wherein the fluoroelastomer has interpolymerized units of vinylidene fluoride, hexafluoropropylene, and optionally tetrafluoroethylene; (B) a polyol or polyamine vulcanizing agent; (C) an organic peroxide; and (D) a polyfunctional unsaturated compound.

Description

TITLE

A NULCANIZABLE FLUOROELASTOMER COMPOSITION FIELD OF THE INVENTION

The present invention concerns a novel vulcanizable fluoroelastomer composition. More specifically, the present invention concerns a vulcanizable fluoroelastomer composition which when vulcanized, provides a product having good heat resistance, solvent resistance, chemical resistance, and improved mechanical properties and compression set. BACKGROUND OF THE INVENTION

Because they have excellent heat resistance and oil resistance, fluoroelastomers have been used in the past for O-rings, gaskets, oil seals, diaphragms, hoses, rolls, and sheeting materials, in a variety of industrial applications, such as automobiles, boats, aircraft, hydraulic machinery, general machinery, and in fields related to the prevention of pollution. In the automotive field, the heat resistance and oil resistance of these fluoroelastomers are commonly utilized in fuel system parts, especially hoses. Specific examples are fuel hoses, in-tank hoses, and filler hoses. In the industrial field, long tape-like sheets are one application. These hoses and tapes are obtained by extrusion working. However, while fluoroelastomers do have these excellent performance benefits, their workability is inferior to that of other elastomers, and satisfactory results are not obtained on extrusion. The method that is generally adopted to improve workability is to lower the molecular weight, but a fluoroelastomer whose molecular weight has been lowered and its fluidity raised presents operational problems in that severe roll sticking occurs. In addition, the low molecular weight component is not readily crosslinked by polyol vulcanization, so compression set and other important properties also suffer. Higher fatty acid esters, silicone compounds, low molecular weight polyethylenes, and other such adjuvants are used in order to improve workability (eg, Japanese Patent Publication 52-44896). When used in a small amount, however, an adjuvant does not have enough of an effect, and if it is used in the amount required for an improvement in workability to be achieved, there is a significant drop in tensile strength and high temperature sealing. Another method that has been proposed to improve extrudability is to change the molecular weight distribution to a multi-peak (multi-modal) type (Japanese Laid-Open Patent Application 2-160810). This method is extremely effective, but since the low molecular weight content is relatively high, the elastomer sticks to the rolls and screws, and with conventional polyol vulcanization, the low molecular weight component cannot be sufficiently vulcanized, and the properties of the product are inferior.

Recently, however, it has become increasingly difficult to satisfy performance requirements for vulcanization by using conventional polyol vulcanization, polyamine vulcanization, or peroxide vulcanization in applications that demand extrusion workability, mold flow, and other aspects of molding workability. This includes applications in which the elastomer is used as a composite material and applications in which the elastomer is used in the presence of an alcohol. Of the above vulcanization methods, polyamine vulcanization generally produces a vulcanized product that is low in strength and has poor compression set. Polyol vulcanization is the most widely used curing method at the present time, but the problem is that the resulting vulcanized product has inferior solvent resistance, chemical resistance, alkali resistance, and steam resistance. Furthermore, neither of these two methods is suited for use with a low molecular weight polymer.

In contrast, these problems are solved by peroxide vulcanization, and it is known that this method gives a vulcanized product with relatively good properties. However, since the adhesion of the peroxide vulcanized product to metals is inferior, this product is difficult to use in applications in which a metal is used in combination with the vulcanized product, such as oil seals and valves. Furthermore, vulcanization comes to an abrupt halt when the material comes into contact with air during vulcanization. As a result it is difficult to remove the flash during molding and the mold is susceptible to fouling, among other drawbacks. Also, polymers with a high molecular weight are not readily vulcanized, resulting in inferior strength and compression set. Consequently, several attempts have been made at finding a method that would simultaneously solve the various problems in these vulcanization methods. For example, a method has been proposed in which two different polymers are blended and covulcanized by means of a polyol or polyamine vulcanizing agent and a peroxide vulcanizing agent (Japanese Laid-Open Patent Applications 60-72950, 62-30142, and 62-30143). All of these involve the use of a blend of a ternary copolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene and a binary copolymer of tetrafluoroethylene and propylene. However, this vulcanization reaction does not proceed well. The use of a combination of a polyol vulcanization compounding agent and a peroxide vulcanization agent has also been proposed (Japanese Laid-Open Patent Application 62-79251) for use with a blend of a ternary copolymer of vinylidene fluoride, hexafluoropropylene, and tetrafluoroethylene and a binary copolymer of tetrafluoroethylene and propylene. However, this method involves the blending of two different polymers, and the resulting properties are not satisfactory because of the weak adhesion between the different polymers. A laminate of NBR and a fluororubber obtained by blending a combination of a polyol vulcanization agent and a peroxide vulcanization agent into a fluororubber has been proposed in an effort to improve the adhesion of a fluororubber with NBR (Japanese Laid-Open Patent Application 61-244545). However, the workability, roll sticking, and the like are not satisfactory.

In addition, a composition composed of a bimodal polymer, a polyol vulcanization system, and a mixed vulcanization system comprising a polyamine vulcanization system and a peroxide vulcanization system is disclosed in Japanese Laid-Open Patent Application 4-209643.

SUMMARY OF THE INVENTION The present invention provides a fluoroelastomer composition comprising (A) a bromine-containing fluoroelastomer having a multi-modal molecular weight distribution, an intrinsic viscosity of 40 to 200 mL/g, and a M_w/M_n ratio of weight average molecular weight (M_w) and number average molecular weight (M_n) between 3 and 25, comprising interpolymerized units of (i) vinylidene fluoride and (ii) hexafluoropropylene wherein the weight ratio of (i):(ii) is from 40:60 to 80:20;

(B) a vulcanization agent comprising either (i) a mixture of a polyhydroxy aromatic compound, at least one salt selected from the group consisting of ammonium salts, phosphonium salts, and iminium salts and a divalent metal oxide or divalent metal hydroxide, or (ii) a mixture of a polyamine and a divalent metal oxide;

(C) an organic peroxide; and

(D) a polyfunctional unsaturated compound. In another embodiment of the invention, the bromine- containing fluoroelastomer comprises interpolymerized units of (i) vinylidene fluoride, (ii) hexafluoropropylene, and (iii) no more than 35 wt% tetrafluoroethylene.

DETAILED DESCRIPTION OF THE INVENTION It has been discovered that a fluoroelastomer composition having superior performance, for example, extrusion workability superior to that of a conventional fluoroelastomer and better optical stability than iodine-containing fluoroelastomers, can be produced by blending a specific vulcanization agent and an organic peroxide into a bromine- containing fluoroelastomer.

The present invention eliminates the drawbacks of the prior art encountered in polyamine vulcanization, polyol vulcanization, and peroxide vulcanization, and provides a vulcanizable fluoroelastomer that has excellent characteristics, such as improved strength, mechanical properties, compression set, good heat resistance, greatly enhanced chemical resistance, solvent resistance, and solvent extractability. In addition, it allows production of vulcanized products having good metal adhesion with ease of flash removal during molding and low mold fouling. Further, low molecular weight components and high molecular weight components may be simultaneously vulcanized, thereby achieving excellent workability, in particular, extrusion workability. The fluoroelastomer compositions of the present invention can be used as materials for fuel system hoses, O-rings, seal rings, packings, gaskets, and other such seals, diaphragms, solenoid valves, needle valves, photocopier blades and fixing rolls, various industrial valves, and composite parts with other types of materials, and can be used to particular advantage as materials for fuel hoses, valves, O-rings, and other components wherein chemical resistance and solvent resistance are required.

The bromine-containing fluoroelastomer that is used as component (A) of the present invention is a fluoroelastomer comprising, as principal constituents, interpolymerized units of vinylidene fluoride (hereinafter referred to as NDF), hexafluoropropylene (hereinafter referred to as HFP), and, in some cases, tetrafluoroethylene (hereinafter referred to as TFE). The proportions of said NDF units and HFP units in the fluoroelastomer are such that the weight ratio is between 40:60 and 80:20. If the proportion of said NDF units is lower than this, polymerization will be extremely slow and it will be difficult to obtain a high molecular weight product. If the ratio is greater, the resulting fluoroelastomer will be in a resinous form and elasticity will tend to decrease. In ternary fluoroelastomers containing TFE, the TFE content is no more than 35 wt%, preferably between 5 and 25 wt%. If the TFE content exceeds 35 wt%, the elasticity of the resulting fluoroelastomer will tend to decrease.

The preferable proportions by weight of the NDF units and HFP units are in the range of 55:45 to 75:25 in a binary fluoroelastomer containing no TFE units. The preferable proportions are in the range of 45:55 to 70:30 in the case of ternary fluoroelastomers that contain TFE. Binary fluoroelastomers are used in applications that require a low fluorine content (65 wt% or less), and ternary fluoroelastomers are used in applications that require a high fluorine content (over 65 wt%), such as automotive parts and chemical apparatus that require oil resistance and chemical resistance. As used herein, "binary" and "ternary" refer to principal constituents, which do not include units derived from the bromine-containing monomers discussed below. The fluoroelastomer has a molecular weight distribution that is a multi-modal type having two or more peaks. Generally, fluoroelastomers have molecular weight distributions that consist of a single peak, but when the molecular weight distribution is multi-modal, as in the present invention, it is possible to obtain most of the excellent properties associated with the high molecular weight component and also to obtain the excellent workability of the low molecular weight component. It is exceedingly difficult to obtain both excellent properties and workability at the same time with an elastomer that has a single-peak molecular weight distribution. The fluoroelastomer also has an intrinsic viscosity (η), which is an index of molecular weight, of between 40 and 200 mL/g. If η is less than 40 mL/g, the low molecular weight content will be very high, resulting in diminished compression set resistance and mechanical properties as well as high adhesion during roll kneading and decreased ability to part the mold. On the other hand, if η is greater than 200 mL/g, the molecular weight will be very high, fluidity will decrease, and good extrusion molding will be impossible. It will also be difficult to create a thick sheet using a roll, particularly when the fluorine content is high. The ratio M_w/M_n between the weight average molecular weight (M_w) and the number average molecular weight (M_n) of the fluoroelastomer is between 3 and 25. If M /M_n exceeds 25, die swell during extrusion molding will occur. If M_w/M_n is less than 3, there will be no obvious benefit to having a multi-peak type of molecular weight distribution in the elastomer. Fluoroelastomers having specific molecular weight distributions can be used to advantage. Specifically, with respect to the multi-modal molecular weight distribution of the present invention, an elastomer having a specific molecular weight distribution weight ratio will exhibit superior extrusion characteristics, roll workability, vulcanization properties, and solvent resistance. The following three types of compositions are examples of such fluoroelastomers.

A first preferred type is one defined by the following characteristics (a) through (f):

(a) The fluoroelastomer is a multi-modal type. (b) The intrinsic viscosity is 100 to 170 mL/g.

(c) The ratio M50/η between the low molecular weight (molecular weight of 50,000 or less) polymer weight fraction (M50, wt%) and the intrinsic viscosity (η) is 0.25 to 0.60. (d) The ratio M_w/M_n between the weight average molecular weight (M_w) and the number average molecular weight (M_n) of said fluoroelastomer is between 10 and 25.

(e) The low molecular weight (molecular weight of 10,000 or less) polymer weight fraction (M10) is less than 15 wt%.

(f) The high molecular weight (molecular weight of 2,000,000 or more) polymer fraction (M2000) is 4 to 10 wt%.

With respect to this fluoroelastomer, the ratio M_w/M_n should preferably be between 10 and 25. If M_w/M_n exceeds 25, die swelling during extrusion molding will tend to worsen. If M_w/M_n is less than 10, the narrow molecular weight distribution will result in a relatively low content of low molecular weight component, and extrusion velocity, extrusion texture, and other aspects of extrusion moldability with suffer. It is preferable for the intrinsic viscosity (η), which is an index of molecular weight, to be between 100 and 170 mL/g. If η is less than 100 mL/g, there is danger of high adhesion during roll kneading, and if 170 mL/g is exceeded, fluidity will decrease, and good extrusion molding will be impossible.

It is also preferable for the ratio M50/η between the low molecular weight (molecular weight of 50,000 or less) polymer weight fraction M50 (wt%) and the intrinsic viscosity (η) to be between 0.25 and 0.60, with a range of 0.30 to 0.50 being preferred. M50 and η affect each other and also affect extrusion moldability such that extrusion velocity and extrusion texture tend to be improved as M50 increases, while extrusion velocity and extrusion texture tend to deteriorate as η increases. Therefore, the value of M50/η should be within the above range in order for good extrusion moldability to be achieved. If M50/η is less than 0.25, extrusion will become difficult and there will be marked deterioration in extrusion velocity and extrusion texture. If M50/η exceeds 0.60, green strength will decrease and will tend to vary during extrusion molding. Consequently, there will be the danger of a decrease in the mechanical strength of the vulcanization product.

It is also preferable for the low molecular weight (molecular weight of 10,000 or less) polymer weight fraction Ml 0 to be less than 15 wt%, with 12 wt% or less being most preferred. There is a correlation between M10 and the amount of extraction into the solvent when the vulcanized and molded article is immersed in methanol or another such solvent. The greater the value of M10, the greater is the amount of extraction into the solvent. Therefore, if Ml 0 is less than 15 wt%, the amount of extraction can be kept at a level that poses no practical problem.

Finally, the high molecular weight (molecular weight of

2,000,000 or more) polymer weight fraction M2000 should be 4 to 10 wt%. If M2000 is less than 4 wt%, green strength will decrease and will tend to vary during extrusion molding, and if M2000 is over 10 wt%, die swelling will tend to increase during extrusion.

A second preferred composition is one defined by the following charcteristics (a) through (d): (a) The fluoroelastomer is a multi-modal type.

(b) The intrinsic viscosity is 60 to 130 mL/g.

(c) The ratio M50/η is 0.15 to 0.60.

(d) The M_w/M_n ratio of said fluoroelastomer is between 4 and 8.

With respect to this fluoroelastomer, the M_w/M_n ratio should preferably be at least 4 and less than 8. If M_w/M_n is less than 4, the molecular weight distribution will be narrower, the low molecular weight component content will decrease, and the extrusion velocity, extrusion texture, and other aspects of extrusion moldability with suffer, or the high molecular weight component content will decrease and mechanical strength will decrease and adhesion to the rolls, etc., will increase. On the other hand, if the ratio is greater than or equal to 8, the solvent extraction resistance of the vulcanized product will suffer. A preferred M_w/M_n range is 5 to 7. The intrinsic viscosity (η) should be from 60 to 130 mL/g, and preferably 70 to 120 mL/g. If η is less than 60 mL/g, there will be the danger of adhesion during roll kneading, and if 130 mL/g is exceeded, the molecular weight will be very high, fluidity will decrease, and good extrusion molding may be impossible.

The ratio M50/η between the low molecular weight (molecular weight of 50,000 or less) polymer weight fraction M50 (wt%) and the intrinsic viscosity (η) should be from 0.15 to 0.60, and preferably 0.20 to 0.50. If M50/η is less than 0.15, extrusion will become difficult and there will be marked deterioration in extrusion velocity and extrusion texture. If 0.60 is exceeded, green strength will decrease and will tend to vary during extrusion molding, and there will be the danger of a decrease in the mechanical strength of the vulcanization product.

A third preferred composition is one defined by the following characteristics (a) through (e):

(a) The fluoroelastomer is a multi-modal type.

(b) The intrinsic viscosity is 50 to 150 mL/g. (c) The ratio M50/η is 0.30 to 0.70.

(d) The ratio Mw/Mn of said fluoroelastomer is between 8 and 25.

(e) The high molecular weight polymer fraction M2000 is less than 4 wt%.

With respect to this fluoroelastomer, the M_w/M_n ratio should preferably be between 8 and 20. If M_w/M_n exceeds 20, die swelling during extrusion molding will tend to worsen. If M_w/M_n is less than 8, the narrow molecular weight distribution will result in a relatively low content of low molecular weight component, and extrusion velocity, extrusion texture, and other aspects of extrusion moldability with suffer. It is preferable that the intrinsic viscosity (η) be between

50 and 150 mL/g. If η is less than 50 mL/g, there is the danger of high adhesion during roll kneading, and if 150 mL/g is exceeded, the molecular weight will be very high, fluidity will decrease, and good extrusion molding will be impossible. It is also preferable for the ratio M50/η to be between 0.30 and 0.70, with a range of 0.35 to 0.65 being most preferred. If M50/η is less than 0.30, extrusion will become difficult and there will be marked deterioration in extrusion velocity and extrusion texture. If 0.70 is exceeded, green strength will decrease and will tend to vary during extrusion molding, and there will be the danger of a decrease in the mechanical strength of the vulcanization product.

The high molecular weight polymer fraction M2000 should be no more than 4 wt%. If M2000 exceeds 4 wt%, die swelling and extrusion texture will tend to worsen during extrusion. Each of the above three types of composition has its advantages, and the one most suited to the intended application should be selected. For example, an elastomer in which M_w/M_n is at least 4 and less than 8 has a low content of super-high molecular weight component, so the kneading operation can be conducted easily without any sticking, even when the roll surface is at a relatively high temperature during roll kneading. An elastomer in which M_w/M_n is 10 to 25 and M2000 is from 4 to 10 wt% has a high content of both high molecular weight component and low molecular weight component, so it has good extrusion workability without any sacrifice in properties. An elastomer in which M_w/M_n is 8 to 20 and M2000 is less than 4 wt% has a relatively high content of low molecular weight component, so its extrusion workability is extremely good, and good extrusion characteristics are obtained even at a low extrusion temperature. The elastomer best suited to extrusion will also vary with the size and design of the screw and die and with the extrusion temperature when an extrusion molding machine or other such working machine is used. Polymers having different molecular weight distributions must be selected according to the apparatus used and the operating conditions thereof. The fluoroelastomer used as the above-mentioned component (A) in the composition of the present invention is a bromine- containing fluoroelastomer. That is, it must have bound bromine in its molecular chain. Removal of the bromine by organic peroxide during vulcanization results in formation of a radical on the polymer chain and the radical becomes a crosslinking point. It is difficult to vulcanize a low molecular weight fluoroelastomer by polyol vulcanization, but extremely good properties are obtained when the fluoroelastomer is a bromine- containing fluoroelastomer and the product is vulcanized using both a polyol and a peroxide. There is no extraction of the low molecular weight component by a solvent, etc., from the vulcanization product.

Methods for introducing bromine into the polymer chain include methods in which polymerization is conducted in the presence of a bromine compound (Japanese Patent Publication 3-42302) and methods in which a monomer that contains bromine is copolymerized (Japanese Patent Publication 53-4115). An alkyl bromide compound or a perfluoro compound thereof can be used as the bromine compound in those methods in which polymerization is conducted in the presence of a bromine compound. Examples of such compounds include CF₂Br₂, CF₂BrCF₂Br, CF₃CFBrCF₂Br, CF₃Br, CH₃Br, and CH₂Br₂.

A bromine-containing olefin or vinyl ether can be used as the bromine-containing monomer in methods wherein bromine is introduced into the fluoroelastomer by copolymerization. Examples of such monomers include bromotrifluoroethylene, 4-bromo-3,3,4,4- tetrafluorobutene- 1 , CF₂-=CF-0-CF₂CF₂Br, vinyl bromide, bromodifluoroethylene, and the like.

The bromine content of the polymer is usually 0.01 to 5 wt%, and a range of 0.1 to 2.5 wt% is preferable. If less than 0.01 wt% is present the crosslinking will be inadequate, and if greater than 5 wt% is present it will be difficult to obtain an elastomer.

The fluoroelastomers of the present invention can be polymerized by a variety of known methods, such as suspension polymerization or emulsion polymerization. The multi-modal type of fluoroelastomer used in the compositions of the present invention can be manufactured, for example, by blending a high molecular weight polymer and a low molecular weight polymer that have each been prepared separately, or by adding a chain transfer agent during polymerization and then continuing the polymerization. Of these, a method in which a chain transfer agent is added during suspension polymerization is preferable because it produces a polymer with a multi-modal molecular weight distribution that has relatively sharp peaks. The chain transfer agent used in this case can be any of the bromine compounds listed above.

A preferred example of a suspension polymerization is illustrated by the following method. An inert organic solvent containing the specific monomer mixture (feed monomer) is dispersed in an aqueous medium. A suspension stabilizer and an oil-soluble catalyst are added, chain transfer agent is added as needed, and the temperature is held at 50° to 60°C under mechanical stirring. Additional monomer mixture (additional monomer) is added such that the pressure will remain constant, preferably between 5 and 17 kg/cm^2,G, and polymerization is allowed to proceed. The composition of the monomers in the fluoroelastomer thus produced is determined by the relationship between the feed monomer and additional monomer composition. The monomer composition is measured by gas chromatography, and the composition of the monomer units in the elastomer is measured by F-NMR. Adjustment of the molecular weight distribution and introduction of the bromine are accomplished by adding the above-mentioned chain transfer agent midway through the polymerization.

As the inert organic solvent, 1,1,2-trichloro- 1,2,2,- trifluoroethane or the like can be used. Methyl cellulose or the like can be used as the suspension stabilizer. Diisopropyl peroxydicarbonate or other dialkyl peroxydicarbonates are preferable as the oil-soluble catalyst because they have high decomposition temperatures.

A polyol vulcanization agent or a polyamine vulcanization agent, or both, can be used as component (B) of the present invention.

The polyol vulcanization agent is composed of a mixture of a polyhydroxy aromatic compound, at least one type of salt selected from the group consisting of ammonium salts, phosphonium salts, and iminium salts, and at least one type of compound selected from among divalent metal oxides and divalent metal hydroxides.

Examples of the polyhydroxy aromatic compound include bisphenol AF, bisphenol A, bisphenol S, dihydroxybenzophenone, hydroquinone, 2,4,6-tricapto-S-triazine, 4,4'-thiodiphenol, and metal salts of these. The proportion in which the crosslinking agent is blended into the fluoroelastomer vulcanization composition of the present invention is usually 0.1 to 10 parts by weight, and preferably 0.5 to 5 parts by weight, per 100 parts by weight of the A component.

Specific examples of the ammonium salt, phosphonium salt, or iminium salt include tetramethylammonium chloride, tetrabutylammonium chloride, tetramethylammonium bromide, benzyltriphenylphosphonium chloride, bis(benzyldiphenylphosphine)imidium chloride, and DBU salts. The proportion in which the vulcanization promoter is blended into the fluoroelastomer vulcanization composition of the present invention is usually 0.05 to 10 parts by weight, and preferably 0.1 to 5 parts by weight, per 100 parts by weight of component (A).

Examples of divalent metal hydroxides and oxides include hydroxides and oxides of magnesium, calcium, zinc, and lead. The divalent metal hydroxide and divalent metal oxide are usually used in an amount of 1 to 10 parts by weight each per 100 parts by weight of the A component, and the combined amount of the two is 2 to 10 parts by weight.

A variety of vulcanization promoting activators can also be added as needed in order to promote the vulcanization. Typical examples of these vulcanization promotion activators include dimethyl sulfone, dichlorodiphenyl sulfone, and other sulfone compounds.

The polyamine vulcanization agent is composed of a polyamine compound and a divalent metal oxide. Examples of polyamine compounds include hexamethylenediamine carbamate, N,N'-dicinnamylidene-l,6- hexamethylenediamine, and 4,4'-bis(amino-cyclohexyl)methane carbamate. The amount of such compound added is usually 0.1 to 10 parts by weight, and preferably 0.5 to 5 parts by weight , per 100 parts by weight of the elastomer.

Examples of divalent metal oxides include oxides of magnesium, calcium, zinc, and lead. The divalent metal oxide content is usually 1 to 30 parts by weight, and preferably 2 to 20 parts by weight, per 100 parts by weight of the component (A). Examples of the organic peroxide that serves as component

(C) of the present invention include organic peroxides that readily generate peroxy radicals under heating such as 2,5-dimethyl-2,5- di(t-butylperoxy) hexyne-3, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, and other dialkyl peroxides. The amount of such compound added should be selected according to the amount of active oxygen, the decomposition temperature, and other factors, but is usually selected from a range of 0.05 to 10 parts by weight, and preferably 0.05 to 5 parts by weight, per 100 parts by weight of the elastomer.

Preferred examples of the polyfunctional unsaturated compound that serves as component (D) of the present invention include triallyl isocyanurate and triallyl cyanurate. The amount used is generally 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, per 100 parts by weight of the elastomer.

In addition, other components such as carbon black, austin black, graphite, silica clay, diatomaceous earth, talc, wollastonite, calcium carbonate, calcium silicate, calcium fluoride, barium sulfate, sulfone compounds, phosphoric acid esters, aliphatic amines, higher fatty acid esters, fatty acid calcium, fatty acid amide, low molecular weight polyethylene, silicone oil, silicone grease, metal soap, stearic acid, calcium stearate, magnesium stearate, aluminum stearate, zinc stearate, titanium white, iron oxide red, and other fillers, working adjuvants, plasticizers, coloring agents, and the like can be blended as needed into the vulcanizable fluoroelastomer composition of the present invention. Vulcanization of the fluoroelastomer composition of the present invention may be performed by thoroughly kneading the composition with an open kneading roll or a closed kneading roll (such as a Banbury mixer or a pressure kneader). The resultant composition is then cut into the form of a ribbon and molded by extrusion molding, and the product is then vulcanized. Vulcanization methods include vapor vulcanization and continuous vulcanization. Other vulcanization means include processes in which the composition is subjected to primary vulcanization by compression molding and then to secondary vulcanization, and methods in which a solution or dispersion is prepared using one or more media such as methyl ethyl ketone, acetone, or another ketone or tetrahydrofuran or another ether, and the surface of a paper, fiber, film, sheet, board, tube, pipe, tank, large vessel, or another molded article is covered with this solution or dispersion and then vulcanized. It is also possible to create a laminated molded article such as a multilayer sheet or multilayer hose by laminating with another type of rubber, such as NBR, acrylic rubber, or EP rubber.

The bromine-containing fluoroelastomer used in the present invention contains bound bromine, and this bromine is removed by organic peroxide during vulcanization. A number of molecular chains are then covalently bonded at the reaction sites via polyfunctional unsaturated compounds to form a crosslinked structure. Furthermore, the introduction of bromine into the low molecular weight component allows low molecular weight components, which do not lend themselves to polyol vulcanization, to be vulcanized. Therefore, the use of both a polyol vulcanization agent and a polyamine vulcanization agent results in sufficient vulcanization of components from low to high molecular weight, and produces a vulcanized product that exhibits excellent mechanical properties and also exhibits high strength and high elongation. Also, since the vulcanization density is increased, compression set is improved. Further, since a super-low molecular weight component can be vulcanized, which is impossible with polyol vulcanization or polyamine vulcanization alone, the vulcanized product has significantly enhanced gasoline permeation resistance and gasoline extraction resistance.

In conventional polyol or polyamine vulcanization, the chemical resistance can be poor, but with the present invention, these crosslinks are reinforced by reticulated chains formed by carbon-carbon bonds as a result of peroxide vulcanization, so the chemical resistance is improved. Also, with conventional peroxide vulcanization, the vulcanization reaction is inhibited in the presence of air, so flash portions that have come into contact with air are not sufficiently vulcanized and are difficult to remove, and instead stick to and foul the mold. In contrast, in the present invention, those portions that have come into contact with air are also thoroughly vulcanized by a polyol vulcanization agent or polyamine vulcanization agent, so the flash is easy to remove and there is no fouling of the mold. An elastomer blend that has excellent performance in terms of vulcanization properties as well as extremely good workability, and extrusion workability in particular, can be obtained with the present invention by using an elastomer that has a certain specific molecular weight distribution. Specifically, an elastomer having at least two peaks for a low molecular weight component and a high molecular weight component which contains bromine in at least the low molecular weight component has excellent workability because of the low molecular weight component, and also has excellent vulcanization properties because the low molecular weight component. In addition, there is no extraction of the low molecular weight component when the elastomer is immersed in a solvent or fuel oil.

In recent years there has been an increase in the use of parts, typified by fuel hoses and parts used in the engine compartment of an automobile, that require heat resistance, solvent resistance, and fuel oil resistance and are difficult to work because they have a complicated shape or are created by extrusion molding or injection molding. It is also desirable that the amount of extracted components be small when the part is immersed in a fuel oil. The blend of the present invention is ideally suited to such applications because it satisfies these requirements.

EXAMPLES The present invention will now be described in further detail by practical examples, but the present invention is not limited to or by these examples in any way. The physical properties and workability of the fluoroelastomer were determined by the following methods: (1) Intrinsic viscosity:

The intrinsic viscosity of a concentrated solution of 0.1 g/100 mL using methyl ethyl ketone as the solvent was measured at 35°C using a capillary viscosimeter. (2) Molecular weight distribution:

Liquid chromatograph: model LC-3A (Shimadzu Seisakusho) Columns: KF80M (two) & KF800P (Showa Denko) Detector: ERC-7510S (Elmer Optical) Developing solvent: tetrahydrofuran Concentration: 0.1 wt%

Temperature: 35°C

(3) Presence of bromine in the polymer:

Fluorescent X-ray

(4) Physical properties of the vulcanization product: Hardness measured according to JIS A.

100% tensile stress, tensile strength, elongation, and compression set measured according to JIS K 6301.

(5) Roll sticking:

Using an 8-inch roll kneader, raw rubber was wound around the roll, a vulcanization compounding agent, carbon, or another compounding agent was kneaded in, and the ease with which the kneaded material could be peeled off the roll was evaluated.

(6) Extrusion test:

Using a model 10E extruder made by Brabender (D = 19.1 mm, L/D = 10), the composition was extruded from a tube die (outside diameter 10 mm; inside diameter 8 mm) at a screw temperature of 60°C, a head temperature of 100°C, and a screw speed of 50 rpm.

Extrusion texture was evaluated by looking at the fineness of the surface texture and grading this fineness on a scale of 1 to 5 (with 5 being the best). Extrusion velocity was computed from the discharge length per unit of time. The amount of screw adhesion was evaluated from the amount of rubber that stuck to the screw after 500 g of composition had been extruded and the screw wiped off.

(7) Methanol extraction: Vulcanized rubber (50 g) was cut into a piece 5 mm square and immersed for five days in 60°C methanol, after which the immersion liquid was concentrated to dryness and the weight of the precipitate measured.

Example 1 An autoclave with an internal volume of approximately

50 liters and equipped with an electromagnetic induction type of agitator was thoroughly evacuated with nitrogen gas, and a cycle of pressure reduction and nitrogen filling was repeated three times. After this nitrogen replacement, 23.6 kg of pure water that had been deoxygenated in a reduced pressure state, 2.96 L of 1 , 1 ,2-trichloro- 1 ,2,2,-trifluoroethane (hereinafter referred to as Freon^® 113), and 23.6 g of methyl cellulose (viscosity 50 cp; used as a suspension stabilizer) were supplied to the autoclave, and the temperature was held at 50°C while the contents were stirred at 80 rpm. Next, a monomer mixture composed of 14.5 wt% VDF, 79.1 wt% HFP, and 6.4 wt% TFE was supplied as the feed gas until a pressure of 15 kg/cm²*G was reached. A solution (57.0 g) of Freon^® 113 containing 20.1 wt% diisopropyl peroxydicarbonate was introduced under pressure as a catalyst, and polymerization was commenced. When the pressure of the polymerization decreased to 14.5 kg/cm²*G, a monomer mixture composed of 43.5 wt% VDF, 29.5 w % HFP, and 27.0 wt% TFE was added as additional gas, and the pressure was returned to 15 kg/cm^2,G. This operation was conducted repeatedly to carry out a polymerization reaction. Dibromotetrafluoroethane (CF2BrCF2Br, 226 g) and 57.0 g of a solution of Freon^® 113 containing 20.1 wt% diisopropyl peroxydicarbonate were added at a point 6.3 hours after the start of the polymerization, and the polymerization reaction was continued for another 15.8 hours, again with the pressure between 14.5 and 15 kg/cm²*G, for a total polymerization reaction time of 22.1 hours.

Upon completion of the polymerization reaction, the remaining monomer mixture was evacuated, the suspension thus obtained was dehydrated in a centrifuge, and then thoroughly washed with water, after which it was vacuum dried at 100°C, which gave approximately 25.4 kg of elastomer. The fluoroelastomer thus obtained was analyzed by F-NMR and found to contain 44 wt% VDF units, 30 wt% HFP units, and 26 wt% TFE units.

The η of this elastomer was 119 mL/g, there were two peaks on a chart of its molecular weight distribution, Mn was 2.5 x 10⁴, and Mw/Mn was 18.4. M50/η was 0.49, M10 was 8.8 wt%, and M2000 was 6.8 wt%. Bromine was also detected in the elastomer.

Example 2 A commercially available fluoroelastomer for use in extrusion (Fluorel^® FT2320, available from 3M) was purchased and analyzed by F-NMR, which showed it contained 44 wt% VDF units, 30 wt% HFP units, and 26 wt% TFE units. The η of this elastomer was 65 mL/g. There was only one peak on a chart of its molecular weight distribution, Mn was 5.3 x 10⁴, and M_w/M_n was 4.6. M50/η was 0.36 and M10 was 2.7 wt%. Bromine was not detected in the elastomer. A polyol vulcanization agent had already been added to this elastomer. Example 1 and Comparative Examples 1-2

Using the elastomers from Examples 1 and 2, compositions were kneaded in the blend proportions shown in Table 1 and vulcanized, and the various properties and characteristics thereof were measured. These results are given in Table 1. It can be seen that the composition of the present invention exhibited excellent physical properties, and also exhibited excellent operation characteristics in that there was no sticking to the screw during extrusion. It can also be seen that there was only a small amount of extraction of the fluoroelastomer vulcanization composition of the present invention with respect to a solvent typified by methanol, to which fluororubbers are susceptible, despite the high content of a low molecular weight component.

The following components were used in the blends:

• SRF carbon: "Shiest S" (Tokai Carbon) • Ca(OH)2: "Carbit" (Chikae Chemical Industries)

• MgO (#150): "Kyowamag 150" (Kyowa Chemical Industries)

• AC-30: a polyol vulcanization agent (Asahi Chemical Industries)

• AC-40: a polyol vulcanization agent (Asahi Chemical Industries)

• Perhexa 25B40: an organic peroxide (Nippon Oil & Fats) • TAIC: triallylisocyanurate (Nippon Kasei Chemical)

Table 1. Summary of Formulations and Results

Comp. Comp

Ex. 1 Ex. 1 Ex. 2

Blend

Elastomer of Ex. 1 100 100

Elastomer of Ex. 2 100

SRF Carbon Black 12 12 12

Ca(OH)₂ 6 6 6

MgO (#150) 3 3 3

AC-30 4 4

AC-40 2 2

Perhexa 25B40 0.5

TAIC 0.5

Vulcanization Properties

Tensile Strength (kg/cm²) 144 100 159

Elongation (%) 377 405 277

100% Modulus (kg/cm²) 25 21 54

Hardness (JIS A) 75 71 79

Extrusion Characteristics

Extrusion Velocity (cm/min) 130 128 50

Extrusion Texture 4.5 4.5 2

Die Swelling (Thickness; %) 15 16 8

Roll Sticking O O X

Screw Sticking 0 O X

Methanol Extraction 0.8 3.5 0.7

Claims

CLAIMS:

1. A fluoroelastomer composition comprising

(A) a bromine-containing fluoroelastomer having a multi-modal molecular weight distribution, an intrinsic viscosity of 40 to 200 mL/g, and a M_w/M_n ratio of weight average molecular weight (M_w) and number average molecular weight (M_n) between 3 and 25, comprising interpolymerized units of (i) vinylidene fluoride and (ii) hexafluoropropylene wherein the weight ratio of (i):(ii) is from 40:60 to 80:20; (B) a vulcanization agent comprising either (i) a mixture of a polyhydroxy aromatic compound, at least one salt selected from the group consisting of ammonium salts, phosphonium salts, and iminium salts and a divalent metal oxide or divalent metal hydroxide, or (ii) a mixture of a polyamine and a divalent metal oxide;

(C) an organic peroxide; and

(D) a polyfunctional unsaturated compound.

2. A fluoroelastomer composition comprising (A) a bromine-containing fluoroelastomer having a multi-modal molecular weight distribution, an intrinsic viscosity of 40 to 200 mL/g, and a M_w/M_n ratio of weight average molecular weight (M_w) and number average molecular weight (M_n) between 3 and 25, comprising interpolymerized units of (i) vinylidene fluoride, (ii) hexafluoropropylene, and

(iii) no more than 35 weight % tetrafluoroethylene;

(C) an organic peroxide; and

(D) a polyfunctional unsaturated compound.

3. The composition of Claim 1 wherein the weight ratio of (i):(ii) is between 55:45 and 75:25.

4. The composition of Claim 2 wherein the interpolymerized units of tetrafluoroethylene are present in an amount of between 5 and 25 wt. %.

5. The composition of Claim 1 wherein the bromine content of the fluoroelastomer is 0.01 to 5 wt. %.

6. The composition of Claim 2 wherein the bromine content of the fluoroelastomer is 0.01 to 5 wt. %.

7. The composition of Claim 1 wherein the vulcanization agent of B) is a mixture of a polyhydroxy aromatic compound, at least one salt selected from the group consisting of ammonium salts, phosphonium salts, and iminium salts and a divalent metal oxide or divalent metal hydroxide.

8. The composition of Claim 7 wherein the polyhydroxy aromatic compound is bisphenol AF.

9. The composition of Claim 2 wherein the vulcanization agent of B) is a mixture of a polyhydroxy aromatic compound, at least one salt selected from the group consisting of ammonium salts, phosphonium salts, and iminium salts and a divalent metal oxide or divalent metal hydroxide.

10. The composition of Claim 9 wherein the polyhydroxy aromatic compound is bisphenol AF.