JP5765341B2 - Friction material composition, friction material and friction member using the same - Google Patents

Description

  The present invention relates to a friction material composition suitable for a friction material such as a disc brake pad and a brake lining used for braking an automobile or the like, a friction material using the friction material composition, and a friction member.

  In automobiles and the like, friction materials such as disc brake pads, brake linings, and clutch facings are used for braking. The friction material usually contains a binder, a fiber substrate, an abrasive, an inorganic filler, an organic filler, and the like as a composition. The friction material currently used, for example, a disc brake pad, is a non-asbestos-organic (Non-Asbestos-Organic) (asbestos-free) as a fiber base in consideration of the influence on the environment and the human body ( Hereinafter, a friction material of a type called “NAO material” has become mainstream (see, for example, Patent Documents 1 and 2).

  By the way, as a binder for the friction material, a phenol resin is generally used from the viewpoint of heat resistance and strength. In conventional friction materials, under severe conditions (high load, high temperature, etc.) where the friction sliding surface is at a high temperature of 300 ° C. or higher, liquid decomposition products generated by the thermal decomposition of phenol resin lubricate the sliding surface. Since it exists as a component, a phenomenon in which the friction coefficient is significantly reduced is likely to occur. For this reason, it is required that the friction coefficient decrease little (also referred to as fade characteristics) at high loads, high temperatures, and the like.

However, the conventional NAO material has a tendency that sufficient fade characteristics cannot be obtained, and further improvement of the fade characteristics is required.
Examples of attempts to improve the fade characteristics of NAO materials so far include, for example, reports of improvements made by the addition of activated alumina and a fluoropolymer (see Patent Document 3).

  On the other hand, in recent years, the demand for performance on brakes is becoming increasingly sophisticated, and not only the above-mentioned fade characteristics but also the need for further performance improvements such as the occurrence of abnormal noise and squealing (also called squealing characteristics) is required. Is done.

JP-A-2-132175 JP-A-6-184525 WO2004 / 069954

  However, various studies have been made on the fading characteristics of the NAO material, and when considering the improvement of the squealing characteristics in addition to the fading characteristics, it cannot be said to be sufficient, and satisfactory results have not been obtained.

  Further, it has been found that when the friction material composition adsorbs a large amount of moisture in the air, cracks are likely to occur after press molding. The present inventors have found that when activated alumina having a high specific surface area disclosed in Patent Document 3 is used, the water absorption increases as the specific surface area increases, and cracks are likely to occur after press molding. The present inventors have also found that the occurrence of this crack has an effect on the strength reduction of the friction material.

  In the present invention, it is an object to obtain a friction material composition suitable for a friction material having improved squealing characteristics, a friction material using the friction composition, and a friction member without significantly reducing the coefficient of friction at high temperatures. It was.

  In order to solve the above-mentioned problems, the present inventors have intensively studied the relationship between combinations of various friction material compositions, fade characteristics, and squeal characteristics, and have solved the problems by using specific abrasives.

  Specifically, it is a friction material composition containing a binder, a fiber substrate, an abrasive, an inorganic filler, and an organic filler, and has a specific surface area as an abrasive, more preferably a specific hardness. By including a silicate, for example, a friction material composition that is less likely to decrease in the friction coefficient even under severe conditions where the frictional sliding surface is at a high temperature of 300 ° C. or higher, and that has excellent squeal characteristics in an actual vehicle test according to JASO C402. It was found that a product was obtained.

That is, the present invention is as follows.
(1) A friction material composition containing a binder, a fiber substrate, an abrasive, an inorganic filler, and an organic filler,
A friction material composition comprising a silicate having a specific surface area calculated by the BET method of 400 to 800 m ² / g as the abrasive.
(2) The friction material composition according to (1), wherein the silicate having a specific surface area calculated by the BET method of 400 to 800 m ² / g has a Mohs hardness of 6 or less.

(3) A silicate having a specific surface area calculated by the BET method of 400 to 800 m ² / g and a Mohs hardness of 6 or less is magnesium silicate, aluminum silicate, calcium silicate, sodium silicate, silicic acid The friction material composition according to (2), wherein the friction material composition is at least one selected from potassium and lithium silicate.

(4) A silicate having a specific surface area calculated by the BET method of 400 to 800 m ² / g and a Mohs hardness of 6 or less is contained in an amount of 1 to 10 wt% based on the whole composition (2 Or the friction material composition according to (3).

(5) A friction material formed by molding the friction material composition according to any one of (1) to (4) above.
(6) A friction member formed by integrating a friction material obtained by molding the friction material composition according to any one of (1) to (4) and a back metal.

  ADVANTAGE OF THE INVENTION According to this invention, the friction material composition which improved the squeal characteristic, the friction material using the same, and a friction member can be obtained, without reducing the friction coefficient at the time of high temperature significantly.

  The disclosure of the present application is related to the subject matter described in Japanese Patent Application No. 2010-178690 filed on Aug. 9, 2010, the disclosure of which is incorporated herein by reference.

  Hereinafter, the friction material composition of the present invention, the friction material using the same, and the friction member will be described in detail.

The friction material composition of the present invention is a friction material composition containing a binder, a fiber base material, an abrasive, an inorganic filler, and an organic filler, and has a specific surface area calculated by the BET method as the abrasive. It is 400-800 m < ² > / g, More preferably, it further contains the silicate whose Mohs hardness is 6 or less.

  By including the silicate having the specific surface area, liquid pyrolyzate generated by thermal decomposition is easily adsorbed in the pores of the silicate having the specific surface area, and the friction coefficient is greatly reduced. Can be suppressed.

  As described above, it is known that when the friction material composition adsorbs a large amount of moisture in the air, cracks are likely to occur after press molding. When activated alumina having a high specific surface area disclosed in Patent Document 3 is used, the water absorption increases as the specific surface area increases, and cracks are likely to occur after press molding. However, in the case of silicate, even if the specific surface area is too high with activated alumina, it is not easily affected by moisture. This property is considered to suppress the generation of crispness even when a material having a large specific surface area is used, but the present invention is not limited to such an estimation theory.

  In addition, when the silicate which has a specific specific surface area is used as an abrasive, this inventor found out that it is excellent also in the squealing characteristic and the fade characteristic compared with the case where activated alumina is used.

Although the range of the specific surface area is 400 to 800 m ² / g, more preferably 500~750m ² / g, more preferably 600~700m ² / g. When the specific surface area exceeds 800 m ² / g, the adhesive strength of the friction material may be lowered and the friction performance may be lowered. If the specific surface area is less than 400 m ² / g, the coefficient of friction at high temperatures and the like decreases.
In addition, the specific surface area in this invention is taken as the value measured by BET method by nitrogen gas adsorption.

  A silicate having a desired specific surface area can be obtained by selecting a commercial product. Further, for example, a silicate having a desired specific surface area can also be prepared by adjusting the particle diameter, performing heat treatment, performing mechanical treatment, performing chemical treatment, and the like.

The Mohs hardness of the silicate having a specific surface area calculated by the BET method of 400 to 800 m ² / g is preferably 6 or less. When the Mohs hardness is 6 or less, the squeal characteristics are hardly adversely affected. Further, the shape of the “silicate having a Mohs hardness of 6 or less” is not particularly limited.

The silicate having the specific surface area in the present invention is a compound containing silicon oxide and metal oxide, and is represented by xMmOn · ySiO ₂ · zH ₂ O. Here, M represents a metal element and satisfies (valence of M) × m = 2n. X and y are represented by natural numbers exceeding 0, and z represents a natural number exceeding 0 or 0.

Examples of the silicate include magnesium silicate (for example, 2MgO · 6SiO ₂ (arbitrary crystal water)), aluminum silicate (for example, Al ₂ O ₃ • 9SiO ₂ (arbitrary crystal water)), Examples include calcium silicate, sodium silicate, potassium silicate, lithium silicate, and the like. These can be used alone or in combination of two or more. When the silicate has silicic acid and contains bound water or crystal water, the temperature rise of the friction material composition can be suppressed and the wear resistance tends to be excellent.
The silicates exemplified above all have a Mohs hardness of 6 or less.

  Moreover, it is preferable that the average particle diameter of a silicate is 1-300 micrometers, It is more preferable that it is 10-250 micrometers, It is still more preferable that it is 20-50 micrometers. When the average particle diameter is 300 μm or less, it is difficult to adversely affect the squeal characteristics.

  The average particle diameter is measured by D50 (median diameter) in laser diffraction particle size distribution measurement. The median diameter means a 50% diameter obtained from a volume distribution measured by laser diffraction particle size distribution measurement.

  It is preferable that the addition amount of the said silicate is 1-10 wt% with respect to the whole composition. When the addition amount of the silicate is more than 1 wt%, fading characteristics are easily obtained. Further, when the amount of the silicate added is 10 wt% or less with respect to the entire composition, a friction material that is less likely to crack during molding of the friction material, has excellent wear resistance, and has high strength is obtained. be able to. Moreover, from a viewpoint of suppressing the generation | occurrence | production of the crack at the time of shaping | molding of a friction material, it is more preferable that it is 1-7 wt%, and it is still more preferable that it is 2-7 wt%.

In the present invention, as described above, the silicate has a specific surface area of 400 to 800 m ² / g, more preferably 500 to 750 m ² / g, still more preferably 600 to 700 m ² / g, and Furthermore, it is preferable to use a silicate having a Mohs hardness of 6 or less. However, as long as the effects of the invention are not impaired, other abrasives may be contained in addition to the silicate.

  Examples of other abrasives include zirconium silicate, zirconium oxide, mullite, chromite, titanium oxide, magnesium oxide, silica, iron oxide, and the like, and these can be used alone or in combination of two or more.

  In addition, the content of the other abrasive is preferably 10 to 45 wt%, more preferably 15 to 40 wt% in the friction material composition. By setting it within this range, the braking effect, wear resistance, and squeal characteristics can be improved.

  The binder contained in the friction material composition of the present invention integrates an organic filler, an inorganic filler, a fiber base material and the like contained in the friction material composition, and gives strength. As the binder contained in the friction material composition of the present invention, a thermosetting resin used for a friction material can be usually used. Examples of the thermosetting resin include various modified phenol resins such as phenol resin, acrylic modified phenol resin, silicone modified phenol resin, cashew modified phenol resin, epoxy modified phenol resin, and alkylbenzene modified phenol resin. Phenol resins, acrylic-modified phenol resins, silicone-modified phenol resins, and alkylbenzene-modified phenol resins are preferred because they give particularly good heat resistance, moldability, and friction coefficient, and these should be used alone or in combination of two or more. Can do.

  Further, the binder is preferably contained in the entire composition at 5 to 20 wt%, more preferably 5 to 15 wt%, and further preferably 5 to 10 wt%. By setting it within this range, a decrease in strength of the friction material can be avoided, and the deterioration of sound vibration performance such as squeal due to a decrease in the porosity of the friction material and an increase in the elastic modulus can be suppressed.

  Examples of the fiber substrate used in the present invention include metal fibers, inorganic fibers, organic fibers, and carbon fibers. The fiber base material exhibits a reinforcing action in the friction material.

  As the metal fibers, copper fibers, brass fibers, bronze fibers, titanium fibers, aluminum fibers, iron fibers such as steel fibers and stainless fibers, and the like can be used, and one or a combination of two or more can be used. .

  As inorganic fibers, ceramic fibers, biodegradable ceramic fibers, mineral fibers, glass fibers, potassium titanate fibers, silicate fibers, wollastonite fibers, etc. can be used, and one or a combination of two or more types can be used. Can do. From the viewpoint of reducing environmental substances, it is preferable not to contain attractive potassium titanate fibers or ceramic fibers.

The mineral fiber referred to here is a man-made inorganic fiber melt-spun mainly composed of blast furnace slag such as slag wool, basalt such as basalt fiber, and other natural rocks, and is a natural mineral containing Al element. Is more preferable. Specifically, those containing SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na ₂ O, or the like, or those containing one or more of these compounds can be used. More preferably, those containing Al element can be used as mineral fibers.

  Since the adhesive strength with each component in the friction composition tends to decrease as the average fiber length of the entire mineral fiber contained in the friction material composition increases, the average fiber length of the entire mineral fiber is preferably 500 μm or less, More preferably, it is 100-400 micrometers.

  Here, the average fiber length refers to a number average fiber length indicating an average value of the lengths of all corresponding fibers. For example, the average fiber length of 200 μm indicates that 50 mineral fibers used as a friction material composition raw material are randomly selected, the fiber length is measured with an optical microscope, and the average value is 200 μm.

The mineral fiber used in the present invention is preferably biosoluble from the viewpoint of human harm. The term “biosoluble mineral fiber” as used herein refers to a mineral fiber having a characteristic that even if it is taken into the human body, it is partially decomposed and discharged outside the body in a short time. Specifically, the chemical composition is alkali oxide, alkaline earth oxide total amount (total amount of oxides of sodium, potassium, calcium, magnesium, barium) is 18% by mass or more, and in a short-term biopermanent test by respiration, A fiber that has a mass half-life of 20 μm or more within 40 days or no evidence of excessive carcinogenicity in an intraperitoneal test or that has no associated pathogenicity or tumor development in a long-term respiratory test (EU Directive 97 / 69 / EC Nota Q (carcinogenic exclusion)). Examples of such biodegradable mineral fibers include SiO ₂ —Al ₂ O ₃ —CaO—MgO—FeO—Na ₂ O fibers and the like, and include SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na. Examples thereof include fibers containing ₂ O or the like in any combination. As a commercial item, LAPINUS FIBERS B.M. Examples include V Roxul series. “Roxul” includes SiO ₂ , Al ₂ O ₃ , CaO, MgO, FeO, Na ₂ O and the like.

  As an organic fiber, an aramid fiber, an acrylic fiber, a phenol resin fiber, a cellulose fiber, etc. can be used, and it can be used 1 type or in combination of 2 or more types. From the viewpoint of wear resistance, it is preferable to use an aramid fiber as the organic fiber.

  As the carbon-based fibers, flame-resistant fibers, pitch-based carbon fibers, PAN-based carbon fibers, activated carbon fibers, and the like can be used, and one or a combination of two or more types can be used.

  All fiber base materials are preferably contained in the entire composition at 5 to 40 wt%, more preferably 10 to 30 wt%, and even more preferably 10 to 20 wt%. By setting it as this range, the optimal porosity as a friction material can be obtained, the noise can be prevented, the appropriate material strength can be obtained, and the moldability can be improved.

  The friction material composition of the present invention contains an inorganic filler as a friction modifier for avoiding deterioration of the heat resistance of the friction material. As the inorganic filler used in the present invention, an inorganic filler usually used for a friction material can be used. For example, antimony trisulfide, tin sulfide, molybdenum disulfide, iron sulfide, bismuth sulfide, zinc sulfide, calcium hydroxide, calcium oxide, sodium carbonate, calcium carbonate, magnesium carbonate, barium sulfate, dolomite, coke, graphite, mica, oxidation Iron, vermiculite, granular potassium titanate, calcium sulfate, plate-like potassium titanate, talc, clay, zeolite and the like can be used, and these can be used alone or in combination of two or more. Among these, it is preferable to contain graphite and barium sulfate from the viewpoint of reducing the aggressiveness to the facing material.

  Further, the content of the inorganic filler is preferably 10 to 50 wt%, more preferably 10 to 40 wt%, and still more preferably 15 to 35 wt% in the friction material composition. By setting it as this range, deterioration of heat resistance can be avoided, and the content balance of the other components of the friction material is also preferable.

  The friction material composition of the present invention contains an organic filler as a friction modifier for improving the sound vibration performance and wear resistance of the friction material. Examples of the organic filler used in the present invention include cashew dust, tire rubber powder, acrylic rubber powder, isoprene rubber, NBR (nitrile butadiene rubber) powder, SBR (styrene butadiene rubber) powder, and the like. Alternatively, two or more types can be used in combination. The cashew dust is not particularly limited as long as it is obtained by pulverizing a hardened cashew nut shell oil and is usually used for a friction material.

  The content of the organic filler is preferably 1 to 20 wt% in the friction material composition, more preferably 1 to 10 wt%, and still more preferably 3 to 8 wt%. By setting it as this range, the elastic modulus of the friction material can be increased, deterioration of sound vibration performance such as squealing can be avoided, and deterioration of heat resistance and strength reduction due to thermal history can be avoided.

  Moreover, the friction material composition of the present invention can contain other materials as needed in addition to the above materials, such as copper powder, brass powder, bronze powder, zinc powder, tin powder, aluminum powder, etc. An organic additive such as a fluorine-based polymer such as metal powder or PTFE (polytetrafluoroethylene) can be blended.

In particular, when PTFE is used, the fade characteristics can be improved. The content of PTFE is preferably in the range of 0.3 to 6 wt%, more preferably 1 to 5 wt%, and still more preferably 2 to 4 wt% in the friction material composition.
The fluorine-based polymer is preferably used in powder form, but the same effect can be expected even when used as an emulsion and contained in the friction material composition by wet mixing.

  The friction material composition of the present invention can be used as a friction material for disc brake pads and brake linings of automobiles, etc., or by subjecting the friction material composition of the present invention to a desired shape, processing, pasting, and the like. It can also be used as a friction material for facings, electromagnetic brakes and holding brakes.

In addition, the friction material composition of the present invention can be used as a friction material itself that becomes a friction surface to obtain a friction member. Examples of the friction member using the same include the following configurations.
(1) Configuration of friction material only.
(2) A structure having a backing metal and a friction material formed on the backing metal and made of the friction material composition of the present invention to be a friction surface.
(3) In the configuration of (2) above, a primer layer for the purpose of surface modification for enhancing the adhesion effect of the back metal, and an adhesive layer for the purpose of bonding the back metal and the friction material between the back metal and the friction material The configuration that further intervenes.

  The backing metal is usually used as a friction member in order to improve the mechanical strength of the friction member. As the material, metal or fiber reinforced plastic can be used. Examples of the metal include iron and stainless steel, and examples of the fiber reinforced plastic include inorganic fiber reinforced plastic and carbon fiber reinforced plastic.

  The primer layer and the adhesive layer may be those usually used for friction members such as brake shoes.

  The friction material of the present invention can be produced by a generally used method, and is produced by molding the friction material composition of the present invention, preferably by hot pressing. Specifically, the friction material composition of the present invention was uniformly mixed using a mixer such as a Readyge mixer, a pressure kneader, or an Eirich mixer, and this mixture was preformed in a molding die, and obtained. The preform is molded at a molding temperature of 130 ° C. to 160 ° C. and a molding pressure of 20 to 50 MPa for 2 to 10 minutes, and the resulting molded product is heat-treated at 150 to 250 ° C. for 2 to 10 hours. In addition, painting, scorch treatment, and polishing treatment are performed as necessary.

  Since the friction material composition of the present invention has a high reinforcing effect, it is useful as a “upper material” of a friction material, and can also be used after being molded as a “underlay material” of a friction member. The “upper material” is a friction material that becomes the friction surface of the friction member, and the “underlay material” is the friction material and the back metal interposed between the friction material that becomes the friction surface of the friction member and the back metal. It is a layer for the purpose of improving the shear strength.

  The friction material composition of the present invention will be further described with reference to examples.

(Production of disc brake pad)
The materials were blended according to the blending ratio shown in Table 1, and the friction material compositions of Examples 1 to 6 and Comparative Examples 1 and 2 were obtained. This friction material composition is mixed with a ladyge mixer (manufactured by Matsubo Co., Ltd., trade name: ladyge mixer M20), and this mixture is preformed with a molding press (manufactured by Oji Kikai Kogyo Co., Ltd.). The product was heat and pressure molded using a molding press (manufactured by Sanki Seiko Co., Ltd.) for 5 minutes under conditions of a molding temperature of 145 ° C. and a molding pressure of 30 MPa, and the resulting molded product was heat treated at 200 ° C. for 4.5 hours, Polishing was performed using a rotary polishing machine, and scorch treatment at 500 ° C. was performed to obtain a disc brake pad.

In this example and comparative example, a disc brake pad having a friction material projected area of 52 cm ² was produced.

※配合量：摩擦材組成物全体に対するｗｔ％

* Blending amount: wt% of the friction material composition as a whole

The physical properties of various abrasives are as follows.
(Zirconium oxide)
Specific surface area: 1.4 m ² / g, average particle size: 5.2 μm, Mohs hardness: 6.5
(Zirconium silicate)
Specific surface area: 5.5 m ² / g, average particle size: 1.5 μm, Mohs hardness: 7.5
(Magnesium silicate (A): Kyoward manufactured by Kyowa Chemical Co., Ltd.)
Specific surface area: 680 m ² / g, average particle size: 50 μm, Mohs hardness: ≦ 5
(Aluminum silicate (B): Kyoward manufactured by Kyowa Chemical Co., Ltd.)
Specific surface area: 620 m ² / g, average particle size: 20 μm, Mohs hardness: ≦ 5
(Aluminum silicate (C): Kyoward manufactured by Kyowa Chemical Co., Ltd.)
Specific surface area: 650 m ² / g, average particle size: 250 μm, Mohs hardness: ≦ 5
(Activated alumina (D): γ-alumina manufactured by Mizusawa Chemical Co., Ltd.)
Specific surface area: 180 m ² / g, average particle size: 20 μm, Mohs hardness: ≦ 6
(Magnesium silicate (E): Kyoward manufactured by Kyowa Chemical Co., Ltd.)
Specific surface area: 130 m ² / g, average particle size: 30 μm, Mohs hardness: ≦ 5

(Evaluation of fade characteristics)
The fade characteristics of the disc brake pads of Examples 1 to 6 and Comparative Examples 1 and 2 produced by the above method were evaluated using a brake dynamo tester. In the experiment, a general pin slide type collet caliper and a ventilated disc rotor (FC190) manufactured by Kiriu Co., Ltd. were used, and evaluation was performed based on the moment of inertia of the Nissan Skyline V35.

  Efficacy tests in accordance with SAE J2522 were carried out, and among the friction coefficients generated during a total of 15 brakings in FADE1 SECTION, the minimum average friction coefficient (the minimum value of average μ) and the friction coefficient during one braking The minimum value of (μ) was evaluated.

(Evaluation of wear resistance)
An efficacy test based on SAE J2522 was performed, and the amount of wear was evaluated from the pad thickness before and after the test.

(Evaluation of squeal characteristics)
An actual vehicle test was performed in accordance with JASO C402, and the brake squeal and abnormal noise during the test were measured to determine the occurrence rate of brake squeal of 70 dB or more.

(Evaluation of crack generation during molding of friction material)
When molding the friction material compositions of Examples 1 to 6 and Comparative Examples 1 and 2 obtained by the above method, a crack of 0.5 mm × 0.5 mm × 2.0 mm was visually observed on the friction material surface. It was evaluated by doing. The evaluation criteria are as follows.
A: The number of disc brake pads with cracks was 0% with respect to the total number of molded disc brake pads.
B: The number of disc brake pads in which cracks occurred with respect to the total number of molded disc brake pads is more than 0%.

  The results are shown in Table 2.

※摩擦係数（μ）は大きいほど良好であることを示す。
※ブレーキ鳴き発生率は、数値が小さいほど良好であることを示す。

* The larger the friction coefficient (μ), the better.
* The smaller the numerical value, the better the brake squeak occurrence rate.

  As shown in Table 2, it is clear that the disc brake pads of Examples 1 to 6 show a fading characteristic superior to those of Comparative Examples 1 and 2, and a remarkably high squealing characteristic.

The friction material composition of the present invention has the following excellent effects.
According to the present invention, a friction material composition capable of improving fade characteristics and suppressing the occurrence of abnormal noise and squealing without significantly reducing the coefficient of friction at high temperatures compared to conventional products, A friction material and a friction member using the same can be provided.

Claims (6)

A friction material composition containing a binder, a fiber substrate, an abrasive, an inorganic filler, and an organic filler,
A non-asbestos-organic friction material composition comprising, as the abrasive, a silicate having a specific surface area calculated by the BET method of 600 to 800 m ² / g. The friction material composition according to claim 1, wherein the silicate having a specific surface area calculated by the BET method of 600 to 800 m ² / g contains a silicate having a Mohs hardness of 6 or less. Silicates having a specific surface area calculated by the BET method of 600 to 800 m ² / g and a Mohs hardness of 6 or less are magnesium silicate, aluminum silicate, calcium silicate, sodium silicate, potassium silicate and silica. The friction material composition according to claim 2, wherein the friction material composition is at least one selected from lithium acid. 4. The silicate having a specific surface area calculated by the BET method of 600 to 800 m ² / g and a Mohs hardness of 6 or less is contained in an amount of 1 to 10 wt% based on the entire composition. The friction material composition.   The friction material formed by shape | molding the friction material composition as described in any one of Claims 1-4.   The friction member formed by integrating the friction material formed by shape | molding the friction material composition as described in any one of Claims 1-4, and a back metal.