Adhesive composition and uses thereof

Abstract

Disclosed herein is an adhesive composition for clutch disc application comprising of an epoxy resin of bisphenol A and epichlorohydrin, partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20, and optionally with additives to obtain improved lap shear strength and cushioning properties.

Claims

1. An adhesive composition consisting of from 2-20 parts by weight ATBN, from 2-5 parts by weight of an amino propyl triethoxy silane coupling agent, and the remainder an epoxy resin.

Description

DETAILED DESCRIPTION OF INVENTION

(1) In an aspect the present invention relates to adhesive composition comprising of Henkel adhesive, an elastomer such as CTBN or ATBN optionally with a coupling agent and additives. In a preferred aspect, the current invention provides an adhesive composition comprising of an epoxy resin basically of bisphenol A and epichlorohydrin; and partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20 optionally with additives to obtain improved lap shear strength and cushioning properties. The adhesive composition of the instant invention is stable at high temperature and has improved lap shear strength that can withstand temperature upto 0.160 C. without compromising the cushioning effect.

(2) The present invention provides high temperature resistant epoxy based adhesive composition consisting of an epoxy resin component, elastomer, toughening agent, a coupling agent, optionally with additives such as diluents, fillers, pigments to obtain improved lap shear strength and cushioning properties for clutch disc application.

(3) Examples of epoxy resin suitable for use in the present invention include HPA 1044 of Henkel; or polyepoxides formed by reacting epichlorohydrin with 4, 4 isopropylidene diphenol and having a molecular weight ranging from about 340 to about 10,000. Most preferably, the polyepoxides have a molecular weight range from about 330 to 560 and contain at least two oxirane groups; i.e., two epoxy groups; or include monofunctional and multifunctional glycidyl ethers of bisphenol A and bisphenol F, and cycloaliphatic epoxy resins or a combination thereof. The cycloaliphatic epoxides are preferably selected from non-glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule such as 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, which contains two epoxide groups that are part of the ring structures and an ester linkage, vinylcyclohexene dioxide, which contains two epoxide groups and one of which is part of the ring structure, 3,4-epoxy-6-methyl cyclohexyl methyl-3,4-epoxycyclohexane carboxylate and dicyclopentadiene dioxide. Glycidyl ether epoxides are used either separately or in combination with the non-glycidyl ether epoxides. These resins are selected from glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. A preferred epoxy resin of this type is Bisphenol A resin which includes 2,2-bis(4-hydroxyphenyl) propane-epichlorohydrin copolymer. These resins are generally prepared by the reaction of one mole of bisphenol A resin and two moles of epichlorohydrin. The preferred epoxy for the adhesive of the present invention is selected from HPA 1044 of Henkel or Bisphenol A resin. Bisphenol-A type resin is commercially available from Resolution Technology a., EPON 828, 828EL or 828XA. The epoxy resin component of the resin comprises from about 50 to about 90 weight percent of the resin component and, preferably, about 75 to about 85 weight percent of the resin component.

(4) The elastomers of the present invention are selected from butadiene acrylonitrile copolymers namely amino terminated butadiene acrylonitrile co-polymer (ATBN), carboxyl terminated butadiene acrylonitrile co-polymer (CTBN), vinyl terminated butadiene acrylonitrile co-polymer (VTBN), epoxy terminated butadiene acrylonitrile co-polymer (ETBN), polyether, polyester, polyacrylates, silicone, hydroxyl terminated poly butadiene (HTPB) and such like.

(5) The adhesive composition comprises silane coupling agents, selected from, but not limited to glycidyloxypropyl trialkoxy silane, mercaptopropyl trialkoxy silane, aminopropyl trialkoxy silane, and such like. In addition, organo-silanes may contain moieties, such as, for example, ester, vinyl, methacryloxy, sulfur, amino, ureido, isocyanurate, and isocyanato groups.

(6) The toughening agents are primarily the polymers other than epoxy resins capable of increasing the toughness of the epoxy resin. The toughness is measured by the peel strength of the eoxy resin. Typical toughening agents are selected from carboxyl terminated butadiene nitrile rubbers, acrylic polymers and copolymers etc. However, the unsaturated polymers have low resistance to heat, water, and impact. To withstand the high temperature and high peel strength, the toughening agents in the present invention is selected from partially hydrogenated carboxylated butadiene nitrile rubbers in the range of 20 wt %.

(7) Hydrogenated Nitrile Butadiene Rubber (HNBR) is a special class of nitrile rubber (NBR) that is hydrogenated to increase saturation of the butadiene segment of the carbon polymer backbone. Substantial improvements to the material properties, over that of a nitrile rubber (NBR), include greater thermal stability, broader chemical resistance, and greater tensile strength. Moreover, addition of carboxylic acid groups to the NBR polymer's backbone significantly alters processing and cured properties. It also results is a polymer matrix with significantly increased strength, measured by improved tensile, tear, modulus and abrasion resistance.

(8) Present invention provides an adhesive composition comprising of HPA 1044 of Henkel and an elastomer CTBN or ATBN optionally with a coupling agent and additives having following specifications;

(9) a. Viscosity: 295,000 mPa.Math.s

(10) b. Specific gravity: 1.66

(11) c. Lap shear strength: 322 kg/cm2

(12) d. Tg (DSC): 118 C.

(13) e. Cure conditions: @ 150 C. for more than 15 minutes

(14) The epoxy resin in the adhesive composition of the invention is in the range of 50-90 parts by weight and elastomer is in the range of 2-50 parts by weight. The coupling agent is in the range of 2-5 parts by weight of the adhesive composition.

(15) The present invention provides an adhesive composition for clutch disc application comprising of an epoxy resin basically of bisphenol A and epichlorohydrin; and partially hydrogenated carboxylated nitrile butadiene rubber (HX-NBR) in solid form as a toughening agent in the ratio 80:20 optionally with additives with improved lap shear strength and cushioning properties.

(16) The epoxy resin is in the range of 50-90 parts by weight and the toughening agent n the range of 2-50 parts by weight optionally with additives in the range of 2-5 parts by weight

(17) The adhesive composition of the instant invention is stable at a temperature in the range of 25 C. to 160 C. and has a lap shear strength not less than 10 kg/cm.sup.2 with an average cushioning of 0.4-0.6 mm.

(18) The diluent may be added to the adhesive composition to control the flow characteristics and is selected from diglycidyl ether of resorcinol, diglycidyl ether of cyclohexane dimethanol, diglycidyl ether of neopentyl glycol, triglycidyl ether of trimethylolpropane.

(19) Fillers may include adhesion promoters, corrosion inhibitors and rheology controlling agents and may be selected from silica-gels, Ca-silicates, phosphates, molybdates, fumed silica, clays such as bentonite or wollastonite, organoclays, aluminium-trihydrates, hollow-glass-micro spheres; hollow-polymeric microspheres and calcium-carbonate.

(20) Pigments may include inorganic or organic pigments including ferric oxide, brick dust, carbon black, titanium oxide and the like.

(21) The adhesive composition of the instant invention may be a one-part or two part composition; preferably as a two part composition.

(22) The invention provides a one-pot process for the preparation of the adhesive composition comprising mixing compounded epoxy resin with toughening agent in the ratio 80:20. The contents are mixed thoroughly and applied on the substrate previously treated with silane coupling agent.

(23) The physical properties of HPA 1044 (Henkel Adhesives) used in the present invention are given in Table 1 below:

(24) TABLE-US-00001 TABLE 1 Properties Observation Appearance Brownish Grey Paste Viscosity Brookfield RV #7@10 rpm 295,000 mPa .Math. s HAAKE Viscosity (RS-1, CS35/2-Ti) 97,000 mPa .Math. s @ 20 s.sup.1 HAAKE Viscosity (RS-1, CS35/2-Ti) 2.23 Thixo ratio (2 s.sup.1/20 s.sup.1) Specific Gravity 1.66 Lap Shear Strength (GB Steel, 0 gap@ 32.2 N/mm.sup.2 150 C. 30 min) Tg (DSC) 118 C.

(25) The adhesive of the present invention can be applied as liquid, paste, and semi-solid or solid that can be liquefied upon heating, or the adhesive may be applied as a spray. It can be applied as a continuous bead, in intermediate dots, stripes, diagonals or any other geometrical form that will conform to forming a useful bond. Preferably, the adhesive composition is in a liquid or paste form. The composition may be used as a metal-metal adhesive, metal-carbon fiber adhesive, carbon fiber-carbon fiber adhesive, metal-glass adhesive, carbon fiber-glass adhesive.

(26) The adhesive composition of the present invention contains low amount of volatile organic compounds thus providing an environment friendly, economical option for the mechanical rivet. Such compositions of the invention find use in clutch disc applications.

EXAMPLE

(27) Following examples are given by way of illustration therefore should not be construed to limit the scope of the present invention in any manner.

Example 1

(28) TABLE-US-00002 Ingredients Parts by weight HPA-1044 95 CTBN (elastomer) 5 APTES (Aminopropyl triethoxy silane) is used as coupling agent.

Example 2

(29) TABLE-US-00003 Ingredients Parts by weight HPA-1044 85 ATBN 15 APTES (Aminopropyl triethoxy silane) is used as coupling agent.

Example 3

(30) TABLE-US-00004 ingredients Parts by weight HPA-1044 80 HXNBR 20 MEK (Methyl ethyl ketone) is used to dissolve these ingredients. APTES (Aminopropyl triethoxy silane) is used as coupling agent.
Test for Lap Shear Strength and Cushioning

(31) The lap shear strength (LSS) test specimens were prepared as per the ASTM D1002. For this the test specimens in the form of strips of dimension 100 mm in length and 25 mm in width were prepared from mild steel (1.6 mm thick) and organo-metallic friction material (4.2 mm thick). Test specimens, were cleaned to remove oil, dust and grease materials from the surface. Amino functional silane was applied over the cleaned surface in an area of one inch by half inch. An adhesive composition was prepared by mixing the ingredients as given herein. Silane coated test specimens were bonded together with this adhesive and cured at 150 C. for 90 minutes. Testing was done at 150 C. after seven days of post curing at 27 C.

(32) Test Results for Lap Shear Strength and Cushioning

(33) I) Measurement of Lap Shear Strength

(34) The strips bonded with adhesive were evaluated at 27 C. and at 150 C. for lap shear strength using a Universal tensile tester (Instron) as per procedure in ASTM D 1002-05.

(35) II) Measurement of Cushioning Property

(36) The adhesive bonded test specimen was kept in between two stainless steel plates and a load of 10 kg/cm.sup.2 was applied. The gap between the plates was measured before and after the application of the load. From this the cushion parameters were calculated.

(37) TABLE-US-00005 TABLE 2 Test results for lap shear strength and cushioning LSS (kg/cm.sup.2) @ 150 C. Cushioning (mm) Example 1 15 0.08 Example 2 9.5 0.15 Example 3 11 0.5

Advantages of the Invention

(38) 1. Adhesively bonded clutch disc provide 100% utilization of the friction material. 2. There is no loss of friction material. 3. Life time of clutch disc is increased. 4. There is a reduction in the overall weight of clutch disc. 5. The process for the preparation of adhesively bonded clutch disc is easier and economical.