Title of Invention

PROCESS FOR MANUFACTURING EPOXY FOAM

Abstract

A process for making epoxy resin foam blocks of varying density comprising mixing together (i) a foam resin comprising: a first epoxy resin, a foaming agent to the extent of 2% to 10% of the mass of the epoxy resin, a surfactant to the extent of 2% to 6% of the mass of the epoxy resin, a filler, a toughening agent and (ii) a curing agent comprising: a hardner and a second epoxy resin, the ratio of the foam resin to curing agent being in the range of about 100:20 to 100:25 by mass to form a reaction mixture; pouring the reaction mixture inside a mold maintained at a temperature in the range of 70º to 80ºC and allowing the mixture to cure in the mold for 60 to 100 min.; allowing the mold to cool at a temperature in the range of 15º to 30ºC and demolding to obtain a green block; and post-curing the green block in an air circulatory oven for 10 to 15 hrs to obtain a final hard foam block.

Full Text

FORM-2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 PROVISIONAL Specification (See section 10 and rule 13) PROCESS FOR MANUFACTURING EPOXY FOAM ADITYA BIRLA CHEMICALS (THAILAND) LTD. A Thailand Company of 888/167, 16th floor, Mahatun Plaza Building, Ploenchit Road, Lumpini, Bangkok 10330, Thailand THE FOLLOWING SPEC IFICATION DESCRIBES THE INVENTION. Field of invention This invention relates to a process for manufacturing Epoxy foam. Background of the Invention Historically epoxy resins are known for excellent electrical insulation and adhesion properties. Bisphenol-A based epoxy resins are most common among various types of epoxy resins available commercially. Curing of epoxy resin is achieved by reacting it with polyamines, polyamides, carboxylic anhydrides, poly-phenols, and amine complexes. The epoxy or the 'oxirane' ring opens up and reacts with the hardener without forming any byproduct at ambient or elevated temperatures depending upon the nature and use of hardeners. Recently, epoxy foams have been investigated because they exhibit excellent combination of mechanical properties like tensile strength, adhesion strength, compression strength, electrical properties like dissipation factor, dielectric constant, volume resistivity and adhesion properties including low shrinkage, low density, low water absorption and low flammability. In order to make epoxy foams, suitable foaming agents are required. The foaming agents may be chemicals such as carbonates, bicarbonates, hydrazides and the like which decompose during exothermic reactions and liberate gases. The chemical agents may also react with resins / hardeners and release the gases necessary for the foaming action. Foaming agents can also be physical agents such as toluene, fluorocarbons and the like which simply vaporize during exothermic reactions and the liberated vapors help in forming foam structures. Chemical surfactants also play important roles in mixing or dispersing of foaming agents, foam cell sizes and structures. Surfactants may be silicon based or polyol based materials. Micronised inert fillers of particle size in nanometers are also very important to control cell size, cell structure, and foam density by nucleating effects. Higher concentration of fillers also helps in reducing cost and exothermic temperatures. Processing of epoxy foams is a challenging task and needs synchronization of several parameters such as rheology of the mix, curing rate, and rate of reaction of foaming agents. An appropriate rise in the viscosity during reactions allows formation of uniform cell structures. Too low and/or fast rise in the viscosity restrict the development of foam structures and that may collapse completely. Too fast and/ or too slow reactions between resins and curing agents also spoil the network and cause the foams to be irregular, in appropriate in density, and with disturbed cell structures. The density of the foam is dependent on several factors such as the selection of resins, hardeners, types and amount of foaming agents, fillers, and processing parameters like temperature, mass of the mix, and mold shapes and sizes. Epoxy foams with density up to 170 kgs/m3 are reported with silicon type blowing agents. US patent no. 6110982 discloses epoxy foam and a process for the preparation of the same. This epoxy foam comprises a resin, a curing agent, at least one blowing agent, at least one surfactant and optionally at least one filler and also a process for making the same. In this invention, an epoxy foam is prepared with admixing a plurality of resins with a plurality of curing agents, a surfactant and blowing agent, whereby a foam able mixture is formed a at a temperature greater than the boiling temperature of the blowing agent where this mixture is foamed and cured. US patent no. 4546118 discloses an epoxy foam product which is produced by frothing in an intensive mixer. An epoxy functional reactant stream and a curing agent stream in the presence of a surfactant and gaseous frothing agent. In this patent, the blowing agent used is an inert gas which is difficult to handle and also increases the number of steps of the process. Objects of the invention One of the objects of the present invention is to provide a process for preparation of epoxy foam of varying density. Another object of the present invention is to provide a process for preparation of epoxy foam which is economical. Yet another object of the present invention is to provide a process for preparation of epoxy foam which has improved mechanical properties Yet another object of the present invention is to provide a process for preparation of epoxy foam which has improved electrical properties. Yet another object of the present invention is to provide a process for preparation of epoxy foam which has improved adhesion properties like low shrinkage and low water absorption. It is also an object of the present invention to provide a process for preparation of epoxy foam whereby the reactants are easily handlable and the parameters are easily controllable Brief description of the drawings FIG 1 & 2 shows a process flow diagram for a preferred embodiment of the present invention for preparation of reaction resin. FIG 3 shows a process flow diagram for a preferred embodiment of the present invention for preparation of foam resin. FIG 4 shows a process flow diagram for a preferred embodiment of the present invention for preparation of foam resin with varied ratio of foam resin to foaming agent. FIG 5 & 6 shows a process flow diagram for a preferred embodiment of the present invention for preparation of foam hardener. FIG 7 shows a process flow diagram for a preferred embodiment of the present invention for preparation of a vertical aluminum foam mold. FIG 8 shows a process flow diagram for a preferred embodiment of the present invention for preparation of a horizontal tray foam mold. FIG 9 shows a process flow diagram for a preferred embodiment of the present invention for preparation of a pan coated Teflon mold. FIG 10 shows a PFD for a preferred embodiment of the present invention for preparation of foam block. Detailed description of the invention In accordance with the present invention, there is provided a process for the preparation of epoxy foam of varying density by the reaction of a mixture of hydroxyl groups of epoxy resins and hydrogen silicon, a foaming agent with a surfactant, a filler and a curing agent. In the present invention epoxy foams of varying density between 80 kg/m3 to 600 kg/m3 is formed by varying the amount of foaming agent and processing temperature in molds of different size and shape. The epoxy foam prepared according to this invention can be used as an adhesive, encapsultant and as a core material in light weight structural composites. Typically, a Bisphenol - A based liquid epoxy resin is taken in a reaction vessel and mixed with appropriate quantity of a foaming agent. Preferably, the epoxy resin is diglycidyl ether of Bisphenol-A, and the foaming agent is a hydrogen silicon based compound like methyl hydrogen polysiloxane. This mixture is agitated at 500 - 600 rpm to achieve a homogeneous mix. The mixing is continued till the solution turns milky. This milky solution is heated to a temperature of about 70 -80 degree C and stirred continuously. The stirring is further continued by incresaing the speed to about 800 - 2000 rpm to achieve a reaction temperature of 150 - 190 degree C. This is continued for 3 - 4 hours till froth is formed. The reaction mixture is cooled to an ambient temperature and the froth and bubbles are skimmed off to obtain the reaction resin as shown in FIG 1 and 2. This process of mixing resin with the foaming agent takes about 1 - 7 hrs. The reaction resin obtained above is charged into a reaction vessel along with appropriate quantities of a surfactant, a filler and optionally a toughening agent. Preferably the surfactant is a polyol, which is a block copolymers of polypropylene glycol and polyethylene glycol and the filler is hydrophilic fumed silica of different bulk densities. Varying level of filler is added in the foamed resin for maintaining the viscosity of the foam resin. Typically, the toughening agent is selected from the group consisting of polyurethane acrylates, acrylate monomers and their blends like HDDA monomer. These reactants are mixed at a speed of 80 - 150 rpm for 8 - 15 minutes to form a homogeneous mixture of foam resin as shown in FIG 3. Optionally, an additional foaming agent may be added to the foam resin formed above to obtain a foam resin of varying density as shown in FIG 4. Foam hardener or the curing agent is prepared separately and then added to the foam resin to obtain a foam block. The curing agent is prepared by making an aliphatic amine adduct with bisphenol - A epoxy resin and accelerating by adding appropriate quantity of bisphenol - A. Typically, an appropriate quantity of trimethylene hexamethylene diamine (TMD) with or without polyamide (Versamid 140) along with an appropriate quantity of bisphenol -A epoxy resin is charged into a reaction vessel. These two reactants are mixed thoroughly at a speed of 200 - 400 rpm and are heated to about 70 - 80 degree C for about 1 - 2 hours. The resultant mixture is accelerated by adding a further appropriate quantity of bisphenol -A epoxy resin with further stirring for 20 - 30 minutes till the bisphenol -A epoxy resin is dissolved in the resultant mixture. This mixture is then cooled to ambient temperature to obtain the hardener resin as shown in FIG 5 and 6. Foam mold is then prepared of different size and shape as shown in FIG. 7, 8 and 9. Foam blocks are prepared by mixing the foam resin and the hardener resin and pouring the resultant mixture in a hot foam mold of selected size and shape. Firstly, the pot life and foaming behavior of mixture of foam resin and hardener resin is tested by taking a sample in a 150 ml paper coffee cup. Preferably the ratio of foam resin to hardener resin in the sample is 100:20-25 by weight. Pot life or foaming time is observed at 70 deg. C between 10-20 minutes and density of 100 - 200 kg/m . Variable density, 200 to 800 kg /m is achieved by changing amount of foaming agent and surfactant. Thereafter, to prepare the foam blocks, a foam resin to hardener resin ratio of 100: 20-25 is charged into a reaction vessel and mixed thoroughly at 600 - 700 rpm for 2 - 8 minutes. The resultant mixture is poured into a hot mold at a temperature of 60 - 80 degree C and transferred to an oven for further curing for 80 - 90 min. The mold is allowed to cool to an ambient temperature and demolded to obtain a hard uniform foam block is obtained. Foam density is determined according to ISO 845. The foam block was sanded to remove silicon grease on the surface and cut in to a size of 100 x 100 x 25.4 mm. The weight and volume of the foam sample were measured to calculate the density. Post curing is performed at 60 - 80 degree C for a period of 10-15 hours in air circulatory oven. A foam block of density 100-200 kgs/m is obtained and tested for mechanical, electrical and thermal properties Compression test is performed in accordance with ISO 844. Specimens, foam was cut to 30 mm square by 25.4 mm thick. The specimens were compressed between two stainless steel plates, and the load was applied with a crosshead speed of 2.5 mm/min. Further, specimens were tested as per ASTM and ISO test standards for mechanical, electrical and thermal properties. The properties thus achieved are illustrated in table 1. Table 1 Typical Performance Properties Mechanical Property Unit Test Method Value Foam 1 Foam 2 Foam 3 Nominal Density gm/cc ISO 845 0.25-0.30 0.35-0.40 0.45-0.50 Compression StrengthCompression modulus MPaMPa ASTMD 1621 4.0-4.5 330-360 9.0-9.5 650-700 12.5-13.0 900-950 Tensile strength Tensile Modulus MPa MPa ASTM D1623 3.5-4.5 170-200 7.0-8.0 250-300 9.0-10.0 300-400 AdhesionstrengthSteel-Steel, 0.5mm MPa ASTM D1002 4.0-5.0 6.5-7.5 10.0-11.0 Glass Transition Temp.( Tg) °C DSC 90-95 90-95 90-95 Electrical Property Unit Test Method Value Foam 1 Foam 2 Foam 3 Dielectric constant (1 MHz) - IEC 60250 1.4-1.5 1.5-1.6 1.8-1.9 Dissipation factor (1 MHz) - IEC 60250 0.003-0.005 0.008-.0.010 0.010-0.013 VolumeResistivity(500 V) Ohm-cm IEC 60093 1015 1015 1015 SurfaceResistance(500 V) Ohm IEC 60093 1013 1013 1013 Dielectric Strength KV/m m IEC 60243 4.0-4.5 4.5-5.0 5.5-6.0 In accordance with this invention the product formed from the reaction mixtures act as in-situ surfactants and helps in the dispersion of additional foaming agents and maintains uniform cell sizes in the foam structures. The modification of epoxy resins with polyurethane - HDDA solution provides a cross link reactions with amine hardener and improves mechanical strength of low density foam considerably. Epoxy foams up to 170 kgs/m3 are reported with silicon type blowing agents whereas, in the present invention it is demonstrated that it is possible to prepare epoxy foams up to 80 kgs/m3 density with uniform cell size and high mechanical strength. While considerable emphasis has been placed herein on the specific structure of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation

Documents:

2587-MUM-2007-ABSTRACT(21-10-2008).pdf

2587-MUM-2007-CLAIMS(21-10-2008).pdf

2587-MUM-2007-CLAIMS(AMENDED)-(29-10-2012).pdf

2587-MUM-2007-CLAIMS(MARKED COPY)-(29-10-2012).pdf

2587-MUM-2007-CORRESPONDENCE(16-4-2009).pdf

2587-MUM-2007-CORRESPONDENCE(21-10-2008).pdf

2587-MUM-2007-CORRESPONDENCE(24-9-2010).pdf

2587-MUM-2007-CORRESPONDENCE(3-2-2009).pdf

2587-mum-2007-correspondence-received.pdf

2587-mum-2007-description (provisional).pdf

2587-MUM-2007-DESCRIPTION(COMPLETE)-(21-10-2008).pdf

2587-MUM-2007-DRAWING(21-10-2008).pdf

2587-mum-2007-drawing(27-12-2007).pdf

2587-mum-2007-drawings.pdf

2587-mum-2007-form 1(25-6-2008).pdf

2587-MUM-2007-FORM 18(16-4-2009).pdf

2587-mum-2007-form 2(21-10-2008).pdf

2587-MUM-2007-FORM 2(TITLE PAGE)-(21-10-2008).pdf

2587-mum-2007-form 2(title page)-(27-12-2007).pdf

2587-MUM-2007-FORM 3(24-9-2010).pdf

2587-mum-2007-form 3(27-12-2007).pdf

2587-MUM-2007-FORM 3(3-2-2009).pdf

2587-MUM-2007-FORM 5(21-10-2008).pdf

2587-mum-2007-form-1.pdf

2587-mum-2007-form-2.doc

2587-mum-2007-form-2.pdf

2587-mum-2007-form-26.pdf

2587-mum-2007-form-3.pdf

2587-MUM-2007-PETITION UNDER RULE 137(29-10-2012).pdf

2587-MUM-2007-REPLY TO EXAMINATION REPORT(29-10-2012).pdf