WO2005047393A1

WO2005047393A1 - Reactive hot melt adhesive

Info

Publication number: WO2005047393A1
Application number: PCT/EP2004/012476
Authority: WO
Inventors: Franciscus J. T. Krabbenborg; Philippe Belot; Jacobus Jan Houg; Martine Rousse
Original assignee: Dow Global Technologies Inc.
Priority date: 2003-11-11
Filing date: 2004-11-04
Publication date: 2005-05-26

Abstract

A reactive hot melt composition having a softening point of at least 50°C comprising an epoxy resin having a softening point of at least 50°C, at least one random interpolymer of ethylene and at least one olefinically unsaturated carboxylic acid comonomer, olefinically unsaturated carboxylicl acid ester comonomer, or vinyl ester comonomer. The epoxy resin is such that the composition may be caused to adhere to a surface by heating the composition to an application temperature in excess of the softening point of the composition, to form a melted adhesive composition. The composition is thereafter curable by heating to a curing temperature to cure the epoxy resin, the curing temperature being in excess of the application temperature. Methods for making the composition are also disclosed, as well as a method for adhering a first component to a second component using the compositions.

Description

Reactive Hot Melt Adhesive

This invention relates to adhesive compositions, and in particular to compositions of the type able to form an initial bond between the parts to be bonded such that the parts can be handled after the initial bonding process, and which subsequently form a permanent bond by a reactive curing process. Such adhesives are generally known as reactive hot melt adhesives (RHMAs). In the automotive industry, RHMAs may find application, for example as "sealer" adhesives for use in an automotive body shop or paint-shop (for example to protect weld-points or flange/gaps from corrosive attacks and humidity, water, dust particles intrusion), or to bond two metal or plastics substrates and/or to increase damping or stiffening.

Currently, these functions are usually fulfilled by compositions with paste-like or liquid consistency, with a range of viscosity depending on the application. Generally, existing reactive compositions are based on rubber, PVC, epoxy resins, acrylics or mixtures thereof. However, these liquid adhesives have a number of problems or difficulties associated with them. In particular, liquid adhesives may be difficult or messy to handle or apply, may be flammable, may present environmental concerns involving volatile organic compounds ("VOCs") and solvent recovery, or may present toxicological concerns. When used to adhere steel and or aluminium, liquid and low viscous adhesives have a tendency to "bleed through" other areas which can . destroy the visible decorative surface. The "bleed through" problem associated with liquid adhesives can be solved to some extent using thickeners. Often, due to its high viscosity, the paste needs to be heated to allow efficient application, narrowing the utilization window of the formulated paste.

It is known to utilize liquid epoxy adhesives as Reactive Hot Melt Adhesives, for example BETAMATE 1493 from The Dow Chemical Company, to adhere steel and other substrates including aluminium substrates. WO02/50184 discloses a vibration damping composition which is typically in the form of a paste comprising an epoxy resin, a crosslinking agent and a thermoplastic alpha-olefin/vinyl aromatic interpolymer. For use in body-shops in the automotive industry, where parts can be oily, compositions need to have enough viscosity/strength after application in order to withstand the panel degreasing and pre-treatment process (so called wash-off resistance to dipping and jet-spray of water/alkaline/dispersion solutions).

Even the high viscosity level of pasty compositions is often not sufficient to guarantee resistance to wash-off in critical areas of the body, does not give enough green strength, and can not prevent de-localisation of the adhesive during the body- shop process if the part is compressed.

A post-application pre-curing step prior to the final cure, to eliminate the above mentioned issues would affect the cycle time, space requirement, and quality of the parts produced.

It would be desirable to provide materials which do not have the handling difficulties of viscous liquid or pasty compositions, but give good wash-off and squeeze resistance, for example by providing a hot melt adhesive in the form of pellets or sheets.

WO-A-0172922 discloses a so-called "dryblend" adhesive, comprising thermoplastic polymer particles. Such adhesives require to be shipped in the absence of air and moisture, and require high shear melting before application. As soon as such blending has taken place, the curing action begins, and therefore the adhesives must be homogenised immediately before use. They are applied immediately after they are homogenised, because after homogenisation, the reaction is initiated and the batches only have a limited pot life. The homogenised composition does not have the lapshear strength required for use as so-called "semi-structural" adhesives. A "semi- structural" adhesive is generally considered to be one with a Lap Shear strength of at least 4 MPa.

DE3938376 discloses a one component heat-curing powder adhesive comprising a mixture of solid and liquid epoxy resins and a polyvinyl acetate plastomer. This adhesive is useful for bonding friction linings with steel, especially in brake and clutch linings for vehicles. A two-step process is used to produce the adhesive, and the resulting composition is not storage stable under pressure, such as when it is stored in large quantities.

US4,517,340 discloses an adhesive composition comprising a thermoplastic polyamide, a thermoplastic copolymer of an alkene with an unsaturated ester of an alfanol and a carboxylic acid, and a thermoplastic epoxy resin. These compositions cure when heated to the melting or softening point of the components and therefore will cure on application. These compositions are not suitable for forming an initial bond and subsequently curing the composition to form a permanent bond.

We have now discovered a reactive hot melt composition which is a solid at ambient temperature (20°C), and which has excellent initial adhesion as well as excellent properties of the final cured composition. The composition can be formulated into free-flowing pellets or beads, which can be heated to form an extrudable mass, and thereafter applied using conventional extrusion techniques. It can also, if desired, be formulated into sheets or films for use between two parts to be adhered. The composition therefore overcomes many of the difficulties encountered by prior art reactive hotmelt adhesives for "semi-structural" applications used in car body construction.

According to a first aspect of the invention, there is provided a reactive hot melt composition having a softening point of at least 45°C, preferably at least 50°C comprising: an epoxy resin having a softening point of at least 45°C, preferably at least 50°C, and at least one random inteφolymer of ethylene with at least one additional comonomer, which is an olefinically unsaturated carboxylic acid or anhydride, an olefinically unsaturated carboxylic acid ester, or a vinyl ester.

The epoxy resin is such that the composition may be caused to adhere to a surface by heating the composition to an application temperature in excess of the softening point of the composition, to IOΠΠ. a eitβ auuesive composition. Tue composition, is thereafter curable by heating to a curing temperature to cure the epoxy resin, the curing temperature being in excess of the application temperature. Preferably, the composition maybe melted, extruded and applied to a surface at a temperature of from 110 to 140°C without curing, and the composition is thereafter curable by heating to a curing temperature of greater than 140°C, preferably greater than 180°C for a time of more than 5 minutes.

The term "softening point" as used herein is intended to refer to "Mettler Softening Point", as determined by ASTM D3104-99

Preferably, at least 90 percent by weight of the composition consists of the epoxy resin, the at least one random inteφolymer of ethylene, optionally a polyester, and optionally a curing agent. More preferably, the composition consists essentially of the epoxy resin, the at least one random inteφolymer of ethylene, optionally the polyester and optionally the curing agent. In a particularly preferred embodiment, the composition consists essentially of the epoxy resin, the at least one random inteφolymer of ethylene, the curing agent and optionally the polyester.

The ethylene inteφolymer serves to increase and control the viscosity of the composition at low shear rates, and so increase polymer bead stability both during pellet formation and on application to a surface for bonding at 100 to 150°C.

The comonomer is preferably selected from acrylic acid, methacrylic acid, methylacrylate, methylmethacrylate, ethylacrylate, ethylmethacrylate, butylacrylate, butylmethacrylate, vinyl acetate, maleic anhydride, and/or glycidyl methacrylate. The ethylene inteφolymer may be, for example, an ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, an ethylene-acrylic acid-methacrylic acid teφolymer, an ethylene- vinyl acetate copolymer, an ethylene-methyl acrylate copolymer an ethylene-ethyl acrylate copolymer, an ethylene-maleic anhydride copolymer, an ethylene-glycidyl methacrylate copolymer, an ethylene-vinyl acetate- maleic anhydride teφolymer or ethylene-ethyl acrylate-glycidyl methacrylate teφolymer.

The preferred ethylene inteφolymers are made by free-radical polymerisation and contain 20-30% of a comonomer selected from alkyl acrylates, alkyl methacrylates, vinyl esters, olefinically unsaturated carboxylic acids, glycidyl methacrylate and maleic anhydride.

The ethylene inteφolymer maybe used in a total an amount of from 10 to 60 %, preferably from 10 to 30 %, more preferably from 10 to 20 % by weight, based on the total composition.

When the ethylene inteφolymer is an ethylene-acrylic acid (EAA) copolymer, the copolymer preferably contains from 10 to 30%, preferably 20 to 30% by weight acrylic acid. Preferably the EAA has a melt flow rate (MFR), when measured according to ISOl 133 at 190°C and 2.16 kg, of more than 100 g/10 (more preferably from 300 to 1300g/10 min). Examples of suitable commercially available ethylene- acrylic acid or ethylene-methacrylic acid copolymers are Primacor™ 5980 and 5990 from The Dow Chemical Company, Nucrel™ from Dupont and Escor™ from Exxon Mobil Chemical. Particularly preferred is Primacor™ 5990.

When the ethylene inteφolymer is an ethylene-methacrylic acid (EMAA) copolymer, the copolymer preferably contains from 10 to 30%, preferably 20 to 30% by weight methacrylic acid. The EMAA preferably has a MFR, when measured according to ISOl 133 at 190°C and 2.16 kg, of from 300 to 1300g/10min. An example of a suitable commercially available ethylene-methacrylic acid copolymer is Nucrel™ 2940 from Dupont. When the ethylene inteφolymer is an ethylene-vinyl acetate copolymer, the copolymer preferably has a vinyl acetate content of greater than 20%, preferably from 30 to 40% by weight. The EVA copolymer preferably has a MFR when measured according to ISO 1133 at 190°C and 2.16kg of greater than 50 g 10min., more preferably from 200 to 600 g/min. Suitable commercially available EVA copolymers include Evatane™ from Atofina and Escorεne™ from Exxon Mobil. Particularly preferred are Escorene™ UL05540 (MFR of 60g/10 min.) and Evatane™ 33400 (MFR of 350 to 450 g/10 min. and a vinyl acetate content of 30%).

When the ethylene inteφolymer is a copolymer having a monomer selected from the acrylate, or methacrylate, the inteφolymer has an acrylate content of greater than 18%, preferably 20-30%. Suitable inteφolymers are, for example, ethylene- methylacrylic ester copolymers, ethylene-ethylacrylic ester copolymers, or ethylene- butylacrylic ester copolymers. Commercially available examples of suitable inteφolymers include Lotryl™ from Atofina, Enable™ and Optema™ from Exxon Mobil Chemical and Amplify EA series from The Dow Chemical Company (Amplify EA 100, 101, 102 and 104).

Suitable teφolymers are ethylene- vinyl-acetate-maleic anhydride polymers (for example Orevac T™ ), ethylene-acrylate-maleic anhydride polymers (for example Lotader™ AX4720), ethylene-acrylate-glycidyl methacrylate polymers (for example Lotader™ AX8900 and AX8950) and teφolymers containing acrylate and/or methacrylate units and/or methyl acrylate units (for example Escor™ teφolymer from Exxon Mobil Chemical).

Methacrylate and/or acrylate-containing polymers, for example ethylene-acrylic ester- glycidyl methacrylate polymers, preferably contain at least 25% by weight of ethylenically unsaturated monomer units and have an MFR when measured according to ISO 1133 of less than 10 g/lOmin. at 190°C and 2.16kg. Preferred commercial polymers include Lotader™ AX 8900 which has a MFR of 6 g/10 min. and 32% by weight of ethylenically unsaturated monomer units and AX4720 which has a MFR of 7 g/10 min. and 30 % by weight of ethylenically unsaturated monomer units. Iono er resins of carboxylic copolymers (for example Surlyn resins from Dupont) with sodium, zinc, lithium or other inorganic salts have been found to be useful optional ethylene copolymers for use in the composition.

In addition to the ethylene inteφolymer. the composition may also include minor amounts of additional polymers and copolymers, for example non-random copolymers, e.g., grafted copolymers. Examples of such grafted copolymers which may be used are maleic anhydride grafted elastomers with a high content of maleic anhydride, for example having a maleic anhydride content of from 0.5 to 2 weight %. Suitable commercial examples of maleic anhydride grafted elastomers include Lotader™ 8200, Lotryl™ 35BA, Lotryl™28BA 175 and Orevac™teφolymer EVA 9305 from ATO, Exxelor™ VA1801 (Semi crystalline) and Exxelor™ 1803(Amoφhous) from Exxon, Fusabond™ N series: MF416D, MN493D, MN494D and MO525D and Fusabond ™ C series MCI 90D and MC250D from Dupont.

Other polymers which may be useful in addition to the ethylene inteφolymers include other olefϊnic and or styrenic base adhesive polymers which have carboxylic acid functionality and/or anhydride functionality. Examples include polybutylene- maleic anhydride, polybutylene-graft-maleic anhydride, polypropylene-graft-maleic anhydride, and styrenic-butadiene block copolymer-graft-maleic anhydride.

Such additional polymers and copolymers are preferably present in an amount of from 5 to 10 percent, based on the total composition.

Polyamide is detrimental to the composition as it reduces the curing temperature of the composition such that the composition will cure at the application temperature. Accordingly, the composition preferably comprises less than 10 percent by weight of a thermoplastic polyamide and more preferably is substantially free of thermoplastic polyamide. The ethylene inteφolymer(s) should preferably have a melting point less than 105°C and preferably less than 95 °C. Additionally the inteφθlymer(s) should preferably have a melt index of at least 2 g 10 minutes, more preferably at least 5 g/10 minutes and most preferably at least 20 g/10 minutes when tested according to ASTM D-1238 (190°C, 2.16kg). If the melt index of the ethylene inteφolymers is too low, it will result in insufficient flow and poor wet-out of the composition at application.

Where acrylic acid monomers are present in the ethylene inteφolymer, it is preferable that the ethylene inteφolymer having a relatively high melt index. This is because of the reaction between carboxylic acid and epoxy resin which occurs during compounding and results in an increase of viscosity.

The ethylene inteφolymers are chosen to allow high levels of epoxy resin (up to 90% by weight), along with the optional curing agent and polyester to be used, and the yet still be able to produce the composition in a one step mixing process

The composition includes an epoxy resin which has a softening point of at least 50°C, and thus is solid at ambient temperature (20°C). The solid epoxy resin preferably constitutes from 40 to 90%, more preferably from 60 to 80 % and most preferably from 70 to 80 % based on the total weight of the composition. The use of a material with a softening point of at least 50°C enables the composition to be produced in the form of hard granules which are non blocking, i.e., free flowing at room temperature. The solid epoxy resin may be any resin known by those skilled in the art having one or more epoxy groups, and may include aromatic and aliphatic types, and mixtures thereof.

Preferred aromatic epoxy resins are epoxy resins having bisphenol moieties in the backbone of the epoxy resin. Representative of preferred bisphenol resins useful in this invention are those disclosed in U.S. Patent No. 5,308,895 at column 8, line 6 and represented by Formula 6. The most preferred aromatic epoxy resins are bisphenol-A based epoxy resins and bisphenol-F based epoxy resins. Bisphenol-A based epoxy resin are preferred. Particularly preferred epoxy resins include resins based on diglycidyl ethers of Bisphenol A, for example the products supplied by The Dow Chemical Company under the Trade Marks D.E.R. or DERAKANE (in particular D.E.R. 662) and Novalac modified epoxy resins, for example, products supplied by The Dow Chemical Company under the Trade Mark D.E.N.

In addition to the solid epoxy resin, minor amounts of a further epoxy resin with a lower softening point may also be employed, provided that the overall softening point of the composition is not less than 50°C. Examples, of such additional epoxy resins are the reaction product of DGEBA, bis-A and a fatty acid and or a dimer fatty acid derived from a natural oil such as for example linseed, tall, or castor oil fatty acids. Those resins are typically highly viscous liquids to solids at room temperature. Processes for making such resins are described in column 8, line 6 of U.S. Patent No. 5,308,895. Such fatty acid modification of a bisphenol-A epoxy resin, as well as other known modifications, permit the adjustment of the mechanical performance of the final cured product

Other epoxy resins which may be used either alone or in combination with bisphenol-A based epoxies , those are for example, so called novolac epoxy resins, reaction products of epichlorohydrin with a novolac resins (e.g. type D.E.R.* 642U, available from The Dow Chemical Company ), and vinylester resins, (i.e., the reaction of product of acrylic acid/methacrylic acid with an epoxy resin). Example are Derakane* grades from The Dow Chemical Company.

Further examples of suitable epoxy resins are bisphenol-A type solid epoxy resins might be modified by aliphatic epoxy resins derived from containing polyether chains. Such epoxy resins are preferably prepared from one or more alkylene oxides. Representative examples of such aliphatic epoxy resins are those described in U.S. Patent No. 5,308,895 at column 8, line 9 and formula 9 and the description thereof following. Preferably, the aliphatic epoxy resin contains in its backbone ethylene oxide, propylene oxide or a mixture thereof.

The epoxy resin may also include a mixture of a bisphenol-A type epoxy resin and an aliphatic epoxy resin. Example of such mixtures are the materials described in WO 99/16840. The more flexible aliphatic epoxy resin is used in combination with the more rigid bisphenol-A based epoxy resin in a ratio which provide the desired the glass transition temperature of the final cured product.

The aliphatic epoxy resin can be included as a reactive partner during the manufacturing process of the bisphenol-A based epoxy resin together with the DGEBA and bisphenol-A reactants. In this case aromatic-aliphatic hybrid epoxy resin structures are obtained.

The number average molecular weight (M_n) of the bisphenol-A based epoxy resin is preferably greater than 700, more preferably greater than 800, and more preferably still, greater than 900. Such resins show decreased tendency to skin-sensitizing. Generally M_n is in the range of from 700 to 5000, preferably from 800 to 5000, more preferably from 900 to 3000, and more preferably still from 900 to 2000.

The molecular weight of the additional (normally aliphatic) liquid epoxy resin is generally from 300 to 4000, preferably from 500 to 2000, and more preferably from 500 to 1000.

The epoxy resin is preferably one which is non-irritating and non-sensitizing by skin contact.

A curing agent (also referred to as a cure initiator) may be used to cure the epoxy resin between 180 to 190°C thereby developing final adhesive strength. Curing agents useful in the present invention include amines, amides, amidoamine, onium halides, boron trifluorides or hydrazides. Preferred curing agents are dicyandiamine (for example Dyhard 100S supplied by SKW Trostberg) and crosslinking catalysts (for example 2-methylimidazole) and TDI-uron latent accelerators (e.g., Dyhard UR 500 supplied by SKW Trostberg). The curing agent is preferably used in an amount of from 3 to 5 weight % of the total composition. The amount of curing agent to be used depends on the EEW of the epoxy resin and can readily be calculated by on of skill in the art. For example, when the curing agent is dicyandiamine the amount can be calculated using the formula: Mass of epoxy EEW = 4.5*Mass of dicyandiamine/82.

Curing accelerators or catalysts can be used in addition to or instead of the curing agent to lower the curing temperature of the reactive hotmelt composition. Preferred curing accelerators are imidazoles and modified imidazoles, such as 2-methylimidazole, onium halides, such as tetrabutyl ammonium bromide, tetrabutyl phosphonium bromide or ethyltriphenylphosphonium acetate and epoxy amine adducts such as Ajicure My-24 available from Ajinomoto. A particular preferred accelerator is 2-methylimidazole (for example Dyhard UR500).

The curing initiator can act as a latent catalyst in the reactive hotmelt composition, and is effective to accelerate the curing reaction of the epoxy resin and lower the curing reaction, for example to 140-150°C. The curing accelerator is preferably employed in an amount of from 0.5 to 1 weight % of the total reactive hotmelt composition.

Evaluation of curing kinetics, cure initiation temperature, extent of cure, and polymeric viscosity changes can be accomplished using dynamic mechanical thermal analysis. A melt rheometer, such as a Brabender Plasticorder Rheometer or a Haake Rheometer can be used to monitor rheological changes with respect to time and or temperature. A Rheometrics RDS-2 parallel plate rheometer can be utilized with a dynamic temperature ramp to evaluate melt viscosity versus increasing temperature. A non-curing composition will typically decrease in viscosity as temperature is increased, while a curable composition will initially exhibit a viscosity reduction with increasing temperature until the cure reaction is initiated, whereupon the viscosity will increase as the temperature (or time) is increased. The composition may preferably also comprise from 0 to 40 % based on the total weight of the composition, of a polyester. The addition of a polyester resins can serve to improve the adhesion of the composition, in particular to steel substrates, both before and after curing. The polyester is preferably poly-e-caprolactone (for example those available from The Dow Chemical Company under the tradename Tone™, in particular those sold under the designations Tone P-737, P-752, P-767 and P-787) Tone P-767 is particularly preferred. An alternative preferred polyester is polyepoxyundecylenic acid (PEUDA). The polyester resin serves to improve the adhesion of the composition, in particular to steel substrates, at temperatures above 70-80°C and also increase the storage stability of the reactive hotmelt granulate at room temperature. Preferably the polyester is used in an amount of from 5 to 20 weight %, most preferably 5 to 10 weight %

The composition of the invention optionally also contains a filler. The filler serves to decrease the tendency of the molten material to form threads and tails when the molten material is applied to a surface by extrusion. Certain fillers can also increase the viscosity at low shear rates by producing a thixotropic effect. The filler may preferably be employed in an amount of from 0 % to 40 %, more preferably from 0 % to 25 %, and most preferably from 0 to 15 %, by weight, based on the total composition. The filler is typically an inorganic mineral, such as calcium carbonate, magnesium silicate (talc), or calcium silicate (wollastonite). The use of basic materials such as calcium carbonate, which are capable of neutralising any acids which may be present in the resin, is desirable, as such materials act as corrosion inhibitors. Suitable fillers are precipitated calcium carbonate or ground calcium carbonate, magnesium silicate, and calcium silicate.

Compositions of the above type have been found to have good initial adhesion properties to steel, particularly oily steel, whilst being capable of formulation into pellets which can be conveniently handled. They can be easily melted and applied, using conventional extrusion apparatus.

The compositions of the present invention are useful as RHMAs, in particular as adhesives for oily steel parts in car assembly plants, and have the advantage that because they are solids ad ambient temperatures, they maybe shipped and stored in a more convenient manner than conventional liquid or pasty resins.

According to a second aspect of the invention, there is provided a method of preparing a reactive hot melt composition comprising compounding together a solid epoxy resin, and at least one random inteφolymer of ethylene as described above, together with, if desired, one or more of the optional additional ingredients referred to above. The compounded composition may be pelletised to produce a dry free-flowing material.

The composition may generally be prepared by compounding the ingredients using any conventional form of compounding apparatus, for example single screw extruders, twin screw extruders, planetary extruders, ring extruders, batch internal mixers, kneaders or mixers such as those sold by Banbury, Farrell, Buss, or Kobe. In order to produce the compositions of the present invention, the mixing process preferably has a maximum processing temperature of less that 150°C, more preferably less than 130°C and a mixing time of less than 5 minutes, more preferably less than 2 minutes. The processing temperature and mixing time are important to ensure that the epoxy resin has not been activated during the production of the RHMA composition.

In an alternative embodiment all of the components with the exception of the curing agent can be compounded initially to form a pre-blend and then the curing agent may be added separately in a hotmelt extrusion or hot melt film extrusion step. However, the more preferable method of producing the reactive hot melt adhesive is by compounding all of the ingredients together at process conditions such that the curing reaction does not take place until a the heat activation step. In the preferred process, the ingredients are melt blended and compounded in a Twin Screw Extruder (TSE) with a residence times of less than two minutes in the extruder and subsequently pelletised under water using a Gala™ Underwater granulator. The compositions according to the invention generally have excellent shelf life, and can be processed as hotmelt adhesives in a hotmelt extruder or extruded into a reactive hotmelt film at temperatures above the melting point of the composition (typically 90°C) and below the cure activation temperature of the composition (typically 180°C). Extruding the reactive composition at a temperature below the normal curing temperature of the composition minimizes the amount of curing that takes place during extrusion.

The extruded adhesive bead or film can be applied at a higher temperature than the curing temperature, causing the adhesive to cure.

Pelletised compositions of the present invention are free flowing at room temperature but may be transported in large containers, in which temperatures can reach 40 to 50 °C. In order to improve the free-flowing properties of the pellets, it may be desirable to apply a coating. The pellet coating is preferably a powder coating comprising the filler, applied to the composition in an amount of from 0.2 to 2.0 % based on the weight of the composition. Optionally an anti-cluster additive maybe incoφorated in the water into which the pellets are extruded. The water additive may be a siloxane oil (for example those supplied under the trade Marks DC290 or DC200/350 from Dow Corning), an oxyalkylate (for example EC9092A™ from Nalco Exxon) or a water dispersion of polyethylene (for example Hordammer PE 03™ from Hoechst). The application of 0.5 to 2 % talc results in free-flowing pellets at temperatures of up to 45°C

In a further aspect of the present invention the composition may be processed to form a film, for example by melt compounding the ingredients using an extruder fitted with a film die. The entire mix is melt blended and extruded directly into reactive hotmelt film. As before, the resulting film can be applied onto steel as steel coating and stored prior to use in a particular application.

Granules and films of the present invention are non blocking and storage stable. By storage stable, it is meant that the granules can be stored at room temperature (22.2°C (72°F), 50 percent relative humidity) for long periods of time until needed in a particular application, without spontaneously blocking or curing.

In a fourth aspect of the invention, there is provided a method of adhering a first component to a second component, comprising the steps of melting a composition as described above, contacting the first and second components with the melted composition to form an initial bond between the components; and applying heat to cure the composition.

Preferably, the composition is applied to a substrate at a temperature of from 110 to 140°C and is cured at a temperature above 140 °C, preferably above 180 °C for a time of more than 5 minutes.

The composition of the present invention is preferably applied to a substrate by means of an applicator which limits the temperature and time exposure of the composition as the composition is applied to the substrate. Conventional RHMA equipment can be used if the temperature of application is less than 150°C, preferably less than 130°C and the time at the temperature of application is less than 10 minutes, preferably less than 3 minutes. A preferred application system uses a heated pumping screw equipped with an accumulator which feeds the RHMA directly onto the substrate.

When cured the compositions of the present invention generally have excellent Lap Shear Strength (LSS) (measured according to DIN EN 1465) and a strong cohesive bond strength, particularly with steel or aluminium, as determined by 180° peel strength (measured according to DIN 53282). This test is generally referred to herein as "T-Peel" strength). The preferred compositions according to the invention, after curing at 190 to 200°C for between 5 and 20 minutes, can achieve LSS values of from 4 to 30 MPa and T-Peel strengths of from 3.5 to 10 N/mm.

The cured adhesive can also provide desirable characteristics such as excellent temperature and chemical resistance, and excellent dimensional stability. In addition, the uncured adhesive bead or film exhibits significantly excellent "green strength" and "melt strength" at application temperatures, which prevents adhesive bleed through. The phrase "green strength" and the phrase "melt strength" refer to an adhesive 's bond strength and dimensional stability respectively while still in a molten state.

Adhesive beads or films of the present invention can be used to bond two pieces of steel together or bond aluminium with steel or other metals in car body construction replacing or partially replacing hem flanges and welding operations.

Examples 1 to 6

Compositions according to the invention were prepared by compounding the components shown in Table 1, in a Twin Screw Extruder (TSE) at melt temperature of 110 to 120°C with a residence time of less than two minutes, and subsequently pelletising the composition using a Gala™ Underwater granulator.

The amounts of the components used in the compositions are shown in Table 1.

TABLE 1 Example 1 2 3 4 5 6 Component Weight Percent of Component Epoxy resin 75 52 36 72 43 52 (DER 662) Ethylene Inteφolymer (Lotader 10 30 30 10 30 30 AX8900) Ethylene Inteφolymer 0 0 10 12 (Primacor 5990) Polyester resin 10 12 30 12 12 0 (Tone 767) Curing Agent 6 (Dyhard 100S)

The above compositions were processed to produce granular adhesives, having a granular particle size 2-3mm. The compositions were storage stable at temperatures of up to 30°C without blocking or becoming sticky. They could however be melted, by heating to temperatures of approximately 100°C and applied onto steel as a hotmelt adhesive and subsequently adhere steel panels before and after curing as shown in Table 2. Table 2 shows the Yield (MPa), the Elongation (%) and the T-peel strength (N/mm) before curing and T-peel strength (N/mm) and Lapshear strength (MPa) after curing.

TABLE 2

Examples_l_tg_6 Lapshear test and Peel strength

The adhesive properties ("T-peel" strength) of the compositions of Examples 1 to 6 were tested according to DIN 53253, before and after oven curing at 200°C for 20 minutes. The lap shear (LSS) test was carried out according to DIN EN 1456 after curing at 200°C for 20 minutes.

Brief details of the LSS test and the "T-peel" test are as follows.

Lap shear test: degreased steel samples were used and the shear strength test was performed at lOmm/minute. The polymer adhesive film was 1-1.5mm thick, 25 mm wide and bond line length was 10mm. Samples are cured at 200°C for 30 minutes to obtain bond line thickness of 0.5mm. The results are reported as force in Newtons/surface area.

T-peel test: again degreased steel samples were used and a peel rate of lOmm/minute. The polymer adhesive film was 1- 1.5mm thick, 25 mm wide and bond line length was 10mm. Samples are pre-cured at 200°C for 5 minutes and post cured at 200°C for 20 minutes to obtain final bond line thickness of 0.5 mm. The results are reported as force in Newton/bond line length.

Before curing at 200°C for 20 minutes the Samples are fairly brittle, in some cases too brittle for reliable testing when the epoxy level is high i.e. greater than 70%. Curing the test samples increases adhesion to steel surface from 1-2 N/mm to 3- 9N/mm as measured by the T-peel strength test, depending on the compound composition. The failure mode changes from adhesive failure to cohesive failure in the T-peel strength test after curing. Curing results in compositions having Lapshear values ranging from 4 to 30 MPa. The lapshear strength is the highest when epoxy content is the highest. Whilst the invention has been described with reference to the preferred embodiments, it is to be appreciated that many modifications and variations are possible within the scope of the invention.

Claims

1. A reactive hot melt composition having a softening point of at least 50°C comprising: an epoxy resin having a softening point of at least 50°C, and at least one random inteφolymer of ethylene with at least one additional comonomer, which is an olefinically unsaturated carboxylic acid or anhydride, an olefinically unsaturated carboxylic acid ester, or a vinyl ester, wherein the epoxy resin is such that the composition may be caused to adhere to a surface by heating the composition to an application temperature in excess of the softening point of the composition to form a melted adhesive composition, and wherein the composition is thereafter curable by heating to a curing temperature to cure the epoxy resin, the said curing temperature being in excess of the application temperature.

2. A composition as claimed in Claim 1, which also comprises an epoxy resin having a softening point of below 50°C

3. A composition as claimed in claim 1, in the form of free-flowing pellets or in the form of a film.

4. A composition as claimed in any one of the preceding claims, wherein the inteφolymer is an inteφolymer of ethylene with one or more of (meth)acrylic acid, methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, vinyl acetate, maleic anhydride, and/or glycidyl methacrylate.

5. A composition as claimed in any one of the preceding claims, wherein the epoxy resin is such that the composition is curable by heating to a curing temperature 180°C for a period of 10 minutes.

6. A composition as claimed in any one of the preceding claims, wherein the epoxy resin having a softening point of at least 50°C constitutes from 40 to 90 % based on the total weight of the composition.

7. A composition as claimed in any one of the preceding claims, wherein the composition additionally comprises a curing agent, in an amount of from 1 to 5% based on the total weight of the composition.

8. A composition as claimed in any one of the preceding claims, wherein the composition additionally comprises at least one polyester.

9. A composition as claimed in claim 8, wherein the said at least polyester includes poly-e-caprolactone or polyepoxyundecylenic acid.

10. A composition as claimed in any one of the preceding claims, wherein the epoxy resin having a softening point of at least 50°C is a diglycidyl ether of bisphenol-A.

11. A method of preparing a reactive hot melt composition adhesive composition as claimed in any one of claims 1 to 10, comprising: compounding the epoxy resin having a softening point of at least 50°C and the inteφolymer at a temperature in excess of the softening point of the composition, but below the curing temperature.

12. A method as claimed in claim 11, comprising the additional step of pelletising the compounded composition to produce a dry free-flowing material.

13. A method as claimed in Claim 11 or Claim 12, wherein the said compounding is carried out at a temperature of less than 150°C.

14. A method as claimed in any one of Claims 11 to 13, wherein the said compounding is carried out for a time of less than 5 minutes.

15. A method of adhering a first component to a second component, comprising the steps of melting a composition as claimed in any one of claims 1 to 10, contacting the first and second components with the melted composition; and applying heat to cure the composition.

16. The use of a composition as claimed in any one of claims 1 to 10 as a reactive hot-melt adhesive.