HK1116814A - Amphiphilic block copolymer-toughened epoxy resins and powder coatings made therefrom - Google Patents

Description

Amphiphilic block copolymer toughened epoxy resins and powder coatings made therefrom

The present invention relates to epoxy resin powder coating compositions modified with amphiphilic polyether block copolymers to improve the fracture resistance or toughness of the cured powder coating compositions.

Epoxy resins are typically cured with a hardener or curing agent, and after curing, these resins are known for their heat and chemical resistance. Cured epoxy resins also exhibit good mechanical properties, but they lack toughness and tend to become very brittle when cured. The lack of toughness of the resin is particularly true when the crosslink density or Tg of the resin is increased.

Recently, there have been some studies related to improving fracture resistance or toughness of epoxy resins by adding various block copolymers to the epoxy resins. Much of the previous work has focused on the use of amphiphilic diblock copolymers having an epoxy miscible block and an epoxy immiscible block, where the epoxy miscible block is poly (ethylene oxide) (PEO) and the immiscible block is a saturated polymeric hydrocarbon. Although effective in providing templated epoxy resins with an attractive combination of properties, known block copolymer materials are too expensive to be useful in certain applications.

For example, Journal of Polymer Science, Part B: polymer Physics, 2001, 39(23), 2996-. Journal of the American Chemical Society, 1997, 119(11), 2749-2750 describes epoxy systems with self-assembled microstructures created using amphiphilic PEO-PEP and poly (ethylene oxide) -b-poly (ethyl ethylene) (PEO-PEE) diblock copolymers. These block copolymer containing systems exhibit self-assembly characteristics.

Other block copolymers containing epoxy-reactive functionality in one block have been used as modifiers for epoxy resins to achieve nanostructured epoxy thermosets. For example, Macromolecules, 2000, 33(26)9522-9534 describe the use of poly (epoxyisoprene) -b-polybutadiene (BIxn) and poly (methacrylate-co-glycidyl methacrylate) -b-polyisoprene (MG-I) diblock copolymers which are amphiphilic in nature and are designed so that one of the blocks can react into the epoxy matrix upon curing of the resin. In addition, journal of Applied Polymer Science, 1994, 54, 815 describes epoxy systems with submicron dispersions of poly (caprolactone) -b-poly (dimethylsiloxane) -b-poly (caprolactone) triblock copolymers.

Although some of the previously known diblock and triblock copolymers mentioned above may be used to improve the toughness of epoxy resins, the preparation of these known block copolymers is complicated. These known block copolymers require multiple steps to synthesize and are therefore less economically attractive from a commercial standpoint.

Still other self-assembling amphiphilic block copolymers for modifying thermosetting epoxy resins (to form nanostructured epoxy thermosets) are known. For example, Macromolecules, 2000, 33, 5235-. Polyether block copolymers such as PEO-PPO-PEO triblock are also known for use with epoxy resins such as those disclosed in Japanese patent application laid-open No. H9-324110.

Japanese patent publication No. 56-28253 discloses the possible use of ethylene oxide and propylene oxide for epoxy/anhydride powder coating systems, but does not disclose the use of amphiphilic polyether block copolymers or any benefit thereof.

Epoxy resin compositions supplied to the Fusion Bonded Epoxy (FBE) powder coating industry, such as Solid Epoxy Resins (SER), are excellent at providing corrosion protection to articles such as metal pipe. However, a key drawback inherent to epoxy systems is their lack of flexibility and abrasion resistance. Thus, there remains a need to improve the toughness of epoxy resins used in powder coating applications while maintaining all other key properties of the resulting powder coating, such as modulus and Tg.

Therefore, there is a need for alternative amphiphilic block copolymers (preferably amphiphilic block copolymers containing an elastomeric polymer as one of the components) that self-assemble in a host epoxy resin on a nanometer scale, can be used to improve the toughness of epoxy resins, and do not suffer from any of the disadvantages of previously known block copolymers.

It is also desirable to provide thermosetting epoxy resin compositions for use as powder coating compositions that provide a more flexible coating while maintaining its other beneficial properties.

It is also an object of the present invention to provide a modified SER for use in powder coating applications.

One aspect of the present invention relates to a curable solid resin composition for use in powder coating compositions comprising

(a) An epoxy resin; and

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased; wherein the final resin composition is in solid form.

One embodiment of the present invention relates to an epoxy resin modified with an amphiphilic polyether block copolymer containing at least one epoxy resin miscible block segment and at least one epoxy resin immiscible block segment; wherein both the miscible block segment and the immiscible block segment comprise at least one polyether structure.

Another aspect of the present invention relates to a curable powder coating composition comprising the above epoxy resin and amphiphilic polyether block copolymer, further comprising the following components: (c) at least one curing agent; wherein the final coating composition is in solid form. The curing agent is capable of crosslinking the epoxy resin for a predetermined time and at a predetermined temperature schedule to form a solid coating composition.

As an example of the present invention, an amphiphilic block copolymer is added to an epoxy resin. By adding a small amount (e.g., 1 to 10 wt%) of the amphiphilic block copolymer to the epoxy resin, a nanoscale (15-25 nm) second phase morphology is created in the epoxy resin due to self-assembly, which gives the epoxy powder resin a great toughness and ductility improvement without adversely affecting other properties such as glass transition temperature, modulus, and viscosity. In addition, epoxy powder coatings retain their appearance, which is important in certain applications. These features are useful in powder coating applications where epoxy resins currently face challenges in their low temperature flexibility and durability.

Some beneficial features of toughening resins using the amphiphilic polyether block copolymers of the present invention include, for example: (1) the self-assembly properties of amphiphilic block copolymers, (2) the ability of the block copolymers to assemble at the nanometer length scale, (3) the ability of the block copolymers to produce very uniform dispersion throughout the resin monomer matrix, and (4) the ability to achieve toughening effects using low loading of block copolymer tougheners.

Some advantages of using the amphiphilic polyether block copolymers of the present invention include, for example: (1) the ability of the block copolymer to improve the toughness of the host resin without adversely affecting other critical properties of the host resin such as glass transition temperature, modulus, and viscosity, (2) the ability of the resin to maintain certain aesthetic qualities, such as critical appearance in certain applications, and (3) the ability to consistently and reproducibly create morphology before or during curing of the resin itself.

FIG. 1 is a photograph showing five steel bars coated with a powder coating composition of the present invention that has been toughened with a toughening agent of the present invention.

Panel a (prior art) is a photograph showing five steel bars coated with a powder coating composition that is not toughened with a toughening agent.

The present invention includes powder coating compositions having improved toughness comprising an epoxy resin monomer system modified with an amphiphilic block copolymer (e.g., a polyether block copolymer) as a toughening agent for the resin system. These modified ringsThe oxygen resin, when cured, exhibits fracture toughness (from K)_1cDetermined) and only minimally changes the modulus and glass transition temperature (Tg) properties.

Templated thermosetting epoxy polymers with nanoscale self-assembled morphologies exhibit an attractive combination of the following properties: improved toughness and retention of material properties such as modulus and Tg. Epoxy thermosetting polymers can be prepared, for example, by dispersing an amphiphilic block copolymer in a resin oligomer matrix where the copolymer can self-assemble and then curing the resin. Self-assembling resins exhibiting surfactant-like morphology provide improved fracture toughness at very low (e.g., 1 wt% to 10 wt%) block copolymer loadings. An amphiphilic diblock copolymer capable of self-assembly when mixed with a resin oligomer must have at least one block that is miscible with the resin/curing agent mixture prior to curing, and at least one block that is immiscible with the resin/curing agent mixture prior to curing.

One embodiment of the present invention is directed to the preparation of fully polyether block copolymers, such as diblock copolymers, for example those based on poly (ethylene oxide) -b- (butylene oxide) (PEO-PBO), which self-assemble in an epoxy resin system. At sufficiently high butylene oxide block lengths (e.g., Mn 1000 or higher), these block structures have been found to be effective in templating resin monomers into micellar structures, such as spherical micelles.

Polyether block copolymers useful in the present invention include one or more polyether block copolymers comprising at least one epoxy miscible polyether block derived from an alkylene oxide, such as Ethylene Oxide (EO), and at least one epoxy immiscible polyether block derived from an alkylene oxide having at least greater than 3 carbon atoms, such as 1, 2-butylene oxide, commonly referred to as Butylene Oxide (BO). The immiscible block segment can also be composed of a mixture of C4 or higher carbon similar monomers that are copolymerized together to provide the immiscible block segment. The immiscible block may also contain a lower molecular weight comonomer, such as EO. The polyether block copolymer contains at least one epoxy resin miscible polyether block, E, and at least one epoxy resin immiscible polyether block, M.

The polyether block copolymer component of the present invention may contain at least two or more amphiphilic polyether block copolymer segments. Examples of amphiphilic polyether block copolymers may be selected from the diblock (EM); linear triblock (EME or EME); linear tetrablock (EMEM); higher order multiblock structures (EMEM)_xE or (MEME)_xM, wherein X is an integer value from 1 to 3; a branched block structure; or a star block structure; or any combination thereof. The amphiphilic polyether block copolymer consisting of a branched block structure or a star block structure contains at least one epoxy monomer miscible block segment and at least one epoxy monomer immiscible block segment.

Examples of epoxy resin miscible polyether blocks E include polyethylene oxide blocks, propylene oxide blocks, poly (ethylene oxide-co-propylene oxide) blocks, poly (ethylene oxide-ran-propylene oxide) blocks, and mixtures thereof. Preferably, the epoxy resin miscible polyether blocks useful in the present invention are polyethylene oxide blocks.

In general, the epoxy resin-immiscible polyether blocks M which can be used in the present invention are those containing C₄To C₂₀An epoxidized alpha olefin of carbon atoms. Examples of epoxy resin immiscible polyether blocks M include polybutylene oxide blocks, polyhexamethylene oxide blocks derived from 1, 2-epoxyhexane, polyepoxydodecane blocks derived from 1, 2-epoxydodecane, and mixtures thereof. Preferably, the epoxy resin immiscible polyether blocks useful in the present invention are polybutylene oxide blocks.

In another embodiment of the present invention, when the polyether block copolymer has a multiblock copolymer structure, blocks other than E and M may be present in the block copolymer. Examples of other miscible blocks of the block copolymer include polyethylene oxide, polymethyl acrylate, and mixtures thereof. Examples of other immiscible blocks of the block copolymer include polyethylene propylene (PEP), polybutadiene, polyisoprene, polydimethylsiloxane, polybutylene oxide, polyhexamethylene oxide, polyalkylmethacrylates such as ethylhexyl methacrylate, and mixtures thereof.

Amphiphilic polyether block copolymers useful in the practice of the present invention include, for example, but are not limited to, diblock copolymers, linear triblock, linear tetrablock, higher order multiblock structures, branched block structures, or star block structures. For example, the polyether block copolymer may contain poly (ethylene oxide) blocks, poly (propylene oxide) blocks, or poly (ethylene oxide-co-propylene oxide) blocks; and with C₄Or higher carbon analogous blocks, for example 1, 2-epoxybutane, 1, 2-epoxyhexane, 1, 2-epoxydodecane or 1, 2-epoxyhexadecane blocks. Other examples of alkylene oxide blocks may include Vikolox^TMEpoxidized alpha olefins, including C10 to C30+ olefins, are commercially available from Atofina.

Preferred examples of suitable block copolymers useful in the present invention include amphiphilic polyether diblock copolymers, such as poly (ethylene oxide) -b-poly (butylene oxide) (PEO-PBO), or amphiphilic polyether triblock copolymers, such as poly (ethylene oxide) -b-poly (butylene oxide) -b-poly (ethylene oxide) (PEO-PBO-PEO).

For combinations of both block lengths, the amphiphilic polyether block copolymer used in the present invention can have a number average molecular weight (Mn) of 1,000 to 30,000. Most preferably, the polyether block copolymer has a molecular weight of 3,000 to 20,000. Prior art materials derived from block copolymers in which the immiscible block has a very low melting point parameter (polymeric hydrocarbons) produce microphase separation prior to curing. On the other hand, the polyether containing the block structure of the present invention may be microphase-separated before curing at a preferable molecular weight, or form micelles while curing is performed.

The composition of the block copolymer can be from 90% epoxy resin miscible polyalkylene oxide block and 10% epoxy resin immiscible polyalkylene oxide block to 10% epoxy resin miscible polyalkylene oxide block and 90% epoxy resin immiscible polyalkylene oxide block.

Minor amounts of homopolymer of each block may be present in the final amphiphilic polyether block copolymer of the present invention. For example, from 1 wt% to 50 wt%, preferably from 1 wt% to 10 wt%, of a homopolymer structurally similar or identical to the miscible or immiscible block segment may be added to the composition of the present invention comprising the epoxy monomer system and amphiphilic polyether block copolymer.

The amount of amphiphilic polyether block copolymer used in the epoxy resin composition of the present invention depends on a number of factors, including the equivalent weight of the polymer, and the desired properties of the product made from the composition. In general, the amount of amphiphilic polyether block copolymer used in the present invention can range from 0.1 wt% to 30 wt%, preferably from 0.5 wt% to 15 wt%, most preferably from 2 wt% to 8 wt% by weight of the resin composition.

The amphiphilic polyether block copolymers of the present invention preferably increase the toughness or fracture resistance of the epoxy resin, preferably at low block copolymer loadings (e.g., less than 10 wt%) in the epoxy resin composition. Typically, the addition of 1 to 10 wt% of the polyether block copolymer to the epoxy resin composition increases the toughness of the resin composition by a factor of 1.5 to 2.5 compared to the control.

The epoxy resin composition of the present invention may contain at least one or more amphiphilic polyether block copolymers mixed with an epoxy resin. Further, two or more different amphiphilic block copolymers may be blended together to constitute the block copolymer component of the present invention, as long as one of the block copolymers is a polyether block copolymer. More than one block copolymer may be combined to obtain additional control over the nanostructure, i.e., shape and size.

In addition to the polyether block copolymer used in the present invention, other amphiphilic block copolymers may be used as the minor block copolymer component in the resin composition of the present invention. Examples of other amphiphilic block copolymers that may be used in the practice of the present invention, in addition to the polyether block copolymer of the present invention, include, for example, but are not limited to, poly (ethylene oxide) -b-poly (ethylene-alt-propylene) (PEO-PEP), poly (isoprene-ethylene oxide) block copolymer (PI-b-PEO), poly (ethylene propylene-b-ethylene oxide) block copolymer (PEP-b-PEO), poly (butadiene-b-ethylene oxide) block copolymer (PB-b-PEO), poly (isoprene-b-ethylene oxide-b-isoprene) block copolymer (PI-b-PEO-PI), poly (isoprene-b-ethylene oxide-b-methyl methacrylate) block copolymer (PI-b-PEO-b- PMMA); and mixtures thereof. Generally, the amount of the minor amphiphilic block copolymer used in the resin composition may be 0.1 wt% to 30 wt%.

The polyether block copolymers of the present invention provide uniformly dispersed and uniformly graded (scaled) nano-sized structures, which are preferably formed (templated) in a liquid resin matrix due to micellization caused by a balance of immiscibility of one block and miscibility of another block. The micelle structures are preserved into, or formed during, the cured epoxy thermoset, resulting in an epoxy thermoset that exhibits improved toughness, improved fracture resistance and impact resistance while maintaining the same levels of Tg, modulus and other properties as the unmodified epoxy thermoset. The micellar morphology of the nano-templated resin can be, for example, spherical, worm-like, and vesicular. Micellar morphology is advantageously obtained at low block copolymer concentrations (e.g., less than 5 wt%); that is, the morphological features are not connected to each other or packed into a three-dimensional lattice. At higher concentrations, self-assembled structures can form spherical, cylindrical or lamellar morphological features that are connected to each other by lattice interactions, also on the nanometer scale.

It is believed that the fracture resistance is increased when the block copolymer self-assembles into nanoscale morphologies, such as wormlike, vesicular, or spherical micelle morphologies. Although it is not well understood how to predict which, if any, micelle morphology will occur in different resins, we believe that some of the factors that determine the self-assembled morphology include, for example, (i) the choice of monomers in the block copolymer, (ii) the degree of asymmetry in the block copolymer, (iii) the molecular weight of the block copolymer, (iv) the composition of the thermosetting resin, and (v) the choice of curing agent for the resin. Clearly, the nanoscale morphology plays an important role in creating toughness in the epoxy resin product of the present invention.

As an example of one embodiment of the invention, a thermosetting resin, such as an epoxy resin, may be blended with a polyether block copolymer, such as a poly (ethylene oxide) -b-poly (butylene oxide) (PEO-PBO) diblock copolymer, where PBO is the epoxy-immiscible hydrophobic soft component of the diblock copolymer and PEO is the epoxy-miscible component of the diblock copolymer. The curable epoxy resin composition comprising a PEO-PBO diblock copolymer improves the impact resistance of the cured epoxy resin body.

The PEO-PBO diblock copolymer may be generally represented by the formula (PEO)_x-(PBO)_yWhere subscripts x and y are the number of monomer units of polyethylene oxide and polybutylene oxide, respectively, in each block and are positive numbers. Generally, x should be 15 to 85, and the moiety (PEO)_xShould have a molecular weight of 750 to 100,000. Subscript y should be 15 to 85 and moiety (PBO)_yThe molecular weight should be represented as 1,000 to 30,000. In addition, a single PEO-PBO diblock copolymer may be used alone, or more than one PEO-PBO diblock copolymer may be used in combination.

In one embodiment of the invention, a PEO-PBO diblock copolymer is used, wherein the diblock copolymer has 20% PEO and 80% PBO, to 80% PEO and 20% PBO; and the block size is molecular weight (Mn) of PBO of 2000 or more and molecular weight of PEO of 750 or more; and provide various self-assembled configurations. For example, the present invention includes diblock blocks of PBO blocks 2,500 to 3,900 in length, which provide spherical micelles. Another example of the present invention includes a diblock with PBO blocks of 6,400, which provides worm-like micelles. Yet another example of the present invention is a diblock with a short (Mn-750) PEO block, which provides an aggregated vesicle morphology. Yet another example of the present invention includes a mixture of PEO-PBO diblock with a low molecular weight PBO homopolymer, which provides spherical micelles in which the PBO homopolymer is sequestered in the micelles without forming a separate macro-phase (macrophase); when added in the absence of diblock, the PBO homopolymer produces macro-phase separation.

In general, the amphiphilic block copolymers used in the present invention can be prepared in a single continuous synthetic polymerization process in which one monomer is polymerized to prepare an initial block, followed by the simple addition of a second monomer type, which is then polymerized onto the end of the first block copolymer until the polymerization process is complete. It is also possible to make the blocks separately, prepare the first block and then polymerize the second block onto the end of the first block in a second synthesis step. The solubility difference of the two blocks is sufficient to make the block copolymer useful for modifying various epoxy materials. Block copolymers can be prepared by moderate (modified) anionic polymerization of group I metals, such as sodium, potassium or cesium. The polymerization can be carried out undoped or using a solvent. The temperature of the polymerization reaction may be, for example, 100 ℃ to 140 ℃ under atmospheric pressure to slightly above atmospheric pressure. The synthesis of block copolymers can be, for example, as Whitmarsh, R.H. in nonionics Surfactants Polyoxosylene Block copolymers; nice, v.m., ed; surfactant Science Series; a roll 60; MarcelDekker, n.y., 1996; the procedure is described in chapter 1.

In a preferred embodiment, the blocks of the block copolymer are prepared by ring-opening polymerization of 1, 2-epoxyalkene.

Thermosets are composed of polymer chains of variable length that are bonded to each other via covalent bonds to form a three-dimensional network. Thermosetting epoxy materials can be obtained, for example, by reaction of a thermosetting epoxy resin with a hardener (for example of the amine type).

Epoxy resins useful in the present invention include a variety of epoxy compounds. Typically, the epoxy compound is an epoxy resin also known as a polyepoxide. The polyepoxides useful herein can be monomeric (e.g., diglycidyl ether of bisphenol a, linear phenolic-based epoxy resins, and triepoxy resins), higher molecular weight advanced (advanced) resins (e.g., diglycidyl ether of bisphenol a advanced with bisphenol a) or polymerized unsaturated monoepoxides (e.g., glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, and the like), homopolymers or copolymers. Most desirably, the epoxy compound contains on average at least one pendant or terminal 1, 2-epoxy group (i.e., vicinal epoxy group) per molecule.

Examples of useful polyepoxides include the polyglycidyl ethers of polyhydric alcohols and polyhydric phenols; polyglycidyl amine; polyglycinamides; a polyglycidyl imide; polyglycidyl ethyllactam; polyglycidyl thioethers; epoxidized fatty acids or drying oils; an epoxidized polyolefin; an epoxidized di-unsaturated acid ester; an epoxidized unsaturated polyester; and mixtures thereof. Polyepoxides can also be made by reacting a diglycidyl ether with an isocyanate to obtain an epoxy-terminated oligomer containing oxazolidone structures, such as the reaction product of a diglycidyl ether of bisphenol a and MDI.

Many polyepoxides made from polyhydric phenols include those disclosed in U.S. patent 4,431,782. Polyepoxides can be made from monohydric, dihydric and trihydric phenols, and can include novolak resins. Polyepoxides may include epoxidized cycloolefins; and polymeric polyepoxides, which are polymers and copolymers of glycidyl acrylate, glycidyl methacrylate, and allyl glycidyl ether. Suitable polyepoxides are disclosed in U.S. Pat. Nos. 3,804,735, 3,892,819, 3,948,698, 4,014,771 and 4,119,609 and Lee and Neville, Handbook of Epoxyresins, Chapter 2, McGraw Hill, N.Y. (1967).

While the present invention is generally applicable to polyepoxides, it is preferred that the polyepoxides be those having an Epoxide Equivalent Weight (EEW) of from 150 to 3000; glycidyl polyethers of polyols or polyphenols of EEW of 170 to 2000 are preferred. These polyepoxides are generally made as follows: reacting at least 2 moles of epihalohydrin or glycerodihalohydrin with 1 mole of polyol or polyphenol and combining a sufficient amount of caustic with the halohydrin. The product is characterized by the presence of more than one epoxide group, i.e., a 1, 2-epoxide equivalent weight greater than 1.

The polyepoxides useful in the present invention may also be cycloaliphatic diene derived epoxides. These polyepoxides can be thermally cured, cationically cured, or photo-initiated (e.g., ultraviolet initiated). There are several cycloaliphatic epoxides manufactured and sold by The Dow Chemical Company, such as 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexylcarboxylate, 1, 2-epoxy-4-vinylcyclohexane, bis (7-oxabicyclo [4.1.0] hept-3-ylmethyl adipate, methyl 3, 4-epoxycyclohexanecarboxylate, and mixtures thereof.

Generally, the amount of polyepoxide used in the present invention can range from 30 to 95 weight percent.

The curing agent component (also referred to as a hardener or crosslinker) useful in the present invention may be any compound having a reactive group that can react with the epoxy group of the epoxy resin. The chemistry of such curing agents is described in the books previously cited for epoxy resins. Curing agents useful in the present invention include nitrogen-containing compounds such as amines and their derivatives; oxygen-containing compounds, such as carboxylic acid-terminated polyesters, anhydrides, phenolic resins, amino-formaldehyde resins, phenols, bisphenol a and cresol-novolac resins, phenol-terminated epoxy resins; and catalytic curing agents such as tertiary amines, lewis acids, lewis bases, and combinations of two or more of the foregoing curing agents.

Preferred suitable curing agents include, but are not limited to, Dicyandiamide (DICY), derivatives and adducts thereof, such as o-tolylbiguanide (OTB); amino group-containing compounds, imidazole and imidazole adducts, phenol resins such as bisphenol a group, phenol novolac resins or cresol-novolac resins; carboxyl functional resins such as polyesters and acrylics, blocked isocyanates, anhydrides, and others.

In fact, polyamines, dicyandiamide, diaminodiphenyl sulfone and isomers thereof, aminobenzoates, various acid anhydrides, phenol novolac resins or cresol-phenol novolac resins may be used in the present invention, but the present invention is not limited to the use of these compounds.

Generally, the amount of the curing agent used in the present invention may be 1 to 70 wt%.

One optional component useful in the present invention is a curing catalyst that may be added to the epoxy resin composition. Examples of the curing catalyst include imidazole derivatives, tertiary amines, and organic metal salts. Preferably, the curing catalyst is used in an amount of 0 to 6 parts by weight based on the total weight of the curable composition.

The curable epoxy resin compositions of the present invention may also contain additives such as fillers, dyes, pigments, thixotropic agents, photoinitiators, latent catalysts, inhibitors, additives to modify specific processing or coating properties, such as flow modifiers, accelerators, drying additives, surfactants, tackifiers; surfactants, fluidity control agents, stabilizers, processing aid additives, tackifiers, flexibilizers, and flame retardants; and any other material required for the manufacture, application, or suitable performance of the powder coating. The amount of optional additives used in the epoxy resin composition is typically from 0 to 70% by weight of the final formulation.

Fillers useful in the present invention may include, for example, wollastonite, barite, mica, feldspar, talc, calcium carbonate; and pigments such as titanium dioxide, carbon black, iron oxide, chromium oxide, organic pigments, and dyes.

In the preparation of the mixtures or compositions of the present invention, the components are mixed together by means known in the art under conditions to form a curable composition. The curable epoxy resin composition of the present invention can be made by mixing all the components of the composition together in any order.

Alternatively, the curable resin composition of the present invention may be produced as follows: preparing a first composition comprising an epoxy resin component and a block copolymer; and a second composition, for example, comprising a curing agent component.

In another embodiment, the curable resin composition of the present invention may be made as follows: preparing a first composition comprising an epoxy resin component; and a second composition, for example, comprising a block copolymer and a curing agent component. All other components useful in making the resin composition may be present in the same composition, or some may be present in the first composition and some in the second composition. The first composition is then mixed with a second composition to form a curable resin composition. The curable resin composition mixture is then cured to produce a thermoset epoxy resin material.

Another method of making the toughened resin of the present invention includes adding the toughening agent directly to an epoxy build-up (advance) reactor in the resin making step. In this embodiment, the composition of the present invention comprises a liquid epoxy resin, such as a diglycidyl ether of bisphenol a, a polyol (such as bisphenol a), and a toughening agent, such as an EO/BO block copolymer.

If the processing of the epoxy resin includes an advancement step, a toughening agent (copolymer) may be added with the reactants prior to the advancement reaction. The copolymer may be added at the beginning of the process, especially when the resin is a liquid, and may participate in the entire build-up process to make the SER. Such modified SERs may be used in combination with other powder coatings.

Yet another method of the present invention for making a toughened resin includes adding a toughening agent to a curing agent used to cure an epoxy resin.

The toughening agents may be used at a concentration of 0.5 to 10 w/w%, preferably 2 to 6 w/w% of the formulated solids content of the cured epoxy system used in the powder coating application. The concentration of the toughening agent in the resin can be adjusted to provide the desired concentration in the final formulation, or can be stored at a higher concentration (masterbatch) and adjusted down to the desired final concentration with the unmodified resin.

The present invention comprises a mixture of a solid epoxy resin suitable for use in the manufacture of powder coatings and a toughening agent (which may be, for example, an EO/BO block copolymer or any other copolymer having a similar structure). The epoxy resin is melted, mixed with the toughening additive, re-cured and crushed and then added to the powder coating manufacture.

The curable epoxy resin composition containing the polyether block copolymer of the present invention is used to prepare a powder coating composition. The powder coating composition is then used to provide coatings on various substrates.

The powder coating composition can be applied to the substrate by any known method, such as electrostatic spraying, fluidized bed, electromagnetic brushing, powder cloud, or spraying the powder onto the preheated substrate with conventional powder spray equipment in the case of electromagnetically or non-electromagnetically charged powder, wherein (this method is also referred to as sintering).

The mixture of epoxy resin, curing agent, block copolymer and any other modifiers present in the composition can be cured according to typical methods of industrial practice. The curing temperature may be typically 10 ℃ to 200 ℃. These methods include ambient temperature curing (e.g., 20 ℃) to high temperature curing (e.g., 100 ℃ to 200 ℃) using thermal energy, radiant energy, or a combination of energy sources.

As is well known, the curing time may be typically several seconds to several hours, depending on the curing agent and the components in the resin composition. Typically, the curing time may be, for example, 1 minute to 30 minutes.

The curable composition may be cured in one or more steps, or the curable composition may be post-cured using a different temperature or energy source after the initial curing cycle.

The following examples are given to illustrate the invention and should not be construed as limiting its scope. All parts and percentages are by weight unless otherwise indicated.

Some of the raw materials used in the examples are as follows:

a "modified resin" is a solid epoxy resin that has been modified with the block copolymer toughener of the present invention.

D.e.r.662E is a solid epoxy resin having an EEW of 550 and available from The Dow chemical company.

D.e.r. 664UE is a solid epoxy resin having an EEW of 900 and available from The Dow chemical company.

"DICY" stands for dicyandiamide and is used as a curing agent.

Amicure^TMCG 1200 is a DICY curing agent available from Air Products.

EPICURE^TM101 is an imidazole adduct available from Resolution Performance Polymers; and acts as an accelerator.

Resinflow^TMP67 is an acrylic flow agent available from Estron.

NYAD^TM#325 is wollastonite #325 filler available from NYCO.

Cab-O-Sil^TMM5 is fumed silica available from Cabot; and acts as a fluidizing agent.

"PEO-PBO" represents a poly (ethylene oxide) -b-poly (butylene oxide) diblock copolymer.

"PEO-PBO-PEO" stands for poly (ethylene oxide) -poly (butylene oxide) -poly (ethylene oxide) triblock copolymer.

Preparation example a: preparation of PEO-PBO-PEO triblock copolymer

The basic procedure for making the PEO-PBO-PEO triblock copolymer is based on example 1 of U.S. Pat. No. 5,600,019. The changes to this procedure are as follows. The final PEO-PBO-PEO triblock product contained the following mole ratios of initiator/monomer:

1 mol propylene glycol/56 mol butylene oxide/62 mol ethylene oxide

Part A: preparation of catalyzed initiators

Propylene glycol was used instead of Dvowanol DM. In addition, aqueous KOH (46 wt% solids) was used. Aqueous KOH solution was added in an amount to produce a final catalyst concentration of 9 wt%. Water is not removed from the reaction product.

And part B: preparation of butylene oxide polymers

Butylene oxide was added in two portions. The amount of butylene oxide was adjusted so that the middle butylene oxide block had a number average molecular weight (Mn) of about 1000. When the digestion was complete, more aqueous KOH (46 wt%) was added to bring the final catalyst concentration to about 1 wt%. Water was removed under vacuum; butylene oxide was then added to produce the final butylene oxide polymer. The final butylene oxide polymer had a number average molecular weight of about 3500.

And part C: preparation of the Final PEO-PBO-PEO triblock copolymer

To obtain a liquid product, a mixture of ethylene oxide and butylene oxide (80/20 wt%) was added to the butylene oxide made in part B above. The addition of a small amount of butylene oxide in this step helps to interfere with the tendency of the PEO to crystallize and form a solid. The amount of this mixture added is adjusted so that the final triblock has a number average molecular weight of about 6800 g/mole. The final reaction mixture was cooled to 60 ℃ and then neutralized through a bed of magnesium silicate to produce the final PEO-PBO-PEO triblock copolymer.

Example 1 and comparative example A

Part A: preparation of toughened resins

A sample of 930 grams of DER 664UE flake solid epoxy resin was added to a 2 liter vessel and heated to 180 ℃ until the solid epoxy resin was completely melted (fluid).

70.2 grams of the PEO-PBO-PEO triblock copolymer prepared as described in preparation A above was added to the molten resin and stirred for 15 minutes.

The resulting molten material was poured onto an aluminum foil tray and allowed to cool to ambient temperature (25 ℃). The molten material solidifies at ambient temperature. The solid material was then crushed with a mill into 1/4 inch (6 mm) flakes and the crushed particles were added to the other ingredients having the formulations described in table 1.

TABLE 1

Powder coating composition	Example 1 (toughening System) (g)	COMPARATIVE EXAMPLE A (CONTROL) (gram)
			Components
Modified resin	804.5	0
			D.E.R.662E epoxy resin	132.1	152.2
DER 664UE epoxy resin	0	862.5

Amicure CG 1200 DICY	12.9	15.7
			EPICURE P101	10.4	12.0
Resinflow P67	6.5	7.5
			NYAD#325	390.1	450.2
Cab-O-Sil M5(1)	6.5	6.5
			Performance of
Cracking of each coated steel strip	0 cracking	15 cracks
			Tg(℃)	117.24	116.61

⁽¹⁾Adding into powder coating

And part B: preparation of powder coatings

The formulations described in table 1 above were weighed in a semi-resolving scale and pre-mixed in a high intensity mixer PRIZM PILOT 3 at 2300rpm for 30 seconds.

The premix was then extruded through a PRIZM 24 mm extruder using 35 ℃ in the feed zone of the extruder, 70 ℃ in the middle zone of the extruder, and 90 ℃ at 400rpm at the top of the extruder. The extruded material is fed into a chill roll and then passed through a crusher to crush the chilled material into flakes. The splits were then charged to a Hosokawa MicropulACM-2 mill and ground to a powder having an average particle size of about 43 microns.

And part C: application of powder coating

A 1 inch x 6 inch x 5/8 inch (2.5 x 15.0 x 1.6 cm) cold rolled steel strip was prepared by shot blasting with steel grit to a white metal finish with a 2.5 to 4.5 mil anchoring profile.

The steel strip was preheated to 250 ℃ for 30 minutes in a convection oven. The steel strip was then removed from the furnace and immediately immersed in a fluidized bed containing the powder coating produced in section B above. The dip time is controlled to provide a coating on the steel strip, wherein the coating thickness is from 14 mils to 16 mils. The coated steel strip was then placed back in the furnace at 250 ℃. After 2 minutes in the furnace, the steel strip was removed, cooled outside the furnace at ambient temperature for 2 minutes, and immersed in running water at ambient temperature until cooled.

And part D: test procedure and results

The toughness of the coatings on the coated steel strips made in section C above were measured using a four-point bending apparatus as described in NACE standard RP0394-2002, section H4.3. However, the test method described in NACE Standard RP0394-2002, section H4.3, was varied slightly, and included bending the bars to a fixed deformation of 1.5 inches and counting the number of cracks on each bar, rather than bending the bars to the point where the first crack occurred and measuring the deformation angle. In addition, tests were conducted at-38 ℃ rather than-30 ℃ to enhance the performance difference between the toughened material and the control.

As described in table 1 above, the toughened paint formulation on steel bars (example 1, invention) showed 0 cracks per steel bar, while the non-toughened paint formulation on steel bars (comparative example a, control) showed 15 cracks per steel bar and severe delamination.

The glass transition temperature of the cured coatings was measured using a TA instruments DSC Q100. The Tg was measured at a 10 ℃/minute ramp rate from 30 ℃ to 150 ℃ and taking into account the inflection point of the glass transition temperature curve. As shown in Table 1 above, the toughened coating (example 1) had a Tg of 117.24 deg.C, and the control coating (comparative example A) had a Tg of 116.61 deg.C.

As shown in the examples in table 1 above, the higher flexibility results combined with the nearly constant Tg values indicate that the resin of the present invention (example 1) is indeed toughened rather than simply plasticized.

Claims (27)

1. A curable solid resin composition for use in powder coating compositions comprising

(a) An epoxy resin, and

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased; wherein the final resin composition is in solid form.

2. The composition of claim 1, wherein the amphiphilic block copolymer is an amphiphilic polyether block copolymer containing at least one epoxy resin miscible block segment and at least one epoxy resin immiscible block segment; wherein the miscible block segment comprises at least one polyether structure.

3. A curable powder coating composition comprising:

(a) an epoxy resin, and a curing agent,

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased, and

(c) at least one curing agent, wherein the final coating composition is in solid form.

4. The composition of claim 3, wherein the amphiphilic block copolymer is an amphiphilic polyether block copolymer containing at least one epoxy resin miscible block segment and at least one epoxy resin immiscible block segment; wherein the miscible block segment comprises at least one polyether structure.

5. The composition of claim 3, wherein the curing agent is a nitrogen-containing compound.

6. The composition of claim 5, wherein the nitrogen-containing compound is selected from Dicyandiamide (DICY), derivatives and adducts thereof, such as o-tolylbiguanide (OTB); amino-containing compounds, imidazole and imidazole adducts, phenolic resins, amino-formaldehyde resins, phenol, bisphenol a and cresol-novolac resins, phenol-terminated epoxy resins; polycarboxylic acids, such as dodecanedioic acid and carboxy-functional resins, such as polyesters and acrylic resins, blocked isocyanates, anhydrides and catalytic curing agents, such as tertiary amines, lewis acids, lewis bases; or a combination thereof.

7. The composition according to claim 5, which comprises (d) a flow modifier.

8. The composition of claim 1 or 3, wherein the amphiphilic polyether block copolymer is selected from the group consisting of diblock, linear triblock, linear tetrablock, higher order multiblock structures; a branched block structure; or a star block structure.

9. The composition of claim 1 or 3, wherein the miscible block contains a polyethylene oxide block, a propylene oxide block, or a poly (ethylene oxide-co-propylene oxide) block; the immiscible block contains a polybutylene oxide block, a polyhexamethylene oxide block or a polydiodecane oxide block.

10. The composition of claim 1 or 3, wherein at least one miscible block of the amphiphilic block copolymer is poly (ethylene oxide); and at least one immiscible block of the amphiphilic block copolymer is poly (butylene oxide).

11. The composition of claim 1 or 3, wherein the amphiphilic block copolymer is poly (ethylene oxide) -poly (butylene oxide) or poly (ethylene oxide) -poly (butylene oxide) -poly (ethylene oxide).

12. The composition of claim 1 or 3, wherein the amphiphilic block copolymer has a molecular weight of 1000 to 50,000.

13. The composition of claim 1 or 3, wherein the ratio of miscible blocks of the amphiphilic block copolymer to immiscible blocks of the amphiphilic block copolymer is from 10: 1 to 1: 10.

14. The composition of claim 1 or 3, wherein the amphiphilic block copolymer is present in an amount of 0.1 wt% to 30 wt% by weight of the composition.

15. The composition according to claim 1 or 3, wherein the epoxy resin is selected from polyglycidyl ethers of polyhydric alcohols, polyglycidyl ethers of polyhydric phenols, polyglycidyl amines, polyglycidyl amides, polyglycidyl imides, polyglycidyl acetolactams, polyglycidyl thioethers, epoxidized fatty acids or drying oils, epoxidized polyolefins; an epoxidized di-unsaturated acid ester; epoxidized unsaturated polyester, epoxy-isocyanate resin containing oxazolidone groups; or mixtures thereof.

16. A composition according to claim 1 or 3, wherein the epoxy resin is a glycidyl polyether of a polyol or a glycidyl polyether of a polyphenol.

17. The composition of claim 1 or 3 wherein the epoxy resin is selected from the group consisting of 3, 4-epoxycyclohexylmethyl-3, 4-epoxycyclohexylcarboxylate, 1, 2-epoxy-4-vinylcyclohexane, bis (7-oxabicyclo [4.1.0] hept-3-ylmethyl adipate, methyl 3, 4-epoxycyclohexanecarboxylate, or mixtures thereof.

18. A composition according to claim 1 or 3 comprising a homopolymer having the same composition as the epoxy-immiscible block.

19. A composition according to claim 1 or 3 comprising a homopolymer having the same composition as the epoxy miscible block.

20. The composition of claim 1 or 3, wherein the epoxy resin has an epoxide equivalent weight of 150 to 3000.

21. The composition of claim 3, comprising a curing catalyst.

22. The composition of claim 21, wherein the curing catalyst is selected from an imidazole derivative, a tertiary amine, a phosphine, or a phosphonium compound, an imine compound, an organometallic salt, or mixtures thereof.

23. A process for preparing a curable solid resin composition for use in powder coating compositions comprising mixing

(a) An epoxy resin; and

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased; wherein the final resin composition is in solid form.

24. A process for preparing a curable powder coating composition comprising mixing

(a) An epoxy resin;

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased; and

(c) at least one curing agent; wherein the final coating composition is in solid form.

25. A method of preparing a coated substrate comprising

(I) Contacting a substrate with a powder coating composition comprising

(a) An epoxy resin;

(b) an amphiphilic block copolymer containing at least one epoxy resin miscible block and at least one epoxy resin immiscible block; wherein the immiscible block segment comprises at least one polyether structure, provided that the polyether structure of the immiscible block segment contains at least one or more alkylene oxide monomer units containing at least four carbon atoms; such that when the epoxy resin composition is cured, the toughness of the resulting cured epoxy resin composition is increased; and

(c) at least one curing agent;

(II) heating the powder coating composition at a temperature sufficient to cure the composition.

26. A coated article made by the method of claim 25.

27. The composition of claim 1 or 3, wherein the epoxy resin is a solid epoxy resin.