Process for producing thermosettable resin dispersions

Abstract

Disclosed is a process for preparing a thermosettable resin dispersion comprising bringing a first organic medium showing partial solubility in water into contact with an aqueous latex of elastomeric polymer particles; then bringing a second organic medium having a lower partial solubility in water than that of the first organic medium into contact therewith to separate an aqueous layer from the elastomeric polymer particles; discharging the aqueous layer to obtain a dispersion consisting essentially of the elastomeric polymer particles and the mixed first and second organic mediums, without isolating the elastomeric polymer particles as a coagulated material, dissolving a thermosettable resin in the dispersion to form a thermosettable resin dispersion comprising the elastomeric polymer particles dispersed therein; wherein, prior to discharging the aqueous layer, an ionic separation aide is contacted with the solution comprising the first organic medium and the elastomeric polymer particles or the solution comprising the first and second organic mediums and the elastomeric polymer particles.

Description

PROCESS FOR PRODUCING THERMOSETTABLE RESIN DISPERSIONSFIELD OF THE INVENTION

[0001] The invention relates to processes for producing thermosettable resin dispersions.BACKGROUND

[0002] Thermosettable resins, including epoxy resins, possess many excellent physical and chemical properties, making them useful in a wide variety of applications. However, these thermosettable resins, when used by themselves, often lack toughness and can exhibit brittleness. Therefore, it is known to strengthen or reinforce thermosettable resins with elastomeric materials to improve their properties. For example, U.S. Patent 4,778,851 discloses epoxy compounds that are modified with elastomeric compounds.

[0003] Several issues are encountered when modifying thermosettable resins with elastomeric materials. One issue is the need to disperse the elastomeric materials within the thermosettable resin to achieve the desired properties. Another issue is the need to remove water and possibly other components that are used to form the elastomeric materials when adding the elastomeric materials to the thermosettable resin.

[0004] U.S. Patent No. 8,222,324 discloses a process for producing epoxy resin compositions containing core / shell rubber particles dispersed therein. In the method, an aqueous latex of rubber- like polymer particles are contacted with a first organic medium having partial solubility in water, and then contacting the resulting solution with a second organic medium having a lower partial solubility in water than the first organic medium to substantially separate the water and remove the rubber-like polymer particles as a dispersion prior to mixing with an epoxy resin.

[0005] There is a need, however, for a process for preparing resin dispersions containing rubber-like polymer particles more quickly with better removal of water. The present invention is directed to producing resin dispersions that address at least some of the issues associated with forming resin dispersions.SUMMARY OF THE INVENTION

[0006] Disclosed herein is a process for preparing a thermosettable resin dispersion comprising bringing a first organic medium showing partial solubility in water into contactwith an aqueous latex of elastomeric polymer particles; then bringing a second organic medium having a lower partial solubility in water than that of the first organic medium into contact therewith to separate an aqueous layer from the elastomeric polymer particles; discharging the aqueous layer to obtain a dispersion consisting essentially of the elastomeric polymer particles and the mixed first and second organic mediums, without isolating the elastomeric polymer particles as a coagulated material, dissolving a thermosettable resin in the dispersion to form a thermosettable resin dispersion comprising the elastomeric polymer particles dispersed therein; wherein, prior to discharging the aqueous layer, an ionic separation aide is contacted with the solution comprising the first organic medium and the elastomeric polymer particles or the solution comprising the first and second organic mediums and the elastomeric polymer particles.DETAILED DESCRIPTION OF THE INVENTION

[0007] Disclosed herein is a process for preparing a thermosettable resin dispersion.

[0008] As used herein, “average particle size” is the arithmetic mean of all possible diameters. The aspect ratio of the particles is the ratio of the longest to the shortest diameters. The particles may have any shape, including for example, spherical, cylindrical, oblong, cuboid, prismatic, or irregular.

[0009] The thermosettable resin dispersions are stable dispersions of polymer in the thermosettable resin. As used herein, the term “stable” is meant to refer to dispersions which remain substantially constant (i.e., do not undergo substantial reprecipitation or redispersion) under conditions of preparation as well as conditions of thermal cure. For example, the thermosettable resin dispersions remain stable under normal preparation, handling, and processing conditions by maintaining a substantially constant morphology (e.g., size and distribution) in the continuous phase from ambient through curing conditions. The dispersions can also be substantially stable under conventional storage conditions for extended periods of time. Thermosettable resins suitable for use in the present invention include epoxy resins, vinyl esters, urethanes, and polyesters.

[0010] The thermosettable resin dispersion of the present invention is preferably an epoxy resin comprising elastomeric or rubber-like polymer particles dispersed therein. Epoxy resins include epoxy compounds and other compounds present during curing of the epoxy compounds, such as curing and hardening agents. Epoxy compounds include polyepoxides.

[0011] Polyepoxides may be monomeric (e.g., the diglycidyl ether of bisphenol A, novolac-based epoxy resins, and tris-epoxy resins), higher molecular weight advanced resins (e.g. the diglycidyl ether of bisphenol A advanced with bisphenol A) or polymerized unsaturated monoepoxides (e.g., glycidyl acrylates, glycidyl methacrylate, allyl glycidyl ether, etc.) to homopolymers or copolymers. Preferably the epoxy compounds contain, on the average, at least one pendant or terminal 1,2-epoxy group (i.e., vicinal epoxy group) per molecule.

[0012] Examples of polyepoxides include the polyglycidyl ethers of both polyhydric alcohols and polyhydric phenols; polyglycidyl amines, polyglycidyl amides, polyglycidyl imides, polyglycidyl hydantoins, polyglycidyl thioethers, epoxidized fatty acids or drying oils, epoxidized polyolefins, epoxidized di-unsaturated acid esters, epoxidized unsaturated polyesters, and mixtures thereof. Numerous polyepoxides prepared from polyhydric phenols include those which are disclosed, for example, in U.S. Pat. No. 4,431,782. Polyepoxides can be prepared from mono-, di- and tri-hydric phenols, and can include the novolac resins.Poly epoxides can include the epoxidized cyoloolefins; as well as the polymeric poly epoxides which are polymers and copolymers of glycidyl acrylate, glycidyl methacrylate and allylglycidyl 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 Epoxy Resins, Chapter 2, McGraw Hill, N. Y. (1967).

[0013] Preferred poly epoxides include glycidyl polyethers of polyhydric alcohols or polyhydric phenols having weights per epoxide group of 150 to 2,000. These polyepoxides are usually made by reacting at least about two moles of an epihalohydrin or glycerol dihalohydrin with one mole of the polyhydric alcohol or polyhydric phenol, and a sufficient amount of a caustic alkali to combine with the halohydrin. The products are characterized by the presence of more than one epoxide group, i.e., a 1,2-epoxy equivalency greater than one.

[0014] The polyepoxide may also include a minor amount of a monoepoxide, such as butyl and higher aliphatic glycidyl ethers, phenyl glycidyl ether, or cresyl glycidyl ether, as a reactive diluent. Such reactive diluents are commonly added to polyepoxide formulations to reduce the working viscosity thereof, and to give better wetting to the formulation. As is known in the art, a monoepoxide affects the stoichiometry of the polyepoxide formulation and adjustments are made in the amount of curing agent and other parameters to reflect that change.

[0015] The elastomeric polymer particles suitable for use in the present invention may include known elastomeric polymer particles for toughening or providing impact resistance to thermosettable resins such as epoxy resins. The elastomeric polymer particles preferably have a core / shell structure. The core may comprise an elastomeric or rubber-like material. Preferably, the core is crosslinked to render it substantially insoluble in the epoxy resin phase. The cores are presized and maintain their morphology through curing of the resin. The core can range in size from about 30 nm to about 2,000 nm in diameter. For toughening applications, a high amount of elastomeric core relative to the total particle is preferably employed. However, for other applications, a low amount of elastomeric core may be suitable. The core may comprise at least 15 weight percent, preferably at least 50 weight percent and more preferably at least 70 weight percent but less than 90 weight percent of the total weight of elastomeric polymer particles. The weight of the components of the particles refers to the average weight of the components in the total amount of particles.

[0016] Although the cores of the particles are preferably crosslinked to render them insoluble in the thermosettable resins, the cores can in themselves be insoluble in the resins, such as for example triblock copolymers or long-chain acrylate rubbers. By insoluble in the resin phase is meant that the elastomeric or rubbery core is rendered insoluble in the thermosettable resin phase, or suitable solvents for the resins or inert diluents for the particles. That is, the elastomeric or rubbery component of the elastomeric polymer particles forms a gel and swells in the resin phase, but does not dissolve. Typically, in such a situation, the percent gel ranges from about 50 to about 95 percent of the weight of the particles, and the swelling index ranges from about 3 to about 50. The elastomeric or rubbery core components include conjugated dienes, acrylate rubbers and interpolymers of the type disclosed in U.S. Pat. No. 4,419,496, for example, polymerized butadiene, isoprene and acrylate monomers such as 2-ethylhexyl acrylate and butyl acrylate, and polysulfides, silicone rubbers, and the like. Preferably, the cores are crosslinked butadiene rubber.

[0017] The shell may be grafted to the core and preferably contains a functionality which is reactive with a functionality of the thermosettable resin phase. The shell is compatible with the thermosettable resin to contribute to steric stabilization. Such compatibility is exemplified by solubility in the resin when not attached to the core. If the shell is not compatible, coagulation of the particles can result. The shell can be a homopolymer or interpolymer. The shell performs two functions. One of the functions is to graft to the core and stabilize the particles in the thermosettable resin phase. The otherfunction is to react with the thermosettable resin phase during curing so that the particles are co-cured into the resin phase.

[0018] The amount of shell component is selected to effectively stabilize the reactive grafted rubber particles in the thermosettable resin phase. This amount can vary depending on the size of the particles. For large particles, a relatively smaller amount of shell is sufficient to stabilize the particles in the resin. For 100 nm particles, typically, at least about 0.05 to about 0.5 parts, preferably to about 0.1 parts by weight of shell component per 1 part by weight of elastomeric core component will effectively stabilize the elastomeric polymer particles in the thermosettable resin phase.

[0019] The weight average molecular weight of the shell can vary and generally ranges from about 10,000 to about 250,000. Lower molecular weight grafts typically result in dispersions with low viscosity, while higher molecular weight grafts result in dispersions with high viscosity. High molecular weight grafts may provide the highest degree of improved toughness to the epoxy resin composition. The weight average molecular weight can be determined using techniques such as gel permeation chromotography.100020] The grafted shell compounds provide a compatibilizing interface which allows for dispersion of rubber particles in the thermosettable resin compound. Preferred shell compounds are polymers which are soluble in the thermosettable resin compound. Typically, the shell is comprised of ethylenically unsaturated compounds such as polymerized styrenics, acrylates and methacrylates, acrylonitrile, acrylic acid, methacrylic acid, hydroxypropyl acrylate, hydroxyethyl acrylate, vinylized glycidyl ethers such as glycidyl acrylate and methacrylate, and the like, and combinations thereof. Other preferred shell components are epoxy containing monomers, in polymerized form. The shell compounds contain a functionality which reacts with functionalities of the thermosettable resin continuous phase. Included within the term thermosettable resin continuous phase are curing agents, hardening agents, reactive and inert diluents, and initiators or catalysts. The amount of the resin phase- reactive compound in the shell is sufficient to attach the elastomeric polymer particles to the thermosettable resin phase to impart toughening to the resin phase. This amount can vary according to the molecular weight of the shell. For example, for higher molecular weight shells, a lower amount of the resin phase-reactive compound is required. The amount of resin phase-reactive compound typically ranges from about 0.5 to about 20 weight percent based on the weight of the shell compound. Preferred resin phase-reactive compounds are epoxycontaining compounds, especially glycidyl methacrylate. Any combination of monomerswhich provides a polymer which is soluble in the epoxy resin continuous phase before curing, can be employed. Preferred combinations of monomers which polymerize to form functionalized shell polymers include styrene / acrylonitrile / glycidyl methacrylate; styrene / acrylonitrile / acrylic acid; and ethyl acrylate / methacrylic acid, styrene / methyl methylacrylate / glycidyl methacrylate, and styrene / acrylonitrile / methyl methylacrylate / glycidyl methacrylate.

[0021] The elastomeric polymer particles may be made by any method known in the art. Preferably, the elastomeric polymer particles are made hy emulsion polymerization. Prior to incorporation in the thermosettable resin, the elastomeric polymer particles are present in the form of an aqueous latex of elastomeric polymer particles.

[0022] In the process of the present invention, the aqueous latex of elastomeric polymer particles are subjected to solvent swapping to remove the water while keeping the elastomeric polymer particles in suspension. At no time during the solvent swapping process should the elastomeric polymer particles be coagulated or precipitate.

[0023] To remove the water, the aqueous latex of elastomeric polymer particles is contacted with a first organic medium having a partial solubility in water. The first organic medium comprises an organic solvent or a mixture thereof in which the solubility of water in the organic solvent at 25°C is 9 to 40 wt%, and preferably 10 to 30 wt%.

[0024] Examples of the first organic medium include, but are not limited to, esters such as methyl acetate, ethyl acetate, propyl acetate and butyl acetate, ketones such as acetone, methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone, alcohols such as ethanol, (iso) propanol and butanol, ethers such as tetrahydrofuran, tetrahydropyran, dioxane and diethyl ether, aromatic hydrocarbons such as benzene, toluene and xylene, and halogenated hydrocarbons such as methylene chloride and chloroform, or a mixture thereof. Preferably, the first organic medium comprises methyl ethyl ketone.

[0025] The amount of the first organic medium may depend on the type of the elastomeric polymer particles and the amount of the elastomeric polymer particles in the aqueous latex. Preferably, the first organic medium is added to the aqueous latex of elastomeric polymer particles in an amount ranging from 50 to 350 parts by weight, more preferably 70 to 250 parts by weight, still more preferably 50 to 200 parts by weight, relative to 100 parts by weight of the latex of the elastomeric polymer particles.

[0026] After contacting the aqueous latex of elastomeric polymer particles with the first organic medium, the resulting solution is then contacted with a second organic medium.The second organic medium has a lower partial water solubility than that of the first organic medium. Like the first organic medium, the second organic medium is preferably an organic solvent, or a mixture of two or more organic solvents. The solubility of water in the second organic medium at 25 °C is not higher than 8% by weight, preferably not higher than 6% by weight, and more preferably not higher than 4% by weight.

[0027] Examples of the second organic medium include, but are not limited to, esters such as ethyl acetate, propyl acetate and butyl acetate, ketones such as diethyl ketone and methyl isobutyl ketone, ethers such as diethyl ether and butyl ether, aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as hexane, and halogenated hydrocarbons such as methylene chloride and chloroform, or a mixture thereof. Preferably, the second organic medium comprises methyl isobutyl ketone.

[0028] The second organic medium can be used in such an amount as to be effective in promoting the separation of the organic layer from the aqueous layer. The amount of the second organic medium preferably ranges from 20 to 1000 parts by weight, more preferably 50 to 400 parts by weight, still more preferably 50 to 200 parts by weight relative to 100 parts by weight of the first organic medium.

[0029] The first organic medium and the second organic medium should not form an azeotropic mixture.

[0030] Prior to discharging the aqueous layer, an ionic separation aide is contacted with a solution comprising the first organic medium and the elastomeric polymer particles or a solution comprising the first and second organic mediums and the elastomeric polymer particles.

[0031] Preferably, the ionic separation aide is present in the form of an aqueous wash. The solutions resulting from the addition of the first organic medium and / or both the first and second organic mediums may be washed with an aqueous solution comprising the ionic separation aide. Without wishing to be limited to theory, it is believed that the ionic separation aide assists in the transfer of the elastomeric polymer particles from the aqueous phase to the organic phase without coagulating or precipitating the elastomeric polymeric particles. Preferably, the aqueous wash with the ionic separation aide is performed after the second organic medium has been added.

[0032] The ionic separation aide may be selected from ionic salts and ionic polymers. Examples of ionic salts include, but are not limited to chlorides, sulphates, phosphates, carbonates, nitrates, and acetates of alkali metals, alkaline earth metals. Copper, zinc, iron,manganese, chromium, silver, aluminum, and ammonium cations of formula -NR4, where each R is independently selected from hydrogen, methyl and ethyl groups. Preferably, the ionic salts is selected from sodium chloride, potassium chloride, calcium chloride, magnesium chloride, lithium chloride, tetramethyl ammonium chloride, and magnesium sulphate. Examples of ionic polymers include polyacrylic acids and their polyacrylate salts, such as, polyacrylate salts of sodium, lithium, potassium, rubidium, cesium, beryllium, magnesium, calcium, and strontium. Suitable examples of ionic polymers include Acumer® 1000 and TAMOL™ 2002 available from The Dow Chemical Co.

[0033] Preferably, the ionic separation aide is more soluble in water than the first organic medium and the second organic medium. More preferably, the ionic separation aide has a solubility of at least 10 wt% in water at 25 °C and a solubility less than 0.5 wt% in the first organic medium and the second organic medium at 25 °C. Even more preferably, the ionic separation aide has a solubility of at least 15 wt% in water at 25 °C and a solubility less than 0.1 wt% in the first organic medium and the second organic medium at 25 °C .

[0034] The amount of the ionic separation aide may be selected based on the amount of elastomeric polymer particles present in the solution to be treated. For example, an aqueous wash comprising a 1 molar (IM) concentration of the ionic separation aide may be used in an amount of 20 parts to 100 parts, preferably from 30 parts to 80 parts, per 100 parts by weight of the elastomeric polymer particles.

[0035] Following contact with the second organic medium and the ionic separation aide, the resulting mixture is allowed to phase separate and the aqueous layer is discharged by any known separation method. Substantially all of the elastomeric polymer particles should be dispersed within the organic phase. Preferably, less than 5 wt%, more preferably less than 3 wt%, even more preferably less than 2 wt%, and still more preferably less than 1 wt%, of the total weight of the elastomeric polymer particles are contained within the aqueous phase.

[0036] Once the aqueous phase has been discharged, the elastomeric polymer particles dispersed in the organic phase may be mixed with the thermosettable resin to form the thermosettable resin dispersion.

[0037] The resulting thermosettable resin dispersion may be in the form of a master batch which may be further mixed with additional thermosettable resin, or the thermosettable resin dispersion may be formed in the desired final concentration for use.

[0038] The resulting thermosettable resin dispersion may be used in any application where such thermosettable resins are used.Examples

[0039] Two different latex compositions were prepared. Latex 1 was prepared using Paraloid™ TMS-2670 Impact Modifier, a commercially available methyl methacrylate butadiene styrene (MBS) core shell rubber impact modifier developed for epoxy resins sold by The Dow Chemical Company. Latex 2 was prepared using a MBS core with an acrylonitrile shell.Master Batch 1 (MB1)

[0040] Master Batch 1 was prepared using the process disclosed in U.S. Patent No. 8,222,324. Methyl ethyl ketone (500 g) was added to a separatory funnel followed by 420 g of Latex 1. Methyl isobytyl ketone (450 g) was then added and the separatory funnel was gently shaken.

[0041] The resulting mixture was then washing with 210 g of a IM sodium chloride solution. The mixture was allowed to phase separate followed by removal of the water layer. To the resulting organic phase was added 340 g of D.E.R.® 31® bis-phenol A based liquid epoxy resin from Olin Corp. The mixture was gently shaken in the separatory funnel and transferred to a rotavap flask and the volatiles were removed under reduced pressure (<5 mmHg, 60°C water bath temperature). The results of Master Batch 1 are summarized below in Table 1.Master Batch 2 (MB2)

[0042] Master Batch 2 was prepared in a similar manner to Master Batch 1. Latex 2 was used in Master Batch 2 in place of Latex 1, and IM of an Acumer® 1000 solution was used in place of the IM sodium chloride solution during the wash step. The results of Master Batch 2 are summarized below in Table 1.Comparative Master Batch 1 (CMB1)

[0043] Comparative Master Batch 1 was prepared in a similar manner to Master Batch 1. The wash step used to prepare Comparative Master Batch 1 used 210 g of deionized water in place of the IM sodium chloride solution.Comparative Master Batch 2 (CMB1)

[0044] Comparative Master Batch 2 was prepared in a similar manner to MasterBatch 2. The wash step used to prepare Comparative Master Batch 2 used 210 g of deionized water in place of the IM Acumer® 1000 solution.Table 1

[0045] As shown in Table 1, the thermosettable resin dispersions prepared according to the present invention (MB 1 and MB2) exhibited a significantly reduced phase separation time and a significant reduction in the amount of water retained in the organic phase when compared to the comparative examples, CMB1 and CMB2.

Claims

What is claimed is:

1. A process for preparing a thermosettable resin dispersion comprising: bringing a first organic medium having a partial solubility in water into contact with an aqueous latex of elastomeric polymer particles; then bringing a second organic medium having a lower partial solubility in water than that of the first organic medium into contact therewith to separate an aqueous layer from the elastomeric polymer particles; discharging the aqueous layer to obtain a dispersion consisting essentially of the elastomeric polymer particles and the mixed first and second organic mediums, without isolating the elastomeric polymer particles as a coagulated material, dissolving a thermosettable resin in the dispersion to form a thermosettable resin dispersion comprising the elastomeric polymer particles dispersed therein; wherein, prior to discharging the aqueous layer, an ionic separation aide is contacted with the solution comprising the first organic medium and the elastomeric polymer particles or the solution comprising the first and second organic mediums and the elastomeric polymer particles.

2. The process of claim 1 wherein the elastomeric polymer particles comprise core-shell polymer particles.

3. The process of claim 2 wherein the core-shell polymer particles comprise a rubber core and a shell comprising a functionality that is reactive with a functionality of the thermosettable resin.

4. The process of any one of the preceding claims wherein the thermosettable resin is selected from the group consisting of epoxy resins, vinyl esters, urethanes, and polyesters.

5. The process of any one of the preceding claims wherein the thermosettable resin is an epoxy resin.

6. The process of any one of the preceding claims wherein the ionic separation aide is selected from the group consisting of an ionic salt and an ionic polymer.

7. The process of claim 6 wherein the ionic separation aide is an ionic salt selected from the group consisting of chlorides, sulphates, sulfonates, phosphates, carbonates, acetates, halogens, and nitrates of alkali metals, alkaline earth metals, copper, zinc, iron, manganese,chromium, silver, aluminum, and ammonium cations of formula -NR4, wherein each R is independently selected from hydrogen, methyl and ethyl groups.

8. The process of claim 7, wherein the ionic separation aide is selected from sodium chloride, potassium chloride, magnesium chloride, calcium chloride, tetramethyl ammonium chloride, and lithium chloride.

9. The process of claim 6 wherein the ionic separation aide is an ionic polymer selected from the group of polyacrylic acids and their corresponding polyacrylate salts .

10. The process of any of the preceding claims wherein the partial solubility of the first organic medium ranges from 9 to 40 wt% of water in the first organic medium at 25 °C.

11. The process of any one of the preceding claims wherein the partial solubility of the second organic medium ranges from greater than 0 to 8 wt% of water in the second organic medium at 25 °C.

12. The process of any one of the preceding claims wherein the ionic separation aide is more soluble in water than in the first organic medium and the second organic medium.

13. The process of any one of the preceding claims further comprising washing with water one or both of the solution comprising the first organic medium and the elastomeric polymer particles and the solution comprising the first and second organic mediums and the elastomeric polymer particles.

14. The process of claim 13 wherein washing with water comprises washing with water comprising the ionic separation aide.

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