WO2022164480A1

WO2022164480A1 - Syntactic foam compositions

Info

Publication number: WO2022164480A1
Application number: PCT/US2021/043015
Authority: WO
Inventors: Kazuhiro Yoshida
Original assignee: Kaneka Americas Holding, Inc.
Priority date: 2021-01-28
Filing date: 2021-07-23
Publication date: 2022-08-04

Abstract

A thermosetting resin composition including a thermosetting resin, a core-shell polymer, a low-density filler, and a curing agent is provided. The composition includes from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the composition not including the low-density filler, and at least 30 vol. % of the low-density filler with respect to the total volume of the thermosetting resin composition. A syntactic foam made from the thermosetting resin composition and a method of making the syntactic foam are also provided. The method of making the syntactic foam includes blending an epoxy resin composition and curing the epoxy resin composition to form the syntactic foam.

Description

SYNTACTIC FOAM COMPOSITIONS BACKGROUND [0001] Syntactic foams are composite materials that include low density fillers. Syntactic foams are commonly made with hollow glass spheres dispersed in high strength matrix resins, such as epoxy resins. Low density fillers provide advantages such as weight reduction, high specific strength, and low thermal conductivity. Due to these unique properties, syntactic foams are used in a wide variety of industries such as marine and subsea, aerospace, automotive, among others. [0002] In order to maximize the effects of weight reduction, high specific strength, and low thermal conductivity, a high volume of hollow glass spheres may be used in syntactic foam formulations. However, there are technical challenges associated with high volumes of hollow glass spheres because viscosity is increased with increasing hollow glass spheres content, and mechanical properties, such as impact resistance, decrease with increasing the filler loading. Various tougheners may be employed to improve mechanical properties. SUMMARY [0003] This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter. _[0004] In one aspect, embodiments disclosed herein relate to a thermosetting resin composition comprising a thermosetting resin, a core-shell polymer, a low-density filler, and a curing agent. The composition includes from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the composition not including the low- density filler, and at least 30 vol. % of the low-density filler with respect to the total volume of the thermosetting resin composition. [0005] In another aspect, embodiments disclosed herein relate to a syntactic foam comprising a cured thermoset resin, a core-shell polymer, and a low-density filler. The syntactic foam includes from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the syntactic foam not including the low-density filler, and at least 30 vol. % of the low-density filler with respect to the total volume of the thermoset resin. [0006] In yet another aspect, embodiments disclosed herein relate to a method of making a syntactic foam, the method comprising blending an epoxy resin composition and curing the epoxy resin composition to form the syntactic foam. The epoxy resin composition comprises a thermosetting resin, 0.5 to 15 wt.% of a core-shell polymer, at least 30 vol. % of a low-density filler, and a curing agent. [0007] Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims. BRIEF DESCRIPTION OF DRAWINGS [0008] FIG. 1 is photographs of shavings from thermosets having different core-shell polymer content in accordance with one or more embodiments. [0009] FIG. 2 is photographs of shavings from thermosets having different core-shell polymer content in accordance with one or more embodiments. [0010] FIG. 3 is photographs of shavings from thermosets having different core-shell polymer content in accordance with one or more embodiments. [0011] FIG. 4 is photographs showing phase separation of compositions having different core-shell polymer content in accordance with one or more embodiments. DETAILED DESCRIPTION [0012] The present disclosure generally relates to thermosetting resin compositions used for preparing syntactic foams. A high loading of low-density fillers, such as hollow glass spheres, reduces density and improves properties such as specific strength in syntactic foam compositions. However, high filler loading can cause processability issues and affect final foam properties. Generally, the viscosity of resin compositions increases as more low-density filler is included. Furthermore, some tougheners used to enhance mechanical properties in syntactic foams also lead to increases in viscosity of thermosetting resin compositions. [0013] Compositions disclosed herein include a combination of resin components that provides improved physical properties without detrimental increases in viscosity. In particular, embodiments of the present disclosure relate to a thermosetting composition comprising an epoxy resin, a core-shell polymer particle, a low-density filler and a curing agent. Disclosed compositions may provide a combination of improved processability of the resin and improved toughness of a cured thermoset product. [0014] Compositions disclosed herein include a thermosetting resin. In one or more embodiments, the thermosetting resin is an epoxy resin. However, the thermosetting resin is not limited to epoxy resins, and may also include unsaturated polyesters, vinyl ester resins, polyurethanes, phenolic resin, cyanate esters, and bismaleimides. In embodiments in which an epoxy resin is the thermosetting resin, the epoxy resin is not particular limited, provided that the epoxy resin is a compound having an epoxy group. In one or more embodiments, the epoxy resin may be a polyepoxide. The epoxy resin may be a polyglycidyl ether, such as addition reaction products of polyhydric phenols. Addition reaction products of polyhydric phenol may include, but are not limited to, bisphenol A, bisphenol F, bisphenol, and phenol novolac with epichlorohydrin. The epoxy resin may include polyglycidylamine compounds from monoamines and polyamines such as aniline, diaminobenzene, aminophenol, phenylenediamine, diaminophenylether. Alicyclic epoxy resins having an alicyclic epoxy structure may also be included, such as cyclohexylepoxy. Other suitable epoxy resins may include addition reaction products of polyhydric alcohols and epichlorohydrin, halogenated epoxy resins in which hydrogen is partially substituted with halogen elements such as bromine, and homopolymers or copolymers made from the polymerization of monomers containing unsaturated monoepoxide such as allylglycidyl ether. In particular embodiments, the epoxy resin may be diglycidyl ether of bisphenol A (DGEBA). The previously described epoxy resins may be used alone or in combination. [0015] In order to achieve an appropriately low density for a syntactic foam thermoset composition, one or more low-density fillers may be included in the thermosetting resin composition. Low-density fillers may include, but are not limited to, glass, ceramic, polymer, and carbon fillers. In particular embodiments, hollow glass spheres may be used. In embodiments in which hollow glass spheres are used, hollow glass spheres having an appropriate particle size and density for the application may be used. For example, in one or more embodiments, the volume mean particle diameter (D₅₀) of the hollow glass spheres may be in a range of about 15 to 60 µm. In particular embodiments, the D₅₀ particle size of the hollow glass spheres may be about 18 µm or about 40 µm or about 55 µm. Additionally, the hollow glass spheres may have a suitable density for use as a low-density filler. For example, in one or more embodiments, the hollow glass spheres may have a density ranging from about 0.13 to about 0.63 g/cm³. In one or more embodiments, the hollow glass spheres may have a density of less than 0.7 g/cm³. Hollow glass spheres may also have an adequate crush strength to provide enhanced mechanical properties. For example, in one or more embodiments, the hollow glass spheres may have a crush strength of from about 300 psi (pounds per square inch) to about 27,000 psi. In particular embodiments, the crush strength of the hollow glass spheres may be about 300 psi, about 2,000 psi or about 27,000 psi. [0016] The low-density filler may be included in an amount sufficient to achieve an appropriately low density without hindering the mechanical properties of the thermoset composition or the viscosity of the resin. Thus, in one or more embodiments, the low-density filler may be included in an amount ranging from about 10 to 70 vol.% (volume percent) based on the total volume of the thermosetting resin composition. The low-density filler may have a lower limit of one of 10, 15, 20, 25, 30, 35 and 40 vol. % and an upper limit of one of 45, 50, 55, 60, 65, and 70 vol. % based on the total volume of the thermosetting resin composition, where any lower limit may be paired with any mathematically compatible upper limit. [0017] In order to provide improved mechanical properties in a syntactic foam composition, core-shell polymer particles may be included in the composition as a toughener. Advantageously, core-shell polymer particles may also provide an advantage of decreasing the viscosity of the thermosetting resin composition, which generally sees an increase with increasing quantities of low density filler, thereby resulting in improved processability. [0018] Core-shell polymers in accordance with the present disclosure generally have at least two components, a core of the particle and a shell surrounding the core. It may also have a structure of three or more components constituted by an intermediate layer covering the core layer and a shell layer further covering the intermediate layer. In order to improve physical properties, the core is may be a rubber polymer having a glass transition temperature (Tg) of less than 0°C, -20^o°°,°° -°4°0°°°C°°,° o°°r° -°6°0°°°°C°.°C The core may be a rubber elastic body comprising 50 wt.% or more of at least one monomer selected from the group consisting of a diene monomer and a (meth) acrylate monomer and less than 50 wt.% of the other vinyl monomers copolymerizable to the core, a polysiloxane rubber-based elastic body, or a mixture thereof. The monomer forming the shell may be an aromatic vinyl, a vinyl cyan, a (meth) acrylate, an unsaturated acid derivative, a (meth) acrylamide derivative and a maleimide derivative. Additionally, these monomers forming the shell may have at least one reactive functional group reacted with at least one of the thermosetting resin compositions. Also, these monomers comprising the shell may be used alone or in appropriate combination. [0019] In one or more embodiments, the core-shell polymer of the present disclosure may be a core-shell polymer obtained by graft-polymerizing a monomer to form the shell in the presence of a rubber polymer, which serves as the core. Thus, the resultant structure of the core-shell polymer includes a rubber polymer core surrounded by a graft-polymerized shell. [0020] The weight ratio of the core to the shell of the core-shell polymers of present disclosure may be in a range of about 50:50 to 99:1, or 60:40 to 95:5, or 70:30 to 95:5 (as a weight ratio of monomers for forming each polymer). The core-shell polymers of the present disclosure may have a volume average particle diameter of from about 0.01 to 1.0 µm or 0.05 to 0.8 µm. [0021] In one or more embodiments, the core-shell polymer may be dispersed in an epoxy resin. As described herein, amounts of core-shell polymer (in weight percent) include both core-shell polymer and also epoxy resin in which the core-shell polymers are dispersed. In such dispersions, the core shell polymer may be about 15-50 wt.% (weight percent) of the total weight of the dispersion while the epoxy resin is about 50-85 wt.% of the total weight of the dispersion. In particular embodiments, the core- shell polymer may be a commercially available product such as Kane Ace® MX-257 (37wt.% core-shell polymer dispersed in DGEBA epoxy) and Kane Ace® MX-150 (40wt.% core-shell polymer dispersed in DGEBA epoxy) available from Kaneka Corporation. In one or more embodiments, the core-shell polymer (including the resin in which it is dispersed) may be included in the thermosetting resin composition in an amount ranging from 0.5 wt.% to 15 wt.% based on the weight of the thermosetting resin composition other than low-density fillers. The core-shell polymer may have a lower limit of one of 0.5, 1, 2, 3, 4, 5, 6, and 7 wt.% and an upper limit of one of 9, 10, 11, 12, 13, 14 and 15 wt.% based on the weight of the thermosetting resin composition other than low-density fillers, where any lower limit may be paired with any mathematically compatible upper limit. [0022] A curing agent may be included to facilitate curing reactions in the resin composition. Any suitable curing agents known in the art for epoxy resin systems may be included. Examples of suitable curing agents may include, but are not limited to, amine-type curing agents, such as aliphatic diamines and aromatic diamines, cycloaliphatic amines, acid anhydrides, such as hexahydrophthalic anhydride, novolac-type phenolic resins, imidazole compounds, tertiary amines, triphenylphosphines, aliphatic polyamines, aromatic polyamines, polyamides, polymercaptans, dicyandiamides, dibasic acid dihydrazides, N,N-dialkyl urea derivatives, N,N-dialkyl thiourea derivatives, alkylaminophenol derivatives, melamine and guanamine. In particular embodiments, the curing agent may be selected from the group consisting of tetraethylenepentamine, polyetheramine, isophorone diamine, methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride, and combinations thereof. Curing agents may be used alone or in combination. [0023] The amount of curing agent included in the composition may vary depending on the chemical properties of the curing agent, the desired properties of the epoxy resin composition and the desired properties of the cured product. In the case of a curing agent that includes an amine group, an acid anhydride group, or a phenolic hydroxy group, the curing agent may be included in an amount such that the amine group, the acid anhydride group, or the phenolic hydroxy group is present in an amount of 0.7 to 1.3 per equivalent of one epoxy group. [0024] Additionally, in one or more embodiments, in order to accelerate resin curing, a curing accelerator may be optionally included in the thermosetting resin composition. Examples of suitable curing accelerators include, but are not limited to, tertiary amines, imidazoles, organic phosphorus compounds, quaternary phosphonium salts, diazabicycloalkenes, organometallic compounds, quaternary ammonium salts, boron compounds, and metal halogen compounds. In particular embodiments, the accelerator may be 1-methyl imidazole. Any of the previously described curing accelerators may be used alone or in combination. When included in the composition, the curing accelerator may be included in an amount ranging from 0.01 to 10 wt.% based on the weight of the epoxy resin. [0025] A reactive diluent may be optionally included in the thermosetting resin composition. Reactive diluents including those disclosed herein may have a lower viscosity relative to the epoxy resin. A reactive diluent may provide a balance of processability and final properties of the thermoset composition, and may also allow for a higher volume of low-density fillers to be included in the composition. Reactive diluents may include, but are not limited to, aliphatic monoglycidyl ethers, aromatic monoglycidyl ethers, polyalkylene glycol diglycidyl ethers, glycol diglycidyl ethers, diglycidyl esters of aliphatic polybasic acids, glycidyl ethers of polyvalent aliphatic alcohols, and aliphatic triglycidyl ethers. In particular embodiments, the reactive diluent may be neopentyl glycol diglycidyl ether. Reactive diluents may be used alone or in combination.. [0026] The reactive diluent may be included in an amount sufficient to achieve a suitable viscosity for processing the thermosetting resin. In one or more embodiments, the reactive diluent may be included in an amount ranging from 0.5 to 25 wt.% based on the weight of the epoxy resin. The reactive diluent may have a lower limit of one of 0.5, 1.0, 2.5, 5.0, 7.5, and 10 wt.% and an upper limit of one of 12.5, 15, 17.5, 20, 22.5, and 25 wt.% based on the weight of the epoxy resin, where any lower limit may be paired with any mathematically compatible upper limit. [0027] In one or more embodiments, a defoamer may be optionally included to reduce air bubbles that can be trapped in the relatively viscous thermosetting resin compositions. Any suitable defoamers known in the art for thermosetting resin compositions may be included. Examples of suitable defoamers may include, but are not limited to, silicone-based, fluorine-based, acrylic-based, poly oxyethylene-based, and poly oxypropylene-based defoamers. In particular embodiments, the defoamer may be a silicon-free air release additive, such a commercially available BYK® A- 501. In one or more embodiments, the defoamer may be included in an amount ranging from 0.01 to 4 wt.% based on the weight of the epoxy resin. [0028] In one or more embodiments, a coupling agent may be optionally included to improve interfacial adhesion between the surface of hollow glass spheres and the matrix of resins. Silane coupling agents may be used in the disclosed composition. In particular embodiments, a commercially available polymeric coupling agent, such as BYK® C-8001 may be used. In one or more embodiments, the coupling agent may be included in an amount ranging from 0.5 to 10 wt.% based on the weight of the low density filler. [0029] Additional components may be optionally included in the thermosetting resin composition. For example, fillers (such as calcium carbonate and silica), dehydrating agents (such as calcium oxide), anti-tracking agents, flame retardants (such as aluminum hydroxide), heat dissipation agents (such as aluminum oxide), anti-settling agents, thixotropic agents, colorants (such as pigments and dyes), extender pigments, UV absorbers, antioxidants, stabilizers (anti-gelling agents), plasticizers, leveling agents, antistatic agents, lubricants, thickeners, low shrinkage agents, organic fillers, thermoplastic resins, desiccants, dispersants and the like. Additionally, glass fiber, carbon fiber, and other fibers which are used for fiber reinforced resins may be included. [0030] Thermosetting resin compositions in accordance with one or more embodiments of the present disclosure may be prepared via conventional device or mixing means. Additionally, the resin compositions may be degassed by pulling vacuum on the resin compositions during or after blending. However, devices which generate high shear conditions may be avoided to minimize breakage of low-density fillers. In order to prepare a homogeneous resin composition, components other than the low-density fillers may first be blended to create the base resin composition, and then the low- density fillers may be blended with the other resin components. [0031] In order to prepare a thermoset composition, the blended mixture may be thermally cured for a suitable time at a suitable temperature for the resin composition. However, the curing method is not limited to thermal curing, and may also include, light (such as ultraviolet rays), a radiation beam (such as an electron beam), and a combination thereof. The resin composition may be cured in a single step or in multiple steps. In one or more embodiments, the resin may be cured at a temperature of from about 80 °C to 130 °C for a time ranging from about 60 minutes to about 240 minutes. In embodiments in which multiple curing steps are employed, the resin may be cured at a first temperature, and then the temperature may be increased for a second curing step at a higher temperature. [0032] The thermosetting resins disclosed herein may have an appropriately low density for making a syntactic foam. The density may be tuned by adjusting the amount of the low-density filler and the amount of core-shell rubber. The density may be measured before curing (i.e., uncured density) and/or after curing (i.e., cured density). Resin compositions in accordance with one or more embodiments may have an uncured density of 1.0 g/cm³ or less, 0.9 g/cm³ or less, 0.8 g/cm³ or less, 0.7 g/cm³ or less, or 0.6 g/cm³ or less at 23 °C. Resin compositions in accordance with one or more embodiments may have a cured density of 1.0 g/cm³ or less, 0.9 g/cm³ or less, 0.8 g/cm³ or less, 0.7 g/cm³ or less, or 0.6 g/cm³ or less at 23 °C. [0033] A particular advantage of the thermosetting resin compositions disclosed herein is an improvement in viscosity as compared to conventional syntactic foam compositions. Syntactic foam compositions can be difficult to process due to the high viscosity from the inclusion of a high volume of low-density fillers and/or the inclusion of tougheners. However, due to a synergistic effect of the combination of components in the compositions disclosed herein, the viscosity of the thermosetting resin composition may be the same or lower than comparative compositions. [0034] The improvement in viscosity of the compositions disclosed herein and a comparative sample may be described using a viscosity ratio (ƞ₁/ƞ₀). In the viscosity ratio, ƞ1 is the viscosity of the composition in accordance with the present disclosure, and ƞ₀ is viscosity of a composition having the same components in the same amounts, but where core-shell polymer particles are not included. In one or more embodiments, the thermosetting resin may have a viscosity ratio ƞ₁/ƞ₀ of less than 1.8, or less than 1.6, or less than 1.4, or less than 1.2, or less than 1.0. [0035] An additional advantage of the resin compositions of the present disclosure is a suppression of phase separation during resin processing. In conventional syntactic foam compositions, phase separation can be problematic due to the difference in density of the low-density fillers and the overall resin matrix. The compositions disclosed herein may reduce phase separation as compared to compositions that do not include core-shell polymer particles. [0036] Thermosets made from the resin compositions of the present disclosure may achieve high impact strength. The impact strength may be tuned based on the amount of core-shell rubber particles in the resin composition, with impact strength generally increasing with core-shell polymer content. When tested in accordance with ASTM D5420, thermosets in accordance with one or more embodiments may achieve an impact strength of at least 3.0, 3.2, 3.5, 3.7, 3.8, 4.0, 4.2, 4.5, 4.7, 5.7, 5.5 or 6.0 in*lb. [0037] Thermosets made from the resin compositions of the present disclosure may also provide an advantage in processing of the cured thermoset. When thermosets are machined or cut into final product shapes, thermoset shavings or dust is generated. Finer shavings (meaning small particles) may be more difficult to manage and can cause safety issues in machining. Thermosets in accordance with one or more embodiments of the present disclosure may produce coarser shavings when cut as compared to conventional compositions. [0038] EXAMPLES [0039] Materials [0040] EPON 828 (Hexion, diglycidyl ether of bisphenol A (DGEBA), epoxy equivalent weight: 185-192 g/eq) was used as the epoxy resin. ERISYS GE-20 (Huntsman, neopentyl glycol diglycidyl ether, epoxy equivalent weight: 125-137 g/eq) was used as a reactive diluent. Kane Ace® MX-257 (Kaneka Corporation, DGEBA epoxy resin: 63 wt.%, poly butadiene type core-shell polymer: 37 wt.%.) and Kane Ace® MX-150 (Kaneka Corporation, DGEBA epoxy resin: 60 wt.%, poly butadiene type core-shell polymer: 40 wt.%.) were used to provide core-shell polymer particles (“CSR”). ECA 100 NC (Dixie Chemical Company, Inc., a blend of methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, and methyltetrahydrophthalic anhydride), tetraethylenepentamine (TEPA) (Huntsman), Jeffamine® D230 (Huntsman, polyetheramine) and Vestamin® IPD (Evonik Corporation USA, isophorone diamine (IPDA)) were used as curing agents. 1-methyl imidazole (1MZ) (Sigma-Aldrich) was used as a catalyst. BYK® A501 (BYK USA, Inc.) was used as a defoamer. BYK®-C 8001 (BYK USA, Inc.) was used as a coupling agent. S32 (3M, density: 0.29 to 0.35 g/cm³, volume mean particle size: 40 µm), S15 (3M, density: 0.13 to 0.17 g/cm³, volume mean particle size: 55 µm), and iM30K (3M, density: 0.57 to 0.63 g/cm³, volume mean particle size: 18 µm) hollow glass spheres (“HGS”) were used as low density fillers. Hypox® RA840 (Huntsman, acrylonitrile-butadiene rubber-modified epoxy resin: 40 wt.%, DGEBA epoxy resin : 60 wt.%, epoxy equivalent weight: 325 to 360 g/eq) and Hypox® RA1340 (Huntsman, acrylonitrile-butadiene rubber-modified epoxy resin: 40 wt.%, DGEBA epoxy resin : 60 wt.%, epoxy equivalent weight: 325 to 375 g/eq) was used as a liquid rubber toughening agent (referred to as “toughener” in the data below). [0041] Methods [0042] Resin compositions were made via the following blending procedure by using a FlackTek SpeedMixer® (FlackTek Manufacturing, inc.). Epoxy resin, diluent, core- shell polymer particles and a defoamer were blended in the mixer at 1,800 rpm for 180 seconds and 2,300 rpm for 120 seconds. The curing agent and accelerator were added, and the mixture was blended in the mixer at 1,800 rpm for 60-90 seconds and 2,300 rpm for 60-90 seconds. Finally, the hollow glass spheres were added, and the final mixture was mixed in the mixer at 800 rpm for 30-60 seconds, then 1,800 rpm for 60-90 seconds and 2,300 rpm for 60-90 seconds. [0043] Glass plate molds were prepared with glass plates and silicon tubing using metal spacers. Sprayon® MR311 dry film release agent was applied to glass plates and baked at 200°C for 30 min before use. Resin compositions were poured into glass plates molds to be cured in an oven. [0044] Density of uncured materials were measured at 23°C with 8.32ml of BYK® density cup (BYK-Gardner USA). Density of cured materials were measured at 23°C with an electronic densimeter, ED-120T (Mirage Trading). Viscosity was measured immediately following resin blending by a cone plate type viscometer. In particular, a Brookfield DV1 digital viscometer was used. Viscosity was measured by using spindle CPE-41 or CPE-52 at 30°C at shear rate 10s^-1. [0045] Testing specimens for flexural testing were cut by CNC Carving Machine (ICONIC) with 1 flute drill (63-712 by LMT-ONSRUD. Cutting diameter was 0.125 inch. The spindle speed was 18,000 rpm, the feed speed was 18 inches per minute, the plunge rate was 18 inches per minute. The cutting speed was 180 meters per minute and the feed rate was 0.0254 mm per rev. 5 passes were done at 1.06 mm for each pass depth. Shavings were collected for comparison of shaving size. The other testing specimens for Gardner impact and DMA were cut by a diamond blade. [0046] Flexural properties were evaluated by a three-point bending test based on ASTM D790. The specimen size was 100 mm x 10 mm x 5 mm and the support span was 80 mm. [0047] Gardner impact was measured by evaluating the impact resistance using a method according to ASTM D5420. The specimen size was 40 mm x 40 mm x 5 mm. Striker diameter was 0.625 inch, striker weight was 1 lbs, and support plate inside diameter was 0.640 inch. [0048] Glass transition temperature (Tg) was evaluated by dynamic mechanical analysis (DMA). In particular, a Discovery Hybrid Rheometer HR-2 (TA Instruments) was used. The Specimen size was 64 mm x 12 mm x 3 mm and the support span was 50 mm. Samples were tested at a frequency of 1 Hz, a strain of 0.03%, and at a temperature range of 30 to 190 °C with a ramp rate of 3 °C/min. The peak of Tan δ was used as Tg. [0049] An initial set of samples was prepared to determine viscosity and density trends over a range of core-shell polymer and hollow glass sphere contents. The composition of these samples are provided in Table 1 Unless otherwise indicated, the units in Table 1 are in phr (parts per hundred resin by weight with respect to 100 parts by weight of the epoxy resin and the reactive diluent). The CSR wt.% in Table 1 represents the percent by weight for resin components except for hollow glass spheres. The HGS vol.% in Table 1 represents the percent by volume with respect to all resin components. Table 1

[0050] Uncured density and viscosity values of samples are provided in Table 2. Table 2

,

, [0051] The cured density and mechanical properties of some of the samples in Table 1 are provided in Table 3. Table 3

,

[_0052] Tg of sample 9, 11, 12 and 13 was 150 °C, 150 °C, 150 °C, 149 °C respectively. [0053] Shavings from the cutting of samples 18, 20, 21 and 22 were saved to compare the effect of the core-shell polymer content on the size of the shavings. Photographs of the shavings for samples 18, 20, 21 and 22 are shown in FIG. 1 from left to right. As can be seen from the photos, an increasing the core-shell polymer content also increases the size of the shavings produced during cutting. [0054] The next set of resin compositions is shown in Table 4. In contrast to the samples shown in Table 1, these samples include two curing agents, but do not include a 1-methyl imidazole catalyst. Table 4

[0055] The viscosity, density and mechanical properties of the samples in Table 4 are provided in Table 5. For these compositions, the cure schedule was to cure at 80 °C for 60 minutes and then 120 °C for 120 minutes. Table 5

[0056] Tg of sample 44, 45, 46 and 47 was 135 °C, 135 °C, 136 °C, 135 °C respectively. [0057] Shavings from the cutting of samples 40, 41, 42 and 43 were saved to compare the effect of the core-shell polymer content on the size of the shavings. Photographs of the shavings for samples 40, 41, 42 and 43 are shown in FIG. 2 from left to right. As can be seen from the photos, an increasing the core-shell polymer content also increases the size of the shavings produced during cutting. [0058] The next set of resin compositions is shown in Table 6. These compositions are similar to those provided in Table 4, but use a different curing agent, Jeffamine® D230, instead of TEPA. Table 6

[0059] The viscosity, density and mechanical properties of the compositions in Table 6 are provided in Table 7. For these compositions, the cure schedule was to cure at 80 °C for 60 minutes and then 120 °C for 120 minutes.

Table 7

[0060] Tg of sample 56, 57, 58 and 59 was 115°C, 115°C, 115°C, 114°C respectively.

[0061] Shavings from the cutting of samples 52, 33, 54 and 55 were saved to compare the effect of the core-shell polymer content on the size of the shavings. Photographs of the shavings for samples 52, 33, 54 and 55 are shown in FIG. 3 from left to right. As can be seen from the photo, an increasing the core-shell polymer content also increases the size of the shavings produced during cutting.

[0062] The next set of resin compositions is shown in Table 8. These compositions are similar to those provided in Table 1, but include a coupling agent.

Table 8

[0063] The mechanical properties of the compositions in Table 8 are provided in Table 9. For these compositions, the cure schedule was to cure at 90 °C for 60 minutes and then 130 °C for 120 minutes. Table 9

[0064] The final set of resin compositions is shown in Table 10. The compositions in Table 10 include different type of core-shell polymer particles (MX-150) and also include two different types of a liquid rubber toughening agent (RA840 and RA1340). Table 10

[0065] The viscosity, density, mechanical properties and Tg of the samples in Table 10 are provided in Table 11. For these compositions, the cure schedule was to cure at 80 °C for 60 minutes and then 120 °C for 120 minutes. Table 11

, [0066] As shown by the data provided in Tables 1-11, the inclusion of core-shell polymer particles provides a dramatic improvement in mechanical properties, such as impact resistance while maintaining Tg. Additionally, in the compositions disclosed herein, the inclusion of core-shell polymer particles does not necessarily increase the viscosity of the samples and in many cases a reasonable viscosity is maintained. Indeed, in many samples, especially those including about 2 to 15 wt.% of the core- shell polymer particles, the viscosity is decreased with the inclusion of about 2 to 15 wt.% of the core-shell polymer particles. This lower viscosity provides substantial improvements in the processability of the samples while maintaining appropriately low density and good mechanical properties. [0067] As shown by the data provided in Tables 1, 2, 9, and 10, liquid tougheners increased the viscosity drastically. Additionally, as shown by the data provided for samples 1, 2, 3, and 4, the viscosity of the resin composition was generally increased if core shell polymer is included in the absence of hollow glass spheres. [0068] Phase separation of samples 18, 19, 20, 21, and 22 was observed after gelled at 50°C to compare the effect of the core-shell polymer content on phase separation. Photographs of the phase separation for samples 18, 19, 20, 21, and 22 are shown in FIG. 4 from left to right. As can be seen from the photos, increasing the core-shell polymer content also decreases the phase separation. [0069] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112(f) for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.

Claims

CLAIMS What is claimed: 1. A thermosetting resin composition comprising: a thermosetting resin; a core-shell polymer; a low-density filler; and a curing agent; wherein the composition comprises from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the composition not including the low-density filler, and at least 30 vol. % of the low-density filler with respect to the total volume of the thermosetting resin composition. 2. The composition of claim 1, wherein the thermosetting resin is an epoxy resin. 3. The composition of claim 1, further comprising at least one of a reactive diluent, a defoamer, and a coupling agent. 4. The composition of claim 1, wherein the thermosetting resin has an uncured density of less than 1.0 g/cm³. 5. The composition of claim 1, wherein the thermosetting resin has a viscosity ratio ƞ₁/ ƞ₀ of less than 1.8 when ƞ₁ is the viscosity of the composition of claim 1 and ƞ₀ is viscosity of composition of claim 1 other than core-shell polymer. 6. The composition of claim 1, wherein the low-density filler is hollow glass spheres having a density of less than 0.7 g/cm³. 7. The composition of claim 1, wherein the core-shell polymer has a volume average particle size of from 0.05 to 0.8 µm, and a core of core-shell polymer has a glass transition temperature of less than 0 °C. 8. A syntactic foam comprising: a cured thermoset resin; a core-shell polymer; and a low-density filler; wherein the syntactic foam comprises from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the syntactic foam not including the low-density filler, and at least 30 vol. % of the low-density filler with respect to the total volume of the thermoset resin. 9. The syntactic foam of claim 8, wherein the cured thermoset resin is a cured epoxy resin. 10. The syntactic foam of claim 8, comprising a density of less than 1.0 g/cm³. 11. The syntactic foam of claim 8, wherein the low-density filler is hollow glass spheres having a density of less than 0.7 g/cm³. 12. The syntactic foam of claim 8, wherein the core-shell polymer has a volume average particle size of from 0.05 to 0.8 µm, and a core of core-shell polymer has a glass transition temperature of less than 0 °C. 13. The syntactic foam of claim 8, comprising an impact strength of at least 3.0 in*lb when measured according to ASTM D5420. 14. A method of making a syntactic foam, the method comprising: blending an epoxy resin composition, the epoxy resin composition comprising: a thermosetting resin; 0.5 to 15 wt.% of a core-shell polymer; at least 30 vol. % of a low-density filler; and a curing agent; wherein the epoxy resin composition comprises from 0.5 to 15 wt.% of the core shell polymer with respect to the weight of the epoxy resin composition not including the low-density filler, and at least 30 vol. % of the low- density filler with respect to the total volume of the thermosetting resin; and curing the epoxy resin composition to form the syntactic foam. 15. The method of claim 14, wherein the epoxy resin composition further comprises at least one of a reactive diluent, a defoamer, and a coupling agent.