Block copolymer / thermoplastic epoxy resin composition

Abstract

The present invention relates to: a composition of a block copolymer and a thermoplastic epoxy resin; the use thereof in the mechanical reinforcement of filled or unfilled thermoset epoxy formulations; and, the resulting filled or unfilled thermoset epoxy formulation. The invention also relates to a method for producing said block copolymer / thermoplastic epoxy resin composition.

Description

[0001] The present invention relates to: a composition of a block copolymer and a thermoplastic epoxy resin; its use in the mechanical reinforcement of a filled or unfilled thermosetting epoxy formulation; and, the obtained filled or unfilled thermosetting epoxy formulation. The present invention also relates to a process for preparing these compositions of a block copolymer and a thermoplastic epoxy resin.

[0002] Epoxy resins are used in a variety of fields, including the manufacture of articles intended for use in articles in the automotive, aviation or sports fields. They are used in structural adhesives, as a matrix for composites or in applications for protecting electronic components.

[0003] Epoxy articles or materials are obtained by reacting a functional epoxy resin with a functional curing agent. When more than two functional groups are used on the epoxy resin and / or the curing agent, a thermosetting material is obtained, i.e., a material having a certain crosslink density. Through the crosslink density, the properties of the epoxy resin as well as the properties of the performance and the curing agent can be adjusted. Thermally cured epoxy materials generally have a high crosslink density; this ensures a high glass transition temperature (Tg), making the final material have good thermomechanical properties.

[0004] However, the sudden stresses experienced by mechanical components under high loads (e.g., in the aviation field) have urgently required the improvement of certain properties (such as impact resistance and crack propagation limitation).

[0005] Solutions have been provided by combining these formulations with core-shell particles or with block copolymers containing flexible blocks having a low Tg (glass transition temperature). In the case of block copolymers, this is described in EP1290088. In FR2880895, further improvements are provided by the presence of functional monomers in the block copolymer.

[0006] This type of block copolymer and in particular those in which at least one block has polar and / or hydrophilic functional groups are hitherto the best candidates known for improving the mechanical properties of epoxy resins.

[0007] When seeking a suitable formulation of a block copolymer with an epoxy resin, there are still technical problems. The mechanical properties of the final material are optimal when the block copolymer is in a so-called "nanostructured" state, which can only be obtained by thermodynamic steps that are not always controllable. The block copolymers that can be used to reinforce epoxy resins are in the form of pellets at ambient temperature. Epoxy resins are in liquid or solid form at ambient temperature, and the mixing with block copolymers requires stirring, time, and temperature conditions, which are restrictive for formulators. One solution that has been used involves grinding the pellets of the block copolymer to facilitate their dilution, but this adds steps. The use of liquid epoxy resins or solid epoxy resins facilitates the dissolution of the block copolymer in powder or pellet form, but requires long heating and vigorous stirring. This results in the presence of foams and bubbles, which cannot be completely eliminated even by performing additional degassing, and the foams and bubbles weaken the final material.

[0008] Another solution that has been adopted involves pre-diluting the block copolymer in a liquid epoxy resin in the form of a masterbatch, followed by dilution in the epoxy resin of the final formulation. This solution does not eliminate the need for the step of mixing the block copolymer in a liquid epoxy resin at a content of up to 25%, which makes this academic method unavailable in industry because the above-mentioned drawbacks (foaming, bubbling, time) are exacerbated by the high proportion (up to 25%) of the block copolymer in these mixtures of the block copolymer in solid form in the liquid epoxy. Such a method is described, for example, on page 40 of the thesis by Andreas Peter Klingler (ISBN registration number 978-3-944440-44-6).

[0009] To avoid the drawbacks associated with dissolving block copolymers in epoxy resins, the present applicant has developed a composition that promotes the dispersion of the block copolymer in the epoxy resin when present in the form of pellets with a high block copolymer content in a solid thermoplastic epoxy resin. These pellets are obtained in a kneader-type or extruder-type mixing device. These pellets are much easier to mix, while avoiding problems related to foaming or bubbling and mixing time that occur during the formulation process.

[0010] In addition, the obtained composition allows for a better balance of final properties at an equal block copolymer content than those obtained in the prior art. Summary of the Invention

[0011] The present invention relates to a composition that consists, by weight, of the following mixture M:

[0012] - at least one thermoplastic epoxy resin (1) having one or more glass transition temperatures above 25 °C measured by DSC,

[0013] - At least one block copolymer (2), in a weight proportion of 25% - 70% of the total of (1)+(2), wherein the at least one block copolymer has at least one block A and at least one block B, the at least one block A has a glass transition temperature Tg above 25 °C measured by DMA, the at least one block B has a glass transition temperature Tg below 0 °C measured by DMA, and at least one polar and / or hydrophilic functional monomer is present in at least one of the blocks, the polar and / or hydrophilic functional monomer being present in a weight proportion of 5% - 50% relative to the block concerned, and the composition being in solid form at a temperature below 50 °C. Detailed description

[0014] The Tg of the thermoplastic epoxy resin present in the composition of the present invention is above 25 °C, preferably above 30 °C, and more preferably above 50 °C, as measured by DSC (differential scanning calorimetry).

[0015] These are compounds of the pure epoxy, epoxy polyester, novolac or epoxy acrylate type. They include diglycidyl ethers of bisphenol A and bisphenol F type, aromatic glycidylamines and cycloaliphatic epoxides, these compounds having an ethylene oxide functionality greater than or equal to 2. They may contain fluorine, phosphorus or silicon. They may be of renewable origin, based on natural oils (soybean oil, linseed oil, castor oil, etc.), based on isosorbide, based on epoxidized natural rubber, based on epoxy lignin derivatives, or based on rosin.

[0016] The block copolymers useful in the context of the present invention are multiblock copolymers, preferably free of butadiene. They are composed of block A (called the hard block) having a glass transition temperature Tg above 25 °C (preferably above 50 °C and more preferably above 70 °C) and block B (called the soft block) having a Tg below 0 °C (preferably below -25 °C), and they are of formula (A) n B or (B) n A (and preferably (A) n B) linear or star-shaped, where n takes values from 2 to 8, preferably from 2 to 6, preferably from 2 to 4, and more preferably from 2 to 3, i.e., linear or star-shaped copolymers of diblock or triblock (preferably triblock). The combination of these copolymers constitutes a variant of the present invention. At least one of block A or B contains at least one polar and / or hydrophilic monomer, wherein the weight proportion of the polar and / or hydrophilic monomer is 5% to 50% of the block concerned.

[0017] The term "glass transition temperature" or "Tg" refers to the temperature at which a polymeric material transitions from a glassy state to a non-glassy state, corresponding to a certain mobility of the polymer chains relative to each other. The glass transition temperature of a block copolymer is determined by dynamic mechanical analysis (DMA).

[0018] The expression "block copolymer" refers to a copolymer having a plurality of different polymer segments, where each segment (also referred to as a "block") consists of a sequence of monomers, which may be the same or different. Thus, each segment or block may be a homopolymer or a copolymer.

[0019] Preferably, block A comprises a sequence of monomers selected from: linear or branched, cyclic or acyclic C1 to C 18 alkyl esters of (meth)acrylic acid, and in particular methyl methacrylate, optionally obtained from a recycling process by depolymerization; styrene or substituted styrene; isobornyl (meth)acrylate; or acrylates or methacrylates substituted with polar and / or hydrophilic functional groups; and combinations thereof. Polar and / or hydrophilic is understood to mean groups such as carboxyl (-COOH), hydroxyl (-OH) or amide (-CONH) type groups, or ethylene glycol or polyethylene glycol optionally substituted at its terminal functional groups with alkyl, phosphate, phosphonate or sulfonate groups. These particularly include (meth)acrylic acid and alkylacrylamides, in particular dimethylacrylamide, diethylacrylamide or isopropylacrylamide.

[0020] Preferably, block B will preferably consist of a sequence of monomers selected from butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, nonyl acrylate, lauryl acrylate and mixtures thereof, optionally in the form of a mixture with styrene, acrylate or methacrylate substituted with polar and / or hydrophilic functional groups.

[0021] Such compounds particularly include (meth)acrylic acid and alkylacrylamides, in particular dimethylacrylamide, diethylacrylamide or isopropylacrylamide.

[0022] More preferably, block B consists of a sequence of butyl acrylate monomers with or without polar and / or hydrophilic functional monomers.

[0023] Preferably, at least one of blocks A or B comprises at least one polar and / or hydrophilic functional monomer, and the weight proportion of the polar and / or hydrophilic functional monomer is between 5% by weight and 50% by weight, preferably between 5% by weight and 30% by weight, more preferably between 5% by weight and 20% by weight, and when at least one polar and / or hydrophilic functional monomer is present in the soft block B, more preferably between 5% by weight and 12% by weight, and when at least one polar and / or hydrophilic functional monomer is present in the hard block A, preferably between 5% by weight and 12% by weight.

[0024] More preferably, and when there is at least one polar and / or hydrophilic functional monomer, the polar and / or hydrophilic functional monomer is present in the hard block A.

[0025] Thus, the triblock, diblock and star triblock copolymers that can be used without limitation in the context of the present invention include the following substances, either alone or as a mixture:

[0026] p(MMAcoMAA)-pBuA-p(MMAcoMAA), p(MMAcoAA)-pBuA-p(MMAcoAA), pMMA-p(BuAcoAA)-pMMA, p(MMAcoDMA)-pBuA-p(MMAcoDMA), p(MMAcoIPA)-pBuA-p(MMAcoIPA) and preferably p(MMAcoDMA)-pBuA-p(MMAcoDMA), p(MMAcoIPA)-pBuA-p(MMAcoIPA), p(MMAcoDEA)-pBuA-p(MMAcoDEA), p(MMAcoMAA)-pBuA, p(MMAcoAA)-pBuA, p(MMAcoMAA)-p(BuAcoSty), pMMA-p(BuAcoAA), p(MMAcoDMA)-pBuA-, p(MMAcoIPA)-pBuA, p(MMAcoDEA)-pBuA and preferably p(MMAcoDMA)-pBuA, p(MMAcoIPA)-pBuA, and p(MMAcoDEA)-pBuA.

[0027] pBuA-(p(MMAcoMAA))3, pBuA-(p(MMAcoAA))3, p(BuAcoAA)-(pMMA)3, pBuA-(p(MMAcoDMA))3, pBuA-(p(MMAcoIPA))3, pBuA-(p(MMAcoDEA))3, and preferably pBuA-(p(MMAcoDMA))3, pBuA-(p(MMAcoIPA))3, p(BuAcoSty)-(p(MMAcoMAA))3, and pBuA-(p(MMAcoDEA))3.

[0028] In all these block copolymers, MMA can be completely or partially replaced by IBOA and / or IBOMA.

[0029] In the foregoing, MMA = methyl methacrylate, MAA = methacrylic acid, AA = acrylic acid, BuA = butyl acrylate, Sty = styrene, DMA = dimethylacrylamide, IPA = isopropylacrylamide, DEA = diethylacrylamide, IBOA = isobornyl acrylate, IBOMA = isobornyl methacrylate.

[0030] Block copolymers useful in the context of the present invention typically have a weight-average molecular weight measured by SEC (size exclusion chromatography) under polystyrene calibration between 10,000 and 200,000 g / mol, preferably between 30,000 and 150,000 g / mol, and even more preferably between 30,000 and 100,000 g / mol, wherein the weight ratio of hard block / soft block is between 20 / 80 and 80 / 20.

[0031] Block copolymers useful in the context of the present invention are preferably prepared by controlled radical polymerization, without excluding other preparation methods. Controlled radical polymerization makes it possible to obtain block copolymers in sequential steps within the same process operation. For example, block copolymers can be prepared by RAFT (reversible addition-fragmentation chain transfer) polymerization or by nitroxide-mediated polymerization (also known as NMP (nitroxide-mediated polymerization)). Preferably, block copolymers are prepared by NMP, in particular by NMP using N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide as the counter radical. The synthesis of block copolymers using this counter radical is particularly described in EP1526138.

[0032] The composition of the present invention consists of one or more epoxy resins having a Tg > 25 °C measured by DSC and at least one block copolymer, wherein the weight proportion of the block copolymer is 25% to 70%, and preferably 27% to 55%, of the total weight of the epoxy resin and the block copolymer.

[0033] It has in fact been shown that at contents below 25%, the relevant rheology does not provide properly extruded pellets and they do not achieve any additional effect on the properties observed when using these masterbatches. Above 70%, when the composition of the present invention is mixed with the final formulation of the ready-to-use epoxy resin composition, the advantage of diluting the resin with the block copolymer is no longer significant compared to using the block copolymer alone.

[0034] The composition of the present invention has a viscosity greater than 50 Pa·s at a shear gradient of 0.1 to 100 s within a temperature range of 120 to 210 °C, and preferably 140 to 190 °C. -1

[0035] The composition of the present invention is prepared at a temperature of 120 to 210 °C using a mixing device or kneader of the single-screw or twin-screw extruder type (preferably twin-screw). A degassing well (preferably a degassing well according to the present invention) may be present under reduced pressure to completely eliminate the bubbling phenomenon within the resulting pellets.

[0036] Therefore, the present invention also relates to a process for preparing the composition of the present invention, comprising the following steps:

[0037] - Extruding a mixture of at least one epoxy resin and a block copolymer, the resin having a Tg above 25 °C as measured by DSC, wherein the weight proportion of the block copolymer is between 25% and 70% and preferably between 27% and 55%.

[0038] - Optionally degassing by means of an exhaust port.

[0039] - Granulating the obtained extrudate into pellets.

[0040] The present invention also relates to the use of the composition of the present invention in a formulation of a ready-to-use epoxy resin, i.e., as a component of the composition of the article once the article has undergone polymerization. The ready-to-use epoxy resin formulation is a formulation using the composition of the present invention in combination with at least one other epoxy resin and at least one crosslinking agent (also referred to as a curing agent). The composition of the present invention will preferably be combined with at least one epoxy resin that is liquid at ambient temperature (25 °C) and at least one epoxy resin that is allegedly solid at ambient temperature and has a Tg above 25 °C and preferably above 50 °C as measured by DSC.

[0041] The curing agents employed include compounds capable of reacting within a temperature range between 15 °C and 200 °C. They can be acidic or basic. They can be amine compounds and aliphatic anhydride type compounds having a functionality greater than or equal to 2.

[0042] ​The present invention also relates to an epoxy-based thermosetting composition formulated with the composition of the present invention, at least one epoxy resin (3), and at least one curing agent suitable for its polymerization, in the presence or absence of woven or non-woven fibers of fillers such as carbon, glass, aramid, boron, or silica, and optionally in the presence of other auxiliaries such as solvents, reactive diluents such as glycidyl ethers and esters, pigments and dyes, plasticizers, flame retardants, the foregoing list being non-exhaustive. "Formulated" is understood to mean a homogenized mixture of the composition of the present invention consisting of a thermoplastic epoxy resin and a block copolymer, at least one second epoxy resin, and at least one curing agent.

[0043] The present invention also relates to a composite material obtained using the composition of the present invention, whether in the form of a prepreg or as a thermally cured composite article.

[0044] Example 1: Preparation of the composition of the present invention

[0045] Starting materials used:

[0046] The block copolymer designated as BCP has blocks with a Tg below 0 °C and blocks with a Tg above 25 °C. The block copolymer has acrylamide functional groups. This type of copolymer is available under the trade name Nanostrength obtained from Arkema.

[0047] The epoxy resin with CAS No. 25036-25-3 used has a Tg of 31 °C (measured by DSC (differential scanning calorimetry)) and is available under the trade name EPON TM Resin 1001F (Hexion).

[0048] Under the following conditions, the composition M was extruded using a Labtech LTE 26-40 twin-screw pilot extruder (screw diameter 26 mm, L / D ratio 40) with different weight percentages of BCP and epoxy resin as shown in Table 1:

[0049] - Temperature profile: 70 - 100 - 130 - 160 - 180 - 180 - 180 - 180 - 180 - 180 °C.

[0050] - Screw speed: 350 rpm, flow rate: 8 kg / h, cooling the strand with water.

[0051] The different components were metered in through two weight metering devices.

[0052] The first metering device was used to meter in the polymer (which was introduced into the main hopper).

[0053] The second metering device is used to meter the addition of epoxy flake.

[0054] The product is introduced into the extruder in the main hopper. The composition by weight is given in Table 1:

[0055] Table 1

[0056]

[0057] Where M0 is 100% epoxy resin and M5 is 100% BCP.

[0058] Example 2: Rheology of Composition M

[0059] The resin EPON used TM Resin 1001F is the worst case because its Tg is 31 °C and it has a low molecular weight. Any other resin with a Tg higher than 31 °C will exhibit a rheological behavior more favorable for preparing the compositions of the present invention by extrusion (where pellets may be obtained).

[0060] The viscosity of the formulation was measured on a stress-controlled rheometer of type MCR301 from Anton Paar.

[0061] Measurements were carried out by flow stress scans at the desired measurement temperatures. The geometries used were of the Couette or plane-plane type.

[0062] Then a flow plot of the viscosity as a function of the shear gradient can be obtained ( Figure 2 ).

[0063] Figure 1 : 140 °C,

[0064] Figure 2 : 160 °C,

[0065] Figure 3 : 175 °C,

[0066] Figure 4 : 190 °C.

[0067] The compositions of the present invention have a viscosity greater than 50 Pa·s at shear gradients of 0.1 to 100 s -1 in the temperature range of 120 to 210 °C, and preferably 140 to 190 °C.

[0068] Table 2 gives the Eta0 viscosities of Compositions M0 to M5 on the Newtonian plateau at different temperatures. Pelletizing is possible when the composition has an Eta0 viscosity greater than 50 Pa·s.

[0069] Table 2

[0070]

[0071]

[0072] Example 3: Thermally cured compositions and mechanical evaluation

[0073] This example compares the properties of thermally cured compositions in the presence of block copolymers when the block copolymers of the present invention or block copolymers of the prior art are introduced.

[0074] Starting materials used:

[0075] - Epoxy resin of bisphenol A type: can be named Araldite LY556 obtained from Huntsman.

[0076] - EPON TM Resin 1001F.

[0077] - Epikote TM 828.

[0078] - BCP copolymer, available under the trade name Nanostrength Obtained from supplier Arkema.

[0079] Dicyandiamide (DICY) CAS 461-58-3 Dyhard 100SF (supplier Alzchem)

[0080] TDI: catalyst TDI 1,1-dimethyl-3-phenylurea CAS: 101-42-8, TDI UR300 (supplier Degussa).

[0081] BYK - P 9920: defoamer (supplier BYK).

[0082] 1) Prepare the following formulations according to Table 3:

[0083] Stir at 95 °C and 200 rpm, and weigh the epoxy resin LY556 into the tank of a glass reactor equipped with a toothed flat disk dispersing impeller.

[0084] At 95 °C, the amount of masterbatch M52N+1001F was introduced through a funnel while stirring at 400 rpm for 3 or 4 hours. Then defoamer BYK P9920 was introduced and the mixture was degassed. Then the mixture was cooled to 80 °C. After the vacuum had been released, the twin curing agent / promoter was introduced by means of a funnel. The mixture was dissolved for 15 minutes and then reduced pressure was applied again for 35 minutes. The still liquid solution (80 °C) was poured into a stainless-steel mold (previously placed in an oven at 160 °C). For the K1C and G1C tests, the stainless-steel mold had a thickness of 6 mm, and for the tensile test specimens, the stainless-steel mold had a thickness of 2 mm.

[0085] Table 3

[0086]

[0087] 2) Evaluation of mechanical properties:

[0088] All test specimens were cut by a Charly robot (milling cutter)

[0089] Tests: K1C G1C conform to standard ISO 13586:2000

[0090] Tensile standard according to standard ISO 527-2:2012

[0091] Table 4 collates the values obtained, demonstrating the superiority of the formulations obtained using the compositions of the present invention.

[0092] Table 4

[0093]

[0094] Example 4: Dissolution of the formulation

[0095] At ambient temperature, in a beaker, with the aid of a magnetic stirrer bar, the masterbatch was dissolved in Epikote 828 resin to a content of 10%. In the reference solution, 5% block copolymer and 5% Epon 1001F were introduced into Epikote 828 resin.

[0096] After 3 hours, the solution containing the masterbatch (invention 2) was completely homogeneous, while the reference solution 3 still contained undissolved granules and had bubbles, Table 5:

[0097] Table 5

[0098]

[0099] Thus, the composition of the present invention enables better mechanical properties to be obtained in formulations having epoxy resins and is easier to use.

Claims

1. A composition consisting of a mixture M by weight: - At least one thermoplastic epoxy resin (1) having one or more glass transition temperatures above 25 °C measured by DSC, - At least one block copolymer (2) in a weight proportion of 25% - 70% of the total amount of (1)+(2), wherein at least one block copolymer has at least one block A and at least one block B, the at least one block A has a glass transition temperature Tg above 25 °C measured by DMA, the at least one block B has a transition temperature Tg below 0 °C measured by DMA, and has at least one polar and / or hydrophilic functional monomer in at least one of the blocks, and the polar and / or hydrophilic functional monomer is present in a weight proportion of 5% - 50% relative to the block involved, and the composition is in solid form at a temperature below 50 °C.

2. A composition comprising the following homogenized mixture: the composition according to claim 1, at least one second epoxy resin (3), and at least one curing agent.

3. The composition according to claim 2, further comprising at least one woven or non-woven fiber.

4. A prepreg comprising the composition according to claim 3.

5. A composite material obtained using one of the compositions according to any one of claims 3 or 4.

6. A process for preparing the composition according to claim 1, comprising the following steps: - Extruding a mixture of at least one epoxy resin and a block copolymer at a temperature of 120 - 200 °C, the resin having a Tg above 25 °C measured by DSC, wherein the weight proportion of the block copolymer is 25% - 70%, - Optionally, degassing by means of an exhaust port, - Granulating the obtained extrudate into pellets.

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