Patent Application
20210061987
The present invention relates to resin compositions and materials containing resin compositions, particularly but not exclusively to resin compositions containing epoxy resin based on an alkylol alkane triglycidyl ether monomer that can be used as the curable matrix in the production of moulding compounds, adhesives and prepregs.
Composite materials are produced in many forms. A fibrous layer impregnated with a curable resin matrix composition or resin composition is known herein as a prepreg. Moulding compounds generally comprise a fibrous material in a chopped, isotropic or quasi-isotropic form in combination with a resin matrix composition. The resin matrix compositions in these materials may be uncured or partially cured.
Resin matrix compositions can be selected from a wide range of polymerisable components and additives. Common polymerisable components comprise epoxies, polyesters, vinylester, polyisocyanates, and phenolics. Compositions containing these components are generally referred to as epoxy, polyester, vinylester, polyisocyanate and phenolic compositions respectively.
Epoxy resin compositions are widely used in composite materials. The epoxy components in these compositions are selected from a wide range of epoxy containing materials according to the cure cycle to be employed and the nature of the finished article to be produced. Epoxy resins can be solid, liquid or semi-solid and are characterised by their functionality and epoxy equivalent weight. The functionality of an epoxy resin is the number of reactive epoxy sites per molecule that are available to react and cure to form the cured structure. For example, a bisphenol-A epoxy resin has a functionality of 2, while certain glycidyl amines can have a functionality of more than 4. The EEW is the weight of epoxy resin material in grams containing 1 gram/mol of epoxy groups.
Epoxy resin compositions are generally cured in a mould where fibrous reinforcement, such as carbon fibre, glass fibre, Kevlar and/or aramid fibre, are superimposed to form a lay-up. The systems are then cured in the mould by heating whilst often pressure is also applied.
Although cured epoxy resin composition have desirable mechanical properties, these properties can be further enhanced by including modifiers and additives. For example it is well known to include impact modifiers in the epoxy resin systems in order to enhance their toughness. Typical impact modifiers that have been proposed are thermoplastic materials such as polyamides including nylon 6, nylon 11, nylon 12 and nylon 66, or polyethers, polysulfones and core shell rubbers.
The properties required of a composite material are that when cured it has the desired glass transition temperature (Tg), and also has the desired mechanical properties according to the use to which it is to be put. In certain applications it is important that the Tg is retained under damp or humid conditions.
Epoxy compositions also include catalysts and/or curatives, and these are also selected according to the nature of the epoxy resin, the product to be produced and the cure cycle that is required.
The curing of composite materials to support high volume manufacturing rates requires very short cure cycles. A cure cycle of 2.5 minutes can provide for rate manufacture of ca. 166000 parts per mould per year (assuming a 30 second unload-re loading time and 95% utilisation). It is desirable to use thermosetting materials for structural components as they have superior mechanical performance and creep resistance compared to thermoplastics. For these applications, the thermosetting matrix must have an initial cured Tg that is high enough to allow demoulding at the cure temperature. A higher cured Tg capability enables curing at higher cure temperature and higher cure temperature will enable faster cure cycles as reactivity increases with temperature.
Very fast cure at lower temperature can be achieved with multi-component mixed epoxy compositions which are prepared and injected into a fibrous preform. However this requires additional mixing and metering equipment which increases the complexity and therefore the occurrence of failures which can be costly in high volume production environments. In addition, these methods require the construction, in an additional prior step, of a dry fibrous preform. This dry preform can be time consuming to produce and difficult to position accurately into the required complex shaped mould. Therefore prepreg materials that contain both the fibrous reinforcement and a curable resin composition are more preferred for structural part manufacture in large volumes. Such materials can be cut, oriented and stacked in automated processes allowing easy placement into the mould for curing.
Curable thermosetting matrix compositions which remain stable (latent) at room temperature (21° C.) and are fast curing at their selected cure temperature, typically use a latent amine curative which is accelerated by a urone based curative. Although effective for initial cure these curatives can result in low and therefore undesired in service Tg temperatures as the latent amine and urone combination is susceptible to high levels of water uptake and matrix plasticization.
Cured epoxy resin compositions when exposed to water at 70° C. for 14 days have a retained Tg (referred to as the “wet Tg”) of less than 80° C. Attempts to make even faster curing compositions through use of additional curative/accelerator conventionally result in cured resin compositions with a wet Tg of less than 70° C. In both cases the retained wet Tg as a percentage of the initial ‘dry’ cured Tg is less than 60%. For many Industrial applications for structural components, this performance is inadequate as a wet Tg of greater than 85° C. is usually required for load bearing structural components that might be exposed to sunlight, such as vehicle components and aircraft parts.
The present invention aims to obviate or at least mitigate the above described problems and/or to provide improvements generally.
According to the inventions there are provided a resin composition, a moulding material and an adhesive as defined in any one of the accompanying claims.
In an embodiment of the invention there is provided a resin composition comprising:
In an embodiment, this composition provides at least 95% of cure in 2 minutes or less at 170° C. with a dry Tg of over 130° C. and a hot wet Tg (cured sample exposed to water at 70° C. for 14 days in short, “wet Tg”) of over 100° C. whilst having desired mechanical properties for structural applications.
In an embodiment E′ Tg is in the range of from 135 to 145° C., preferably from 140 to 144° C. for the dry Tg and in the range of from 100 to 110° C., preferably from 100 to 105° C. for the wet Tg.
In a further embodiment, the resin composition has a time to peak exotherm enthalpy as measured using DEA in accordance with ASTM D2471 in the range of from 0.2 to 1.6 mins, preferably from 0.4 to 1.0 minute.
In another embodiment E″ Tg is in the range of from 140 to 175° C., preferably from 140 to 170° C. for the dry Tg and in the range of from 105 to 125° C., preferably from 110 to 120° C. for the wet Tg.
The percentage cure (cure %) is measured in accordance with method as described above. The dry Tg is measured in accordance with ASTM E1640 using a ramp rate of 5° C./min (Standard Test Method for Assignment of the Glass Transition Temperature by Dynamic Mechanical Analysis (DMA)) and the retained or hot wet Tg is measured following isothermal curing at 170° C. for 2 minutes of the neat resin composition and exposing the cured composition to water at 70° C. for 14 days, and then measuring the Tg of the sample using the same measurement standard ASTM E1640 using a ramp rate of 5° C./min.
The loss modulus E″ is measured in accordance with ASTM E1640 using dynamic mechanical analysis (DMA) at a ramp rate of 5° C./min. The hot wet loss modulus E″w is measured using the same standard at a ramp rate of 5° C./min following immersion of the cured composition to water at a temperature of 70° C. for 14 days.
The storage modulus E′ is measured in accordance with ASTM E1640 using dynamic mechanical analysis (DMA) at a ramp rate of 5° C./min. The hot wet loss modulus E′w is measured using the same standard at a ramp rate of 5° C./min following immersion of the cured composition to water at a temperature of 70° C. for 14 days.
Corresponding Tg values are derived from the storage and loss moduli for both dry samples and hot wet treated samples as outlined in ASTM E1640.
In another embodiment, the alkylol alkene triglycidylether monomer is a trialkylol alkene triglycidylether monomer. The alkylol alkene triglycidylether monomer is selected from the group of monomers consisting of trimethylolethane triglycidyl ether, trimethylolmethane triglycidyl ether, trimethylolpropane triglycidyl ether, triphenylolmethane triglycidyl ether, trisphenol triglycidyl ether, tetraphenylol ethane triglycidyl ether, p-aminophenol triglycidyl ether, 1,2,6-hexanetriol triglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidyl ether, glycerol ethoxylate triglycidyl ether, castor oil triglycidyl ether, propoxylated glycerine triglycidyl ether, and/or combinations thereof.
Preferably, component (i) is based on at least two alkylol alkane triglycidyl ether monomers each having a different structure. The component (i) may comprise an epoxy novolac resin and a phenol novolac epoxy resin which differs in structure from the epoxy novolac resin.
The average epoxy equivalent weight range of component (i) is in the range of from 120 to 220, preferably from 150 to 215, more preferably from 150 to 200.
In another embodiment, component (ii) is selected from a cycloaliphatic epoxy resin, a bisphenol-A epoxy resin, or a further novolac epoxy resin.
Preferably, the component (ii) comprises a multifunctional epoxy resin derived from polyaddition of a dicyclopentadiene component and phenol component.
In a further embodiment, the composition may comprise additional epoxy resin components. The composition may comprise a component (iv) comprising at least one difunctional epoxy resin. Preferably, the composition comprises one or more difunctional epoxy resin components in the range of from 20 to 55% by weight, preferably from 25 to 32% and more preferably from 28 to 41% by weight based on the total weight of the composition and/or combinations of the aforesaid weight ranges.
Advantageously we have found that for an average epoxy equivalent weight to amine stoichiometric ratio in the range of from 0.86 to 1.29, preferably in the range of from to 1.183 to 0.864 and more preferably from 1.022 to 1.13.
In yet another embodiment, the composition comprises the first component (i) in the range of from 5 to 30% by weight based on the total weight of the composition, preferably from 12 to 25% by weight based on the total weight of the composition.
The composition may comprise the second component (i) in the range of from 5 to 20% by weight based on the total weight of the composition, preferably from 8 to 10% by weight based on the total weight of the composition.
In another embodiment of the invention, the component (iii) is in the range of from 12 to 20% by weight based on the total weight of the composition.
In a further embodiment, the hydrazide based curative is a dihydrazide curative and wherein preferably the urone based curative (a) is selected from phenyl ureas. We have discovered that the combination of a dihydrazide curative, a urone based curative comprising a phenyl urea and cycloaliphatic epoxy resins result in a fast curing composition which has a cured Tg of over 130° C. when cured at temperatures over 170° C. and a retained Tg (or wet Tg) of over whilst the cured loss modulus E″ is at values over 130° C. and the hot wet loss modulus E″w is at values over 120° C.
In an optional embodiment, the composition may comprise an additional curative in the form of an imidazole curative. Alternatively, the urone based curative may be substituted by an imidazole curative.
However in a preferred embodiment no imidazole is present in the composition.
In another embodiment of the invention there is provided a moulding material comprising a resin composition as hereinbefore described in combination with a fibrous reinforcement material. The fibrous reinforcement material may be provided in differed forms: as a woven fabric or a multi-axial fabric to form a prepreg, as individual fiber tows for impregnation with the resin composition to form towpregs, or as chopped fibers, short fibers or filaments to form a moulding compound.
In a further embodiment of the invention there is provided an adhesive comprising a composition as defined in any of preceding claims in combination with at least one filler.
The resin composition as described herein contains a number of epoxy resins comprising a dicyclopentadiene based epoxy resin, epoxy novolacs and a combination of a dihydrazide curative and a urone based curative. Preferably, the urone based curative comprises an aryl urea or an alkyl-aryl urea; and more preferably, the urone based curative comprises a phenyl urea.
The composition is capable of fast curing whilst the Tg, retained Tg and mechanical properties enable use of this in Industrial structural applications particularly automotive structural applications.
The resin composition preferably comprises a first polyfunctional epoxy component (i) comprising an epoxy resin based on a alkylol alkane triglycidyl ether monomer, a second component (ii) comprising an epoxy resin, and a third component (iii) comprising a hydrazide based curative in combination with a urone based curative.
Alkylol Alkene Triglycidylether Monomers
The alkylol alkene triglycidylether monomer is selected from the group of monomers consisting of trimethylolethane triglycidyl ether, trimethylolmethane triglycidyl ether, trimethylolpropane triglycidyl ether, triphenylolmethane triglycidyl ether, trisphenol triglycidyl ether, tetraphenylol ethane triglycidyl ether, p-aminophenol triglycidyl ether, 1,2,6-hexanetriol triglycidyl ether, glycerol triglycidyl ether, diglycerol triglycidyl ether, glycerol ethoxylate triglycidyl ether, castor oil triglycidyl ether, propoxylated glycerine triglycidyl ether. In a preferred embodiment, the alkylol alkene triglycidylether monomer comprises an epoxy novolac resin and a phenol novolac epoxy resin which differs in structure from the epoxy novolac resin.
Curatives
The urone based curative may be selected from 1,3-diphenylurea, benzylurea, 1,1-dimethyl-3-phenylurea, N-ethylurea, N-(2-Chloro-4-pyridyl)-N′-phenylurea, N,N′-dibenzylurea, N-(4-chlorophenyl) N,N-dimethyl urea, N-(4-chlorophenyl) n,n-Dimethyl urea, N-phenyl-N,N-dimethylurea, 2,4 toluene bis dimethyl urea, 2,4 toluene bis dimethyl urea, cycloaliphatic bisurea, toluene bis dimethyl urea, 4,4′ methylene bis (phenyl dimethyl urea), N,N-dimethyl-N′-[3-(trifluoromethyl)phenyl]-urea, 3-(3,4-dichlorophenyl)-1,1-dimethylurea and/or combinations of the aforesaid ureas. In a preferred embodiment, the urone based curative is 1,1-dimethyl-3-phenylurea.
The imidazole based curative may be selected from the group consisting of compounds represented by formula (I):
The curative may be selected from one or more of the following imidazoles including 2-ethyl-4-methylimidazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 2-undecylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 1-benzyl-2-phenylimidazole, 1,2-dimethylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, 1-cyanoethyl-2-undecylimidazole, 1-cyanoethyl-2-phenylimidazole, and 2-phenyl-4,5-dihydroxymethylimidazole, and imidazole, 2-ethyl-4-methylimidazole, 1-methylimidazole, 2-methylimidazole, 4-methylimidazole, 1-benzyl-2-methylimidazole, 2-heptadecylimidazole, 2-undecylimidazole, 1,2-dimethylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, imidazolines including 2-methylimidazoline, 2-phenylimidazoline, 2-undecylimidazoline, 2-heptadecylimidazoline, 2-ethylimidazoline, 2-isopropylimidazoline, 2,4-dimethylimidazoline, and 2-phenyl-4-methylimidazoline, and 2-methylimidazoline or 2-phenylimidazoline, 1-isopropyl-2-methyl imidazole, 1-(2-hydroxypropyl)-2-methylimidazole, isopropyl-2-aryl imidazole, 1-isopropyl-2-aryl imidazoline and/or combinations of the aforesaid imidazoles.
The hydrazide based curative may be a dihydrazide having the following chemical structure:
Wherein R comprises (—CH2—)n or (—Ar—); wherein n is a number from 0 to 10; and wherein Ar is an aromatic ring.
Preferably, the hydrazide curative comprises at least one compound selected from the group consisting of: an aromatic hydrazide, an aliphatic hydrazide, and any combination thereof.
The hydrazide curative may be selected from the group consisting of: adipic dihydrazide, adipic acid dihydrazide, 3, 4-diaminobenzhydrazide, succinic dihydrazide, 4-aminobenzoic hydrazide, (+)-biotinamidohexanoic acid hydrazide, oxalyldihydrazide, maleic hydrazide, dodecanoic acid dihydrazide, isophthalic acid dihydrazide, 1,4-cyclohexyl dihydrazide, 4,4′-(propane-1,3-diylbisoxy) dibenzoic dihydrazide, terephthalic acid dihydrazide, isophthalic dihydrazide, and/or any combination thereof.
Various additives may be included in the composition.
Impact Modifiers
The composition may comprise an impact modifier. Impact modifiers are widely used to improve the impact strength for epoxy resin compositions with the aim to compensate their inherent brittleness and crack propagation. Impact modifiers may comprise rubber particles such as CTBN rubbers (carboxyl-terminated butadiene-acrylonitrile) or core shell particles which contain a rubber or other elastomeric compound encased in a polymer shell. The advantage of core shell particles over rubber particles is that they have a controlled particle size of the rubber core for effective toughening and the grafted polymer shell ensures adhesion and compatibility with the epoxy resin composition. Examples of such core shell rubbers are disclosed in EP0985692 and in WO 2014062531.
Alternative impact modifiers may include methylacrylate based polymers, polyamides, acrylics, polyacrylates, acrylate copolymers, and polyethersulphones.
Fillers
In addition the composition may comprise one or more fillers to enhance the flow properties of the composition. Suitable fillers may comprise talc, microballoons, flock, glass beads, silica, fumed silica, carbon black, fibers, filaments and recycled derivatives, and titanium dioxide.
Importantly, and preferably, a phenoxy polymer component is absent in the composition of the present invention. We have found that the absence of a phenoxy polymer component results in the achievement of the desired E′ Tg, E″ Tg (for both dry and hot wet treated samples) whilst also providing a composition with advantageous fast cure properties when cured at temperatures of over 120° C., preferably at 170° C. This renders the composition of the present invention particularly suitable for applications in compression moulding and for high volume production of compression moulded parts.
To measure the degree of cure using Digital Scanning Calorimetry the heat released during the curing reaction is related to the total heat for fully curing. This can be measured as follows. A reference resin composition sample is heated from 10° C. to 250° C. at 10° C./min rate to full cure (100%) and the generated heat ΔHi is recorded. The degree of cure of a particular resin sample of the same composition as the reference resin composition sample can then be measured by curing the composition sample to the desired temperature and at the desired rate and for the desired time by heating the sample at these conditions and measuring the heat ΔHe generated by this cure reaction. The degree of cure (Cure %) is then defined by:
Cure %=[(ΔHI−ΔHe)/ΔHi]×100 [%] (-)
where ΔHi is the heat generated by the uncured resin heated from 10° C. up to fully cured at 250° C. and ΔHe is the heat generated by the certain degree cured resin heated up to a desired temperature and rate.
The glass transition temperature for a dry Tg and a hot wet Tg can be derived from both the storage modulus and the loss modulus using dynamic mechanical analysis.
In dynamic mechanical analysis (DMA) a resin composition sample being probed is subjected to a time-varying deformation and the sample response is measured. In the DMA experiment, a sinusoidal time-varying strain (controlled deformation) is applied to the sample:
γ=γo sin(ωt) (i)
Where γ is the applied strain, γo is the strain amplitude and ω is the frequency.
The DMA instrument measures the resultant stress:
σ=σo sin(ωt+δ) (ii)
Where σ is the resultant stress, σo is the stress amplitude and δ is the phase angle.
For most resin compositions due to the viscoelastic nature (both viscous component and an elastic component) there is a phase lag due to the contribution of the viscous component called the phase angle. The phase angle is important since it is used to calculate the dynamic moduli.
For small strain amplitudes and time independent polymers (linear viscoelastic regime) the resulting stress can be written in terms of the (dynamic) storage modulus (E′) and the (dynamic) loss modulus (E″):
σ=γo[E′ sin(ωt)=E″ cos(ωt)] (iii)
The storage modulus (E′) and the loss modulus (E″) can thus be calculated using the following equations derived from (iii):
A typical DMA experiment is to measure E′ and E″ as a function of temperature using a precise temperature-controlled oven with a linear heating ramp to the desired end temperature. Typical heating rates are in the range of 2 to 5° C./minute.
A standard test for assigning the glass transition temperature Tg by DMA is found in ASTM E1640 and is derived from the storage modulus, the loss modulus and from tan δ which is the ratio of the loss and storage moduli:
From the respective moduli and tan δ diagrams derived by DMA, different glass transition temperatures associated with the storage modulus (E′ Tg), the loss modulus (E″ Tg) and tan δ (tan δ Tg) can be readily identified.
As defined and illustrated in ASTM standard E1640, the Tg can be labeled for a DMA resin composition sample using the following parameters:
E′ Tg: Occurs at the lowest temperature and is identified by the intersecting tangents corresponding to a tangent to the storage modulus curve below the transition temperature and a tangent to the storage modulus curve at the inflection point approximately midway through the sigmoidal change associated with the transitions.
E″ Tg: Occurs at the middle temperature and is identified as the maximum in the E″ curve.
Tan Delta Tg: Occurs at the highest temperature and is identified as the maximum of the tan delta curve.
Embodiments of the invention will now be described by way of example only.
The following constituent components were used in the preparation of the compositions of the Examples.
In the Examples the following parameters were measured:
Various resin compositions were prepared by heating an novolac epoxy component and subsequently blending in the other epoxy resin components followed by the other constituent components of the compositions as outlined in Table 1.
The compositions for Examples 1 to 6 are set out in the below Table 1. All amounts are weight % based on the total weight of the composition for each composition of each Example.
The resin compositions of Examples 1 to 6 were exposed to a temperature of 170° C. and the time to peak exotherm and the time to cure to reach 95% cure were measured. The results are shown in Table 2.
The Tg and wet Tg were also measured in addition to a number of additional parameters after exposing the compositions to a temperature of 170° C. for 3 minutes to cure the compositions.
The resin composition of the invention can thus be cured to at least 95% of cure in under 2 minutes at 170° C. (as measured using DSC (Digital Scanning Calorimetry) or DEA (dielectric cure monitoring)) with a cured Tg of over 130° C. and a hot wet Tg of over 100° C. and can thus provide the desired mechanical properties for structural applications.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1714292.8 | Sep 2017 | GB | national |
| 1803854.7 | Mar 2018 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/074305 | 9/10/2018 | WO | 00 |
