Method for providing a moulding composition and moulding composition

Abstract

Treating an uncured resin matrix composition to impart energy to the resin matrix composition enables a stable Tg to be achieved whereby the resin matrix composition may be stored and has a low tack enabling subsequent processing and handling. The invention provides a method of achieving a stable Tg without the resin matrix composition starting to cure and a method of determining the treatment regime by which a resin matrix composition with a stable Tg may be obtained. The resin matrix composition may be fresh or reused uncured resin matrix composition and may contain fibrous reinforcement.

Claims

1. A method of producing a moulding composition comprising providing a fibrous reinforcement material impregnated with a stabilised uncured epoxy resin matrix composition and combining the stabilised uncured epoxy resin matrix composition and impregnated fibrous reinforcement material with a further resin matrix composition, wherein the stabilized uncured resin matrix composition is conceived by providing a resin matrix composition having an initial Tg and subjecting the resin matrix composition to: a first regime comprising imparting energy by heating to the resin matrix composition to raise the Tg by at least 5 C. to provide a raised Tg without substantially curing the resin; and a second regime comprising storing the resin matrix composition to provide a stabilised resin matrix composition wherein the Tg of the stabilised uncured resin is such that it does not increase by more than 10 C. from the raised Tg when stored for at least 24 hours; wherein the stabilized epoxy resin matrix composition and the further resin matrix composition comprise different compositions; and wherein said uncured epoxy resin matrix composition comprises a previously formed prepreg, in the form of discrete elements.

2. The method according to claim 1 wherein the stabilised uncured resin matrix composition with fibrous reinforcement material is stored prior to combining with the further resin matrix composition.

3. A The method according to claim 2 wherein the discrete elements have a tack F/Fref of not more than 0.6 at room temperature where Fref=28.19N and F is the maximum debonding force.

4. A The method according to claim 3 wherein treatment of the uncured resin matrix composition comprises imparting energy by heating to the uncured resin matrix composition to raise the Tg of the resin matrix composition by at least 5 C. to provide a raised Tg without curing the resin matrix composition wherein the raised Tg of the stabilised uncured resin matrix composition is such that it does not increase by more than 10% when stored for 14 days.

5. The method according to claim 4 wherein the stabilised resin matrix composition is stored at ambient temperature prior to combining with the second resin matrix composition.

6. The method according to claim 5 wherein the stabilised resin matrix composition is stored for a period of at least 24 hours to 90 days at ambient temperature.

Description

(1) The invention is illustrated by the following non-limiting examples and with reference to the accompanying drawings in which

(2) FIG. 1 presents a diagrammatic view of a lay-up of a resin matrix composition according to an embodiment of the invention using a vacuum bag;

(3) FIG. 2 presents a diagrammatic view of gripping layers of a sample according to another embodiment of the invention;

(4) FIG. 3 presents a diagram showing the relationship between peel torque (in N/10 mm) in relation to Tg (in C.) according to an embodiment of the invention;

(5) FIG. 4 presents a diagram showing the relationship between glas transition temperature T.sub.g ( C.) and aging time (weeks) according to an embodiment of the invention;

(6) FIG. 5 presents a diagram showing another relationship between glas transition temperature T.sub.g ( C.) and aging time (hours) according to an embodiment of the invention;

(7) FIG. 6 shows a preform according to a further embodiment of the invention;

(8) FIG. 7 shows a cured product according to another embodiment of the invention;

(9) FIG. 8 shows another cured product according to a further embodiment of the invention;

(10) FIG. 9 presents a bar chart based on Table 4 of this application; and

(11) FIG. 10 presents cured products according to further embodiments of the invention illustrating the flow behaviour of the material of the invention.

EXAMPLE 1

(12) Several batches of pre-preg products comprising uncured resin matrix composition and carbon fibres were subjected to T Peel testing. The pre-preg product was as follows:

(13) 3 batches of M21E/34%/UD 194/IMA-12K: Batch 1: N23C14 02A Batch 2: N14302 12A Batch 3: N14205 05A

(14) 1 batch of M21E/34%/UD 268/IMA-12K: Batch 1*: N22A1801A

(15) Stabilizing T.sub.g

(16) Five samples from each batch were subjected to a first regime by heating in an oven at 50 C. under a dry atmosphere during following periods: 24 h, 72 h, 144 h, 152 h and 200 h. For each batch, a sample of fresh material was kept without being subjected to the first regime, And referred to as TO below. After the first regime, the samples were held in a freezer at 18 C. (0 F.) Furthermore, each specimen was analyzed by DSC.sup.1 test just after the first regime and prior to the second regime to determine Tg. The Tg results are shown in Table 1.

(17) The DSC cycle used for analysis consisted in a ramp of 10 C./min from 60 C. (76 F.) to 315 C. (600 F.) samples comprised 7 mg of resin matrix composition (approximately 20 mg of prepreg). The Tg value measured is the midpoint temperature. Unless otherwise stated, DSC measurements may be carried out using this method.

(18) TABLE-US-00001 TABLE 1 Tg for each batch T0 24 h @ 50 C. 72 h @ 50 C. 144 h @50 C. 152 h@50 C. 200 h@50 C. BATCH 1 0.99 C. 1.1 C. 7.39 C. 17.63 C. 18.19 C. 29.74 C. BATCH 2 2 C. 0.97 C. 6.24 C. 16.6 C. 19.33 C. 26.13 C. BATCH 3 0.84 C. 2.91 C. 9.19 C. 15.41 C. 23.04 C. 27.39 C. BATCH 1* 0.24 C. 2.63 C. 8.15 C. 17.41 C. 19.71 C. 27.91 C. .sup.1 Differential scanning calorimetry

(19) Storage Simulation

(20) The samples were subjected to a process to simulate storage of resin matrix composition chips in a bulk quantity in a storage bag under harsh conditions of storage. This simulation increased the chance that clustering or agglomeration of chips might occur A temperature of 60 C. to simulate bright sunlight and a pressure of 1 bar (14.5 psi) was applied, corresponding to the higher pressure that a chip could perceive at the bottom of a storage bag. The storage conditions were performed by using a vacuum bag method as set out below and with reference to FIG. 1.

(21) Apparatus for the vacuum bag method is shown in FIG. 1 which shows a tool 1 upon which is mounted a vacuum bag 2 having a first side 2a and a second side 2b sealed with mastic 2c and a sandwich arrangement comprising two layers of Teflon coated glass, referred to as breathers, 3a, 3b, layers of resin matrix composition product 4a and 4b and a Teflon coated glass primer 5 (length 50 mm) with which to commence the T Peel test.

(22) Two layers of the sample resin matrix composition are mounted in the apparatus and the assembly was placed in an oven for 15 hours at 60 C. and a pressure of 1 bar was applied using a vacuum pump.

(23) Samples Preparation and T Peel Test

(24) Once the samples had been subjected to the Storage Simulation the samples were prepared for use in T Peel tests. The T Peel test allows the adhesion strength between two layers of a sample bonded to each other to be determined using a tensile machine. An average strength of debonding between layers is measured and a Peel torque is determined. The Peel torque is equal to the average strength normalized to a 10 mm width. For each batch and each treatment, 3 samples were tested according to T Peel test ISO11339. The samples were cut to the following dimensions: Width: 30 mm Length: 300 mm Depth: 2 plies Orientation: 0

(25) The two layers of the sample were gripped respectively in a fixed jaw and a mobile jaw as shown in FIG. 2. The two layers of the sample are then separated by moving the mobile jaw away from the fixed jaw in the direction shown. The force applied in the test to separate the layers and its variation is measured using software in accordance with ASTM D1876, from which an average value of debonding strength and Peel torque value are determined.

(26) The results of the T Peel test are set out in Tables 2 to 5. For each batch three samples were tested under each regime and the results are the mean value of the three tests.

(27) TABLE-US-00002 TABLE 2 Average debonding Average Peel torque BATCH 1 strength .sup.2(N) .sup.3(N/10 mm) T0 34.8 11.6 24 h @ 50 C. 38.7 12.9 72 h @ 50 C. 2.2 0.7 144 h @ 50 C. 0.1 0.0 152 h @ 50 C. 0.4 0.2 200 h @ 50 C. 0.2 0.1 .sup.2Mean value calculated from 3 specimens results .sup.3Mean value calculated from 3 specimens results

(28) TABLE-US-00003 TABLE 3 Average debonding Average Peel torque BATCH 2 strength .sup.4(N) .sup.5(N/10 mm) T0 34 11.3 24 h @ 50 C. 43.2 14.4 72 h @ 50 C. 2.1 0.7 144 h @ 50 C. 0.4 0.1 152 h @ 50 C. 0.2 0.1 200 h @ 50 C. 0 0 .sup.4Mean value calculated from 3 specimens results .sup.5Mean value calculated from 3 specimens results

(29) TABLE-US-00004 TABLE 4 Average debonding Average Peel torque BATCH 3 strength .sup.6(N) .sup.7(N/10 mm) T0 40.2 13.4 24 h @ 50 C. 47.1 15.7 72 h @ 50 C. 1.5 0.5 144 h @ 50 C. 0.9 0.3 152 h @ 50 C. 0.2 0.1 200 h @ 50 C. 0.3 0.1 .sup.6Mean value calculated from 3 specimens results .sup.7Mean value calculated from 3 specimens results

(30) TABLE-US-00005 TABLE 5 Average debonding Average Peel torque BATCH 1* strength .sup.8(N) .sup.9(N/10 mm) T0 42.0 14.0 24 h @ 50 C. 41.4 13.8 72 h @ 50 C. 15.5 5.1 144 h @ 50 C. 1.7 0.6 152 h @ 50 C. 1.6 0.5 200 h @ 50 C. 1.4 0.5 .sup.8Mean value calculated from 3 specimens results .sup.9Mean value calculated from 3 specimens results

(31) A plot of the T Peel value versus Tg midpoint value for each batch was plotted and is shown in FIG. 3.

(32) For batches 1, 2 and 3 adhesion decreases significantly around 5 C. of Tg and debonding occurs at approximately 15 C. A slight difference is noticed with results of batch 1* in that the adhesion decreases less abruptly than with the other batches and debonding occurs at around a Tg of 20 C. The batch 1* plies were thicker than the batches 1, 2 and 3 plies which may contribute to the tailing effect observed for batch1*.

(33) For every batch debonding is reduced where the Tg is 5 C. and debonding occurs completely where the Tg value is above 20 C. for chips which have been treated according to the method of the invention and subjected to a simulation of harsh storage conditions.

(34) In summary, resin matrix composition material staged so that it has a Tg over 20 C. is suitable for storage over an extended period at ambient temperature without there being significant clustering or agglomeration irrespective of whether the storage temperature is regulated.

EXAMPLE 2

(35) Samples of M21E-34%-UD194 and M21E-34%-UD268 (fresh and Tg stabilized) were subjected to a clustering study to determine the Tg above which no significant levels of clustering were observed. The samples were heated at 60 C. for 15 hours under a pressure of 1 bar.

(36) The DSC cycle used for analysis consisted in a ramp of 10 C./min from 60 C. (76 F.) to 315 C. (600 F.).

(37) We observed that where Tg of the sample was above 20 C., no significant clustering was observed.

EXAMPLE 3

(38) Samples of M21E-34%-UD194 were subjected to a staging process and were held at 50 C. for 24, 192 hours and 40 days respectively to simulate storage conditions. A fresh sample was stored at 23 C. to simulate storage conditions. The Tg of the samples was tested using a DSC cycle consisting in a ramp of 10 C./min from 60 C. (76 F.) to 315 C. (600 F.).

(39) The Tg of the samples was plotted against storage time and is shown in FIG. 4.

(40) The Tg of the uncured resin matrix composition stabilized at a Tg of around 50 to 60 C. By stabilization, we mean that once treated to obtain a raised or sub-ambient Tg, the Tg did not subsequently vary during storage by more than 5 C.

EXAMPLE 4

(41) Samples of M21E/34%/UD 194/IMA were subjected to a staging process and were heated to at 60 C. for 72 hours and then stored at room temperature for periods up to 154 days. The Tg of a sample was tested after 12 days, 39 days, 83 days, 122 days and 154 days. The Tg of the samples was tested using a DSC cycle consisting in a ramp of 10 C./min from 60 C. (76 F.) to 315 C. (600 F.).

(42) The Tg of the samples was plotted against storage time and is shown in FIG. 5.

EXAMPLE 5

(43) A moulding test was carried out using M21E/Selvedge Dublin sheet moulding compound which had been stored at room temperature (21 C.) for 154 days. 2 plies were manually cut from the SMC and pre-heated for 10 minutes at 90 C. and shaped. Photographs of the shaped preform are shown in FIG. 6.

(44) The preform was moulded at a temperature of 185 C. with a pressure of 90 tons being applied 30 seconds after the mould had been closed. The product was left to cure for 40 minutes to produce the product shown in the photographs of FIG. 7.

(45) The preform weighed 71 g and after moulding and curing and deflashing, the formed part weighed 70.4 g.

(46) These results demonstrate that a re-used prepreg may be suitable for compression moulding and may be so used even after storage at room temperature for more than 6 months. The resin matrix composition did not flow to a level which required the mould to be cleaned

EXAMPLE 6

(47) Flow behaviour of a prepreg with and without a second resin matrix composition being added was tested by assessing the extent to which the material of the invention when applied to a central mould cavity was able to flow into an extension cavity during compression moulding.

(48) FIG. 8 shows photographs of the flow behaviour of the product with additional resin matrix composition, shown on the left and without additional resin matrix composition, shown on the right.

(49) The results show that by adding a further resin matrix composition to the fibrous reinforcement material impregnated with a first resin matrix composition, flow may be reduced thereby aiding downstream processing of the moulding composition.

EXAMPLE 7

(50) Several HexMC M21E 194 plies were stabilised by aging in an oven at 27 C. during 3 periods of time: 30 Days 60 Days 90 Days

(51) After each period, sub ambient Tg was measured, then two fresh multifunctional epoxy resin matrix composition films (one per side) were added on each ply, and panels moulded under pressure. The mechanical properties of the products were evaluated and compared to fresh material which had not been subjected to the stabilisation/aging

(52) The panels tested were moulded using the following conditions in Table 6.

(53) TABLE-US-00006 TABLE 6 Ply Additional number resin matrix 330 330 composition Mould Pre- Curing Post Material mm file (2 per ply) temp Staging Heating Pressure time Cure Aged 3 Epoxy 188 C. 1 min 100 bars 30 mn 2 h @ HexMc matrix90 gsm 180 C. M21E 194 Batch 34% Batch 50402N03 50130M01

(54) Various mechanical properties of the panels were tested and the results are set out below in Table 7.

(55) TABLE-US-00007 No ageing 30 days at 27 C. 60 days at 27 C. 90 days at 27 C. Tensile Strength AITM 312 6.3% 312 14.4% 355 9.9% 270 27.9% (Mpa) 1.0007 Modulus 45 13.7% 41.9 21.9% 49.5 14% 41.8 12.1% (Gpa) Flexural Strength ASTM 505 11.6% 501 .sup.17% 477 16% 426 .sup.27% (Mpa) D2764 Modulus 38.3 11.8% 35.9 26.8% 39 26.1%.sup. 33 22.8% (Gpa) Compression Strength AITM 337 13.2% 333 6% 353 0.9% 344 9% (Mpa) 1.008 Modulus 42.5 23.3% 46.2 18.5% 45.9 20% 44.5 16.8% (Gpa) IIss Strength ASTM 66.4 18.2% 78.2 .sup.18% 80.2 12% 76.5 .sup.11% (Mpa) D2344 Flow Length Internal 9-9 7-6.5 8-7 6-5 (Inches) DMA Tg( C.) AITM 125/132 C. 135/139 C. 114/142 C. 134/148 C. (before/after 1.0003 Post Cure) 142/135 C. 132/140 C. 136/142 C. 136/162 C. DSC Sub 2.5 C. 17.3 C. 39.4 C. 47.7 C. Ambient Tg( C.)

(56) The properties of the 4 samples are shown in a bar chart in FIG. 9.

(57) The samples were subjected to a flow test and photographs of the samples are shown in FIG. 10: top leftnon-staged, bottom left30 days, top right60 days and bottom right 90 days.

(58) The results show that the aging conditions which allow the material to be stabilised and stored do not materially affect the mechanical properties of the product up to 60 days storage. Thereafter, flexural and tensile strength fall to a degree as compared to fresh material.

(59) The flow capability was also reduced with storage at 90 days whereas it as stable up to 60 days. The material can be moulded after 90 days at 27 C.