CA2057512A1

CA2057512A1 - Epoxy resin mixtures for fiber composites

Info

Publication number: CA2057512A1
Application number: CA 2057512
Authority: CA
Inventors: Michael Staengle; Thomas Weber; Helmut Tesch; Thomas Allspach; Volker Altstaedt; Herbert Stutz
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1990-12-13
Filing date: 1991-12-12
Publication date: 1992-06-14
Also published as: DE4039715A1; EP0490230A3; JPH04275358A; EP0490230A2

Abstract

O.Z. 0050/42088 Abstract of the Disclosure: An epoxy resin mixture contains A. an epoxy resin of high functionality, B. a bisphenol F epoxy resin of low functionality, C. optionally an epoxy resin of low functionality and low molecular weight, D. an N-containing hardener, E. optionally an accelerant, F. optionally a rubber, and G. optionally a high temperature resistant thermoplastic.

Description

~ O ~ 7 ~ 1 2 o. z . 0o5o/42o88 The pres~nt invention rela~s to hea~ cu~able epoxy xesi~ mixtures for fiber composite~ ha~ing impro~ed toughnes3 and hot/moist properti~s~
Epoxy re~ins for preparing high performance compo~ites by Lmpregnation of reinforcing fibers and subsequent thermal curing are kno~n. Essenkial requirements of composite materials are high stiffness and strength, high damage tolerance following impact, and high temp~ratule resistance. Because epoxy resins in c~mposite materials take up watar, a decrease takes place under re~l hmbient condition-~ in the softening temperatures of the materials and consequently also in the ~treng~h properties at elevated temperatures (hot/moist properties). , Use in primary structures Ln air~raft construction, in particular, requires components ~aving improved damage tolerance and hot/moist properties. To obtain such Lmproved structural components it is necessary to ha~e resins of hiyher toughness and softening temperature following watex 2Q uptake coupled with high stiffness.
However, most Xnown measures for Lmproving the toughness of epoxy resins lead to a decreas2 in the ~oftening temperature and sti~fnes~. Conrer3ely, meas~res for rai~ing the softening tempera~ure and the modulus gener-ally lead to e~brittlement of the mate~ial.
Epoxy re~ins which are u~ed in aircraf~cons~ruc~ion are cu3tomarily composed o~ epoxide u~it~ of high ~unctionality. A unit which i~ used ln many epoxy re~in formul~tiun~ is ~-~unctional te~raglycidyldiamino~
diphenylmethane ~TGDDM). The high crosslinXing density following curing does gi~e a high ~tiffnes3 and ~e~p~rature xesistance, but i3 also the reason why ~he material lac~s toughnes~, ' To reduce th~ crossli~king density i~ is cus~omary ~ 2 -$~ 7 ~ ~ ~ a. z . 0050/4208B
~o use mixtures of 4 functional and low molecular weight 2-functional epoxide units. It is ~xu~ ~hat higher concentra~i~ns o~ the 2-func~ional componen~bring about an Lmpro~ement in the ~oughness, bu~ at ~he cos~ of a pronounced drop in stiffnes~ and temperature resistance.
~his has been shown by Niederstad~ in Kunststoffberater 11/12 (1983), 25l on mixtures of TGDDM and Bisphe~ol A
diglycidyl ether (DGEBA~ ha~ing an a~erage molecular weight of about 380 (corresponding to an epoxy equi~alent weight lQ of about l90) which are cured with 4,4~-diaminodiphenyl sulfone.
DE-A-3B 29 662 (US Ser. NoO 07~3~Z 695) describes epoxy resin mixtures for fiber composite~, containing A. an epo~y resin of high functionality, B. an epoxy resin of low functionality and high moleculax weight (high epoxy equivalent weight), and optionally C. an epoxy resin of low functiona~ity and low molecular weight.
I~ is true that such epo~y re~in mixtures cure to give articles of high toughness and hea~ resis~ance; but the water uptake i8 too high and the shear modulus in thP moi~t state is too low.
It i~ an ob~ect of the presen~ in~ention to develop epoxy resin mixtures which cure to giYe articles of impro~ed ~tiffnes~ without any notice~hle reduotion intoughnes~ and heat re~istance More particularly, the article~ ~hall have a comparatî~ely low water-lptak~ and a hiyh stif~ness i.n the rooist 3tate.
We have found, surprisingly, that thi~ object i~
achieved by using mixtures of epoxy resin~ o comparati~ely high func~ionality with 2-func~ional bisph~nol ~ epoxy resins in a certain mi~ing ratio and curing these mixtures with customary h~rden~rs.
The present invention accordingly provide~ epoxy 2 ~ ~ 7 ~ ~ 2 resirl mixtures con~ainLn~
A. 100 parts by weight o~ a~epo~y resin having an average functio~ality of 3 or greater, B. from 73 to 200, preferably from 80 ko 150, parts by weight of a bisphenol F epoxy resin ha~i~g an a~erage funotio~ality of from 1,5 to 2.2~ preferably from 1.8 to 2, and an epoxy equivalent weight of less than 250;
B~o less than 10 parts by weight, preferably 12ss than 1 part by weight and in particular 0 part by weight, of a bisphenol F ~poxy resin having a~ epoxy equivalent weight of greater than 250;
C. optionally from 1 to 100, preferably from 5 to 50, par~s by weigh~ of an 2poxy resin having an a~erage functionali~y of les~ than 2.5 and an epo~y equivalent weight of less than 500~ preferably less than 250, D. from 3 to 300, pre~erably from 5 to 250, parts by weight (based on A to C~ of an ~-contai~ing hardener;
E. optionally from 0.1 to 10 part~ by weight (based on A
to C~ of a hardening accelera~t; 0 F. optionally from 1 to 10 parts by weight (based on.A to C) of a rubber; and G. optionally from 1 to 50 parts by weight (based on A to C~ o~ a thermoplastic polymer having a softening temp~rature of above 90~C.
The ma~erials used will now be more particul.arly descri~ed.
A) As EP re~in ha~ing an average functionality o~ 3 or gr~a~er it is pxe~er~ble ~o u~e aromatic EP resins which ha~e 3 or 4 ~P group~ per molecule and a softening tamperature of below 30~C.
Suitable ~P resins are or e~ample tetraglycidyl diæminodiphen~lmethane (~raldite ~ 720 and Araldite N7 721 from CIBA-G~IGY) 9 triglycidylaminophenol (Araldite M~ 0510) and triglycidyl~riphenolmethane ~ 4 ~ ~ 7 ~ 1~ ~ æ 005Q/4Z0~8 (Tactix 742 from DOW~. It ~ als~ po~sible to u~e mixture~ of two or more EP resi~s.
~) Bisphe~ol F epoxy~e5ins have an averag~unctionality of from 1.5 to 2.2 and their epoxy equlvalen~ weigh~
is Less ~han 250. The So~eniny temperature is preferably within the range from -10 to -30C. The underlying bisphenol E is a monomer mixture of ~he formula HO OH
~ CH2 ~

Preferably, in the mixture the proportion o o,o-sub~titution is greater than 5%, in particul~r gr~ater than 10%, and the proportion of p,p-substi-tution is less than 60~, in parti~ular less than 50%.
It is particularly ad~antageous ~o use PY 306 (CIBA-GEIGY) contai~ing 14.5% of o,o- and 37% of p~p-substitution, but it is al~o possible to use Rutapox 0 158 (~ARELITE) containing 6.8% o o,o- and 50.5~ o p,p-s~bstitution.
C) Preferred ~urther EP resins are those havi~g a functionali~y of less than 2.5 and an epoxy equivalen~
weight of less than 500, preferably les~ than 250.
E~amples are bisphenol A diglycidyl ether; ~. g. Epikote 828 rom SHELI. ha~ing an EEN of about 190, DE~R 332 ~rom DOW (EEW about 170), D~R 661 (EEW ahou~ 500) /
dic:~clopentadienyl diglycid~l eth2r (Tac:~:ix 556 ~rom DOW) and also :Eluorene diglycid~l ether ( RSS 1079 :from SHEI-L ) .
D ~ Preferred hardener3 are aliphatic, alicyclic and aromatic ~lamines haviIlg a mol~sular weight of below 700 and also dicyandiamide~ Particular preference is gi~ren to aromatic am:Lnes, e.g. 4,4'-diaminodipherlyl ~7~
sul~one (DDS), in a concen~ration o~ about 0~5 - 1.8 NH group~ p~x EP group, E) Cu~tomary curing accel~ran~ are ~or example boron trifluoride ethylamine, imidazol~ compounds and al o N-4-chlorophe~yl-N'-dLmethylureaandN-3~4~di~hloro-ph0nyl~N' dimethylurea.
F) Customary rubbPrs used for toughening EP resins are for example carboxyl-terminated acrylonitrile-~utadiene rubbers, organofunctionalsiloxanes andalso acrylate rubbers.
G~ Preference is given to aromatic l~w or high molecular weight thermoplastics, e~g. polyhydro~yethers, polyimides, polyether sulfones ~e.g. Ultrason E lO10 ~rom ~ASF) or polysulfone~, which are pref~rably soluble in the EP resin mixture.
Themixturemayadditionallyco~tainothercustomary addi~ives such as pi~ments/ ~lam~ re~ardantg or other auxiliarie~.
The resins of the presen~ invention are suitable for use as impregnatin~ resins for preparing prepregs. This involves impregnating for e~ample glass, carbon or aramid fibers either from the melt or ~rom the solu~ion to ~orm unidirectional preprPgs, woven prepreg~ or prepreg rovings.
The resin mixture used is prepared by ~i~ing the components in a sol~ent or directly in khe melt, If mixing is directly in the melt, ~irst the EP component~ are added ~ogether at from about 80 to lSO~C and then any additive~
such a~ rubber~ or thermoplastics are dis~olved in the mixture~ I~ carboxyl-terminated butadiene~acrylonitrile rubber are u~edr the mixture i9 held at ~bou~ 110 - 130C
for ~ome time in the presence of cus~omary catalys~s, e.g.
triphenylphosphine, to ensure chemical bind~^ng of the rubber to the EP resins. Thereaf~er the mixture i~ eeoled and thP
hardener and any accelerant to be u~ed are addedO In the 5 ~ Z . 0050 /42 08B
: cas~ of the preferred aromatic amine hardeners/ this is done a~ about 80 - 110C. The r~ady~prepared re~in mixture i~
proces5ed on~commerci 1 prepreg traiAs~ for example by ~he resin film transfer process. I~ the prepregs are to bQ
prepared by impreynatiny the fiberæ with re3in ~olution~, then the mixture ~s prepared in a solvent, preferably acetone, the fibers are impregnated, and the solvent is evaporated off.
The curing of the prepregs to gi~e the fiber composite takes place at ~rom 150 to 250C, preferably at from 160 to 200C.
EXAMPLES
Preparation of resin formulations EXAMP~ES
An epoxy resin mixture (see Table) i~ heated to 120C. Once the mix~ure i5 completely homoge~eous, it is cooled down t~ 95 - ~00C, and ground 4,4'~diaminodiphenyl sulfo~e i~ added. To ensure hQmogeneous dispersion, the mixtur~ is thoroughly stirred for 30 min. ~hen the mixture is e~acuated to remove trapped air bubble~.
This method is used to prepare all the resi~
mixtures described hereinafter. In Example 6, the thermopla~tic i~ dissolved in the epoxy re~in mixture ak from 140C b2~0re the hardener is added.

Specimen preparation and testiRg (unreinforced sp~cimens) The re~in mixtures are cuxed in a ~hruugh cix-culation cabinet between preheated steal plates, which have been sprayed with a relea~e agen~, ~o form 4 mm thick pla~es o~ ~ize 250 x ~50 mm (curing. 2 h at 150C followed by 2 h 30 At 200~). Speoimens are milled out of the cured pla~e~ for th~ fellowing tests 5 - critical ~tre~s in~en~ity fac~or ~IC ~ A5TM E-399~
- softening ~emp~ra~Lre Ts (dry and moist stor~d 7 ~ QO~n/~2~8 spec ~en3~ 2 0~7 ~1 2 - shear modulus ~' at ~3~ (dxy) ~ ~hear modulus G' at 82C (moist~
- water uptake on moist storage The shear moduli and softening tempera~ures are determined with an RDA 70n ~rom Rhe~metrics at a frequency of 1 ~z and a heating-up rate of ~ ~/min (specimen dimensions 53 x ~1 x 4 mm). ~he so~ening temper~ture is defined as the point of intersec~ion o~ the tangent with the shear modulus curve. To determine the data following moist storage, samples are stored in distilled water ak 70C fo~
30 days. The water uptake is determined gravimetrically.
Erom the Examples listed in Table 1 - 1 to 3 according to the invention, 4 and 5 comparative - and the corresponding properties in Table 2 it is clear that the resin formulati~ns according to the present inYentio~ are ad~an~ageou~.

T~BL~ 1 Composition of mixtures (part~ by weigh~) Example Component 1 2 3 4 5 6 A Tactix 742 31.9 23.7 20.3 2307 31.9 20.1 NX 0510 - 17.~ ~3.2 17.~ - 15.1 B PY 306 31.9 17.8 11.6 - - 15.1 C DER 332 - 3.1 17.8 31.9 D DVS 36.2 40.8 ~0.8 40.8 36.2 3~.7 G Ultra~on E ~ lS.0 TA~LE 2 Proper~ies of cured pieces ~xample . 301 ~ 3 4 5 6 RIC tMPa ml/2~0.500.56 0O5~ 0.53 0.59 0.~6 ~ 0 ~ ~ ~ 1 2 TS drY ~C~ 202 215 214 228 229 216 T~ mOiS~ ~C] 153 147 144 150 157 152 ~' drY 23C [MPa] 1265 1264 1231 1191 1091 1179 G9 mOi5t 82G C~PaJ941 915 884 869 834 873 Water UPtake t%] 3.8 4.6 5.1 4.9 4.1 4.7, PrePreg makin~ .
~ he reSin miXtUre~ are PrO~eSSed in a COating maChine tO PrePare a re5in fi1m On re1ea5e PaPer, WhiCh i5 PrOCeSSed On a PrePreg maChine bY the reSin fi1m tranSfer PrOCeSS tOgether With Para11e1iZed CarbOn fiber rO~ingS Of tYPe Ce1iOn G30-5U0~12~ (BASF StrUCtUra1 ~ateria1S3 tO fO~m a UnidireCtiOna1 PrePreg. ReSin COntent and fiber Sh0et Weight are ad;USted 1n SUCh a WaY aS tO Obtain~ On CUring~
a 1aminate haVing a fiber COntent O~ 60% bY YO1Ume and a thiCkneSS Of 0.125 mm Per PrePreg 1aYer. ~he PrePreg5 aXe PrOVided With a PrOteCtiVe ~i1m, WOUnd UP and 5tOred at -18C Unti1 reqUired fOr 1aminatiOn.

SPeCLmen PreParatiOn and teSti~g The PrePregS are USed tO PrePare 1aminateS fOr teSt8 Of meChanira1 PrOPeXtieS tO SACMA SRN 1/8d (0 COmPreSSiVe Strength)~ SRM 2/88 (C~mPreSSiOn after imPaCt), SRM 4/88 (tenSile Strength)~ SRM 8/88 (interlaminar 9hear Strength ILS) and MASA RP 1092 (inter1aminar CraCk tOUYhne~8 G~) and a dO~b1e Canti1eV2r beam fOr mea~Uring the in~er1aminar CraCk kOUghneSS GII~ (end not~hed flexure) . The curing takes place in a vacuum bag within an autocla~e at .a Pra~3SUre O:E 6 bar, with a heating~up :rate of from 1 to 3C/min ~rom room temperature to 177C and in the course of a c:uring time of 120 min at 177C. ~he fiber volume content of ~he laminate is 60%.
The carbon fiber laminate~ prepared using resin formulation 6 are found to have the following properties a~

v~
- 9 2 ~ ~ 7 ~ o z . ~5~/42~88 a test t~nperature of 23C:

GIC 3~5 J m2 " 820 3 . m~2 ~IIC
Cornpression after impact ( 6 . 7 J~ 195 ~a 0 tensile streng~h 220~ MPa 90 tensile strength 84 ~Pa O compressive str2ngth, dry, 23 C 1545 ~Pa Q ~ compressive str~ngth, mois~, 82nC 1261 MPa ILS, dry, 23 C 124 ~Pa

Claims

1. An epoxy resin mixture containing A. 100 parts by weight of an epoxy resin having an average functionality of 3 or greater, B. from 70 to 200 parts by weight of a bisphenol F
epoxy resin having an average functionality of from 1.5 to 2.2 and an epoxy equivalent weight of less than 250;
B'. less than 10 parts by weight of a bisphenol F epoxy resin having an epoxy equivalent weight of greater than 250;
C. optionally from 1 to 100 parts by weight of an epoxy resin different from B and having an average functionality of less than 2.5 and an epoxy equivalent weight of less than 500 D. from 3 to 300 parts by weight (based on A to C) of an N-containing hardener;
E. optionally from 0.1 to 10 parts by weight (based on A to C) of a hardening accelerant;
F. optionally from 1 to 10 parts by weight (based on A
to C) of a rubber; and G. optionally from 1 to 50 parts by weight (based on A
to C) of a thermoplastic polymer having a softening temperature of above 90°C.

2. An epoxy resin mixture as claimed in claim 1, wherein the bisphenol F on which the epoxy resin B is based is an isomer mixture containing more than 10% of 0,0-substitution and less than 50% of p,p-substitution.

3. A perpreg for high performance composites, containing an epoxy resin mixture as claimed in claim 1 and from 30 to 80% by weight of reinforcing fibers.