CA1062843A - Cross-linked copolymers as vibration damping material - Google Patents

Abstract

Abstract of the Disclosure Cross-linked copolymers are obtained by free radical Copolymerization of ethylenically unsaturated monomers in the presence of a cross-linking agent and a dissolved polymer.
These copolymers have valuable sound-deadening properties and are applied to metallic substrates as vibration damping materials.

Description

~IOI~ 7 2 /I? 3 6 .~

TM3 present invention relates to cross-linked copolymers of monomers, cross-linking agents and optionally polymers, the USe of same as vibration damping material, as well as a process for preparing these copolymers~
In the scope of the effor-ts to improve environmental con-; d:~ions, the importance of sound-control is growing steadily.
To suppress noise on metal sur~aces slasceptible to conduct resonance vibrations, damping masses of synthetic or natural high polymers are applied onto the substrate which use up part of the vibration energy by relaxation movements of the polymer molecules. The vibr~tion energy is converted to heat, thus dimil1ishillg the radiation of interference noise. The measure for the dampin~ of mass conduction is the mechanical loss facl;or "d" whlch indicates the vibration energy being converted to heat for each vibration period in proportion to the vi-bration energy which had been imparted as a whole to the matt?rial.
It is known to use polymers with specific viscoelastic - properties, particularly those with high internal damping values, as vibration damping layers, e.g. for sheet metal constructions. Same are used as one-sided coating layer3 -sprayed, troweled or pasted on, often pro~ided with fillers or combined to other materials. They are further used as inter~-layers in composite metal sheet or sandwich constructions. The purpose for using them lS mostly a reduction of the undesirab'e noise effect; inherent to metal sheet constructions and the imprc-vement of the vibration damping of metal sheet ~alls. ~or certain frequency and temperature ranges satisfactory dampen;ng may thus be obtajn-?d. q'he frequency ran~e gerle~rally correspoMds 29 to the range of audible frequencies appro~imately bet~een 1(~0 -- ~ 2 ~
q~

~062843 and 1000 c.p.s.
Our Canadian Patents 812,211 and 812,212 disclose that it is pos-sible to prepare valuable noise suppressing materials for a broad temperature bandwidth so as to dampen the bending vibrations of metal sheet constructions by copolymerizing monomers, the homopolymers of which differ in their second order transition temperatures by at least 20C. As damping materials are used amorphous copolymers of vinyl acetate, n-butyl- or 2-ethylhexyl-acrylate, dibutyl-maleate and crotonic acid. Moreover, our Canadian Patent 878,454 describes graft polymers of styrene or of styrene with a copolymerizable car-boxylic acid onto the a.m. amorphous copolymers which are used as vibrationdamping interlayers.
The thermoplasts known as damping materials have in common that they show a pronounced cold flow and a tendency - especially at high tempera-tures - to leak out of the metal sheet constructions. Furthermore it is often difficult to apply the known copolymers onto metal surfaces, because in some cases a chemical degradation is observed already at elevated process-ing temperatures and because the distinctive superficial stickiness hampers a homogenous spreading on large surfaces. For example, in motor car industry for suppressing the roaring of a motor, the lack of dimensional stability and resistance to dislocation under heat of known damping masses are very disad-vantageous.
The present invention provides noise vibration damping materials for a broad bandwidth which are dimensionally and thermally stable and do not leak out of the constructional parts at elevated temperaturesJ which materials comprise a cross-linked copolymer obtained by means of free radical copoly-merization of (a) at least two ethylenically unsaturated monomers the homo-polymers of which differ in their second order transition temperatures by at least 20C, the monomers being selected from vinyl esters of saturated straight-chain or branched monocarboxylic acids having from 1 to 12 carbon atoms, esters of acrylic acid or methacrylic acid with a saturated monohydric aliphatic alco-~J

hols having from 1 to 8 carbon atoms, mono- and diester of maleic, fumaric and itaconic acids with saturated monohydric aliphatic alcohols having from l to 8 carbon atoms, styrene, vinyl toluene and vinyl xylene; with ~b) at least one cross-linking agent selected from diallyl phthalate, diallyl maleate, triallyl cyanurate, tetraallyl oxyethane, divinyl benzene, butane-diol-1,4-dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate and triethylene glycol dimethacrylate and unsaturated poly-ester resins; and, (c) if desired, a polymer of one or more ethylenically unsaturated monomers ~a) which polymer is soluble in the monomers (a).
Suitable vinyl esters of saturated, straight-chain or branched monocarboxylic acids having from 1 - 12 carbon atoms are vinyl acetate, vinyl propionate and vinyl versatate ~R), preferably vinyl acetate; preferred esters of acrylic or methacrylic acid with saturated monohydric aliphatic alcohols having from 1 - 8 carbon atoms are 2-ethylhexyl acrylate and n-butyl acry-late; and a preferred mono- or diester of maleic acid, fumaric acid or ita-conic acid with a saturated monohydric aliphatic alcohol having from 1 - 8 carbon atoms is dibutyl maleate.
The polymers from ethylenically unsaturated monomers, dissolved in the monomers, are essentially also composed of said monomers. The mixture to be polymerized contains from 0 to 95% by weight, preferably from 20 to 80 wt % of polymer, prior to the addition of the cross-linking agent.
As cross-linking agents are used ethylenically unsaturated compounds having at least two ethylenic double bonds in the molecule, namely cross-linking comonomers selected from diallyl phthalate, diallyl maleate, triallyl cyanurate, tetraallyl-oxethanel divinyl benzene, butanediol-1,4-dimethacrylate, ethylene-glycol-dimethacrylate, diethylene-glycol-dimethacrylate, r~

~or~ ~2/l' 362 ~06284~
~x~ tr;.ethylelle-~lycol-dimetllacry].ate. However, it i.s also posslble to use as cross-:Linking agents unsa~urat~d polyester resins having the form of the well-known condensation produc-ts ~rom diols and saturated as we:Ll as ethylenically unsaturated dicarboxylic acids, particularly aliphatic unsaturated poly-esters f`rom ethylene-glycol, diethylene-~l.ycol or triethylene-glycol, 1,2- or 1,3 - propanediol, 1,3- or 1,4 butanediol, 1,6-he~anediol, 2,2~dimethylpropallediol-1,3 or 2-metlly]-2--eth~
propanediol- 1,3~adipic acid, azelaic acid or sebacic aci.d as saturatecl acids and maleic acid resp. its a.nhydride, fum~ric acid, itaconic acid, citraconic acid or me.saconic acid as ethylenlcally unsaturated acids.
The cros~s-lin~ing comonomers are preferably used in quantities o~ from 0.01 - 10 wt. $, ca].culated on the monorr.ers resp. on the soluti.on of the polymer in the monomer, whilst the unsaturated polyester resins - due to less ethyleni.cal double bonds per weight unit - are used in quantities of fro~
10 - 70 wt %, calculated on the total mixture.
Mixtures specifically pr~erred for prepari.ng the cross-linked copolymers of the invention are cornposed as follows:
1. 20 - 80 wt. % of a polymer, which was obtained by poly-merization of` frorn 20 - 60 wt. ~o of 2-ethy].hexyl acrg-lat¢, 20 - 50 wt $ of vinyl acetate and 10 - l~o wt ~0 Oî bi'butyl ma].eatc, are dissolved in c~0 - 20 wt $ of vinylace-tate.
To the polymer solution are f'urther added 0.0'l - 10.0 wl.',~-calculatecl on the polymer solution - oi` a cross-linki comono]ncr.

2. 20 -~ ~0 wl; ~,'o of o poly-mer accordill~ to 1 arc- dissolved in 29 80 -~ 20 -~t. ~0 of a monomer mixture conslsting or` f`rorm ~IOE -72/F 362 .

10 - 90 wt. % of vinyl acetate and from 90 - 10 wt ~ of butyl acrylate, To the polymer so]ution are added from 0.01 to 10.0 ~t. qO - calculated 011 the polymer so]ution -of a cross-linking comonomer.

3. 20 - 80 wt. ~o of a polymer according to 1 are dissolved in from 80 - 20 wt. qO of a monomer mixture consist,ing of from 10 - 90 wt. % of vinyl acetate and 90 - 10 wt. qO of 2-ethylhexyl acrylate. To the polymer solution are added 0.01 - 10.0 wt. qO ~ calculated on the polvmer solution -of a cross~linking comonomer.

4. 20 - 80 wt. % of a polymer prepared by polymeri~ation of from 30 - 70 wt. ~ of styl-ene and 70 - 30 wt. ~0 of butyl acrylate, are disso]ved in 80 - 20 wt. % of a mi~ture of monomers consisting of 10 - 90 wt. ~0 of vinyl acetate and 90 - 10 wt. $ of butyl acrylate. To the polymer solution are added 0.01 - 10.0 wt. % - calcu]a~ed 011 the polymer solution - of a cross-linking comonomer.

5. 20 - 80 wt. $ of a polymer, prepared by polymerization of from 40 - 80 wt. ~0 of vinyl acetate and from 60 - 20 wt. $
of dibu*yl maleate, are dissolved in 80 - 20 wt. % of a mixture of monomers consis~ing of 10 - 90 wt. $ of vinyl acetate and 90 - 10 wt. qO of butyl acrylate. To the polymer so]ution are added 0.01 - 10.0 wt. ~0 - calculated on the polymer solut~n - of a cross-lin1~ing comonomer.

6. 10 - 60 wt. qO of an aliphatic polyester resin consisting of fronI 20 - 60 wt. ~0 ol` diol, 20 - 60 wt. o~10 of sclturated aliphatic dicarbo~ylic acid and 5 ~ 30 wt. ~o of unsatura1;ecl dicar;~o:~ylic acic' are dissolved in from 20 ~ 80 wt. ,~ of 29 buty1 acrylate and 5 - 30 wt. ~ of 2-ethylhe~yl acrylate.

o~, ~
lQ6Z843

7. 10 - 70 wt. ~ of an aliphatic polyester re.sin consisting of from 20 - 60 wt. $ of diol, 20 - 60 wt. ~ of saturated aliphatlc dicarboxylic acid and 5 - 30 wt. ~ of unsaturated dicarbo~ylic acid are dissolved in from 10 - 80 wt. ~ of`
butyl acrylate and 5 - 50 wt. ~p o~` a vinyl ester of a saturated strai,~lt-chain or brallched monocarboxylic acid having from 1 - 12 carbon atoms.
The weight percentages of polymer or of unsaturated poly-ester resin and of monomers contained in the solution add up to 100 ~o for each mixture. In the same way, 100 ~ are reached for the sum of the weight percentages of the components of the polymer or of the unsaturated polyester resin.
By means of these cross-lin}ced copolymers, the noise suppressing effect of whicll depends upon the weight proportion of tbe nonomers" it is possible to obtain very broad damping curves with h:igh maximum damping val1les within the frequency range between 'lO0 and 1000 c.p.s.
To all mixtures of monomers, cross-linking agent~s and polymers may be added extra fillers. Particularly good results have been obtained with ~rermiculite and other minerals'belonging to t,he group of the micaceous stratiform silicates. l~hen adding Yermiculite, the loss factor ~alues for composite systems c1imb up remarkably at higher temperatures, so that the total temper-ature bandwidt,h increases. Besides the strat:iform silica-tes are also suitable for example heavy spar, calcium carbonate, graphite or soot. The quantily I,o be added depellds uIjon t]-le application purpose in mind for the noise suppressing mass.
In case that the noise suppressing mass :is to be used as an 29 interlayer between two resonance plcltes - as an e~arn~le -, t}le ,~ liO]~ 72~` 352 quantity oI the filler does not e~ceed pre.fer.lbly 20 wt. ~0 of the mass. On the other hand, the noise suppressing mass being intended as coating on the outsicle ol' a resonance plate, the mass may contain up to 70 w-t. % of filler. A special advantage of the crGss-linked copolymers according to the inven~i.on is the possibility they offer to adjust the bandwidth eIficiency of the noi.se suppressing mass to suit any need by variation of the monomers, the cross-linking agents and -th~ dissolved poly-mers.
It is furthermore possible to a.da.pt the viscosity of tho monomer mixture to any need by addition of the polyMer. The mixtures may thus be applied onto the substrate either as liquids or as pastes, i.e. the reaction comp~t~ which contain i.niti.ator systems and accelerator systems possibly in separate vessels, are mixed prior to their app1ication, the mixture is applied to the substrate either by l-neans of slot-dies, spray ~uns of even manually with a brush or a roll, and polymerizes on the substr~te. The polymerization on the substrate offers the advanta.ge that thus the annoying and costly meltillg of thermoplastic masses is avoided.
The polymerization of the mixtures may also be initiated by UV-radiation, electron radiation or ~-radiation. In the case of u~ing UV-radiation as energy source for the polymer:i7.ation, ~sensibilizers such as benzoin or derivatives of beilzoin may be used.
The polyrneri.7.ation is carried out wi-thin a temperat-llre : ran~c between 0 ar-ld 100C, preferahl.v between 20C and 1~oc.
I-t is preferably ini.tiated with deep temperat(l:re pero~:ide 29 c~talysts, ~uch as acet:ylcyclohexatle-sul.fonylperoxide, d-icyclo--~ 72/F 36?

hexyl percarl~onate, di.isopropyl percarbollate, 2-ethylhexyl per-carbonate, 1;ert.-blltylcyclohexy]. perca~bonate, di-isononanoy].
pero~ide or telt.-butyl perpivalate. For the norlnally us~-3d per~
oxide ca.alysts, such as benzoyl peroxi.de or cyclohexanone peroYide the activation energy for the decomposition may be reduced by m~ans of accelerators to such an extent that even at room tomperature a sufficiently rapid polymerization is possible. Suitable accel.erators or acti-vators for the peroxides be.;.ng used are essentially tertiary amines, such as dimethyl anil.ine, clil.~thyl ani].ine, dimethyl-p-toluidine and salts of heavy metals, for example cobalt salts or vanadium salts.
The cross-linked copolymers according to the invention are particularly suitable for the formation of laminated systetns or saIldwich systems ]ami.nated constructions, -the interla.yers of which may be plates or sheets in-between two resonance plates each, one of same at least consisting Or metal or another resonance material. The laminates resp. the laminatod collstructions are produced by the applioation o~
the mixtures to be polytnerized onto the plates and by sub-seqllent polymeriY.ation.
T.he cross--linked copolytners according to the invention do not cn~y excel by very good vi.bration damping propertics 5 but by good adhesion as well. For this reason i]l most of -the cases it i3 nei.ther necessary to subtni.t tlle meta] pla.,es to a further pre-t:reat~en-t other than degreasing, nor to use an adhesive.
The sanclwicll constructi.ons with the cross~li.nkecl copol.y-tners acco-r~ g 1o tha invention rnay ba 1?~-3nt, ribbed, bevel.:led, 29 ri~-eted or deel~-dra~n ~lthout .. he risk of the croc.s-].inkecl _ 9 _ ~10~, _7~/l' 36~
~62843 copolymers st.art:ing to f`low. The sanclwieh-construction may be heated up to a tcm~erature of 150C without the noise sup-pressin~ mass ].eaking o-ut, regardless the position of the C0l1 s1;ruetion. 'l'his enables the composite eonstructiolls to resist wi.thout any damage to ten1peratures like the drying of a pro-tective coating requir~iquite frequel1tly. ~oreover, the cross-lin~ed copolymets according to the invention have a good re-sistanee to solvents, whieh is also of speeial importance when app].ying synthetie resins or lacquers onto the eomposite systems (dip varnishlng).
The CoMpOSite systems with the cross-linked copolymers aeeordin~ to the invention may be used in all the fields of noisc-3 reduetion (sound-eontrol), ~here the radiation of noi.ses and resonanc0s of audible vibrations are undesirable, for example for ellcasing machine unlts, ~netallic partitio]ls, metal furniture and mainly for metal bodieci of ~.otor ears, airplanes or ships. The sandwieh systems eomposed of interlayers of -the A~ . ` J.~
vibration da.~ping mass having a thiekness from 0.05 to ~k~lm, ~referably from 0.1 - 0.5 mm~ and metal plates have a to-te.l thiekness of preferably from 1 to 10 mm.
The following examples illustrate tlle invention. All the parts specified are parts by weight.

X A ~1 ~ L E
A polymel- ~soluti.on of 70 parts of a poly~er consistillg of 3cy parts of 2~ethylllexyl acryla1;e, 33 parts of vinyl acetate and 28 parts Or dibutyl ~na]eate in 30 parts of ~inyl acetate is ~li.xed ~i.th 0.5 p.art of tel,raall.ylo-xetlla.ne and 0.3 p,)rt oI`
2~ diCyClOilOXyi. percarl)onatC alld h-3ateci to 30 - 40C fol 3 hours~

~or~ 7.? /J~
~06Z843 . clear transparent resin is ob~ainecl l~aving a good surficjal tackiness and an exce]lent adhesion io metal, glass and mineral substrates. A composite system composed Or 0.5 mm steel sheet/
0.3 mm cross~linked copolymer/0.5 mm steel sheet was exarnined according to the bending vibration test (ref. II.Oberst, TOBohn and E.Linhardt, "Kunststof~e" 51 (1961), 495).
The loss factor values dComb for 100 and 1000 c.p.s are plotted in ~ig. 1 against the temperature. In the case Or conn-posite nleta] sheet systems it is useful to define as barJdwidth the width of the temperature interval at which the value d ~ b = 0.05 is surpassed. The damping o~` metal sheets ~.~hich have not been damped by additional noise suppressing measures in mctal sheet constructions of various kinds corresponds to values of d~omb = 0.01. It is obvious that the re~erence -Talue of dComb = -5 represents a noticeable damping improvement (b-y approx. 15 decibGl) compared to a "nil d~ plng" of dComb =
0.01. In Fig. 1 the reference value dcOTnb = -5 is surpassed in the frequency range of specia] interest between 100 and 1000 c.p.s. at temperatures be-tween approx. -20 and --70 C
(100 c.p.s.) and -30 C and ~50 C (1000 c.p.s.). 'l`he damping centers mainly around a range from ~10 C to ~20 C
with maYimul~l damping values Or 0.5. The temperature band~Tidth is 90 C for 100 c.p.s. and 80 C for 1000 c.p.s. E~en at a temperature of ~140 C, the damping mass of Example I remains absolutely position stable and subsequent meas~1r:ings sho~ -~he same excelleIIt damping properties as bc~f`ore.

_ A polynier solutioll consisting Or 70 parts of a pû'ytn~r 29 according to R.~ample 1 in 30 paI'ts of a mixture of 50 parts of - HOE 7 /~' 362 vinyl acetate and 50 parts of butyl acrylate is mixed wlth 0.5 part of divinyl ben.~ene and 0.5 part of diisopropyl perca~bonate and heated to 40 C for 3 hours. A cross-linke~ noise suppress~g ma~ss is obtained ha-~ring a very good surficial tackiness and a good resistance to aliphatic, aromatic and ester-like solvents~
. Eig. 2 shows the loss factor values being found by the bending vibration test for composite steel sheets accor~ing to Example1.
The damping centers mainly near +20C with maximum damping values of 0.5. The temporature bandwidth is 110C for 100 c.p.s.
and 70 C for 1000 c.p.s. Up to a temperature of 150 C the noise suppress.ing mass did not leak out of the composite syste~.

A polymer solution consisting of 70 parts of a polymer according to Example 1 in 30 parts of a monomer mixture of 5 parts of vinyl acetate and 50 parts of 2-ethylhexyl acrylate is mixed with 0.2 part of tetraallyloxethane and 0.5 part of dicyclohexy]percarbonate and polymerized at 40 C Fig. 3, Example 3 ShOl-'S the damping properties of this cross-linked copolymer having a bandwidth of abt. 80 - 90C and a damping value of 0.8.
E X A M P L E 1l.
Tlle polyrner solution according to Example 3 was rnodified.
in such a way that instead of 0.2 part of tetraallyloxethane 0.4 part of same was blended lnto the polymer solution.
Fig. 3, Example 11 sholrs the damping properties of th.is cro~s-li.rlke~ copolyn1er having a band~i.dtll of abt. 100 C for 10~ c.p.s. and abt, 90C for 1000 c.p.s. and a damping value o~ O.Ç.

- 1 :3. -~I0~ ~2/r~` 362 E X A ~ P I, E 5 __ .
polymer solution consisting of 70 parts of` a. po].ymer ~eing eomposed Or 50 parts of styrene and 50 parts o~ butyl acrylate, in 30 parts of a monomer mix1;ure bc-ing composed of 5 50 parts of vinyl acetate and 50 parts of butyl acrylate is mixed with 0.2 part Or tetraally].o~ethane and 0.5 part of dicyclohexyl percarbonate and polymeri~ed at 40 C.
Eig. 4, Example 5 shows the damping properties of l;his eross-linked copolynler having a bandwidth of abt. 70 C for 100 e.p.s.. and of abt. ~5C for 1000 e.p.s, and a da1npillg value of o.8.

While stirring, 0.4 part of tetrallyloxethane instead of only 0.2 part is blended into the polymer solution according to Example 5.
Fig. 4, Example 6 sho~is the damping properties of this eross-li.nked eopolymer ha~ing a bandwidth of 65 C for 100 e~p.s.
and of abt. 55 C for 10Q0 e,p.s. at a damping ~alue of 0.7, Having a damping maximum ~alue of 0.8 (Example 5) and a temperature bandwidth of from 55 - 70C, the cross-linked products aeeording to Examples 5 and 6 represcnt excellent temperature broadband - noise suppr~'ss.ing masses for appli -eations ranging from ~10 C to l-80 C (such as housebc,lrl apparatus, maehinery in heated roorr.s, etc.), In analogy to the preeeding examples, the produets accordiIlg to examples 5 an.d 6 show as well v~ry good adhe.~.ion to g~lass, mei;al and ~r.i1.elal substrates. TJp to f 150C the cross~ ked copo].ymQrs did no-t l~ak out of the composite constructions.

, . - 13 _ }IOI~ ` 3~2 E X A M P L 1~ __7 A polymer sollltion consistlng of 70 part.s of a polymer being composed of 70 parts of vinyl acetate and 30 parts of di.butyl maleate in 30 parts of a monomer mixture being composed of 50 parts of vinyl acetate and 50 parts of butyl acrylate i.s blended with 0.2 part of tetraal].ylo~e-thane and 0.5 part of dicy.clohexyl percarbonate and polymeri~.ed at 40 c~
Fig. 5, example 7 shows the damping properties of the cross-l.inked copolymer having a bandwidth of abt. 65 C for 100 c.p.s, and of abt. 50 C for 1000 c.p.s~ and a damping value of 1Ø

E X A M P L ~ _ 'rO the polymer solution according to cxample 7 is admi~ed '4 part of tetraallylo~ethane instead of only 0.2 part and subsequently polymeriæation takes place, Fig. 5.jexample 8 shows the damping properties of the cross-linked. copolymer having a bandwidth of abt. 65 C for 100 c.p.s. and of abt. 55C for 1000 c.p.s. and a damping value - 20 of lØ The products according to examples 7 and 8 are especially suitable for a specific broadband damping at t-amperat1lreS ~
between ~20C and +80 C, due to their high ma~imum damping values; The products show as well good adhesion on metal., glass and minera]. substrates and even at temperatures up to ~.150 C
the~r are not prone to any modifi-~ation of shape.

X A ~ 9 10 palts of ve:rmiculite - calcul.ated on the poly~me-l so]llt;.on^-29 we1-e adce-i to the pol~mer so~ution according to e~aMple 2.

~ 14 -- IIOJ~ 72~F 3fi~

Fig. ~ srlows the <lanlping propertics of` the cross-linked, fi,11e~-.
containlIlg copo],ymer having a bandwidth of abt. 110C for 1 00 C . p . 9 . and of abt. 80 C for 1OGO c.p.s. and a da.mpin.g v~lue of o.6.

r, ~ A M P L E 10 20 parts of ~err.1iculite, ca:Lculated OII the pol.ymer solutlon were added ~.epo:Lymer solution according to examp]e 2.
Fig. 7 shows the dampi.ng proper-ties o:t~ the cross--linked f:iller-contai,ning copol~mer h.aving a band~idth oP abt, 110 C for 100 c.p.s. and of abt. 90C for 1000 c.p. 5 . and a damping value of o.6.

E X A M l' L E 11 ' A solution of 100 parts of an unsaturated aliph,atic poly-ester resin which. has been prepared of 42 parts of butane~iol-(1 4), 43 parts of adipic acid and 15 parts of maleic anhydride (acid number - 12), in a mixture of 100 parts of butyl acrylate and 50 parts of 2-ethylhexyl acrylate is heatod to 40C under a nit~ogen atmosphere with an initiator system composed of 5 parts of cyclohexanone peroxide and 5 parts of a 10 /~0 cobalt naphthenate solution in styrenc. Sticky, soft, yellowish plates are obtained whi,ch show distinctive cross-linklng ~lerl being submitted to the torsion vibration test. A composite sys-tem composed of 0.5 mm steel, sheet/0.3 mm cross-li.nked copolymer/
0.5 mni s-t6G]. sheet; is exarnined according to the bendi.ng vibla-tion -test. The :I.oss factor values for 100 and 1000 c.p.s, ar.c p],ot-te~J in r:i ~. 8 agai.ns-t the temI);?rature. 'I'he reference va' 29 .dCo ~ = ~,~j is s1n~p3ssed according i;o -fig. ~ w;.th:;n th.e --. ' - 15 -1-TOF 7 ~ 36~

~ frequeney range of main interest being between 100 and 1000 C.p.3 at temperatures of ~etween abt, -50 C and ~10 C (1000 e,p,s.) and -50 C and ~35 C (100 c,p~s,),so that the temperature bandw;dth is approx, 60 C (1000 c,p,s,) or ~5 C (100 c,p.s~), For that reason, this composite system is appropri.ltQ f'or numerous technical applieations requiring a good broadband damping at low temperatures (for example snow plows, special-purpose vehicles for the winter s~ason), A solution of 100 parts of an unsaturated aliphatic poly-ester resin aceording to example 11 in a mixture eonsisting of' 100 part~ of butyl aerylate and 50 parts of vinyl aeetate is heated up to 40 C for 4 hours under a nitrogen atmospllere with an initiator system eomposed of 5 parts of cyclohexanone per--- oxide and 5 parts of a 10 ~ cobalt octoate solution ill styrenc-.
S~ieky, soft, slightly yellowish plates are obtained which show noticQable eross-linking when being submitted to the torsion vibration test, In fig, 9 are plotted the loss faetor values dComb Or the compc~ite system 0,5 mm steel sheet/0,~7 mm cross-linked copol~rmer/0,5 mm steel sheet repr~senting t;he results, Or bending ~ibration tests for 100 and 1000 e,p,s, against; the temperature, Damping centers in fig, 9 n~ar 0 C to 20 C with maximurll damping ~alues of 0.4, T~e temperat;ure bandw;c7th ls 7 C for 100 e,p.s, and 1000 e,p,s, ~or eomparison7s salce fig, 9 also S]lOWS t,he values of one of the best known noise suppressing mater;als for composite metal sheots, being a ~rirly-l acQtate~ utyl maleate-2 et~yllle~yl acrylate-polymer, T]le 29 temperature bandwidths of both these composite s~rstellls a-re ~o~ ~ _36z appro~imate~lr the same, ho~ever the tempcrature band of the cross-linked copolymer according to the invention is sli.ghtl-y shifted to lowor temperatures; this is a valuable advantage for outdoor application. Moreover, the comparativo product has the teDdel~cy to leak out of the composite construction - contrary to th~ c~oss-linkcd oopolymer aocording to es~ple 1Z.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A vibration damping material comprising a cross-linked copolymer obtained by means of free radical copolymerization of (a) at least two ethylenically unsaturated monomers the homopolymers of which differ in their second order transition temperatures by at least 20°C, the monomers being selected from vinyl esters of saturated straight-chain or branched monocarboxy-lic acids having from 1 to 12 carbon atoms, esters of acrylic acid or metha-crylic acid with a saturated monohydric aliphatic alcohols having from 1 to 8 carbon atoms, mono- and diester of maleic, fumaric and itaconic acids with saturated monohydric aliphatic alcohols having from 1 to 8 carbon atoms, sty-rene, vinyl toluene and vinyl xylene; with (b) at least one cross-linking agent selected from diallyl phthalate, diallyl maleate, triallyl cyanurate, tetraallyl oxyethane, divinyl benzene, butanediol-1,4-dimethacrylate, ethy-lene glycol dimethacrylate, diethylene glycol dimethacrylate and triethylene glycol dimethacrylate and unsaturated polyester resins; and, (c) if desired, a polymer of one or more ethylenically unsaturated monomers (a) which polymer is soluble in the monomers (a).

2. The material of claim 1, wherein the ethylenically unsaturated mono-mers (a) are selected from vinyl acetate, dibutyl maleate, 2-ethylhexyl acry-late, butyl acrylate and styrene.

3. The material of claim 1 or 2, wherein the cross-linked copolymer contains up to 70 weight % of fillers.

4. The material of claim 1 or 2, wherein component (c) was used in an amount of 20 to 80 weight %, calculated on the mixture to be polymerized, and was mixed with component (a) before adding the cross-linking agent (b).

5. The material of claim 1 wherein the mixture to be polymerized was applied as a liquid or a paste onto a substrate to be damped and subsequently polymerized in situ.

6. The material of claim 5, wherein the substrate is a laminated system or a sandwich system.