US2639257A

US2639257A - Process for making transducer devices having bonded elements

Info

Publication number: US2639257A
Application number: US159746A
Authority: US
Inventors: Szegvari Andrew; Charles K Gravley
Original assignee: Brush Development Co
Current assignee: Brush Development Co
Priority date: 1950-05-03
Filing date: 1950-05-03
Publication date: 1953-05-19
Anticipated expiration: 1970-05-19
Also published as: GB694987A

Description

May 19, 1953 A. SZEGVARI ET AL PROCESS FOR MAKING TRANSDUCER DEVICES HAVING BONDED ELEMENTS Filed May 5, 1950 IN VEN TOR.

ANDREW SZEGVARI BY CHARLES K.GRAVLEY ATTORNEY not highly elevated, and which is in a state of molecular dispersion in a quantity of a polymerizable liquid solvent material to increase the liquidity of the bonding material and permit a satisfactory bonding contact with elemental areas of the aforesaid surfaces in spite of the substantially large average molecular size of the par tially polymerized bonding material. The process further comprises placing the two surfaces one against the other with the introduction therebetween of a catalyst to effect a polymerization reaction involving simultaneously the partially polymerized bonding material and the polymerizable solvent material at a temperature under 90 0. without evolution of any volatile material, thereby effecting strong adhesion of the two surfaces.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing,

Fig. 1 is a perspective view partially cut away, of an expander transducer device assembled in accordance with the process of the invention; and

Fig. 2 is a perspective view of a series-connected bender transducer made in accordance with the invention.

Referring to Fig. 1 of the drawing, there is shown a transducer assembly including a base surface II on which rests a block or bar it of piezoelectric material. The bar [2 rests on the base H at a surface portion I3 of the base H, visible where a corner portion of the bar It has been cutaway. The bar I2 is provided with electrodes l4 and [5 on individual opposed surfaces of the bar. The bar [2 may be cut from a single crystal of Rochelle salt in a well known manner so that distortion of the bar, involving a vertical movement of the upper surface of the bar, as indicated by the double arrow, is associated with the application or appearance of an electrical voltage or charge at the electrodes I l and IS. The length dimension of the bar is assumed to be the vertical dimension in Fig. l, but it is understood that this vertical dimension of the bar may be considerably smaller and may even be the thickness dimension of the bar. The bar l2 resting on the surface I I may be placed in a body of liquid such as oil, in which case movements of the upper surface of the bar are communicated to the liquid and may cause the generation of,

acoustical elastic wave energy in the liquid. Many forms of such electroacoustical transducers are known to the art. For example, a number of other bars, not shown, similar to the bar 12 may be placed on the base surface I l side by side with the bar I2 and their respective electrodes connected to the same source of electrical energy. The top surfaces of such a plurality of piezoelectric bars may be connnected to a relatively large diaphragm, not shown, covering all of the bars to obtain the desired acoustical coupling to a fluid or liquid medium.

In such devices it is necessary that the lower surface of the bar l2 and of any similarly arranged bars in the electroacoustical transducer be well secured to the base H at the surface or surfaces l3 of contact, Not only must the assembly remain secure during transportation and in use, even if the base surface H is turned on its side or is turned over so as to face vertically downward, but also the bond must be secure against acoustical vibrations in the liquid, to which the free end surface of the bar is coupled and which may exert forces on the bar tending to pull it away from the base ll. The process of the invention for making a transducer device such, for example, as the device in which the electromechanically sensitive element 12 is secured to the surface it will be described in detail hereinbelow.

Referring now to Fig. 2 of the drawing, there is shown a series-connected bending-sensitive transducer assembly of the sandwich type including a base 2 l. The transducer also includes two electromechanically

sensitive elements

22 and 23. A major surface of one of these elements is placed against a major surface of the other element, and one end portion of the resulting assembly is fastened within a depression machined in the base 2|. This fastening may be accomplished by clamping, by the insertion of shims around the end portion of the electromechanically sensitive assembly, or with the use of the cementing procedure specified in accordance with the present invention as described in detail hereinbelow. The exposed or outer major surfaces of the

elements

22 and 23 are provided with respective electrodes Z l and 26, a portion of the latter being visible in Fig. 2 where the electrode 24 and the

elements

22 and 23 have been cut away. The free end portion of the composite element assembly is provided with a channel member 21 clamped se curely thereover. To the channel member is fastened, as by welding, a rod 28.

The electrodes 25 and 25 may be connected to respective electrical terminals, not shown, Any voltage appearing across such electrodes is ap plied in series across the

elements

22 and 23. For this reason the composite sandwich element may be called a series-connected sandwich type trancducer. The

elements

22 and 23 may be plates cut from single crystals of a piezoelectric sub stance such as Rochelle salt or ammonium dihy drogen phosphate. The two plates may be identi cal, but during assembly the plates are turned so that the thickness directions of the two plates are oriented oppositely with respect to the piezo electric axes of the crystalline substance. Accordingly one plate tends to expand while the other contracts, so that an electric field across the plates is associated with piezoelectric deformations of the regions near the two adjacent surfaces in opposite senses, these deformations in turn being associated with flexural movements of the composite element, specifically bending movements of vertical lines in the composite element as seen in Fig. 2. When the composite element bends, the rod 28 moves axially, as indicated by the double arrow. Likewise forces applied are ially to the rod 28 are transmitted through the channel 2'5 to cause over-all bending movements of the composite element, one element being elongated While the other element is shortened. This is the same type of transducer device illustrated in Figs. 4 and 5 of the Sawyer reissue patent, referred to hereinabove.

In sandwich type transducer devices such as that shown in Fig. 2, it frequently is desirable to electrode the inner surfaces of each of the

plates

22 and 23 before placing them together. This permits a parallel rather than a series connection of the two elements. Moreover, very thin electrodes of finely divided conductive particles may be applied to make intimate contact with the surfaces, so that when the two electroded suracacgzv:

faces-are placed incontact each other there are no spaces between the #crystalline surfaces? across which? voltage. drops mightidevclop. due 'to the relatively low' dielectric rconstants of f che-1 cc- In such cases it is customarymenting materials. to leave substantial unel'ectrodedamargins:around theedges of: thezopposedsurfaces; When 1these partially" electroded surfaces I are-placed in: prose imity to each other; a'nnarticularlya strong. bond: may be achievedin accordancewith'theipresentf invention between the unelectroded marginal surface portions of. the. two-single-crystalline plates of piezoelectric material. The bonding process" described" hereinbelow: also produces very good bond between electrodedcportions 'a of the two crystal. surfaces.

The :DIOCCSS in' accordance with the invention== for making. atransducerdevice, suchv as-thedevice-in: which the electromechanically sensitive elementsli and 23 ofFig. 2.are'securedtozeach other,. now will. be described.

polymerized to enable furtherirapidpolymerization for bonding purposes at temperatures not highly elevated. If a monomeric compound such as the monoester of a dicarboxylic acid and a glycol were used as the bonding material, or if a slightly polymerized material such as the dimer of such a monoester were used,.thetpolymerizae Y ,7

tionineeded to. aehieveacsatisiactory bond "is .so

extensive that inconveniently r large periods of 5 time, or temperatures so elevated as to 'be'damaging 5 to piezoelectric crystals; or 'both; would be required to make the bonding; material A set or;

harden.- However, the partially polymerized'maa terials"whichiconvenientlyamay: be further :poly; merized have 1ost'1t0.'a" noticeable extent. their? ability'sastliquids .to .spreads over the surfaces-ate. bevb'onded tand to penetrate toiall minute-pore tionsof such. surfaces. Accordinglythe partial.- I 1y polymerized r bonding. material .is applied to at "least one'of ithesesuriaces in'a: state of moles-:- ular dispersion m :a quantity of a rpolymerizablesr liquidxsolvent material to increase the liquidity-oi the "bonding material: and permit. a satisfactory bonding contact"withielemental areas of the sur-v faces :izispite 'of ithe substantially large 1 average molecular size. of the partiallygpolymerizedbond-r process. broadly: expressed, then compriseszplacingthe'two surfaces :so treated. one :against the other with the introduction:v therebetweenof a catalyst to-efiect a polymeriza tion reactioninvolvingmost or all citric-material 1 ing material;

whichhad been. applied, thus eflfe'ctingthe bond,ias described and-exemplified in detail ihereinbelow.

It would be permissible to include -.between.:the

surfaces to be-secured together some *inertsubstance,v provided the settingnprocessrcan. beccar riedout ata temperature underQCl C; without However; its

evolution of any volatile material. I isspreferred. to use only active or polymerizable substances in the bonding materialfso that. when the surfaces areplaced together in the presence of the catalyst a. polymerization reaction -is..ef-- fected. involving directly all materials used .1 in.

the-bonding operation;

and a'aglycol: The partially polymerized-state 10f the "polyester bonding material: zpreferably pro; videsmolecular weights :of1the order of 2000; but.

in any" case the apolyesters should "have "a molec ular weight less1thanabout5000r The condensetion polymerization of the esters of dicarboxylic acids and dihydric:aloholstd form linear polyesters is well known. This polymerization reaction-carrbe made to proceed-smoothly in the presence of catalysts conventionally used'for this purpose; particularly when the acid and alcohol are present in' fairly pure forms'and in stoichiometrically equivalent amounts.'- An identical polyester may ee obtainedwhen' the corresponding imonomeric ester" or monoester, which is both" anacid ester and "an ester alcohol is formed by" reacting' the glycol with the anhydride'" of the Accordingly" the preferred process ofthe-present invention'maybej.-carried out using polyesters obtained-"from" such anh'yd-r'ides or many other suitable manner, even particular" dicarboxylic acid.

though the original 'reaction forming the mono ester cannot be'designated strictly as a condensa The ex pression, apolyester of a dicarboxylic-acid and a glycol,"as-used in this'specification and ir'rth'e appended claims; is intended to include poly estersihaving the specified composition whether or not"actually formed'by the esterificationmf" .a di'carb'oxylic acid and'aglycol under polymeriz tion or even' an esterification reaction;-

ing conditions: i

The monoester ofa givendicarboxylic acid and a given glycol can be formed. For example,".

equirn'olecular amounts of maleicacid COOILCHE'CHLCOOHY and-.idiethylene glycol; CHOHCHaOCHz' .CHZOH'; woul'dforma monesterydiethylene glycol maleate; havingraa' molecular weight or 204,1 having a: hydroxygroupxzat one end ioi the FmoIecuIeand a 'carboxy' group at the other: tend,'iand having one olefinic ilinkage r in the molecular chain containing" eight. carbon atoms 1 and the 6 oxygen atom. from: I the diethylene glycol! proximate multiples of the molecular weight of the monoester.

polymerized lpolyester having a. moderate molec-"- ular 7 weight; as v mentioned hereinabove polyester. thus formed may .be :very' viscous; and itsclassificationreitlier as avliquid oras a :solid may not be obvious. from zpolybasicfacids or. anhydri'des anda-polye hydric alcohols-by the condensation polymeriza tionxofa monoester are'known asalkyd resins."

Viscous,:-parti.ally polymerized resins of this type maybe used "directly as bonding agents by :causing i further polymerizatiom. but, asmentioned" above, :the local mobility and the liquidity'of thematerial are-.sorlow 'that a-goodbond is dificultto achieva;

Therefore, .beforethe. partially polymerized.

bonding .material is used. inwmaking the trans-. ducerdevice in. accordance with. the invention, it isplaced ina-state of molecular dispersion a quantity ofxawpolymerizable. liquid solvent. ma-. 'terial; preferably ,a polymerizable liquid aromatic However," with or without some .fcatalytic action .or rthe raid of tan-'- acceleraton'.the zpolymerization of this mon'oe' esteri'usually proceeds-to some "degree; and so "is carried outat least to 'azsignificant extent. before the material is used in the process .of'the present invention; Thus polyesters areiform'erl having-1 molecular weights which. i presumably are ape- Accordingly; it is desirable f to carry out fa:=substantial.partial polymerizationrof; the'iesteriflcationi product to ohta in awpartially The Such polyesters formed compound with an olefinic side chain. The individual molecules of the partially polymerized material are dispersed in the liquid without chemical breakdown of the molecules. A quantity of essentially monomeric styrene CsHs.CI-IICH2 is admirably suited for this purpose, but other compounds of this type, such as diallyl phthalate, O-CaI-I4(CO.O.CHz.CI-IICH2)2, also are suitable.

When the polyester bonding material is in solution in a quantity of styrene, as just described, the resulting material not only has high local mobility and in general rather low viscosity but also can be polymerized quite readily and completely at temperatures not at all highly elevated. This high liquidity permits easy spreading of the material to all portions of the surfaces to be bonded, and it has been observed that these polyesters dissolved in styrene tend to wet the surfaces of the usual electromechanically sensitive elements. Once having spread over and covered these surfaces, the local mobility of the material tends to insure active contact of the solution with each submicroscopic portion of the surface of the element. The effectiveness of this active contact seems to be particularly great when the surface covered is that of a body of a substance which is polar, so that especially good bonding may be obtained when at least one of the two surfaces to be secured together is cut from a single crystal of a polar compound.

The phrase a dicarboxylic acid is used herein in the collective sense, and such an acid may contain in admixture or in solution more than one dicarboxylic acid. Likewise, more than one glycol might be used. In such cases presumably the dicarboxylic acids and the glycols enter the linear polymeric chain in the approximate relative proportions of their original molecular ratios. However, it is generally important that, considering all dicarboxylic acid substances present on the one hand and all glycol substances present on the other hand, these substances be present originally in stoichiometrically equivalent ratios.

Thus, when the polyester is of the type formed by the condensation of a single dibasic acid and a single glycol, the polyester may be produced from equimolecular, amounts of the particular acid and the particular glycol.

The polyester used advantageously is at least partially olefinic. of the: monoester units making up the polyester molecule advantageously should be olefinic. This can be accomplished by using either a dicarboxylic acid, Or a glycol, or both, which contains an olefinic acid or glycol, as the case may be.

In a preferred form of the process of the invention, the dicarboxylic acid contains at least substantial portions of an olefinic dicarboxylic acid to provide in the polyester at least a substantial number of olefinic monoester components, making the corresponding polyester at least partially olefinic. Accordingly the dicarboxylic acid may contain at least substantial portions of maleic acid. The dicarboxylic acid may consist solely of an olefinic dicarboxylic acid to make the polyester produced by reaction with a glycol under polymerizing conditions an olefinic polyester. When the dicarboxylic acid, contains substantial portions of an olefinic dicarboxylic acid, it may also contain a saturated dicarboxylic acid, such as sebacic acid, COOH(CH2) BCOOH. Thus the dicarboxylic acid constituents of the In other words, at least some polyester may contain or consist of sebacic acid and substantial portions of maleic acid, or the olefinic polyester may be the polyester of a single dicarboxylic acid, preferably maleic acid, and a glycol.

A variety of glyc-ols is available for the formation of the polyester used in connection with the invention. The simpler glycols are preferred, and excellent results have been obtained with the olefinic polyester of ethylene glycol,

CH2OH.CI-I2OH and a dicarboxylic acid containing substantial portions of maleic acid. Diethylene glycol may be used, and one o-lefinic polyester which has given particularly good results is the polyester of maleic acid and diethylene glycol, the monoester of which is mentioned hereinabove. It will be understood that the particular polyester just referred to does not contain in its molecules any appreciable acidic or alcoholic components other than those which may be derived by the polyesterification mechanism from the specified di' basic acid and glycol; however, it will be clear that identical polyesters, described and defined by the same names, may be formed with anhydrides instead of acids, for example, by the use of maleic anhydride,

C0.0H:CH.COO

instead of maleic acid.

After the olefinic polyester has been dissolved in the styrene, it is applied to at least one of the two surfaces to be secured together.

In a preferred embodiment of the invention, parts by weight of the product formed by the condensation of maleic acid and diethylene glycol are dissolved in 30 parts of nominally monomeric styrene by stirring vigorously until a homogeneous solution is obtained. In this form the solution has a shelf life of several months. The solution is applied to one of the two surfaces,

while a catalyst is applied to the other of the surfaces, so that when the two surfaces subsequently are placed one against the other the catalyst automatically is introduced therebetween and immediately starts to bring about the desired polymerization reaction involving simultaneously the partially polymerized polyester bonding material and the polymerizable solvent styrene material, thereby effecting strong adhesion of the two surfaces. Four parts of a peroxide catalyst in the form of benzoyl peroxide, (C6H5.CO)2O2, may be used with the maleatestyrene solution specified above. This peroxide material conveniently is dissolved in a non-aqueous solvent and applied in liquid form, for example as a 5% solution in benzene. The liquid catalyst solution is allowed to dry before the surface to which it has been applied is pressed against the surface to which the polyester-styrene solution has been applied.

Other catalysts, mostly of the peroxide type, suitable for use in the present process are well known in the art. For example, lauroyl peroxide, (CH3(CH2)10CO)2O2, or a cyclic organic peroxide may be used, preferably in combinations with an accelerator such as a cobalt salt of naphthenic acids. The polymerization reaction proceeds in a period of time of the order of one hour, and frequently less than half an hour, to provide a aeasgacr well set-:bond: of the; plastic: material; and; this setting 'OCCllISl in l'thec-shortiperiod of time-; ate a temperature under--90? C. Usin'gamansi of the specific materials mentioned; hereinabover the polymerization; proceeds inthe neighborhood; of room ltemperature to substantial :zcompletionjnoa short period. of v time, so that "the: process :of .:the invention is particularly, useful when materials are involved which shouldno-t beysubjected; to higher-temperatures.

In .another preferred embodimentrot .the'invem tion, .100 parts loyaweightroi 1a partiallyzpolymer: ized polyester material are.dissolved.in-35 parts of styrene, and about 0.1 part of cobalt naphthe: natecis added totheliquid. This liquidahasra long shelf rlife. Within :about ;half: an'shour .be.-' fore the time of applying: the sbondingcmaterial, 018 spartx of lauroyl peroxide powdcryis added'ato the-liquidate .a catalyst The resultingzsolutionais appliedpromptly to .both;surfacesdzozhe: secured together, so: that. the catalyst :is;intrduced::be:-. tween the surfaces at 1 the r time 0i application alongzwith the bonding: material itself: a The ratazs lyzed 5 material hasla setting. time of zaboutsthree h0li1S atl50'C., during. which time the .two sur faces are maintained pressedtogether; This;pro-. cedure, vusing the. specified: materials; has .v been particularly successiul. The polyester. material used lconvem'entlylis: made". up. of: 25. parts of Paraplex A1 48 and 75 parts of: Paraplea A245, these being products obtainable-efromthe Rohm. ,Sz': Haas Company, Philadelphia. These products-;are;polyestersrwhichlare essentiallygthe condensation products; of. sebacic, acid;v maleic acid, and ethylene. glycol, the "A1948? material having proportionately less of the-.olefinicmaleic acidthan' the -.AP45, material.

While anwunderstanding of thermechan-ism =of thepolymerization reaction is not a part of. the present invention, it Y will appear: that all: the cementing materials ,used; with t the. possible ex-. ception of the catalyst itself are polymerizable and-:should take an'active partpinthe cementing process. This occurswithout evolution of any volatile, material, since no .such material need he presentbetween-the: two surfacesuwhen they are placed" together." It isV-tbelieved: that ,th'e-lstyrene serveslto provide a-substantiahnumber of cross linkages; with linearpolyester: chains; by virtue of the double bonds in theunsaturated polyester and in the styrene itself. Thus the-catalyst acts tcpefiect apolymerizationand: cross-linking are: action: A tensileestrengthtgreaterrthan.;that;,0f the piezoelectric a crystals t-themselvessmay; be i chitained, and i the bonding material is quite: res sista-nt .to moisture and non-.aqueous-solvents: In the :usual transduceri'configurations: the:exot-herev mic natureofthe polymerization reaction "causes onlyr-a small temperaturerise.v Thispolymerizae tion' tends-to .b'ecinhibited by air; making-sit .pose sible'to-wipeoff 'surpluscement after the joint has set While there have been described; whatat present: are. consideredto be the preferred em: bodiments of this'invention; itwillb'e obviousto those skilled inthe artthat various-changesand modifications may he: made therein without de parting from the invention It is-aimedg: there-1;- fore, inithe appended claims to cover all such changes and modifications whichsiall' within the true spirit and scope of the inventiom.

What isclaimed is:

1'. The process for'makingatransducerdevice having an electromechanically sensitive 'element one surfa'ceaof which-is-secured to another similarlyyshaped: surface comprising; applying-to. at least: oneaof :saidrtwo-suriaces. a=bondingmaterial, which ,is .-partial1y;polymerizedt to enable:,:further rapid polymerization, for bonding; purposes.- at temperatures:notihighlyqelevated; and" which: is in a. state. of molecular dispersion :in a l quantity oi aapolymerizaioleilliquid-solvent1materalto: ine crease the liquidity vofzsaidcbonding materialand permitzai.satisfactory; bonding; contactwith ele-J. mental area-snot saidsuriaces in spite lofzthe sub,- stantial-ly large average molecular: size. of a said partially polymerized bonding: material; and placing; said two: surfaces vone :against ithe -other with r the introduction; therebetween of; a cata: lyst to effect a polymerization. reaction involving simultaneously saidmartially: polymerizedfbondill-g material andsaid polymerizable solvent mae terial at as temperatureaunder (3.; Wil'ihOll'blEBNOii lutiorr; 0L:any'xvolatilermaterial; thereby i-efiecting strong; adhesion otisaid: twoosuriacesl I 2.; The process for makingatransducer; device having:.an-electromechanically sensitive element one -surfacesof :which ;is secured .110. another simie larlyi shapedesurfaceccomprising applying .;t0; a,t leastone opsaidtwo surf acesgaapclyester', whichris partially polymerized; to; enab1e:.:furthe1tr rapid polymerization: for bondingnnurposes .atrtemperaa tures notuhighly elevated, and whichr-isssin a: state of molecularxdispersionsin a-lquantity of tat-poly merizaelecliquidisolvent material ton-increaselthe liquidity :of: saidrpolyester;'andripermit z ai-satisface toryi bonding contact with; elemental:v areasr of said surfaces in spite:oiithezsubstantially; large average: molecular: sizes of' said;v partially polymerized'ipotyester; tandaplacing:saidztwosurfaces one against; the: other; with; the introduction therebetween. of; aecatalyst 1 to effect a polymer.- ization: reactionr involving simultaneously said partiallyr polymerized: polyester and} saidLpply merizable;solventunaterial at astemperaturevune der; 90?" C; without evolution of anyzvolatile ma teriaLr. thereby: eflecting; strong adhesion ;ofsaid two-surfaces:

3s Thezprocessdorvmakingsra.ltransducehdevice havinggamelectromechanicallyl sensitive element one. surfacerof which is: securedrtowanother,isimiq larlyo shapedsurfacercomprising; applying to at least ones of;.; said; two: surfaces an, essentially linear polyester; whiclhisupartiallyr polymerized torenable' c-fnrt-herl rapidapolymerization' for bonding purposes 1 at; temperatures not highly. detvated, .andlwhich: issin ;astate:.o-f;molecular; dis: persion:v in; a:.; quantity of a; polymerizable liquid solventxmaterial tomincreasenthe liquidity oflsaid polyesterzand permit ga'lsatisfa'ntory,v bonding cona tact: with elemental areas: oflsaidiisurfacesrin spite :of ;.the' substantially large; averagezl-molecu-ve lan: size: 0t: said ipartiallyr polyrnerized: polyester; and aplacingc; said: two; surfaces 1 one against; the others: the introduction; therebetwecn 1,051; a catalyst: to efiects; a polymerization. reactioninvolving; sin'iultaneouslyc said: partially, polymer:- ized: polyester and; said;- polymerizable. solvent material at a temperature under 90 0. without evolutions. of; any; volatile material, thereby effecting lstrongzr-adhesion'lof "SQjdTiFWOl surfaces;

4Theaprocess forrmaking-taz .transducerzdevice having an; electromechanical-1y sensitive element one: surfaceco-f ;whicb:-is :securedto ,anothen simie larlyishaped surf ace:- comprising: applyingotcxiat least one: of i said: surfaces :an essentially: linear olefinic polyester; .whi'ch islpartiallyi'polymerized to enable furtherrapid polymerization for b'onding purposes at temperatures not highly elevated; ancliwhiclr issin a state of molecular dispersion in a quantity of a polymerizable liquid aromatic compound with an olefinic side chain to increase the liquidity of said polyester and permit a satisfactory bonding contact with elemental areas of said surfaces in spite of the substantially large average molecular size of said partially polymerized polyester; and placing said two surfaces one against the other with the introduction therebetween of a catalyst to effect a polymerization and cross-linking reaction involving simultaneously said partially polymerized polyester and said polymerizable aromatic compound at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

5. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to an other similarly shaped surface comprising: ap-

plying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, at least some of whose monoester units are olefinic, which has a molecular weight less than about 5000, and which is in solution in a quantity of a polymerizable liquid aromatic compound with an olefinic side chain; and placing said two surfaces one against the other with the introduction therebetween of a catalyst to effect a polymerization and cross-linking reaction involving said polyester and said aromatic compound at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

6. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, at least some of whose monoester units are olefinic, which a has a molecular weight less than about 5000, and which is in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

7. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces an olefinic alkyd resin which has a molecular weight less than about 5000 and which is in solution in a quantity of styrene; and placing said two surfaces one against the other with introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said resin and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two sur-. faces.

8. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, said dicarboxylic acid containing at least substantial portions of an olefinic dicarboxylic acid to provide in said polyester at least a substantial number of olefinic monoester components, making said polyester at least partially olefinic, and said polyester havmg a molecular weight less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

9. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, said dicarboxylic acid containing a saturated dicarboxylic acid and substantial portions of an olefinic dicarboxylic acid to provide in said polyester a substantial number of olefinic monoester components, making said polyester partially olefinic, and said polyester having a molecular weight less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

10. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, said dicarboxylic acid containing sebacic acid and substantial portions of an olefinic dicarboxylic acid to provide in said polyester a substantial number of olefinic monoester components, making said polyester partially olefinic, and said polyester having a molecular weight less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

11. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a polyester of a dicarboxylic acid and a glycol, said dicarboxylic acid containing at least substantial portions of maleic acid to provide in said polyester at least a substantial number of olefinic monoester components, making said polyester at least partially olefinic, and said polyester having a molecular weight of less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at atemperature under 90 C. without evolutionof any volatile material, thereby effectin strong adhe sion of said two surfaces.

12. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying .to at least oneof said twosurfaces a polyester of a.

- idlcarboxylic acid and a glycol, saiddiciarboxy'lic acid consisting of sebacic acid and substantial tion in a quantib of styrene; and placingsaid .two" surfaces one against 'the other with the introduction therebetween f atperoxide. catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

13. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces an olefinic polyester of ethylene glycol and a dicarboxylic acid containing substantial portions of maleic acid, said polyester having a molecular weight less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

14. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces an olefinic polyester of diethylene glycol and a dicarboxylic acid containing substantial portions of maleic acid, said polyester having a molecular weight less than about 5000 and being in solution in a quantity of styrene; and placing said two surfaces one against the other with the introduction therebetween of a peroxide catalyst to effect a polymerization reaction involving said polyester and said styrene at a temperature under 90 C. without evolution of any volatile material, thereby efiecting strong adhesion of said two surfaces.

15. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to one of said two surfaces a polyester of a dicarboxylic acid and a glycol, at least some of whose monoester units are olefinic, which has a molecular weightless than about 5000, and which is in solution in a quantity of a polymerizable liquid aromatic compound with an olefinic side chain; applying to the other of said surfaces a peroxide catalyst; and subsequently placing said two surfaces one against the other to effect a polymerization and cross-linking reaction involving said polyester and said aromatic compound at a temperature under 90 C. without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

16. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces an essentially linear olefinic polyester, which is partially polymerized to enable further rapid polymerization for bonding purposes at unelevated temperatures, and

i114 which. is ina state. of molecular: dispersiona quantity of a polymerizable liquid aromatic compound with an olefinic side chain to increase the liquidity of said polyester and permit a satisfactory bonding-contact with elemental areas of said 'surfaces'in spite of the substantially large average molecular size of said partially polymerized polyester; and placing said two surfaces one against the other with the introduction therebetween of a catalyst to effect a'polymerizationand cross-linking. reaction involving simultaneously. saidpartially polymerized polyester and said polymerizable aromatic compound at a temperature in the neighborhood of room temperature without evolution of any volatile material, thereby effecting strong adhesion of said two surfaces.

17. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a bonding material, which is partially polymerized to enable further rapid polymerization for bonding purposes at temperatures not highly elevated, and which is in a state of molecular dispersion in a quantity of a polymerizable liquid solvent material to increase the liquidity of said bonding material and permit a satisfactory bonding contact with elemental areas of said surfaces in spite of the substantially large average molecular size of said partially polymerized bonding material; and placing said two surfaces one against the other with the introduction therebetween of a catalyst to effect a polymerization reaction involving simultaneously said partially polymerized bonding material and said polymerizable solvent material at a temperature under 0. without evolution of any volatile material, at least one of said surfaces being out from a single crystal of a polar compound, thereby effecting strong adhesion of said last-mentioned surface and the other of said two surfaces.

18. The process for making a transducer device having an electromechanically sensitive element one surface of which is secured to another similarly shaped surface comprising: applying to at least one of said two surfaces a bonding material, which is partially polymerized to enable further rapid polymerization for bonding purposes at temperatures not highly elevated, and which is in a state of molecular dispersion in a quantity of a polymerizable liquid solvent material to increase the liquidity of said bonding material and permit a satisfactory bonding contact with elemental areas of said surfaces in spite of the substantially large average molecular size of said partially polymerized bonding material; and placing said two surfaces one against the other with the introduction therebetween of a catalyst to effect a polymerization reaction involving simultaneously said partially polymerized bonding material and said polymerizable solvent material at a temperature under 90 C. without evolution of any volatile material, both of said surfaces being surfaces of single-crystalline plates of a polar compound, thereby effecting a strong adhesion of said two plates so that piezoelectric deformations of the regions near said two surfaces in opposite senses are associated with fiexural movements of the composite element.

ANDREW SZEGVARI. CHARLES K. GRAVLEY.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Sawyer Dec. 22, 1936 Sawyer Mar. 19, 1935 Kropa Nov. 9, 1948 Kropa Nov. 9, 1948 Singleton June 14, 1949 OTHER REFERENCES Experimental Plastics and Synthetic Resins,

16 DAlelio, Low Pressure Laminating, 1946, pp. 67-8.

Industrial and Engineering Chemistry, Polyester Styrene Resin Systems, Ebers et a1., Jan 1950, pp. 114-119.

Proceedings of the I.R.E., Standards on Piezoelectric Crystals, vol. 37, Issue 12, pp. 1378-1395, Dec. 1949.

Optical Methods of Chemical Analysis, Gibb, The Nichol Prism, pages 256-7, 1942.

Claims

1. THE PRESSURE FOR MAKING A TRANSDUCER DEVICE HAVING AN ELECTROMECHANICALLY SENSITIVE ELEMENT ONE SURFACE OF WHICH IS SECURED TO ANOTHER SIMILARLY SHAPED SURFACE COMPRISING: APPLYING TO AT LEAST ONE OF SAID TWO SURFACES A BONDING MATERIAL, WHICH IS PARTIALLY POLYMERIZED TO ENABLE FURTHER RAPID POLYMERIZATION FOR BONDING PURPOSES AT TEMPERATURES NOT HIGHLY ELEVATED, AND WHICH IS IN A STATE OF MOLECULAR DISPERSION IN A QUANTITY OF A POLYMERIZABLE LIQUID SOLVENT MATERIAL TO INCREASE THE LIQUIDITY OF SAID BONDING MATERIAL AND PERMIT A SATISFACTORY BONDING CONTACT WITH ELEMENTAL AREAS OF SAID SURFACES IN SPITE OF THE SUBSTANTIALLY LARGE AVERAGE MOLECULAR SIZE OF SAID PARTIALLY POLYMERIZED BONDING MATERIAL; AND PLACING SAID TWO SURFACES ONE AGAINST THE OTHER WITH THE INTRODUCTION THEREBETWEEN OF A CATALYST TO EFFECT A POLYMERIZATION REACTION INVOLVING SIMULTANEOUSLY SAID PARTIALLY POLYMERIZED BONDING MATERIAL AND SAID POLYMERIZABLE SOLVENT MATERIAL AT A TEMPERATURE UNDER 90*. WITHOUT EVOLUTION OF ANY VOLATILE MATERIAL, THEREBY EFFECTING STRONG ADHESION OF SAID TWO SURFACES.