JPH0754782B2 - Capacitor having dielectric composed of polymer of diacrylate polyether prepolymer - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to dielectrics for electrical capacitors, and more particularly to polyacrylate polyether prepolymers and polymers thereof for capacitor dielectrics.

RELATED DISTRIBUTIONS The present invention relates to the following co-pending commonly assigned US patent applications and patents:

U.S. Patent Application No. 562,779 entitled "Miniaturized Monolithic Multilayer Capacitor and Device and Manufacturing Method Thereof" filed on Dec. 19, 1983 and abandoned; Feb. 12, 1985
U.S. Pat. No. 4,499,520 entitled "Capacitor with Dielectric Consisting of Polyfunctional Acrylate Polymer and Manufacturing Method Thereof" issued on Dec. 25, 1984, " U.S. Pat. No. 4,490,774, entitled "Capacitor Containing Functional Acrylate Polymer," issued August 6, 1985, "1,2-
US Pat. No. 4,533,710, entitled "Alkanediol Diacrylate Monomers and Polymers Useful as Capacitor Dielectrics," issued April 23, 1985, "Used as Acrylate-Containing Mixed Ester Monomers and Capacitor Dielectrics." US Pat. No. 4,513,349 entitled "Polymer Acrylic Monomer" and US Patent entitled "Polyfunctional Acrylic Monomer and Its Polymer Useful as Capacitor Dielectric" issued May 7, 1985. No. 4,515,931. All of these are included herein by reference.

BACKGROUND AND OBJECTS OF THE INVENTION Capacitors are used in a variety of electrical circuits, such as relatively high voltage AC.
Power system (eg normal 110 volt system), relatively low voltage (eg 50 volt or less) DC often found in printed circuits
Used in systems etc. The important factors that must be considered in the manufacture of such capacitors are volumetric efficiency, especially in AC systems.
It is the operating temperature, the dissipation factor and the behavior at failure.

The development of small electrical devices and circuits has increased volume efficiency,
That is, it has led to the need for significantly smaller capacitors having a capacitance per unit volume. Monolithic capacitors have been used for such applications.

Monolithic capacitors are, for example, capacitors in which the electrode and dielectric layers are bonded together in a single structure, as opposed to metallized film capacitors in which a self-supporting film is rolled or wound into a capacitor form. Miniaturized capacitors are of very small dimensions to suit microcircuits. The intervening dielectric layer adversely affects the capacitance between adjacent electrodes, and the small overall size represents a small actual value of the low capacitance, except that the number of electrode pairs and the dielectric constant of the dielectric directly affect the capacitance. Will. Therefore, from the basic capacitor theory, a capacitor with a very thin dielectric layer and many pairs of electrodes, i.e. a capacitor with a high dielectric constant, is a small size with a very small electrode active area. Nevertheless, it could have a substantial capacitance.

One of the above types of monolithic multilayer capacitors is described in US patent application Ser. No. 562,779, which is hereby incorporated by reference. The capacitor has a capacitive active portion and two electrode coupling portions each separated from the capacitive active portion by a ramp portion. The capacitor includes first and second sets of electrode layers interleaved with each other, with each layer of each set extending from the capacitively active portion of the capacitor in stacked and spaced relationship with the active regions of all other layers. It has an active region that contributes to this. The electrode layers are stacked and joined at the ends in an electrically contacting relationship, each layer having a bevel between its end and its active region that contributes to the bevel of the capacitor. A dielectric coating abuts between each adjacent pair of electrodes. The dielectric coating has a substantially uniform thickness in the capacitively active portion and tapers to zero thickness through the ramped portion.

The capacity efficiency of capacitors, including the monolithic multilayer capacitors, is usually measured in capacitance per unit capacity. Generally, high efficiencies are desired, with values of at least about 0.1 microfarads per cubic mm per 50V DC grade unit being preferred.

A wide variety of dielectrics are known and are currently used in commercially available capacitors. Such dielectrics include polyethylene terephthalate (commonly known as Mylar (trademark of DuPont)), polycarbonate, polysulfone, polypropylene. The dielectric constant of these materials is generally less than about 4. More recently, multifunctional acrylate polymers and mixtures thereof useful as dielectrics have been identified in the above-referenced related patent applications,
In particular, it has been described in US Pat. No. 4,499,520. The dielectric constants of these materials are also generally less than about 4.5.

According to basic capacitor theory, the volumetric efficiency of capacitors can be increased by reducing the thickness of the dielectric layer and / or by increasing the number of electrode pairs when the above materials are used as dielectrics. However, both of these may be limited depending on the type of capacitor and its end use. Thus, there remains a need to increase the volumetric efficiency of capacitors of a given size and construction by providing a material having a higher dielectric constant than that of currently commercially available materials.

Therefore, the main object of the present invention is to provide a capacitor having a higher capacitance per unit volume. A related object is to provide a capacitor having a dielectric having a higher dielectric constant than previously provided dielectrics.

Yet another object is to provide a monolithic multilayer capacitor having a high capacitance per unit volume.

Yet another more specific object is to provide a capacitor suitable for direct current.

These and other objects and advantages of the invention will be apparent upon reading the detailed description. Although the present invention is described with respect to preferred embodiments, it is to be understood that the invention is not intended to be limited to these embodiments. On the contrary, it is intended that all variations, modifications and equivalents be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention, there is provided a capacitor comprising at least two electrodes separated by a dielectric member comprising a polymer of at least one diacrylate polyether prepolymer. The capacitors are characterized by a relatively high volumetric efficiency due to the increased dielectric constant of the diacrylate polyether prepolymer. While polymers of diacrylate polyether prepolymers are generally suitable for capacitors, they are particularly suitable for the monolithic capacitors described in US Patent Application No. 562,779, which is hereby incorporated by reference.

Without being bound to a particular theory of operation, it is generally believed that orientational polarization is the predominant dielectric polarization mechanism in polar polymers, such as the diacrylate polyether prepolymer polymers described herein. Oriented polarization is believed to be caused by thermally activated molecular motion of polymer chains containing an asymmetric arrangement of permanent dipoles. Molecular motion and the number and strength of net dipoles are both factors of the dielectric constant of the molecule. However, it is believed that molecular motion contributes significantly to the orientational polarization and thus to the dielectric constant of the polymeric material. This is the ability of the dipoles to move and thus be oriented in the electric field which gives the dielectric properties of the molecule. Thus, for example, the electrostatic permittivity of a polymer is expected to be low independent of the number and strength of the net dipoles in the polymer if the dipole is stationary at the measured temperature.

In amorphous polymers, such as the polymers obtained by polymerizing the diacrylate polyether prepolymers described herein, the predominant transition during molecular motion occurs at the glass transition temperature (Tg) of the polymer. Large-scale (or structural) molecular motions at Tg are frozen, causing marked changes in mechanical properties.

Diacrylate polyether prepolymers are thus characterized by their high dipole character and their molecular motion at their use temperatures, typically around room temperature (25 ° C). The ether linkage (COC) in the backbone of the prepolymer imparts intramolecular polarity and thus imparts dipole character to the molecule. Similarly, ether linkages are inherently chain-flexible and carbon-carbon due to the absence of steric hindrance. Increased rotational degrees of freedom around the oxygen-carbon bonds can be obtained and thus the Tg of the prepolymer can be relatively low temperature, eg room temperature or slightly above room temperature. The polymer thus formed from the prepolymer has the desired molecular mobility leading to a higher dielectric constant than other polymers that do not have mobility, such as polycarbonate, polysulfone, and the like.

The diacrylate polyether prepolymer has the general formula Wherein R is hydrogen or an alkyl group containing 1 to 5 carbon atoms, m, n and p may each be an integer from 0 to about 4, and the value of s is an integer from 0 to 5 S is selected such that it forms a continuous film free of pinholes when the prepolymer is deposited by vapor deposition.) As mentioned above, R is hydrogen or an alkyl containing from 1 to 5 carbon atoms. Can be a group. Usually, R is hydrogen or methyl,
Especially hydrogen. Thus, the term “acrylate” as used herein includes both acrylates and α-substituted acrylates, methacrylates and α-substituted methacrylates, but acrylates, i.e., where R is hydrogen, have a rate at which they polymerize. Generally preferred because it is quick.

The values of m, n and p, ie the branch length of the branches, can depend on the components used to make the polyether backbone.
Thus, for example, when ethylene oxide is used to prepare the polyether backbone, there are no branched chains. On the other hand, when an alkylene oxide having 3 or more carbon atoms is used,
The number of carbon atoms in the branch is 2 less than the total number of carbon atoms of the alkylene oxide used to prepare the polyether. Thus, when the polyether backbone is prepared from propylene oxide, the branch length is 1
If it is a carbon atom and the polyether backbone is prepared from butylene oxide, the branched chain length will be 2 carbon atoms.
Similarly, the backbone can be formed from a mixture of oxides such as propylene oxide and ethylene oxide, which can provide a particular distribution of branches in the polyether backbone.

The dielectric constant of the polymers produced from the prepolymers described herein is higher than the dielectric constants of the polymers conventionally used as dielectrics in capacitors. The polymers disclosed herein have a dielectric constant of at least 6.

The diacrylate polyether prepolymer may be prepared by first forming a polyether polyol as known to those skilled in the art, and then esterifying the polyether polyol with acrylic acid as is also apparent to those skilled in the art. For example, the above acids and polyether polyols may be reacted in a suitable solvent in the presence of a small amount of an acidic esterification catalyst such as sulfuric acid, p-toluene sulfonic acid, an acidic ion exchange resin or acidic clay. Usually, a stoichiometric excess of acid is used and the equivalent ratio of acid to diol is typically about 2: 1.
It is between about 4: 1. The above reaction is usually performed at a temperature of about 100 to 200 ° C, often about 100 to 150 ° C. A small amount of p-methoxyphenol, 2,6-di-t-butylphenol or 2,
It is sometimes preferred to incorporate a polymerization inhibitor such as 4,6-tri-t-butyl-phenol into the esterification mixture. The reaction conditions may be suitably modified to replace acrylic acid with its functional dielectric conductor such as an acrylic halide, lower alkyl ester or amide. Similarly, the introduction of dipolar halogen, carbonyl or nitrile residues can be done by techniques known to those skilled in the art.

Diacrylate polyether prepolymers suitable for use in the preparation of monolithic multilayer capacitors of the type described in the above-referenced U.S. Patent Application No. 562,779 are high quality capacitors that can be manufactured economically and efficiently. It should have the chemical and physical properties described below to give Thus, the prepolymer should be vaporizable at the temperatures used to effect the vapor deposition of the prepolymer, such as the temperatures described in US Pat. No. 562,779, and wherein the prepolymer is on the order of about 1 micron or less. Should be provided in thin film form. Further, the prepolymer is preferably curable by heat, electron beam or ultraviolet irradiation. The prepolymer is cross-linked during polymerization to provide the structural integrity required to provide a high quality, tough dielectric. Thus, the prepolymer should be capable of being crosslinked or polymerized at a rate fast enough to be useful in the process described in U.S. Patent Application No. 562,779 so as to optimize the time required to manufacture monolithic capacitors. For certain applications, such as AC capacitors, it is further desirable that the prepolymer, alone or with other monomers, form a polymer with low wastage and high thermal stability.

Thus, a wide variety of diacrylate polyether prepolymers can be used in the manufacture of capacitors, including monolithic capacitors. Suitable diacrylate polyether prepolymers are unbranched glycol diacrylates such as diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, and the like, as well as dipropylene glycol diacrylate, tripropylene glycol diacrylate, tetrapropylene glycol diacrylate. Includes branched glycol diacrylates such as acrylates.

The diacrylate polyether polymers described herein can be polymerized under free radical conditions either alone or in the presence of other monomers. "Polymer" as used herein
The term includes addition homopolymers and copolymers with one or more other monomers.

Polymerization by the free radical method can be carried out in bulk, in solution, in suspension or in emulsion by contacting the polymerization initiator with the prepolymer in the absence or presence of a diluent at a temperature of about 0 to 200 ° C. Suitable initiators are benzoyl peroxide, tertiary butyl hydroperoxide, acetyl peroxide, hydrogen peroxide, azobisisobutyronitrile, persulfate-bisphite,
Persulfate-sodium formaldehyde sulfoxylate, chlorate-sulfite and the like are included.

The polymerization can also be carried out by irradiation techniques such as by UV, electron beam or plasma irradiation.

A wide variety of polymerizable compounds may be used for the copolymer with the diacrylate polyether prepolymer.

Polymerizable copolymers include:

1. Allyl alcohol, methallyl alcohol, crotyl alcohol, 1-chloroallyl alcohol, 2-chloroallyl alcohol, cinnamyl alcohol, vinyl alcohol, methyl vinyl alcohol, 1-phenaryl alcohol and butenyl alcohol; and (i) Saturated acids such as acetic acid, propionic acid, butyric acid, valeroic acid, caproic acid and stearic acid, (ii) acrylic acid, α-substituted acrylic acid (alkyl acrylic acid such as methacrylic acid, ethyl acrylic acid, propyl acrylic acid, etc., and (Including arylacrylic acids such as phenylacrylic acid), unsaturated acids such as crotonic acid, oleic acid, linoleic acid and linolenic acid, (iii) oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, Polysalts such as suberic acid, azelaic acid and sebacic acid Acid, (iv) maleic acid,
Unsaturated polybasic acids such as fumaric acid, citraconic acid, mesaconic acid, itaconic acid, methylenemalonic acid, acetylenedicarboxylic acid, and aconitic acid; and (v) aromatic acids such as benzoic acid, phenylacetic acid, phthalic acid, terephthalate Esters of acids and benzoylphthalic acid with the above alcohols; 2. Unsaturated acids (examples of which are given above) and methyl alcohol, ethyl alcohol, propyl alcohol,
Esters with lower saturated alcohols such as isopropyl alcohol, butyl alcohol, isobutyl alcohol, sec-butyl alcohol, tert-butyl alcohol, 2-ethylhexyl alcohol and cyclohexyl alcohol and ethylene glycol, propylene glycol,
Esters with saturated lower polyhydric alcohols such as tetramethylene glycol, neopentyl glycol and trimethylolpropane, 3. Unsaturated lower polyhydric alcohols, such as butenediol and saturated and unsaturated aliphatic compounds with which the above examples are given. And an ester of an aromatic monobasic acid and a polybasic acid, 4. The unsaturated acid, particularly acrylic acid and methacrylic acid,
Esters with higher molecular weight monohydroxy and polyhydroxy substances such as decyl alcohol, isodecyl alcohol, oleyl alcohol, stearyl alcohol, epoxy resins and polybutadiene derived polyols, 5. Styrene, o-, m-, p-chlorostyrene , Bromostyrene, fluorostyrene, methylstyrene, ethylstyrene and cyanostyrene; di-, tri- and tetrachlorostyrene, bromostyrene, fluorostyrene,
Methylstyrene, ethylstyrene, cyanostyrene; such as vinylnaphthalene, vinylcyclohexane, divinylbenzene, trivinylbenzene, allylbenzene and vinylfuran, vinylpyridine, vinylbenzofuran, N-vinylcarbazole, N-vinylpyrrolidine and N-vinyloxazolidone. Vinyl cyclic compounds including heterocyclic compounds, 6. methyl vinyl ether, ethyl vinyl ether, cyclohexyl vinyl ether, octyl vinyl ether,
Unsaturated ethers such as diallyl ether, ethyl methallyl ether and allyl ethyl ether, 7. unsaturated ketones such as methyl vinyl ketone and ethyl vinyl ketone, 8. acrylamide, methacrylamide, N-methyl acrylamide, N-phenyl acrylamide, N- Acrylacrylamide, N-methylolacrylamide, N-
Allyl caprolactam, diacetone acrylamide, hydroxy-methoxylated diacetone acrylamide and 2-acrylamido-2-methylpropanesulfonic acid,
Unsaturated amides, such as 9. unsaturated aliphatic hydrocarbons such as ethylene, propylene, butene, butadiene, isoprene, 2-chlorobutadiene and common α-olefins, 10. unsaturated alkyl halides such as vinyl fluoride, Vinyl chloride, vinyl bromide, vinylidene chloride, vinylidene bromide, allyl chloride and allyl bromide, 11. Unsaturated acid anhydrides such as maleic anhydride, citraconic anhydride, itaconic anhydride, cis-4-cyclohexene-1, 2-dicarboxylic acid anhydride, and bicyclo (2,
2,1) -5-heptene-2,3-dicarboxylic acid anhydride, 12.cinnamyl chloride or bromide, acrylyl chloride or bromide, methacrylyl chloride or bromide, crotonyl chloride or bromide, oleyl chloride or bromide, And unsaturated acid halides such as fumaryl chloride or bromide, 13. unsaturated nitriles such as acrylonitrile, methacrylonitrile and other substituted acrylonitriles.

As noted above, the prepolymers disclosed herein have high volumetric efficiency and suitability for the manufacture of capacitors with low wastage factors, especially at about room temperature (ie, about 25 ° C.) due to their dielectric composition in capacitors. Is extremely useful as

Capacitors utilizing the prepolymers disclosed herein can be made of materials and arrangements known to those of ordinary skill in the art. Conductors are typically aluminum, copper, zinc, tin,
Stainless steel, and alloys thereof, with aluminum being preferred. For example, the present invention may include a first electrode, which may be, for example, an aluminum foil, such as vacuum evaporation, roll coating, flowing, spraying, dipping, brushing, drawing down, etc. on the surface of the first electrode.
On a dielectric coating of a polymer of a diacrylate polyether prepolymer which may be formed by optionally depositing the diacrylate polyether prepolymer in solution, evaporating the solvent and then polymerizing appropriately, and said dielectric film. A capacitor is provided that includes a second electrode that is a thin metallization layer, preferably deposited on aluminum. Suitable leads are attached to the first and second electrodes.

The present invention also provides a monolithic multilayer capacitor as described in US Pat. No. 562,799. Capacitors of this type (generally described on pages 9 and 10 of this specification) are in a relationship protruding from the stack and electrically coupled to each other as more fully described in the above application. It can be manufactured by depositing an AC electrode layer and a dielectric layer so as to obtain an AC electrode layer having a contact portion. The dielectric coating consists of a polymer of diacrylate polyether prepolymer formed by depositing the prepolymer on the electrode and subsequently polymerizing the prepolymer. It is particularly preferred to use electron beam polymerization, because electron beam polymerization gives a rapid polymerization of the above prepolymers without the need for an additional curing agent, thus leading to an economical production of very thin coatings.

The following examples illustrate the invention but do not limit it.

Example 1 This example illustrates the production of a uniform proto-type capacitor using a diacrylate polyether prepolymer and also includes a diacrylate prepolymer without an ether backbone for comparison purposes.

A uniform proto-type capacitor was drawn down on an aluminum foil substrate with a prepolymer layer and the above layer was
It was produced by contacting with an electron beam of Megarad to polymerize it, and depositing a metal aluminum layer thereon. The thickness of the aluminum foil electrode was 12.5 microns, the thickness of the dielectric layer was 3-6 microns and the thickness of the deposited aluminum electrode was 300-500Å (0.03-0.05 microns).
The area of each proto-type capacitor was approximately 1 square inch.

The following prepolymers were used in Examples 1a, 1b, and 1c. In Example 1a, the prepolymer is SR-268, which is tetraethylene glycol diacrylate. This prepolymer has a molecular weight of 302 and a density of 1.1 at 25 ° C.
It has a viscosity of 15 to 1.125 and a viscosity of 50 cps at 25 ° C. Example
In 1b, the prepolymer is SR-230, which is diethylene glycol diacrylate. This prepolymer has a molecular weight of 214, a density of 1.1110 at 25 ° C and a viscosity of 24 cps at 25 ° C. In Example 1c, the prepolymer is SR-238, which is 1,6-hexanediol diacrylate. This prepolymer has a molecular weight of 22.
It has a density of 1.010 at 6 and 25 ° C and a viscosity of 12 cps at 25 ° C. SR-268, SR-230 and SR-238 are Atlantic. Litchfield. Company (Atlantic Richfie
ld Company) is a subsidiary of Sartomer. Commercially available from Company (SERTOMER Company).

The wastage factor D (%) of the test capacitor was measured at 60Hz using an AC bridge, and the permittivity of the dielectric of the test capacitor was about 25 ° C at room temperature.
ackard) Calculated with reference to the measured capacitance observed at 100 Hz on the LCR bridge. Four proto-type capacitors were made for each of the prepolymers. The thickness (T) of dielectric coating (unit: micron), measured capacitance (C) (unit: nanofarad), dielectric constant (DK) and capacitor waste factor (D%) are shown in the table below for each test. .

The above data show the improved volumetric efficiency of capacitors in which the dielectric is formed from a prepolymer of the type disclosed herein. It can be seen that the dielectric constant of a dielectric made from a diacrylate polyether prepolymer is significantly higher than the dielectric constant of a dielectric made from an acrylate prepolymer with no ether linkages in the prepolymer backbone. Furthermore, it will be appreciated that capacitors particularly suitable for direct current can be made using the diacrylate polyether prepolymers disclosed in this invention and with the improved dielectric constant of the dielectrics produced therefrom.

Similarly, depending on the waste factor of the dielectric, a capacitor useful for alternating current can be made. Thus, the prepolymer used in Example 1a had an AC below about 30 ° C.
The capacitor is suitable for use up to at least about 85 ° C. for the prepolymer used in Example 1b.

Thus, as can be seen from the above description and the illustrative examples, the present invention provides a capacitor having improved volumetric efficiency due to the high dielectric constant of the dielectric formed from the diacrylate polyether prepolymer. The capacitors are particularly suitable for direct current, but may also be useful for certain alternating currents depending on the diacrylate polyether prepolymer.

Claims (12)

[Claims] 1. At least one pair of electrodes separated by a dielectric member, that is, a pair of electrodes and more than one electrode material, the dielectric member comprising: Where R is hydrogen or alkyl of 1 to 5 carbon atoms, m, n and p may each be an integer from 0 to about 4,
A polymer of at least one diacrylate polyether prepolymer, the value of which is such that the diacrylate polyether prepolymer forms a continuous film without pinholes during vapor deposition). Consisting of a capacitor. 2. The capacitor according to claim 1, wherein the electrode is aluminum. 3. The capacitor according to claim 1, wherein the diacrylate polyether prepolymer is an unbranched glycol diacrylate. 4. The capacitor according to claim 3, wherein the unbranched glycol diacrylate is diethylene glycol diacrylate, triethylene glycol diacrylate or tetraethylene glycol diacrylate. 5. The capacitor according to claim 1, wherein the diacrylate polyether prepolymer is branched glycol diacrylate. 6. The capacitor according to claim 5, wherein the branched glycol acrylate is dipropylene glycol diacrylate, tripropylene glycol diacrylate or tetrapropylene glycol diacrylate. 7. A monolithic multilayer capacitor having a capacitive active portion and two electrode coupling portions each separated from the active portion by a sloping portion, the first and second sets having the capacitors interleaved with each other. An active portion consisting of two sets of electrode layers, each layer of each set extending through the capacitive active portion of the capacitor in a stacked relationship with the active regions of all other layers and contributing to the capacitive active portion. And each layer has an electrode coupling end in stacked and electrically contacting relationship with the ends of the other layers in the set to form an electrode coupling portion of the capacitor, and each layer has its active region. And a dielectric coating adhering thereto between each adjacent electrode layer pair, the dielectric coating having a sloped portion passing between the capacitor and its end that contributes to the sloped portion of the capacitor, the dielectric coating in the capacitively active portion. Inclined portion with substantially uniform thickness Through gradually reduced to a thickness of zero, the dielectric coating has the formula Where R is hydrogen or alkyl of 1 to 5 carbon atoms, m, n and p can each be an integer from 0 to about 4, and s is of a value that the prepolymer is a pin during deposition. A monolithic multilayer capacitor consisting of a polymer of at least one diacrylate polyether prepolymer with the proviso that it forms a continuous film without holes). 8. The capacitor according to claim 7, wherein the electrode is aluminum. 9. The capacitor according to claim 7, wherein the diacrylate polyether prepolymer is an unbranched glycol diacrylate. 10. The capacitor according to claim 9, wherein the unbranched glycol diacrylate is diethylene glycol diacrylate, triethylene glycol diacrylate or tetraethylene glycol diacrylate. 11. The capacitor according to claim 7, wherein the diacrylate polyether prepolymer is branched glycol diacrylate. 12. The capacitor according to claim 11, wherein the branched glycol diacrylate is dipropylene glycol diacrylate, tripropylene glycol diacrylate or tetrapropylene glycol diacrylate.