DE1614922C3 - Capacitor and process for its manufacture - Google Patents

Description

H ₂ C

CH,

consist of a vapor-deposited, uniform, continuous coating of linear p-xylylene polymer.

The object of the invention is to provide a capacitor with an improved, plastic-coated dielectric material particularly suitable for the application of alternating current, wherein the previous difficulties in the application of high voltages and frequencies are resolved should, and of a relatively small size compared to others, possibly with plastic-coated Paper-equipped paper wound capacitors with similar properties.

The invention relates to a capacitor which has a plurality of metal foils forming the deposits and intervening dielectric interlayers of porous material formed thereby characterized in that the porous material has a uniform, continuous coating of linear p-xylylene polymer is coated.

Another object of the invention is a method for producing the capacitor, the characterized in that the polymer coating is applied to the porous material by condensation of reactive p-xylylene diradicals with the general structure

(R)

in which R stands for a customary substituent and χ stands for 0, 1, 2 or 3, at temperatures below the condensation temperature of the diradicals, and uses this material as a dielectric intermediate layer.

35

The invention relates to a capacitor made of a plurality of metal foils and forming the deposits intermediate dielectric layers made of porous material coated with plastic.

There are a number of electrical circuits for the paper wound capacitors, with or without a plastic coating on paper are best suited. The application of alternating current and others Applications with fairly high voltages and frequencies bring problems in terms of electrical Stress and temperature that many plastic film capacitors do not withstand, or which would require the use of relatively large units.

Wound capacitors made of paper and plastic-coated paper - although otherwise for many areas of application suitable - show a strong increase in the positive temperature coefficient with regard to energy loss above 50 ° C, which can lead to self-discharge if the capacitors are subjected to limit loads get abandoned.

So is z. B. in DT-PS 8 90 843 a capacitor made of a plurality of deposits forming metal foils and described intervening dielectric layers, the latter made of paper or polystyrene can exist and are covered with a smoothing material. As covering materials are in particular insulating or adhesive paints proposed. Also by superficial paraffining of the Paper should have smooth surfaces.

Furthermore, in FR-PS 13 85 707 a capacitor is described with metal foils that form the coverings and intervening dielectric layers made of H ₂ C

CH ₂ -

in which R is a customary substituent and χ 0, 1, 2 or 3 is applied at temperatures below the condensation temperature of the diradical. The capacitor according to the invention and the method according to the invention for its production are explained in more detail with reference to the graphic representation and the exemplary embodiments in the figures. It shows

F i g. 1 is a graph showing the performance of the capacitor according to the invention when compared to a known capacitor,

Fig. 2 is a perspective view of an embodiment of a wound capacitor, from the type, components and its structure can be seen,

F i g. 3 is an enlarged view in section along line 3-3 of the wound components of FIG. 1;

4 is an enlarged view in section of the plastic-coated dielectric material;

F i g. 5 is a schematic representation of a plastic-coated one used to manufacture the one used Dielectric suitable device.

In Fig. 2 and 3, a tubular capacitor 10 wound on a core 11 is shown. Metal foils 12 and 13 are alternately arranged between layers 14 and 15 of dielectric material. The metal foils 12 and 13 have the width Wf, which is smaller than the width Wo of the dielectric layers 14 and 15. The edges of the foils 12 and 13 are arranged on opposite edges of the dielectric layers 14 and 15 so that the metal foils overlap in a central part W ₀ , whereby an area with capacitance effect is created in the unit. The outer, non-overlapping parts of the foils are used for the electrical connection line. One connecting wire is connected to the right edge of the foil 12 and the other connecting wire to the left edge of the foil 13.

The conductive foils 12 and 13 can be made of aluminum, copper, steel or some other suitable Made of metal. The dielectric layers 14 and 15 are each made up of a sheet or strip porous material 16, such as paper, formed with a uniform, continuous coating 17 from a linear p-xylylene polymer, as in Figure 4 shown is coated.

After winding, the capacitor body 10 is removed from the core and one end, e.g. B. 18, through Application of a copper coating by means of a flame spray process for attaching the connecting wire prepared to connect the edges of each turn of the metal foil 13 of a covering with this. A Conductive wire (not shown) is soldered to the copper clad end 18. At the other end of the The procedure for the capacitor winding is similar. The unit is then sheathed by known methods such as hot dipping, resin dipping, plastic dipping or placing in a molded housing etc.

In addition to the film-wound capacitor described, the capacitors can also be designed in other forms exist; for example in the form of sheet or disc capacitors.

The porous material used in the dielectric can be cellulosic material such as paper. Kraft paper is preferred, but paper made from hemp can also be used.

The paper strip can be coated with a linear p-xylylene polymer using an apparatus as in Fig. 5 shown, namely a bell-shaped vessel 19 which encloses a vapor deposition system, be coated. The vessel can be through a line indicated schematically with an arrow be pumped out. The evaporation system consists essentially of a container 20, which is to vaporizing organic material containing a cyclic p-xylylene dimer. The container 20 is with Heating devices (not shown) equipped so that the material evaporate and then into a Steam pipe 21 can be passed. The vaporous cyclic p-xylylene dimer is then in this tube further heated (by heating devices not shown surrounding the pipe) to add the steam Pyrolize p-xylylene diradicals. Through the outlet pipe 22 with at least one outlet pipe 23, the stream 24 of p-xylylene diradicals becomes a carrier 25 directed. A roll of paper 26 can be arranged so that a strip of paper 27 continuously over the Carrier 25 can roll away onto another roller 28. The p-xylylene diradicals condense on the Paper strips and form a uniform, continuous coating of linear p-xylylene polymer. The strip can be turned over and coated on the other side of the paper in the same way.

The apparatus described above is only used as an example of a device for Coating paper with the polymer. Other apparatus and methods can also be used will. For example, the steam generator could be outside the bell and only the outlet port 23 or the apparatus may be designed so that both sides of the paper strip be coated at the same time.

The capacitor has a dielectric made of paper with a uniform, continuous coating is coated from linear p-xylylene polymer, has superior electrical properties. the Capacitor has a relatively high capacity; and compared to other paper or plastic covered Paper capacitors, it shows a higher insulation resistance, less loss, a lower one Temperature coefficient of capacitance and a higher dielectric effect. A particularly important one The characteristic of this capacitor is the negative temperature coefficient in relation to energy loss, which allows a higher charge.

The loss factor of the capacitor is from about 0.1 to about 0.25% and decreases with temperature to about 0.05% to 150%. The insulation resistance is in the range of about 70 000 m Ω per μΡ at 25 ° C to 2000 Ω per μΡ at 125 ° C. The capacitance variation is about 5% at room temperature as compared to -65 ° C and 15O ⁰ C. The breakdown voltage is between 250-600 volts DC.

These and the following properties are for a wound capacitor manufactured as follows characteristic. A capacitor made of 0.006 mm thick paper was placed on both sides with a uniform, continuous, 0.002 mm thick coating of linear p-xylylene polymer (as above described) covered. About 0.006 mm thick aluminum foils were used as coverings.

The coating was smooth and continuous on the outside and enclosed the fibrous paper so tightly that the The plastic layer and the paper could not be separated. The p-xylylene appears in the interstices penetrate the paper and coat every fiber. The coating did not appear to be bridging. One Series of capacitors were wound using the materials described above. the Capacitors have not been wound on accurate winding machines and so variations have been made of the properties achieved.

However, the values given here are typical for such a capacitor. The capacity fluctuates from 0.007 μΡ to 0.054 μΡ because of the different number of turns and the different degree of overlap. The loss factor was constantly in the range from 0.1 to 0.25% at 25 ^° C. and 1000 Hz. This is considerably lower than the loss factor of other paper capacitors, possibly plastic-coated. In general, a loss factor below 1% at 25 ^° C. and 1000 Hz is viewed as very satisfactory.

Experiments with cyclical variation of the temperature were carried out using various experimental methods and temperatures carried out, as can be seen from Table 1.

Table 1

Temperature variation and type of test

TCC test

IR test

TCD test

1. 25 ° C

2. -65 ° C

3. 85 ° C

4. 100 ° C

5. 150 ° C

6. 25 ° C

7. 50 ° C

8. 100 ° C

9. 125 ⁰ C
10. 25 ° C

11. -65 ° C

12. 85 ⁰ C

13. 100 ° C

14. 150 ° C

15. 25 ° C

In the TCC test, the sample is placed in a test chamber at the desired temperature held and the capacitance measured with a suitable measuring bridge after equilibrium conditions were achieved.

In the IR test, the sample is kept at the desired temperature in a test chamber and the Current loss measured at constant voltage after equilibrium conditions have been reached was.

Table 2

Capacity and dissipation factor measurements

In the TCD test, the sample is kept at a temperature in a test chamber and afterwards Equilibrium conditions were reached, the loss factor was measured with a suitable measuring bridge. The results are given in Table 2.

Test No. begins. capacity

Initially Final capacity loss factor

More final

Loss factor

o / o

1 0.0225 0.09 0.0228 0.11 2 0.0208 0.11 0.0208 0.13 3 0.0220 0.12 0.0220 0.13 4th 0.0430 0.19 0.0427 0.22 5 0.0190 0.10 0.0192 0.16 6th 0.0200 0.10 0.0200 0.11 7th 0.0544 0.20 0.0543 0.25 8th 0.0129 0.14 0.0132 0.15 9 0.0264 0.11 0.0264 0.12 10 0.0145 0.11 0.0146 0.15 11th 0.0073 0.12 0.0074 0.13 12th 0.0201 0.14 0.0202 0.16 13th 0.0445 0.18 0.0440 0.20

The change in capacity after the end of the temperature cycle averaged less than 1% a maximum change of about 2%. A slight increase in the loss factor was due to the Notice temperature cycle.

The temperature coefficient of capacitance is positive over the range of -65 ° C to 150 ⁰ C and has an average of 0.045 at -65 ° C, 0.025 at 85 ° C, 0.027 at 100 ⁰ C and 150 ⁰ C 00:04 at what in % per ⁰ C is expressed. Table 3 also shows this change in% at the various temperatures.

Table 3

Temperature-dependent change in capacity

(Capacitor made of paper-p-xylylene polymer)

test

No.

Percentage change in capacity
-65 ⁰ C 85 ° C 100 ⁰ C 150 ° C

30th

10 2 1 1 4th 11th 2 1 1.5 1.5 12th 4th 1 1.5 3 13th 7th 3 4th 8th

1.5

Percentage change in capacity
-65 ° C 85 ⁰ C 100 ⁰ C 150 ⁰ C

1 3 1.5 2 4th 2 3 1.0 1.5 4th 3 3 1.5 2 4th 4th 4.5 3 3 9 5 3.5 1.5 2 5 6th 3 1.5 1.5 3 7th 6th 4th 4th 9 8th 4th 1 1 6th 9 3 1.5 2 3

The different results from Table 3 come from the different number of turns of the various capacitors examined, as well as the different degrees of overlap.

It is an important feature of the capacitor according to the invention that with increasing temperature a remarkable decrease in loss is achieved over a wide temperature range. In Table 4 shows the percentage change in loss with increasing temperature for some Winding capacitors shown, viz

1. Coated with linear p-xylylene polymer Paper capacitor,

2. a capacitor made of strong paper and

3. a paper-plastic capacitor (a double dielectric made from paper and a polyester film).

Table 4

Percentage loss with increasing temperature

capacitor

Temperatures ⁰ C

-55 ° 25 °

50 °

75 °

100 °

125 °

1. Linear p-xylylol 0.6 .15 .10 .08 .06 .05 paper 2. paper 2.0 .35 .30 .25 .20 .15 3. Paper-plastic 2.0 .30 .25 .30 .42 .75

As can be seen from the table, the linear p-xylylene-containing paper capacitor has only one low loss factor and a negative temperature coefficient in terms of loss. Known Paper and paper-plastic capacitors produce higher losses and often exhibit one

increasing positive temperature coefficient with respect to the loss above 50 ° C, which is at limit loads with alternating current can lead to self-discharge. Such a loss of energy with alternating current through a a paper capacitor, possibly containing another plastic, causes heating, which leads to losses increases and consequently generates even more heat. This mechanism of progressive temperature increase continues until the capacitor fails. To this disadvantage of the known, optionally plastic containing paper capacitors, they had to be used well below the limit load and that means that they had to be larger than an ideal capacitor. One of those limit loads exposed paper capacitor with linear p-xylylene has self-regulating properties because the temperature rises due to the loss of alternating current, the dissipation factor decreases, the heat effect is reduced and the capacitor a Equilibrium reached at normal temperature. Although some paper capacitors are also negative Have temperature coefficients with respect to loss, they are considerably larger than those of Paper capacitors with linear p-xylylene, which makes such paper capacitors only up to lower Limit loads can be used.

The graphic representation of FIG. 1 shows the temperature dependence of the dissipation factor for the capacitor according to the invention (solid line) and that of a typical known capacitor (dashed line) with a dielectric composed of a polyester film and paper.

The capacitor according to the invention has a high insulation resistance, especially when it is increased Temperatures, around 2000 Ω per μΡ at 125 ° C. That is about ten times higher than the resistance of paper, Polyester film / paper or polyester film capacitors. A high insulation resistance is in applications with AC power is desirable and is for AC / DC applications especially important where the AC losses (a function of charge loss) and the DC losses (a function of the insulation resistance) together to exceed the limit load being able to lead.

The capacitors of the invention have a dielectric resistance in excess of 390 volts per μπι (direct current). In Table 5, the DC breakdown voltage of three capacitors, each of which has a dielectric with a thickness of 10 μπι, compared:

1. a capacitor with a 6 μm thick paper and a 2 μίτι thick coating of linear p-xylylene polymer on each side,

2. capacitor made of strong paper,

3. Impregnated paper capacitor.

Table 5
DC breakdown voltage

capacitor

volt

1. Linear p-xylylene paper

2. paper

3. Impregnated paper

4000

500

1500

The capacitors of the invention have desirable dielectric absorption properties.

This property describes the effectiveness with which a capacitor releases its charge when it is is short-circuited, which ideally happens completely and immediately. Table 6 shows the superior ones Properties of the capacitor according to the invention compared to the properties of other capacitors.

Table 6

Dielectric absorption

capacitor

Percentage
dielectric
absorption

1. Linear p-xylylene paper

2. paper

3. Paper-polyester coating

4. Polyester film

0.2

0.6 to 3

0.9

0.5

The specified properties and tables show that the capacitors according to the invention, if necessary Superior to paper capacitors with other plastic coatings in many respects are. The capacitors according to the invention have particular advantages when used with alternating current, where imperative requirements are made in terms of dielectric performance. The involves passing a relatively large current (compared to the leakage current with direct current) through the Dielectric back, which generates heat, resulting in increased losses and a decrease in Resistance is accompanied. These effects usually increase with increasing frequency. The invention Capacitors are excellent for use at AC frequencies (60 to 400 Hz) and can also be used at higher frequencies, such as the frequency range of radios, be used.

A linear polymer coating can be produced by condensing reactive diradicals obtained by pyrolysis of cyclic dimers of di-p-xylylene of the formula

CH-

CH ₂
CH ₂

in which R is a customary substituent on the aromatic rings and is identical or different and x is O, 1, 2 or 3, can be obtained.

The optionally present substituents R are organic or inorganic groups, such as usually found on aromatic rings. Examples of such substituents are alkyl, aryl, Alkenyl, amino, cyano, carboxyl, alkoxy, hydroxyalkyl, carbalkoxy and the like, as well as inorganic ones Residues such as hydroxyl, nitro, halogen and similar customary groups, in addition preferably the simple ones Hydrocarbon groups such as lower alkyl groups e.g. B. methyl, ethyl, propyl, butyl, hexyl groups; Halogens, especially fluorine, chlorine, bromine, iodine and also the cyano groups. It goes without saying that in the absence of substituents, the bond is saturated by hydrogen.

40? 5 * 4/176

Since the binding and polymerization reaction of the reactive diradicals during their condensation Any unsubstituted or substituted p-xylylene polymer can not adversely affect the aromatic ring are produced, especially since the substituents are essentially inert groups.

However, since the polymers here serve as a dielectric and many of the above-mentioned are substituted p-xylylene polymers have a considerable dipole moment not all derivatives will give the same results when used in the capacitor. the The loss factor of certain p-xylylene polymers with highly polar substituents can be somewhat higher than with other p-xylylene polymers, but can Such substituted p-xylylene polymers may also be desirable because they often have a higher dielectric Have constants as e.g. B. unsubstituted polymers.

Certain physical properties of individual substituted p-xylylene polymers may be desirable so that somewhat poorer dielectric properties are tolerated. For example is Poly (2-chloro-p-xylylene) a very tough polymer with mechanical advantages over other p-xylylene polymers.

Poly (aAA ', a'-tetrafluoro-p-xylylene) is very temperature-resistant and can even ^{withstand 300 °} C. for 100 hours without changing the physical strength. Of the substituted p-xylylene polymers, these two are preferred. For general purposes, however, unsubstituted p-xylylenediradicals are normally preferred (ie, where x = 0 and all substituents = hydrogen), since the polymer produced therefrom has the most stable electrical properties and the most preferred dielectric constant and power factor compared to the other polymers.

The terms "di-p-xylylene" and "p-xylylene diradicals" therefore preferably denote unsubstituted dimers or diradicals or substituted dimers or Diradicals which are suitable for producing an optionally substituted p-xylylene polymer and when applied to paper or other porous materials, the desired combination of electrical and physical properties give, in some cases, resistance to high temperatures includes. Cyclic dimeric di-p-xylylene and corresponding substituted dimers, according to the invention are known. Substituted dimers can be prepared from di-p-xylylene by conventional methods to introduce substituents.

The cyclic dimer (I) is pyrolyzed to produce the reactive diradicals (II). Preferably, the cyclic dimer is vaporized prior to pyrolysis at low temperatures, which begins at temperatures above at least 100 ⁰ C. However, evaporation is not critical to performing this process.

The pyrolysis of the vaporous di-p-xylylene takes place at temperatures above about 400 ⁰ C, preferably held between about 550 ⁰ C and 700 ⁰ C. As a result of the pyrolysis, the di-p-xylylene (I) is split quantitatively and reactive diradicals of the structure

owns. The pyrolytic cleavage does not change the aromatic part of the di-p-xylylene, and no lower molecular weight units are present in the vapor of pyrolysis.

The diradicals formed in the manner described above hit the surface of the paper or of another porous material, the surface being kept at temperatures below the condensation temperature of the diradicals. This

ίο polymerize spontaneously after condensation and form a uniform, continuous coating of a linear p-xylylene polymer with the general structure

H, C

CH,

in which R and χ are as defined above and η is the number of repeating units in the chain, usually e.g. B. about 5000.

It has been found that for each type of diradical there is a maximum condensation temperature above which the diradical does not condense and polymerize. All observed maximum temperatures of p-Xylylendiradikalen were below about 25O ⁰ C, but vary somewhat with the pressure applied. For example, at a pressure of 0.5 mm Hg, typical condensation and polymerization temperatures have been observed for the following diradicals:

p-xylylene

Chlorine-p-xylylene

Dichloro-p-xylylene

25- 30 ⁰ C

70- 8O ⁰ C

200-250 ° C

CH, - <> --CH ₂ · (II)

formed, where (R) _{x has} the meaning already defined. Depending on the substituents on the cyclic dimer, either homopolymers or copolymers can be formed. If z. B. (R) _x is the same in each of the repeating units, homopolymers are formed after condensation of the diradicals. If R or χ in the repeating units are different or a mixture of cyclic dimers is pyrolyzed, copolymers can be formed if the condensation temperature is kept below the lowest maximum condensation temperature of the substituted diradicals. In this way, the polymerization in the condensation does not affect the aromatic parts of the diradicals (II) the substituent group. As stated previously, the choice of substituents should be based on the desired properties of the dielectric. p-Xylylene polymers have an unusually good resistance to practically all solvents, which is an indication that there are no other components with low molecular weight in the polymer.

In a preferred embodiment of the coating process, a weighed amount of one is added suitable di-p-xylylene in the container 20 (evaporation zone) of the evaporation pyrolysis oven. The system is evacuated up to the stated pressure and then di-p-xylylene into the steam pipe 21 (pyrolysis zone) given. The diradicals formed in the pyrolysis zone are through the outlet opening 23 to Carrier 25 passed where the diradicals with the paper 2i or another porous material in contact come on the surface of these objects

condense and thus form a polymer coating from p-xylylene polymer. The surface of the paper is brought to the appropriate condensation temperature by cooling devices (not shown) on the support 25 held.

The thickness of the polymer coating can be regulated by the duration of the vapor deposition on the paper will. In a previous example, a 2 μm thick coating was used on each side of a 6 μm thick Paper strip applied. The coating can be varied up to a thickness of 25 μm or more.

The preferred p-xylylene polymers for coating of paper or other materials for making superior dielectric material unsubstituted p-xylylene, 2-chloro-p-xylylene and α, α, αΆ'-tetrafluoro-p-xylylene.

The temperature resistance and the dielectric

Free film constant from these materials is given in Table 7 for comparison:

Table 7

Preferred p-xylylene polymers

Polymer

Highest dielectric

Process-tric temperature constant

> 175 ° C. 2.7 > 175 ° C. 3.0 > 300 ° C. 2.6

1. p-xylylene (unsubstituted)

2. 2-chloro-p-xylylene

3. α, α, α ', α'-tetrafluorop-xylylene

When applied to paper, the highest process temperature and dielectric constant differ from the values given above, but in each case an improved dielectric is produced.

For this purpose 2 sheets of drawings

Claims (5)

Patent claims: 1. Capacitor made of a plurality of metal foils forming the deposits and intermediate ones dielectric interlayers made of porous material coated with plastic, thereby characterized in that the porous material has a uniform, continuous coating linear p-xylylene polymer is coated. 2. Capacitor according to claim 1, characterized ι ο characterized in that the capacitor as a wound capacitor is trained. 3. Capacitor according to claim 1 and 2, characterized in that the porous material is paper. 4. Capacitor according to claim 1 to 3, characterized in that the coating consists of a linear polymer of 2-chloro-p-xylylene or α, α, α ', α'-tetrafluoro-p-xylylene. 5. A method for producing a capacitor according to claim 1 to 4, characterized in that the coating is applied to the porous material by condensation of reactive p-xylylene diradicals with the structure