JP2012067298A - Resin film, production method of the same, and film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the withstand voltage strength of a film capacitor.SOLUTION: A dielectric resin film obtained through a primary dissolution step of dissolving a thermoplastic resin like a polymer having a cyclic ring to thereby obtain a primary solution, a secondary dissolution step of subjecting the primary solution obtained in the primary dissolution step to a high dispersion treatment to thereby obtain a secondary solution, and a film-making step of making the secondary solution into a film and drying and removing the solvent, is used as dielectric resin films 3, 4 located between first and second mutually-opposing electrodes 5, 6. The secondary dissolution step is carried out until the relative molecular weight M1 of the primary solution and the relative molecular weight M2 of the secondary solution after the high dispersion treatment satisfy the relationship of (M1-M2)/M1≥15%.

Description

  The present invention relates to a resin film, a method for producing the same, and a film capacitor which is a typical use of the resin film, and particularly relates to an improvement for improving the withstand voltage strength of the resin film.

  As a type of capacitor, a metal film that serves as the first and second counter electrodes is disposed on each main surface of the resin film so as to face each other with the resin film interposed therebetween while using a flexible resin film as a dielectric. There is a film capacitor that is arranged along. The film capacitor usually has a columnar shape formed by winding the above-described dielectric resin film, and the first and second end surfaces of the column opposite to each other are first and second, respectively. External terminal electrodes are formed. The first counter electrode described above is electrically connected to the first external terminal electrode, and the second counter electrode is electrically connected to the second external terminal electrode.

  Due to the increase in frequency of electronic equipment, electronic components used therein are required to have good high-frequency characteristics. For example, with respect to capacitors, the dielectric loss tangent tan δ at high frequencies becomes a problem. The dielectric loss tangent tan δ is preferably small and ideally zero. This is because if the dielectric loss tangent tan δ is large, energy loss and accompanying heat generation occur, causing problems such as unstable operation of the high-frequency circuit.

  Under such a background, in a film capacitor for high-frequency applications, a dielectric resin film whose main component is polypropylene having a very small dielectric loss tangent tan δ at 1 kHz of 0.01% or less is used.

  However, as electronic components are being made into chips and the use environment is becoming harsh (especially high temperatures), there are many situations where polypropylene with relatively low heat resistance cannot be used.

  As a solution to this problem, there is a composite dielectric sheet for a high heat resistance film capacitor described in, for example, International Publication No. 2006/100833 (Patent Document 1). This composite dielectric sheet has a composition in which polyvinyl acetal crosslinked with polyisocyanate is a main component and a dielectric filler is added thereto for the purpose of improving the dielectric constant. More specifically, the composite dielectric sheet is present in a state of being dispersed in polyvinyl acetal, polyvinyl acetal, which is surface-treated with a coupling agent, a high dielectric constant filler, polyvinyl acetal, and And a cross-linking agent having two or more functional groups that react with both of the high dielectric constant filler surfaces.

  Note that the composite dielectric sheet described in Patent Document 1 is blended with a high dielectric constant filler, so that the dielectric loss tangent tan δ increases, and is difficult to use in high frequency applications. Therefore, if the dielectric sheet is composed only of the resin component, since the filler is not blended, it is presumed that the dielectric loss tangent tan δ can be reduced as compared with the case of containing the filler. However, even in that case, the dielectric loss tangent tan δ at 1 kHz is as large as about 0.75% compared to 0.01% or less of polypropylene, and it is difficult to use in high frequency applications.

  On the other hand, Japanese Patent Application Laid-Open No. 2004-281777 (Patent Document 2) describes a film capacitor having a heat resistance of 125 ° C. and a low dielectric loss tangent. The film capacitor described in Patent Document 2 includes a dielectric resin film made of a polymer having a cyclo ring. The dielectric loss tangent tan δ at 1 kHz of the polymer having a cyclo ring is as small as about 0.15%. However, a capacitor using a polymer having a cyclo ring has a problem that the dielectric breakdown strength is as low as about 250 V / μm, so that it cannot be used in applications where a high withstand voltage is required.

International Publication No. 2006/100833 Pamphlet JP 2004-281777 A

  Accordingly, an object of the present invention is to provide a resin film that can solve the above-described problems and a method for producing the same.

  Another object of the present invention is to provide a film capacitor constituted by using the resin film described above.

  The present invention is first directed to a method for producing a resin film, and is characterized by having the following configuration in order to solve the technical problems described above.

That is, in the method for producing a resin film according to the present invention, a thermoplastic resin is dissolved in a solvent, thereby obtaining a primary solution, a primary dissolution step, and a high dispersion treatment for the primary solution obtained in the primary dissolution step. A secondary dissolution step, thereby obtaining a secondary solution, and forming the secondary solution into a film and drying and removing the solvent, thereby obtaining a resin film. Is the relative molecular weight M1 of the primary solution and the relative molecular weight M2 of the secondary solution after the high dispersion treatment, as measured by gel permeation chromatography (Gel Permeation Chromatography).
(M1-M2) / M1 ≧ 15%
It is characterized by being implemented until it satisfies the relationship.

  The weight average molecular weight of the secondary solution obtained in the secondary dissolution step described above is preferably 10,000 or more.

  In the method for producing a resin film according to the present invention, a polymer having a cyclo ring is preferably used as the thermoplastic resin.

  The method for producing a resin film according to the present invention is advantageously applied to produce a dielectric resin film for a film capacitor.

  The present invention is also directed to a resin film manufactured by the above manufacturing method.

  Furthermore, the present invention is also directed to a film capacitor including the resin film and first and second counter electrodes facing each other across the resin film.

  According to this invention, the thermoplastic resin is used until the relative molecular weight M1 of the primary solution and the relative molecular weight M2 of the secondary solution after the high dispersion treatment satisfy the relationship of (M1-M2) / M1 ≧ 15%. As will become clear from the experimental examples described later, the dielectric breakdown strength of the resin film obtained by forming the secondary solution into a film can be increased. Therefore, if a film capacitor is constituted with this resin film, the dielectric breakdown strength of the film capacitor can be increased. Thus, the film capacitor can be advantageously directed to applications where a high withstand voltage is required.

  Further, when the thermoplastic resin is a polymer having a cyclo ring, since the dielectric loss tangent tan δ of the polymer having a cyclo ring is small, a film capacitor including a resin film obtained using a polymer having a cyclo ring is It can be advantageously directed to high frequency applications.

It is a longitudinal section showing an example of a film capacitor constituted using a resin film concerning this invention. It is a figure which shows the Weibull curve of the dielectric breakdown strength of the samples 2 and 7 produced in the experiment example. It is a figure which shows the Weibull curve of the dielectric breakdown strength of the samples 9 and 10 as a comparative example produced in the experiment example.

  Examples of the resin film according to the present invention include dielectric resin films for film capacitors, optical films, protective films for liquid crystals, antireflection films, food films, packaging films, gas barrier films, antistatic films, and high heat resistance adhesives There are various resin films such as a conductive film. Hereinafter, as a resin film according to the present invention, a dielectric resin film for a film capacitor is taken as an example, and a mode for carrying out the present invention will be described.

  First, a film capacitor will be described with reference to FIG.

  The film capacitor 1 shown in FIG. 1 is of a winding type. In brief, first and second dielectric resin films 3 and 4 wound around a winding shaft 2, The first and second counter electrodes 5 and 6 that are opposed to each other with the first or second dielectric resin film 3 or 4 interposed therebetween are electrically connected to the first and second counter electrodes 5 and 6, respectively. First and second external terminal electrodes 7 and 8 to be connected are provided.

  More specifically, the first counter electrode 5 is formed on the first dielectric resin film 3, and the second counter electrode 6 is formed on the second dielectric resin film 4. At this time, the first counter electrode 5 is formed so as to reach one side edge of the first dielectric resin film 3 but not to the other side edge. On the other hand, the second counter electrode 6 is formed so as not to reach one side edge of the second dielectric resin film 4, but is formed so as to reach the other side edge.

  The above-described first and second dielectric resin films 3 and 4 are in a stacked state when being wound around the winding shaft 2. At this time, as can be seen from FIG. 1, the end of the first counter electrode 5 on the side reaching the side edge of the first dielectric resin film 3 and the second dielectric in the second counter electrode 6. The first dielectric resin film 3 and the second dielectric resin film 4 are shifted from each other in the width direction so that both end portions reaching the side edges of the resin film 4 are exposed. Then, the first and second resin films 3 and 4 are wound around the winding shaft 2 as described above, whereby a substantially cylindrical capacitor body 9 is obtained.

  In the film capacitor 1 shown in FIG. 1, the first and second dielectric resin films 3 and 4 are arranged so that the second dielectric resin film 4 is outside the first dielectric resin film 3. Each of the first and second counter electrodes 5 and 6 is wound so as to face inward.

  The first and second external terminal electrodes 7 and 8 are formed by spraying, for example, zinc on each end face of the substantially cylindrical capacitor body 9 obtained as described above. The first external terminal electrode 7 is in contact with the exposed end portion of the first counter electrode 5, thereby being electrically connected to the first counter electrode 5. On the other hand, the second external terminal electrode 8 is in contact with the exposed end of the second counter electrode 6, thereby being electrically connected to the second counter electrode 6.

  Dielectric resin films 3 and 4 provided in such a film capacitor 1 are formed of the dielectric resin film according to the present invention. The dielectric resin film according to the present invention is not limited to a wound film capacitor 1 as shown in FIG. 1, but also a laminated film capacitor formed by laminating a plurality of planar dielectric resin films. Can be applied.

  The dielectric resin film according to the present invention is manufactured as follows.

  First, as a thermoplastic resin, for example, a polymer having a cyclo ring is prepared. Here, the polymer having a cyclo ring refers to a resin containing an alicyclic structure as a main skeleton, and examples thereof include a cycloolefin resin and a norbornene resin. In addition, since the name changes depending on which skeleton of the polymer is focused, there may be a polymer having a cyclo ring, which is a norbornene resin, although it is a cycloolefin resin. The norbornene-based resin includes a polymer having a cyclo ring obtained by ring-opening polymerization of a norbornene monomer, a polymer having a cyclo ring obtained by addition copolymerization of norbornene monomer and ethylene, and a modification of cyclopentadiene added to a polymer of norbornene monomer. Examples thereof include a polymer having a cyclo ring.

  Next, a primary dissolution step is performed in which a polymer having a cyclo ring is dissolved in a solvent, thereby obtaining a primary solution. Here, the solvent is not particularly limited as long as it can dissolve the polymer having a cyclo ring. Any organic solvent, water, acid, alkali or the like can be used as the solvent.

  Next, a secondary dissolution step is performed in which the primary solution obtained in the primary dissolution step is subjected to a high dispersion treatment, thereby obtaining a secondary solution. Here, the high dispersion treatment refers to a treatment for applying a shear force to a polymer chain in the primary solution to achieve dispersion as follows. For example, a method in which a primary solution pressurized to a high pressure collides with a wall, a method in which a primary solution is passed through a small-diameter orifice under high pressure, or a method in which a taper is passed and a diameter is gradually reduced, Or the method etc. which pressurize a primary solution to a high voltage | pressure or an ultrahigh pressure, and exert the shear force at the time of passing through a slit (gap) to a primary solution, etc. are mentioned.

  In the secondary dissolution step described above, the relationship between the relative molecular weight M1 of the primary solution and the relative molecular weight M2 of the secondary solution after the high dispersion treatment is (M1-M2) / M1 ≧ 15%, as measured by gel permeation chromatography. It is carried out until it becomes satisfied. Thereby, the withstand voltage strength of the obtained dielectric resin film can be increased. This is presumed to be because the entanglement of the molecules constituting the polymer dissolved in the primary solution is sufficiently unwound and the withstand voltage strength inherent to the polymer can be extracted to the maximum.

  Next, a film forming process is performed in which the secondary solution is formed into a film and the solvent is removed by drying, thereby obtaining a dielectric resin film.

  In the dielectric resin film production method described above, a polymer having a cyclo ring was used as the thermoplastic resin. However, in the resin film production method according to the present invention, as the thermoplastic resin other than the polymer having a cyclo ring, For example, polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polysulfone (PSF), polyethersulfone (PES), polyarylate (PAR), polyamideimide (PAI), polyetherimide (PEI), liquid crystal polymer (LCP), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbonate resin (PC), polyphenylene ether, cellulose, polystyrene, thermoplastic epoxy resin, thermoplastic acrylic resin, etc. can be used. That.

  In the above high dispersion treatment, it is not important to reduce the molecular weight by itself, but it is important that the molecular entanglement is loosened as a result of the low molecular weight satisfying the above conditions. It is done. In other words, reducing the molecular weight can have rather bad results. That is, the weight average molecular weight of the secondary solution after the high dispersion treatment obtained in the secondary dissolution step is preferably 10,000 or more, more preferably 20000 or more, from the viewpoint of the handleability of the resin film, and 100,000. The above is most preferable. When the weight average molecular weight is less than 10,000, the handling property of the resin film is lowered.

  An experimental example 1 conducted to confirm this will be described below.

[Experimental Example 1]
In Experimental Example 1, handling was evaluated by a bending test. That is, it was evaluated whether or not the strip-shaped film was broken when it was bent so that both end faces thereof were matched. Here, the strip-shaped film has a planar size of 50 mm × 10 mm and a thickness of 5 μm, and the secondary solution after the high dispersion treatment has a weight average molecular weight of 9000 and 10,000. Two types were prepared. For each sample, the number of samples was 10, and the number of samples in which fracture occurred as a result of the bending test was counted.

  As a result, in the film having a weight average molecular weight of 9000, breakage occurred in two samples, but in the film having a weight average molecular weight of 10,000, no breakage occurred in any sample. This shows that the weight average molecular weight of the secondary solution after the high dispersion treatment is preferably 10,000 or more.

  Next, Experimental Example 2 conducted to confirm the effect of the present invention will be described below.

[Experiment 2]
First, samples having the following samples 1 to 8 were prepared using a polymer having a cyclo ring as a thermoplastic resin.

  A cycloolefin resin having a weight average molecular weight of 160000 was prepared as a polymer having a cyclo ring. This cycloolefin resin is also a norbornene-based resin, and more specifically, a polymer having a cyclo ring obtained by ring-opening polymerization of a norbornene monomer.

  Next, the cycloolefin resin was dissolved in an organic solvent composed of toluene and methyl ethyl ketone, and stirred and mixed with a magnetic stirrer at 200 rpm for 24 hours to obtain a primary solution having a solid content concentration of 10% by weight. The above-mentioned weight average molecular weight is measured by gel permeation chromatography and calculated on the basis of a polystyrene standard sample.

  Next, this primary solution was processed with a high-pressure disperser to obtain a secondary solution. More specifically, a secondary solution was obtained by applying a shearing force through the primary solution to an orifice having a diameter of 0.125 mm and a length of 5 mm provided in the high-pressure processor. Here, the pressure applied by the high-pressure disperser and the number of times of passing through the high-pressure disperser are shown in the column of “pressure and number of times in high-pressure disperser” in Table 1.

  Even after the high-pressure dispersion treatment, the weight average molecular weight of the cycloolefin resin was calculated by gel permeation chromatography based on the polystyrene standard sample. The result is shown in the column of “weight average molecular weight” in Table 1. Then, the molecular weight before the high dispersion treatment was M1, the molecular weight after the high dispersion treatment was M2, and the change rate [%] of the molecular weight was obtained by the equation (M1-M2) / M1. The result is shown in the column of “molecular weight change rate” in Table 1.

Next, using a coater, a secondary solution obtained by treating with a high-pressure disperser as described above is applied onto a film made of polyethylene terephthalate and dried, and then a dielectric resin film having a thickness of 4 μm. Was molded. The molded dielectric resin film was placed in an N ₂ dry oven and dried at a temperature of 150 ° C. for 3 hours.

  A dielectric strength film was subjected to a withstand voltage test by forming aluminum electrodes on both surfaces of the dielectric resin film thus obtained, and using a 5 mm × 20 mm film piece as an evaluation sample.

  First, a withstand voltage test was performed by an electric field application method in which a voltage was applied to the electrodes on both sides of the sample for evaluation, the electric field strength was increased in increments of 25 V / μm, and each electric field strength was maintained for 10 minutes. The measurement was 25 ° C. Here, the electrostatic capacity after the voltage application for each electric field strength was obtained, and the electric field strength at which the electrostatic capacity decreased due to the breakdown of the film and became 0% of the initial value was defined as the dielectric breakdown strength. The number of samples was 20, and each electric field strength destroyed by the evaluation sample was recorded to obtain the minimum value and maximum value, and the value at which the failure frequency was 50% in the Weibull distribution was taken as the average value of the dielectric breakdown strength. . These results are shown in each column of “MIN”, “MAX”, and “Weibull average” in “Dielectric breakdown strength” in Table 1.

  Further, the number of failures after the withstand voltage test in which a voltage of 300 V / μm was applied to the number of samples for 20 samples was counted, and the number of failures in 20 samples was determined as the failure probability. The measurement was 25 ° C. This result is shown in the column “Probability of failure after withstand voltage test” in Table 1.

  Further, as shown in Table 1, the dielectric loss tangent tan δ was obtained for each sample. The measurement was 25 ° C. The dielectric loss tangent tan δ was measured using an LCR meter (“4284A” manufactured by Agilent) at a measurement frequency of 1 kHz and a measurement voltage of 1 V.

  On the other hand, the following samples 9 and 10 were produced as comparative examples.

  Polyvinyl acetoacetal (PVAA) having a weight average molecular weight of 330000 and ethyl acetate are mixed and stirred to prepare a resin solution having a polyvinyl acetoacetal concentration of 7% by weight, and tolylene diisocyanate (TDI) is added thereto. In addition, they were mixed and stirred so that the resin mixed solution became homogeneous. The TDI used here is a block type trimethylpropanol (TMP) adduct type tolylene diisocyanate of methyl ethyl ketone (MEK) oxime.

  Next, the resin mixed solution was processed in a high-pressure disperser as shown in the column of “pressure and number of times in high-pressure disperser” in Table 1. After this high pressure dispersion treatment, the weight average molecular weight was determined. The result is shown in the column of “weight average molecular weight” in Table 1. Then, from the weight average molecular weight before and after the high-pressure dispersion treatment, as shown in Table 1, the “molecular weight change rate” was determined. In Sample 9, the weight average molecular weight did not substantially change due to the high-pressure dispersion treatment.

  After that, for Samples 9 and 10, as in Table 1 above, as shown in Table 1, “failure probability after withstand voltage test”, “dielectric breakdown strength”, and “dielectric loss tangent tan δ” were obtained. It was.

  In Table 1, for “overall judgment”, a sample satisfying the condition that tan δ is 0.2% or less and the Weibull average of dielectric breakdown strength is 400 V / μm or more is “◯”, and the sample that does not satisfy is “×”. .

  In the samples 1 to 8 produced using the cycloolefin resin, when the relationship between the molecular weight change rate: (M1-M2) / M1 and the Weibull average of the dielectric breakdown strength is seen, the higher the former, the larger the latter The value is shown. FIG. 2 shows Weibull curves of dielectric strength for Sample 2 with a molecular weight change rate of 1% and Sample 7 with a molecular weight change rate of 20%. As can be seen from FIG. 2, as a result of the high-pressure dispersion treatment, the absolute value of the dielectric breakdown strength itself improves as the change rate of the molecular weight increases.

  Among Samples 1 to 8, according to Samples 5 to 8 having a molecular weight change rate of 15% or more, the “overall determination” is “◯”, tan δ is 0.2% or less, and the dielectric breakdown strength is The condition where the Weibull average was 400 V / μm or more was satisfied. Further, the failure probability after the withstand voltage test was 10% or less.

  In particular, according to Samples 7 and 8 having a change rate of the molecular weight of 20% or more, the Weibull average of the dielectric breakdown strength is 420 V / μm, and the failure probability after the withstand voltage test is 0%. showed that.

  When attention is paid to the relationship between “pressure and number of times in the high-pressure disperser” and “change rate of molecular weight” between the samples 6 to 8, the dispersion treatment conditions become more severe, “150 MPa, once” sample 6, “150 MPa , 3 times ”sample 7 and“ 150 MPa, 6 times ”sample 8 in the order of 15%, 20%, and 23%.

  Further, as in Sample 6, if the “pressure in the high-pressure disperser” is sufficiently high as “150 MPa”, even if the “number of times” is simply “once”, a “molecular weight change rate” of 15% is obtained, It can be seen that a result in which “overall determination” is “◯” is obtained.

  Further, comparing sample 5 and sample 6, as in sample 5, even when “pressure in the high-pressure disperser” is relatively low, “50 MPa”, “number of times” is set to “20 times”. If it is increased, it can be seen that a “molecular weight change rate” such as 15%, which is equivalent to that of the sample 6 having a relatively high “pressure in a high-pressure disperser” of “150 MPa”.

  In addition, when the “pressure in the high-pressure disperser” is as low as “25 MPa” as in the sample 2, the “molecular weight change rate” is as low as 1% even if the “number of times” is increased to “20 times”. , It can be seen that only the result of “overall determination” being “×” can be obtained.

  Next, with respect to Samples 9 and 10 as comparative examples manufactured using PVAA / TDI as a material, although the effect of reducing the variation in dielectric breakdown strength was recognized as a result of the treatment by the high-pressure disperser, the absolute value of the dielectric breakdown strength was confirmed. There was no effect of improving the value itself.

  FIG. 3 shows a Weibull curve of dielectric strength for samples 9 and 10. Sample 7 has the same “pressure and number of times in high-pressure disperser” as “25 MPa, 20 times” as in sample 2 shown in FIG. 2, and sample 10 has “pressure and number of times in high-pressure disperser” in FIG. It is the same as the sample 7 shown in “150 MPa, 3 times”. As can be seen from FIG. 3, in samples 9 and 10, the absolute value of the dielectric breakdown strength itself does not improve as a result of the high-pressure dispersion treatment.

  In the above experimental examples, the polymer having a cyclo ring was a cycloolefin resin, and a polymer having a cyclo ring obtained by ring-opening polymerization of a norbornene monomer of a norbornene-based resin was used. Similar results are obtained when a polymer having a cyclo ring obtained by addition copolymerization of norbornene monomer and ethylene is used, or when a polymer having a modified cyclo ring in which cyclopentadiene is added to a polymer of norbornene monomer is used. It was confirmed that it was obtained.

  Further, it was confirmed that even when a thermoplastic resin other than the polymer having a cyclo ring was used, at least the dielectric breakdown strength could be increased by performing the high dispersion treatment according to the present invention.

1 Film capacitor 3, 4 Dielectric resin film 5, 6 Counter electrode

Claims (6)

A primary dissolving step, in which a thermoplastic resin is dissolved in a solvent, thereby obtaining a primary solution;
A secondary dissolution step of subjecting the primary solution obtained in the primary dissolution step to high dispersion treatment, thereby obtaining a secondary solution;
The secondary solution is formed into a film, and the solvent is removed by drying, thereby obtaining a resin film, and a film forming step,
In the secondary dissolution step, the relative molecular weight M1 of the primary solution and the relative molecular weight M2 of the secondary solution after high dispersion treatment, as measured by gel permeation chromatography,
(M1-M2) / M1 ≧ 15%
It is carried out until the relationship is satisfied,
A method for producing a resin film.   The manufacturing method of the resin film of Claim 1 whose weight average molecular weights of the said secondary solution obtained in the said secondary melt | dissolution process are 10,000 or more.   The method for producing a resin film according to claim 1, wherein the thermoplastic resin is a polymer having a cyclo ring.   The method for producing a resin film according to claim 1, wherein the resin film is a dielectric resin film for a film capacitor.   The resin film manufactured by the manufacturing method in any one of Claims 1 thru | or 4. A resin film according to claim 5;
A film capacitor comprising first and second counter electrodes facing each other across the resin film.

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