JPH11121270A - Dielectric polyester film for capacitor and plastic film capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent blocking phenomena during storage, after winding a dielectric film for a capacitor by improving adhesion between the dielectric film and an aluminum-deposited film. SOLUTION: A dielectric polyester film for a capacitor is coated with a polyester paint on one surface or both the surfaces of the film. The glass transition point (Tg) of the polyester resin A constituting the polyester paint is equal to or higher than 0 to equal to or lower than 4 deg.C, and the average molecular weight thereof is equal to or larger than 18,000 and equal to or smaller than 40,000. As a result, blocking phenomena are prevented during storage, after winding a dielectric film for a capacitor by improving adhesion between the dielectric film and the aluminum-deposited film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a dielectric polyester film for a capacitor and a plastic film capacitor using the same as a dielectric.

[0002]

2. Description of the Related Art Conventionally, a dielectric film for a capacitor in which a polyester film is provided with a coating layer made of polyester and a capacitor using the same have been disclosed in, for example,
It is known from US Pat. In addition, Japanese Unexamined Patent Publication
JP-A-3-140511 discloses a film in which a polyester obtained by copolymerizing isophthalic acid is laminated by coextrusion as a film for exterior of a capacitor.

[0003] Aluminum deposited film and polyester coating film (dielectric film for capacitors)
Are wound alternately, it is necessary to completely adhere the two types of films. In other words, the improvement of the adhesion between the aluminum-deposited film and the film coated with the polyester resin prevents infiltration of an impregnating agent such as an epoxy resin onto the aluminum-deposited surface after winding, and together with the yield of the final product, This is to improve the life of the capacitor.

In general, in order to improve the adhesion, the softening point of the coating material to be coated should be as low as possible.
A method of thermocompression bonding at 00 ° C. to 200 ° C. is used. For this purpose, a polyether-based coating obtained by copolymerizing various dicarboxylic acid components and glycol components is used.

[0005] However, in the prior art, even when the temperature is increased at the time of thermocompression bonding, a sufficient adhesion cannot be obtained, and the performance of the product is degraded. In addition, after coating with paint, if left at room temperature for a long time, the blocking phenomenon often occurs between the polyester resin coating layer and the polyester base film, or between the polyester resin coating layers when the coating is performed on both sides of the base film. It is the cause of the trouble.

Further, when the polyester resin is coated on both sides of the base film, the step of impregnating the epoxy resin or the like can be omitted. However, in the conventional paint, the performance such as withstand voltage is inferior to that of the capacitor impregnated with the resin. The main reason is that when the coated surface of the polyester coating film and the uncoated polyester are wound, slippage between the two is poor and voids are easily formed between the two.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to have a high adhesive strength to an aluminum vapor-deposited film by low-temperature thermocompression bonding, and to provide a high adhesion between a polyester resin coating layer and a polyester base film or on both sides of a base film. An object of the present invention is to provide a capacitor dielectric polyester film which does not cause a blocking phenomenon between polyester resin coating layers when applied to a polyester resin coating layer. Another object of the present invention is to provide a capacitor using a dielectric polyester film for a capacitor, which improves the slippage between the coated surface of the polyester coating film and the uncoated polyester when the polyester film is wound. And

[0008]

As a result of investigations to solve the above problems, the present inventors have determined that the structure and composition of the polyester resin, which is the main component of the polyester-based coating, can be controlled at a low temperature by controlling the specific range. High adhesion is obtained by thermocompression bonding,
Further, they have found that an effect of preventing blocking during storage can be obtained. That is, by setting the glass transition point (Tg) of the polyester resin, which is the main component of the polyester-based coating applied on one or both sides, to 0 ° C. or more and 40 ° C. or less and the average molecular weight of 18,000 or more to 40000 or less, at normal temperature. The blocking phenomenon is less likely to occur due to the reduced adhesiveness, and the crystallinity of the polyester resin during thermocompression bonding is significantly reduced, so that the adhesion between the polyester resin coating film and the base film or the aluminum vapor-deposited film becomes stronger. I found something.

Further, when the polyester paint is applied to both sides of the polyester film, the thickness of the polyester resin coating film (coating A) to be adhered to metal deposition or metal foil is 0.1 μm or more and 1.0 μm or less. A polyester resin-based coating film (coating B) to be adhered to a polyester film or a polypropylene film is provided on a surface opposite to one surface of the polyester film on which the polyester-based resin coating film is provided. Has been found to strengthen the adhesion between the polyester resin coating film and the base film or the aluminum vapor-deposited film. Furthermore, the average molecular weight of the polyester resin constituting the coating film A to be brought into close contact with metal vapor deposition or metal foil is 18,000 or more, and one side of the polyester film on which the polyester resin coating film A is provided. The average molecular weight of the polyester resin constituting the polyester resin coating film B to be brought into close contact with the polyester film or the polypropylene film provided on the opposite surface is 19000 or more, and the average molecular weight of the polyester resin constituting the coating film A is As a result, the adhesiveness at room temperature can be further reduced, and the adhesion between the polyester resin coated surface and the uncoated raw polyester film or polypropylene film surface is increased. Was completed.

That is, the above-mentioned object of the present invention has been industrially advantageously achieved by the present invention having the following constitution.

[1] In a dielectric polyester film for a capacitor in which one or both sides of a polyester film are coated with a polyester-based paint, the polyester resin A constituting the polyester-based paint has a Tg of 0 ° C.
At least 40 ° C. and an average molecular weight of 18,000 to 40,000.

[2] In the above item [1], the polyester resin constituting the polyester resin has a Tg of 5 ° C. or more and 35 ° C. or less. .

[3] In the above item [1] or [2], the polyester resin is the same as the polyester A and Tg.
Is greater than 40 ° C. and the average molecular weight is 18,000 or more 4
0000 or less of polyester B is used in combination, and the constituent molar ratio of polyester A is larger than the molar ratio of polyester B. .

[4] The polyester resin paint according to any one of the above items [1] to [3] is applied to both sides of a polyester film.

[5] In the above item [4], the film thickness of the polyester resin-based coating film (coating film A) to be adhered to the metal vapor deposition or metal foil is set within a range of 0.1 μm or more and 1.0 μm or less. It is assumed that a polyester resin-based coating film (coating film B) to be brought into close contact with the polyester film or the polypropylene film is provided on a surface opposite to one surface of the polyester film provided with the system resin coating film.

[6] In the above item [4] or [5], the coating film A to be adhered to metal deposition or metal foil.
Having an average molecular weight of 18,000
The polyester constituting the polyester resin-based coating film B to be in close contact with the polyester film or the polypropylene film provided on the surface opposite to the one surface of the polyester film on which the polyester-based resin coating film A is provided. Average molecular weight of 190
The average molecular weight is not less than 00 and larger than the average molecular weight of the polyester resin constituting the coating film A.

[7] The dielectric polyester film for a capacitor according to any one of the above items [1] to [6] is applied to a plastic film capacitor as a dielectric.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

The polyester base film of the polyester film in the present invention is not particularly limited, but polyethylene terephthalate in which at least 80 mol% of the constituent units is ethylene terephthalate,
Preferably, polyethylene naphthalate in which at least mol% is ethylene naphthalate, or poly-1,4-cyclohexane dimethylene terephthalate in which 80 mol% of its structural units are 1,4-cyclohexane dimethylene terephthalate, is particularly preferable. Is polyethylene terephthalate. Examples of the copolymerization components other than the above-mentioned superior components include diol components such as diethylene glycol, propylene glycol, neopentyl glycol, polyethylene glycol and polytetramethylene glycol, isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodium glycol. Examples include, but are not limited to, dicarboxylic acid components such as dium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid and its ester-forming derivatives, and oxymonocarboxylic acids such as oxybenzoate and its ester-forming derivatives. Not something.
The polyester film may be blended with titanium oxide, carbon, or the like, or may be blended with silicon oxide, calcium carbonate, or the like for roughening the surface of the film.
Desirably, the melting point of the polyester base film is higher than 255 ° C.

In general, a plastic film capacitor may be formed by co-winding a metalized film and a resin-coated film as well as a raw film which is not metallized or coated. In some cases, a polypropylene film may be used in addition to the polyester film.

The thickness of the base film used in the present invention, that is, the polyester film coated with the polyester-based paint is preferably 2 μm or more and 20 μm or less. If it is 2 μm or less, it is difficult to obtain a sufficient capacitor capacity, and if it is 20 μm or more, there is a disadvantage that the capacitor becomes too large.

The polyester paint in the present invention is:
It is a paint composed of a polyester resin, and the Tg of the polyester resin constituting the polyester resin is 0 ° C. or higher and 4
0 ° C. or less and an average molecular weight of 18,000 to 400
It must be less than 00. If the Tg is lower than 0 ° C., blocking tends to occur due to adhesion at room temperature, and if the Tg exceeds 40 ° C., the level of adhesion is not satisfactory. A more preferable range of Tg is 5 ° C. or more and 35 ° C. or less. Further, when the average molecular weight of the polyester resin is less than 18,000, the tackiness is increased, and the friction between the film and the film is increased. Therefore, the winding is not performed smoothly, and a void is easily generated between the film and the coated surface. . On the other hand, if the molecular weight exceeds 40,000, the viscosity of the coating liquid tends to increase, and it tends to be difficult to apply the liquid stably.

It is desirable that 60 mol% or more of the dicarboxylic acid component of the polyester resin constituting the polyester resin is an aromatic carboxylic acid having a benzene ring. In the present invention, the ratio of ethylene glycol in the diol component of the polyester resin is 30.
It is desirably about 90% by mole. The constituents other than the above-mentioned glycol component may be copolymerized or blended as required. It is.

The polycarboxylic acids constituting the polyester resin in the present invention include terephthalic acid, isophthalic acid, orthophthalic acid, phthalic acid, 4,4'-diphenyldicarboxylic acid, 2,5-naphthalenedicarboxylic acid,
2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 2-potassium sulfoterephthalic acid,
5-sodium sulfoisophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, succinic acid, trimellitic acid, trimesic acid, trimellitic anhydride, phthalic anhydride, p-hydroxybenzoic acid, tri Monopotassium melitate and ester-forming derivatives thereof can be used. Examples of the polyvalent hydroxy compound include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, neopentyl glycol, 1,4 -Butanediol, 1,
6-hexanediol, 2-methyl-1,5-pentadiol, 1,4-cyclohexanedimethanol, p-xylene glycol, bisphenol A-ethylene glycol adduct, diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol , Polytetramethylene glycol, polytetramethylene oxide glycol, dimethylolpropionic acid, glycerin, trimethylolpropane, sodium dimethylolesulfonate, potassium dimethylolpropionate, and the like.

Of these compounds, 1
One or more polyester resins can be selected and synthesized by a conventional polymerization reaction, but if the proportion of the aromatic carboxylic acid is less than 60 mol%, the adhesion to the polyester base film may be reduced. Not preferred. Further, aliphatic carboxylic acids such as adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, glutaric acid, and succinic acid are also preferably used, but the Tg of the polyester resin is limited to a range of 0 ° C. or higher, and is substantially limited. Is limited to a copolymerization amount of less than 40 mol%.

In the present invention, these polyester resins may be used by blending as necessary. Also,
When blocking resistance is particularly required, Tg is 40 ° C.
Above the polymer is blended to the extent not beyond the scope of the invention. In this case, the molecular weight of the polymer to be blended is 1
The molecular ratio of the polymer to be blended is preferably lower than the molar ratio of the polymer having Tg of 40 ° C. or lower. If the molecular weight of the polymer having a Tg exceeding 40 ° C. is lower than 18,000, the tackiness is undesirably high. On the other hand, if the molecular weight exceeds 40,000, the viscosity of the coating liquid tends to increase, and it becomes difficult to apply the liquid stably, which is not preferable.

The coating material to be coated preferably contains calcium carbonate, silicon oxide, aluminum oxide or the like having an average particle size of 1 μm or less, in an amount of 1% by weight or more and 20% by weight or less based on the polyester resin, preferably 2% by weight. Above, 15
% By weight or less is more preferred. The purpose of blending these additives is to improve the anti-blocking effect. By blending these additives, a polyester resin having a lower softening point can be used. If the amount is less than 1% by weight, the effect of preventing blocking is insufficient, and 20% by weight.
When the ratio exceeds 2, the number of secondary aggregated particles increases, the coated surface becomes rough, and the adhesion performance decreases.

The polyester film coated with the polyester paint of the present invention can be brought into close contact with an aluminum-deposited film by low-temperature thermocompression bonding, and the content of the organic solvent in the film is reduced in order to reduce the incidence of problems such as blocking. The concentration is preferably 0.1 ppm or more and 3.0 ppm or less, more preferably 0.5 ppm or more and 2.0 ppm or less. When the content is less than this range, stable adhesion cannot be obtained, and when the content is large, blocking tends to occur.

The organic solvent for dissolving the polyester resin used in the present invention includes ethyl acetate, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene,
Examples thereof include cyclohexanone, and among them, aromatic compounds such as toluene and xylene are preferable. However, it is not limited to this.

The amount of the organic solvent can be controlled by adjusting the type and amount of the organic solvent used in the coating material, the drying temperature after coating, the drying speed, and the like.

As a method of applying the coating material of the present invention to a polyester film, a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, and the like other than those described in “Coating Method”, published by Yuji Harasaki, Maki Shoten, 1979, are used. Using a coating device of
A method of applying the coating solution outside the biaxially stretched polyester film manufacturing process, or a method of applying the coating solution within the film manufacturing process is used.

The coating of the present invention may be applied on only one side of the polyester film, and the coating amount is 0.1 g / m ^2.
As described above, the content is preferably 1.0 g / m ² or less.
More preferably, it is 3 g / m ² or more and 0.8 g / m ² or less. When the coating amount is less than 0.1 g / m ^2, it is difficult to obtain a uniform coating amount, so that not only the coating unevenness tends to occur on the product, but also the adhesive strength tends to decrease, and the coating amount tends to be 1.0 g / m 2.
^When it exceeds ² , not only the adhesion strength is saturated, but also blocking is liable to occur, which is not practical. The present invention is to improve the adhesion between a polyester film coated with a polyester film-based paint and a metallized dielectric film, but the metallized dielectric film used in the present invention is a general polyester film. It is a film on which metal is deposited, and the metal to be deposited is aluminum, palladium, zinc, nickel, gold,
Silver, copper, indium, tin, chromium, titanium and the like can be mentioned, and the most preferred metal is aluminum (Al). The thickness of the metal deposition film is preferably in the range of 10 to 5000 angstroms. The method of vapor deposition is generally a vacuum vapor deposition method, but may be a method such as an electroplating method or a sputtering method. In addition, the metal deposition layer may be provided on both sides of the polyester film. Although the present invention improves the adhesion between a polyester film coated with a polyester film-based paint and a metallized dielectric film, the capacitor is designed so that the metallized surface of the two films is in contact with the paint-coated surface. A capacitor element is formed by winding a pair of the elements that are superimposed on each other, and may be formed by laminating a large number. Capacitor elements, for example, hot press, taping,
A capacitor can be obtained by performing metallikon, voltage treatment, both ends sealing, lead wire attachment, etc., but is not limited to these.

Further, the polyester resin paint of the present invention can be suitably applied to both sides of a polyester film. In this case, the film thickness of the polyester resin-based coating film (coating A) to be brought into close contact with metal deposition or metal foil is 0.1 μm or more and 1.0 μm or less, and the polyester film provided with the polyester resin coating film It is preferable that a polyester resin-based coating film (coating film B) to be brought into close contact with the polyester film or the polypropylene film is provided on the surface opposite to the one surface.

By doing so, the metal deposition surface,
It is possible to improve all the adhesion to the metal foil surface or the raw polyester film surface.

The polyester resin constituting the coating film A to be adhered to the metal foil or the metal foil has an average molecular weight of 18,000 or more, and one of the polyester films on which the polyester resin coating film A is provided. The average molecular weight of the polyester resin constituting the polyester resin coating film B to be brought into close contact with the polyester film or the polypropylene film provided on the surface opposite to the surface is 19000 or more, and the average of the polyester resin constituting the coating film A Desirably, it is larger than the molecular weight. By doing so, the slipperiness between the coating surface and the raw polyester film surface can be improved, and as a result, voids are less likely to be formed between the two.

[0036]

The present invention will be described in more detail with reference to the following examples. In addition, the physical property in an Example was measured as follows.

(A) Glass transition point (Tg) of polyester resin Measured using a differential scanning calorimeter (DSC) according to the technique of measuring fibers and polymers (edited by the Society of Fiber Science and Technology).

(B) Adhesive Strength of Film A film coated with a polyester paint is 50 m wide.
m, cut to a length of 200 mm. On the coating layer side of this film, an aluminum vapor-deposited film also cut into a width of 50 mm and a length of 200 mm was superimposed, and the temperature was set at 120 ° C. ±
On a 2 ° C flat hot plate, 1 with a 2100 g silicone rubber roll
After thermocompression bonding the sample at a speed of 00 mm / min, the sample width is 25 m
m and a universal pulling tester, pulling speed 300m
/ Min was measured for adhesion.

(C) Blocking evaluation Ten samples cut into a square of 50 mm were overlapped so that the film surface and the coated surface were in contact with each other, sandwiched with a glass plate, and a load of 1 g / cm ² was applied.
It was left for 7 days. Thereafter, the sealed film was cut into a width of 25 mm, and a force when peeled at a rate of 200 mm / min in a 180-degree direction using a tensile tester was measured, and the measured force was used as an index of the blocking property. If this value is 30 g or less, there is no practical problem, but it is preferably 20 g or less.

Example 1 Methyl ethyl ketone (hereinafter M
40 parts, toluene 37 parts, average particle size 005μ
m, 3 parts of calcium carbonate and terephthalic acid and isophthalic acid in a molar ratio of 80:20 as polycarboxylic acids, and 60 mol% of ethylene glycol, 30 mol% of triethylene glycol, and 10 mol% of neopentyl glycol as glycol components. 120 parts of the copolymerized polyethylene terephthalate copolymer (hereinafter referred to as polyester resin A) were mixed and dissolved at 50 ° C. for 12 hours. This paint stock solution is designated as A. Toluene and xylene were added to this coating stock solution, and a coating thickness of 0.4 μm was applied to a 12-μm polyester film having a width of 1000 mm. Using a general gravure coater, coating and drying were performed to obtain dielectrics having physical properties shown in Table 1.

Example 2 A coating material was prepared in the same manner as in Example 1 except that the Tg of the polyester resin in Example 1 was not substantially changed and the molecular weight was changed to the value shown in Table 1.
Application was performed.

Example 3 The polyester resin A in Example 1 was prepared using terephthalic acid as a polyvalent carboxylic acid and a resin containing 60 mol% of ethylene glycol and 40 mol% of triethylene glycol as a glycol component. Example 1 except that the values shown in Table 1 were obtained.
A coating material was prepared and applied in the same manner as described above.

Examples 4 and 5 In Examples 4 and 5, terephthalic acid (50 mol%) and isophthalic acid (50 mol%) were used as polyester resin B with respect to 100 parts of polyester resin A similar to those in Examples 1 and 3, respectively. %) Ethylene glycol (50 mol%) and neopentyl glycol (50 mol%) were blended in an amount of 20 parts.

Comparative Example 1 All of Example 1 was repeated except that the molecular weight of the polyester resin was changed to 16,000.
The coating was performed in the same manner as described above.

Comparative Example 2 In Example 1, terephthalic acid and adipic acid were used as the polycarboxylic acid constituting the polyester resin in a molar ratio of 50:50 and a molecular weight of 16,000.
The coating was performed in the same manner as in Example 1 except that the above conditions were satisfied.

Table 1 shows the physical properties of these dielectrics.

[0047]

[Table 1] As is clear from Table 1, it can be seen that all of those in the range of the present invention show a high level of adhesion to the aluminum vapor-deposited film and are less likely to cause blocking.

[Examples 6 to 7] and [Comparative Example 3] Except that the coating material of Example 1 was applied to both surfaces of a polyester base film at the application thickness shown in Table 2 (A layer, B layer). A polyester film for a dielectric was obtained in the same manner as in Example 1. Comparative Example 3 was performed in the same manner as in Comparative Example 1 except that the paint of Comparative Example 1 was applied to both surfaces of the polyester base film at the application thickness shown in Table 2 (A layer, B layer). A film was obtained.

Example 8 The procedure of Example 7 was repeated, except that the polyester paint used in Example 2 was used as the paint for the coating layer (layer B) having a coating thickness of 1 μm. Was done.

Table 2 shows the physical properties of these dielectrics. In this table, in evaluating the adhesion of the layer B, the center line surface roughness (Ra) was used instead of the aluminum vapor-deposited film.
Was performed using a raw polyester film of 50 nm. Also, after winding the coating film for dielectric and the raw polyester film, 10-6To under reduced pressure.
Perform air void elimination treatment for 8 hours under the conditions of rr and 40 ° C., then gradually raise the temperature to 120 ° C. under reduced pressure at 10-3 Torr and heat treatment at 120 ° C. for 2 hours. Was evaluated visually.

[0051]

[Table 2] As is evident from Table 2, all of those in the range of the present invention show a high level of adhesion to the aluminum vapor-deposited film, have excellent adhesion to the raw polyester film, and furthermore have a polyester film It can be seen that the area of the void on the mating surface can also be reduced.

[0052]

According to the dielectric polyester film for a capacitor in which one or both surfaces of a polyester film are coated with a polyester coating, the polyester resin A constituting the polyester coating has a Tg of 0 ° C. or more and 40 ° C. or less and an average molecular weight. Is 18000 or more and 40
By setting it to 000 or less, the adhesion between the capacitor dielectric film and the aluminum vapor-deposited film was enhanced, and the blocking phenomenon during storage after winding the capacitor dielectric film could be prevented.

Claims (7)

[Claims] 1. A dielectric polyester film for a capacitor in which one or both sides of a polyester film are coated with a polyester paint, wherein the polyester resin A constituting the polyester paint has a Tg of 0 ° C. or higher.
0 ° C. or less and an average molecular weight of 18,000 to 400
A dielectric polyester film for capacitors, having a molecular weight of 00 or less. 2. The dielectric polyester film for a capacitor according to claim 1, wherein the polyester resin constituting the polyester resin has a Tg of 5 ° C. or more and 35 ° C. or less. 3. The polyester resin, wherein the polyester A and the Tg are higher than 40 ° C. and the average molecular weight is 1800.
3. The dielectric polyester film for a capacitor according to claim 1, wherein the polyester polyester B is used in combination with 0 to 40,000 or less and the molar ratio of the polyester A is larger than the molar ratio of the polyester B. 4. 4. The dielectric polyester film for a capacitor according to claim 1, wherein a polyester resin paint is applied to both sides of the polyester film. 5. A polyester resin-based coating film (coating A) to be adhered to metal vapor deposition or a metal foil has a film thickness of 0.1 μm or more and 1.0 μm or less, and the polyester resin coating film is provided. 5. The dielectric film for a capacitor according to claim 4, wherein a polyester resin-based coating film (coating film B) to be adhered to the polyester film or the polypropylene film is provided on a surface opposite to one surface of the polyester film. Body polyester film. 6. The polyester resin constituting the coating film A to be adhered to a metal foil or a metal foil has an average molecular weight of 1
8000 or more, and constitutes a polyester resin-based coating film B to be brought into close contact with a polyester film or a polypropylene film provided on a surface opposite to one surface of the polyester film on which the polyester-based resin coating film A is provided. The dielectric polyester film for a capacitor according to claim 4 or 5, wherein the polyester resin has an average molecular weight of 19000 or more and is larger than the average molecular weight of the polyester resin constituting the coating film A. 7. A plastic film capacitor using the dielectric polyester film for a capacitor according to claim 1 as a dielectric.