JP2612276B2 - Aramid film for electrical insulation - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tough aramid film for electrical insulation having excellent heat resistance and tear resistance.

[Conventional technology]

Polyethylene terephthalate (hereinafter sometimes abbreviated as PET) is used as a plastic film for electrical insulation.
Film has been overwhelmingly used. But PET
Despite having many excellent features including the price, the film is not enough in terms of heat resistance, and is used in the field of electric insulation film (for example, heavy electric motors) where heat resistance is required. Has the disadvantage that it cannot be used.

On the other hand, a polyimide film is known as a film having an excellent heat resistance. However, the use of this film has been avoided because it is very expensive. In addition, dissatisfaction remains in terms of tear resistance.

For this reason, the appearance of a heat-resistant electrical insulating film having an excellent (performance / price) ratio has been desired. (For example, see Textile Society of Japan, Vol. 41, No. 9, page P-341 (1985)).

As a material meeting such a demand, a meta-oriented aramid film has been studied. For example, JP-A-51-7134
No. 8 discloses an aramid film prepared from an amide solvent. However, most of the films disclosed in this publication are meta-oriented aramids, and therefore have a high moisture absorption rate, and therefore have extremely poor dimensional stability of the film due to moisture absorption (JP-A-59-108035 discloses such a film). Although improved technology is disclosed, it is still not at a sufficient level even after "improvement".)
(3) Although disclosed, the copolymer is not satisfactory in moisture absorption properties as in the case of the meta-oriented type due to being a copolymer, or has poor mechanical performance due to low logarithmic viscosity (ηinh). Lithium chloride and calcium chloride are required to enhance the properties, and this has the disadvantage that chlorine atoms remain in the resulting film and are unsuitable for electrical applications. Further, in Example 1 of JP-A-53-42266 and JP-A-53-89999, a para-oriented aramid film formed from an organic solvent doped with lithium chloride or calcium chloride is disclosed. I have. However, since it is a film from the above-mentioned organic dope, residual chlorine atoms are inevitable, and aramids having a large logarithmic viscosity (ηinh) cannot be used (actually, they are 3.10 and 1.75, respectively). Electrical insulation film with good electrical performance cannot be obtained.

Therefore, it should be said that the above-mentioned problem of a heat-resistant electrically insulating film having an excellent (performance / price) ratio has not yet been achieved.

[Problems to be solved by the invention]

The present inventors have studied films of a wide variety of materials in order to meet the above-mentioned needs, and found that aramid films manufactured by a special method can satisfy the above-mentioned needs. It has been completed as an invention. That is, an object of the present invention is to provide a heat-resistant electrically insulating film having excellent cost performance. Another object of the present invention is to provide an aramid film which has excellent tear resistance and is therefore suitable for use as a slot liner for electrical insulation.

[Means for solving the problem]

The present invention substantially comprises a para-oriented aramid having a logarithmic viscosity (ηinh) of 3.5 or more, a thickness of 15 μm or more, an elongation of 5% or more, a crack resistance of 15 kgf or more, and a dielectric breakdown voltage of 100 KV.
aramid film for electrical insulation, characterized in that the content of chlorine atoms is 10 to 82 ppm or more. With such a configuration of the present invention, the above object is conveniently achieved.

The aramid consisting essentially of the para-oriented aramid used in the present invention is defined as having an amide bond in the para-position of an aromatic ring or in an equivalent orientation thereof (4,4'-biphenylene, 1,5-naphthalene, 2,6. -Consisting essentially of repeating units linked in opposite directions, such as naphthalene or the like, coaxially or in parallel, for example, poly (p-phenyleneterephthalamide) (hereinafter abbreviated as PPTA). , Poly (p-benzamide), poly (4,4'-benzanilide terephthalamide), poly (p-phenylene-4,4'-
Examples thereof include aramid having a para-oriented structure or a structure close to the para-oriented structure, such as biphenylenedicarbonamide) and poly (p-phenylene-2,6-naphthalenedicarbonamide). These polyamides are conveniently produced from aromatic diamines and aromatic dicarboxylic acid chlorides by a conventionally known low-temperature solution polymerization method. In particular, poly (p-phenylene terephthalamide) is inexpensive because it can be polymerized from a simple monomer, and is preferable from an industrial viewpoint.

If the degree of polymerization of the polymer of the present invention is too low, a film having good mechanical properties cannot be obtained. Therefore, the logarithmic viscosity ηinh of 3.5 or more, preferably 4.5 or more (measured at 30 ° C. by dissolving 0.5 g of the polymer in 100 ml of sulfuric acid, at 30 ° C.) The degree of polymerization which gives the given value) is selected.

The film of the present invention must satisfy the following five requirements.

First, the film of the present invention has a thickness of 15 μm.
It is necessary to be at least 20 μm, most preferably at least 25 μm. The upper limit of the thickness is not particularly limited, but is usually 500 μm or less. 1
Films smaller than 5 μm should be avoided in terms of electrical insulation resistance and workability and handling during mounting.

The film of the present invention should also have an elongation of 5% or more, preferably 8% or more. Films having an elongation of less than 5% are brittle, and are not preferred because they are easily broken by an external force, particularly when they are mounted, or are broken when bent.

Third, the film of the present invention must have a tear resistance of 15 kgf or more, and preferably has a tear resistance of 18 kgf or more. The size of the crack resistance is also related to the workability when mounting for electrical insulation, and has a crack resistance of 15 kgf or more so that it does not break even if a complicated external force such as shearing force is applied. Need to be. Films with high tear resistance
For example, as will be described later, it can be conveniently manufactured by causing a certain degree of shrinkage in the drying step.

Fourth, the film of the present invention needs to have a dielectric breakdown voltage of 100 KV / mm or more. Films having a breakdown voltage of less than 100 KV / mm are subject to various restrictions when used in electrical insulation applications. 100K
It was found that a film having a dielectric breakdown voltage of less than V / mm often reflects unevenness of the film thickness, the remaining inorganic ionic compound, and the presence of pinholes and voids. The film of the present invention is preferably 150 KV / mm
It has the above breakdown voltage.

The film of the present invention further has a chlorine atom content of 10 to
82 ppm. If the chlorine atom content in the film exceeds 82 ppm, the metal (e.g., copper, aluminum, solder, etc.) in contact with the film when used as an electrical component may be corroded, especially when used at high temperatures, and This is not preferable because the chemical change of the metal promotes the deterioration of the film. The content of chlorine atoms in the film is preferably 50 ppm or less, and most preferably 30 ppm or less. As described above, the film of the present invention substantially containing no chlorine atom can be prepared by, for example, a method described below, that is, dissolving a raw material polymer containing no chlorine atom in a solvent containing no chlorine atom to form a dope, and washing with water. Also in the scouring step, it can be produced by using water or the like containing no chlorine atom.

The film of the present invention preferably has a dimensional change rate due to moisture absorption of 6 × 10 ⁻⁵ mm / mm /% RH or less. Such a film with good moisture absorption dimensional stability generally has a small moisture absorption rate, and its performance changes are small even if there is a change in the humidity of the environment in which it is used. More preferably, the rate of change in dimensional change in moisture absorption is 4 × 10 ⁻⁵ mm / mm /% RH or less. Films having good dimensional stability due to moisture absorption are, for example, heat-treated (about
(300-400 ° C.), and can be achieved by means such as improvement in crystallinity, introduction of an alkyl side chain into a polymer, and hydrophobicity by introduction of an alkyl terminal group.

The film of the present invention also preferably has one or both surfaces having a coefficient of kinetic friction of 0.35 or less. A film having a small dynamic friction coefficient is excellent in workability when mounted on an electric device as an electric insulating material. A film having a low dynamic friction coefficient can be obtained, for example, by adjusting the surface roughness level or adding a lubricant.

The film of the present invention preferably has a coefficient of thermal expansion of 20 × 10 ⁻⁶ mm / mm / ° C. or less.

The film of the present invention preferably has a tensile modulus of about 200 to 700 kg / mm ² . This is because a film having an elastic modulus in this range has a moderate waist with good workability at the time of mounting as a material for electrical insulation.

The film of the present invention further has a heat shrinkage at 250 ° C. of preferably 0.8% or less.

Next, an example of a method for obtaining the film of the present invention will be described. The film of the present invention cannot be obtained by a conventionally known method.

In obtaining the film of the present invention, it is first necessary to adjust the optically anisotropic doping of the para-oriented aramid. A suitable solvent for adjusting the dope is sulfuric acid at a concentration of 95% by weight or more. With less than 95% sulfuric acid, dissolution is difficult or the dope after dissolution becomes abnormally high in viscosity. 100 sulfuric acid
While those having a concentration of at least 100% by weight are possible, a concentration of 98 to 100% by weight is preferably used from the viewpoint of the stability and solubility of the polymer. The polymer concentration in the dope should be room temperature (about 20 ° C to 30 ° C).
° C) or more, and is preferably used in a concentration exhibiting optical anisotropy at a temperature of at least about 10% by weight, more preferably at least about 11% by weight. At a polymer concentration lower than this, that is, a polymer concentration that does not exhibit optical anisotropy at room temperature or higher, the molded film often does not have favorable mechanical properties. The upper limit of the polymer concentration of the dope is not particularly limited, but is usually 20% by weight or less, and particularly high logarithmic viscosity (ηinh)
Is preferably 18% by weight or less, more preferably 16% by weight or less.

Whether the dope is optically anisotropic or optically isotropic can be determined by a known method, for example, the method described in Japanese Patent Publication No. 50-8474, but its critical point is determined by the type of solvent, temperature, and polymer. Concentration, the degree of polymerization of the polymer, the content of non-solvent, etc., by examining these relationships in advance,
By making an optically anisotropic dope and changing the condition to be an optically isotropic dope, it is possible to change from optically anisotropic to optically isotropic. It is preferred that the dope is removed by filtration or the like to remove insoluble dust and foreign matter as much as possible prior to molding and solidification, and that gas such as air generated or entrained during melting is removed. Degassing can be performed after the dope is once adjusted, or can be achieved by performing vacuum (reduced pressure) consistently from the stage of charging the raw materials for adjustment. Adjustment of the dope can be performed continuously or batchwise.

The dope adjusted in this manner is cast on a support surface from a die, for example, a slit die, while maintaining optical anisotropy. In addition, experimentally, it can be cast on a glass plate with a doctor knife. In the present invention, casting and subsequent conversion to optical isotropy, coagulation, washing, stretching, even if performed continuously, such as drying, all or some of these intermittently, that is, batchwise May go.

The adjustment of the film thickness depends on the polymer concentration in the dope,
The draft rate (the ratio of the moving speed of the support surface to the linear velocity of the discharge from the die), the gap between the die and the doctor knife, and the like can be used.

In order to obtain the film of the present invention, it is necessary to convert the dope from optically anisotropic to optically isotropic prior to solidification after casting the dope on the supporting surface.

To make the optically anisotropic from optical anisotropy, specifically, prior to solidification, the optically anisotropic dope cast on the support surface is absorbed to reduce the concentration of the solvent that forms the dope, The dope is transferred to the optically isotropic region by changing the dissolving ability and the polymer concentration, or the temperature of the dope is raised by heating to transfer the phase of the dope to the optical isotropic, or the moisture absorption and the heating are performed simultaneously or sequentially. It can be achieved by using them together. In particular, a method utilizing moisture absorption is useful because it can efficiently optically anisotropy the optical anisotropy and can cause no decomposition of the polymer, including a method using heating in combination.

In order to absorb the dope, air at a normal temperature and humidity may be used, but preferably humidified or heated and humidified air is used. The humidified air may contain water in the form of mist exceeding the saturated vapor pressure, or may be so-called steam. However, supersaturated steam at about 45 ° C. or lower is not preferable because it often contains large granular condensed water. The moisture absorption is usually carried out by humidified air at room temperature to about 180 ° C, preferably at 50 ° C to 150 ° C.

In the case of the method by heating, the means of heating is not particularly limited, and includes a method of applying the humidified air to the casting dope, a method of irradiating an infrared lamp, a method of dielectric heating, and the like.

The casting dope optically isotropic on the support surface is then subjected to solidification. Examples of the coagulable liquid include water, an aqueous solution of sulfuric acid, an aqueous alkali solution such as sodium hydroxide, an aqueous salt solution such as sodium sulfate, an organic solvent such as methanol, and an aqueous solution thereof. It should be noted that a coagulating solution containing a chlorine atom should be avoided. The temperature of the coagulating liquid is not particularly limited,
The temperature is usually 50 ° C. or lower, preferably 30 ° C. or lower, and a lower temperature makes it easier to obtain a dense film with less voids.

Since the coagulated film contains acid as it is, it is necessary to wash and remove acid components as much as possible in order to produce a film with little decrease in mechanical properties due to heating or a film with excellent electrical insulation. . Acid removal is
Specifically, it is desirable to carry out to about 500 ppm or less. Water is usually used as a washing liquid, but if necessary, washing may be performed with warm water, or after neutralizing and washing with an aqueous alkaline solution, washing with water or the like. Here, attention should be paid to the chlorine content in water and the aqueous solution, and it is preferable that the chlorine content be as low as possible. Washing is performed by, for example, running the film in the washing solution or spraying the washing solution, and it is preferable to reduce the remaining solvent and salt as much as possible.

The washed film is subsequently dried, and it is important to control dimensional changes in the drying process. In other words, the elongation characteristic of the film of the present invention is 5% or more, and the tear resistance is
In order for the film to be 15 kgf or more, it is important that the shrinkage of the film caused by drying is in the range of 0.50 to 0.95 times in each of the vertical direction and the horizontal direction of the rinsing film (the film before drying). This is undesirable because if the film is allowed to shrink less than 0.50 times and dries, the film will wrinkle or become uneven, and if it exceeds 0.95 times (ie stretched or dried to constant length) There is a tendency that the tear resistance becomes small and the elongation becomes small. Other conditions relating to the drying are not particularly limited, a method using a heating gas (air, nitrogen, argon, or the like) or a normal temperature gas, a method using radiant heat such as an electric heater or an infrared lamp,
The drying temperature can be freely selected from means such as a dielectric heating method, and the drying temperature is not particularly limited. However, in order to increase the mechanical strength, it is preferable to use a high temperature, 100 ° C or higher, and more preferably 200 ° C.
The above is used. The maximum drying temperature is not particularly limited, but is preferably 500 ° C. or lower in consideration of drying energy and decomposability of the polymer. Drying may be performed on two or more sheets.

〔Example〕

Hereinafter, Examples and Reference Examples (manufacturing examples of PPTA) will be shown, but these Reference Examples and Examples illustrate the present invention, but do not limit the present invention. Unless otherwise specified in the examples, parts or parts by weight are indicated. The logarithmic viscosity η inh was determined by dissolving 0.5 g of the polymer in 100 ml of 98% sulfuric acid and measuring at 30 ° C. by a conventional method.

The thickness of the film was measured with a dial gauge having a measuring surface with a diameter of 2 mm. For the elongation and modulus, a film sample was measured at 100 mm x 10 m using a constant-speed elongation type elongation meter.
It was cut into a rectangle of m, and a load-elongation curve was drawn five times at an initial grip length of 30 mm and a pulling speed of 30 mm / min, and was calculated from this. Both the tear resistance and the dielectric breakdown voltage were measured based on JISC2318. The content of chlorine atoms in the film was quantified by emission spectrometry. In Examples 1 to 4, the content was in the range of 10 to 50 ppm. Further, the workability when the film was used for electrical insulation was evaluated by the insertability of the slot liner and the wedge. That is, the film was slit in the vertical direction to a width of 30 mm, cut into a length of 50 mm, and used for a slot liner. On the other hand, it was slit in the vertical direction to a width of 16 mm, cut into a length of 43 mm, and used for a wedge. Next, the slot portion was filled with a slot liner, a coil, and a wedge at an occupation ratio of 65% using an automatic molding and insertion machine.
The loaded body was inspected, the presence or absence of buckling occurring at the time of driving was measured, and the insertability was judged as good or bad, and the workability was used as a parameter.

Reference Example (Production of PPTA) PPTA was obtained as follows by a low-temperature solution polymerization method. In a polymerization apparatus, 70 parts of anhydrous lithium chloride was dissolved in 1000 parts of N-methylpyrrolidone, and then 48.6 parts of paraphenylenediamine were dissolved. After cooling to 8 ° C., 91.4 parts of terephthalic acid dichloride were added at once in powder form. After a few minutes, the polymerization reaction product solidified in a cheese-like form. The polymerization reaction product was discharged from the polymerization apparatus, immediately transferred to a twin-screw closed kneader, and finely pulverized in the kneader. Next, the finely pulverized product was transferred into a Hensiel mixer, added with an approximately equal amount of water, further pulverized, filtered, washed several times in warm water, and dried in hot air at 110 ° C. Light yellow PPTA with logarithmic viscosity (ηinh) of 5.8
95 parts of the polymer were obtained. In addition, polymers having different ηinh can be easily obtained by changing the ratio of N-methylpyrrolidone and the monomer (paraphenylenediamine and terephthalic acid dichloride) or / and the ratio between the monomers.

Example 1 PPTA having a logarithmic viscosity (ηinh) of 5.8 was dissolved in 99.1% sulfuric acid at a polymer concentration of 12.5% to obtain a dope having optical anisotropy at 70 ° C. The dope exhibited 6200 poise at about 70 ° C.
The dope was degassed under vacuum at about 65-70 ° C for 5 hours. Keep the 1.5m curved pipe from the tank through the filter, through the gear pump to the die at about 70 ° C, 0.60mm x 300mm
With a discharge linear speed of 3.5 m / min from a die with a slit of
Cast to a mirror-polished tantalum belt and blow air at about 90 ° C with a relative humidity of about 85% to make the casting dope optically isotropic. Along with the belt, a 30% by weight sulfuric acid aqueous solution at -5 ° C And solidified. Next, the coagulated film was peeled off from the belt and washed by running in hot water at about 40 ° C. The washed film is guided to a tenter and shrunk to about 90% in both the running direction and the direction perpendicular to the film, and dried with hot air at 150 ° C. did.

The resulting film has a logarithmic viscosity (ηinh) = 5.0, thickness
25μm, tensile strength 18Kg / mm ² (winding direction) and 17Kg / mm ²
(In the direction perpendicular to the winding direction), elongation 29% (in the winding direction) and 32%
(Coiling direction perpendicular), elastic modulus 370 kg / mm ² (coiling direction) and 340 kg / mm ² (coiling direction perpendicular), edge-cracking resistance 21 kgf (both directions), the breakdown voltage 180 kV / mm, 25 ° C. The dimensional change measured at 90% relative humidity was 3.2 × 10 ⁻⁵ mm / mm /% RH (in both directions), the coefficient of kinetic friction was 0.31, and the insertability into the slot liner and wedge was good.

For comparison, make the die slit 0.8mm x 300mm,
When a film was made under the same conditions as above except that drying was performed under stretching of 1.05 times, the thickness was 24 μm, and the elongation was 21.
% (In both directions), modulus of elasticity 760Kg / mm ² (winding direction) and 690Kg / mm ² (in the direction perpendicular to winding), end crack resistance 13Kgf, dynamic friction coefficient 0.35, and in insertion tests into slot liners and wedges, A little buckling or tearing of the film occurred.

Examples 2 to 4 PPTA having a logarithmic viscosity (ηinh) of 4.8 was dissolved in 98.5% sulfuric acid at 11% to obtain an 8400 poise dope having optical anisotropy at 50 ° C. After deaeration and filtration, the dope was cast on a tantalum belt from a die having a slit shown in Table 1. The casting dope is converted into a transparent optically isotropic dope by blowing air at about 95 ° C. at a relative humidity of about 80%, and then at −10 ° C.
With a 25% aqueous sulfuric acid solution. After the coagulated film was removed from the belt, the film was washed with water at room temperature, a 2% aqueous solution of sodium hydroxide, and water at about 30 to 40 ° C. in that order.

The wet film which has been washed and contains about 250 to 350% water is sent to a tenter, and the degree of restriction of film shrinkage when the film is dried by the tenter is set under various conditions shown in Table 1 as shrinkage ratios. I got a film.

Table 1 shows the properties of the obtained film. The logarithmic viscosities (ηinh) of all the films were in the range of 3.9 to 4.4.

Example 5 and Comparative Example In the production of the film of Example 3, chlorine sterilization was performed instead of washing with water of about 30 to 40 ° C. substantially free from chloride ions after neutralization washing with an aqueous solution of sodium hydroxide. A film obtained by washing with drinking water, then washing with water containing no chloride ion and drying was used as Example 5, and a film obtained by drying only with washing of drinking water was used as Comparative Example.

The film of Example 5 had substantially the same characteristics as the film of Example 3 except that the chlorine ion content was 82 ppm.

The film of the comparative example has a chlorine ion content of 136 ppm.
, And the characteristics were not substantially different from those of the film of Example 3 except that the dielectric breakdown voltage was 130 KV / mm.

Next, sandwich these films between two copper plates,
A heat resistance test was performed at 0 ° C. for 30 minutes. The film of Example 3 showed almost no decrease in the logarithmic viscosity (ηinh) and almost no discoloration of the copper plate. However, the film of Example 5 had a logarithmic viscosity (ηinh) reduced by 0.3 and contacted the film. The copper plate was slightly discolored. On the other hand, the film of the comparative example had a logarithmic viscosity (ηinh) as low as 1.4, and the copper plate in contact with the film was corroded and rough.

〔The invention's effect〕

The aramid film for electrical insulation of the present invention can be adjusted from a simple monomer, is excellent in heat resistance, excellent in tear resistance, and is a tough film. Because of its excellent chemical properties, it has excellent workability when incorporated into electrical equipment, and also has excellent product durability. Taking advantage of these features, motors (especially for refrigerators and refrigerator rotary compressors,
Suitable for slot liners, wedges, interphase insulation, coil insulation of transformers, interstage insulation, static rectifiers, power capacitors, sheet heating elements, flexible printed circuit boards, flat cables, etc. Used for

Claims (1)

(57) [Claims] (1) It is substantially composed of para-oriented aramid having a logarithmic viscosity (ηinh) of 3.5 or more, a thickness of 15 μm or more, an elongation of 5% or more, a crack resistance of 15 kgf or more, and a dielectric breakdown voltage of 100 KV.
Aramid film for electrical insulation, characterized in that the content of chlorine atoms is 10 to 82 ppm or more.