CN111690323B

CN111690323B - Polyimide varnish, preparation method and application thereof

Info

Publication number: CN111690323B
Application number: CN202010588661.6A
Authority: CN
Inventors: 尹勇
Original assignee: Living Well Industry Hunan Co ltd
Current assignee: Living Well Industry Hunan Co ltd
Priority date: 2020-06-24
Filing date: 2020-06-24
Publication date: 2021-09-10
Anticipated expiration: 2040-06-24
Also published as: CN111690323A

Abstract

The invention provides polyimide varnish, and a preparation method and application thereof. The polyimide varnish is obtained by dispersing nano silicon dioxide subjected to surface modification by a silane coupling agent in a polyimide precursor solution, wherein the silane coupling agent is a triazine silane coupling agent.

Description

Polyimide varnish, preparation method and application thereof

Technical Field

The invention belongs to the field of high polymer materials, and particularly relates to polyimide varnish, and a preparation method and application thereof.

Background

In order to achieve a reduction in size and an increase in output of a motor, a material that can achieve high insulation with a thin film as much as possible in a winding wire is desired, and an insulating film that does not short-circuit for a certain period of time even when discharged is desired. Generally, a surge-resistant wire enamel in which an inorganic filler is uniformly dispersed in a resin to impart resistance to electric discharge is used, but there is a disadvantage that the toughness of the coating film is poor due to the partially aggregated inorganic filler or coarse filler. If the toughness of the coating film is significantly deteriorated as described above, cracks are locally generated in the coating film during the motor processing, so that the defect rate is deteriorated, and an interlayer short circuit may be generated in the motor.

In view of this, it is considered that the inorganic filler is surface-modified with a silane coupling agent and then redispersed in a resin, and for example, patent document 1(CN101235201A) discloses that nano silica is surface-modified with KH-550 and then the modified nano silica is dispersed in a polyamic acid solution. The method can improve the dispersibility of the nano-silica in the polyimide resin to a certain extent and enable the nano-silica particles to be tightly combined with the interface of the polyimide, but the electrical characteristics, the wear resistance and the adhesion with a conductor of the coating film still need to be improved.

Disclosure of Invention

Technical problem to be solved by the invention

In view of the above problems, an object of the present invention is to provide a polyimide varnish in which a film obtained using the polyimide varnish has toughness, surge resistance, adhesion to a conductor, and abrasion resistance in combination, and a method for producing the same and use thereof.

Means for solving the problems

The first invention provides a polyimide varnish obtained by dispersing nano silica surface-modified with a silane coupling agent in a polyimide precursor solution, wherein the silane coupling agent is a triazine silane coupling agent.

Preferably, the silane coupling agent is VD-5.

Preferably, the weight average molecular weight of the polyimide precursor is 3000-200000.

Preferably, the particle size of the nano silica is 100nm or less.

Preferably, the polyimide varnish is obtained by mixing and stirring a polyimide precursor solution and a colloidal nano silica solution treated by a silane coupling agent.

Preferably, the mass of the silane coupling agent is 5-30% of the mass of the silica in the colloidal nano silica solution.

Preferably, the method of stirring is mechanical stirring.

Preferably, the polyimide precursor is derived from a diamine and a dianhydride.

Preferably, the amount of the nanosilica added to the polyimide precursor is 5 to 50 wt%.

The second invention provides a film obtained using any of the above polyimide varnishes.

The third invention provides a coil provided with the film.

Effects of the invention

According to the present invention, a transparent polyimide varnish can be obtained by surface-modifying nanosilica with a triazine-based silane coupling agent to uniformly disperse nanosilica in a polyimide precursor solution, and a coating film obtained using the polyimide varnish has toughness, surge resistance, adhesion to a conductor, and abrasion resistance.

Detailed Description

The present invention is further described below in conjunction with the following embodiments, which are to be understood as merely illustrative, and not restrictive, of the invention.

In order to prevent the toughness of the polyimide film from decreasing, it is considered that: reducing the size of the inorganic filler to a nanometer size; dispersing uniformly in a form that prevents these fillers from agglomerating; improving the adhesive force between the involucra and the conductor.

The present inventors have made extensive studies and, as a result, have found that the problems of the above-mentioned (i) to (iii) can be solved by using colloidal silica and treating the surface of the silica with a specific silane coupling agent, thereby completing the present invention.

The polyimide varnish according to one embodiment of the present invention is obtained by dispersing nano silica surface-modified with a triazine silane coupling agent in a polyimide precursor solution.

The triazine silane coupling agent is a silane coupling agent having a triazine structure in a molecule.

In some embodiments, the triazine-based silane coupling agent comprises the following structural fragment:

in some embodiments, the triazine-based silane coupling agent has the following structural formula. In one embodiment, the triazine silane coupling agent is VD-5 manufactured by Sination chemical company;

in the formula, R⁵Is- (CH)₂)_n-. n is an integer of 1 or more, and preferably, n is 1 to 16.

The polyimide precursor solution contains a polyimide precursor and a solvent. The solvent is not particularly limited, and may be an organic solvent, and may be at least one selected from the group consisting of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, and xylene.

Polyimide precursors include any polyimide precursor material derived from diamine and dianhydride monomers and capable of being converted to polyimide, such as polyamic acids and the like.

The diamine is preferably an aromatic diamine, and examples thereof include phenylenediamine (PPD), diaminodiphenyl ether (ODA), 4 '-diamino-2, 2' -dimethylbiphenyl, 4 '-diamino-3, 3' -dimethylbiphenyl, bis (4-aminophenyl) sulfide, 3 '-diaminodiphenyl sulfone, 1, 4-bis (4-aminophenoxy) benzene, 1, 3-bis (3-aminophenoxy) benzene, 2-bis [4- (4-aminophenoxy) ] phenyl ] hexafluoropropane, 2-bis (4-aminophenyl) hexafluoropropane, 9-bis (4-aminophenyl) fluorene, 2-bis [4- (4-aminophenoxy) phenyl ] propane, 4' -bis (4-aminophenoxy) biphenyl, 1, 3-bis (4-aminophenoxy) benzene, 2' -bis (trifluoromethyl) benzidine, and the like. These diamines may be used alone or in combination of two or more.

The dianhydride is preferably an aromatic dianhydride, and examples thereof include pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 3',4,4' -benzophenonetetracarboxylic dianhydride, bicyclo [2.2.2] oct-7-ene-2, 3,5, 6-tetracarboxylic dianhydride, 1,2,3, 4-cyclopentanetetracarboxylic dianhydride, 1,2,3, 4-cyclobutanetetracarboxylic dianhydride, 1,2,4, 5-cyclohexanetetracarboxylic dianhydride, 3',4,4' -diphenylsulfonetetracarboxylic dianhydride, 4,4'- (hexafluoroisopropylidene) diphthalic anhydride, 4,4' - (4,4 '-isopropylidenediphenoxy) diphthalic anhydride, 4,4' -oxydiphthalic anhydride, bis (1, 3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylic acid) -1, 4-phenylene ester, and the like. These dianhydrides may be used singly or in combination of two or more.

The weight average molecular weight of the polyimide precursor is 3000-200000. The weight average molecular weight is a value measured by Gel Permeation Chromatography (GPC). If the weight average molecular weight is less than 3000, the toughness of the coating film decreases, and if the weight average molecular weight is more than 200000, the viscosity of the varnish becomes too high, and the handling property deteriorates. The weight average molecular weight of the polyimide precursor is preferably 15000 to 100000 in view of controlling the viscosity range in which the film has good toughness and is easy to handle.

The particle size of the nano silica dispersed in the polyimide varnish may be 100nm or less, preferably 10 to 100 nm. By making the particle size of the dispersed nano-silica 100nm or less, the film toughness can be made excellent.

In some embodiments, the polyimide varnish is obtained by mixing and stirring a polyimide precursor solution (also referred to as a base varnish) and a colloidal nano silica solution treated with a triazine-based silane coupling agent.

The polyimide precursor solution may be used as it is as a commercial product, or may be prepared by a method known in the art, for example, by reacting a dianhydride with a diamine in a solvent.

The colloidal nano-silica solution treated by the triazine silane coupling agent is obtained by treating the colloidal nano-silica with the triazine silane coupling agent.

Colloidal nanosilica (or called colloidal silica, organosilicone) refers to a colloid in which nano-sized silica (or called nano-silica) has been dispersed in a solvent.

In the present embodiment, colloidal nanosilica is used, and the affinity between the nanosilica and the polyimide precursor can be improved by surface-treating the nanosilica with a silane coupling agent, and the silica particles can maintain the original particle diameter after the colloidal nanosilica and the polyimide precursor are mixed and after the polyimide varnish is formed into a film as described below. That is, the silica in the resulting polyimide varnish was dispersed in a nano size. Thus, light is not scattered, and the polyimide varnish is transparent. Further, the polyimide varnish had good storage stability. The coating film of the polyimide varnish has good toughness. If the nano silica powder is used as it is, it is agglomerated into secondary, tertiary, and quaternary particles, and it is difficult to break the particles by means of ultrasound or the like. The polyimide varnish thus obtained was very cloudy and had poor toughness of the coating film. The silane coupling agent used is a triazine-based silane coupling agent, and adhesion and abrasion resistance between the polyimide film and the conductor can be improved as compared with the case where a general silane coupling agent such as 3-aminopropyltriethoxysilane is used. The reason for this may be that the N atom in the triazine skeleton may form a coordinate bond with a conductor such as a copper conductor.

The nano-sized silica in the colloidal nanosilica has a size of the order of nanometers in at least one dimension, and preferably has a size of the order of nanometers in each dimension. In a preferred embodiment, the nanosilica has a size in at least one dimension of 5 to 100 nm. This makes it possible to impart surge resistance without impairing the toughness of the obtained coating film.

The solvent in the colloidal nanosilica is an organic solvent, and may be, for example, at least one selected from the group consisting of N, N-dimethylacetamide, N-dimethylformamide, N-methylpyrrolidone, and xylene.

The concentration of silica in the colloidal nano-silica can be 5 to 40 wt%. Colloidal silica can be prepared on its own or purchased.

The amount of the triazine-based silane coupling agent used may be 5 to 30%, preferably 5 to 25%, of the mass of silica in the colloidal nanosilica. If the proportion is less than 5%, the varnish may be cloudy, the creep rupture film may be seriously floated, and the abrasion resistance and the surge resistance may be lowered; if the ratio is more than 30%, the colloidal silica is gelled.

In one example, the colloidal nanosilica is mixed with a triazine-based silane coupling agent and stirred to obtain a colloidal nanosilica solution treated with the silane coupling agent. The stirring method may be a usual stirring method, for example, a usual mechanical stirring method. The stirring temperature can be 20-70 ℃, and the stirring time can be 1-24 hours.

The mixing ratio of the polyimide precursor solution to the colloidal nano-silica solution treated by the silane coupling agent is preferably as follows: the amount of the nanosilicon dioxide added is 5 to 50 wt% with respect to the polyimide precursor. The amount of the nanosilica added is more preferably 10 to 20% by weight from the viewpoint of achieving both flexibility and surge resistance.

The method of mixing and stirring the polyimide precursor solution and the colloidal nanosilica solution treated with the silane coupling agent may be a general stirring method, for example, a general mechanical stirring method. The stirring temperature can be 20-70 ℃, and the stirring time can be 1-24 hours. In the present embodiment, the nano silica can be uniformly dispersed in the polyimide precursor solution by a general stirring method without a special mixing method such as 3-roll or planetary stirring.

Also provided are films (or "films" and "skins") obtained using the above polyimide varnish. The film contains polyimide and nano silica filler.

The creep rupture of the film has a film floating height of 7mm or less, a unidirectional abrasion of 1550 or more in accordance with JIS C3216-320116.1, a flexibility of 1d in accordance with JIS C3216-320115.1.1, and a V-t rupture time of 32 hours or more.

In one embodiment, a polyimide varnish is coated and heated to perform imidization, thereby obtaining a film.

There is also provided a coil having the above membrane. More specifically, in the coil, a film is coated on the surface of the lead.

The film of the present embodiment has excellent toughness, surge resistance, adhesion to a conductor, and abrasion resistance at the same time, and a coil having the film can be widely applied to motors for EVs and HEVs.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

And (3) preparing polyimide varnish.

First, a silane coupling agent is added to colloidal silica (DMAC-ST, manufactured by Nissan chemical Co., Ltd., silica concentration 20 wt%, silica particle diameter 10 to 15nm) so that the silane coupling agent is opposed to SiO₂The amount of (b) was as shown in Table 1, and the mixture was stirred at 70 ℃ for 1 hour to obtain treated colloidal silica. The treated colloidal silica was then added to a base varnish (Ulmide-D28, polyimide varnish manufactured by the Living well industry, weight average molecular weight 36000) to make SiO₂The polyimide varnish was prepared by stirring the mixture at room temperature for 1 hour, as shown in Table 1. VD-5 was obtained from Sitopanachemical K.K., and KBE903 (3-aminopropyltriethoxysilane) was obtained from Kyoto chemical industries.

Production of enameled wire

An enameled wire was produced using the above polyimide varnish. The specific method comprises the following steps: copper was cast, drawn and softened to obtain a conductor having a circular cross section and an average diameter of 1mm, and the polyimide varnish prepared by the above method was applied to the outer peripheral surface of the conductor and fired under conditions of a furnace inlet temperature of 350 ℃ and a furnace outlet temperature of 450 ℃ to laminate the insulating layers to obtain an insulated wire. The insulating layer was a single layer having an average thickness of 45 μm.

The obtained enameled wire was subjected to various characteristic evaluations. The test methods for each property are as follows:

slowly stretching, cutting off and membrane floating: drawing the enameled wire at a speed of 5mm per second until the enameled wire is cut off, and measuring the film floating length of a fracture part; unidirectional abrasion: evaluation was carried out in accordance with JIS C3216-320116.1;

and (3) flexibility test: a sample having an elongation of 10% was wound in different diameters and observed for the occurrence of cracks in the evaluation in accordance with JIS C3216-320115.1.1. for example, in the case of an electric wire having a diameter of 1.0mm, the result was recorded as 1d when the wire was not cracked when wound on a rod having a diameter of 1.0 mm. 2d is 2.0 mm. If the cracking at 1d is not occurred at 2d, it is designated as 2 d. If the crack is not generated when the crack is generated in 2d and when the crack is generated in 3d, the crack is recorded as 3 d;

v-t destruction time: 1500Vp voltage is applied to the coating at the frequency of 50Hz under the environment temperature of 155 ℃, and the time of the coating burning loss and short circuit is V-t failure time.

TABLE 1

。

As is clear from Table 1, it is understood that the addition of VD-5 improves the dispersibility by making the varnish transparent and greatly improving the V-t fracture time, and that the addition of VD-5 improves the one-way abrasion and the adhesion to the conductor by reducing the film floating.

Claims

1. A polyimide varnish is characterized in that a nano silicon dioxide surface-modified by a triazine silane coupling agent is dispersed in a polyimide precursor solution to promote N atoms in triazine skeletons to form coordinate bonds with conductors; the mass of the silane coupling agent is 5-30% of that of the silicon dioxide in the colloidal nano silicon dioxide; the adding mass of the nano silicon dioxide relative to the polyimide precursor is 5-50%;

a creep rupture film obtained using the polyimide varnish has a creep rupture film floating height of 7mm or less;

the unidirectional abrasion of an enameled wire produced by using the polyimide varnish is 1550 or more based on a JIS C3216-320116.1 test;

the flexibility of the enamel wire manufactured by using the polyimide varnish is tested to be 1d based on JIS C3216-320115.1.1;

applying 1500Vp voltage to the skin membrane at the frequency of 50Hz at the ambient temperature of 155 ℃, wherein the tested V-t failure time is more than 32 hours; the V-t failure time is the time during which the skin burns out and becomes short-circuited.

2. The polyimide varnish according to claim 1, wherein the silane coupling agent is VD-5.

3. The polyimide varnish according to claim 1, wherein the weight average molecular weight of the polyimide precursor is 3000 to 200000.

4. The polyimide varnish according to claim 1, wherein the nano silica has a particle size of 100nm or less.

5. The polyimide varnish according to claim 1, wherein the polyimide varnish is obtained by mixing and stirring a polyimide precursor solution and a colloidal nano silica solution treated with a silane coupling agent.

6. The polyimide varnish according to claim 1, wherein the polyimide precursor is derived from a diamine and a dianhydride.

7. A film obtained using the polyimide varnish described in any one of claims 1 to 6.

8. A coil comprising the film of claim 7.