JP7579977B2 - Low dielectric polyimide film with improved dimensional stability and method for producing same - Google Patents

Description

The present invention relates to a low dielectric polyimide film with improved heat resistance (particularly glass transition temperature characteristics) and dimensional stability (particularly thermal dimensional stability), and a method for producing the same.

Polyimide (PI) is based on imide rings, which have excellent chemical stability, along with a strong aromatic main chain, and is a polymer material that has the highest levels of heat resistance, chemical resistance, electrical insulation, chemical resistance, and weather resistance among organic materials.
In particular, due to its excellent electrical properties, such as its excellent insulating properties, i.e., low dielectric constant, it has been attracting attention as a highly functional polymer material in a range of fields, including electrical, electronic and optical fields.
2. Description of the Related Art In recent years, with the trend toward lighter and smaller electronic products, flexible thin circuit boards with a high degree of integration have been actively developed.
Such thin circuit boards tend to have a structure in which a circuit containing metal foil is formed on a polyimide film, which has excellent heat resistance, low temperature resistance, and insulating properties and is easily flexible.
Flexible metal-clad laminates are mainly used for such thin circuit boards, such as flexible copper clad laminates (FCCLs) that use thin copper plates as metal foils. Polyimides are also sometimes used as protective films, insulating films, etc. for thin circuit boards.

On the other hand, in recent years, as electronic devices have come to incorporate a variety of functions, there is a demand for high calculation speeds and communication speeds in the electronic devices. To meet this demand, thin circuit boards capable of high-speed communication at high frequencies have been developed.
In order to realize high-frequency and high-speed communication, an insulator having high impedance capable of maintaining electrical insulation even at high frequencies is required. Since impedance is inversely proportional to the frequency and dielectric constant (Dk) formed in an insulator, the dielectric constant needs to be as low as possible in order to maintain insulation even at high frequencies.
However, the dielectric properties of ordinary polyimides are not currently excellent enough to maintain sufficient insulation properties for high frequency communications.
In addition, it is known that the lower the dielectric properties of the insulator, the less undesirable stray capacitance and noise can be generated in a thin circuit board, thereby significantly eliminating the causes of communication delays.
Therefore, the low dielectric properties of polyimide are now recognized as the most important factor in the performance of thin circuit boards.
In particular, in high frequency communication, dielectric loss due to polyimide inevitably occurs. The dielectric loss factor (Df) indicates the degree of electrical energy wasted in a thin circuit board and is closely related to the signal transmission delay that determines the communication speed. Therefore, maintaining the dielectric loss factor of polyimide as low as possible is recognized as an important factor in the performance of a thin circuit board.
In addition, the more moisture a polyimide film contains, the larger its dielectric constant becomes, and the higher its dielectric loss factor becomes. Although polyimide film has excellent inherent properties and is suitable as a material for thin circuit boards, it is relatively vulnerable to moisture due to the imide group, which exhibits polarity, and this can cause a deterioration in its insulating properties.
In particular, conventional low dielectric polyimide films have a problem in that their glass transition temperature is low, resulting in poor heat resistance, which makes it difficult to manufacture them in film form.
In order to improve this, if the glass transition temperature of the polyimide film is increased, the dielectric properties are deteriorated (the dielectric loss factor increases). In addition, the high glass transition temperature reduces the thermal expansion coefficient, which makes it difficult to manufacture flexible copper clad laminates.
In some cases, mismatching with the copper foil occurred during the manufacture of the FCC Laminate (FCCL).
Therefore, there is a need to develop a polyimide film that has dielectric properties, particularly a low dielectric loss factor, while maintaining the inherent mechanical and thermal properties of polyimide at a certain level.

Korean Patent Publication No. 10-2015-0069318

In order to solve the above problems, an object of the present invention is to provide a polyimide film having both high dimensional stability and low dielectric properties, and a method for producing the same.
Therefore, a substantial object of the present invention is to provide a specific embodiment thereof.

In one embodiment of the present invention for achieving the above object, a first block obtained by imidizing a dianhydride component including 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and a diamine component including p-phenylenediamine (PPD) is provided;
Provided is a polyimide film comprising a block copolymer including a second block obtained by imidization reaction of a dianhydride acid component including 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a diamine component including m-tolidine.

Based on 100 mol % of the total content of the diamine components of the first block and the second block, the content of m-tolidine may be 15 mol % or more and 45 mol % or less, and the content of paraphenylenediamine may be 55 mol % or more and 85 mol % or less.
In addition, based on 100 mol% of the total content of the dianhydride acid components of the first block and the second block, the content of benzophenone tetracarboxylic dianhydride may be 20 mol% or more and 55 mol% or less, the content of biphenyl tetracarboxylic dianhydride may be 25 mol% or more and 55 mol% or less, and the content of pyromellitic dianhydride may be 15 mol% or more and 30 mol% or less.
The polyimide film may have a dielectric loss factor (Df) of 0.004 or less, a coefficient of thermal expansion (CTE) of 19 ppm/° C. or less, and a glass transition temperature (Tg) of 330° C. or more.

Another embodiment of the present invention is a process for producing a polyamic acid comprising the steps of: (a) polymerizing a first dianhydride acid component and a first diamine component in an organic solvent to produce a first polyamic acid;
(b) polymerizing a second dianhydride acid component and a second diamine component in an organic solvent to produce a second polyamic acid;
(c) copolymerizing the first polyamic acid and the second polyamic acid in an organic solvent to produce a third polyamic acid;
(d) forming a film of the precursor composition containing the third polyamic acid on a support, and then imidizing the film;
the first dianhydride acid component comprises biphenyltetracarboxylic dianhydride (BPDA);
the second dianhydride acid component comprises benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA);
the first diamine component comprises paraphenylenediamine (PPD);
The second diamine component includes m-tolidine.

As described above, the present invention provides a polyimide film that combines thermal dimensional stability and low dielectric properties through a polyimide film composed of specific components and a specific composition ratio and a method for producing the same, and is therefore useful in a variety of fields where such properties are required, particularly electronic components such as flexible metal-clad laminates.

Below, the embodiments of the invention will be described in more detail in the order of the "polyimide film" and "method of manufacturing a polyimide film" according to the present invention.

Before that, the terms and words used in this specification and the claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted in a meaning and concept that is consistent with the technical idea of the present invention, in accordance with the principle that the inventor can appropriately define the concept of the term in order to best describe his/her invention.
Therefore, it should be understood that the configurations of the embodiments described in this specification are merely one of the most preferred embodiments of the present invention and do not represent the entire technical idea of the present invention, and therefore there may be various equivalents and modifications that can be substituted for them at the time of this application.

In this specification, the singular includes the plural unless the context clearly indicates otherwise. In this specification, the terms "comprise", "include", "comprise", "have", and the like are intended to specify the presence of implemented features, numbers, steps, components, or combinations thereof, and should be understood not to preclude the presence or additional possibility of one or more other features, numbers, steps, components, or combinations thereof.

Whenever an amount, concentration, or other value or parameter is recited herein as a range, a preferred range, or an upper preferred value and a lower preferred value, this is to be understood as specifically disclosing all ranges consisting of any pair of any upper range limit or preferred value, and any lower range limit or preferred value, whether or not a range is otherwise disclosed.
Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the invention be limited to the specific values recited when defining a range.

As used herein, "dianhydride acid" is intended to include precursors or derivatives thereof that may not technically be dianhydrides, but which nonetheless would react with a diamine to form a polyamic acid, which may be further converted to a polyimide.

As used herein, "diamine" is intended to include precursors or derivatives thereof that may not technically be diamines, but which nonetheless would react with a dianhydride to form a polyamic acid, which may be further converted to a polyimide.

The polyimide film according to the present invention is
a first block obtained by imidization reaction of a dianhydride component containing biphenyltetracarboxylic dianhydride (BPDA) and a diamine component containing paraphenylenediamine (PPD);
The polyimide film includes a block copolymer including a second block obtained by imidization reaction of a dianhydride component including benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a diamine component including m-tolidine.

Based on 100 mol % of the total content of the diamine components of the first block and the second block, the content of m-tolidine may be 15 mol % or more and 45 mol % or less, and the content of paraphenylenediamine may be 55 mol % or more and 85 mol % or less.
In particular, the content of m-tolidine may preferably be 20 mol % or more and 40 mol % or less, and the content of paraphenylenediamine may preferably be 60 mol % or more and 80 mol % or less.
In particular, m-tolidine has a methyl group that exhibits hydrophobicity, and therefore contributes to the low moisture absorption properties of the polyimide film.

In addition, based on 100 mol% of the total content of the dianhydride acid components of the first block and the second block, the content of benzophenone tetracarboxylic dianhydride may be 20 mol% or more and 55 mol% or less, the content of biphenyl tetracarboxylic dianhydride may be 25 mol% or more and 55 mol% or less, and the content of pyromellitic dianhydride may be 15 mol% or more and 30 mol% or less.
In particular, it is preferable that the content of the benzophenone tetracarboxylic dianhydride is 25 mol% or more and 50 mol% or less, the content of the biphenyl tetracarboxylic dianhydride is 30 mol% or more and 50 mol% or less, and the content of the pyromellitic dianhydride is 20 mol% or more and 27 mol% or less.

The polyimide chain derived from the biphenyltetracarboxylic dianhydride of the present invention has a structure named charge transfer complex (CTC), that is, a regular linear structure in which the electron donor and electron acceptor are located close to each other, and the intermolecular interaction is strengthened.

In addition, benzophenone tetracarboxylic dianhydride, which has a carbonyl group, also contributes to the expression of CTC in the same manner as biphenyl tetracarboxylic dianhydride.
Such a structure has the effect of preventing hydrogen bonding with moisture, which has an effect of lowering the moisture absorption rate, and thus can maximize the effect of lowering the moisture absorption of the polyimide film.

In one embodiment, the dianhydride acid component may further include pyromellitic dianhydride, which is a dianhydride acid component having a relatively strong structure and is preferred in that it can impart appropriate elasticity to the polyimide film.
In order for the polyimide film to have both appropriate elasticity and moisture absorption, the content ratio of the dianhydride is particularly important. For example, the lower the content ratio of biphenyltetracarboxylic dianhydride, the less likely it is that the low moisture absorption rate due to the CTC structure will be achieved.

In addition, biphenyl tetracarboxylic dianhydride and benzophenone tetracarboxylic dianhydride contain two benzene rings that correspond to the aromatic portion, whereas pyromelitic dianhydride contains one benzene ring that corresponds to the aromatic portion.

In the dianhydride acid component, an increase in the content of pyromellitic dianhydride can be understood as an increase in the imide groups in the molecule when the same molecular weight is used as a standard, and this can be understood as a relative increase in the proportion of imide groups derived from the pyromellitic dianhydride in the polyimide polymer chain compared to the imide groups derived from biphenyltetracarboxylic dianhydride and benzophenonetetracarboxylic dianhydride.
That is, an increase in the content of pyromellitic dianhydride is regarded as a relative increase in imide groups in the entire polyimide film, which makes it difficult to expect a low moisture absorption rate.
Conversely, if the content ratio of the pyromellitic dianhydride is decreased, the components having a strong structure will relatively decrease, and there is a risk that the elasticity of the polyimide film will decrease below a desired level.

For this reason, if the content of biphenyltetracarboxylic dianhydride and benzophenonetetracarboxylic dianhydride exceeds the above range or the content of pyromellitic dianhydride is below the above range, the mechanical properties of the polyimide film are deteriorated, and it is not possible to ensure an appropriate level of heat resistance for producing a flexible metal-clad laminate.
Conversely, if the content of the biphenyltetracarboxylic dianhydride and the benzophenonetetracarboxylic dianhydride is below the above range or the content of the pyromellitic dianhydride is above the above range, it is difficult to achieve appropriate levels of dielectric constant, dielectric loss factor, and moisture absorption rate, which is not preferred.

The polyimide film may have a dielectric loss factor (Df) of 0.004 or less, a coefficient of thermal expansion (CTE) of 19 ppm/° C. or less, and a glass transition temperature (Tg) of 330° C. or more.
Preferably, the polyimide film may have a dielectric loss factor (Df) of 0.0036 or less, a coefficient of thermal expansion (CTE) of 13.9 ppm/°C or more and 18.8 ppm/°C or less, and a glass transition temperature (Tg) of 335°C or more and 355°C or less.
The low dielectric loss factor and high glass transition temperature of the polyimide film are ensured by optimizing the content ratio of biphenyltetracarboxylic dianhydride and paraphenylenediamine in the first block of the block copolymer. In particular, the high glass transition temperature improves the heat resistance of the polyimide film, ensuring the film formability.

In addition, by optimizing the content ratio of benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, and m-tolidine in the second block of the block copolymer, the heat resistance and low dielectric properties of the polyimide film are further enhanced.
In particular, since the range of the thermal expansion coefficient of the low dielectric polyimide film coincides with the range of the thermal expansion coefficient of the copper foil, mismatch with the copper foil during the manufacture of the FCCL can be minimized.
In this regard, a polyimide film that satisfies the dielectric loss factor (Df), glass transition temperature, and thermal expansion coefficient can be used as an insulating film for flexible metal-clad laminates, and even when the manufactured flexible metal-clad laminates are used in electrical signal transmission circuits that transmit signals at high frequencies of 10 GHz or more, the insulation stability can be ensured and signal transmission delay can be minimized.
A polyimide film satisfying all of the above conditions is a novel polyimide film that has not been known until now, and the dielectric loss factor (Df) will be described in detail below.

<Dielectric loss factor>
"Dielectric loss factor" refers to the force dissipated by a dielectric (or insulator) when molecular friction impedes molecular motion induced by an alternating electric field.
The dielectric loss factor is usually used as an index that indicates the ease of loss of electric charge (dielectric loss), and the higher the dielectric loss factor, the easier it is for electric charge to be lost, and conversely, the lower the dielectric loss factor, the harder it is for electric charge to be lost. In other words, the dielectric loss factor is a measure of power loss, and the lower the dielectric loss factor, the more the signal transmission delay caused by power loss is alleviated, and the faster the communication speed can be maintained.
This is a strong requirement for a polyimide film, which is an insulating film, and the polyimide film according to the present invention can have a dielectric loss factor of 0.004 or less at a very high frequency of 10 GHz.

In the present invention, the polyamic acid can be produced, for example, by
(1) A method in which the entire amount of the diamine component is placed in a solvent, and then a dianhydride component is added in an amount substantially equimolar to the diamine component to polymerize it;
(2) A method in which the entire amount of the dianhydride component is placed in a solvent, and then a diamine component is added in an amount substantially equimolar to the dianhydride component to polymerize the mixture;
(3) A method in which a part of the diamine component is placed in a solvent, a part of the dianhydride component is mixed in a ratio of about 95 to 105 mol % based on the reaction components, the remaining diamine component is added, and the remaining dianhydride component is added continuously thereto, so that the diamine component and the dianhydride component are polymerized in substantially equimolar amounts;
(4) A method in which a dianhydride component is placed in a solvent, a portion of a diamine compound is mixed in a ratio of 95 to 105 mol % based on the reaction components, and then another dianhydride component is added, followed by the remaining diamine component, so that the diamine component and the dianhydride component are substantially equimolar, thereby polymerizing the mixture;
(5) A method of forming a first composition by reacting a part of the diamine component and a part of the dianhydride acid component in a solvent so that one of them is in an excess amount, and forming a second composition by reacting a part of the diamine component and a part of the dianhydride acid component in another solvent so that one of them is in an excess amount, and then mixing the first and second compositions to complete polymerization, in which, if the diamine component is in excess when the first composition is formed, the dianhydride acid component is in an excess amount in the second composition, and if the dianhydride acid component is in excess in the first composition, the first and second compositions are mixed together to polymerize so that the total amount of diamine components and dianhydride acid components used in these reactions are substantially equimolar.
However, the polymerization method is not limited to the above example, and it goes without saying that any known method may be used to produce the first to third polyamic acids.

In one embodiment, the method for producing a polyimide film according to the present invention includes the steps of:
(a) polymerizing a first dianhydride acid component and a first diamine component in an organic solvent to produce a first polyamic acid;
(b) polymerizing a second dianhydride acid component and a second diamine component in an organic solvent to produce a second polyamic acid;
(c) copolymerizing the first polyamic acid and the second polyamic acid in an organic solvent to produce a third polyamic acid;
(d) forming a film of the precursor composition containing the third polyamic acid on a support, and then imidizing the film;
The first dianhydride acid component is biphenyltetracarboxylic dianhydride (B
PDAs),
the second dianhydride acid component comprises benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA);
the first diamine component comprises paraphenylenediamine (PPD);
The second diamine component may include m-tolidine.
Based on 100 mol % of the total content of the first diamine component and the second diamine component, the content of m-tolidine may be 15 mol % to 45 mol % and the content of paraphenylenediamine may be 55 mol % to 85 mol %.

Also, based on a total content of the first dianhydride and the second dianhydride components of 100 mol%, the content of benzophenone tetracarboxylic dianhydride may be 20 mol% or more and 55 mol% or less, the content of biphenyl tetracarboxylic dianhydride may be 25 mol% or more and 55 mol% or less, and the content of pyromellitic dianhydride may be 15 mol% or more and 30 mol% or less.

In the present invention, the above-mentioned polyamic acid polymerization method can be defined as a random polymerization method, and the polyimide film produced from the polyamic acid of the present invention produced by the above-mentioned steps can be preferably applied in terms of maximizing the effect of the present invention, which is to reduce the dielectric loss factor (Df) and moisture absorption rate.

However, the above-mentioned polymerization method produces a polymer chain with a relatively short repeating unit length, so there may be a limit to the excellent properties of the polyimide chain derived from the dianhydride acid component. Therefore, a method for polymerizing polyamic acid that can be particularly preferably used in the present invention may be a block polymerization method.

On the other hand, the solvent for synthesizing the polyamic acid is not particularly limited, and any solvent that dissolves the polyamic acid can be used, but an amide-based solvent is preferable.
Specifically, the solvent may be an organic polar solvent, and more specifically, may be an aprotic polar solvent, for example, one or more selected from the group consisting of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, N-methyl-pyrrolidone (NMP), gamma-butyrolactone (GBL), and diglyme, but is not limited thereto, and may be used alone or in combination of two or more kinds as necessary.
In one example, the solvent is preferably N,N-dimethylformamide or N,N-dimethylacetamide.

In addition, in the manufacturing process of polyamic acid, a filler may be added to improve various film properties such as sliding properties, thermal conductivity, corona resistance, and loop stiffness. There are no particular limitations on the filler to be added, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica.

The particle size of the filler is not particularly limited and may be determined depending on the film properties to be modified and the type of filler to be added. In general, the average particle size is 0.05 to 100 μm, preferably 0.1 to 75 μm, more preferably 0.1 to 50 μm, and particularly preferably 0.1 to 25 μm.
If the particle size is below this range, the effect of the modification is unlikely to be apparent, whereas if the particle size exceeds this range, the surface properties may be significantly impaired or the mechanical properties may be significantly reduced.

The amount of the filler to be added is not particularly limited, and may be determined depending on the film properties to be modified, the particle size of the filler, etc. In general, the amount of the filler to be added is 0.01 to 100 parts by weight, preferably 0.01 to 90 parts by weight, and more preferably 0.02 to 80 parts by weight, per 100 parts by weight of polyimide.
If the amount of the filler added is less than this range, the effect of the filler modification is unlikely to be observed, and if the amount exceeds this range, the mechanical properties of the film may be significantly impaired. The method of adding the filler is not particularly limited, and any known method may be used.

In the production method of the present invention, the polyimide film can be produced by a thermal imidization method or a chemical imidization method.
It can also be produced by a hybrid imidization method in which thermal imidization and chemical imidization are carried out simultaneously.

The thermal imidization method is a method in which a chemical catalyst is excluded and the imidization reaction is induced by a heat source such as hot air or an infrared drier.
The thermal imidization method can imidize the amic acid groups present in the gel film by heat-treating the gel film at a variable temperature in the range of 100 to 600°C, specifically, by heat-treating the gel film at 200 to 500°C, more specifically, by heat-treating the gel film at 300 to 500°C, the amic acid groups present in the gel film can be imidized.
However, a portion of the amic acid (about 0.1 mol % to 10 mol %) can be imidized during the process of forming the gel film, and therefore the polyamic acid composition can be dried at a variable temperature in the range of 50° C. to 200° C., which can also be included in the category of the thermal imidization method.
The chemical imidization method can produce a polyimide film using a dehydrating agent and an imidization agent by methods known in the art.
As an example of the composite imidization method, a dehydrating agent and an imidization agent are added to a polyamic acid solution, which is then heated at 80 to 200° C., preferably 100 to 180° C., partially cured and dried, and then heated at 200 to 400° C. for 5 to 400 seconds to produce a polyimide film.

The polyimide film of the present invention produced by the above-mentioned production method can have a dielectric loss factor (Df) of 0.004 or less, a coefficient of thermal expansion (CTE) of 19 ppm/°C or less, and a glass transition temperature (Tg) of 330°C or more.

The present invention provides a multilayer film including the above-mentioned polyimide film and a thermoplastic resin layer, and a flexible metal-clad laminate including the above-mentioned polyimide film and an electrically conductive metal foil.

The thermoplastic resin layer may be, for example, a thermoplastic polyimide resin layer.

The metal foil to be used is not particularly limited, but when the flexible metal-clad laminate of the present invention is used for electronic or electrical equipment applications, the metal foil may be, for example, copper or a copper alloy, stainless steel or an alloy thereof, nickel or a nickel alloy (including alloy 42), or aluminum or an aluminum alloy.
In general flexible metal-clad laminates, copper foils such as rolled copper foils and electrolytic copper foils are often used, and can be preferably used in the present invention. In addition, the surface of these metal foils may be coated with an anti-rust layer, a heat-resistant layer, or an adhesive layer.
In the present invention, the thickness of the metal foil is not particularly limited, and may be any thickness that can exhibit sufficient function depending on the application.

The flexible metal-clad laminate according to the present invention may have a structure in which a metal foil is laminated on one side of the polyimide film, or an adhesive layer containing a thermoplastic polyimide is added to one side of the polyimide film, and the metal foil is laminated in a state of adhering to the adhesive layer.
The present invention also provides an electronic component including the flexible metal-clad laminate as an electrical signal transmission circuit, the electrical signal transmission circuit being an electronic component that transmits signals at a high frequency of at least 2 GHz, particularly at a high frequency of at least 5 GHz, and more particularly at a high frequency of at least 10 GHz.
The electronic component may be, for example, but is not limited to, a communication circuit for a mobile terminal, a communication circuit for a computer, or a communication circuit for an aerospace application.

Below, the functions and effects of the invention will be described in more detail using specific examples of the invention. However, these examples are presented only as examples of the invention, and do not determine the scope of the invention's rights.

<Production Example>
DMF was added to a 500 ml reactor equipped with a stirrer and nitrogen inlet/outlet tubes while injecting nitrogen, and the temperature of the reactor was set to 30° C. or less, and then paraphenylenediamine as a diamine component and biphenyltetracarboxylic dianhydride as a dianhydride component were added and confirmed to be completely dissolved. After stirring for 120 minutes while heating to 40° C. under a nitrogen atmosphere, a first polyamic acid having a viscosity of 200,000 cP at 23° C. was produced.
NMP was added to a 500 ml reactor equipped with a stirrer and nitrogen inlet/outlet tubes while injecting nitrogen, and the temperature of the reactor was set to 30° C., and then m-tolidine as a diamine component, and benzophenone tetracarboxylic dianhydride and pyromellitic dianhydride as dianhydride components were added and confirmed to be completely dissolved. After stirring for 120 minutes while heating to 40° C. under a nitrogen atmosphere, a second polyamic acid having a viscosity of 200,000 cP at 23° C. was produced.
Next, the first polyamic acid and the second polyamic acid were heated to 40° C. under a nitrogen atmosphere and stirred for 120 minutes to produce a third polyamic acid having a final viscosity of 200,000 cP at 23° C. and containing a diamine component and a dianhydride component as shown in Table 1 below.
The third polyamic acid prepared above was rotated at a high speed of 1,500 rpm or more to remove bubbles. The defoamed polyimide precursor composition was then applied to a glass substrate using a spin coater. The composition was then dried for 30 minutes at 120° C. under a nitrogen atmosphere to prepare a gel film. The gel film was heated to 450° C. at a rate of 2° C./min, heat-treated at 450° C. for 60 minutes, and cooled to 30° C. at a rate of 2° C./min to obtain a polyimide film.
Then, the polyimide film was peeled off from the glass substrate by dipping in distilled water. The thickness of the polyimide film was 15 μm. The thickness of the polyimide film was measured using an Electric Film Thickness Tester manufactured by Anritsu Corporation.

<Examples 1 to 4 and Comparative Examples 1 to 5>
When the above-mentioned production examples were used, the composition ratios of the dianhydride acid component and the diamine component were adjusted as shown in Table 1 below.
However, in Comparative Example 3, 13 mol % and 15 mol % of benzophenone tetracarboxylic dianhydride were used in producing the first polyamic acid and the second polyamic acid, respectively.

<Experimental Example> Evaluation of Dielectric Loss Factor, Thermal Expansion Coefficient, and Glass Transition Temperature The dielectric loss factor, thermal expansion coefficient, and glass transition temperature of the polyimide films produced in Examples 1 to 4 and Comparative Examples 1 to 5 were measured, and the results are shown in Table 2 below.
(1) Measurement of dielectric loss factor
The dielectric loss factor (Df) was measured using an Agilent 4294A resistance meter by leaving the flexible metal-clad laminate for 72 hours.
(2) Measurement of thermal expansion coefficient
The coefficient of thermal expansion (CTE) was measured using a thermomechanical analyzer from TA.
Using a Thermocouple Analyzer Q400 model, the polyimide film was cut into a width of 4 mm and a length of 20 mm, and then the film was heated from room temperature to 300°C at a rate of 10°C/min while applying a tension of 0.05 N under a nitrogen atmosphere, and then cooled at a rate of 10°C/min while measuring the gradient in the range from 100°C to 200°C.
(3) Measurement of glass transition temperature
The glass transition temperature (T _g ) was measured by determining the loss modulus and storage modulus of each film using DMA, and taking the inflection point in the tangent graph of these as the glass transition temperature.

As shown in Table 2, the polyimide film prepared according to the embodiment of the present invention not only exhibits a significantly low dielectric loss factor of 0.004 or less, but also has a desired level of thermal expansion coefficient and glass transition temperature.
That is, the range of the thermal expansion coefficient is 13.9 to 18.8 ppm/° C., which corresponds to a range of 19 ppm/° C. or less, which also corresponds to the range of the thermal expansion coefficient of copper foil used in FCCLs (about 14 to 19 ppm/° C.), so that it is possible to minimize mismatch between the polyimide film and the copper foil during the manufacture of FCCLs.
Moreover, the glass transition temperature was 330° C. or higher, and it was confirmed that the heat resistance of the polyimide film of the present invention was at an appropriate level.
These results are achieved by the components and composition ratios specified herein, and it is understood that the content of each component plays a decisive role.

In contrast, the polyimide films of Comparative Examples 1 to 5, which have composition ratios different from those of the Examples, are expected to have difficulty being used in electronic components that transmit signals at high frequencies in the gigahertz range in at least one aspect of the dielectric loss factor, thermal expansion coefficient, and glass transition temperature compared to the polyimide films of the Examples.

The present invention has been described above with reference to examples, but anyone with ordinary knowledge in the field to which the present invention pertains can make various applications and modifications within the scope of the present invention based on the above content.

The present invention provides a polyimide film consisting of specific components and in a specific composition ratio, and a method for producing the same, which provides a polyimide film having both thermal dimensional stability and low dielectric properties. The polyimide film can be usefully applied in various fields where such properties are required, particularly to electronic components such as flexible metal-clad laminates.

Claims (5)

a first block obtained by imidization reaction of a dianhydride component containing biphenyltetracarboxylic dianhydride (BPDA) and a diamine component containing paraphenylenediamine (PPD);
The block copolymer includes a second block obtained by imidization reaction of a dianhydride component including benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA) with a diamine component including m-tolidine,
The content of m-tolidine is 15 mol% or more and 45 mol% or less, and the content of p-phenylenediamine is 55 mol% or more and 85 mol% or less, based on 100 mol% of the total content of the diamine components of the first block and the second block;
The content of benzophenone tetracarboxylic dianhydride is 20 mol% or more and 55 mol% or less, the content of biphenyl tetracarboxylic dianhydride is 25 mol% or more and 55 mol% or less, and the content of pyromellitic dianhydride is 15 mol% or more and 30 mol% or less, based on 100 mol% of the total content of dianhydride acid components of the first block and the second block;
The dielectric loss factor (Df) is 0.004 or less, the coefficient of thermal expansion (CTE) is 19 ppm/°C or less, and the glass transition temperature (Tg) is 330°C or more.
Polyimide film. (a) polymerizing a first dianhydride acid component and a first diamine component in an organic solvent to produce a first polyamic acid;
(b) polymerizing a second dianhydride acid component and a second diamine component in an organic solvent to produce a second polyamic acid;
(c) copolymerizing the first polyamic acid and the second polyamic acid in an organic solvent to produce a third polyamic acid;
(d) forming a film of the precursor composition containing the third polyamic acid on a support, and then imidizing the film;
the first dianhydride acid component comprises biphenyltetracarboxylic dianhydride (BPDA);
the second dianhydride acid component comprises benzophenone tetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA);
the first diamine component comprises paraphenylenediamine (PPD);
The second diamine component includes m-tolidine,
The content of m-tolidine is 15 mol% to 45 mol% and the content of p-phenylenediamine is 55 mol% to 85 mol% based on 100 mol% of the total content of the first diamine and the second diamine components,
Based on a total content of the first dianhydride and the second dianhydride components (100 mol%), the content of benzophenone tetracarboxylic dianhydride is 20 mol% to 55 mol%, the content of biphenyl tetracarboxylic dianhydride is 25 mol% to 55 mol%, and the content of pyromellitic dianhydride is 15 mol% to 30 mol%,
The polyimide film has a dielectric loss factor (Df) of 0.004 or less, a coefficient of thermal expansion (CTE) of 19 ppm/°C or less, and a glass transition temperature (Tg) of 330°C or more.
A method for producing a polyimide film. A multilayer film comprising the polyimide film according to claim 1 and a thermoplastic resin layer. A flexible metal-clad laminate comprising the polyimide film of claim 1 and an electrically conductive metal foil. An electronic component comprising the flexible metal-clad laminate of claim 4.