KR20230143380A - Manufacturing method of the polyimide film - Google Patents

Abstract

The present invention includes the steps of applying a varnish containing a polyamic acid solution onto a substrate; fixing at least one of the edges of the varnish with a fixing device; gelling the varnish by drying it while being fixed with the fixing device; and performing imidization by performing heat treatment. Disclosed is a method for producing a polyimide film, including:

Description

Manufacturing method of polyimide film {MANUFACTURING METHOD OF THE POLYIMIDE FILM}

The present invention relates to a method for producing polyimide films.

Polyimide film is a high-performance heat-resistant polymer that has excellent thermal stability, mechanical strength, and chemical resistance. It has a low dielectric constant and is widely used in semiconductor insulating films, electrical insulators, and FPC (Flexible Printed Circuit). Recently, electrical and electronic devices such as computers have been made smaller and lighter, and the wiring boards and IC package materials used therein have also been required to be smaller and lighter, and the wiring patterns applied to them are becoming finer. Therefore, films used as wiring board materials or IC package materials have been required to have high dimensional stability across the entire width direction of the film. Polyimide film is a film that is difficult to melt process. For example, a self-supporting film (“gel film”) obtained by applying and drying a polyimide precursor organic solvent solution such as polyamic acid on a substrate such as a belt or drum. It can be manufactured by continuous heat treatment while conveying.

The gel film refers to a state in which solid properties are higher than liquid properties, and varnish refers to a state in which liquid properties are higher than solid properties. When the gel film is continuously heat treated by the above manufacturing method, entanglement increases. As a result, the gel film shrinks as a difference occurs in the stretching state of the gel film at the end and center of the film.

Representative factors that cause shrinkage of the gel film include drying temperature, solid content of the varnish, catalyst conditions, etc. First, during the manufacturing process of the polyimide film, there is a high probability that shrinkage will occur on the drying belt, and the thicker the polyimide film is manufactured, the higher the temperature is required for smooth drying. In this case, the higher the drying temperature, the more it tends to shrink.

Meanwhile, as the solid content of the varnish increases or the molar number of the imidization catalyst and dehydrating agent increases, the gel film tends to shrink.

In addition, in order to improve the physical properties of the final polyimide film, various conditions must be changed, and as a result, shrinkage of the gel film tends to inevitably occur.

Therefore, there is a need to develop technology to prevent the shrinkage and ensure dimensional stability across the entire width direction of the gel film.

Additionally, graphite sheets have higher thermal conductivity than metal sheets such as copper or aluminum, and are attracting attention as heat dissipation members for electronic devices. In particular, research is being actively conducted on high-thickness graphite sheets, which are advantageous in terms of heat capacity compared to thin graphite sheets (for example, graphite sheets with a thickness of about 40 μm or less).

Graphite sheets can be manufactured in a variety of ways, for example, by carbonizing and graphitizing polymer films. In particular, polyimide films are attracting attention as polymer films for manufacturing graphite sheets due to their excellent mechanical, thermal, dimensional and chemical stability.

In order to manufacture a high-thickness graphite sheet, the manufacture of a high-thickness polyimide film (for example, a polyimide film with a thickness of about 100㎛ or more) must be preceded. The polyimide film is made by applying a polyamic acid solution, drying, and heat-treating. There is a problem in the production of high-flux polyimide film because it is difficult to evenly cure the inside and outside using the normal manufacturing method, resulting in split layers and bubbles. Therefore, there is a demand for high-thickness polyimide films for manufacturing high-quality graphite sheets.

Republic of Korea Patent Publication No. 10-2021-0056150

The purpose of the present invention is to provide a method for manufacturing a polyimide film under various conditions, such as a high-duty polyimide film, by preventing shrinkage of the polyimide film by suppressing entanglement by fixing it with a fixing device in a varnished state.

One embodiment of the present invention for achieving the above object includes applying a varnish containing a polyamic acid solution onto a substrate; fixing at least one of the edges of the varnish with a fixing device; gelling the varnish by drying it while being fixed with the fixing device; and performing imidization by performing heat treatment. It provides a method for producing a polyimide film, including a step.

Another embodiment of the present invention provides a method for producing a polyimide film, wherein the drying and gelation temperature is 180°C or higher, and the heat treatment and imidization temperature is 500°C or more and 600°C or less.

Another embodiment of the present invention provides a method for producing a polyimide film, wherein the varnish has a viscosity of 50,000 cP or more and 300,000 cP or less and the weight average molecular weight of the varnish is 150,000 Mw or more and 300,000 Mw or less.

In another embodiment of the present invention, the solid content of the varnish is 15 to 25% by weight,

A method for manufacturing a polyimide film is provided.

Another embodiment of the present invention provides a method for producing a polyimide film in which the varnish has a thickness of 100 μm or more.

Another embodiment of the present invention provides a method for manufacturing a polyimide film in which a pin is attached to the fixing device.

In another embodiment of the present invention, the polyamic acid solution further includes an imidization catalyst and a dehydrating agent, and the imidization catalyst is included in an amount of 0.3 mole or more and 1 mole or less per 1 mole of amic acid groups of the polyamic acid, Provided is a method for producing a polyimide film, wherein the dehydrating agent is contained in an amount of 2 mol or more and 3 mol or less per 1 mol of amic acid groups of the polyamic acid.

Another embodiment of the present invention provides a method for producing a polyimide film, wherein the shrinkage rate of the polyimide film produced by the above production method is expressed by Equation 1 below.

[Equation 1]

0.00 ≤(L ₀ - L ₁ )/L ₀ ≤ 0.05

In Equation 1, L ₀ is the length in the TD direction of the varnish applied to the substrate, and L ₁ is the length in the TD direction of the gel film gelled by drying the varnish while fixed with the fixing device.

Another embodiment of the present invention provides a method for producing a polyimide film, wherein the polyimide film is used for producing graphite sheets.

According to the present invention, by preventing shrinkage of the polyimide film by suppressing entanglement by fixing it with a fixing device in the varnish state, there is an effect of providing a method for manufacturing polyimide films under various conditions, such as high-temperature polyimide films. have

Figure 1 shows a schematic diagram of an example of a polyimide film manufacturing apparatus used in a polyimide film manufacturing method to which the fixing device of the present invention is applied.
Figure 2 shows each step of the gel film manufacturing method according to an embodiment of the present invention.
Figure 3 shows a gel film prepared according to an example of the present invention.
Figure 4 shows each step of the method for manufacturing a gel film according to a comparative example of the present invention.
Figure 5 shows a gel film prepared according to a comparative example of the present invention.

Below, embodiments of the present invention will be described in more detail.

Prior to this, the terms or words used in this specification and claims should not be construed as limited to their usual or dictionary meanings, and the inventor should appropriately define the concept of terms in order to explain his or her invention in the best way. It must be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle of definability.

Therefore, the configuration of the embodiments described in this specification is only one of the most preferred embodiments of the present invention and does not represent the entire technical idea of the present invention, so various equivalents and modifications that can replace them at the time of filing the present application It should be understood that examples may exist.

In this specification, singular expressions include plural expressions, unless the context clearly dictates otherwise. In this specification, terms such as “comprise,” “comprise,” or “have” are intended to designate the presence of implemented features, numbers, steps, components, or a combination thereof, and are intended to indicate the presence of one or more other features or It should be understood that this does not exclude in advance the possibility of the presence or addition of numbers, steps, components, or combinations thereof.

When amounts, concentrations, or other values or parameters are given herein as ranges, preferred ranges, or enumerations of upper preferred values and lower preferred values, any pair of upper range limits or It is to be understood that the preferred values and any lower range limits or all ranges formed from the preferred values are specifically disclosed.

When a range of numerical values is stated herein, unless otherwise stated, the range is intended to include the endpoints and all integers and fractions within the range. The scope of the invention is not intended to be limited to the specific values recited when defining the scope.

When the positional relationship between two parts is described as 'on top', 'at the top', 'at the bottom', 'next to', etc., unless 'immediately' or 'directly' is used, between the two parts One or more different parts may be located in .

In explaining the drawings, positional relationships such as 'top', 'top', 'bottom', 'bottom', etc. are only described based on the drawings and do not represent absolute positional relationships. In other words, depending on the observation position, the positions of 'top' and 'bottom' or 'top' and 'bottom' may change.

In the present specification, in “a to b” indicating a numerical range, “to” is defined as ≥a and ≤b.

The method for producing a polyimide film according to the present invention includes applying a varnish containing a polyamic acid solution onto a substrate; fixing at least one of the edges of the varnish with a fixing device; gelling the varnish by drying it while being fixed with the fixing device; and performing imidization by performing heat treatment.

For example, if the border of the applied varnish is square, at least one of the edges of the varnish may be at least one side of a square.

In the present invention, the production of the polyamic acid is, for example,

(1) A method of polymerizing the entire amount of diamine monomer in a solvent and then adding dianhydride monomer in substantially equimolar amounts to the diamine monomer,

(2) A method of polymerizing the entire amount of dianhydride monomer in a solvent, and then adding diamine monomer in substantially equimolar amounts to the dianhydride monomer,

After adding some of the diamine monomers into the solvent, mixing some of the dianhydride monomers in a ratio of about 95 to 105 mol% with respect to the reaction components, adding the remaining diamine monomers, and then continuously adding the remaining dianhydride monomers. A method of polymerizing by adding a diamine monomer and a dianhydride monomer so that they are substantially equimolar,

(3) After adding the dianhydride monomer to the solvent, mixing some of the diamine compounds in a ratio of 95 to 105 mol% with respect to the reaction components, adding another dianhydride monomer, and then adding the remaining diamine monomer. Thus, a method of polymerizing the diamine monomer and the dianhydride monomer so that they are substantially equimolar,

(4) In a solvent, some diamine monomers and some dianhydride monomers are reacted so that either one is in excess, to form a first composition, and in another solvent, some diamine monomers and some dianhydride monomers are reacted in an excess amount of either one. A method of forming a second composition by reacting as much as possible, mixing the first and second compositions, and completing polymerization. In this case, when the diamine monomer is excessive when forming the first composition, dianhyde is added to the second composition. When the dianhydride monomer is excessive in the first composition and the dianhydride monomer is excessive in the first composition, the diamine monomer is in excess in the second composition, and the first and second compositions are mixed to mix all diamine monomers and dianhydride used in these reactions. A method of polymerizing the hydride monomers in substantially equimolar amounts may be included.

However, the polymerization method is not limited to the above examples, and of course, any known method can be used to produce polyamic acid.

In the present invention, the dianhydride monomer and diamine monomer used to polymerize the polyamic acid solution may be various monomers commonly used in the field of polyimide film production. For example, the dianhydride monomer may be an aromatic dianhydride monomer, and the diamine monomer may be an aromatic diamine monomer.

The dianhydride monomers include pyromellitic acid dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), and 2,3,3',4'-biphenyl. Tetracarboxylic acid dianhydride, oxydiphthalic acid dianhydride, diphenylsulfone-3,4,3',4'-tetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl)sulfide dianhydride, 2, 2-bis(3,4-dicarboxyphenyl)-1,1,1,3,3,3-hexafluoropropane dianhydride, 2,3,3',4'-benzophenonetetracarboxylic acid dianhydride , 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride Hydride, p-phenylenebis(trimellitate anhydride) (TAHQ), p-phenylenebis(trimellitic acid monoester anhydride), p-biphenylenebis(trimellitic acid monoester anhydride), m-ter Phenyl-3,4,3',4'-tetracarboxylic acid dianhydride, p-terphenyl-3,4,3',4'-tetracarboxylic acid dianhydride, 1,3-bis (3,4-di Carboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride, 1,4-bis(3,4-dicarboxyphenoxy)biphenyl dianhydride, 2,2-bis[(3,4-dicarboxy phenoxy)phenyl]propane dianhydride, 2,3,6,7-naphthalenetetracarboxylic acid dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid dianhydride hydride, 4,4'-(2,2-hexafluoroisopropylidene)diphthalic acid dianhydride, or a combination thereof may be used, but is not limited thereto.

The diamine monomer includes a diamine monomer containing one benzene ring (e.g., 1,4-diaminobenzene (paraphenylene diamine) (PPD), 1,3-diaminobenzene, 2,4-diaminotoluene , 2,6-diaminotoluene, 3,5-diaminobenzoic acid, etc.), diamine monomers containing two benzene rings (e.g., 4,4'-diaminodiphenyl ether, 3,4'-diamino Diaminodiphenyl ethers such as diphenyl ether (oxydianiline, ODA), 4,4'-diaminodiphenylmethane, 3,3'-dimethyl-4,4'-diaminobiphenyl, 2,2' -Dimethyl-4,4'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 3,3'-dimethyl-4,4'-diamino Diphenylmethane, 3,3'-dicarboxy-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, bis(4 -Aminophenyl) sulfide, 4,4'-diaminobenzanilide, 3,3'-dimethylbenzidine, 2,2'-dimethylbenzidine (m-tolidine), 3,3'-dimethoxybenzidine, 2,2 '-dimethoxybenzidine, 3,3'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl sulfide, 3,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfide, 3,3'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 4,4'-dia Minodiphenylsulfone, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diamino-4,4'-dichlorobenzophenone, 3,3'-diamino- 4,4'-dimethoxybenzophenone, 3,3'-diaminodiphenylmethane, 3,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 2,2-bis (3 -aminophenyl)propane, 2,2-bis(4-aminophenyl)propane, 2,2-bis(3-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 2, 2-bis(4-aminophenyl)-1,1,1,3,3,3-hexafluoropropane, 3,3'-diaminodiphenyl sulfoxide, 3,4'-diaminodiphenyl sulfoxide , 4,4'-diaminodiphenyl sulfoxide, etc.), diamine monomers containing three benzene rings (e.g., 1,3-bis (3-aminophenyl) benzene, 1,3-bis (4-amino) Phenyl)benzene, 1,4-bis(3-aminophenyl)benzene, 1,4-bis(4-aminophenyl)benzene, 1,3-bis(4-aminophenoxy)benzene, 1,4-bis( 3-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)-4-trifluoromethylbenzene, 3,3'-diamino-4-(4-phenyl)phenoxybenzophenone, 3 ,3'-diamino-4,4'-di(4-phenylphenoxy)benzophenone, 1,3-bis(3-aminophenyl sulfide)benzene, 1,3-bis(4-aminophenyl sulfide)benzene , 1,4-bis (4-aminophenyl sulfide) benzene, 1,3-bis (3-aminophenyl sulfone) benzene, 1,3-bis (4-aminophenyl sulfone) benzene, 1,4-bis (4) -aminophenylsulfone)benzene, 1,3-bis[2-(4-aminophenyl)isopropyl]benzene, 1,4-bis[2-(3-aminophenyl)isopropyl]benzene, 1,4-bis [2-(4-aminophenyl)isopropyl]benzene, etc.), diamine monomers containing 4 benzene rings (e.g., 3,3'-bis(3-aminophenoxy)biphenyl, 3,3'- Bis(4-aminophenoxy)biphenyl, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, bis[3-(3- Aminophenoxy)phenyl]ether, bis[3-(4-aminophenoxy)phenyl]ether, bis[4-(3-aminophenoxy)phenyl]ether, bis[4-(4-aminophenoxy)phenyl ]Ether, bis[3-(3-aminophenoxy)phenyl]ketone, bis[3-(4-aminophenoxy)phenyl]ketone, bis[4-(3-aminophenoxy)phenyl]ketone, bis[ 4-(4-aminophenoxy)phenyl]ketone, bis[3-(3-aminophenoxy)phenyl]sulfide, bis[3-(4-aminophenoxy)phenyl]sulfide, bis[4-(3- Aminophenoxy)phenyl]sulfide, bis[4-(4-aminophenoxy)phenyl]sulfide, bis[3-(3-aminophenoxy)phenyl]sulfone, bis[3-(4-aminophenoxy)phenyl ]Sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, bis[4-(4-aminophenoxy)phenyl]sulfone, bis[3-(3-aminophenoxy)phenyl]methane, bis[ 3-(4-aminophenoxy)phenyl]methane, bis[4-(3-aminophenoxy)phenyl]methane, bis[4-(4-aminophenoxy)phenyl]methane, 2,2-bis[3 -(3-aminophenoxy)phenyl]propane, 2,2-bis[3-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[3-(3-aminophenoxy)phenyl]-1,1,1,3,3,3-hexa Fluoropropane, 2,2-bis[3-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(3- aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3, 3,3-hexafluoropropane, etc.), or a combination thereof may be used, but is not limited thereto.

Preferably, the diamine monomer is one selected from the group consisting of 3,4'-Oxydianiline (ODA), m-tolidine, and p-Phenylenediamine (PPD). It may include more. The dianhydride monomers include Biphenyltetracarboxylic dianhydride (BPDA), Pyromellitic Diangydride (PMDA), and p-phenylenebis (trimellitate anhydride). anhydride) and TAHQ).

More preferably, the diamine monomer may be oxydianiline (ODA), and the dianhydride monomer may be pyromellitic dianhydride (PMDA).

In the present invention, the polymerization method of the polyamic acid as described above can be defined as any polymerization method, and the polymerization method of the polyamic acid that can be preferably used may be a block polymerization method.

Meanwhile, the solvent for synthesizing the polyamic acid is not particularly limited, and any solvent can be used as long as it dissolves the polyamic acid, but an amide-based solvent is preferable.

Specifically, the solvent may be an organic polar solvent, and in particular, may be an aprotic polar solvent, for example, N,N-dimethylformamide (DMF), N,N- It may be one or more selected from the group consisting of dimethylacetamide, N-methyl-pyrrolidone (NMP), gamma butyrolactone (GBL), and Diglyme, but is not limited thereto, and may be used alone or as necessary. Two or more types can be used in combination.

In one example, N,N-dimethylformamide and N,N-dimethylacetamide may be more preferably used as the solvent.

Additionally, in the polyamic acid manufacturing process, fillers may be added to improve various properties of the film such as sliding properties, thermal conductivity, corona resistance, and loop hardness. The added filler is not particularly limited, 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. Generally, the average particle diameter is 0.05 to 100 μm, preferably 0.1 to 75 μm, more preferably 0.1 to 50 μm, and still more preferably 0.1 to 25 μm.

If the particle size is below this range, it becomes difficult to achieve a reforming effect, and if the particle size is above this range, the surface properties may be greatly damaged or the mechanical properties may be greatly reduced.

Additionally, the amount of filler added is not particularly limited and may be determined based on the film properties to be modified, the particle size of the filler, etc. Generally, the amount of filler 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, based on 100 parts by weight of polyimide.

If the amount of filler added is less than this range, it is difficult to achieve a reforming effect due to the filler, and if it is more than this range, the mechanical properties of the film may be significantly damaged. The method of adding the filler is not particularly limited, and any known method may be used.

Meanwhile, a gel film can be manufactured by applying the varnish on the substrate and drying it.

The substrate may include, but is not limited to, a glass plate, aluminum foil, endless stainless steel belt, and stainless drum.

Also, the method of applying the varnish on the substrate is not particularly limited and may be, for example, a casting method.

According to one embodiment, the temperature at which the varnish is dried and gelled while fixed with the fixing device may be 180° C. or higher, and the drying time may be 15 seconds to 30 minutes.

Additionally, the air volume can be adjusted in the drying and gelation step. Specifically, the air volume can be adjusted by adjusting the rotation of the air supply fan and exhaust fan of the drying device to a speed of 1,000 rpm or more and 2,000 rpm or less depending on the drying state of the gel film.

Additionally, the gelation temperature may be 250°C or lower.

If the temperature is outside the above range, the solvent in the gel film may cause foaming of the gel film, such as the gel film swelling like a balloon or bubbles bursting due to the solvent. Even if the drying time is outside the above drying time, This may cause foaming of the gel film, making it difficult to produce a homogeneous polyimide film.

In some cases, the step of stretching the gel film may be further included to control the thickness and size of the final polyimide film and improve orientation, and stretching may be performed in at least one of MD (machine direction) and TD (transverse direction). It can be done in one direction.

Thereafter, the gel film can be heat treated to produce a polyimide film.

According to one embodiment, the temperature for imidizing the heat treatment may be 500°C or more and 600°C or less, and the heat treatment time may be 30 seconds to 40 minutes.

If the temperature range and heat treatment time are outside the above range, imidization may be affected and a film with a low degree of imidization may be formed or the film may be thermally decomposed.

In particular, if excessive imidization occurs outside the above temperature range and heat treatment time, the Color L* value of the polyimide film may be greatly reduced.

Additionally, if the temperature range and heat treatment time are outside the above range, it may be difficult to manufacture a high-thickness graphite sheet with excellent surface quality and thermal conductivity.

In the production method of the present invention, the polyimide film can be produced by thermal imidization and chemical imidization.

In addition, it may be manufactured by a complex imidization method in which thermal imidization and chemical imidization are combined.

The thermal imidization method is a method of inducing an imidization reaction using a heat source such as hot air or an infrared dryer, excluding chemical catalysts.

The thermal imidization method can imidize the amic acid group present in the gel film by heat treating the gel film at a variable temperature in the range of 100 to 600°C.

In the case of chemical imidization, a polyimide film can be produced using a dehydrating agent and an imidizing agent according to methods known in the art.

As an example of a composite imidization method, a polyimide film can be manufactured by adding a dehydrating agent and an imidizing agent to a polyamic acid solution and then heating it, partially curing and drying the solution, and then further heating it.

When applying the varnish containing a polyamic acid solution on the substrate, according to one embodiment, the viscosity of the varnish may be 50,000 cP or more and 300,000 cP or less.

If the viscosity of the varnish exceeds 300,000 cP, the film production device may be overloaded or it may be difficult to mix with the catalyst, making it difficult to produce a homogeneous polyimide film. Additionally, if the viscosity of the varnish is less than 50,000 cP, the varnish may not be imidized and it may be difficult for the gel film to maintain its shape.

According to one embodiment, the weight average molecular weight (Mw) of the varnish may be 150,000 or more and 300,000 or less.

If the weight average molecular weight of the varnish exceeds 300,000 Mw, it may be difficult to produce a homogeneous film because the film production device may be overloaded or it may be difficult to mix with the catalyst. Additionally, if the weight average molecular weight of the varnish is less than 150,000 Mw, the varnish may not be imidized and it may be difficult for the gel film to maintain its shape.

According to one embodiment, the solid content of the varnish may be 15 to 25% by weight.

If the solid content of the varnish exceeds 25%, it may cause an overload of the film production equipment or it may be difficult to mix with the catalyst, making it difficult to produce a homogeneous film. If the solid content of the varnish is less than 15%, the varnish may not reach imidization and the above It may be difficult for the gel film to maintain its shape.

According to one embodiment, the thickness of the varnish may be 100 μm or more, for example, 150 μm or 200 μm or more, and may be 1,500 μm or less.

According to one embodiment of the fixing device for fixing the varnish, the fixing device may have pins attached, and there is no limit to the number of pins and the shape of the fixing device. Preferably, it may be in the form of a pin sheet, belt or square frame.

According to one embodiment, the pin of the fixing device may have a semicircular cross section at its end. Since the end of the pin is configured in a shape other than a sharp and pointed shape, the disadvantage that occurs when the end of the film is fixed with the fixing device is that the solvent seeping out from the pin hole attached to the fixing device flows into the inside of the film. It can be suppressed. Additionally, the pins of the fixing device may be made of a material that is less strong than the belt being used (eg, a steel belt).

According to one embodiment, the fixing device can fix the varnish by pressing it with a certain pressure.

When applying the fixing device, the number of pins of the fixing device may be 100 or more and 300 or less per 100 g of varnish.

Additionally, per 100g of varnish, the fixing device can fix the varnish with a weight of 100g or more and 500g or less.

Meanwhile, when applying the fixing device, the speed of the endless belt may be 0.5 m/m or more and 3.0 m/m or less.

The fixing device may be fixed or movable.

1 is a schematic diagram of an example of a polyimide film manufacturing apparatus used in the polyimide film manufacturing method according to the present invention by applying the above-described fixing device. Specifically, the varnish is applied on a drying belt and then dried while the varnish is fixed with the fixing device equipped with a pin to produce a gel film. The fixture uses a pin driving line.

Meanwhile, the polyamic acid solution further includes an imidization catalyst and a dehydrating agent, and the imidization catalyst promotes a ring-closure reaction for the polyamic acid. Examples of the imidization catalyst include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. Among them, heterocyclic tertiary amines can be used from the viewpoint of reactivity as a catalyst. Examples of heterocyclic tertiary amines include quinoline, isoquinoline, beta-picoline, and pyridine, and they can be used alone or in a mixture of two or more.

According to one embodiment, the imidization catalyst may be added in an amount of 0.3 to 1 mole per mole of amic acid groups in the polyamic acid. If the content of the imidization catalyst is below the above range, the varnish may not become a gel film, or a long time may be required to become a gel film, which may reduce economic efficiency, and if the content of the imidization catalyst is above the above range, , shrinkage of the gel film may become severe.

The dehydrating agent promotes ring closure reaction through a dehydrating effect on the polyamic acid. Examples of the dehydrating agent include aliphatic acid anhydride, aromatic acid anhydride, N,N'-dialkylcarbodiimide, lower aliphatic halide, halogenated lower aliphatic acid anhydride, arylphosphonic acid dihalide, thionyl halide, etc. These can be used alone or in combination of two or more types. Among them, aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and lactic anhydride can be used from the viewpoint of ease of availability and cost.

According to one embodiment, the dehydrating agent may be added in an amount of 2 to 3 moles per 1 mole of amic acid groups in the polyamic acid. If the content of the dehydrating agent is below the above range, the varnish may not become a gel film, or a long time may be required to become a gel film, which may reduce economic efficiency, and if the content of the dehydrating agent is above the above range, the gel film may Contractions may become more severe.

According to one embodiment, the shrinkage rate of the polyimide film manufactured according to the above manufacturing method can be expressed by Equation 1 below.

[Equation 1]

0.00 ≤(L ₀ - L ₁ )/L ₀ ≤ 0.05

In Equation 1, L ₀ is the length in the TD direction of the varnish applied to the substrate, and L ₁ is the length in the TD direction of the gel film gelled by drying the varnish while fixed with the fixing device.

The polyimide film manufactured by the above-described manufacturing method has excellent surface quality and thermal conductivity, and can be advantageous in implementing a graphite sheet that can secure high thickness.

A graphite sheet formed by carbonizing and graphitizing the polyimide film for producing the graphite sheet is provided. At this time, the thickness of the graphite sheet may be 100 ㎛ or more (for example, 100 ㎛ to 400 ㎛), and as a result, it can have excellent heat capacity and advantageous characteristics for use as a heat dissipation means applied to electronic devices.

The 'carbonization' is a process of thermally decomposing the polymer chain of the polyimide film to form a preliminary graphite sheet containing an amorphous carbon body, an amorphous carbon body, and/or an amorphous carbon body. The carbonization can be performed, for example, by raising the temperature of the polyimide film to a temperature in the range of 1,100°C to 1,300°C over a period of 0.3°C/min to 10°C/min, and in the above range, the surface quality and thermal conductivity are excellent. It may be more advantageous for manufacturing graphite sheets, but is not limited to this. The carbonization may be performed under reduced pressure or in an inert gas atmosphere.

The 'graphitization' is a process of rearranging the carbon of an amorphous carbon body, an amorphous carbon body, and/or an amorphous carbon body to form a graphite sheet. The graphitization may be performed, for example, by raising the temperature of the preliminary graphite sheet to a temperature in the range of 2,500°C to 3,000°C at a rate of 0.3°C/min to 20°C/min, and the graphite sheet having excellent surface quality and thermal conductivity in the above range may be performed. It may also be more advantageous for manufacturing graphite sheets, but is not limited thereto. The graphitization may be performed under reduced pressure or in an inert gas atmosphere, and optionally, pressure may be applied to the preliminary graphite sheet using a hot press or the like during graphitization to achieve high orientation of carbon. The pressure at this time may be, for example, 100 kg/cm ² or more, for example, 200 kg/cm ² or more, and for another example, 300 kg/cm ² or more, but is not limited thereto.

The polyimide film may contain a sublimable inorganic filler. The 'sublimable inorganic filler' may refer to an inorganic filler that is sublimated by heat during the carbonization and/or graphitization process when manufacturing a graphite sheet. When the polyimide film contains a sublimable inorganic filler, voids may be formed in the graphite sheet by gas generated through sublimation of the sublimable inorganic filler during production of the graphite sheet. Therefore, this not only facilitates the exhaustion of the sublimation gas generated during the production of the graphite sheet to obtain a high-quality graphite sheet, but also improves the flexibility of the graphite sheet, ultimately improving the handleability and formability of the graphite sheet. . Examples of sublimable inorganic fillers include, but are not limited to, dicalcium phosphate, barium sulfate, and calcium carbonate. The average particle diameter (D50) of the sublimable inorganic filler may be 1㎛ to 10㎛ (for example, 1㎛ to 5㎛), and it may be advantageous to obtain a high-quality graphite sheet in the above range, but is not limited thereto. The sublimable inorganic filler may be included in an amount of 0.15 to 0.25 parts by weight (for example, 0.2 to 0.25 parts by weight) based on 100 parts by weight of the polyimide film, and a high-quality graphite sheet can be obtained within the above range. It is not limited to this.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are merely presented as examples of the invention, and the scope of the invention is not determined by them.

Example

341.5 g of dimethylformamide as a solvent was added to the reactor and the temperature was set to 20°C. Here, 51.5 g of 4,4'-oxydianiline (ODA) was added, followed by 55.5 g of pyromellitic dianhydride (PMDA). After raising the temperature to 40°C, pyromellitic acid dianhydride (PMDA) was added little by little to prepare a polyamic acid solution.

In the prepared polyamic acid solution, based on the total weight of the catalyst composition, 57.7% by weight of acetic anhydride (AA) as a dehydrating agent, 7.1% by weight of β-picoline (BP) as an imidization catalyst, and diphosphate. A catalyst composition containing 0.1% by weight of calcium (average particle diameter (D50): 2.0 ㎛) and the remaining amount of dimethylformamide was added.

Regarding the characteristics of the varnish, the viscosity was 200,000 cP, the weight average molecular weight was 200,000 Mw, the solid content was adjusted to 15% by weight, and the varnish was manufactured to have a thickness of 500 ㎛.

The prepared varnish was cast to a thickness of 500㎛ on a SUS plate (100SA, Sandvik) using a doctor blade, and dried at 180°C for 4 minutes while fixed with the fixing device to prepare a gel film.

After separating the prepared gel film from the SUS plate, the gel film was heat treated at 500°C for 5 minutes to prepare a polyimide film with a thickness of 100 μm.

Figure 2 shows each step of the gel film manufacturing method according to an embodiment of the present invention.

Figure 3 shows a gel film manufactured according to an example of the present invention, and it was confirmed that no shrinkage occurred when the varnish was fixed with a fixer in the form of a square frame with pins and then dried using an oven.

Comparative example

A polyimide film was manufactured using the same method as in the example, except that the prepared varnish was not fixed with the fixing device.

Figure 4 shows each step of the gel film manufacturing method according to the comparative example of the present invention.

Figure 5 shows a gel film manufactured according to a comparative example of the present invention, and it was confirmed that shrinkage occurred during the drying process using an oven when the varnish was not fixed with the fixing device.

Evaluation example

(1) Viscosity: Using a viscosity measuring device (Rheostress 600, Haake), the polyamic acid solution and precursor composition according to time (unit: seconds) under the conditions of a shear rate of 1/s, temperature of 23°C, and 1mm plate gap. Viscosity (unit: cps) was measured.

(2) Weight average molecular weight (Mw): The weight average molecular weight (unit: g/mol) of polyamic acid converted to polystyrene was determined using molecular weight measuring equipment (Sykam GPC SYSTEM, Laser Chrome).

(3) Shrinkage rate: Apply the varnish to a width of 100 mm and length of 100 mm, dry in an oven at 150°C for 30 minutes to prepare a gel film, and then measure the length of the gel film in the TD direction at room temperature, using Equation 1 below: The shrinkage rate was calculated using The shrinkage rate was reported only to two decimal places.

[Equation 1]

0.00 ≤ (L ₀ - L ₁ )/L ₀ ≤ 0.05

In Equation 1 above,

L ₀ is the length in the TD direction of the varnish applied to the substrate, and L ₁ is the length in the TD direction of the gel film obtained by drying and gelling the varnish while fixed with the fixing device.

Manufacturing example (manufacture of graphite sheet)

The polyimide film prepared according to the example was heated to 1,210°C at a rate of 3.3°C/min under nitrogen gas using an electric furnace capable of carbonization, and maintained at 1,210°C for about 2 hours.

Next, the first calcination step was performed by raising the temperature from 1,210°C to 2,200°C at a temperature increase rate of 2.5°C/min under argon gas using an electric furnace capable of graphitization.

After reaching 2,200°C, the temperature increase rate was changed to 1.25°C/min and the temperature was continuously raised to 2,500°C to perform the second calcination step.

After reaching 2,500℃, the temperature increase rate was changed to 10℃/min and the third firing step was performed by continuously raising the temperature to 2,800℃. After standing at 2,800℃ for several minutes, graphitization was completed and graphite sheets were produced. was manufactured.

Finally, the graphite sheet was cooled at a rate of 10°C/min.

It was found that the graphite sheet manufactured from the polyimide film manufactured using the manufacturing method of the present invention had excellent thermal conductivity.

From the above examples and comparative examples, it was confirmed that shrinkage of the polyimide film could be prevented by fixing it with the fixing device in the varnished state. The shrinkage rate according to the comparative example was so severe that the shrinkage rate expressed by Equation 1 could not be measured, and the shrinkage rate of the gel film according to the example was 0.00.

In addition, it was confirmed that when fixing the varnish with the fixing device, the disadvantage caused by the solvent seeping out from the pin hole attached to the fixing device flowing into the inside of the film could be suppressed.

The embodiments of the manufacturing method of the present invention are only preferred embodiments that enable those skilled in the art in the technical field to which the present invention pertains to easily practice the present invention, and are limited to the above-described embodiments. This does not limit the scope of the present invention. Therefore, the true scope of technical protection of the present invention should be determined by the technical spirit of the attached patent claims. In addition, it will be clear to those skilled in the art that various substitutions, modifications and changes can be made without departing from the technical spirit of the present invention. It is obvious that parts that can be easily changed by a person with ordinary knowledge are also included in the scope of the rights of the present invention.

Claims (9)

Applying a varnish containing a polyamic acid solution onto a substrate;
fixing at least one of the edges of the varnish with a fixing device;
gelling the varnish by drying it while being fixed with the fixing device; and
Comprising: performing imidization by performing heat treatment,
Method for producing polyimide film.
According to paragraph 1,
The drying and gelation temperature is 180°C or higher,
The heat treatment and imidization temperature is 500 ℃ or more and 600 ℃ or less,
Method for producing polyimide film.
According to paragraph 1,
The viscosity of the varnish is 50,000 cP or more and 300,000 cP or less,
The weight average molecular weight of the varnish is 150,000 Mw or more and 300,000 Mw or less,
Method for producing polyimide film.
According to paragraph 1,
The solid content of the varnish is 15 to 25% by weight,
Method for producing polyimide film.
According to paragraph 1,
The thickness of the varnish is 100㎛ or more,
Method for producing polyimide film.
According to paragraph 1,
A pin is attached to the fixture,
Method for producing polyimide film.
According to paragraph 1,
The polyamic acid solution further contains an imidization catalyst and a dehydrating agent,
Per 1 mole of amic acid groups of the polyamic acid, the imidization catalyst is included in an amount of 0.3 mole or more and 1 mole or less,
Per 1 mole of amic acid groups of the polyamic acid, the dehydrating agent is contained in an amount of 2 moles or more and 3 moles or less,
Method for producing polyimide film.
According to any one of claims 1 to 7,
The shrinkage rate of the polyimide film is expressed by equation 1 below,
Method for producing polyimide film.

[Equation 1]
0.00 ≤ (L ₀ - L ₁ )/L ₀ ≤ 0.05
In Equation 1 above,
L ₀ is the length in the TD direction of the varnish applied to the substrate,
L ₁ is the length in the TD direction of the gel film obtained by drying and gelling the varnish while fixed with the fixing device.
According to any one of claims 1 to 7,
The polyimide film is for producing graphite sheets,
Method for producing polyimide film.