JP4538216B2 - A polyimide precursor, a polyimide precursor manufacturing method, a polyimide precursor organic solvent solution manufacturing method, a cast film manufacturing method, and a polyimide film manufacturing method. - Google Patents

Description

  The present invention provides a practically useful polyimide film having a low dielectric constant, a low linear thermal expansion coefficient, a high glass transition temperature, a high transparency, a sufficient toughness and a film forming processability, and a precursor having excellent solution storage stability. It relates to the manufacturing method.

  Generally, polyimide has a high degree of polymerization that can be easily obtained by equimolar reaction of aromatic tetracarboxylic dianhydride such as pyromellitic anhydride and aromatic diamine such as diaminodiphenyl ether in an aprotic polar solvent such as dimethylacetamide. The polyimide precursor is formed into a film and cured by heating.

  Such wholly aromatic polyimides have excellent heat resistance, chemical resistance, radiation resistance, electrical insulation, mechanical properties, etc., so flexible printed circuit boards, tape automation bonding substrates, Currently, it is widely used in various electronic devices such as protective films for semiconductor elements and interlayer insulating films for integrated circuits.

  Recently, increasing the calculation speed of the microprocessor and shortening the rise time of the clock signal have become important issues in the information processing and communication fields. For this purpose, the dielectric of the polyimide film used as the interlayer insulating film is used. It is necessary to lower the rate.

  In order to lower the dielectric constant of polyimide, introduction of a fluorine group into the polyimide structure is effective (for example, see Non-Patent Document 1). The fluorinated polyimide film obtained from 2,2-bis (3,4-carboxyphenyl) hexafluoropropanoic dianhydride and 2,2'-bis (trifluoromethyl) benzidine is estimated from the average refractive index. Further, the dielectric constant is 2.8, which is a very low value (see Non-Patent Document 2, for example).

  In addition, intermolecular conjugation and charge transfer complex formation can be prevented by replacing aromatic units with alicyclic units to reduce π electrons (see Non-Patent Document 3, for example). It is.

  A non-aromatic polyimide film obtained from 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 4,4'-methylenebis (cyclohexylamine) has a dielectric constant estimated from the average refractive index of 2.6. It is also known to show very low values (see, for example, Non-Patent Document 4).

  On the other hand, when a polyimide film is laminated with a metal substrate such as copper as an interlayer insulating film, residual stress is generated due to mismatch of the respective linear thermal expansion coefficients, which may cause serious problems such as curling, film peeling and cracking. Are known.

  In order to avoid this problem, it is necessary to make the linear thermal expansion coefficient of the polyimide film close to that of the metal substrate, that is, to lower the thermal expansion of the polyimide. Most of the currently known polyimides have a linear thermal expansion coefficient of 40 to 90 ppm / K, much higher than the 18 ppm / K for copper substrates. Recently, with the increase in the density of electronic circuits, the necessity of multilayer wiring boards has increased, but the residual stress in the multilayer board significantly reduces device reliability.

  In general, it is known that a low thermal expansion coefficient expression of polyimide is a necessary condition that the main chain structure is linear and the internal rotation is constrained and rigid (see, for example, Non-Patent Document 5). .

Currently, polyimides formed from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and paraphenylenediamine are best known as practical low thermal expansion polyimide materials. This polyimide film is known to exhibit a very low linear thermal expansion coefficient of 5 to 10 ppm / K, although it depends on the film thickness and production conditions (see, for example, Non-Patent Document 6).
However, it is not easy in terms of molecular design to obtain a polyimide having both a low dielectric constant and a low thermal expansion coefficient and having solder heat resistance. Low dielectric constant polymer materials and inorganic materials other than polyimide are also being studied, but at present the required properties are not sufficiently satisfied in terms of dielectric constant, linear thermal expansion coefficient, heat resistance and toughness.

  In general, introduction of a fluorine group into a polyimide structure weakens intermolecular interaction, and tends to hinder spontaneous molecular orientation during imidization, which is a factor of low thermal expansion. It is also disadvantageous in terms of cost. As mentioned above, a typical fluorinated polyimide film obtained from 2,2-bis (3,4-carboxyphenyl) hexafluoropropanoic dianhydride and 2,2′-bis (trifluoromethyl) benzidine is Thus, although the dielectric constant is low, the coefficient of linear thermal expansion is as high as 64 ppm / K and does not show low thermal expansion characteristics (see, for example, Non-Patent Document 2).

  Also, the introduction of the alicyclic structural unit has a problem that the linearity and rigidity of the polyimide main chain skeleton are lowered and the linear thermal expansion coefficient is increased. For example, when a highly flexible alicyclic diamine such as 4,4′-methylenebis (cyclohexylamine) represented by the following chemical formula (3) is used, the polymerization proceeds easily with various acid dianhydrides, and the degree of polymerization is high. Although a polyimide precursor is produced, the polyimide film obtained by the ring closure reaction does not exhibit low thermal expansion characteristics.

  As described above, a polyimide film obtained from 1,2,3,4-cyclobutanetetracarboxylic dianhydride and 4,4′-methylenebis (cyclohexylamine) exhibits a low dielectric constant, but its linear thermal expansion coefficient is 70 ppm / K is very high and does not show low thermal expansion characteristics.

  So far, polyimides using various aliphatic diamines have been reported, but no semi-aliphatic polyimide film showing a linear thermal expansion coefficient lower than 25 ppm / K has been reported so far. This means that a polyimide produced from an alicyclic diamine cannot avoid deterioration of linearity and rigidity of the main chain skeleton.

  The only alicyclic diamine that retains linearity and rigidity is trans-1,4-diaminocyclohexane (see, for example, Patent Document 1).

  However, synthesis of polyimide precursors from highly linear acid dianhydride and trans-1,4-diaminocyclohexane to simultaneously satisfy the desired requirements, i.e., low dielectric constant and low thermal expansion properties, is critical for synthesis. Face a problem.

  That is, unlike the case of known aromatic diamines, salt formation occurs between aliphatic diamines and low molecular weight amic acids generated in the initial stage of the polymerization reaction due to their high basicity.

  If a flexible alicyclic diamine such as 4,4'-methylenebis (cyclohexylamine) is used, the amount of salt formed is so small that it can be dissolved in a polymerization solvent and simply stirred for a long time. The polymerization reaction can be easily advanced by the method.

On the other hand, when trans-1,4-diaminocyclohexane is used, the formed salt is very strong and the solubility in the polymerization solvent is almost zero, and the polymerization reaction is often completely hindered.
In order to satisfy the above required characteristics, alicyclic dianhydrides having a rigid structure are preferred, but the number of alicyclic dianhydrides known so far is limited.

  From the viewpoint of the molecular design described above, 1,2,3,4-cyclobutanetetracarboxylic dianhydride is combined as alicyclic dianhydride, and trans 1,4-diaminocyclohexane is combined as alicyclic diamine. The fully alicyclic polyimide synthesized and represented by the unit structural formula (2) described later is expected to achieve all of the above required characteristics. This system is advantageous in terms of cost because it does not contain fluorine.

  However, in this system, a serious problem is encountered at the stage of producing the polyimide precursor. That is, the polymerization reaction is completely hindered by the formation of a strong salt as described above. This problem is the main reason that there have been no reports of this system so far.

In addition, it is known that a polyimide precursor having a high degree of polymerization can be obtained by heating the polymerization reaction mixture at an appropriate temperature for a short time after salt formation at the initial stage of the polymerization reaction (for example, Patent Document 2 and Non-Patent Document 2). (See Patent Document 7).
However, in the polymerization reaction system of 1,2,3,4-cyclobutanetetracarboxylic dianhydride and trans 1,4-diaminocyclohexane, the salt formed is strong and the salt does not dissolve at any temperature condition. It is difficult to apply.

An interfacial polymerization method is first disclosed as a method for avoiding salt formation when using an aliphatic diamine. (For example, refer nonpatent literature 8.)
For example, 1,2,3,4-cyclobutanetetracarboxylic dianhydride and alcohol are reacted to form a tetracarboxylic acid diester, which is then chlorinated and dissolved in an oil layer, and this is dissolved in an alkaline aqueous solution. A diamine is polymerized at the oil / water interface to obtain an alkyl ester of polyamic acid.

  However, in this polymerization method, the production process is complicated, and it is difficult to obtain a polyimide precursor having a high degree of polymerization, and the variation in molecular weight from batch to batch also increases. Furthermore, interfacial polymerization generates chlorine, which is not preferable for use as an electronic material.

  As a second method, a method using a silylated diamine for polyimide synthesis is known (see, for example, Patent Documents 3 and 4). However, in this method, it is necessary to purify the silylated diamine after silylating the diamine with a halogen-containing silylating agent, and the polyimide precursor to be produced also has two requirements of low dielectric constant and low thermal expansion characteristics. It did not satisfy the characteristics at the same time.

In addition to the aforementioned problems in controlling the characteristics of the polyimide film and the production of the polyimide precursor, some serious problems remain in the film forming process.
One of the problems is the storage stability of the polyimide precursor solution. A general polyimide precursor synthesized from acid dianhydride and diamine by a known method is polyamic acid, but it is known that the weight average molecular weight decreases due to the reverse reaction of the polymerization reaction during storage of the solution. ing. This change in the viscosity of the solution over time is a serious problem in terms of film thickness control during the film forming process such as spin coating.

  In order to stabilize the viscosity of the polyamic acid solution, a method in which the molecular weight is intentionally lowered by storage at a low temperature or by heating the solution to suppress subsequent changes in the viscosity of the solution is employed. In particular, in the latter measure for avoiding the viscosity change, the polyimide film may be fragile.

  In addition, when a linear and rigid polyimide system is selected with the aim of reducing thermal expansion, the main chain skeleton is relatively rigid even in the precursor, and gelation and liquid crystal formation are not uniform during storage of the precursor solution. It often occurs and it may be difficult to produce a good quality polyimide film. In such a case, the addition of a salt such as lithium chloride increases the storage stability, but it is not preferable for use as an electronic material, and the use of a salt should be avoided.

  Further, in such a rigid system, in most cases, a more serious problem occurs in the film forming process. That is, after the polyimide precursor film is cast, the film is cracked during the thermal imidization process. This is because, in a rigid system, the degree of entanglement between polymer chains is low, so the toughness of the film is inherently poor, and the reverse reaction of the polymerization reaction during the thermal imidation of polyamic acid passes particularly around 200 ° C. It occurs somewhat, and the film toughness is further lowered with a decrease in molecular weight, and the film contraction cannot be tolerated during the imidization reaction.

In addition, a method for producing a polyimide precursor by reacting 1,2,3,4-cyclobutanecarboxylic anhydride and 1,4-cyclohexanediamine is known (for example, see Patent Document 5). . However, in general, 1,4-cyclohexanediamine is a mixture of cis type and trans type, and cis type 1,4-cyclohexanediamine increases the thermal expansion coefficient of the polyimide film due to its bent structure.
“Macromolecules” (USA), Aemrican Chemical Society, 1991, No. 24, p5001 “High Performance Polymers” (UK), Institute of Physics, 2003, Volume 15, p47 "Macromolecules" (USA), Aemrican Chemical Society, 1999, 32, p 4933 "Reactive & Functional Polymers", (Netherlands), Elsevier Science, 1996, 30 volumes, p61 “Polymer” (Netherlands), Elsevier Science, 1987, 28, p2282. “Macromolecules” (USA), Aemrican Chemical Society, 1996, 29, p 7897 “High Performance Polymers” (UK), Institute of Physics, 2001, vol. 13, S93 “High Performance Polymers” (UK), Institute of Physics, 1998, 10 volumes, p11 JP 2002-161136 A JP 2002-323766 A JP 2001-72768 A JP-A-64-63070 JP-A-2-294330

  The present invention provides a practically useful polyimide film having a low dielectric constant, a low linear thermal expansion coefficient, a high glass transition temperature, a high transparency, a sufficient toughness and a film forming processability, and a precursor having excellent solution storage stability. A method for producing a body is provided.

  In view of the above problems, the inventors of the present invention have made extensive studies, and as a result, trans 1,4-diaminocyclohexane silylated with a selected silylating agent within an appropriate silylation rate range, and the trans 1, By carrying out a polymerization reaction of 4-diaminocyclohexane and equimolar 1,2,3,4-cyclobutanetetracarboxylic dianhydride in a limited organic solvent, it has excellent storage stability and has a high degree of polymerization. We succeeded in obtaining an alicyclic polyimide precursor solution.

  Furthermore, the present inventors have found that an all-alicyclic polyimide film produced by imidizing the cast film under limited conditions can achieve all of the above required characteristics, and has completed the present invention.

  FIG. 1 is a diagram showing an example of the steric structure of 1,4-diaminocyclohexane, which is a diamine monomer. In order for the polyimide film shown in the unit structural formula (2) to exhibit low thermal expansion characteristics, 1,4-diamino The two amino groups of cyclohexane are both in an equatorial configuration, that is, the steric structure of 1,4-diaminocyclohexane needs to be in the trans form as shown in FIG.

  The trans configuration at the monomer stage is maintained even in the polyimide precursor and the polyimide skeleton. The use of cis-type 1,4-diaminocyclohexane during polymerization may cause a rapid increase in the linear thermal expansion coefficient of the polyimide film due to its bent structure.

  As disclosed in Japanese Patent Publication No. 51-48198, 1,4-diaminocyclohexane obtained by hydrogenating paraphenylenediamine is usually obtained as a cis / trans mixture, but this was directly subjected to polymerization. In this case, the polymerization proceeds without problems even under known reaction conditions.

  Further, when the diamine component is copolymerized with other flexible aliphatic diamine instead of trans 1,4-diaminocyclohexane alone, the polymerization proceeds without problems even under known reaction conditions. However, the use of a mixture such as the above rather than trans 1,4-diaminocyclohexane alone may cause a rapid increase in the linear thermal expansion coefficient of the resulting polyimide film and a decrease in the glass temperature, and should be avoided. .

  FIG. 2 shows an example of the configuration of 1,2,3,4-cyclobutanetetracarboxylic dianhydride, which is an acid dianhydride monomer, and shows 1,2,3,4-cyclobutanetetracarboxylic dianhydride. Is particularly desirable in the anti-type configuration shown in FIG. The use of syn-type 1,2,3,4-cyclobutanetetracarboxylic dianhydride may lead to an increase in linear thermal expansion coefficient due to its bent structure.

  The invention according to claim 1 made on the basis of such knowledge, after reacting trans 1,4-diaminocyclohexane with a silylating agent to produce an intermediate product, said intermediate product and 1,2,3 , 4-cyclobutanetetracarboxylic dianhydride to produce a fully alicyclic polyimide precursor having a repeating structural unit represented by the following unit structural formula (1).

(In the unit structural formula (1), R is H or a silyl group, and the polyimide precursor is a unit structure in which one or both of substituents R in one unit structural formula are silyl groups. At least one)
According to a second aspect of the invention, a process for the preparation of the polyimide precursor according to claim 1, wherein the silylating agent is a process for the preparation of a chlorine atom such had a polyimide precursor in the chemical structure.
According to a third aspect of the invention, there is provided a method for producing a polyimide precursor according to claim 2, N as before carboxymethyl Lil agent, O- bis (trimethylsilyl) trifluoroacetamide and N, O- bis (trimethylsilyl) This is a method for producing a polyimide precursor using one or both of acetamide.
According to a fourth aspect of the invention, R in the unit structural formula (1 ) is H or Si (CH ₃ ) ₃ group, and the trans 1,4-diaminocyclohexane and the silylating agent are reacted at a predetermined ratio. The method for producing a polyimide precursor according to any one of claims 1 to 3, wherein the number of Rs composed of Si (CH ₃ ) ₃ groups among R contained in the entire chemical structure is defined as A. , When the number of Rs consisting of H is B, the silylating agent and the trans 1,4- It is a manufacturing method of the polyimide precursor made to react with diaminocyclohexane.
Silylation rate = A / (A + B) (1)
In the invention according to claim 5, after trans 1,4-diaminocyclohexane and a silylating agent are reacted in a polymerization solvent to produce an intermediate product, 1,2,3,4- Cyclobutanetetracarboxylic dianhydride is added, the intermediate product is reacted with the 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the polyimide precursor is dispersed or dissolved in the polymerization solvent. It is a manufacturing method of the polyimide precursor organic solvent solution which manufactures the made polyimide precursor organic solvent solution.
The invention according to claim 6 is the production of a polyimide film in which the polyimide precursor organic solvent solution according to claim 5 is applied to a coating object to form a cast film, and then the polyimide precursor in the cast film is imidized. The polymerization solvent includes the trans 1,4-diaminocyclohexane, the silylating agent, the 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the intermediate product. A high-boiling solvent having a high affinity and having a high affinity with the polymerization solvent and having a boiling point lower than that of the polymerization solvent in contact with the cast film, washing the cast film, and then imidizing This is a method for manufacturing a polyimide film.
A seventh aspect of the invention is a method for manufacturing a polyimide film according to the sixth aspect, wherein hexamethylphosphoramide is used as the high boiling point solvent and alcohol is used as the cleaning liquid.
Invention of Claim 8 is manufactured by the manufacturing method of the polyimide precursor of any one of Claim 1 thru | or 3, A repeating structural unit is represented by the said unit structural formula (1), The said unit structure The substituent R in the formula (1) is a fully alicyclic polyimide precursor which is H or Si (CH ₃ ) ₃ group, and one or both of the substituents R in one unit structural formula Measured at 30 ° C. using a mixed solvent of hexamethylphosphoramide and N, N-dimethylacetamide in a volume ratio of 3: 1 having at least one unit structure in which is a Si (CH ₃ ) ₃ group . Is a polyimide precursor having an intrinsic viscosity of 1.0 dl / g or more.
The invention according to claim 9 is the polyimide precursor according to claim 8, wherein the steric structure of each 1,4-cyclohexane residue in the unit structural formula (1) is in a trans configuration. It is a polyimide precursor.
The invention according to claim 10 is the polyimide precursor according to any one of claim 8 or claim 9, wherein the total number of substituents R consisting of Si (CH ₃ ) ₃ groups in the entire chemical structure is calculated. When the total number of substituents R composed of A and hydrogen is B, the silylation rate of the polyimide precursor represented by the following formula (1) is a polyimide precursor in the range of 0.4 to 0.9. .
Silylation rate = A / (A + B) (1)
The invention according to claim 11 is represented by the following unit structural formula (2) in which the repeating structural unit is formed from trans 1,4-diaminocyclohexane and 1,2,3,4-cyclobutanetetracarboxylic dianhydride. The polyimide is characterized in that the steric structure of each 1,4-cyclohexane residue in the following unit structural formula (2) is in a trans configuration.

  A twelfth aspect of the present invention is a polyimide film mainly comprising the polyimide according to the eleventh aspect.

In the present invention, the silylation rate of the polyimide precursor is not determined from the number of Si (CH ₃ ) ₃ groups and hydrogen contained only in one structural unit, but is included in the entire polyimide precursor molecule. It is obtained from the number of substituents R consisting of (CH ₃ ) ₃ groups and the number of substituents R consisting of hydrogen.

  According to the present invention, a polyimide film having both a low dielectric constant, a low linear thermal expansion coefficient, a high glass transition temperature, a high transparency, a sufficient toughness, and a film forming processability can be produced. Moreover, according to the production method of the present invention, a polyimide precursor having high dispersibility in a polymerization solvent is obtained, and an organic solvent solution of such a polyimide precursor is excellent in solution storage stability.

The present invention is described in detail below.
As described above, in the polymerization system of 1,2,3,4-cyclobutanetetracarboxylic dianhydride and trans 1,4-diaminocyclohexane, a strong salt is formed at the initial stage of the reaction, and it depends on the solvent and temperature conditions. It is difficult to allow the polymerization to proceed. Therefore, the use of a silylation method to avoid salt formation has led to the solution of problems relating to the production of polyimide precursors.

  First, trans 1,4-diaminocyclohexane is dissolved in a polymerization solvent, and an appropriate amount of N, O-bis (trimethylsilyl) trifluoroacetamide or N, O-bis (trimethylsilyl) acetamide is added dropwise thereto for silylation. After that, without isolating the silylated diamine, equimolar 1,2,3,4-cyclobutanetetracarboxylic dianhydride powder was gradually added to the solution as it was, and stirred at room temperature for several hours. A homogeneous solution is obtained.

  Trans 1,4-diaminocyclohexane is preferably used after silylation or recrystallization with n-hexane before the reaction with carboxylic dianhydride to completely remove the coloring component. Otherwise, the resulting polyimide film may be colored.

  As a generally known silylation method, there is a method disclosed in the 49th Polymer Symposium Proceedings, p. 1917 (2000). In this silylation method, a representative trimethylsilyl chloride is used as a silylating agent. It is used in the presence of a hydrogen chloride acceptor such as triethylamine, and after silylation of an aliphatic diamine, it is isolated and purified by distillation and subjected to a polymerization reaction with an acid dianhydride.

  Here, hydrogen chloride generated by the reaction of trimethylsilyl chloride and an aliphatic diamine partially adds to not only triethylamine as an acceptor but also an aliphatic diamine as a polymerization reaction component to form a hydrochloride. Since aliphatic diamine hydrochloride loses polymerization reactivity and precipitates due to a decrease in solubility, it is not possible to polymerize by adding acid dianhydride to this reaction solution without isolating silylated diamine. It is impossible because the molar balance is broken.

  This is why a silylated diamine isolation / purification step is generally required. In addition, silylated diamine easily decomposes by reacting with a slight amount of moisture in the air, and in some cases, equipment such as a glove box is required, which complicates the isolation / generation process.

  However, the production process of the polyimide precursor in the present invention does not include any such isolation / purification process of silylated diamine. When a non-halogenated silylating agent having no halogen atom in the chemical structure is used as the silylating agent, hydrogen halide such as hydrogen chloride is not generated as a by-product when the alicyclic diamine is silylated.

  For example, when one or both of N, O-bis (trimethylsilyl) trifluoroacetamide and N, O-bis (trimethylsilyl) acetamide is used as the non-halogenated silylating agent, the alicyclic diamine reacts with the silylating agent. After the silylation, only acetamides that are harmless to the polymerization reaction are generated as by-products, and hydrogen chloride is not generated as a by-product. Therefore, acid dianhydride is continuously added thereto. This is because the molar balance is maintained. In addition, since the acetamide as a by-product produces a polyimide precursor and volatilizes this polyimide precursor with a solvent at the time of a thermal imidation reaction, there is no problem at all.

  Further, since hydrogen chloride is not generated when the alicyclic diamine is silylated, in the present invention, it is not necessary to use a neutralizing agent such as a tertiary amine. Therefore, no salts remain in the formed polyimide film.

  In the all-alicyclic polyimide precursor system represented by the unit structural formula (1), the key to the success of the polymerization reaction is the control of the silylation rate X. The silylation rate x of the alicyclic diamine and the silylation rate X of the polyimide precursor can be controlled by adjusting the addition amount of the silylating agent.

When the alicyclic diamine and the silylating agent are reacted, the hydrogen of the amino group of the alicyclic diamine is replaced with a silyl group (Si (CH ₃ ) ₃ group). Of the amino groups of all intermediate products generated in the polymerization solvent, a is the number of amino groups substituted with silyl groups, and b is the number of amino groups not substituted with silyl groups. The conversion rate x (average silylation rate of all intermediate products) is represented by the following mathematical formula (2).

x = a / (a + b) (2)
Since one alicyclic diamine reacts with one carboxylic dianhydride to form one structural unit, an intermediate product and an equimolar amount or more of carboxylic dianhydride are added to the polymerization solvent, When all of the intermediate product is reacted with carboxylic dianhydride, the silylation rate X of the polyimide precursor produced in the polymerization solvent becomes equal to the silylation rate x of the intermediate product.

  The silylation rate of the intermediate product can be adjusted by the amount of alicyclic diamine and silylating agent added to the polymerization solvent. Since the alicyclic diamine has two amino groups in the chemical structure, assuming that the silylating agent has s silyl groups per mole, the silylation rate X is determined using c moles of the alicyclic diamine. In order to obtain an intermediate product and a polyimide precursor, 2c · X / s mol of silylating agent may be reacted with an alicyclic diamine.

  For example, as a silylating agent, one having two silyl groups in one molecule such as N, O-bis (trimethylsilyl) trifluoroacetamide or N, O-bis (trimethylsilyl) acetamide is used as an intermediate product and polyimide. In order to set the silylation rate of the precursor to 0.4 to 0.9, these silylating agents may be added to 0.4 cmol or more and 0.9 cmol or less.

  The silylation rate X of the intermediate product is preferably in the range of 0.4 to 0.9, and if the silylation rate is within this range, the intermediate product is reacted with the carboxylic dianhydride to be transparent and viscous. A uniform polymerization solution can be obtained.

  When X is less than 0.4, salt formation occurs during polymerization with carboxylic dianhydride, and polymerization does not proceed. If X exceeds 0.9, a uniform polymerization solution cannot be obtained, and it is difficult to obtain a polyimide precursor having a high degree of polymerization. This is because when the silylation rate is very high, due to hydrogen bonding between the polyimide precursor chains, the solubility of the polyimide precursor in the polymerization solvent is extremely reduced, and the polyimide precursor partially precipitates before the polymerization reaction proceeds sufficiently It is because it will do.

  When X is in the range of 0.4 or more and 0.9 or less, the polyimide precursor appropriately retains a carboxy group, which strongly solvates with the polymerization solvent, resulting in an increase in the solubility of the resulting polymer. Until now, silylation was generally considered to dramatically increase the solubility of the polyimide precursor. However, in the present invention, it is rather related to polymerization by controlling the silylation rate of the polyimide precursor to 0.4 to 0.9. The problem was solved.

  In the present invention, selection of a polymerization solvent is extremely important. As the polymerization solvent, hexamethylphosphoramide alone, a mixed solvent of hexamethylphosphoramide and N, N-dimethylacetamide, or a mixed solvent of hexamethylphosphoramide and N-methyl-2-pyrrolidone is preferable. If the polymerization solvent is not appropriate, the polymerization may not proceed at all due to salt formation during polymerization of the alicyclic diamine and tetracarboxylic dianhydride, or the intermediate product and tetracarboxylic dianhydride, or a partial polymerization reaction may occur. Even if it occurs, there is a possibility that a uniform polymerization solution cannot be obtained due to precipitation, gelation, etc., and film formation cannot be performed.

  Polymer dissolution accelerators, that is, metal salts such as lithium bromide and lithium chloride, which are often added during polymerization of polyamide or the like, do not need to be used in the polymerization system according to the present invention. These metal salts should not be used because if the metal ions remain in the polyimide film even in a trace amount, the reliability as an electronic device is remarkably lowered.

  The polymerization does not proceed as described above when the silylation rate X represented by the above formula (1) is outside the range of 0.4 or more and 0.9 or less. However, the effect of promoting the dissolution of the above salts is hardly observed, and the addition of the salts is not observed. Only the polymerization reactivity cannot be improved.

  In the obtained polyimide film, additives such as an antioxidant, a filler, a silane coupling agent, a photosensitizer, a photopolymerization initiator, and a sensitizer may be mixed as necessary.

  The polyimide precursor solution applied onto the substrate that is the object to be applied is dried in a forced circulation hot air dryer or a vacuum dryer in the range of 40 ° C. to 120 ° C. to form a coating film (cast film).

  At this time, if it is less than 40 ° C., it takes a long time to dry, a large amount of solvent remains in the film, and bubbles are likely to be generated due to rapid evaporation of the solvent during imidation, which is not preferable for obtaining a good quality polyimide film. . Also, drying at a high temperature exceeding 120 ° C. tends to make the cast film brittle, which is not preferable for obtaining a tough polyimide film.

  In the known method, the polyimide film is produced by imidizing the polyimide precursor in the cast film by heating the cast film on the substrate as it is to a temperature of 200 ° C. or more and 400 ° C. or less. The unit structure according to the present invention When the polyimide precursor cast film represented by formula (1) is thermally imidized according to a known method, the film is severely torn and blackened in a nitrogen atmosphere or in a vacuum, making it difficult to produce a polyimide film. become. This is because the hexamethylphosphoramide used as a solvent is very difficult to volatilize, so it tends to stay in the film during imidization, causing thermal decomposition of the hexamethylphosphoramide itself and some reaction with the polyimide precursor. it is conceivable that.

  By immersing the cast film of the polyimide precursor in water, it is possible to almost completely extract and remove the water-soluble residual solvent such as hexamethylphosphoramide. However, immersion in water causes a decrease in the adhesion between the substrate and the film, causing not only peeling but also severe contraction of the film. This large film shrinkage induces cracking of the polyimide film during imidization, making it difficult to form the polyimide film on the substrate.

  As a result of diligent research, when the cast film is immersed in a cleaning liquid composed of alcohols such as methanol, and the cleaning liquid is brought into contact with the cast film for cleaning, film shrinkage and peeling from the substrate are suppressed, and at the same time hexamethyl It was found that residual solvents such as phosphoramide can be extracted and removed almost completely, and the problem in film formation was solved.

  The alcohol constituting the cleaning liquid is not limited to methanol, and ethanol, butanol, propanol or the like can also be used. Moreover, these alcohols may be used independently and may be used in mixture of 2 or more types.

  The polyimide precursor film (cast film) formed on the substrate in this way is at a temperature of 200 ° C. or higher and 400 ° C. or lower, preferably 300 ° C. or higher and 350 ° C. or lower, under reduced pressure (under a pressure lower than atmospheric pressure). A tough polyimide film can be obtained by heat treatment.

  If the temperature at which the cast film is heated is less than 300 ° C., imidation may not be completed, and if it exceeds 350 ° C., the polyimide film will be colored. The process of imidizing the polyimide precursor in the cast film is not limited to heat treatment, and the imidation reaction is performed by reacting the polyimide precursor film with a dehydrating reagent such as a mixture of acetic anhydride and tertiary amine. Can also be done.

  Since the polyimide according to the present invention has a wholly alicyclic structure, it is inferior in long-term thermal stability compared to wholly aromatic polyimides that do not contain any alicyclic structure, but both the glass transition temperature and the thermal decomposition temperature in nitrogen are 400. It is higher than ℃, and short-term heat resistance such as solder heat resistance is sufficiently high, and there is no problem in application to the industrial field.

  The polyimide of the present invention represented by the unit structural formula (2) not only has a low dielectric constant of 2.7 or less at 1 MHz, but also has a low coefficient of linear thermal expansion of 25 ppm or less, and high transparency and toughness. Have both.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

<Example 1>
Put recrystallized and purified trans-1,4-diaminocyclohexane (5.710 g, 0.05 mol) in a well-dried sealed reaction vessel equipped with a stirrer and thoroughly dehydrated hexamethylphosphoramide and N, N-dimethylacetamide. After dissolving in 150 mL of a polymerization solvent composed of a mixed solvent (volume ratio 3: 1), 7.0 mL (0.025 mol) of N, O-bis (trimethylsilyl) trifluoroacetamide was slowly added dropwise as a silylating agent with a syringe at room temperature. The mixture was stirred for 1 hour to effect silylation (silylation rate X = 0.5).

  To this solution, 9.806 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride powder was gradually added and stirred at room temperature for 24 hours. The obtained polyimide precursor solution showed very high solution storage stability with no precipitation or gelation even when left for 2 weeks at room temperature and almost no change in viscosity. Intrinsic viscosity measured at 30 ° C. in the same solvent as at the time of polymerization was as high as 4.3 dL / g, indicating that an extremely high polymer polyimide precursor was obtained.

A polyimide precursor film (cast film) obtained by applying this polyimide precursor solution to a glass substrate that is a coating object and drying at 60 ° C. for 2 to 4 hours is immersed in methanol as a cleaning solution for 4 to 24 hours. The residual solvent was completely removed.
This was imidized by heating on a substrate under reduced pressure at 340 ° C. for 3 hours to obtain a transparent and tough fully alicyclic polyimide film having a thickness of 10 μm.

The film properties are as follows: dielectric constant = 1.1 × dielectric constant 2.65 estimated from the square of the average refractive index (corresponding to 1 MHz), linear thermal expansion coefficient 25 ppm / K (average value between 100 ° C. and 200 ° C.), and Glass transition temperature is 423 ° C, cutoff wavelength is 240nm, 5% weight loss temperature in nitrogen atmosphere (temperature increase rate 10 ° C / min) is 437 ° C, and 398 ° C in air. I was able to. Infrared absorption spectra of the synthesized polyimide precursor film and polyimide film are shown in FIG. 3 and FIG. 4, respectively. Peak tables of the polyimide precursor film and polyimide film are shown in Tables 1 and 2 below.
3 and 4, the vertical axis represents the transmittance (%), and the horizontal axis represents the wave number (cm ⁻¹ ).

In Tables 1 and 2, the unit of wave number is cm ⁻¹ and the unit of transmittance is%.
<Comparative Example 1>
Put recrystallized / purified trans-1,4-diaminocyclohexane (5.710 g, 0.05 mol) in a well-dried closed reaction vessel with a stirrer, and dissolve in 150 mL of a fully dehydrated polymerization solvent consisting of N, N-dimethylacetamide. did. Without performing silylation of diamine, 9.806 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride powder was gradually added and stirred at room temperature. However, a strong salt was formed at the initial stage of polymerization, and polymerization did not proceed at all even when stirring was continued for several weeks to one month at room temperature.

  In addition to N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, dimethyl sulfoxide, γ-butyrolactone, diglyme, m -Polymerization using cresol, hexamethylphosphoramide, hexamethylphosphoramide / N, N-dimethylacetamide mixed solvent, hexamethylphosphoramide / N-methyl-2-pyrrolidone mixed solvent, tetrahydrofuran / methanol mixed solvent Attempts did not proceed at all in any solvent system.

  In these solvent systems, a polymerization reaction was attempted in a solute concentration range of 1 to 15% by weight and a temperature range of room temperature to 150 ° C., but no polymerization was performed in the same manner. Further, tertiary amines such as pyridine and triethylamine, or inorganic salts such as lithium chloride were used, but these addition effects were not seen at all and polymerization did not proceed at all.

(Example 2)
Put recrystallized and purified trans-1,4-diaminocyclohexane (5.710 g, 0.05 mol) in a well-dried sealed reaction vessel equipped with a stirrer and thoroughly dehydrated hexamethylphosphoramide and N, N-dimethylacetamide. After dissolving in 150 mL of a polymerization solvent consisting of a mixed solvent (volume ratio 3: 1), 14.1 mL (0.05 mol) of a silylating agent consisting of N, O-bis (trimethylsilyl) trifluoroacetamide was slowly added dropwise with a syringe. The mixture was stirred at room temperature for 1 hour for silylation (silylation rate X = 1.0).

  To this solution, 9.806 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride powder was gradually added and stirred at room temperature. In this method, a polyimide precursor organic solvent solution was obtained, but a part of the polyimide precursor was precipitated in the solution, and a uniform solution was not obtained even if stirring was continued for several weeks. This is because all of the carboxy groups in the polyimide precursor are silylated, so that it is difficult to solvate and partially precipitates during polymerization due to hydrogen bonding between polymer chains. When the silylation rate X was lower than 0.4, a strong salt was formed at the initial stage of polymerization, and the polymerization did not proceed.

<Example 3>
Put recrystallized / purified trans-1,4-diaminocyclohexane (5.710 g, 0.05 mol) in a well-dried closed reaction vessel with a stirrer, and dissolve in 150 mL of a fully dehydrated polymerization solvent consisting of N, N-dimethylacetamide. Then, 7.0 mL (0.025 mol) of a silylating agent consisting of N, O-bis (trimethylsilyl) trifluoroacetamide was slowly added dropwise with a syringe, and the mixture was stirred at room temperature for 1 hour for silylation (silylation rate X = 0.5). )

  To this solution, 9.806 g (0.05 mol) of 1,2,3,4-cyclobutanetetracarboxylic dianhydride powder was gradually added and stirred at room temperature. In this method, a polyimide precursor organic solvent solution was obtained, but a part of the polyimide precursor in the solution was precipitated, and a viscous and uniform solution was not obtained even if stirring was continued for one month. . This is because the partially silylated polyimide precursor has poor solubility in N, N-dimethylacetamide and partially precipitates during polymerization. When hexamethylphosphoramide was not included as a polymerization solvent, a viscous and uniform solution was not obtained at any silylation rate regardless of the addition of lithium chloride.

<Example 4>
The polyimide precursor solution polymerized in Example 1 was applied to a glass substrate and dried at 60 ° C. for 2 hours to obtain a polyimide precursor film. Without undergoing the step of removing the residual solvent, this was thermally imidized on a substrate under reduced pressure at 340 ° C. for 3 hours to obtain a polyimide film.

  However, the obtained polyimide film was partially blackened, and the film was partially broken. This is because the hexamethylphosphoramide used as a solvent is very difficult to volatilize, so it tends to stay in the film during imidization, causing thermal decomposition of the hexamethylphosphoramide itself and some reaction with the polyimide precursor. it is conceivable that.

(Comparative Example 2)
A well-dried sealed reaction vessel with a stirrer is charged with 10.518 g (0.05 mol) of an alicyclic amine consisting of 4,4'-methylenebis (cyclohexylamine), and 200 mL of a fully dehydrated polymerization solvent consisting of N, N-dimethylacetamide Then, 9.806 g (0.05 mol) of carboxylic acid dianhydride powder consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride was gradually added and stirred at room temperature for 24 hours. In this system, polymerization proceeded easily by a known method without silylation of alicyclic diamine.

  The polyimide film obtained by thermal imidization at 300 ° C. for 1 hour under reduced pressure on the substrate showed a low dielectric constant of 2.6, which was estimated from dielectric constant = 1.1 × average refractive index squared. However, the coefficient of linear thermal expansion was 70 ppm / K and did not show low thermal expansion characteristics. This is because the in-plane orientation during thermal imidization was inhibited by the bent structure of the alicyclic diamine used.

(Comparative Example 3)
Polymerization consisting of N, N-dimethylacetamide fully dehydrated by placing 5.710 g (0.05 mol) of an alicyclic amine consisting of 1,4-diaminocyclohexane (trans / cis mixture) in a well-dried closed reaction vessel with a stirrer After dissolving in 150 mL of solvent, 9.806 g (0.05 mol) of carboxylic dianhydride powder consisting of 1,2,3,4-cyclobutanetetracarboxylic dianhydride was gradually added and stirred at room temperature for 24 hours. In this system, polymerization proceeded easily by a known method without silylation of alicyclic diamine. The polyimide film obtained by thermal imidization at 340 ° C. for 1 hour under reduced pressure on a substrate was fragile, but the dielectric constant estimated from the square of dielectric constant = 1.1 × average refractive index was as low as 2.6. The dielectric constant is shown. However, the coefficient of linear thermal expansion was 60ppm / K, showing no low thermal expansion characteristics. This is because the alicyclic diamine used contained a cis 1,4-diaminocyclohexane with a bent structure, which inhibited the spontaneous in-plane orientation during thermal imidization.

(Comparative Example 4)
A well-dried sealed reaction vessel with a stirrer was charged with 5.407 g (0.05 mol) of aromatic diamine composed of paraphenylenediamine, dissolved in 200 mL of a fully dehydrated polymerization solvent composed of N, N-dimethylacetamide, and 3,3 14.711 g (0.05 mol) of carboxylic acid dianhydride powder consisting of ', 4,4'-biphenyltetracarboxylic dianhydride was gradually added and stirred at room temperature for 3 hours. In this system, polymerization proceeded easily by a known method without silylation of diamine. The polyimide film obtained by thermal imidization at 350 ° C for 1 hour under reduced pressure on the substrate showed a low thermal expansion characteristic of 6.0 ppm / K, but the dielectric constant = 1.1 × average refractive index. The dielectric constant estimated from the square of 3.5 was not as low as 3.5. This is due to the use of aromatic monomers.

Diagram showing the three-dimensional structure of 1,4-diaminocyclohexane Diagram showing the molecular structure of 4,4'-methylenebis (cyclohexylamine) The figure which shows the infrared absorption spectrum of the polyimide precursor film | membrane of an example of this invention The figure which shows the infrared absorption spectrum of the polyimide film of an example of this invention

Claims (12)

Trans 1,4-diaminocyclohexane and a silylating agent are reacted to form an intermediate product, and then the intermediate product is reacted with 1,2,3,4-cyclobutanetetracarboxylic dianhydride. The manufacturing method of the polyimide precursor which manufactures the all alicyclic polyimide precursor whose repeating structural unit is represented by the following unit structural formula (1).

(In the unit structural formula (1), R is H or a silyl group, and the polyimide precursor is a unit structure in which one or both of substituents R in one unit structural formula are silyl groups. At least one) The silylating agent, the production method of the polyimide precursor have claim 1, wherein a has a chlorine atom in its chemical structure. N As before carboxymethyl Lil agent, O- bis (trimethylsilyl) trifluoroacetamide and N, O- bis (trimethylsilyl) any method for producing a polyimide precursor according to claim 2, wherein the use of one or both acetamide. The R in the unit structural formula (1 ) is H or Si (CH ₃ ) ₃ group, and the trans 1,4-diaminocyclohexane and the silylating agent are reacted at a predetermined ratio. A method for producing a polyimide precursor according to any one of
Of the R contained in the entire chemical structure, if the number of Rs consisting of Si (CH ₃ ) ₃ groups is A and the number of Rs consisting of H is B, the silylation rate represented by the following formula (1) is A method for producing a polyimide precursor, wherein the silylating agent and the trans 1,4-diaminocyclohexane are reacted at a ratio of 0.4 to 0.9.
Silylation rate = A / (A + B) (1)   Trans 1,4-diaminocyclohexane and a silylating agent are reacted in a polymerization solvent to form an intermediate product, and then 1,2,3,4-cyclobutanetetracarboxylic dianhydride is added to the polymerization solvent. Added, the intermediate product and the 1,2,3,4-cyclobutanetetracarboxylic dianhydride are reacted, and a polyimide precursor organic solvent solution in which a polyimide precursor is dispersed or dissolved in the polymerization solvent The manufacturing method of the polyimide precursor organic solvent solution which manufactures. A polyimide precursor organic solvent solution according to claim 5 is applied to an object to be coated, and after forming a cast film, a polyimide film manufacturing method for imidizing a polyimide precursor in the cast film,
The polymerization solvent has high affinity for the trans 1,4-diaminocyclohexane, the silylating agent, the 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and the intermediate product. Containing a high boiling solvent,
A method for producing a polyimide film, wherein the imidization is carried out after contacting the cast film with a cleaning liquid having a high affinity with the polymerization solvent and having a boiling point lower than that of the polymerization solvent, washing the cast film. Using hexamethylphosphoramide as the high boiling point solvent,
The method for producing a polyimide film according to claim 6, wherein alcohol is used as the cleaning liquid. It manufactures by the manufacturing method of the polyimide precursor of any one of Claim 1 thru | or 3, A repeating structural unit is represented by the said unit structural formula (1), and the substituent in the said unit structural formula (1) R is a fully cycloaliphatic polyimide precursor that is H or Si (CH ₃ ) ₃ group,
Among the substituents R in one unit structure having at least one unit structure is either or both the Si (CH _{3) 3} group, and,
A polyimide precursor having an intrinsic viscosity of 1.0 dl / g or more when measured at 30 ° C. using a mixed solvent of hexamethylphosphoramide and N, N-dimethylacetamide in a volume ratio of 3: 1 as a solvent .   9. The polyimide precursor according to claim 8, wherein the steric structure of each 1,4-cyclohexane residue in the unit structural formula (1) is in a trans configuration. In the total chemical structure, when the total number of substituents R consisting of Si (CH ₃ ) ₃ groups is A and the total number of substituents R consisting of hydrogen is B,
The polyimide precursor according to any one of claims 8 and 9, wherein a silylation rate of the polyimide precursor represented by the following formula (1) is in a range of 0.4 to 0.9.
Silylation rate = A / (A + B) (1) The repeating structural unit is represented by the following unit structural formula (2) formed from trans 1,4-diaminocyclohexane and 1,2,3,4-cyclobutanetetracarboxylic dianhydride. The polyimide in which the steric structure of each 1,4-cyclohexane residue is in the trans configuration.

  A polyimide film comprising the polyimide according to claim 11 as a main component.

Images