JP6336194B2 - Method for producing polyimide laminate and use thereof - Google Patents

Description

  The present invention relates to a method for producing a polyimide laminate and a method for producing a flexible device.

  At present, glass substrates are mainly used as substrates in the field of electronic devices such as flat panel displays and electronic paper. However, since a glass substrate is heavy and fragile, it is not an ideal substrate for an electronic device. In view of this, studies have been actively conducted to realize a flexible device in which the substrate is replaced with glass from a polymer material. However, since many of these technologies require new production techniques and equipment, flexible devices using polymer materials have not been mass produced.

  On the other hand, recently, as a shortcut for efficiently mass-producing flexible devices, it has been proposed to produce flexible devices in a normal glass substrate process by using a laminate in which a polyimide resin layer is formed on a glass substrate. ing. In the process using this laminate, the polyimide resin layer is separated from the glass substrate at the final stage, and a flexible device is obtained.

  In such a process, the laminate is required to have smoothness and low warpage for good handling. That is, the polyimide layer of the laminate needs to have sufficient surface smoothness and a linear expansion coefficient comparable to that of glass. In addition, the linear expansion coefficient of soda-lime glass generally used as a glass substrate is about 8-9 ppm / K, and the linear expansion coefficient of an alkali free glass is about 3-5 ppm / K.

  Further, the process temperature at the time of manufacturing the amorphous silicon thin film transistor reaches 300 to 350 ° C. at the maximum. Since the coefficient of linear expansion of general polyimide is larger than that of glass, materials suitable for such a process are naturally limited.

  For example, Patent Document 1 discloses a polyimide precursor obtained from 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, paraphenylenediamine, and 4,4 ″ diaminoparaterphenyl on an inorganic substrate. A method of casting a body solution and thermal imidizing to obtain a laminate is described.

  Patent Document 2 describes a photosensitive polyimide precursor composition excellent in processability useful for manufacturing an electronic material such as a semiconductor protective film or an interlayer insulating film. In this polyimide precursor solution, a mixed solvent of N-methyl-2-pyrrolidone and 4-methyl-2-pentanone is used.

  Patent Document 3 discloses a polyimide resin comprising a polyimide resin containing a repeating unit represented by a specific formula and a polyimide resin solution containing an organic solvent, and then removing the organic solvent. A method for producing a polyimide resin film is described, which is a method for producing a film, wherein the step of removing the organic solvent is a step of drying the coating film at a temperature of at least two stages.

  Patent Document 4 discloses that a polyimide precursor, which is a polyamic acid homopolymer or copolymer having a repeating unit represented by a specific structural formula and produced by a reaction between an acid component and an amine component, has a low boiling point of less than 100 ° C. A mixed solvent comprising one or more boiling solvents and one or more boiling solvents having a boiling point of 100 ° C. or higher, wherein the high boiling solvent is 5 to 55% by mass of the total solvent. A polyimide precursor solution characterized by being dissolved in a mixed solvent contained in a range is described.

  In Patent Document 5, in a polyamic acid varnish composed of 0.1 to 40% by weight of a polymer and 60 to 99.9% by weight of a solvent, the solvent is at least selected from the specific compound group (A) as the first component. A polyamic acid, which is a mixed solvent containing 5 to 80% by weight of one compound and 95 to 20% by weight of at least one compound selected from the specific compound group B as the second component System varnishes are described.

Japanese Patent Publication “JP 2012-35583 (published February 23, 2012)” Japanese Patent Publication “Japanese Patent Laid-Open No. 2001-89563 (published on April 3, 2001)” Japanese Patent Publication “Japanese Patent Laid-Open No. 2012-77130 (published on April 19, 2012)” International Publication No. 03/074587 pamphlet (published on September 12, 2003) Japanese Patent Publication “Japanese Patent Laid-Open No. 10-7985 (published on January 13, 1998)”

  In patent document 1, although the polyimide precursor of the specific structure which shows low thermal expansibility is reported, the surface smoothness of a polyimide layer is not discussed at all. Moreover, in patent document 2, in order to obtain application | coating uniformity, the solution characteristic is controlled by the ratio of the monomer to be used, and the effect on the surface property of the coating film by a mixed solvent is not described.

  Further, the techniques described in Patent Documents 3 to 5 have room for improvement from the viewpoint of surface smoothness.

  The present invention has been made in view of the above background. And the objective is a manufacturing method of the polyimide laminated body etc. which have a polyimide layer whose surface is sufficiently smooth.

  In the manufacturing method of the polyimide laminated body provided with the polyimide layer and the board | substrate, the polyamic acid synthesize | combined with tetracarboxylic dianhydride and diamine, and the polyamic acid solution containing a solvent are apply | coated on a board | substrate, The board | substrate Forming a polyimide layer thereon;

  The solvent contained in the polyamic acid solution contains N-methyl-2-pyrrolidone and at least one selected from solvent group A consisting of 4-methyl-2-pentanone, cyclohexanone, tetrahydrofuran, and xylene. Furthermore, the viscosity of the polyamic acid solution is 1.0 Pa · s or more and 20.0 Pa · s or less.

  According to the present invention, when a polyimide laminate is produced by casting and heating this solution on an inorganic substrate by using a polyamic acid solution whose solvent is a mixed solvent, the surface of the polyimide laminate is smoothed. A polyimide layer having excellent properties can be obtained.

  An embodiment of the present invention will be described as follows, but the present invention is not limited to this. In the present specification, when “A to B” is described with respect to a numerical range, this description intends “A or more and B or less”.

[1. Polyamic acid solution]
<Solvent used for polyamic acid solution>
In general, a polyamic acid solution in which polyamic acid is dissolved in such a solvent is obtained by polymerizing tetracarboxylic dianhydride, which is a raw material of polyamic acid, and diamine in a solvent.

  In general, for polymerization of polyamic acid, for example, N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP), N, N-dimethylformamide, N, N-dimethylacetamide, or γ-butyrolactone is used. An aprotic polar solvent such as, is preferably used. In addition, it can be said that NMP is suitable as a solvent used for the polymerization of the polyamic acid because the raw material for synthesizing the polyamic acid and the solubility of the polyamic acid are excellent, and further, the storage stability of the polyamic acid solution is excellent.

  In addition to NMP, the polyamic acid solution contains 4-methyl-2-pentanone (hereinafter sometimes referred to as MIBK), cyclohexanone, tetrahydrofuran (hereinafter referred to as THF) in order to smooth the surface of the polyimide layer. And at least one solvent selected from the solvent group consisting of xylene is preferably mixed.

  These solvents may be preliminarily mixed with NMP at the time of polymerization, and polyamic acid may be polymerized in a mixed solvent, or polyamic acid polymerization may be performed with NMP alone, and then a solvent selected from the above solvent group may be added. Also good. The solvent selected from the above solvent group is preferably contained in an amount of 3% by weight to 30% by weight and more preferably 4% by weight to 25% by weight with respect to the total solvent contained in the polyamic acid solution. It is more preferably 5% by weight or more and 15% by weight or less, and particularly preferably 5% by weight or more and 10% by weight or less. In the solvent contained in the polyamic acid solution, the weight ratio of N-methyl-2-pyrrolidone to the solvent included in the solvent group A is preferably 85:15 to 95: 5, and 90:10 More preferably, it is -95: 5. If the weight ratio of a solvent is the said range, it is preferable from a viewpoint of the smoothing effect of the surface of a polyimide layer. Of the above solvent group, MIBK may be selected from the viewpoint of the surface smoothing effect.

<Polyamide acid raw material>
Polyamic acid is generally synthesized from a tetracarboxylic dianhydride component and a diamine component.

≪Tetracarboxylic dianhydride component≫
The tetracarboxylic dianhydride is not particularly limited, but an aromatic tetracarboxylic dianhydride is preferable. For example, as tetracarboxylic dianhydride, 3,3 ′, 4,4′-benzophenonetetracarboxylic dianhydride, 2,3,3 ′, 4′-biphenyltetracarboxylic dianhydride, 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1, 2,5,6-naphthalenetetracarboxylic dianhydride, 4,4′-oxydiphthalic anhydride, 9,9-bis (3,4-dicarboxyphenyl) fluorene dianhydride, 9,9′-bis [ 4- (3,4-dicarboxyphenoxy) phenyl] fluorene dianhydride, 3,3 ′, 4,4′-biphenyl ether tetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride Anhydride 3, 4 , 9,10-perylenetetracarboxylic dianhydride, 4,4′-sulfonyldiphthalic dianhydride, paraterphenyl-3,4,3 ′, 4′-tetracarboxylic dianhydride, metaterphenyl −3,3 ′, 4,4′-tetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenyl ether tetracarboxylic dianhydride, or 3,3 ′, 4,4′-biphenyl Tetracarboxylic dianhydride (hereinafter sometimes abbreviated as BPDA).

  The aromatic ring of the tetracarboxylic dianhydride may have a site where at least one of alkyl group substitution and halogen substitution is performed. A plurality of tetracarboxylic dianhydrides may be used as the aromatic tetracarboxylic dianhydride.

  Further, in order to obtain a polyimide laminate having a polyimide layer having low thermal expansion characteristics (the structure will be described later), it is preferable that at least one of BPDA and pyromellitic acid anhydride is a main component, and in particular, a rigid structure It is preferable to use BPDA having Of all the tetracarboxylic dianhydride components in the polyamic acid (that is, the tetracarboxylic dianhydride constituting the polyamic acid), BPDA is preferably used in an amount of 50% or more, more preferably 70% or more. More preferably, 90% or more is used.

≪Diamine component≫
The diamine component is not particularly limited. For example, 4,4′-diaminodiphenyl ether, 3,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfone, 1,5- (4-aminophenoxy) pentane, 1, 3-bis (4-aminophenoxy) -2,2-dimethylpropane, 2,2-bis (4-aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone and bis [4- ( 3-aminophenoxy) phenyl] sulfone, 9,9-bis (aminophenyl) fluorene, paraphenylenediamine, 1,4-cyclohexanediamine, and the like.

  A plurality of diamines may be used. In such a case, it is preferable to use at least one of paraphenylenediamine and 1,4-cyclohexanediamine having a rigid structure from the viewpoint of reducing thermal expansion. In addition, it is preferable to use 50% or more of at least one of paraphenylenediamine and 1,4-cyclohexanediamine among all diamine components in the polyamic acid (that is, diamine constituting the polyamic acid), and 70% or more is used. More preferably, it is more preferably used at 90% or more. Further, 50% or more of the diamine constituting the polyamic acid may be selected from paraphenylenediamine and 1,4-cyclohexanediamine.

<Polyamide acid polymerization method>
The polyamic acid can be obtained by a generally known polymerization method using the above solvent and raw materials. The ratio of tetracarboxylic anhydride to diamine and the polyamic acid terminal are not particularly limited.

  In addition, when high stability is calculated | required at the time of polyamic acid storage, it is preferable to make high the ratio for which polyamic acid terminal is occupied by an amino group. That is, the molar ratio obtained by dividing the total number of moles of tetracarboxylic dianhydride by the total number of moles of diamine is preferably 0.980 or more and less than 1.000, and is 0.995 or more and 0.998 or less. It is more preferable.

  Because the ratio of the total number of moles of tetracarboxylic dianhydride divided by the total number of moles of diamine is less than 1.000, the proportion of polyamic acid terminals occupied by amino groups is acid anhydride groups. This is because it becomes higher than the occupied ratio, and as a result, the storage stability of the polyamic acid is improved.

  Further, in order to obtain a tough polyimide layer, it is preferable that the molar ratio obtained by dividing the total number of moles of tetracarboxylic dianhydride by the total number of moles of diamine is close to 1.000 and the molecular weight is sufficiently increased. . For example, when the molar ratio obtained by dividing the total number of moles of tetracarboxylic dianhydride by the total number of moles of diamine is 0.980 or more, a strong polyimide layer can be obtained.

  By the way, it is preferable that the reaction apparatus used for the polymerization is provided with a temperature adjusting apparatus for controlling the reaction temperature. And as a reaction temperature in superposing | polymerizing a polyamic acid, 0 degreeC or more and 80 degrees C or less are preferable. In particular, a reaction temperature of 20 ° C. or higher and 60 ° C. or lower is more preferable because dissociation of an amide bond, which is a reverse reaction of polymerization, is suppressed, and a polyamic acid formation reaction easily proceeds and a viscosity is easily increased.

  In addition, for the purpose of adjusting the viscosity, that is, the molecular weight after polymerization, a heat treatment may be performed at about 70 to 90 ° C. for 1 to 24 hours. The heat treatment is an operation conventionally called cooking. By performing this heat treatment, dissociation of the polyamic acid and deactivation of the acid anhydride due to reaction with water in the system are promoted, and the molecular weight of the polyamic acid solution can be adjusted to a desired value. .

  Moreover, it becomes easy to deactivate unreacted tetracarboxylic dianhydride by heat processing. Therefore, it is preferable to perform the polymerization reaction and cooking separately. However, it is also possible to carry out the polymerization reaction and cooking at once by setting the reaction temperature to 70 to 90 ° C. from the beginning.

  The solid content concentration of the polyamic acid dissolved during the polymerization of the polyamic acid is 5 to 30% by weight, preferably 8 to 25% by weight, and more preferably 10 to 20% by weight. This is because when such a solid content concentration is reached, gelation due to abnormal polymerization of the undissolved raw material is suppressed, and the polyamic acid formation reaction easily proceeds.

<Alkoxysilane-modified polyamic acid solution>
As the polyamic acid, an alkoxysilane-modified polyamic acid modified with alkoxysilane may be used. If it is an alkoxysilane modified polyamic acid, the polyimide laminated body excellent in the adhesiveness of a polyimide layer and a board | substrate will be obtained.

  Here, the alkoxysilane-modified polyamic acid will be described. The alkoxysilane-modified polyamic acid is obtained by reacting an alkoxysilane compound containing an amino group with polyamic acid in a solution.

  The modification with the alkoxysilane compound having an amino group is carried out by adding an alkoxysilane compound having an amino group to a polyamic acid solution in which the polyamic acid is dissolved in a solvent, and causing the reaction.

  Examples of the alkoxysilane compound having an amino group include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, and 3- (2-aminoethyl). ) Aminopropyltrimethoxysilane, 3-phenylaminopropyltrimethoxysilane, 2-aminophenyltrimethoxysilane, or 3-aminophenyltrimethoxysilane.

  The blending ratio of these alkoxysilane compounds to 100 parts by weight of polyamic acid is preferably 0.01 to 0.50 parts by weight, more preferably 0.01 to 0.10 parts by weight, More preferably, it is -0.05 weight part.

  When the blending ratio of the alkoxysilane compound is 0.01 parts by weight or more, the polyimide layered product sufficiently exhibits the effect of suppressing the peeling of the polyimide layer with respect to the inorganic substrate. Moreover, since the molecular weight of a polyamic acid is fully maintained as the compounding ratio of an alkoxysilane compound is 0.50 weight part or less, problems, such as embrittlement, do not arise in a polyimide layer.

  By the way, when an alkoxysilane compound containing an amino group is added to a polyamic acid having most of the terminals as amino groups, the viscosity of the polyamic acid solution decreases. In this regard, the inventors proceeded with the modification reaction by reacting the acid dianhydride group regenerated when the amide bond in the polyamic acid was dissociated with the amino group of the alkoxysilane compound. It is estimated that the molecular weight decreases.

  The reaction temperature is preferably 0 ° C. or higher and 80 ° C. or lower, and preferably 20 ° C. or higher and 60 ° C. or lower in order to facilitate the alkoxysilane modification reaction while suppressing the reaction between the acid dianhydride group and water. It is more preferable that

<Viscosity of polyamic acid solution>
The viscosity of the polyamic acid solution is preferably 1.0 Pa · s or more and 20.0 Pa · s or less, more preferably 1.5 Pa · s or more and 15.0 Pa · s or less, and 2.0 Pa · s or less. More preferably, it is s or more and 10.0 Pa · s or less.

  When the viscosity of the polyamic acid solution is 1.0 Pa · s or more, sufficient film thickness accuracy is secured. Further, when the viscosity of the polyamic acid solution is 20.0 Pa · s or less, gelation is suppressed, the time required for the filtration step for removing foreign matters is shortened, and the productivity is also improved. Productivity can be further improved by setting the viscosity of the polyamic acid solution to 15.0 Pa · s or less.

  The viscosity is measured using a viscometer RE-215 / U (manufactured by Toki Sangyo Co., Ltd.), and the viscosity is measured by the method described in JIS K7117-2: 1999. The attached thermostat is set to 23.0 ° C., and the measurement temperature is adjusted to be always constant.

<Providing processing characteristics or various functionalities to the polyamic acid solution>
Various other organic or inorganic low molecular compounds or organic or inorganic polymer compounds may be blended in order to impart processing characteristics or various functionalities to the polyamic acid solution.

  For example, dyes, plasticizers, inorganic fine particles and / or sensitizers may be used. Examples of the inorganic fine particles include inorganic oxide powders such as fine particle silicon dioxide (silica) powder or aluminum oxide powder, or inorganic salt powders such as fine particle calcium carbonate powder or calcium phosphate powder. However, these coarse particles of inorganic fine particles may cause defects in subsequent steps. Therefore, it is preferable that these inorganic fine particles are uniformly dispersed. These inorganic fine particles may have a porous or hollow structure. And as a function of inorganic fine particles, a pigment or a filler is mentioned. Moreover, the form may be a fiber or the like.

<Post treatment of polyamic acid solution>
The polyamic acid solution obtained as described above is subjected to a filtration treatment in order to reduce foreign substances as necessary.

  The filter used for filtration is not particularly limited as long as the solution to be filtered does not attack the material of the filter, and a suitable filter material may be selected as appropriate. The filter pore size can be selected according to the purpose and is not particularly limited, but is preferably 0.01 μm to 3 μm, and more preferably 0.1 μm to 1 μm. In addition, as needed, filtration may be implemented repeatedly and multistage filtration may be implemented combining 2 or more types of filters.

  And by filtering a polyamic acid solution, the foreign material in a polyamic acid solution reduces and the polyimide laminated body with few foreign materials is obtained. In addition, as the number of foreign matters in the polyamic acid solution, a value measured using a light scattering type in-liquid particle counter (detailed measuring apparatus will be described later) is 100 foreign particles or less of 0.5 μm or more. It is preferably 50 / g or less.

<About water content of polyamic acid solution>
The moisture in the above polyamide solution can be measured with a volumetric titration Karl Fischer moisture meter (detailed measuring apparatus and measuring conditions will be described later). The moisture in the polyamic acid solution is preferably 500 ppm or more and 3000 ppm or less. It is preferable that the water content is 3000 ppm or less because the effect of improving storage stability by adjusting the molar ratio is sufficiently exhibited. Furthermore, if it is 1000 ppm or less, the probability that the acid dianhydride group generated by the decomposition of the amide bond in the polyamic acid molecule reacts with water is lowered, and the viscosity change during storage can be suppressed, which is more preferable. The water in the solution can be divided into raw material origin and work environment origin. There are various methods for reducing the moisture, but it is not preferable to reduce the amount more than necessary by using an extra process or excess equipment because the cost increases. For example, since the water content of a commercially available amide-based solvent is about 500 ppm, reducing the water content below that is not preferable because it involves an increase in cost.

  As a method for reducing moisture, it is effective to strictly store raw materials to avoid mixing moisture and to replace the reaction atmosphere with dry air or dry nitrogen. Further, the treatment may be performed under reduced pressure.

[2. Polyimide laminate]
<Method for producing polyimide laminate>
A laminate comprising a polyimide layer and a substrate (for example, a laminate comprising a polyimide layer and a substrate) is casted (applied) on the substrate and imidized by heating. Manufactured by.

  In addition, the board | substrate here intends a support body. Specific examples include a glass substrate and various metal substrates, and a glass substrate is preferably used. As the glass substrate, soda lime glass, borosilicate glass, alkali-free glass, or the like is used. In particular, since alkali-free glass is generally used in the thin film transistor manufacturing process, alkali-free glass is more preferable as the substrate.

  The thickness of the substrate used for the polyimide laminate is preferably 0.4 to 5.0 mm. A substrate of 0.4 mm or more is preferable because the substrate can be easily handled. Moreover, if the substrate is 5.0 mm or less, the heat capacity of the substrate does not increase, and the productivity in the heating step and / or cooling step is improved, which is preferable.

  A known method can be used as a method for casting the polyamic acid solution onto the substrate. For example, a known casting method such as a gravure coating method, a spin coating method, a silk screen method, a dip coating method, a bar coating method, a knife coating method, a roll coating method, or a die coating method can be used.

  The heating temperature and heating time in the case of obtaining a polyimide laminate by heating and imidizing the polyamic acid solution can be appropriately determined and are not particularly limited as long as the properties are not affected. An example is shown below.

  First, an alkoxysilane-modified polyamic acid solution is cast on an inorganic substrate. The inorganic substrate coated with polyamic acid is preferably heated (dried) at a temperature of 60 to 200 ° C. for 3 to 120 minutes. The heating start temperature in this case is preferably 100 ° C. or more from the viewpoint of increasing the production efficiency of the polyimide laminate, and further, heating is started from a temperature of 110 to 130 ° C. from the viewpoint of developing low thermal expansion characteristics. It is particularly preferable that the heating time at temperature is 10 to 60 minutes. Alternatively, the drying may be performed at two stages, for example, at 100 ° C. for 30 minutes and then at 120 ° C. for 30 minutes.

  Next, in order to advance imidation, the inorganic substrate coated with the above-described polyamic acid is heated at a temperature of 200 to 500 ° C. for 3 to 300 minutes. At this time, it is preferable to gradually raise the temperature from a low temperature to a maximum temperature. The heating rate is preferably 2 ° C./min to 10 ° C./min, more preferably 4 ° C./min to 10 ° C./min.

  Moreover, it is preferable that the maximum temperature in imidation is a temperature range of 300-500 degreeC. If the maximum temperature is 300 ° C. or higher, thermal imidization proceeds sufficiently, and if the maximum temperature is 500 ° C. or lower, thermal deterioration of the polyimide can be suppressed. Moreover, you may hold | maintain for arbitrary time at arbitrary temperatures until it reaches the maximum temperature. The heating atmosphere may be in air, under reduced pressure, or in an inert gas such as nitrogen. As the heating device, a known device such as a hot air oven, an infrared oven, a vacuum oven, an inert oven, or a hot plate may be used.

<Imidization catalyst>
In the case of imidization, if necessary, an imidization catalyst may be added to the polyamic acid solution and further heated.

  As the imidization catalyst, a tertiary amine is preferably used. More preferably, the tertiary amine is a heterocyclic tertiary amine. Preferable specific examples of the heterocyclic tertiary amine include pyridine, 2,5-diethylpyridine, picoline, quinoline, isoquinoline and the like.

  The amount of the imidizing agent used is preferably 0.01 to 2.00 equivalents, particularly 0.02 to 1.20 equivalents, based on the reaction site of the alkoxysilane-modified polyamic acid. If the imidization catalyst is 0.01 equivalent or more, the effect of the catalyst is sufficiently obtained. If the imidization catalyst is 2.00 equivalents or less, the ratio of the catalyst not involved in the reaction is small, which is preferable.

<Linear expansion characteristics of polyimide layer>
The polyimide layer of the polyimide laminate has low linear expansion characteristics. For example, when these values are measured by thermal mechanical analysis (TMA), first, the polyimide layer is peeled from the polyimide laminate. And after the film thickness of this polyimide layer film is measured, the film is cut into a size of 10 mm × 3 mm. The cut sample (film sample) was subjected to a load of 29.4 mN on its long side and once heated from 20 ° C. to 500 ° C. at 10 ° C./min in a nitrogen atmosphere, then 20 The solution is cooled to 50 ° C. and further heated to 500 ° C. at 10 ° C./min. In this process, the linear expansion coefficient is obtained from the amount of change in strain of the sample per unit temperature from 100 ° C. to 300 ° C. at the second temperature increase.

  The linear expansion coefficient determined by this measurement method is preferably −10 ppm / K or more and 20 ppm / K or less from the viewpoint of having a linear expansion coefficient equivalent to that of the inorganic substrate, and an inorganic glass generally used as a substrate material It is more preferably 1 ppm / K or more and 15 ppm / K or less from the viewpoint of being equivalent, and 3 ppm / K or more and 10 ppm / K or less from the viewpoint of being equivalent to alkali-free glass generally used for display applications. More preferably, it is 6 ppm / K or more and 8 ppm / K or less. In addition, the linear expansion coefficient in this specification shall show the linear expansion coefficient in the range of 100 to 300 degreeC calculated | required by the said measuring method.

<Film thickness of polyimide layer>
The thickness of the polyimide layer is preferably 5 to 50 μm. If the thickness of the polyimide layer is 5 μm or more, the mechanical strength necessary for the substrate can be ensured. Moreover, if the thickness of a polyimide layer is 50 micrometers or less, the laminated body of a polyimide layer and a board | substrate can be obtained without natural peeling.

<Characteristic example of polyimide laminate>
The polyimide laminate obtained as described above is excellent in storage stability and process consistency, and can be suitably used for manufacturing a flexible device by a known thin film transistor process for liquid crystal panels.

  For example, when an alkoxysilane-modified polyamic acid solution is cast on an alkali-free glass substrate and heated to imidize, when a specific structure is further selected for the polyamic acid skeleton, the linear expansion coefficient is −10 ppm. A laminate including a polyimide layer having a / K value of 20 ppm / K or less and an alkali-free glass substrate is obtained. And the flexible device which has the outstanding characteristic is obtained by using this laminated body.

  Moreover, the polyimide laminated body manufactured from a polyamic-acid solution is excellent in the adhesiveness of a polyimide layer and a board | substrate. In the polyimide laminate, the adhesion between the polyimide layer and the substrate can be evaluated by 90 ° peel strength.

  The peel strength is measured in accordance with ASTM D1876-01 standard (details will be described later). The peel strength is preferably 0.15 N / cm or more. This is because if the peel strength is 0.15 N / cm or more, peeling during the formation of the electronic element can be suppressed.

[3. Electronic element formation and peeling]
By using the polyimide laminate as described above, a flexible display substrate having excellent characteristics can be obtained. That is, an electronic element is formed on the polyimide layer of the polyimide laminate, and then the flexible display substrate is obtained by peeling the polyimide layer from the substrate.

  Examples of the flexible display substrate include a TFT (Thin Film Transistor) substrate, a transparent conductive film substrate such as ITO (Indium Tin Oxide), a solar cell substrate, and the like. A known method can be used as a method of peeling the polyimide layer from the substrate. For example, it may be peeled off by hand, or may be peeled off using a mechanical device such as a drive roll or a robot. Furthermore, the method of providing a peeling layer between a board | substrate and a polyimide layer may be used. In addition, for example, a method in which a silicon oxide film is formed over a substrate having a large number of grooves and the substrate is separated by infiltrating an etching solution, or a method in which an amorphous silicon layer is provided over the substrate and separated by laser light is given. You can also.

  Furthermore, the flexible display substrate can be used for an electronic device (flexible device) such as an organic EL display, a liquid crystal display, electronic paper, or a touch panel.

[4. Method for producing a polyimide laminate and its use]
In addition, it can also express as follows regarding the manufacturing method of the polyimide laminated body provided with the above polyimide layer and a board | substrate, and its utilization.

  In the method for producing a polyimide laminate, a step of applying a polyamic acid synthesized from tetracarboxylic dianhydride and diamine and a polyamic acid solution containing a solvent on a substrate and forming a polyimide layer on the substrate. including.

  The solvent contained in the polyamic acid solution contains N-methyl-2-pyrrolidone and at least one selected from solvent group A consisting of 4-methyl-2-pentanone, cyclohexanone, tetrahydrofuran, and xylene. Furthermore, the viscosity of the polyamic acid solution is 1.0 Pa · s or more and 20.0 Pa · s or less.

  Further, the solid content concentration of the polyamic acid in the polyamic acid solution is preferably 10% by weight or more and 20% by weight or less.

  In addition, it is preferable that at least one selected from the solvent group A in the solvent contained in the polyamic acid solution is contained in an amount of 3% by weight to 30% by weight with respect to the total solvent contained in the polyamic acid solution.

  In the solvent contained in the polyamic acid solution, the weight ratio of N-methyl-2-pyrrolidone to the solvent included in the solvent group A is preferably 85:15 to 95: 5.

  In the solvent contained in the polyamic acid solution, the weight ratio of N-methyl-2-pyrrolidone to the solvent included in the solvent group A is preferably 90:10 to 95: 5.

  The solvent selected from the solvent group A is preferably 4-methyl-2-pentanone.

  The polyamic acid is preferably modified with alkoxysilane.

  Further, 50% or more of the tetracarboxylic dianhydride constituting the polyamic acid is preferably 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride.

  Moreover, it is preferable that 50% or more of the diamine constituting the polyamic acid is selected from paraphenylenediamine and 1,4-cyclohexanediamine.

  Moreover, it is preferable that the linear expansion coefficient of the polyimide layer of a polyimide laminated body is -10 ppm / K or more and 20 ppm / K or less.

  And the flexible which includes the process of forming an electronic element in the polyimide layer in the polyimide laminated body obtained with the manufacturing method of the above polyimide laminated bodies, and the process of peeling the polyimide layer in which the electronic element was formed from a board | substrate. The manufacturing method of a display substrate can also be said to be the present invention.

  Moreover, the flexible device containing the flexible display substrate obtained by the manufacturing method of the flexible display substrate can also be said to be the present invention.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention. Furthermore, a new technical feature can be formed by combining the technical means disclosed in each embodiment.

  Hereinafter, the present invention will be specifically described based on examples. However, the present invention is not limited to these examples, and the embodiments can be changed without departing from the gist of the present invention.

  Under the conditions described in Table 1 below, the weight average molecular weight (Mw) was determined.

［異物測定］
あらかじめ異物量を測定したＮ−メチル−２−ピロリドンを容量１００ｍＬのクリーンボトルに６５ｇ程度に計量し、このクリーンボトルにさらに実施例で得られた各溶液を１５ｇ程度計量する。このクリーンボトルを撹拌脱泡機（ＴＨＩＮＫＹ製：ＡＲ−２５０）にて回転数２０００ｒｐｍで撹拌３分、脱泡２７分処理し、測定用の希釈された溶液を調整した。

[Foreign matter measurement]
About 65 g of N-methyl-2-pyrrolidone whose amount of foreign matter has been measured in advance is weighed into a clean bottle with a capacity of 100 mL and about 15 g of each solution obtained in the example is further weighed into this clean bottle. This clean bottle was treated with a stirring deaerator (manufactured by THINKY: AR-250) at a rotation speed of 2000 rpm for 3 minutes and deaerated for 27 minutes to prepare a diluted solution for measurement.

This adjusted solution was measured with a light scattering particle counter (Spectris: SL1500, minimum measurable particle size: 0.2 μm). The measurement amount at one time was 10 mL (discarding the first 1 mL), and six measurements (54 mL in total) were performed. From the obtained measured values, the number of foreign matters of 0.5 μm or more contained per 1 g of the solution was calculated according to the following formula.
Number of foreign matter contained in 1 g of solution =
(A− (B × Wb / (Wa + Wb))) / 54 / (Wa / (Wa + Wb))
However, the symbols used in the equations represent the following.
A: Measured value of the number of foreign matters of 0.5 μm or more B: Measured value of the number of foreign matters of 0.5 μm or more of N-methyl-2-pyrrolidone used for dilution Wa: The solution obtained in the example was weighed Weight (g)
Wb: Weight (g) of N-methyl-2-pyrrolidone used for dilution
The particle counter used in this measurement was calibrated according to the standard of JIS B9925 before use.

[moisture]
Using a volumetric titration Karl Fischer moisture meter 890 Tightland (manufactured by Metrohm Japan Co., Ltd.), the moisture in the alkoxysilane-modified polyamic acid solution was measured by the method described in the volumetric titration method of JIS K0068. However, a 1: 4 mixed solution of Aquamicron GEX (manufactured by Mitsubishi Chemical Corporation) and N-methylpyrrolidone was used as a titration solvent.

[viscosity]
Using a viscometer RE-215 / U (manufactured by Toki Sangyo Co., Ltd.), the viscosity was measured by the method described in JIS K7117-2: 1999. The attached thermostat was set to 23.0 ° C., and the measurement temperature was always constant.

[Evaluation of surface properties of polyimide layer]
A polyimide laminate was prepared by the methods described in the following examples and comparative examples, and the smoothness of the surface was visually observed and evaluated. The evaluation criteria were as follows.

A: There are no irregularities that can be visually observed on the surface of the polyimide layer. B: There are irregularities that can be visually confirmed at the ends of the polyimide layer. C: Visual confirmation at the ends of the polyimide layer and a part other than the ends. D: There are irregularities that can be visually confirmed on the entire surface of the polyimide layer. In this evaluation method, the surface is sufficiently smooth if it is A or B.

[Linear expansion coefficient]
The linear expansion coefficient was evaluated by thermomechanical analysis using a tensile load method using TMA / SS7100 manufactured by SII Nano Technology. After peeling off the polyimide layer from the polyimide laminate of the example to prepare a sample of 10 mm × 3 mm, applying a load of 29.4 mN to the long side and once raising the temperature from 20 ° C. to 500 ° C. at 10 ° C./min When the sample is cooled to 20 ° C. and further heated to 500 ° C. at a rate of 10 ° C./min, the change in strain of the sample per unit temperature in the range of 100 ° C. to 300 ° C. during the second temperature increase is linearly expanded. Coefficient.

[Peel strength]
In accordance with ASTM D1876-01 standard, the polyimide laminate was cut to a width of 10 mm with a cutter knife, and a tensile tester (Strograph VES1D) manufactured by Toyo Seiki was used at 23 ° C. and 55% RH under a tensile speed of 50 mm / min. Then, the average value of 90 ° peel strength when peeled by 50 mm was evaluated as peel strength.

[Synthesis Example 1]
<Production of polyamic acid solution>
N-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) is placed in a 2 L glass separable flask equipped with a polytetrafluoroethylene stirrer with a sealing stopper, a stirring blade, and a nitrogen introduction tube. 850.0 g was added, 40.1 g of paraphenylenediamine (hereinafter sometimes referred to as PDA) and 0.6 g of 4,4′-diaminodiphenyl ether (hereinafter sometimes referred to as ODA) were added, and the solution was added to an oil bath. And stirred at 50.0 ° C. for 30 minutes under a nitrogen atmosphere.

  After confirming that the raw material was uniformly dissolved, 109.3 g of BPDA was added, and the temperature of the solution was adjusted to about 90 ° C. while stirring for 10 minutes in a nitrogen atmosphere until the raw material was completely dissolved. Furthermore, stirring was continued while heating at a constant temperature to lower the viscosity, and a viscous polyamic acid solution having a viscosity of 190 poise at 23 ° C. was obtained.

  Note that the charged concentration of the diamine compound and tetracarboxylic dianhydride in this polyamic acid solution is 15% by weight with respect to the total reaction solution, and the total number of moles of tetracarboxylic dianhydride is the total number of moles of diamine. The divided molar ratio is 0.995. When the molecular weight of the polyamic acid was measured, it was Mw = 67,000.

<Modification with alkoxysilane compound>
The reaction solution was quickly cooled in a water bath, and the temperature of the solution was adjusted to about 50 ° C. Next, 7.5 g of a 1% NMP solution of 3-aminopropyltriethoxysilane (hereinafter sometimes referred to as γ-APS) was added and stirred for 2 hours.

[Example 1]
NMP and MIBK were added so that the polyamic acid solution obtained in Synthesis Example 1 had a solid content concentration of 13.0% by weight and the ratio of the solvent in the solution was NMP / MIBK = 90/10. Dilution was performed to obtain a polyamic acid solution having a viscosity of 7.3 Pa · s at 23 ° C. and a water content of 1700 ppm.

  The obtained polyamic acid solution was subjected to multistage filtration using a filter having a pore size of 0.5 μm and a filter having a pore size of 0.2 μm. The evaluation results of foreign matters are shown in Table 2 below.

<Manufacture of polyimide laminate>
The obtained polyamic acid solution was cast on a square alkali-free glass plate (Eagle XG manufactured by Corning Co., Ltd.) having a side of 150 mm and a thickness of 0.7 mm so that the thickness after drying with a bar coater was 20 μm. It was dried in an oven at 120 ° C. for 30 minutes. Thereafter, the alkali-free glass plate is heated from 20 ° C. to 180 ° C. at 4 ° C./min under a nitrogen atmosphere, held for 30 minutes, further heated to 450 ° C. at 4 ° C./min, and heated at 450 ° C. at 10 ° C. Heated for minutes. Thereby, the polyimide laminated body whose thickness of a polyimide layer is 20 micrometers was obtained. In addition, the linear expansion coefficient of an alkali free glass plate is 3-4 ppm / K.

[Example 2]
NMP and MIBK were added to the polyamic acid solution obtained in Synthesis Example 1 so that the solid content concentration was 13.0 wt% and the solvent ratio in the solution was NMP / MIBK = 95/5. A polyamide acid solution having a viscosity of 7.3 Pa · s and a water content of 2200 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 3]
NMP and THF were added to the polyamic acid solution obtained in Synthesis Example 1 so that the solid content concentration was 11.5% by weight and the solvent ratio in the solution was NMP / THF = 75/25. A polyamide acid solution having a viscosity of 4.0 Pa · s at 23 ° C. and a water content of 2000 ppm was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 4]
NMP and xylene were added to the polyamic acid solution obtained in Synthesis Example 1 so that the solid content concentration was 13.0% by weight and the ratio of the solvent in the solution was NMP / xylene = 90/10. A polyamide acid solution having a viscosity of 7.8 Pa · s and a water content of 2500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 5]
NMP and cyclohexanone were added to the polyamic acid solution obtained in Synthesis Example 1 so that the solid content concentration was 13.0% by weight and the ratio of the solvent in the solution was NMP / cyclohexanone = 90/10. A polyamide acid solution having a viscosity of 7.0 Pa · s and a water content of 1800 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Synthesis Example 2]
<Production of polyamic acid solution>
850.0 g of NMP was put into a 2 L glass separable flask equipped with a stirrer with a polytetrafluoroethylene seal stopper, a stirring blade, and a nitrogen introduction tube, and 41.4 g of 1,4-cyclohexanediamine was added. The solution was stirred for 30 minutes under a nitrogen atmosphere.

  After confirming that the raw materials were uniformly dissolved, 103.6 g of BPDA was added, and further 5.0 g of 9,9-bis (3,4-dicarboxyphenyl) fluorene dianhydride was added. Under the nitrogen atmosphere, the temperature of the solution was adjusted to about 80 ° C. and stirred for 30 minutes until the polymerization reaction started. Thereafter, the mixture was cooled to room temperature and further stirred for 5 hours to obtain a viscous polyamic acid solution having a viscosity of 226.0 Pa · s at 23 ° C.

  The concentration of the diamine compound and tetracarboxylic dianhydride in this polyamic acid solution is 15% by weight based on the total reaction solution, and the total number of moles of tetracarboxylic dianhydride is the total number of moles of diamine. The molar ratio divided by is 1.000. When the molecular weight of the polyamic acid was measured, it was Mw = 64000.

[Example 6]
NMP and MIBK were added to the polyamic acid solution obtained in Synthesis Example 2 so that the solid concentration was 9.5% by weight and the ratio of the solvent in the solution was NMP / MIBK = 90/10. Dilution was performed to obtain a polyamic acid solution having a viscosity of 7.0 Pa · s at 23 ° C. and a water content of 1300 ppm.

<Manufacture of polyimide laminate>
The obtained polyamic acid solution was cast on a square alkali-free glass plate (Eagle XG manufactured by Corning Co., Ltd.) having a side of 150 mm and a thickness of 0.7 mm so that the thickness after drying with a bar coater was 10 μm. It was dried in an oven at 120 ° C. for 20 minutes. Thereafter, the alkali-free glass plate was heated from 20 ° C. to 350 ° C. at 5 ° C./min in a nitrogen atmosphere and heated at 350 ° C. for 1 hour to obtain a polyimide laminate having a polyimide layer thickness of 10 μm.

[Synthesis Example 3]
<Production of polyamic acid solution>
In a 2 L glass separable flask equipped with a polytetrafluoroethylene stirrer with a sealing stopper, a stirring blade, and a nitrogen introduction tube, 830.0 g of NMP was placed, 45.4 g of PDA, and 0.7 g of ODA In addition, the solution was stirred for 30 minutes under a nitrogen atmosphere while heating to 50.0 ° C. in an oil bath.

  After confirming that the raw material was uniformly dissolved, 123.9 g of BPDA was added, and the temperature of the solution was adjusted to about 90 ° C. while stirring for 10 minutes in a nitrogen atmosphere until the raw material was completely dissolved. Furthermore, stirring was continued while heating at a constant temperature to lower the viscosity, and a viscous polyamic acid solution showing a viscosity of 735 poise at 23 ° C. was obtained.

  Note that the charged concentration of the diamine compound and tetracarboxylic dianhydride in this polyamic acid solution is 17% by weight with respect to the total reaction solution, and the total number of moles of tetracarboxylic dianhydride is the total number of moles of diamine. The divided molar ratio is 0.995. When the molecular weight of the polyamic acid was measured, it was Mw = 70000.

<Modification with alkoxysilane compound>
The reaction solution was quickly cooled in a water bath, and the temperature of the solution was adjusted to about 50 ° C. Next, 8.4 g of 1% NMP solution of γ-APS was added and stirred for 2 hours.

[Example 7]
NMP and MIBK were added to the polyamic acid solution obtained in Synthesis Example 3 so that the solid content concentration was 12.8% by weight and the ratio of the solvent in the solution was NMP / THF = 75/25. A polyamide acid solution having a viscosity of 8.0 Pa · s and a water content of 2500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 8]
NMP and THF were added to the polyamic acid solution obtained in Synthesis Example 3 so that the solid content concentration was 12.8% by weight and the ratio of the solvent in the solution was NMP / THF = 75/25. A polyamide acid solution having a viscosity of 5.6 Pa · s and a water content of 2500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 9]
"NMP and xylene" were added to the polyamic acid solution obtained in Synthesis Example 3 so that the solid content concentration was 12.8% by weight and the ratio of the solvent in the solution was NMP / xylene = 75/25 Thus, a polyamic acid solution having a viscosity of 8.1 Pa · s and a water content of 2500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 10]
To the polyamic acid solution obtained in Synthesis Example 3, NMP and cyclohexanone were added so that the solid content concentration was 12.8% by weight and the ratio of the solvent in the solution was NMP / cyclohexanone = 75/25. A polyamide acid solution having a viscosity of 8.3 Pa · s and a water content of 2500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Observations regarding Examples 1 to 10]
When the obtained laminates of Examples 1 to 10 were observed, no bubbles and floats were observed between the polyimide layer and the alkali-free glass plate, and they did not peel off naturally during heating. And it was possible to peel off a polyimide layer from an alkali free glass plate. The evaluation of the surface property of the polyimide layer is shown in Table 2.

[Comparative Example 1]
The polyamide acid solution obtained in Synthesis Example 1 was diluted by adding NMP so that the solid content concentration would be 13.0% by weight, and the polyamide having a viscosity of 7.0 Pa · s and a water content of 1900 ppm at 23 ° C. An acid solution was obtained.

  The obtained polyamic acid solution was subjected to multistage filtration using a filter having a pore size of 0.5 μm and a filter having a pore size of 0.2 μm. Table 2 shows the evaluation results of the foreign matters.

  An attempt was made to produce a polyimide laminate using the polyamic acid solution after filtration in the same manner as in Example 1. However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface.

  Thereafter, the temperature was raised from 20 ° C. to 180 ° C. at 4 ° C./minute in a nitrogen atmosphere, held for 30 minutes, further heated to 450 ° C. at 4 ° C./minute, heated at 450 ° C. for 10 minutes, A polyimide laminate having a thickness of 20 μm was obtained.

[Comparative Example 2]
An attempt was made to produce a polyimide laminate in the same manner as in Example 1 without diluting the polyamic acid solution obtained in Synthesis Example 1 (note that the viscosity of the polyamic acid solution was 13.5 Pa · s at 23 ° C. ) However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface. Thereafter, in the same manner as in Comparative Example 1, a polyimide laminate having a polyimide layer thickness of 20 μm was obtained.

[Comparative Example 3]
NMP and the polyamic acid solution obtained in Synthesis Example 1 were adjusted so that the solid content concentration was 11.2% by weight and the ratio of the solvent in the solution was NMP / propylene glycol monomethyl ether acetate = 90/10. Propylene glycol monomethyl ether acetate was added for dilution to obtain a polyamic acid solution having a viscosity of 7.5 Pa · s and a water content of 2000 ppm at 23 ° C.

  An attempt was made to produce a polyimide laminate using the obtained polyamic acid solution in the same manner as in Example 1. However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface. Thereafter, in the same manner as in Comparative Example 1, a polyimide laminate having a polyimide layer thickness of 20 μm was obtained.

[Comparative Example 4]
To the polyamic acid solution obtained in Synthesis Example 1, NMP and butyl cellosolve were added so that the solid content concentration was 11.2% by weight and the ratio of the solvent in the solution was NMP / butyl cellosolve = 90/10. A polyamide acid solution having a viscosity of 9.0 Pa · s and a water content of 2000 ppm at 23 ° C. was obtained.

  An attempt was made to produce a polyimide laminate using the obtained polyamic acid solution in the same manner as in Example 1. However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface. Thereafter, in the same manner as in Comparative Example 1, a polyimide laminate having a polyimide layer thickness of 20 μm was obtained.

[Comparative Example 5]
The polyamic acid solution obtained in Synthesis Example 1 was subjected to NMP and γ− so that the solid content concentration was 11.2 wt% and the ratio of the solvent in the solution was NMP / γ-butyrolactone = 90/10. Butyrolactone was added and diluted to obtain a polyamic acid solution having a viscosity of 6.8 Pa · s at 23 ° C. and a water content of 2000 ppm.

  An attempt was made to produce a polyimide laminate using the obtained polyamic acid solution in the same manner as in Example 1. However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface. Thereafter, in the same manner as in Comparative Example 1, a polyimide laminate having a polyimide layer thickness of 20 μm was obtained.

[Comparative Example 6]
The polyamic acid solution obtained in Synthesis Example 1 was mixed with NMP and diisobutyl ketone so that the solid content concentration was 12.8% by weight and the ratio of the solvent in the solution was NMP / diisobutyl ketone = 90/10. It was added and diluted to obtain a polyamic acid solution having a viscosity of 8.0 Pa · s at 23 ° C. and a water content of 2000 ppm.

  An attempt was made to produce a polyimide laminate using the obtained polyamic acid solution in the same manner as in Example 1. However, when such a polyamic acid solution was applied to an alkali-free glass plate and then dried in a hot air oven at 120 ° C. for 30 minutes, a skin-like unevenness was formed on the film surface. Thereafter, in the same manner as in Comparative Example 1, a polyimide laminate having a polyimide layer thickness of 20 μm was obtained.

[Observation regarding Comparative Examples 1 to 6]
When the obtained laminates of Comparative Examples 1 to 6 were observed, the surface condition was poor, and a polyimide layer having a uniform thickness could not be obtained. Therefore, physical properties could not be measured. The evaluation of the surface property of the polyimide layer is shown in Table 2.

[Reference Example 1]
The polyamide acid solution obtained in Synthesis Example 1 was diluted by adding NMP so that the solid content concentration would be 13.0% by weight, and the polyamide having a viscosity of 7.0 Pa · s and a water content of 2000 ppm at 23 ° C. An acid solution was obtained.

  The obtained polyamic acid solution was cast on a square alkali-free glass plate (Eagle XG manufactured by Corning Co., Ltd.) having both sides of 150 mm and a thickness of 0.7 mm so that the thickness after drying with a bar coater was 20 μm, and a hot air oven It was dried at 60 ° C. for 20 minutes. Thereafter, the alkali-free glass plate was heated at 4 ° C./min from 20 ° C. to 150 ° C. under a nitrogen atmosphere, held at 150 ° C. for 20 minutes, and then heated to 350 ° C. at 4 ° C./min. The mixture was heated at 350 ° C. for 20 minutes, then heated to 450 ° C. at 4 ° C./min, and held at 450 ° C. for 10 minutes. Thereby, the polyimide laminated body whose thickness of a polyimide layer is 20 micrometers was obtained.

[Comparative Example 7]
The polyamic acid solution obtained in Synthesis Example 1 was diluted by adding NMP so that the solid content concentration would be 13.0 wt%, and the polyamic acid solution having a viscosity of 7.0 Pa · s at 23 ° C. and a water content of 2000 ppm. Got.

  The obtained polyamic acid solution was cast on a square alkali-free glass plate (Eagle XG manufactured by Corning Co., Ltd.) having both sides of 150 mm and a thickness of 0.7 mm so that the thickness after drying with a bar coater was 20 μm, and a hot air oven And dried at 80 ° C. for 20 minutes. Thereafter, the alkali-free glass plate was heated at 4 ° C./min from 20 ° C. to 150 ° C. under a nitrogen atmosphere, held at 150 ° C. for 20 minutes, and then heated to 350 ° C. at 4 ° C./min. The mixture was heated at 350 ° C. for 20 minutes, then heated to 450 ° C. at 4 ° C./min, and held at 450 ° C. for 10 minutes. Thereby, the polyimide laminated body whose thickness of a polyimide layer is 20 micrometers was obtained.

[Observation concerning Comparative Example 1, Reference Example 1 and Comparative Example 7, and Initial Drying Temperature]
When the obtained laminates of Reference Example 1 and Comparative Example 7 were observed, no bubbles and floats were observed between the polyimide layer and the alkali-free glass, and they did not peel off spontaneously during heating. And it was possible to peel off a polyimide layer from an alkali free glass plate.

  In other words, the surface property is changed from D to B or C by lowering the drying start temperature in Reference Example 1 and Comparative Example 7 from 60 ° C. or 80 ° C. from the drying start temperature of 120 ° C. in Comparative Example 1. Improve. However, at such a drying start temperature of 100 ° C. or lower, the heating time and the cooling time become long, and the productivity is lowered. Furthermore, in Reference Example 1 and Comparative Example 7, the linear expansion coefficients are 15 ppm / K and 17 ppm / K, and the difference in linear expansion coefficient from the glass substrate is 5 ppm / K or more.

[Synthesis Example 4]
<Production of polyamic acid solution>
In a 2 L glass separable flask equipped with a polytetrafluoroethylene stirrer with a sealing stopper, a stirring blade, and a nitrogen introduction tube, 780.0 g of NMP was placed, 59.2 g of PDA, and 0.9 g of ODA In addition, the solution was stirred for 30 minutes under a nitrogen atmosphere while heating to 50.0 ° C. in an oil bath.

  After confirming that the raw material was uniformly dissolved, 151.8 g of BPDA was added, and the temperature of the solution was adjusted to about 90 ° C. while stirring for 10 minutes in a nitrogen atmosphere until the raw material was completely dissolved. Furthermore, stirring was continued while heating at a constant temperature to lower the viscosity, and a viscous polyamic acid solution showing a viscosity of 41 poise at 23 ° C. was obtained.

  Note that the charged concentration of the diamine compound and tetracarboxylic dianhydride in this polyamic acid solution is 22% by weight with respect to the total reaction solution, and the total number of moles of tetracarboxylic dianhydride is the total number of moles of diamine. The molar ratio divided is 0.935. When the molecular weight of the polyamic acid was measured, it was Mw = 20000.

<Modification with alkoxysilane compound>
The reaction solution was quickly cooled in a water bath, and the temperature of the solution was adjusted to about 50 ° C. Next, 11.0 g of 1% NMP solution of γ-APS was added and stirred for 2 hours.

[Example 11]
NMP and MIBK were added to the polyamic acid solution obtained in Synthesis Example 4 so that the solid concentration was 20.5% by weight and the ratio of the solvent in the solution was NMP / MIBK = 95/5. A polyamide acid solution having a viscosity of 2.5 Pa · s and a water content of 1500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Example 12]
NMP and THF were added to the polyamic acid solution obtained in Synthesis Example 4 so that the solid concentration was 20.5% by weight and the ratio of the solvent in the solution was NMP / THF = 95/5. A polyamide acid solution having a viscosity of 2.4 Pa · s and a water content of 1500 ppm at 23 ° C. was obtained. And the polyimide laminated body was obtained like Example 1 using the obtained polyamic-acid solution.

[Observations regarding Examples 11 and 12]
When the obtained laminates of Examples 11 and 12 were observed, the surface properties were good, but the physical properties could not be measured because the uniform thickness of the polyimide layer was brittle and could not be peeled off. The evaluation of the surface property of the polyimide layer is shown in Table 2.

  In addition, the polyimide layers of Examples 1 to 12 did not curl or warp even after peeling from the alkali-free glass plate. This is because the linear expansion coefficient of the polyimide layer is 20 ppm / K or less and is close to the linear expansion coefficient of the substrate immediately below the polyimide layer (the difference in linear expansion coefficient between the substrate and the polyimide layer is 10 ppm / K or less. is there).

  In addition, the water | moisture content of the polyamic-acid solution in all of Examples 1-12, Comparative Examples 1-7, and Reference Example 1 is 500 ppm or more and 3000 ppm or less, and the viscosity change at the time of storage did not affect these results.

  The present invention can be suitably used in the field of electronic devices such as flat panel displays and electronic paper.

Claims (11)

A method for producing a polyimide laminate comprising a polyimide layer and a substrate,
A step of applying a polyamic acid synthesized from tetracarboxylic dianhydride and a diamine, and a polyamic acid solution containing a solvent on a substrate, and forming a polyimide layer on the substrate;
The solvent contained in the polyamic acid solution contains at least one selected from solvent group A consisting of 4-methyl-2-pentanone, cyclohexanone and tetrahydrofuran, and N-methyl-2-pyrrolidone,
In the solvent contained in the polyamic acid solution, at least one selected from the solvent group A is contained in an amount of 3% by weight to 30% by weight with respect to the total solvent contained in the polyamic acid solution,
And the manufacturing method of the polyimide laminated body whose viscosity of the said polyamic-acid solution is 1.0 Pa * s or more and 20.0 Pa * s or less.   2. The polyimide laminate according to claim 1, wherein a weight ratio of N-methyl-2-pyrrolidone and a solvent included in the solvent group A is 85:15 to 95: 5 in the solvent contained in the polyamic acid solution. Body manufacturing method.   The polyimide lamination according to claim 2, wherein the weight ratio of N-methyl-2-pyrrolidone and the solvent included in solvent group A is 90:10 to 95: 5 in the solvent contained in the polyamic acid solution. Body manufacturing method.   The manufacturing method of the polyimide laminated body of any one of Claims 1-3 whose solvent chosen from the said solvent group A is 4-methyl-2-pentanone. A method for producing a polyimide laminate comprising a polyimide layer and a substrate,
A step of applying a polyamic acid synthesized from tetracarboxylic dianhydride and a diamine, and a polyamic acid solution containing a solvent on a substrate, and forming a polyimide layer on the substrate;
The solvent contained in the polyamic acid solution contains xylene and N-methyl-2-pyrrolidone,
In the solvent contained in the polyamic acid solution, the weight ratio of N-methyl-2-pyrrolidone to xylene is 85:15 to 95: 5,
And the manufacturing method of the polyimide laminated body whose viscosity of the said polyamic-acid solution is 1.0 Pa.s or more and 20.0 Pa.s or less.   The manufacturing method of the polyimide laminated body of any one of Claims 1-5 whose solid content concentration of the polyamic acid in the said polyamic-acid solution is 10 to 20 weight%.   The method for producing a polyimide laminate according to claim 1, wherein the polyamic acid is modified with alkoxysilane.   The tetracarboxylic dianhydride constituting the polyamic acid is 50% or more of 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride according to any one of claims 1 to 7. The manufacturing method of the polyimide laminated body of description.   The method for producing a polyimide laminate according to any one of claims 1 to 8, wherein 50% or more of the diamine constituting the polyamic acid is selected from paraphenylenediamine and 1,4-cyclohexanediamine.   The manufacturing method of the polyimide laminated body of any one of Claims 1-9 whose linear expansion coefficient of the polyimide layer of the said polyimide laminated body is -10 ppm / K or more and 20 ppm / K or less. The process of forming an electronic element in the polyimide layer in the polyimide laminated body obtained with the manufacturing method of the polyimide laminated body of any one of Claims 1-10,
Peeling the polyimide layer on which the electronic element is formed from the substrate;
A method for manufacturing a flexible display substrate.