JP2002210765A - Solution forming film low in generation frequency of pinholes and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film not generating pinholes, which is a problem peculiar to solution film forming, in its surface and a method for manufacturing the same. SOLUTION: The solution forming film low in the generation frequency of pinholes is characterized by that the thickness of the product film measured by an electronic microthickness meter is not more than 5 μm and the number of pinholes of 100 μm or more in the product film is 1 or less per 1,000 m2. In manufacturing the solution film, the temperature Tatm of an atmosphere coming into contact with the solvent of a polymer solution and the temperature Tex of a solvent exhaust port satisfy Tex-100<=Tatm<=Tex-1 [ deg.C] and the region L up to the exhaust port immediately after casting is set to 10<=L<=1,000 [cm] and, thereafter, the solution forming film is manufactured through a wet process and stretching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a solution casting film formed by casting a polymer solution on a support, and
After forming into a film, the film is introduced into the wet process,
The present invention relates to a method for producing a solution casting film having a step of transporting a film.

[0002]

2. Description of the Related Art In general, a film is formed when an organic polymer which is in a molten state at a temperature higher than its melting point is discharged from a die as a molten film. However, polymers having a melting point close to the decomposition temperature, or a melting point higher than the decomposition temperature, are decomposed simultaneously with melting, so the polymer is dissolved in an appropriate solvent, and the obtained polymer solution is cast on a support, and then The film is formed by a solution casting method for removing the solvent. Examples of the polymer formed by solution casting include cellulose, vinyl acetate, aromatic polyamide, aromatic polyimide, and the like. For example, para-aromatic polyamide films have been used in the field of magnetic recording, etc., taking advantage of their heat resistance and high rigidity. Higher functions are required by improving quality.

[0003] In the dry-wet method, a polymer solution cast on a support is stripped from the support after removing the solvent until it has a self-holding property, and is introduced into a wet process. Here, the ionic inorganic compound and impurities contained in the film are removed, and the film is obtained through various steps (an example of an aromatic polyamide is disclosed in JP-A-4-139229). In the wet method, a polymer solution cast on a support is immersed in water together with the support, solidified, then separated from the support, introduced into a water tank, and then subjected to various steps to obtain a film ( An example of the aromatic polyamide is described in JP-A-2-28222.)

[0004] However, with the demand for pinhole improvement becoming particularly strong along with the demand for thinning and stable supply, a problem inherent in the production of a solution casting film in which holes (pinholes) tend to be formed on the surface of the film. And the problem that the yield decreases in the subsequent coating process.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems that have become apparent due to thinning and the like, and to obtain a stable workability in a subsequent coating or vapor deposition step, and to reduce the frequency of pinhole occurrence. An object of the present invention is to provide a solution casting film such as an aromatic polyamide film and a method for producing the same.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, a solution casting film having a low pinhole occurrence frequency according to the present invention has a product film thickness of 5 μm or less measured by an electronic micro thickness gauge, It is characterized in that the number of pinholes of 100 μm or more in the product film is 1 or less per 1000 m ² . As a solution casting film,
Particularly, an aromatic polyamide film is preferable.

Further, in the method for producing a solution casting film according to the present invention, the polymer solution is cast on a support and formed into a film, and then the film is introduced into a wet process and the film is transported. The region L from immediately after casting to the exhaust port satisfying the relationship of Tex-100 ≦ Tatm ≦ Tex-1 [° C.] .Ltoreq.L.ltoreq.1000 [cm] A method characterized by being present.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with preferred embodiments. The film referred to in the present invention is a solution containing a polymer and a solvent as main components, which is cast on a support from a die, introduced into a wet process after peeling from the support, and an ionic inorganic compound contained in the film. This is a solution casting film that is formed through various steps after the impurities are removed and, if necessary, stretched in the longitudinal direction. The type of the solvent is not particularly limited as long as it dissolves the polymer. The concentration of the polymer in the solution depends on the type of the polymer, but is generally 4 to 40% by weight. In the solution, a lubricant, a plasticizer, conductive particles, Antioxidants and other additives may be blended.

The polymer to which the method for producing a solution casting film of the present invention is applied is not particularly limited, but is preferably aromatic polyamide, aromatic polyimide, polyarylate, or the like.
Examples include polycarbonate, cellulose polymers such as cellulose diacetate and cellulose triacetate, vinyl acetate, polyvinyl alcohol, and the like, with aromatic polyamide being particularly preferred.

The thickness of the solution casting film according to the present invention is 5 μm or less, preferably 4.5 μm or less, and more preferably 4.5 μm or less, from the viewpoint of satisfying the demand for higher density and smaller size of the magnetic recording medium. Is in the range of 4.4 μm or less, and particularly in producing such a thin film, a pinhole is easily generated due to air mixing or the like in a gap between the cast polymer and the support, and the effect of the present invention is large. .

When the film according to the present invention is used as a base film in a magnetic recording medium, the base material film preferably has a tensile Young's modulus of at least 800 kg / mm ² , more preferably 900 kg / mm ^2. It is more preferably 1000 kg / mm ² or more. By setting the tensile Young's modulus to such a value, it becomes possible to withstand the tension applied during the formation of the magnetic recording medium such as the step of forming the coating layer or the vapor deposition layer and the step of forming the back coat layer, which is advantageous in terms of processing and is therefore desirable. .

In a magnetic recording medium using the film according to the present invention, if the Young's modulus of at least one direction of the base film is 800 kg / mm ² or more, the base film is tensilized or width-wise in the longitudinal direction. It can be tensilized in any direction. The degree of tensilization is not particularly limited, but taking into account properties such as elongation and tear resistance, the tensile Young's modulus in the longitudinal direction Emd and the tensile Young's modulus in the width direction Etd are 0.5 ≦ Emd / Etd ≦ 2. It is practical to be in the range.

The elongation in at least one direction of the base film in the magnetic recording medium is preferably at least 10%, more preferably at least 20%, further preferably at least 30%. This allows the tape to have an appropriate flexibility.

The moisture absorption of the base film in the magnetic recording medium is preferably 5% or less, more preferably 3% or less, and further preferably 2% or less. This allows
Dimensional change of the tape due to humidity change is small and good electromagnetic conversion characteristics can be maintained.

Further, from the viewpoint of preventing meandering and good workability in the step of forming a magnetic layer, it is required that the one-sided elongation of the base film of the magnetic recording medium having a width of 1000 mm and a length of 10 m is ± 40 mm or less. Preferably, it is more preferably ± 30 mm or less, and still more preferably ± 20 mm or less.

Further, in the base film of the magnetic recording medium, the strength F-5 value of the film when the film is stretched by 5% in the width direction of the base film is 250 kg /.
mm ² or more. More preferably 280 kg / m
m ² or more, more preferably 320 kg / mm ² . By having such an F-5 value, it is possible to withstand the tension applied to the magnetic recording medium in the steps of forming the magnetic layer and forming the back coat layer, which is advantageous in processing.

The method for producing a solution casting film of the present invention comprises:
An aromatic polyamide film will be described as an example, but the present invention is not limited to this.

When the aromatic polyamide polymer is obtained from acid chloride and diamine, N-methylpyrrolidone (NM
It is synthesized by solution polymerization in an aprotic organic polar solvent such as P), dimethylacetamide (DMAc), or dimethylformamide (DMF), or by interfacial polymerization using an aqueous medium. When acid chloride and diamine are used as monomers in the polymer solution, hydrogen chloride is produced as a by-product.Therefore, inorganic neutralizers such as calcium hydroxide, calcium carbonate, and lithium carbonate, and ethylene oxide, propylene oxide, ammonia, and triethylamine Organic neutralizing agents such as triethanolamine and diethanolamine are used. When an aromatic polyamide polymer is produced by a reaction between an isocyanate and a carboxylic acid, the production is carried out in an aprotic organic polar solvent in the presence of a catalyst.

These polymer solutions may be used directly as a film forming stock solution, or the polymer may be isolated once and then redissolved in the above organic solvent or an inorganic solvent such as sulfuric acid to prepare a film forming stock solution. Is also good.

In order to form fine irregularities on the surface of the film, it is preferable to add particles. The method of adding the particles is, for example, a method in which the particles are sufficiently slurried in a solvent in advance and then added as a solvent for polymerization or a solvent for dilution, or a method in which the particles are directly added after preparing a stock solution for film formation, but are not particularly limited.

In the film forming solution, inorganic salts such as calcium chloride, magnesium chloride, lithium chloride,
In some cases, lithium nitrate or the like is added. Although a higher polymer concentration in the film forming solution leads to an improvement in productivity, it is preferably 4 to 40%.

The stock solution thus prepared is formed into a film by a so-called solution casting method. In the solution casting method, the casting solution is cast on a support such as an endless belt or a drum, and then dried, peeled, and dried. Wet method with heat treatment after solvent extraction, drying on support,
There are a dry-wet method in which the film is introduced into the wet process after peeling, and a semi-dry semi-wet method in which the support is dried and then introduced into the wet process together with the support. Is preferably applied to a dry-wet method or a semi-dry semi-wet method, but the dry-wet method will be described here as an example.

When a film is formed by a dry-wet method, the solution is first extruded from a die onto a support such as a drum or an endless belt to form a thin film. Next, the solvent is scattered from the thin film layer and dried until the thin film has self-holding property. The solution film thus cast on the support is dried by a method such as hot air, heating of the support or infrared heating to remove the solvent. Drying conditions are from room temperature to the boiling point of the solvent + 20 ° C, 60
Minutes, preferably in the range of room temperature to the boiling point of the solvent. In addition, a region satisfying Tex-100 ≦ Tatm [° C.] ≦ Tex-1, preferably a region L from immediately after casting that satisfies Tex-30 ≦ Tatm ≦ Tex-10 to an exhaust port is 10 ≦ L [cm] ≦ It is preferably present in the range of 1000, more preferably in the range of 20 ≦ L [cm] ≦ 200. Further, the displacement of the solvent is preferably 0.2 vol% or less, more preferably 0.1 vol% or less, based on the total displacement.

The film after the above-mentioned dry process is peeled from the support and introduced into the wet process, where the solvent and impurities contained in the film are removed. This bath is generally composed of an aqueous medium, and may contain an organic solvent, an inorganic salt or the like in addition to water. Generally, the water content is 30%
Or more, preferably 50% or more, and the bath temperature is usually
Used at 0-100 ° C.

In this wet process, the exfoliated film is immersed in such a bath under tension and the inorganic compounds in the film are extracted until it is less than 0.1%, preferably less than 0.05%. In this wet process, the film is conveyed through a nip roll at the bath port and a roll in the bath.
The film that has passed through the wet process is further dried and heat-treated to form a film. The temperature at that time is 200-450 ° C
And the time is 20 seconds or more and 20 minutes or less.

The film thus formed may be stretched during the film forming process for the purpose of improving mechanical properties. The stretching ratio is a value obtained by dividing the winding speed by the casting speed, the longitudinal stretching ratio is 0.95 to 2.0 times, and the area ratio is 0.8 to 4.0 times (the area ratio is the area of the film after stretching. Is defined as a value obtained by dividing by the area of the film before stretching. 1 or less means relaxation.) In the range of local thickness unevenness and mechanical properties, and more preferably the longitudinal stretching ratio is 1. 05-1.5 times, area magnification 1.1-3.0.
Range of double.

The thus obtained film is wound up to obtain an aromatic polyamide product film.

[0028]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. (1) The number of pinholes of 100 μm or more in the product film roll Pin [pieces / 1000 m ² ] After exiting the wet process, transverse stretching, drying,
The number of times that ultraviolet light is irradiated from the lower part of the film obtained by the heat treatment and the relaxation and the light is received by the CCD camera through the filter that transmits only the ultraviolet light installed on the upper part of the film is converted into 1000 m ² of the product film.

(2) Number of fine pinholes (50 μm or more) contained in the product film roll Poff [pieces / 1000 m ² ] The lower part of the film is brought into contact with the metal roll, and a charge of 6.5 kV is applied from the upper part of the film. obtained by converting the number of energized per product film 1000 m ^2.

Example 1 N-methyl-2-pyrrolidone (NMP) was mixed with 2-chloroparaphenylenediamine corresponding to 85 mol% as an aromatic diamine component and 4,4-diaminodiphenyl ether corresponding to 15 mol%. Dissolve, add 99% by mole of 2-chloroterephthalic acid chloride, add colloidal silica with a diameter of 45 nm to 0.2 wt% per polymer before polymerization, and stir for 2 hours to polymerize. Completed. This is neutralized with lithium hydroxide, polymer concentration 10 wt%, intrinsic viscosity 2.6,
An aromatic polyamide solution having a solution viscosity of 3500 poise (30 ° C.) was obtained.

After passing the polymer solution through a 1 μm-cut filter, the polymer solution was cast on an endless belt made of stainless steel.
The process for obtaining the temperature m was set such that the ambient temperature Tatm was 50 ° C. and the temperature of the solvent exhaust port was Tex 65 ° C.
The ratio η of the NMP evaporation amount to the total exhaust amount was set to 0.09 vol%.

On this belt, the polymer solution was heated with hot air at 140 ° C. for 2 minutes to evaporate the solvent, and the film having self-holding property was continuously peeled off from the belt. Next, the film was introduced into a water bath at 50 ° C. to extract the residual solvent and the inorganic salts generated by the neutralization. Further, the moisture is dried and heat-treated for 30 seconds in a tenter at 245 ° C., and the thickness is reduced to 3.
A 6 μm aromatic polyamide film was obtained. During this time, the film was stretched 1.15 times and 1.45 times in the longitudinal direction and the width direction, respectively, and the ratio of the exit width of the tenter to the maximum width of the film in the tenter was set to 0.98. The film formation was very stable.

Example 2 The same polymer solution as in Example 1 was passed through a 1 μm-cut filter, cast on a stainless steel endless belt, and immediately after casting, the area L of the exhaust port became 50 cm. In the process, the ambient temperature Tatm was 33 ° C., and the temperature Tex of the solvent exhaust port was 42 ° C. The ratio η of the NMP evaporation amount to the total exhaust amount was set to 0.09 vol%. The subsequent steps are the same as in the first embodiment.

Comparative Example 1 The same polymer solution as in Examples 1 and 2 was passed through a 1 μm-cut filter, and then cast on an endless belt made of stainless steel.
In the process for obtaining the temperature m, the ambient temperature Tatm was set to 70 ° C., and the temperature Tex of the solvent exhaust port was set to 65 ° C. The ratio η of the NMP evaporation amount to the total exhaust amount was set to 0.09 vol%. The subsequent steps are:
This is similar to the first and second embodiments.

Comparative Example 2 The same polymer solution as in Examples 1 and 2 was passed through a 1 μm-cut filter, cast on an endless belt made of stainless steel, and immediately after casting, the area L of the exhaust port was 5 cm.
The ambient temperature Tatm was set to 33 ° C., and the temperature Tex of the solvent exhaust port was set to 42 ° C. The ratio η of the NMP evaporation amount to the total exhaust amount was set to 0.09 vol%. Subsequent steps are the same as in Examples 1 and 2.

Comparative Example 3 The same polymer solution as in Examples 1 and 2 was passed through a 1 μm-cut filter, and then cast on an endless belt made of stainless steel.
In the process for obtaining the temperature m, the ambient temperature Tatm was set to 33 ° C., and the temperature Tex of the solvent exhaust port was set to 140 ° C. The ratio η of the NMP evaporation amount to the total exhaust amount was set to 0.09 vol%. Subsequent steps are the same as in Examples 1 and 2.

[0037]

[Table 1]

[0038]

As described above, according to the solution casting film having a low frequency of pinhole generation and the method for producing the same according to the present invention, the pinhole which is a problem inherent to the solution casting almost does not exist on the surface of the film. As a result, it is possible to suppress roll contamination that occurs when a recording magnetic medium using the film manufactured according to the present invention is manufactured, and to expect an improvement in yield by stabilizing quality.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 7:00 B29L 7:00 C08L 77:00 C08L 77:00 F term (Reference) 4F071 AA56 AH14 BB02 BC01 BC12 BC13 4F205 AA29 AG01 AR06 AR12 GA07 GB02 GF01 GF24 GN19 GN24 GW31

Claims (4)

[Claims] 1. The product film thickness measured by an electronic micro thickness gauge is 5 μm or less, and 100 μm
A solution casting film having a low frequency of occurrence of pinholes, wherein the number of the above pinholes is one or less per 1000 m ² . 2. The solution cast film according to claim 1, wherein the solution cast film is an aromatic polyamide film. 3. After casting the polymer solution on a support to form a film, in the step of introducing the film into the wet process and transporting the film, the temperature of the atmosphere in contact with the solvent of the polymer solution and the temperature of the solvent are reduced. It is characterized in that a region L from immediately after casting to the exhaust port satisfies the relationship of Tex-100 ≦ Tatm ≦ Tex-1 [° C.] with the exhaust port temperature Tex, and 10 ≦ L ≦ 1000 [cm]. A method for producing a solution casting film. 4. The method for producing a solution cast film according to claim 3, wherein the solution cast film is an aromatic polyamide film.