JPH09288814A - Polyester film for floppy disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of surface defects in a film forming process and working processes such as a magnetic layer applying by giving specific surface roughness and friction coefficient between films with each other to the film for a high density floppy disk having thin film thickness and smooth surface. SOLUTION: The film is made of a polyester resin which has 0.05 to 1.0wt.% particles of >=0.05 to <1.0μm average grain size and substantially contains no particles of >=1.5μm average grain size and, further, the film has 25 to 70μm thickness, 4 to 12nm center line average surface roughness (Ra) on both film surfaces, 0.55 to 0.8 static friction coefficient and 0.35 to 0.53 dynamic friction coefficient between the films.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for a floppy disk, and more particularly to a polyester film for a high density floppy disk which has a thin film and has a smooth surface, but which is free from surface defects.

[0002]

2. Description of the Related Art With the recent spread of personal computers and the like, floppy disk drive devices and floppy disks as storage devices have become widespread.
Increasing the capacity and density of floppy disks is also progressing in parallel. Floppy disks are coated with a magnetic layer on a biaxially stretched polyester film for smoothing,
It is generally manufactured by punching into a disk shape,
An easy adhesion layer is often provided in advance for coating the magnetic layer.

For high density recording of a floppy disk, it is important to reduce the recording error caused by the disk body, but a large part of the recording error caused by the disk is caused by the surface defect of the biaxially stretched polyester film as a support. There is something to do. The surface defects include scratches on the film surface, wrinkles, and deformation such as winding marks when the film is wound into a roll, and these occur during film formation and during floppy disk production. Therefore, a floppy disk manufacturer often requires a polyester film as an easy-adhesion layer for the magnetic layer for the purpose of reducing the number of manufacturing steps and reducing the chance of surface defects. On the other hand, this also has the effect of reducing manufacturing costs. In addition to this, the foreign matter in the film may become a surface defect.

In the past, the film thickness for floppy disks was standardized to 75 μm, but with such a thickness, the rigidity of the film is so high that the wrinkles and film deformation as described above are less likely to occur and surface defects are caused. Was able to be kept at a practical level. In addition, at the recording density of the 3.5-inch type floppy disk which is most popular at present, as the particles to be contained in the polyester for forming the surface, in addition to the relatively small particles as the main component, the average particle size called spike particle is 1 It was allowed to add fairly large particles of the order of 0.5 μm. This was also advantageous in terms of the occurrence of scratches on the film surface.

[0005]

A method recently proposed as a high density recording method for a floppy disk utilizes the flexibility of the floppy disk in recording / reproducing of a magnetic head in order to enable high speed writing / reading. ,
The film thickness is required to be 70 μm or less, further 65 μm or less, instead of the conventional 75 μm. 65 μm
In the case of, the thickness is reduced by about 15% or more,
Considering that the rigidity of the film is proportional to the cube of the thickness of the film, the rigidity is reduced by at least 40%, which is important in the new magnetic recording method, but it is important in the film forming and processing steps. There was a problem that the occurrence of deformation such as wrinkles and winding marks of the film markedly increased. Further, the surface roughness is of course required to be smoothed, and the addition of inorganic particles having a large particle size is not allowed, which is disadvantageous in terms of scratches on the film surface.

[0006] The present invention has found from such a study on the problems of the prior art that a film having a low degree of rigidity and a smooth surface with few surface defects can be obtained by giving a specific friction coefficient to the film. It is an object of the present invention to stably provide a film that meets the requirements for a base film for high density recording floppy disks.

[0007]

To this end, the polyester film for a floppy disk of the present invention contains 0.05 or more particles having an average particle size of 0.05 μm or more and less than 1.0 μm.
To 1.0% by weight, and particles having an average particle size of 1.5 μm or more are made of a polyester resin which is substantially not contained, have a thickness of 25 to 70 μm, and have a center line average surface roughness (Ra) of 4 on both sides of the film. -12 nm, static friction coefficient between films is 0.55-0.8, dynamic friction coefficient is 0.35-0.53
It is characterized by being.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The polyester resin constituting the biaxially oriented polyester film of the present invention is a substantially linear polyester having a main acid component and a glycol component as aromatic dicarboxylic acid and aliphatic glycol, respectively. Examples of the aromatic dicarboxylic acid component include terephthalic acid, naphthalene dicarboxylic acid, isophthalic acid, diphenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid and diphenyl ketone dicarboxylic acid. Examples of the aliphatic glycol include ethylene glycol,
Trimethylene glycol, tetramethylene glycol,
Examples include polymethylene glycol having 2 to 10 carbon atoms such as hexamethylene glycol and alicyclic glycols such as cyclohexanedimethanol. Of these polyesters, polyethylene terephthalate, polyethylene-2,6-naphthalate, or all dicarboxylic acid components and all glycol components are 80 mol% or more of terephthalic acid and / or 2,6-naphthalenedicarboxylic acid and ethylene glycol. Copolyesters are preferred. In addition to the above components, the acid component and the glycol component each of which can be copolymerized in an amount of less than 20 mol% include, as the acid component, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and fats such as cyclohexane-1,4-dicarboxylic acid. There are cyclic dicarboxylic acids and the like, and glycol components include polyalkylene glycols such as polyethylene glycol, polypropylene glycol and polytetramethylene glycol, and aromatic diols such as hydroquinone. The above polyester can be produced by a known method,
The intrinsic viscosity (measured as a solution in o-chlorophenol at 25 ° C.) of 0.5 to 1.0 is preferable.

The polyester resin used in the present invention contains particles having an average particle size of 0.05 μm or more and less than 1.0 μm of 0.0
5 to 1.0 wt% is contained, and particles having an average particle size of 1.5 μm or more are not substantially contained. Externally added particles are preferable as the particles, and it is not preferable to use these as the main particles because it is difficult to control the particle size of the internally precipitated particles. Externally added particles include monodisperse particles or agglomerated particles such as calcium carbonate, colloidal silica, agglomerated silica, alumina, and organic particles. From the viewpoint of reproducibility of surface roughness, reduction of coarse protrusions, etc., it is preferable that colloidal silica and organic particles among the monodisperse particles are contained as main particles, and spherical particles are more preferable.
Further, particles having different particle diameters may be combined and added (for example, colloidal silica and calcium carbonate, organic particles and alumina), and the organic particles include crosslinked divinylbenzene particles and silicone particles. The average particle diameter of the particles contained is 0.05 μm or more and less than 1.0 μm, preferably 0.1 μm to 0.8 μm, more preferably 0.1 to 0.8 μm.
If it is less than 0.05 μm, the slipperiness of the surface is not sufficient, and if it is 1.0 μm or more, the recording output decreases, which is not preferable. The content is appropriately selected within the range of 0.05 to 1.0% by weight in order to obtain a predetermined surface roughness. It is preferably 0.07 to 0.7% by weight, more preferably 0.
1 to 0.5% by weight. Further, in the present invention, in order to deal with the thinning of the magnetic layer in accordance with high density recording, particles having an average particle size of 1.5 μm or more, preferably 1.2 μm, more preferably 1.0 μm or more are substantially contained. Not done.
Here, "not substantially contained" is set to be less than 0.05% by weight.

Since the polyester film of the present invention is for a high density floppy disk as described above, it has a thickness of 2
5 to 70 μm, preferably 25 to 65 μm, and the center line average surface roughness (Ra) on both surfaces of the film is 4 to 12 nm, preferably 6 to 10 nm. These satisfy the demands for a high-density recording system, and if the film thickness is less than 25 μm, the rigidity of the disk is extremely low, and if it exceeds 70 μm, the flexibility of the film becomes insufficient in recording / reproducing with a magnetic head, which is not preferable. Also, the surface roughness is 4 nm
If it is less than 1, scratches are likely to occur during film production, and 1
If it exceeds 2 nm, the recording output is lowered, which is not preferable. The center line average surface roughness means the value measured on the surface of the easy-sliding layer when the later-described easy-sliding layer is laminated on the film surface.

The static friction coefficient between the films of the biaxially oriented polyester film of the present invention is 0.55 to 0.80, preferably 0.60 to 0.75. Dynamic friction coefficient is 0.3
It is 5 to 0.53, preferably 0.40 to 0.50.
Regarding a floppy disk film having a low rigidity and a smooth surface, it is necessary to set the friction coefficient within a specific range in order to prevent surface defects in the film forming step and the magnetic layer processing step. Greater than the range of
Wrinkles and scratches are likely to occur on the film during running on a roll or winding into a roll in the process. On the other hand, when the film is smaller than the range of the present invention, deviation or vibration is likely to occur when the film runs, causing wrinkles or scratches.

In the polyester film of the present invention, a slipping layer containing monodisperse particles may be laminated on the film surface in order to control the friction coefficient. The average particle size of the monodisperse particles is preferably 0.03 to 0.3 μm, and the content is 1.0 × 10 ⁵ particles / mm ^{2 to} 1.0 × 10 ⁸ particles / mm.
² is preferred. If you try to obtain the necessary friction coefficient only with particles added to the polyester resin, many particles will be buried in the film, so the average particle size will be large and the amount added will be large, and large protrusions may be formed. On the other hand, since the particles added to the easy-sliding layer are aligned on the interface of the polyester resin, even if the average particle size is small, it is effective in the easy-sliding property. However, the monodisperse particles are 1.0 × 10 ⁵ particles / mm ²
If it is less than 1.0, the spacing between the monodisperse particles becomes too wide, and the effect of preventing blocking is weakened, which is not preferable, and if it is more than 1.0 × 10 ⁸ particles / mm ² , aggregation of particles tends to occur. This is not preferable because it causes the particles to fall off and causes the formation of coarse protrusions. The monodisperse particles include calcium carbonate, colloidal silica, alumina, organic particles, and the like, and it is preferable that the main particles include colloidal silica and organic particles. The monodisperse particles are preferably spherical particles, and more preferably particles having a spherical ratio of 1.0 to 1.3. Further, particles having different particle sizes may be added in combination (for example, colloidal silica and calcium carbonate, organic particles and alumina, etc.). Examples of the organic particles include crosslinked divinylbenzene particles and silicone particles.

Examples of the resin used for the easy-slip layer include resins of various systems such as polyester, acryl, urethane, nylon and the like, and mixtures thereof. However, since the magnetic layer is laminated on the easy-slip layer. It is preferable that the resin has easy adhesion, and polyester resin, particularly water-soluble polyester resin is preferably used. As the water-soluble polyester, a sulfonate group-containing polyester is typical,
It is a polyester resin in which a sulfonate group is introduced into the molecule by a component such as 5-Nasulfoisophthalic acid, 5-ammoniumsulfoisophthalic acid, 5-Ksulfoisophthalic acid, and 4-Nasulfoisophthalic acid. The polyvalent carboxylic acid component having a sulfonate group is 3 to 50 mol%, preferably 5 to 25 mol% of the total polyvalent carboxylic acid component.
included. Other polyvalent carboxylic acid components include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexane-1,4-dicarboxylic acid, adipic acid, sebacic acid, trimellitic acid and pyromellitic acid. As the glycol component, ethylene glycol, 1,4-butanediol, diethylene glycol,
Dipropylene glycol, hexamethylene glycol,
Examples include cyclohexanedimethanol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like. The polyester resin used for the easy-slip layer preferably has a glass transition point of 40 ° C. or higher. Since the film is heated in both the film forming step and the magnetic layer coating step, the resin having a low glass transition point causes the easy-slip layer to stick to the in-process roll, which may cause wrinkles.

The biaxially oriented polyester film of the present invention can be produced from the above polyester by a known method. The polyester melted by the extruder is extruded in a sheet form from a die, cooled and solidified on a cooling drum, then subjected to sequential stretching or simultaneous biaxial stretching, and after heat setting, wound into a biaxially oriented film. In these production processes, the physical properties of the film are adjusted by appropriately selecting the conditions such as the stretching ratio and stretching temperature in the machine and transverse directions, the heat setting temperature, and the relaxation operation in the machine and transverse directions.

As the method for laminating the easy-slip layer of the present invention, a method of preparing an aqueous coating agent and applying it in the film forming step, a method of coextrusion, a method of forming an organic solvent-based coating agent Although there is a method of applying the coating offline, an aqueous coating method is the most preferable in view of the thickness of the easy-slip layer, the characteristics of the resin, the addition of monodisperse particles, the productivity and the like. As a method for preparing an aqueous coating agent, there are a method of completely dissolving a resin in water, a method of forming an emulsion and a suspension using an emulsifier, a dispersant and the like. At this time, it is preferable to add the monodisperse particles, and therefore it is preferable that the monodisperse particles are also prepared as an aqueous dispersion liquid. A surfactant (anionic type or nonionic type) may be added to the water-based coating agent in order to improve the wettability to the film during coating. The application of the aqueous coating agent needs to be performed before the orientation and crystallization of the polyester film are completed.For example, in the sequential biaxially stretched film forming step, the film is applied to the film after longitudinal stretching, and lateral stretching and heat setting are performed. A general method is to obtain improved adhesion between the easy-adhesion layer and the film body during the time. As a coating method, a gravure coating method, a roll coating method, a Mayer bar method, or the like is used, and a method of improving wettability by a corona treatment or the like on a film surface before coating may be adopted.

[0016]

[Physical property measuring method and effect evaluating method] The characteristic value measuring method and effect evaluating method of the present invention are as follows.

(1) Film surface roughness (center line average surface roughness Ra, maximum height Rt) Using a stylus type surface roughness meter manufactured by Kosaka Laboratory Ltd., stylus load 80 mg, measuring length 4mm, cutoff 0.25mm
It measured on condition of. The definitions of Ra and Rt are given, for example, in Jiro Nara "Measurement / Evaluation Method of Surface Roughness" (General Technology Center, 1983).

(2) Coefficient of static friction and coefficient of dynamic friction Two pieces of cut film samples each having a size of 75 mm (width) × 100 mm (length) were placed on top of each other, and a load (W) of 200 g in weight was applied to the upper film to 150 mm / min. Sliding at a speed, the coefficient of static friction (μ
The dynamic friction coefficient (μd) is calculated from the force (Fd) when sliding s).

Μs = Fs (g) / W (g), μd = F
The d (g) / W (g) film is conditioned at 23 ° C. and 65% RH for 24 hours.

(3) Average Particle Size and Content of Particles in Film The average particle diameter of the particles is observed with a transmission electron microscope (TEM) at a magnification of 100,000 times or more. T
The section thickness of EM is about 100 nm, and the location is changed to 10
Measure 0 fields or more. The aggregated particles are the average value of the equivalent circle equivalent diameters of the aggregates and the monodisperse particle diameters of the monodisperse particles.

The content of particles is such that the polyester dissolves,
A solvent that does not dissolve the particles is selected, the particles are centrifuged from the polyester, and the ratio (% by weight) to the total weight of the particles is taken as the particle content. In some cases, the combined use of infrared spectroscopy is also effective.

(4) Particle Size, Content, and Spherical Ratio of Monodisperse Particles in Easy Sliding Layer The surface of the film on which the easy sliding layer is laminated is observed by a scanning electron microscope (SEM).
The maximum diameter and the minimum diameter were measured for each particle, and the particle diameter of each particle was determined as the average of the maximum diameter and the minimum diameter. 10
The particle size of 0 or more particles was measured, and the average value thereof was defined as the particle size of the monodisperse particles. Further, the number of particles was counted from the SEM photograph, and the number of particles per unit area was calculated as the content. The ratio of the maximum diameter / minimum diameter of each particle was determined for 100 or more particles, and the average thereof was used as the spherical ratio.

(5) Evaluation of Film Surface Defects Scratches on the film surface were visually inspected under transmitted light and reflected light. Regarding the confirmed scratches, the scratch height (or depth) was measured with a three-dimensional roughness meter. The film was visually inspected for wrinkles and deformation due to winding tightness under the same illumination.

[0024]

Next, embodiments of the present invention will be described based on examples.

Example 1 (Preparation of aqueous coating composition) 87 mol% terephthalic acid, 5-Na
Sulfoisophthalic acid 13 mol%, ethylene glycol 1
Polyester powder (glass transition point 52 ° C.) in which a polymer obtained from 100 mol% and polyethylene glycol having a molecular weight of 1000 were mixed in a weight ratio of 85:15 was heated and dissolved in water to give an average particle diameter of 0.08 μm. A spherical colloidal silica having a spherical ratio of 1.3 was added and dispersed to prepare an aqueous coating material having a solid content concentration of 5.0% by weight (particle concentration 1.0% by weight).

(Production of biaxially oriented polyester film)
As a film base, polyethylene terephthalate (polymerization catalyst: magnesium acetate 0.
10% by weight, antimony trioxide 0.03% by weight, and dimethylphenylphosphonate 0.35% by weight as a phosphorus compound were used), and colloidal silica having an average particle diameter of 0.2 μm was added and mixed to 0.3% by weight. After vacuum drying (5 Torr) the raw material pellets at 180 ° C. for 7 hours,
It was fed to an extruder and melted at 280 ° C.

After the molten polymer was filtered with high precision, it was extruded into a sheet form from a die, wound around a casting drum having a surface temperature of 25 ° C., cooled and solidified to form an unstretched film. This unstretched film was stretched 3.3 times in the longitudinal direction at 85 ° C. Next, both sides of the film were subjected to corona discharge treatment, and the above-mentioned aqueous coating agent was applied to both sides by the Mayer bar coating method so that the same coating amount was applied. Then, using a stenter, 105
Stretched 3.5 times in the width direction at ℃, and then heat set at 215 ℃ for 10 seconds under constant length. At 150 ℃, 3.0% in the transverse direction.
Relaxation treatment was performed to obtain a biaxially oriented polyester film having a thickness of 62 μm. The obtained film has a center line average surface roughness (Ra) of 8 nm and a static friction coefficient between films of 0.6.
2. The dynamic friction coefficient was 0.43, and the content of monodisperse particles in the easy-slip layer was 2.1 × 10 ⁷ particles / mm ² .

Next, the film is set to a width of 500 mm and a length of 1000.
The roll was slit on m at a winding tension of 10 kg / m and wound on a 6-inch paper core to form 10 rolls. Each roll was inspected for surface defects, but no scratches, wrinkles, or the like were found on all 10 rolls.

Example 2 0.15% by weight of cross-linked divinylbenzene particles having an average particle size of 0.25 μm and a spherical ratio of 1.3, and calcium carbonate having an average particle size of 0.8 μm were used as the additive particles of the polyester for the film base. A 62 μm-thick film was obtained in the same manner as in Example 1 except that the raw materials added and mixed to 0.02% by weight were used and the aqueous coating agent was not applied. The obtained film had a center line average surface roughness (Ra) of 9 nm, a coefficient of static friction between films of 0.68, and a coefficient of dynamic friction of 0.49.

Next, the same slits as in Example 1 are formed and 10
I made a roll of books. Each roll was inspected for surface defects, but no scratches, wrinkles, or the like were found on all 10 rolls.

Example 3 (Preparation of aqueous coating composition) 85 mol% terephthalic acid, 5-Na
Sulfoisophthalic acid 15 mol%, ethylene glycol 1
A polyester powder (glass transition point 67 ° C.) obtained from 100 mol% was dissolved in water by heating to give an average particle diameter of 0.15 μm.
m, spherical cross-linked divinylbenzene particles having a spherical ratio of 1.3 were added and dispersed to obtain a solid content concentration of 4.0% by weight (particle concentration 1.
0% by weight) aqueous coating was prepared.

(Production of biaxially oriented polyester film)
Crosslinked divinylbenzene particles having an average particle size of 0.25 μm were used as the additive particles of the polyester for the film base.
By the same method as in Example 1 except that the components were added and mixed so as to be 15% by weight, and the components of the aqueous coating composition were different.
A film having a thickness of 62 μm was obtained. The obtained film has a center line average surface roughness (Ra) of 7 nm, a coefficient of static friction between films of 0.72, a coefficient of dynamic friction of 0.50, and the content of monodisperse particles in the easy-sliding layer is 0.8 ×. It was 10 ⁷ pieces / mm ² .

Next, the same slits as in Example 1 are formed and
I made a roll of books. Each roll was inspected for surface defects, but no scratches, wrinkles, or the like were found on all 10 rolls.

Example 4 A film having a thickness of 32 μm was obtained by using the same raw materials and method as in Example 1 except that the aqueous coating agent was not applied.
The obtained film has a center line average surface roughness (Ra) of 9 n.
m, the static friction coefficient between the films was 0.72, and the dynamic friction coefficient was 0.51.

Next, the same slits as in Example 1 are formed and
I made a roll of books. Each roll was inspected for surface defects, but no scratches, wrinkles, or the like were found on all 10 rolls.

Comparative Example 1 As a polyester resin for a film base, a raw material prepared by adding and mixing colloidal silica having an average particle diameter of 0.2 μm to 0.09% by weight was used, and an aqueous coating agent was not applied. A 62 μm biaxially stretched film was formed by the same method. The obtained film has a center line average surface roughness (R
a) is 5 nm, the coefficient of static friction between films is 0.84,
The dynamic friction coefficient was 0.68.

Next, the same slits as in Example 1 are formed and
I made a roll of books. When the surface defects of each roll were inspected, scratches were found on 5 rolls, and wrinkles were formed on 3 rolls.

Comparative Example 2 (Preparation of aqueous coating agent) 87 mol% terephthalic acid, 5-Na
Sulfoisophthalic acid 13 mol%, ethylene glycol 1
A polymer powder (glass transition point 52 ° C.) in which a polymer obtained from 100 mol% and polyethylene glycol having a molecular weight of 1000 were mixed in a weight ratio of 85:15 was heated and dissolved in water to obtain a solid content concentration of 5.0 weight. % Aqueous coating was prepared.

(Production of biaxially oriented polyester film)
A 62 μm biaxially oriented polyester film was obtained in the same manner as in Example 1 except that the coating thickness of the Mayer bar was increased in application of the aqueous coating agent so that the coating thickness was about 3 times that in Example 1. The obtained film has a center line average surface roughness (Ra) of 7 nm and a static friction coefficient between the films of 0.
81, and the coefficient of dynamic friction was 0.59.

Next, the same slits as in Example 1 are formed and
I made a roll of books. When surface defects of each roll were inspected, it was confirmed that two rolls had scratches and wrinkles were formed on the two rolls. The roll also showed a blocking tendency.

[0041]

INDUSTRIAL APPLICABILITY According to the present invention, in a film for a high-density floppy disk which is thin and has a smooth surface, by giving a specific surface roughness and a coefficient of friction between films, a film forming process and a magnetic layer coating process are performed. It is possible to prevent surface defects from being generated in the process.

Claims (3)

[Claims] 1. A polyester resin containing 0.05 to 1.0% by weight of particles having an average particle size of 0.05 μm or more and less than 1.0 μm, and substantially not containing particles having an average particle size of 1.5 μm or more. The thickness is 25 to 70 μm, the center line average surface roughness (Ra) on both sides of the film is 4 to 12 nm, the static friction coefficient between the films is 0.55 to 0.8, and the dynamic friction coefficient is 0.35 to 0.53. A polyester film for floppy disks, which is characterized by being present. 2. The polyester film for a floppy disk according to claim 1, wherein an easy-slip layer containing monodisperse particles having an average particle diameter of 0.03 μm or more and 0.3 μm or less is laminated on both surfaces of the film. 3. A slippery layer mainly comprising a sulfonate group-containing polyester resin having a glass transition point of 40 ° C. or higher is laminated on both surfaces of the film.
Polyester film for floppy disks.