JPH0219525B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved biaxially stretched balanced type base film mainly made of polyester and mainly used for magnetic recording. Traditionally, the material for magnetic recording base films is biaxially oriented and heat-set polyester, especially polyethylene terephthalate (hereinafter referred to as PET).
It is common to use a film whose main component is the balanced type, which has relatively similar biaxial orientation and mechanical properties in the vertical and horizontal directions, and the balanced type, which has relatively similar orientation in the vertical and horizontal directions and mechanical properties compared to the horizontal direction. It is classified into two types: the tensilization type, which is significantly larger. The balanced type is usually manufactured with approximately the same stretching ratio in the vertical and horizontal directions, and its strength at 5% elongation (F
-5 value) is usually below 15Kg/mm ² both vertically and horizontally, more generally below 13Kg/mm ² . On the other hand, the tensile type is manufactured by making the total stretching ratio in the vertical direction much higher than that in the horizontal direction, and the F-5 value in the vertical direction is usually over 15 Kg/ ^mm217
-20Kg/ ^mm2 in many cases. These balanced and tensilized types have advantages and disadvantages in terms of film stiffness, dimensional stability, ease of manufacture, cost, etc., and are used depending on the need, and this invention is directed to balanced films. , the upper limit of the F-5 value is specified at 15Kg/ ^mm2 . Characteristics required of base films for magnetic recording include uniformity of the magnetic agent coating layer, fine and uniform protrusions on the film surface to provide flatness, runnability that can withstand repeated use, and abrasion resistance. . These surface protrusions are generally achieved by incorporating protrusion-forming particles such as polymer insoluble matter (hereinafter referred to as internal particles) made of inorganic substances and catalyst residues into the film, but generally they are created by incorporating protrusion-forming particles such as inorganic substances and catalyst residues (hereinafter referred to as internal particles). The flatness and the fineness and uniformity of surface protrusions (hereinafter referred to as flatness) are contradictory characteristics. In the balanced type, surface protrusions are usually formed in accordance with the size and number of particles contained in the film.For example, if a large number of large particles are contained in the film, running properties are certainly improved. The surface protrusions become coarser, resulting in recording loss (dropout) on magnetic tape, decreased output,
This can cause fatal defects such as increased noise, and conversely, if fine particles are present, fine surface protrusions are formed, which may result in good tape output, dropout, etc., but poor slippage and poor running performance and abrasion resistance. The disadvantage was that it was inferior. An object of the present invention is to eliminate the contradictory drawbacks of the prior art and to provide a film that is excellent in runnability, abrasion resistance, and flatness. In order to achieve the above object, the present invention has the following configuration:
That is, it is a biaxially oriented film whose main component is polyester and whose internal particles are mixed in an amount of 0.05 to 0.5% by weight.
-5 value is 9 to 15 Kg/ ^mm2 , and by calendering during or after the stretching process, the average height of surface protrusions is 0.040μ or less, and the ratio of the average height of surface protrusions to the average diameter of internal particles is The present invention is characterized by a base film for magnetic recording, which is characterized by having a density of 5.1×10 ^-3 or less. The present invention is directed to so-called balanced type tapes with an F-5 value in the range of 9 to 15 kg/mm ^2. If this value is less than 9 kg/mm ² , the processed tape will Elongation occurs due to abnormal tension, etc., which is undesirable. The average height of surface protrusions shall be 0.04μ or less. If this height exceeds 0.04μ, the surface properties will be poor, and even if the ratio of the average height of the surface protrusions to the average diameter of the internal particles (hereinafter referred to as the roughness parameter) satisfies the range of the present invention, the running properties and wear resistance will deteriorate. It is impossible to improve both the flatness and flatness (hereinafter simply referred to as compatibility). Note that this height is preferably 0.035μ or less, more preferably 0.030μ or less, and most preferably
It is 0.025μ or less. The roughness parameter needs to be 5.1×10 ⁻³ or less, preferably 4.6×10 ⁻³ or less, and more preferably 4.1×10 ⁻³ or less. (The roughness parameter is usually about 5.3×10 ^-3 to 5.7×10 ^-3 or more for balanced types, but reducing it to 5.1×10 ^-3 or less as in the present invention is important if the surface roughness is kept the same. This means that the size of the internal particles becomes larger than before, and if the size of the internal particles is kept the same, the surface roughness becomes finer). In the present invention, the smaller this value, the higher the level of compatibility, and conversely, if it exceeds 5.1×10 ^-3 , it cannot be said that compatibility has been achieved. The film of the present invention must be a biaxially stretched polyester film that has mechanical properties suitable for use as a base film for magnetic recording. An example of manufacturing the film of the present invention will be described below. The film of the present invention is produced by melt-extruding polyester containing fine particles through a slit-shaped die to make an unstretched film, or from the unstretched film, a superdraw stretched film with substantially no orientation is produced, and then the film is Vertical,
The film is stretched 2.0 to 4.5 times in the horizontal direction at a normal stretching temperature, e.g., from the glass transition point to 170°C, to achieve biaxial orientation, and a calendering process is performed during or after these stretching steps to reduce the surface protrusions of the film. It is manufactured by pressing the film and adjusting the surface condition of the film. In particular, it is preferable to perform calender treatment during the stretching process. The polyesters used in this case are polyesters, their copolymers, and mixed polymers containing at least 70% of these polyester polymers as main components. In particular, polyester polymers include polyethylene terephthalate, polyethylene terephthalate,
Polyethylene 2.6 naphthalate is preferred. In addition, fine particles (intrinsic particles) contained in the film include CaCO ₃ , SiO ₂ ,
They may be either external particles made of inorganic substances such as Al ₂ O ₃ or calcium phosphate, or internal particles containing components such as Ca, Li, or P. Although not particularly limited, preferred particles include Ca-Li-P particles. A combination of internal and external particles is used. Incidentally, the particle diameter is preferably 2 to 8 μm as measured in a film using a dark field illumination method. Further, the amount of particles mixed is 0.05 to 0.5% by weight. The amount of contamination
If it is less than 0.05% by weight, problems will occur in runnability and durability. Furthermore, if the amount exceeds 0.5% by weight, problems will occur with tape output and dropout. The conditions for the calender treatment are preferably a roll temperature of 80 to 150°C, a linear pressure of 300 to 1000 Kg/cm, and a treatment frequency of about 1 to 5 times. As described above, the present invention is a biaxially stretched polyester film with specific values for the amount of incorporated particles, the F-5 value in the vertical and horizontal directions, the average height of surface protrusions, and the roughness parameter, so that both In other words, it has the excellent effect of improving running properties, wear resistance, and flatness, which are contradictory properties. Note that the specific values of the present invention were measured by the following method. (1) F-5 value According to ASTMD882. (2) Average height of surface protrusions Stylus type surface roughness meter specified by DIN4768
It is expressed as the average roughness Ra at a cut-off of 0.25 mm measured with HOMMEL, TESTER, and T10 types. (3) Roughness parameter Expressed as the ratio of the above Ra value to the average internal particle diameter measured by the method below. The intrinsic particle size is evaluated by melting the film into a thin film between glass preparations and rapidly cooling it, and observing particles with a diameter of 1μ or more under dark field illumination using a microscope. The magnification is 128 times, and the average diameter is expressed as the volume average diameter. Although the particle size under dark field illumination is 2.4 times larger than the original particle size under normal bright field illumination, the present invention is defined by the particle size under dark field illumination. Examples will be described in more detail below, but the present invention is not particularly limited thereto. Examples 1 to 3 and Comparative Examples 1 to 3 Inorganic kaolin (Al ₂ O ₃
2SiO ₂・2H ₂ O) particle size was adjusted to an average diameter of 1.5μ,
Three types of particle sources, 2.5μ and 3.5μ, were obtained. These were added as 0.2% by weight external particles and polymerized according to a conventional method.
A PET of [η] 0.65 was obtained. In Comparative Examples 1 to 3, these were made into balance films with a thickness of 15 μm using a vertical and horizontal stretching method. The stretching ratio was 3.4 x 3.6 times, and heat treatment was performed at 200°C. On the other hand, in Examples 1 and 2, the films of Comparative Examples 2 and 3 were passed through a calendering process at 100°C three times. In Example 3, the film of Comparative Example 2 was momentarily passed through a heat treatment roll at 260° C., and only the surface of the film was heated to soften it. In both cases, the height of the surface protrusions is smaller than in the comparative example, even though the internal particles are the same. These were coated with a 4μ magnetic layer and made into a videotape under the same conditions using a conventional method.
The quality is shown in Table 1. As is clear from the comparative examples, the conventional balance type has surface roughness depending on the internal particles, making it difficult to achieve both good runnability. On the other hand, although the surface roughness of Examples is fine, the running properties and wear resistance are maintained at a good level, making them extremely suitable as magnetic recording materials. Note that the particle size inherent in the film is usually not the same as the particle size of the powder before addition. Example 4 and Comparative Example 4 A transesterification reaction was carried out using 100 parts of dimethyl terephthalate and 70 parts of ethylene glycol using a conventional method using 0.035 parts of manganese acetate as a catalyst, and the resulting product was dissolved in 0.04 parts of antimony trioxide and ethylene glycol. After adding 0.15 parts of lithium acetate, 0.09 parts of calcium acetate, and 0.03 parts of calcium carbonate having an average powder particle size of 2.0μ uniformly dispersed in ethylene glycol, and then adding 0.13 parts of trimethyl phosphate, a polycondensation reaction was performed [η ]0.65, softening point 259.7
PET was obtained at °C. In Comparative Example 4, this PET was melt-extruded at 290° C. and made into a balance film with a thickness of 15 μm by vertical and horizontal stretching. Stretching ratio is 3.4
It was multiplied by 3.6 times and heat treated at 200°C. Note that the film contains external particles made of calcium carbonate (CaCO ₃ ) and internal particles of Ca-Li-P (formed based on thirium acetate, calcium acetate, and trimethyl phosphate). The total amount was 0.43% by weight. Example 4 was carried out in the same manner as Example 1 using Comparative Example 4. Film and tape quality are shown in Table 1. Example 5 The same raw materials as in Example 3 were melted and molded, and a linear pressure of 300 Kg/cm was applied during vertical stretching (100°C, 3.3 times).
Then, a calender treatment was applied to push the protrusions on the film surface, followed by horizontal stretching (120°C, 3.8 times) and heat treatment to obtain a film with a thickness of 15 μm. The surface condition of the obtained film will be explained based on the drawings. 1 to 3 are enlarged plan views schematically showing the uneven portions formed on the surface of the film;
Figure 4 is a sectional view taken along line A-A' in Figure 3, and points 5 to 6.
The figure is a micrograph (magnification: 6000) of the uneven part.
times). Note that 1 is a film, 2 is a depressed portion, 3 is a protrusion, 4 is a raised portion, and 5 is an uneven portion. Further, Table 1 shows the quality of the film and the quality of the tape.

[Table] Examples 6 to 11, Comparative Examples 5 to 8 The particle size of inorganic silica (SiO ₂ ) was adjusted by pulverization and classification to obtain particle sources with particle sizes of 0.8μ and 3.0μ. These were added as external particles in the amounts shown in Table 2, and polymerized according to a conventional method to obtain PET with [η] 0.65. These raw materials were melt-molded and vertically stretched (at 100°C, the stretching ratio was 3.0 times in Examples 6 to 8 and Comparative Examples 5 and 6, and 3.9 times in Examples 9 to 11 and Comparative Examples 7 and 8). linear pressure 300Kg/cm
Calender treatment is applied to push the film surface protrusions, and then horizontal stretching (at 120°C, the stretching ratio is
In Examples 6 to 8 and Comparative Examples 5 and 6, it was 3.0 times, and in Examples 9 to 11 and Comparative Examples 7 and 8, it was 3.8 times)
A film with a thickness of 15 μm was obtained by heat treatment. Table 2 shows the film quality and tape quality. Comparative Examples 5 and 7 in which the amount added was less than 0.05% by weight caused problems in running performance and durability. On the other hand, if the amount added exceeds 0.5% by weight, problems will occur with tape output and drop-out. In Comparative Example 6, the reason why the dropout worsens despite the low surface average protrusion height is presumed to be because the amount of particles added to the film increases, which makes the film more likely to be scratched. Further, in Comparative Example 8, the surface roughness increases, and the output and dropout deteriorate.

[Table] Examples 12 to 26, Comparative Examples 9 to 20 The particle sizes of calcium carbonate (CaCO ₃ ), alumina (Al ₂ O ₃ ), and calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) were adjusted by crushing and classification, The particle size is
Particle sources of 2.0, 2.25, 2.5, 2.75, 3.0, 3.25 and 3.75μ were obtained. These particle sources were added as external particles in the amounts shown in Table 3 and polymerized according to a conventional method to obtain PET with [η] 0.65. These raw materials were melt-molded, subjected to calender treatment during vertical stretching (100°C, 3.4 times), then horizontally stretched (120°C, 3.6 times), and heat treated (200°C) to produce a 15μ thick film. Obtained. Note that the presence or absence of calender treatment and the linear pressure are as shown in Table 3. These were coated with a 4μ magnetic layer and made into a videotape under the same conditions using a conventional method. Table 3 shows the film quality and tape quality. Examples 12 and 13 and Comparative Example 9 examine the influence of roughness parameters when the particle type is calcium carbonate, Examples 13 and 14 and Comparative Example 10 examine the influence of Ra, and Examples 14 to 16 and Comparison Example 11 and
12 shows the effect of the mixing amount, Examples 17 and 18 and Comparative Example 13 show the effect of the roughness parameter when the particle type is alumina, and Examples 18 and 19 and Comparative Example 14 show the effect of Ra. Examples 19 to 21 and Comparative Examples 15 and 16 show the influence of the mixed amount, and Examples 22 and 23 and Comparative Example 17 show the influence of the roughness parameter when the particle type is calcium phosphate.
Examples 23 and 24 and Comparative Example 18 investigated the influence of Ra,
Examples 24 to 26 and Comparative Examples 19 and 20 show the influence of the amount of mixture. Differences depending on particle type are small, and for any particle type, when the roughness parameter exceeds 5.1 × 10 ^-3 (Comparative Examples 9, 13, 17) ) becomes unbalanced, and when the average height (Ra) of surface protrusions exceeds 0.040 μ (Comparative Examples 10, 14, 18), tape output and dropout deteriorate. Furthermore, the amount of contamination is less than 0.05% by weight (Comparative Examples 11, 15,
19) causes problems in running and wear resistance;
When it exceeds 0.5% by weight (Comparative Examples 12, 16, and 20), tape output and dropout deteriorate. As described above, if even one of the constituent requirements of the present invention is violated, some problem will occur in the tape quality, and a well-balanced tape cannot be obtained. It is essential to use a film within the scope of the present invention.

[Table] (1) Tape output Comparative example 2 was used as a standard tape and ranked by chroma S/N. ◎ +2dB or more 〇~◎ +1.5~2dB 〇 +1.0~+1.5dB 〇~△ +0.5~+1.0dB △ 0~+0.5dB △~× −0.5~0dB × −0.5dB or less (2) Dropout The number of dropouts of 15 microseconds or longer was measured. ◎ 10 pcs/min or less 〇 10 to 20 pcs/min △ 20 to 50 pcs/min The occurrence of injuries was ranked. ◎ No scratches or eyelashes 〇 There are a few thin scratches, but they are not a problem △～〇 There are light scratches △ Many thin scratches ×～△ There are severe scratches × All the severe scratches

[Brief explanation of drawings]

1 to 3 are enlarged plan views schematically showing the uneven portions formed on the surface of the film of the present invention, and FIG. 5
-FIG. 6 is a microscopic photograph of the grain structure formed on the film surface, that is, the uneven portion. 1... Film, 2... Depression, 3... Protrusion, 4... Raised part, 5... Uneven part.

Claims (1)

[Scope of Claims] 1. A biaxially stretched film containing polyester as a main component and containing internal particles in an amount of 0.05 to 0.5% by weight, the film having an F-5 value of 9 to 15 kg in both the vertical and horizontal directions. / ^mm2 , and by calendering during or after the stretching process, the average height of the surface protrusions is 0.040 μ or less, and the ratio of the average height of the surface protrusions to the average internal particle diameter is 5.1 × 10 ^-3 or less. A base film for magnetic recording characterized by the following. 2. The magnetic recording base film according to claim 1, wherein the internal particles have a particle size of 2 to 8 μm.