JPH0138661B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an improved biaxially stretched tensilized type base film mainly for magnetic recording, which is mainly made of polyester. [Prior Art] As a material for a base film for magnetic recording, it is common to use a film whose main component is biaxially oriented and heat-set polyester, especially polyethylene terephthalate (hereinafter abbreviated as PET). It is classified into two types: the balanced type, which has biaxial orientation in the vertical and horizontal directions and mechanical properties that are relatively similar, and the tensile type, which has orientation mainly in the vertical direction and mechanical properties that are significantly larger than that in the horizontal direction. .
The balanced type is usually manufactured with approximately the same stretching ratio in the vertical and horizontal directions, and the strength (F-5 value) at 5% elongation is 15 kg/mm ² or less in both the vertical and horizontal directions.
Furthermore, it is generally less than 13Kg/mm ² . On the other hand, the tensilized type is manufactured by making the total stretching ratio in the vertical direction much higher than in the horizontal direction, and the F-5 value in the vertical direction is usually over 15Kg/ ^mm2 , and is 17 to 20Kg/ ^mm2 . There are many things. These balanced and tensile types have advantages and disadvantages in terms of film stiffness, dimensional stability, ease of manufacture, cost, etc., and are used depending on the need. Characteristics required of a base film for magnetic recording include uniformity of the magnetic agent coating layer, fineness and uniformity of the film surface protrusions to provide flatness, runnability to withstand repeated use, and abrasion resistance. These surface protrusions are generally achieved by incorporating protrusion-forming particles such as polymer insoluble matter (hereinafter abbreviated as internal particles) made of inorganic substances and catalyst residues into the film, but in general, running properties and Wear resistance and the fineness and uniformity of surface protrusions (hereinafter abbreviated as surface quality) are contradictory properties. For example, if a large number of large particles are included in the film, running properties will certainly be improved, but the surface protrusions will become coarser, resulting in fatal drawbacks such as dropouts on magnetic tape, decreased output, and increased noise. On the other hand, when fine particles are present, fine surface protrusions are formed and the tape has good output, dropout, etc., but has the disadvantage of poor slippage and poor running performance and abrasion resistance. [Object of the Invention] It is an object of the present invention to overcome the contradictory drawbacks of the prior art and to provide a base film for magnetic recording that is excellent in running properties, abrasion resistance, and surface properties. [Configuration of the Invention] In order to achieve the above object, the present invention has the following configuration,
That is, it is a biaxially stretched film mainly composed of polyester and the amount of internal particles mixed in is 0.05 to 0.5% by weight, and the F-5 value in the longitudinal direction is more than 15 Kg/mm ² and less than 20 Kg/mm ² , F-5 value in horizontal direction is 9 to 15
Kg/mm ² , the average height of surface protrusions is 0.040μ or less, and the ratio of the average height of surface protrusions to the average internal particle diameter is 5.1
The magnetic recording base film is characterized by a magnetic recording base film having a magnetic flux of less than ×10 ^-3 . The present invention is directed to so-called tensilized type tapes having an F-5 value in the above-mentioned range.If the lateral F-5 value is less than 9 kg/ ^mm2 , the processed tape is Elongation occurs due to slight abnormal tension, which is undesirable. The average height of surface protrusions shall be 0.040μ or less. If this height exceeds 0.040μ, the surface properties will be poor, and even if the ratio of the average height of surface protrusions to the average diameter of internal particles (hereinafter referred to as the roughness parameter) satisfies the range of the present invention, the running properties will deteriorate. It is impossible to improve both wear resistance and surface properties (hereinafter simply referred to as compatibility). Note that this height is preferably
It is 0.035μ or less, more preferably 0.030μ or less, and most preferably 0.025μ or less. Further, the roughness parameter is 5.1×10 ^-3 or less, preferably 4.6×10 ^-3 or less, more preferably 4.1×
10 ^-3 or less is required. (The roughness parameter is usually
It is about 5.3×10 ^-3 to 5.7×10 ^-3 or more, but reducing it to 5.1×10 ^-3 or less as in the present invention means that if the surface roughness is kept the same, the size of the internal particles will be smaller than the conventional one. This means that the surface roughness becomes finer when the size of the internal particles is kept the same. ) In the present invention, the smaller this value, the higher the level of compatibility; conversely, 5.1 ×
If it exceeds 10 ^-3 , it cannot be said that both have been achieved. The film of the present invention particularly relates to a biaxially stretched polyester film that has improved mechanical properties and the like as a base film for magnetic recording. An example of the method for manufacturing the film of the present invention will be described below. The film of the present invention can be produced by melt-extruding polyester containing fine particles through a slit-shaped die to produce an unstretched film, or by producing a superdraw-stretched film with substantially no orientation from the unstretched film; The film is stretched 2.0 to 4.5 times vertically and horizontally, and 1.1 to 5 times vertically again to achieve biaxial orientation. During or after these stretching steps, a calendering step is provided to push in the surface protrusions of the film, and the film is It is manufactured by adjusting the surface condition of. In this case, it is preferable to perform calender treatment during the stretching process. In particular, it is preferable to carry out the calendering treatment in the first vertical stretching step, but the method is not limited thereto. 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 , Al ₂ O ₃ ,
They may be external particles made of an inorganic material such as calcium phosphate, or internal particles containing components such as Ca, Si, or P. Preferred particles are Ca-Li-P internal particles and external particles, although they are not particularly limited. A combination of 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 incorporated particles is 0.05 to 0.5% by weight. Contamination amount is 0.05% by weight
If the amount is less than 0.5% by weight, problems will occur in runnability and durability, while if the amount exceeds 0.5% by weight, problems will occur in 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. Note that the adjustment of the surface condition of the film according to the present invention is not limited to the above-mentioned calendering method, but also includes adjustment by a combination of stretching and heat treatment. [Effects of the Invention] As described above, the present invention provides F-5 values in the vertical and horizontal directions, average height of surface protrusions, roughness parameters,
Since we created a biaxially stretched polyester film for magnetic recording with a specific amount of internal particles mixed in, we achieved the excellent effect of improving both of the conflicting properties of runnability, abrasion resistance, and flatness. It is something that plays. 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 T10 type. (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 determined by melting and rapidly cooling the film into a thin film between glass preparations.
Diameter in transmission state under dark field illumination due to microscopic boundary
Observe and evaluate particles larger than 1μ. The magnification is
The average diameter is expressed as the volume average diameter at a magnification of 128 times. 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. Example 1, Comparative Example 1 The particle size of inorganic kaolin was adjusted by crushing and classification to obtain a particle source with an average diameter of 2.5 μm. Add 0.2% by weight of this, polymerize according to the usual method, and obtain a [η] of 0.65.
Obtained PET. Comparative Example 1 uses this raw material and melts and molds, and then increases the thickness by vertical, horizontal, re-vertical, and heat treatment.
A 10μ film was obtained. The following conditions were applied. Vertical stretching; 100°C, 3.0 times horizontal stretching; 120°C, 3.6 times vertical stretching; 150°C, 1.6 times A film was obtained by calendering to compress the film. The surface condition of the obtained film will be explained based on the drawings. Figures 1 to 4 are enlarged plan views schematically showing the uneven portions formed on the film surface, Figure 5 is a sectional view taken along line A-A' in Figure 3, and Figures 6 to 9 are , is a mirror photograph (magnification: 6000x) of the concavo-convex portion. In the figure, 1 is a film, 2 is a depressed portion, 3 is a protrusion, 4 is a raised portion, and 5 is an uneven portion. Next, a 4μ magnetic layer was coated on these films using a conventional method, and a video tape was produced. Table 1 shows the film quality and tape quality. As is clear from the table, the tape quality of Example 1 was excellent. Example 2 The particle size of inorganic silica (SiO ₂ ) was adjusted by crushing and classification to obtain a particle source with an average diameter of 0.7μ. Add 0.5% by weight of this and polymerize according to the usual method, [η]
A PET of 0.65 was obtained. Using this raw material, the following procedure was carried out in the same manner as in Example 1 to obtain a film with a thickness of 10μ,
evaluated. The results are shown in Table-1. Comparative Example 2 The same procedure as in Example 2 was carried out except that 0.7% by weight of the particle source was added. Comparative Example 3 The same procedure as in Example 2 was carried out except that the calendering treatment was not performed. Example 3 The particle size of inorganic silica (SiO ₂ ) was adjusted by crushing and classification to obtain a particle source with an average diameter of 3.0 μm. Add 0.05% by weight of this and polymerize according to the usual method, [η]
A PET of 0.65 was obtained. Using this raw material, the following procedure was carried out in the same manner as in Example 1 to obtain a film with a thickness of 10μ,
evaluated. The results are shown in Table-1. Example 4 The same procedure as in Example 3 was carried out except that 0.2% by weight of the particle source was added. Example 5 The same procedure as in Example 3 was carried out except that 0.5% by weight of the particle source was added. Comparative Example 4 The same procedure as in Example 3 was carried out except that 0.02% by weight of the particle source was added. Comparative Example 5 The same procedure as in Example 3 was carried out except that 0.7% by weight of the particle source was added. Example 6 The particle size of inorganic calcium carbonate (CaCO ₃ ) was adjusted by crushing and classification to obtain a particle source with an average diameter of 2.0 μm. 2.0% by weight of this was added and polymerized according to a conventional method to obtain PET with [η] 0.65. Using this raw material, the same procedure as in Example 1 was carried out to obtain a film with a thickness of 10 μm, which was then evaluated. The results are shown in Table-1. Example 7 The particle size of inorganic calcium carbonate (CaCO ₃ ) was adjusted by crushing and classification to obtain a particle source with an average diameter of 2.5 μm. The following steps were carried out in the same manner as in Example 6. Comparative Example 6 The same procedure as in Example 6 was carried out except that the calendering treatment was not performed. Comparative Example 7 The same procedure as in Example 6 was carried out except that 0.02% by weight of the particle source was added. Comparative Example 8 The same procedure as in Example 6 was carried out except that 0.6% by weight of the particle source was added. As shown in Table-1, the amount added is 0.05% by weight.
If it is less than that, problems will arise in running performance and durability (Comparative Example 4, Comparative Example 7). On the other hand, when the amount added exceeds 0.5% by weight, problems occur in tape output and dropout (Comparative Examples 5 and 8). If the constituent requirements of the present invention are violated in this way, some problems will occur in the quality of the tape, making it impossible to obtain a well-balanced tape.

[Table] However, the tape quality in Table 1 is 1/2
Cut the tape into inch-wide strips made by Victor
It was played on a VHS video tape recorder and evaluated using the following criteria. (1) Tape output Comparative example 1 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 Ranked according to the degree of injury.

[Brief explanation of drawings]

1 to 4 are enlarged plan views of the uneven portions formed on the surface of the film of the present invention, FIG. 5 is a sectional view taken along line A-A' in FIG. 3, and FIGS. This is a micrograph of the grain structure formed in the wafer, that is, the uneven portion. 1; film, 2; depressed portion, 3; protrusion, 4;
Raised portion, 5; uneven portion.

Claims (1)

[Claims] 1 A biaxially oriented film whose main component is polyester and the amount of internal particles mixed in is 0.05 to 0.5% by weight, and whose F-5 value in the longitudinal direction exceeds 15 kg/ ^mm2 .
Kg/mm ² or less, F-5 value in the horizontal direction is 9 to 15 Kg/
mm ² , the average height of surface protrusions is 0.040μ or less, and the ratio of the average height of surface protrusions to the average internal particle diameter is 5.1×
A base film for magnetic recording characterized by having a magnetic recording temperature of 10 ^-3 or less.