JPS6327777B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a base film for magnetic recording materials. More specifically, the present invention relates to a base film made of a biaxially oriented polyethylene terephthalate film having specific characteristics and suitable for manufacturing magnetic recording materials with excellent signal recording and reproducing characteristics with high productivity. Traditionally, intrinsic viscosity is 0.50-0.65, Young's modulus in longitudinal direction
Biaxially oriented polyethylene terephthalate films of 500-630 Kg/ ^mm2 have been used as base films for magnetic recording materials. However, when a magnetic tape for image recording is manufactured using this base film, the screen tends to flicker due to signal dropout during recording and reproduction. Dropouts on magnetic recording tapes are caused by (a) foreign matter embedded in the tape surface, (b) protrusions on the magnetic layer itself, (c) temporarily attached foreign matter, (d) pinholes, and (e) magnetic surface. (f) Protrusions on the surface of the base, etc. are known to occur, and these factors are caused by the composition of the binder in the magnetic layer, dust removal from the base, excessive coating liquid, etc.
The frequency of dropouts has gradually decreased as they have been reduced through innovations and improvements in coating methods, processing methods, etc. However, on the other hand, the characteristics required for magnetic tapes have become more sophisticated, and magnetic tapes with even fewer dropouts are required. Furthermore, the above-mentioned base film has the disadvantage that the image may be distorted during electronic editing of the videotape or when starting or stopping the tape.
The distortion of the image is related to the expansion and contraction of the tape due to tension fluctuations during running of the magnetic recording tape, and the ability to recover from distortion, and these depend on the Young's modulus of the base film and the residual elongation according to JISC5542. However, the expansion/contraction and strain recovery are in an antinomic relationship, and it has been difficult to satisfy them at the same time. These drawbacks can be solved by improving the recording/playback device. For example, high-end recording/playback devices used for television broadcasting have been solved by incorporating an automatic adjustment mechanism, but this mechanism is complicated and the entire device becomes expensive.
Therefore, recording and playback devices commonly used for home, business, and educational purposes do not have this automatic adjustment mechanism, and the above drawbacks are resolved by the base film used, and improvements in this are desired. ing. As a result of extensive research into a base film for magnetic recording materials that does not have these drawbacks, the inventor has found that
It has been discovered that by using a biaxially oriented polyethylene terephthalate film having a specific intrinsic viscosity, Young's modulus, and heat shrinkage coefficient as a base film, the above-mentioned drawbacks can be overcome, and magnetic recording materials can be manufactured from the film with high productivity, This has led to the present invention. That is, the present invention has an intrinsic viscosity in the range of 0.70 to 0.84, a longitudinal Young's modulus of 750 Kg/mm ² or more,
Moreover, it is greater than or equal to Young's modulus in the transverse direction, and
This is a base film for magnetic recording materials, characterized by being made of a biaxially oriented polyethylene terephthalate film with a heat shrinkage rate of 0.7% or less at 105°C. The polyethylene terephthalate constituting the base film of the present invention has an intrinsic viscosity of 0.70 or more, preferably 0.75 or more, particularly preferably 0.80.
That's all. However, the upper limit of the intrinsic viscosity is 0.84. If the intrinsic viscosity is less than 0.70, dropout and image disturbance cannot be improved, which is undesirable. On the other hand, if it exceeds 0.84, the melt viscosity becomes too high, resulting in poor film formability and high polymer cost, which is not preferred. This polyethylene terephthalate is mainly intended for homopolymers, but the acid component is 90 (preferably 95) mol% or more of terephthalic acid,
For example, isophthalic acid, phthalic acid, adipic acid, sebacic acid, succinic acid, oxalic acid, malonic acid, p-
One or more difunctional acids such as hydroxybenzoic acid, ω-hydroxycaproic acid, etc.
consisting of 10 (preferably 5) mol% or less, and/
Or the glycol component is ethylene glycol 90
(preferably 95) mol% or more, such as trimethylene glycol, hexamethylene glycol, cyclohexanedimethanol (1,4), 2,2,
It may be a copolymer consisting of 10 mol% or less (preferably 5 mol%) of one or more diol compounds such as 4,4-tetramethylcyclobutanediol (2,4) and hydroquinone, A mixture of these polymers may also be used. Furthermore, this polyethylene terephthalate may contain other polymers of up to 10% by weight (preferably 5% by weight). The polyethylene terephthalate may contain stabilizers such as phosphoric acid, phosphorous acid and esters thereof, matting agents such as titanium dioxide, particulate silica, kaolin, etc., and lubricants. In the present invention, the polyethylene terephthalate film must have a Young's modulus in the longitudinal direction of 750 Kg/mm ² or more and a Young's modulus in the transverse direction. A preferable longitudinal Young's modulus is 800 Kg/mm ² or more. If the longitudinal Young's modulus is less than 750 Kg/mm ² , image distortion etc. cannot be improved, which is not preferable. Furthermore, if the Young's modulus in the longitudinal direction is smaller than the Young's modulus in the transverse direction, thermal shrinkage in the transverse direction increases, which is undesirable because the productivity of the tape decreases. The difference between the longitudinal Young's modulus and the transverse Young's modulus is preferably in the range of 10 to 500 Kg/mm ² , more preferably 200 to 450 Kg/mm ² . Such Young's modulus can be obtained by stretching and orienting the film. In the present invention, the longitudinal direction is the extrusion direction, and usually means the longitudinal direction of the film. Furthermore, in the present invention, the polyethylene terephthalate film must have a transverse heat shrinkage rate of 0.7% or less at 105°C. The preferred transverse heat shrinkage rate is
Less than 0.3%. If the heat shrinkage rate is greater than 0.7%, the film will shrink in the lateral direction due to heat shrinkage during the processing process into magnetic recording materials, which may cause shrinkage wrinkles on the film or reduce the film width, resulting in a product product. The quality of the product deteriorates and the yield decreases, which is not desirable. Heat shrinkage can be reduced by biaxially stretching the film and then subjecting it to heat setting treatment, and a certain degree of heat shrinkage can also be controlled by relaxation heat treatment. Biaxially oriented polyethylene terephthalate tends to have a disordered molecular orientation and a decrease in Young's modulus due to heat setting treatment, although it depends on the stretching ratio. This tendency increases as the heat setting temperature increases, and as the stretching ratio increases, this tendency increases. On the other hand, when a biaxially oriented polyethylene terephthalate film is formed under the same film forming conditions by changing only the intrinsic viscosity of the polymer, the higher the intrinsic viscosity, the higher the thermal shrinkage rate. Therefore, heat setting under stricter conditions is required to maintain the same heat shrinkage rate. According to these trends, it is presumed that it is difficult to obtain a biaxially oriented polyethylene terephthalate film that has a high Young's modulus and a low thermal shrinkage rate simply by increasing the intrinsic viscosity. However, the present inventor discovered that the lower the Young's modulus due to heat setting treatment at the same stretching ratio is, the greater the intrinsic viscosity of the polymer, and that
Longitudinal Young's modulus of 750Kg/ ^mm2 or more and 105 when 0.84
It has been found that a biaxially oriented film can be obtained that simultaneously satisfies the characteristics of a lateral heat shrinkage rate of 0.7% or less, particularly 0.3% or less at °C, and that this film has excellent properties as a base film for magnetic recording materials. .
It is an unexpected and surprising effect that by setting the intrinsic viscosity of the base film to such a value, it is possible to obtain a magnetic recording material in which dropout is reduced and image disturbance is prevented. The base film of the present invention has an intrinsic viscosity of 0.70 to 0.84.
The polyethylene terephthalate unstretched (amorphous) film of
Stretched 4.5 to 6 times, 2 to 4 times in the transverse direction,
It is then obtained by heat setting. Taking such a stretching ratio, the Young's modulus in the longitudinal direction is 750Kg/mm ²
The above can be achieved, and the film surface is flattened. The heat setting temperature is preferably around 235°C. 210
When heat setting is carried out at a lower temperature such as °C, the heat setting time should be relatively long; for example, a short time of about 5 seconds does not make it possible to sufficiently reduce the heat shrinkage rate. An appropriate combination of heat setting temperature and processing time should be selected to satisfy a transverse heat shrinkage rate of 0.7% or less at 105°C. The thickness of the base film of the present invention is not particularly limited, but is usually 2 to 50 microns. Examples of magnetic recording materials using the base film of the present invention include magnetic tapes and magnetic cards. Examples of magnetic tape include those for computers, recording, recording, and measurement. Magnetic recording materials using the base film of the present invention are primarily useful for video recording applications, but are also useful for other applications such as audio recording. In the present invention, the intrinsic viscosity calculated from the solution viscosity is used as a measure of the molecular weight of polyethylene terephthalate. The measurement method uses o-chlorophenol as the solvent and the measurement temperature is 25℃.
Calculate using the formula below. ηsp/C=[η]+K[η] ² C [where ηsp=solution viscosity/solvent viscosity-1 [η]: Intrinsic viscosity (dl/g) C: Dissolved polymer mass per 100ml of solvent (g/100
ml)...Here it is set to 1.2. K: Huggins constant (set to 0.247) Solution viscosity and solvent viscosity were measured using an Ostwald viscometer. ] Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, the Young's modulus, thermal shrinkage rate, and residual elongation in the examples were determined by the following measuring methods, respectively. <Young's Modulus> A film sample was cut into pieces with a width of 10 mm and a length of 15 cm, and was stretched using an Instron type universal tensile tester at a tension speed of 10 mm/min and a chart speed of 500 mm/min with a chuck distance of 100 mm. Young's modulus was calculated from the tangent to the rising part of the obtained load-elongation curve. <Heat shrinkage rate> 105℃ hot air circulation furnace (e.g. gear aging tester)
The sample was allowed to shrink freely for 30 minutes without any load, and calculated using the formula below from the sample length before and after heat treatment. Thermal shrinkage rate (%) = original length - length after treatment / original length x 100 <Residual elongation> Using a constant load elongation measuring device manufactured by Japan Automatic Control Co., Ltd. in accordance with JIS C5542, the stress was 7.50 Kg/mm. ² , sample width
Measured with a sample length of 6.35 mm and a sample length of 500 mm. Measurements are in the longitudinal direction. Examples 1 to 3 and Comparative Examples 1 to 7 Polyethylene terephthalate having the intrinsic viscosity shown in Table 1 was melt-extruded and rapidly cooled to produce an amorphous unstretched film, which was then stretched 5.0 times in length at 75°C. Stretched at 100℃, then horizontally stretched 3.2 times at 100℃, heat-set at 210℃ or 235℃ for 5 seconds, and then stretched to 20μ
A biaxially oriented polyethylene terephthalate film was obtained. These properties are shown in Table 1.

【table】

[Table] Magnetic paint was applied to these films to a thickness of 4 μm according to a known method, and the films were mirror-finished using a calendar to prepare video tapes. However, Comparative Example 1,
Films Nos. 3, 5, 6, and 7 had large transverse heat shrinkage rates, so they were wrinkled in the vertical direction during the drying process, and were creased during the calendering process, making them unusable as magnetic recording tapes for video. Therefore, video tapes using the films of Comparative Examples 2 and 4 and Examples 1 to 3 as base films were subjected to a recording/playback test using a Sony Umatake video device. As a result, the video tapes obtained from the base films of Comparative Examples 2 and 4 had poor flatness, dropouts, and screen flickering. Furthermore, in Comparative Examples 2 and 4, tape running was stopped and the screen was distorted when restarted. On the other hand, films based on the films of Examples 1 to 3 do not cause drop-outs and do not flicker on the screen.
There was also no screen disturbance when restarting. Examples 4 to 5 and Comparative Examples 7 to 10 Magnetic recording tapes were prepared in the same manner as in Examples 1 to 3 using biaxially oriented polyethylene terephthalate films (thickness 21μ) with different Young's moduli in the longitudinal direction. Videotape characteristics were evaluated. The results are shown in Table 2. The base film had an intrinsic viscosity of 0.84 and a residual elongation of 0.03 to 0.06%.

【table】

Claims (1)

[Claims] 1 The intrinsic viscosity is in the range of 0.70 to 0.84, the Young's modulus in the longitudinal direction is 750 Kg/mm2 ^or more and the Young's modulus in the transverse direction, and the heat shrinkage rate at 105℃ in the transverse direction is 0.7
A base film for magnetic recording materials, characterized in that it is made of a biaxially oriented polyethylene terephthalate film with a biaxially oriented polyethylene terephthalate film of % or less.