JPS647574B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a polyester film suitable for use in magnetic tapes, which has good adhesion to the magnetic layer of magnetic tapes and excellent thermal dimensional stability. Demand for magnetic tapes using polyester films as base materials has increased significantly in recent years, and one of the important properties of the base film for magnetic tapes is its adhesion to the magnetic layer. If the adhesiveness between the magnetic layer and the polyester film is insufficient, the magnetic layer will fall off during use, making it unusable. Conventionally, attempts have been made to improve both the magnetic layer and the polyester in order to improve the adhesion between the polyester film and the magnetic layer. Among the components of the magnetic layer, the component that controls the adhesion to the polyester film is the binder resin. Generally known binder resins include vinyl resins, cellulose resins, urethane resins, epoxy resins, and phenoxy resins. For example, among vinyl resins, vinyl chloride-vinyl acetate copolymer is most often used for audio tapes. To improve adhesion, it is known to mix a vinyl chloride-vinylidene chloride copolymer as the second component of the binder resin (Japanese Patent Publication No. 51-2335). It is also generally known to mix a butadiene-acrylonitrile copolymer as a second component resin. However, when two or three such resins are used in combination, although some improvement in adhesion can be achieved, there are drawbacks such as deterioration of electromagnetic conversion characteristics and abrasion characteristics with magnetic heads. On the other hand, as a method for improving adhesion from the polyester film side, a method of incorporating polyalkylene glycol is known. For example, the 1970s
Publication No. 39375 discloses a film in which a polyether ester block copolymer is laminated on a biaxially stretched polyethylene terephthalate film.
JP-A-51-90346 and JP-A-54-18872 disclose polyester films containing polyalkylene oxide glycols. However, laminated films require processes such as coating, coextrusion, and dry lamination, are generally expensive, and are difficult to obtain the specific homogeneous surface morphology required as a magnetic tape base. The above-mentioned two publications describing polyester films containing polyalkylene glycol do not disclose any specific explanation for improving the adhesiveness with the magnetic layer. Another property required of magnetic tape base films is thermal dimensional stability. The present inventors have developed a polyester film containing a predetermined amount of a polyalkylene glycol component, which has been blended with a copolymerized polyester containing a polyalkylene glycol component, by heat-setting it under specific conditions after biaxial stretching. The inventors have discovered that a polyester film with excellent adhesiveness and thermal dimensional stability can be obtained, and that an excellent magnetic tape can be obtained by using this polyester film as a base material, and have thus arrived at the present invention. That is, in the present invention, polyester A containing polyalkylene glycol as a copolymerization component and having a crystalline melting point of Tm(A) and polyester B containing ethylene terephthalate units as main constituents and having a crystalline melting point of Tm(B) is combined with a polyalkylene glycol. component is 0.5
A manufacturing method for biaxially oriented polyester film for magnetic tapes, which consists of blending the polyester film at ~2% by weight, biaxially stretching, and heat-setting it to satisfy the following conditions: log (wt) ≧ −0.063T + 16.12 ...() Tm(A)+10≦T≦Tm(B)−15 ...() Where, T: Heat setting temperature (℃) t: Heat setting time (seconds) w: Time of polyalkylene glycol component in the film amount (wt%). The present invention will be explained in detail below. Polyester A in the present invention is a copolymerized polyester containing polyalkylene glycol as a glycol component and having a crystal melting point of Tm(A).
The crystal melting point Tm(A) of polyester A is 170-220℃,
Preferably the temperature is 190 to 210°C, and the heat of crystal fusion of polyester A is 5 to 9 cal/g, preferably 6 to 8 cal/g.
It is g. If the crystallinity of polyester A is lower than this, the stickiness will increase and compounding processability will become difficult, and when a mixture of polyester A and polyester B is formed into a biaxially oriented film, the thermal and mechanical properties of the film will be affected. lower. Furthermore, if the crystallinity of polyester A is higher than this, suitable heat setting conditions for improving adhesiveness cannot be obtained. The polyalkylene glycol of the present invention includes:
Examples include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. These may be used alone or in combination of two or more. The preferred molecular weight range for polyalkylene glycol is 300 to 300 for polyethylene glycol.
200,000, preferably 500 to 30,000, and for polytetramethylene glycol it is 500 to 5,000, preferably 800 to 3,000. The copolymerization amount of polyalkylene glycol in polyester A is 5 to 30% by weight, preferably 8 to 20% by weight. The polyester segment of polyester A contains aromatic or aliphatic dicarboxylic acid residues such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, adipic acid, and sebacic acid, and ethylene glycol,
It is composed of aliphatic, aromatic or alicyclic diol residues such as 1,4-butanediol, neopentyl glycol, P-xylylene glycol, and cyclohexanedimethanol. Typical examples of polyester A are poly(butylene terephthalate/isophthalate) polyethylene glycol copolymer, poly(butylene terephthalate/isophthalate)
It is a polytetramethylene glycol copolymer,
The proportion of isophthalic acid in the total acid component is preferably 10 to 30 mol%. The polyester B of the present invention is a polyester whose main component, for example, 80% by weight or more consists of ethylene terephthalate units. Polyester A is blended into polyester B so that the content of the polyalkylene glycol component in the mixture (that is, in the film) is 0.5 to 2% by weight. The content of polyalkylene glycol components is
If it is less than 0.5% by weight, the adhesion is insufficient;
If the amount is more than 2% by weight, the surface shape of the polyester film may change or the mechanical properties may deteriorate, which is not preferable. The polyester film of the present invention can be obtained by heat setting after biaxial stretching under conditions that satisfy the following relational expression. That is, the heat setting temperature T
(°C), heat setting time t (seconds), content of polyalkylene glycol component in the film w (wt%), heat setting at Tm(A)+10≦T≦Tm(B)−15 (°C) The heat fixation condition is such that log(wt)≧−0.063T+16.12 holds within the temperature range. Heat setting temperature is Tm(A)+10(℃)
Lower or heat setting temperature from Tm(A)+10
If the required heat setting time is not reached even within the range of Tm(B) - 15 (℃), the adhesiveness between the polyester film and the magnetic layer is insufficient, and the heat setting temperature is Tm(B) If it is higher than -15 (°C), the mechanical properties of the polyester film will deteriorate, which is not preferable. The density of the polyester film of the present invention is 1.390
It is preferable that it is at least g/cm ³ . When the density of the polyester film is lower than 1.390 g/cm ³ , thermal dimensional stability tends to deteriorate. A polyester film having a density of 1.390 g/cm ³ or more can be obtained by heat-setting at about 200° C. or higher (T≧200). A method for producing a polyester film for use in the magnetic recording medium of the present invention is, for example, by mixing polyethylene terephthalate and a copolymerized polyester containing a polyalkylene glycol component with polymer chips, and then melt-extruding and unstretching using a conventional method for polyester. A film is obtained, which is then biaxially stretched and heat-set to obtain a biaxially oriented film. It may be re-stretched vertically and/or horizontally if necessary. Stretching temperature is 70-120℃, stretching ratio is 2.5 in both length and width.
~5 times, and the heat setting temperature and time may be appropriately selected so as to satisfy the formula shown in the above range. The thickness of the polyester film used in the present invention is not particularly limited, but is usually in the range of 5 to 50 microns. The polyester film thus obtained has excellent adhesion between the magnetic layer and the polyester film and a high degree of thermal dimensional stability, so it is preferably used for magnetic tapes for audio, video, computers, and the like. The present invention will be explained below with reference to Examples. The methods for measuring various properties in the present invention are as follows. (1) Tensile test Toyo Baldwin Tensilon UTM−
Using a mold at 20℃ and 65% humidity, length 50mm,
A sample film with a width of 6.25 mm was stretched at 50 mm/min, and the load at 5% elongation was expressed per initial unit cross-sectional area and was taken as the _F5 value. (2) Density In a mixture of n-heptane and carbon tetrachloride, 25℃
This is the value measured using the float-sink method. (3) Thermal shrinkage rate The dimensional change after being left at 100℃ for 3 minutes in a hot air circulation dryer is shown as a percentage (%) of the original length. (4) Adhesive strength A double-sided adhesive tape made by Scotch was pasted on a 1 mm thick stainless steel plate, and the magnetic layer coated film was cut into 3.8 mm width so that the magnetic layer surface was in contact with the double-sided adhesive tape, and the film was cut perpendicular to the double-sided adhesive tape. Paste together. Next, the load when the polyester base film is peeled off from the magnetic layer at an angle of 180° is measured using a tensile tester at a speed of 1000 mm/min. (5) Crystal melting point and crystal heat of fusion The crystal melting point and crystal heat of fusion are measured by measuring approximately 10 mg of each sample with a PerkinElmer DSC1B model.
It is the value obtained by dividing the endothermic energy obtained from the peak temperature and peak area of the endothermic peak associated with crystal melting obtained at a heating rate of 16° C./min by the sample weight. Example 1 (Production method of copolymerized polyester) 66.0 parts of dimethyl terephthalate, 13.6 parts of dimethyl isophthalate, 42.4 parts of 1,4-butanediol
parts, 10.0 parts of polyethylene glycol with a molecular weight of 8500 and 0.01 parts of tetra-n-butyl titanate as a catalyst.
After putting the mixture into a reaction vessel and carrying out the transesterification reaction while distilling the methanol produced under heating and stirring,
The mixture was transferred to a reaction vessel heated to 210°C. Further, 0.01 part of tetra-n-butyl titanate was added, and the temperature of the reaction system was raised to 245°C after 1 hour, and the pressure was gradually reduced to 3 mmHg or less after 1.5 hours to complete the polycondensation, resulting in a melting point of 200°C and crystals. A poly(ethylene terephthalate/isophthalate)/polyethylene glycol copolymer having a heat of fusion of 6.7 cal/g was obtained. (Film forming method) The copolymerized polyester and polyethylene terephthalate having a crystal melting point of 255°C are mixed together,
The mixture was mixed at a ratio of 10:90 (weight ratio) so that the content of the polyethylene glycol component in the mixture was 1% by weight, and then dried. This mixture was melt-extruded at 285°C to obtain an unstretched film with a thickness of 170μ.
This unstretched film was stretched 4.3 times in the longitudinal direction with a roll, then stretched 3.3 times in the transverse direction with a tenter, and then
Heat setting was performed at 200° C. for 6 seconds to obtain a biaxially oriented film with a thickness of 12 μm. (Sample No. 1) Take out this biaxially oriented film, fix the dimensions on a stainless steel frame, paste it, and put it in an air oven for 215 minutes.
Heat fixation was performed at ~245°C for 6 seconds to 100 seconds. The evaluation results of these films (sample Nos. 1 to 6) are shown in Table-1. For comparison, a film (sample No. 7) obtained using only polyethylene terephthalate using the same film-forming method is also shown in the same table. The sample film used for adhesive evaluation was coated with a magnetic layer by the method shown below. (Magnetic layer coating method) γ-Fe ₂ O ₃ 100 parts by weight Poly(vinyl chloride-vinyl acetate) copolymer (Denkabinyl 1000A manufactured by Denki Kagaku Kogyo) 30.8 Butadiene acrylonitrile copolymer 9.2 Methyl ethyl ketone 150 Toluene 150 Both were mixed in a ball mill for 40 hours to form a coating solution. This coating solution was applied onto the previously prepared biaxially oriented film so that the dry film thickness was 5μ, and then
Dry at °C.

[Table] Example 2 The same copolymerized polyester and polyethylene terephthalate as in Example 1 were mixed together, and the content of the polyethylene glycol component in the mixture was 0.2.
After mixing at a ratio of ~2.5% by weight, the mixture was dried. This mixture was biaxially stretched and heat-set in the same manner as in Example 1, and then placed in a stainless steel fixing frame.
Heat fixation was performed at 235°C for 70 seconds. Table 2 shows the evaluation results for each film (sample Nos. 8 to 12).
The applied magnetic layer was the same as in Example 1.

【table】

Claims (1)

[Scope of Claims] 1. Polyester containing polyalkylene glycol as a copolymerization component and having a crystal melting point of Tm(A) and a polyester whose main constituents are ethylene terephthalate units and having a crystal melting point of Tm(B). A method for producing a biaxially oriented polyester film for magnetic tape, which comprises blending the glycol component to a concentration of 0.5 to 2% by weight, biaxially stretching, and heat-setting the film to satisfy the following conditions. log (wt) ≧ −0.063T + 16.12 ... () Tm (A) + 10 ≦ T ≦ Tm (B) - 15 ... () where T: Heat setting temperature (℃) t: Heat setting time (seconds) w: Amount of polyalkylene glycol component in the film (% by weight)