JPH0416059B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a biaxially oriented polyester film with improved abrasion resistance, slipperiness, adhesiveness, and productivity, and particularly to a biaxially oriented polyester film with a smooth surface. [Problems to be solved by the prior art and the invention] Demand for magnetic tape has increased significantly in recent years, and as a result, the performance of magnetic tape has been gradually improved, and will continue to be improved in the future. Improvements in performance and further cost reduction are being pursued. In particular, in terms of performance, there are higher recording densities, higher output, lower noise, lower dropouts, lower running friction, and even greater adhesion between the magnetic layer and base film.
We are currently in a situation where these measures must be taken into account in the future along with cost reductions. Accordingly, in addition to the magnetic layer constituting the magnetic tape, improvements in the properties of the base film, which is the base material thereof, are required to improve the performance as described above. Biaxially oriented polyester film is generally used as the base film, but for example, in videotape applications, which have developed rapidly in recent years, in order to improve performance, the base film has a flat surface. It is required that the material be smooth, slippery, have high abrasion resistance, and have high adhesion to the magnetic layer. Normally, base films are made by incorporating particles into the raw material polyester using a precipitated particle method in which they are precipitated during polymerization or an additive particle method in which inert external fine particles are added, and the contributions of these particles create protrusions on the film surface. It has smoothness and wear resistance, so if you plan to flatten the surface,
At the same time, slipperiness and abrasion resistance are usually impaired. Note that the surface roughness of the base film directly affects the video output and envelope, and if the base film has poor slipperiness, the tension during tape running will be excessive, causing tape deformation or, in extreme cases, tape stop. A material with poor abrasion resistance causes many problems such as abrasion in the tape manufacturing process and dropout due to generation of abrasion powder due to abrasion within the tape deck. Therefore, when manufacturing a magnetic tape with particularly high performance using a base film with a particularly flat surface, the surface opposite to the magnetic layer on the base film is slippery and has poor abrasion resistance. At present, a back coat is inevitably applied to the surface in order to impart these characteristics. However, it is obvious that applying such a back coat will increase the cost. Therefore, in order to improve performance or reduce costs, relatively flat base films used for magnetic tapes that have relatively high performance even without back coating have been developed to have high wear resistance and slip resistance. On the other hand, for particularly flat base films used for particularly high-performance magnetic tapes that have been coated with a back coat, highly slippery base films that do not require a back coat are needed. The appearance of a base film with improved properties such as durability and abrasion resistance has been awaited. Furthermore, the economical standard type magnetic tape base film has a relatively large surface roughness, and therefore is easy to slip.
It is normal for the wear resistance to be high to some extent. In addition, for applications other than magnetic tapes, such as plate making and tracing, there is a need for base films that have improved transparency and are highly slippery, as well as base films that are highly scratch resistant. It has been long awaited. In order to improve transparency, it is necessary to reduce the amount or size of particles contained in the base film, which is a need that is shared to some extent with the above-mentioned magnetic tape. In response to the above-mentioned requests for improvements to the base film, we have conventionally ()
There are methods for improving slipperiness and abrasion resistance from the aspects of size and distribution, and the convex shape and height and distribution of the film surface. However, this method mainly controls the surface roughness of the base film within a range depending on the intended use, and although it is possible to improve slipperiness and abrasion resistance to some extent, it essentially depends on the surface roughness and ease of use. The fact remains that lubricity and abrasion resistance are in a trade-off relationship, and it is impossible in principle to significantly improve this relationship. Furthermore, there is a method of improving slipperiness, abrasion resistance, and other properties from the viewpoint of film physical properties, such as () film crystallinity, molecular weight, mechanical strength, and the like. In this method, it is particularly important to adjust the crystallinity of the film, and abrasion resistance can sometimes be measured by lowering the crystallinity. However, in this case, there is a trade-off between lowering the degree of crystallinity, in that slitting properties are impaired as well, and in reality, there is only a small range in which such film properties can be changed within the range depending on the intended use. Furthermore, even if the physical properties of the film are changed, if the film material is, for example, only polyethylene terephthalate, it is essentially within the range of the properties of that material, and therefore this method also has a wide range of abrasion resistance. sex,
It was basically impossible to improve slipperiness. Furthermore, various methods have been proposed in which coating is applied during the manufacturing process of the base film (2) to improve wear resistance and slipperiness. in this way,
By using the selected coating material, the effect of imparting wear resistance and slipperiness is significant. However, this is essentially the same as applying the back coat described above, and the difference is whether the coating process is in the base film manufacturing process or in the process of manufacturing the magnetic tape using the base film. However, it is inevitable that costs will increase. [Means for Solving the Problems] Therefore, in view of the above-mentioned current situation, the inventors have greatly improved the abrasion resistance and slipperiness by a so-called polymer blend method. As a result of extensive research into a non-back coated base film, the present invention was achieved. That is, the gist of the present invention is that the poly(alkylene glycol) component is contained in an amount of 0.01 to 2.0% by weight, and its surface roughness Ra (μm) and refractive index n〓 in the thickness direction satisfy the following formula: Ra≦0.023 n〓≧1.491. The present invention relates to a biaxially oriented polyester film characterized in that it is within the range of The present invention will be explained in more detail below. Polyester as used in the present invention refers to aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalene-2,6-dicarboxylic acid or esters thereof, and glycols such as ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, etc. It is a polyester that can be obtained by polycondensing. These polyesters can be obtained by directly reacting aromatic dicarboxylic acids with glycols, or by polycondensation after transesterification of alkyl esters of aromatic dicarboxylic acids and glycols, or by polycondensation of diglycols of aromatic dicarboxylic acids. It can also be obtained by a method such as polycondensation of esters. Typical examples of such polymers include polyethylene terephthalate and polyethylene-2,6-
Examples include naphthalate. This polymer may be a homopolymer or may be a copolymer of a third component. In any case, in the present invention, 80 mol% of ethylene terephthalate units and/or ethylene-2,6-naphthalate units are used.
As mentioned above, polyester having preferably 90 mol% or more is preferable. In the present invention, if the degree of polymerization of the polyester is too low, the mechanical properties will deteriorate, so the intrinsic viscosity is preferably 0.40 or more, preferably 0.50 to 0.90, and more preferably 0.55 to 0.85. In the present invention, a biaxially oriented film is obtained using such polyester as a raw material, and the following method is employed for this purpose. That is, polyester is usually extruded into a sheet from an extruder at a temperature in the range of 280 to 320°C, cooled to a temperature of about 70°C or less to form a substantially amorphous sheet, and then the sheet is A biaxially oriented polyester can be obtained by stretching the polyester film in the same direction at least 4 times, preferably 9 times or more in area magnification, and then heat-treating the film at a temperature in the range of 120 to 250°C. In the present invention, a biaxially oriented polyester film is obtained in this manner, and in the present invention, the center line average roughness (Ra) of the film is 0.023μ or less,
Preferably 0.004 to 0.020μ, more preferably 0.005
It should be ~0.018μ, most preferably 0.006-0.015μ. When Ra exceeds 0.023μ, the surface roughness of the film becomes too large and, for example, when used as a magnetic tape, the electromagnetic conversion characteristics deteriorate. In addition, if the film surface is too flat, it will be difficult to handle in the film manufacturing process and magnetic layer coating process.
It is preferable that Ra is 0.004 or more, since unless special treatment such as back coating is applied, scratches and wrinkles are likely to occur, making it difficult to put it to practical use. In the present invention, in order to give the film such surface roughness, it is preferable to adopt the following method. In other words, it is convenient to add a fine inert compound to the polyester that is normally used for film formation.
Preferably adopted. There are two main types of such methods. One of them is called the addition method, in which kaolin,
Pulverize talc, magnesium carbonate, calcium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, silicon oxide, titanium oxide, or polymer compounds with crosslinked structures as necessary. This is a method in which it is added at any time after the polyester manufacturing process after classification and before the melt extrusion process for film formation. This method is one of the methods suitable for use in the present invention because it is easy to adjust the particle size and has excellent reproducibility, but the following so-called precipitated particle method is also easy to operate,
Since the resulting particles have excellent affinity with polyester, they can be preferably employed. The precipitated particle method is a method in which metal compounds such as lithium compounds, calcium compounds, and magnesium compounds, which are soluble in ethylene glycol and polyester oligomers during polyester production, are precipitated as fine particles in the presence or absence of phosphorus compounds. . Of course, these metal compounds can also function as catalysts, for example, if they are added at the beginning of the transesterification reaction. In the present invention, particles for developing the specific surface roughness necessary for the present invention are blended into polyester by such a method, but regardless of whether the additive particle method or the precipitated particle method is adopted, the The amount of particles is 0.005 to 2% by weight based on polyester.
Preferably 0.01 to 0.6% by weight, more preferably 0.02%
It is best to select from the range of ~0.5% by weight. The average particle diameter of such particles is usually selected from the range of 0.0002 to 4μ, preferably 0.1 to 2μ. Note that, as a matter of course, in the present invention, both methods can be used in combination if necessary. Next, this is the focus of the present invention, and in the present invention, poly(alkylene glycol) is added to a polyester film having a specific surface roughness in a specific trace amount, that is, 0.01 to 2.0% by weight based on the polyester film. Combine. That is, the present inventors have incorporated polyester film with poly(alkylene glycol), so that when used for magnetic tape, for example, the film and roll can be used in the magnetic tape manufacturing process or in the running system in decks and cassettes after magnetic tape production. Alternatively, the generation of abrasion powder due to frictional wear between the pin and the pin is significantly reduced, and this is achieved by adding a very small amount of poly(alkylene glycol), and these effects are achieved when the film surface Ra is 0.023μ. We have arrived at the present invention by discovering that this is particularly noticeable in the following flat areas. The inclusion of poly(alkylene glycol) in order to improve adhesiveness and slipperiness has already been proposed for base films for magnetic recording media and packaging, but in reality, the content is only 2 to 10% by weight. This is the case for base films with large surface roughness. Furthermore, because the content of poly(alkylene glycol) is high in this case, the heat resistance of the melt and the adhesion during electrostatic cooling are poor, and in the base film manufacturing process, low molecular weight substances are In addition, the electrostatic cooling method has the problem that the line speed cannot be increased because of the poor adhesion of the sheet to the casting roll in the electrostatic cooling method. In addition, fixing eyes due to thermal decomposition are likely to occur, and this is especially true when used for magnetic tapes, especially when using a base film with a flat surface like the one of the present invention used for high-performance magnetic tapes. This was a major problem because it was directly linked to defects. The present inventors have studied how to solve these problems and have found that these problems do not occur if the content of poly(alkylene glycol) is 2.0% by weight or less. On the other hand, if the amount of poly(alkylene glycol) blended is too small, for example less than 0.01% by weight, the effect of improving wear resistance, which is the most important feature of the present invention, will not be observed. Therefore, in the present invention, the amount of poly(alkylene glycol) added to the polyester film is 0.01 to 2% by weight, preferably 0.05 to 0.45% by weight, and more preferably 0.08 to 0.25% by weight. Poly(alkylene glycol) in the present invention
Examples include poly(ethylene glycol), poly(trimethylene glycol), poly(tetramethylene glycol), poly(hexamethylene glycol), and the like. Of course, it is also possible to use random or block copolymers, such as copolymers of ethylene oxide and propylene oxide, or ethylene oxide and tetramethylene oxide, or poly(alkylene glycols) whose terminals are substituted with alkyl or alkenyl groups.
Specific examples of the latter include poly(ethylene glycol) dilaurate, poly(ethylene glycol) distearate, poly(ethylene glycol) dibehenate, poly(ethylene glycol)
Dioleate, poly(propylene glycol) distearate, poly(ethylene glycol)-poly(propylene glycol) copolymer distearate, poly(ethylene glycol) monolaurate, poly(ethylene glycol) monostearate, poly(propylene glycol) mono Examples include stearate and the like. In any case, the poly(alkylene glycol) used in the present invention refers to one containing a polyether segment in its molecule, and it does not matter whether or not there is a covalent bond with the polyester component. In the present invention, the method of blending poly(alkylene glycol) into a polyester film is not particularly limited, but since the amount blended is small, a so-called masterbatch method is preferably employed. That is, a masterbatch containing about 1 to 20% by weight of poly(alkylene glycol) based on polyester is usually produced, and the masterbatch is formed into a film so that the amount of poly(alkylene glycol) in the film becomes the desired value. It should be blended with polyester. Such a masterbatch can be produced by a so-called melt polymerization method or by a dry blending method. The molecular weight of the poly(alkylene glycol) used in the present invention is 500 to 5,000,000, preferably
1000-1000000, more preferably 4000-500000,
Most preferably it is 8000-200000. If the molecular weight of the poly(alkylene glycol) is less than 500, the effect of the present invention will hardly be exhibited, and if this value is too large, the dispersibility in the polyester film will be poor, and the film will often have an unacceptably rough surface. Protrusions may occur, leading to dropouts and the like. In this way, in the present invention, it is essential that the film contains poly(alkylene glycol) in a certain range, but furthermore, the refractive index n of the film in the direction perpendicular to the film surface is greater than or equal to a certain value. It must be. That is, this n〓 represents the degree of plane orientation of the polyester film, and the higher this value is, that is, the lower the degree of plane orientation, the more remarkable the effect of improving wear resistance becomes. It has been found that the slipperiness, which is a characteristic characteristic, can be imparted to a sufficiently satisfactory level. On the other hand, if the value of n〓 is too large, the mechanical strength of the film will be poor. From this point of view, in the present invention, n〓 is
It needs to be 1.491 or more, preferably 1.492 to 1.510, more preferably 1.493 to 1.505. Obtaining such a film of the present invention cannot be achieved under conventional stretching conditions, but requires special conditions. For example, in longitudinal-transverse simultaneous biaxial stretching, this can be achieved by slightly lowering the longitudinal stretching ratio and making the longitudinal stretching temperature higher than the normal stretching temperature. Specifically, the longitudinal stretching temperature is preferably about 105 to 115°C, which is 5 to 30°C higher than the normal stretching temperature, but this is not the case if the longitudinal stretching ratio is lowered. Alternatively, the film of the present invention can also be obtained by subjecting it to extensive transverse relaxation after biaxial stretching and before heat treatment. Furthermore, it can also be achieved by a method such as heat treatment at a high temperature of 230° C. or higher, cooling once, and heat treatment at a high temperature again. Of course, when these methods are adopted, not all of them satisfy the requirements of the present invention, and the conditions of the film forming machine, such as the film forming speed and stretching width, or the conditions of the polyester raw material, such as the amount of copolymerization, Since this value depends on the crystallization rate and the like, the requirements of the present invention must be satisfied by appropriately selecting these conditions. Furthermore, in the present invention, when the crystallinity of the film is in a certain range, that is, in the range of 45 to 55%, the effects of improving abrasion resistance, slipperiness, and adhesion are further exhibited, and especially for magnetic recording media. It is preferable as a base film for. If this value is less than 45%, these properties will deteriorate and the mechanical strength will become inferior, and if this value is too large, the surface of the polyester film will become brittle and poly(alkylene glycol)
Despite the presence of , wear resistance deteriorates. The degree of crystallinity can be adjusted by a known method, mainly by changing the crystallization temperature. [Effects of the Invention] According to the present invention, it has been difficult to improve Ra to a satisfactory level in the region of 0.023μ, where flattening is particularly required to improve the performance of electromagnetic characteristics. Abrasion resistance and slipperiness can be improved industrially and easily by adding a specific trace amount of poly(alkylene glycol) and maintaining the refractive index perpendicular to the film surface at a specific value. . [Examples] The present invention will be explained in more detail by Examples below, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. The various physical properties were measured using the following methods. (1) Surface roughness: Ra According to the method described in JIS B0601-1976. Measurement was carried out using Kosaka Institute's surface roughness measuring machine model SE-
3FK was used. The stylus diameter was 5 μR, the stylus pressure was 30 mg, the cutoff value was 0.08 mm, and the measurement length was 2.5 mm. Measurements were made at 12 points, the maximum and minimum values were cut out, and the average value of the 10 points was shown. (2) Crystallinity (%) For polyethylene terephthalate, the density of the amorphous phase is 1.335, the density of the crystalline phase is 1.455, and for polyethylene naphthalate, the density is 1.325, respectively.
Calculated as 1.407. (3) Refractive index in the thickness direction: n〓 Using an Atsube refractometer, the
It was measured by a conventional method. (4) Coefficient of dynamic friction with metal: μd Wrapping the film around the fixed hard chrome-plated fixing pin (diameter 6 mmφ) with an angle of 135° (θ)
Apply a load of 53 g (T ₂ ) to one end, run it at a speed of 1 m/mm, measure the resistance force (T ₁ (g)) at the other end, and calculate the friction during running using the following formula. The coefficients were calculated. μd=1/θln (T ₁ /T ₂ )=0.424ln (T ₁ /53) (5) Evaluation of abrasion resistance Evaluation was performed using the tape abrasion evaluation machine shown in FIG. In other words, a 10mm wide tape-shaped film is
The vehicle was run over a length of 200 m, and the amount of abrasion powder adhering to the fixing pin (diameter 6 mmφ, hard chrome plating finish) shown in the figure was visually evaluated and ranked as shown below. The traveling speed of the film was 10 m/mm, the tension was detected by a tension pickup shown in , the initial tension was 400 g, and the winding angle θ around the pin was 135°. Rank ◎: No adhesion at all Rank ○: Almost no adhesion Rank △: Slight adhesion Rank ×: Large amount of adhesion (6) Formation of magnetic layer and evaluation of adhesive strength The magnetic layer was prepared by the following method. That is, the magnetic paint shown below was applied using a gravure roll to give a dry film thickness of 3 μm. Fe-based metal magnetic powder 100 parts Vinyl chloride-vinyl acetate copolymer 10 parts Polyurethane resin 10 parts Lecithin 3 parts Toluene 60 parts Cyclohexanone 5 parts Methyl ethyl ketone 70 parts After thoroughly mixing and dispersing the above magnetic powder-containing composition in a ball mill, Coronate L ( (manufactured by Nippon Polyurethane Co., Ltd.) was added and mixed uniformly to prepare a magnetic paint. The thus obtained sample was subjected to supercalender treatment and then subjected to measurement of the adhesive strength of the magnetic layer. The adhesive strength of the magnetic layer was measured as follows. That is, a double-sided adhesive tape is pasted onto a stainless steel plate with a thickness of 1 mm, and a magnetic recording film is pasted thereon so that the magnetic layer surface is in contact with the adhesive tape. Thereafter, the peel resistance force when the polyester 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/mm. Adhesive strength was expressed as a relative ratio to the adhesive strength of films obtained from polyethylene terephthalate homopolymer. (7) Number of fissure eyes After applying aluminum vapor deposition to the film surface, interference fringes were produced at a measurement wavelength of 0.54 μm using the two-beam method, and the number of protrusions consisting of fifth-order or higher interference fringes was counted over a measurement area of 25 cm ² . The number was converted to the number per ^200cm2 . Examples 1 to 8 and Comparative Examples 1 to 5 (Poly(alkylene glycol)) Molecular weight 20000 in polyester terephthalate
A master polymer containing 10% by weight of a poly(ethylene glycol) component having a molecular weight of 1000 and a master polymer containing 10% by weight of a poly(tetramethylene glycol) component having a molecular weight of 1000 were manufactured by each conventional method. In each example, the following polyethylene terephthalate (homopolymer) was mixed and diluted to have the content shown in Table 1. (Polyethylene terephthalate (homopolymer)) Three types of polyethylene terephthalate (homopolymer) each containing 0.4% by weight of silica with average particle diameters of 0.3 μm, 0.4 μm, and 0.5 μm were produced by a conventional method, and in each example, these The surface roughness of the film was adjusted by appropriately blending them. (Film Formation) A master polymer containing poly(alkylene glycol) and polyethylene terephthalate (homopolymer) were mixed, melt-extruded using a conventional method, and rapidly solidified by electrostatic cooling on a casting roll maintained at 40°C. An unstretched film was obtained. This unstretched film is passed through a multi-stage longitudinal stretching machine to be longitudinally stretched, and then passed through a stenter at a stretching temperature of 125
The film was laterally stretched 3.7 times at 190° C. and heat-set for 3 seconds at a temperature of 190° C. or above to obtain a biaxially stretched polyester film with a thickness of 14 μm. Here, films with different densities were obtained by varying the heat setting temperature, and films with different refractive indices in the thickness direction were obtained by varying the longitudinal stretching temperature and longitudinal stretching ratio. The evaluation results of the various films obtained are summarized in Table 1. From this, even if a small amount of poly(ethylene glycol) was added, the refractive index was adjusted within the range of the present invention, that is, Examples 1 to 8 were all compared to the comparative example having the same level of surface roughness. By comparison, it can be seen that the wear resistance and/or slipperiness are dramatically improved. Furthermore, the product in which 3.0 wt% of polyethylene glycol was added as in Comparative Example 5 already had problems in terms of productivity and fixability. It can also be seen that all the products of the present invention are also improved in terms of adhesiveness.

[Table] I couldn't do it. In addition, white powdery low-molecular weight substances were frequently generated, and the number of fisheyes in the film was also significantly increased.

[Brief explanation of drawings]

Figure 1 shows the running system for evaluating wear resistance.
indicates a fixed pin of 6 mmφ, indicates a tension meter, and θ is 135°.

Claims (1)

[Claims] 1. The poly(alkylene glycol) component is 0.01 to
A biaxially oriented polyester film containing 2.0% by weight and having a surface roughness Ra (μm) and a refractive index n in the thickness direction within a range satisfying the following formula. Ra≦0.023 n〓≧1.491