JPH0257573B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an aromatic polyester film that has a flat surface, excellent slipperiness, and improved abrasion resistance. Aromatic polyesters, particularly polyethylene terephthalate, are mainly produced by esterifying or transesterifying terephthalic acid or terephthalic acid dimethyl ester with ethylene glycol to obtain bis(2-hydroxyethyl) terephthalate or its low polymer. , and a second stage reaction in which this is further polycondensed. It is well known that demand for biaxially stretched films produced from aromatic polyesters obtained by these methods, particularly polyethylene terephthalate, is increasing due to their excellent mechanical properties. Recently, magnetic tapes using polyethylene terephthalate as a base film have been widely used for video and audio applications, and their consumption is increasing at a remarkable rate. Furthermore, technological trends in magnetic tapes for video and audio applications are moving toward increasing the magnetic recording density per unit area and realizing long-term recording in a compact size. To obtain such a high recording density magnetic tape, a base film with a very flat surface is required. However, with conventional technology, flattening the surface reduces the slipperiness of the film.
Conflicting phenomena were observed, including a decrease in workability in the film manufacturing process and magnetic tape production process. Conventionally, methods have been proposed in which various additives such as clay, calcium carbonate, silica, titanium oxide, and inorganic fine particles such as talc are added to polyester either singly or in combination in order to impart film slipperiness. In order to improve the slipperiness by these methods, the amount of additive must be increased, and the additive may partially aggregate in the polyester.
Therefore, when molded into a film, many coarse particles are scattered on the film surface, causing dropouts. Further, the aggregated additives are scraped off by repeated running of the tape, resulting in the generation of white powder, which poses a problem in that the tape is difficult to use. On the other hand, a method has also been proposed in which the catalyst used in the reaction is reacted with a stabilizer mainly consisting of a phosphorus component in a system, and the resulting particles are used as a lubricant.
This is still insufficient in terms of both flatness and slipperiness and stability of particle formation. In order to obtain a polyester film that has a flat surface, has excellent slipperiness, does not generate white powder, and has good abrasion resistance, the inventors of the present invention have made special indentations on the surface of the film. The present invention has been achieved by discovering that it is sufficient to form such a structure. That is, the present invention disperses and contains a linear polymer that does not substantially undergo a redistribution reaction with aromatic polyester, and has fine particles with an average diameter of 5 μm or less formed on the surface of the film by the linear polymer. 100 hollows
This is an aromatic polyester film characterized in that it has an aromatic polyester film of at least 100% polyester per mm ² . The aromatic polyester referred to in the present invention has terephthalic acid and naphthalene dicarboxylic acid as main acid components, and at least one glycol, preferably at least one alkylene glycol selected from ethylene glycol, trimethylene glycol, and tetramethylene glycol. The main target is aromatic polyesters whose main glycol component is aromatic polyester. It may also be a polyester in which part of the terephthalic acid component is replaced with another bifunctional aromatic carboxylic acid component, and further, part of the glycol component is replaced with the above glycol other than the main component or another diol component. It may also be made of polyester. Examples of difunctional aromatic carboxylic acids other than terephthalic acid and naphthalene dicarboxylic acid used here include isophthalic acid, diphenoxyethane dicarboxylic acid, β-hydroxyethoxybenzoic acid, p-oxybenzoic acid, and 5-sodium Examples include sulfoisophthalic acid. Examples of diol compounds other than the above-mentioned glycols include aliphatic, alicyclic, and aromatic diol compounds such as cyclohexane-1,4-dimethanol, neopentyl glycol, and bisphenol A, and polyoxyalkylene glycols. Can be done. The aromatic polyester film of the present invention has a first
As shown in the figure, it is necessary to have depressions that are recessed from the baseline of the film surface. If a conventional film has only irregularities as shown in Figure 2, the surface of the film will become rough if you try to make it slippery, making it insufficient for use in high-density magnetic tapes. It is unsuitable because it cannot be used and white powder is generated by repeated running, which interferes with the use of the tape. The average size of the depressions is less than 5μ in diameter, and because they are shallow, they hardly contribute to the roughness of the film surface. The preferred average diameter is 3μ or less. here,
The diameter of a depression is the equivalent diameter when the area of the depression is converted into a circle, and the average diameter is this equivalent diameter.
It is the average value of 100. When the average diameter of the depressions exceeds 5 μm, the film surface becomes rough due to the depressions, and problems such as a decrease in the magnetic conversion characteristics of the magnetic tape occur. The number of depressions is 10 ²
The number of particles/mm2 ^or more is required. 10 ² pieces/mm ²
If it is less than that, the improvement in slipperiness and abrasion resistance cannot be achieved. Particularly preferably, the number is 10 ³ pieces/mm ² or more. These "dents" are not created by conventional mechanical stamps such as embossing, but by a combination of aromatic polyester and a linear polymer that does not substantially cause a redistribution reaction with the aromatic polyester. It is formed by That is, the depressions on the film surface are formed by uniformly dispersing linear polymers in aromatic polyester, melt-extruding the resulting molten mixture to form an unstretched film, and then subjecting it to biaxial stretching. It is something that will be done. The shape of the depression can be changed depending on the film stretching conditions, the composition of the linear polymer, the degree of polymerization, etc. For example, depending on the stretching conditions,
When the longitudinal and transverse stretching ratios of the film are made almost the same, the depressions become circular or oval-shaped, and when the stretching ratio in either direction is increased, the depressions tend to become oval. The timing of dispersing and mixing the linear polymer, which does not substantially cause a redistribution reaction with the aromatic polyester, into the aromatic polyester is not particularly limited, and the timing can be uniformly dispersed and mixed with the aromatic polyester. That's fine. Further, as the method, conventionally used methods such as extruding with an extruder after chip blending can be adopted. Here, "does not substantially cause a redistribution reaction with the aromatic polyester" refers to the temperature at which the aromatic polyester is melted (mixed) and extruded, usually from the melting point of the aromatic polyester to the melting point + about 50°C. temperature,
This means that random copolymerization by transesterification reaction with the aromatic polyester hardly occurs during the melt contact time, usually within about 10 minutes. Further, in producing the polyester film of the present invention, there is no problem in containing commonly used stabilizers, color toners, pigments, etc. Examples of linear polymers that do not substantially cause a redistribution reaction with aromatic polyesters include oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanoic acid, and dodecanedioic acid. , brassylic acid, tetradecanedioic acid, pentadecanedioic acid, and tabsic acid as the main acid component; ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl; Preferred examples include aliphatic polyesters whose main glycol component is at least one selected from the group consisting of glycol, cyclohexanedimethanol, and metaxylene glycol. The amount of the linear polymer, especially the aliphatic polyester, to be added is 0.05 to 10 percent by weight, based on the aromatic polyester, to create depressions that are effective for improving slipperiness. If the amount added is less than 0.05% by weight, the number of depressions generated is insufficient and cannot contribute to slipperiness and abrasion resistance, and if it exceeds 5% by weight, the physical properties of the polyester film itself will change. This is not desirable. Further, the aromatic polyester film having dimples of the present invention exhibits even better slipperiness when combined with conventional means for imparting slipperiness by forming fine protrusions on the surface of the film. In the case of conventional projections, in order to impart slipperiness, it is necessary to increase the number of projections, and as a result, the film surface becomes rough, making it unsuitable for use as a high-density magnetic tape. It was enough. However, if the fine depressions of the present invention are combined with conventional protrusions, sufficient slipperiness can be obtained even if the number of protrusions is significantly reduced compared to conventional protrusions, and the number of protrusions is also reduced, reducing the generation of white powder. It can also be suppressed. Note that, as can be understood from the fact that the above-mentioned depressions and protrusions have different formation factors, they basically exist independently. Methods for making protrusions used in combination with the indentations of the present invention include the previously proposed method of adding inorganic fine particles such as clay, calcium carbonate, silica, titanium oxide, and talc, and the method of adding inorganic fine particles such as clay, calcium carbonate, silica, titanium oxide, and talc, and the method of adding catalysts and A method that utilizes precipitated particles generated by the reaction of additives, etc. can be adopted. As explained above, the aromatic polyester film of the present invention has at least ¹⁰² / ^mm2 fine depressions with an average diameter of 5μ or less on its surface.
Because the surface is flat and has excellent slipperiness, it exhibits suitable performance as a high recording density magnetic tape, and even with a small number of protrusions on the surface, sufficient slipperiness can be obtained. The production of white powder caused by the scraping of protrusions due to repeated running of the film tape was significantly suppressed, and the wear resistance was improved. Although the present invention aims to improve base films for magnetic tapes, the film of the present invention is not limited to magnetic tape applications, but can be used in all applications that require smoothness and ease of use. Can be applied. EXAMPLES The present invention will be specifically explained below with reference to Examples, but is not limited thereto. The surface roughness, slipperiness, and abrasion resistance were evaluated using the following methods. (Surface roughness) Surface roughness meter (Surtronic 3: Taylor-
The center line average roughness (Ra) was measured using a method (manufactured by Hobson). (Easy slippage) Static friction coefficient (μs) between films
Measured according to ASTM-D-1894B method. (Abrasion resistance) The film was slit to a width of 1/2" to obtain a tape with a length of 1 m. Both ends were spliced into loops, and the tape was run continuously at a speed of 2 cm/sec on a stainless steel pin with a diameter of 5 mm. The amount of white powder generated on the pin after 24 hours was examined and ranked as follows: Rank 1: Almost no white powder generated. Rank 2: A slight amount of white powder generated, but suitable for use in video applications. There is no problem. Rank 3: A lot of white powder is generated, so it cannot be used for video applications. (Number of depressions) Aluminum is uniformly vacuum-deposited on the film surface to a thickness of 400 to 500 Å or less, and differential interference Reflection microscope (e.g. Carl Zeiss JENA)
Take a photo of any location at 400x magnification, find the number of indentations, and convert it to ^1mm2 . At this time, the field of view of one photo is 0.01 ^mm2 . (Average diameter of dents) After magnifying all or part of the dents counted in the measurement of the number of dents 20,000 times with an electron microscope, they were individually measured using an image analysis device (Ruzex 500: Nippon Regulator). The area of the depression was calculated. From this area, the equivalent diameter when converted to a circle with the same area was calculated. Determine the above equivalent diameter for 100 depressions,
These average values were taken as the average diameter. Examples 1, 2 and Comparative Example 1 Polyester obtained by adding 0.1 part by weight of clay having an average particle size of 0.5 μm to 100 parts by weight of dimethyl terephthalate and 65 parts of ethylene glycol and polycondensing the mixture in a conventional manner was pelletized. It was cut into pieces. The intrinsic viscosity of this pellet was measured in o-chlorophenol at 35 DEG C. and found to be 0.62. To 100 parts by weight of the pellets, polyhexamethylene sebacate pellets were added and mixed in the proportions shown in Table 1, and melt-mixed in an extruder at 280°C for 5 minutes to obtain an unstretched sheet with a thickness of 210μ.
This unstretched sheet was heated to 95° C. using a long stretching machine and simultaneously biaxially stretched to 3.5×4.0 times to obtain a biaxially stretched film, which was then heat-set at 210° C. for 30 seconds.
The evaluation results of this film are shown in Table 1. on the other hand,
For comparison, a film was obtained in exactly the same manner except that polyhexamethylene sebacate was not added, and the results are also shown in Table 1.

[Table] As shown in Table 1, a film containing polyhexamethylene sebacate and having 10 ² or more microscopic pits/mm ² has excellent slip resistance and smoothness with almost no change in surface roughness. It can be seen that it has excellent abrasion resistance. On the other hand, when polyhexamethylene sebacate is not added (Comparative Example 1), no depressions are formed on the film surface, resulting in poor slipperiness and abrasion resistance. Example 3 A film was obtained in exactly the same manner as in Example 1 except that 1% by weight of polytetramethylene adipate was added and mixed in place of the polyhexamethylene sebacate in Example 1. The results are shown in Table 2. Comparative Example 2 The polytetramethylene adipate of Example 3 was
A film was obtained in exactly the same manner as in Example 3 except that the amount was 0.01 part by weight. The results are shown in Table 2. Comparative Example 3 A film was obtained in the same manner as in Comparative Example 1 except that 0.5 parts by weight of clay was added instead of 0.1 part by weight of the clay in Comparative Example 1, and no linear polymer was contained. The results are also listed in Table 2.

[Table] As is clear from Table 2, it contains polytetramethylene adipate and has 10 ² minute indentations.
A film having more than ¹⁰ dents/mm2 has excellent slipperiness and abrasion resistance (Example 3), but the number of dents is ¹⁰² /mm2.
If it is less than mm ² (Comparative Example 2), slipperiness and abrasion resistance will be poor. Furthermore, when attempting to improve slipperiness by increasing the amount of clay added without adding polytetramethylene adipate (Comparative Example 3), the film surface becomes rough and the abrasion resistance deteriorates. Example 4 A film was obtained in exactly the same manner as in Example 1 except that 0.03 parts by weight of calcium carbonate having an average particle size of 0.8 μm was contained in place of the clay of Example 1 having an average particle size of 0.5 μm. This film has depressions, the average diameter of which is 0.3 μm, and the number of depressions is 2 × 10 ⁴ (indentations/
mm ² ), Ra: 0.033 (μm), μs: 0.35, wear resistance: rank 1, and had excellent characteristics as a base film for high recording density magnetic tape.

[Brief explanation of the drawing]

FIG. 1 is a schematic enlarged side view showing the surface condition of the film of the present invention, and FIG. 2 is a schematic enlarged side view showing the surface condition of a conventional film.

Claims (1)

[Scope of Claims] 1. A film containing a dispersed linear polymer that does not substantially undergo a redistribution reaction with the aromatic polyester, and having an average diameter of 5 μm or less formed by the linear polymer on the surface of the film. An aromatic polyester film characterized by having 100 or more microscopic depressions/ ^mm2 . 2 The linear polymer is oxalic acid, malonic acid, glutaric acid, adipic acid, pimelic acid, suberic acid,
The main acid component is at least one acid selected from the group consisting of azelaic acid, sebacic acid, undecanoic acid, dodecanedioic acid, brassic acid, tetradecanedioic acid, pentadecanedioic acid and tabucic acid,
ethylene glycol, trimethylene glycol,
Claim No. 1, which is an aliphatic polyester whose main glycol component is at least one glycol selected from the group consisting of tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, neopentyl glycol, cyclohexanedimethanol, and meta-xylene glycol. Aromatic polyester film according to item 1. 3. The aromatic polyester film according to claim 1 or 2, wherein the content of the linear polymer is 0.05 to 10% by weight based on the aromatic polyester.