JPH0321969B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a magnetic recording medium comprising a flexible support such as a film or sheet made of polyester, and a magnetic layer provided on one or both sides of the surface. More specifically, the present invention relates to a magnetic recording medium whose main feature is the use of a flexible support made of a special polyester that has low moisture absorption and improved moisture absorption dimensional stability. (Prior Art) Magnetic recording media such as magnetic tapes, magnetic cards, floppy disks, etc., in which a magnetic layer is provided on one or both sides of a flexible support made of polyester such as biaxially stretched polyethylene terephthalate film, have been well known. and is still in use in large quantities today (for example, JP-A-53-107314; JP-A-53-107314;
-Refer to Publication No. 93804). The basic physical properties required of the polyester film that serves as the base film for magnetic tapes include its surface properties (slip properties, surface smoothness, abrasion resistance, absence of foreign substances, etc.), mechanical properties (resistance to minute deformation, etc.) Properties - Young's modulus, strength, residual elongation -
creep properties, film stiffness, etc.), heat resistance and dimensional stability, etc. By the way, as devices become more sophisticated, precise, and compact, recording magnetic materials are also required to have even higher densities, and as a result, the dimensional stability of the supports that form the basis of magnetic recording media becomes extremely important. It has become an important characteristic. For magnetic recording media, dimensional stability as well as mechanical properties are important characteristic values. In the case of magnetic recording media using supports such as polyester films, dimensional stability due to heat (e.g. heat shrinkage,
Although changes in flatness (changes in flatness) have been studied from various angles, dimensional changes due to moisture absorption have hardly been recognized. The reason for this is that polyester inherently exhibits low moisture absorption, but now dimensional stability associated with moisture absorption has also become an industrially important characteristic. That is, the hygroscopic expansion coefficient of conventional biaxially stretched polyester films is about 0.06 to 0.1%, but this level of hygroscopic expansion coefficient is not necessarily sufficient as a support for advanced recording media. (Problems to be Solved by the Invention) The present invention has quickly focused on this point and aims to provide a polyester-based magnetic recording medium with improved moisture absorption dimensional stability. As a result of research aimed at achieving this objective, the present inventors have discovered that the composition of the terminal groups of polyester surprisingly has a large effect on the hygroscopicity of polyester, as well as on the dimensional changes associated with moisture absorption, and that the hydroxyl and carboxyl groups at the terminals of polyester The present invention was completed based on the discovery that the moisture absorption dimensional stability can be significantly improved by sealing. (Means for Solving the Problems) The present invention provides a magnetic recording article comprising a flexible support made of polyester and a magnetic layer provided on one or both sides thereof, wherein the polyester has an intrinsic viscosity of 0.4.
The above is a magnetic recording medium with excellent hygroscopic dimensional stability, characterized in that the sum of terminal hydroxyl groups and carboxyl groups is 60% or less of the total terminal group amount by terminal blocking, and that it does not contain hydrophilic groups. be. In the present invention, polyester refers to a polyester whose main repeating unit is ethylene terephthalate or ethylene 2,6-naphthalate, and a portion (for example, 20 mol% or less) of its acid component and/or glycol component is The acid component and/or other acid component or other glycol component may be substituted. Examples of such third components include isophthalic acid, 1,5-naphthalene dicarboxylic acid, 2,7-
naphthalene dicarboxylic acid, 4,4'-diphenyl dicarboxylic acid, 4,4'-diphenoxyethane dicarboxylic acid, 4,4'-diphenyl sulfone dicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid,
p-β-hydroxyethoxybenzoic acid, adipic acid, azelaic acid, sebacic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, ε-oxycaproic acid, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene glycol, Examples include neopentylene glycol. These are 1 type or 2
More than one species may be copolymerized. The polyester may also contain polyfunctional compounds such as pentaerythritol, trimethylolpropane, trimellitic acid, trimesic acid and functional derivatives thereof and/or o-benzoylbenzoic acid, methoxy to the extent that the polyester is substantially linear. It may also be a copolymer of monofunctional compounds such as polyethylene glycol and functional derivatives thereof. Additives such as stabilizers (for example, stabilizers against heat, ultraviolet rays, and oxygen), lubricants, pigments, fillers, mold release agents, antistatic agents, and nucleating agents are added to such polyesters as necessary. However, it is preferable to use highly stable additives. In the present invention, the polymer is polymerized at any stage before the polyester is polymerized and subjected to melt film formation and stretching by a conventional method to produce a base film or sheet-like material that becomes a flexible support. The total amount of terminal hydroxyl groups and carboxyl groups in the polyester (almost 100% in normal polyester films) is reduced to 60% of the total amount of terminal groups.
% or less, preferably 40% or less, particularly preferably 30%
% or less, the moisture absorption dimensional stability can be greatly improved, making it possible to apply it to supports for magnetic recording media with further improved precision. As a means to convert this terminal group and make it inert to moisture, for example, at a stage where the degree of polymerization has increased to a certain degree before the polymerization is completed, diphenyl carbonate, dicyclohexenyl acetate, etc. There is a method of adding an appropriate amount of a terminal capping agent such as , tetraphenyl orthocarbonate, diphenyl terephthalate, or diphenyl oxalate and reacting with the active terminal group to block the terminal hydroxyl group and terminal carboxyl group of the polyester. In addition, hydroxyl groups are converted into carboxyl groups in advance by acid anhydride treatment, etc., and terminal carboxyl groups are blocked by diazomethane treatment in the form of molded products or intermediates (e.g., polymer powder or pellets). , resulting in a reduction in active end groups. In this method, as in the case of adding an end-capping agent, it is necessary to treat the ends of the polyester so as not to leave any hydrophilic groups. Here, the hydrophilic group is copolymerized with polyethylene glycol or 5-sulfoisophthalic acid component, or a group such as a urethane group or an amide group is introduced as a result of an end-blocking process. As mentioned above, it has not been known at all that the hygroscopic dimensional stability of a film can be improved by changing the terminal groups of polyester. Achieving this objective is of extremely great industrial significance. It is essential that the polyester used as the flexible support used in the present invention has an intrinsic viscosity of 0.4 or more when measured in orthochlorophenol at 35°C. If the intrinsic viscosity is below this range, the molecular weight is low, so it is very difficult to form a film and it is not practical. In the present invention, the terminal-capped polyester described above can be formed into a sheet or film by a conventionally known method. That is, the above-mentioned polyester is melt-extruded using an extruder or the like and rapidly cooled on a casting drum, and this substantially unstretched film is subjected to one or more stages of stretching in at least one direction, followed by heat treatment and other treatments as necessary. Perform relaxation treatment under appropriate conditions. Recent magnetic recording conditions require magnetic recording materials to have even higher Young's modulus and dimensional stability, and Young's modulus can be accommodated in a wider range through multi-stage high-magnification stretching through various studies on stretching means. The thickness of the support film or sheet used in the present invention can be arbitrarily selected as required, but is usually 1 to 500 μm, preferably 3 to 125 μm. The method of providing the magnetic layer on the polyester film or sheet serving as the non-magnetic flexible support of the magnetic recording medium of the present invention is not particularly limited, but a magnetic material is mixed with a binder mainly composed of an organic polymer compound. There is a way to apply it. The magnetic materials used are iron oxides such as iron oxide (γ-Fe ₂ O ₃ / Fe ₃ O ₄ ), modified iron oxides by adding Co, or adhering Co or Co-containing Fe ₃ O ₄ . system, chromium oxide (CrO ₂ )
It can be divided into alloys such as iron-cobalt-nickel (or copper), and metal-based materials using surface-modified products thereof. Other methods include forming an iron-cobalt-nickel alloy directly on a support film or sheet by vacuum evaporation, sputtering, ion plating, etc. without using an organic binder; Any method can be applied, such as forming the system compound on a support film or sheet by chemical plating. Furthermore, prior to providing the magnetic layer, the support film or sheet surface may be subjected to treatments or coatings for cleaning, promoting adhesion, improving smoothness, etc. Furthermore, the back side of the support film or sheet (on the side on which the magnetic layer is not provided) has slip properties,
Coating (back coat) for imparting abrasion resistance, antistatic properties, etc. can also be optionally applied. (Example) Next, the present invention will be further explained with reference to Examples. In the examples, "parts" represent parts by weight. The intrinsic viscosity was measured at 35°C using orthochlorophenol as a solvent. In addition, the measurement of carboxyl group is carried out by A.Conix.
The method of Makromol.Chem., 26 , 226 (1958) was adopted. Furthermore, the hydroxyl groups were converted to carboxyl groups by reacting the polymer with succinic anhydride in α-methylnaphthalene, and measured by the method described above, and the difference between the carboxyl group value measured initially and the value after carboxylation treatment was taken as the hydroxyl group. Examples 1 to 4 and Comparative Examples 1 to 3 194 parts of dimethyl terephthalate, 130 parts of ethylene glycol, 0.098 parts of manganese acetate tetrahydrate, and 0.079 parts of antimony trioxide were placed in a reactor equipped with a rectification column, and gradually heated under a nitrogen atmosphere. The mixture was stirred while heating. Methanol produced as a result of the transesterification reaction was taken out of the system via a rectification column, and the collected amount reached a transesterification rate of 98.5%, at which point the temperature inside the system was 235°C. A distillation condenser is installed except for the rectification column, and 0.0395% of phosphoric acid is added as a stabilizer in the system.
and 0.03% kaolin as a lubricant. After raising the temperature in the system to 280°C and continuing the reaction for 30 minutes, the pressure in the system was gradually reduced to a high vacuum of 0.5 mmHg or less over about 40 minutes. 90 as is
The reaction continued for minutes. The intrinsic viscosity obtained from the sample at this time was 0.68. At this point, the inside of the system was returned to normal pressure with nitrogen, 7.5 parts of diphenyl carbonate (3.5 mol% per acid component) was added as an end-blocking agent, stirred for 5 minutes, and then 0.5 mm thick again while being careful not to foam.
A high vacuum below Hg was applied, the mixture was stirred for 15 minutes, and the polymer was taken out. The intrinsic viscosity of this end-capped polymer was 0.60. This polymer was chipped and dried for 7 hours using a hot air dryer at 150°C. This polymer was immediately melt-extruded using an extruder-type film forming machine at a die temperature of 280°C, and then taken as a sheet onto a casting drum. The obtained unstretched sheet was sequentially biaxially stretched under the following conditions. Stretching conditions are 3.9 times at 80℃ in the longitudinal direction and 110℃ in the width direction.
3.5 times. Biaxially stretched film
Fixed-length heat treatment was performed at 200℃. The resulting film had a thickness of 12 μm, good transparency, and an intrinsic viscosity of 0.52. The active terminal groups of this film were measured and found to be 24 equivalents/ton of hydroxyl groups and 14 equivalents/ton of carboxyl groups, and the total proportion of hydroxyl groups and carboxyl groups to all terminal groups was 30% (Example 1). Polyethylene terephthalate films having different degrees of polymerization were also produced in the same manner (Examples 2 to 4). For comparison, various end-blocking samples were prepared in the same way, and ordinary polyester films without diphenyl carbonate treatment (the above ratios are approx.
The dimensional changes due to water absorption in comparison with 100%) are shown in the table below as Comparative Examples 1 to 3. Please note that dimensional changes due to water absorption are based on a sample length of 20 cm.
A test piece of about 100 ℃ was dried by hanging it in a dryer at 50℃ for 16 hours, and then it was immersed in water at 25℃ for 24 hours to determine the change in length before and after immersion (length in the machine direction and/or width direction). change). Furthermore, the degree of swelling due to water absorption can also be measured from the change in weight due to water absorption. The former was expressed as water absorption swelling rate, and the latter was expressed as water absorption rate.

[Table] After corona treatment was applied to one side of the polyester films obtained in Examples 1 to 4, 70% by weight of acicular γ-type ferric oxide fine powder, based on the total solid content, was applied to the same treated side. A magnetic layer with a thickness of 5 μm consisting of 15% by weight of urethane resin, 10% by weight of poly(vinyl chloride/vinyl acetate) resin, and 5% by weight of thermoplastic polyester resin was laminated, and this was made into a magnetic recording material by a conventional method. I slit it to 19mm width and made magnetic tape. Adhesion, running properties, abrasion resistance of the magnetic layer, and distortion/disturbance during playback of drop-out recordings were at a good level. On the other hand, the films using the films of Comparative Examples 1 to 3 were inferior in the above characteristics. (Effects of the Invention) According to the present invention, the support made of polyester has a low water absorption coefficient and a low water absorption expansion coefficient (for example,
(less than 0.05%), a magnetic recording medium with excellent moisture absorption stability is provided. Such media are particularly suitable as audio, video, computer tapes, and the like.

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer is provided on one or both sides of a flexible support made of polyester, in which the intrinsic viscosity of the polyester is 0.4 or more, and the polyester has a total hydroxyl group and a carboxyl group at the end due to terminal blocking. 1. A magnetic recording medium with excellent moisture absorption and dimensional stability, characterized in that the amount of terminal groups is reduced to 60% or less of the total amount of end groups, and that it does not contain hydrophilic groups.