JPH089674B2 - Biaxially oriented polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biaxially oriented polyester film containing monodispersed flat crosslinked polymer particles, which is excellent in surface uniformity and abrasion resistance.

[Problems to be Solved by Conventional Techniques and Inventions]

BACKGROUND OF THE INVENTION Polyester films, especially biaxially oriented films represented by polyethylene terephthalate, have excellent physical and chemical properties and are widely used as base films and capacitor derivatives for magnetic recording media. Further, by utilizing its excellent transparency, it is widely used in the fields of graphic arts, displays and packaging materials.

In each of these applications, the tendency toward higher grades has become remarkable in recent years, and it has been strongly desired that the film surface be uniform. In addition, the friction between the two films or when the film and the base material contact each other at a high speed, the abrasion characteristics typified by the abrasion of the film surface layer due to abrasion and the loss of particles contained in the film are not always sufficient. There is a long-awaited improvement in points. Especially, in magnetic recording applications where higher quality is required, it is necessary to sufficiently satisfy these points.

It is generally known that the surface of the film may be appropriately roughened in order to improve the running property and abrasion resistance of the film. For this reason, a method in which fine particles are present in the raw material polyester has been adopted, and some of them have been put into practical use, but these properties have not been sufficiently satisfied.

For example, in the case of using precipitated particles as fine particles, which are formed by a catalyst residue or the like during the production of polyester, the fine particles are easily broken by stretching, so that the running property and abrasion resistance are inferior and the recycling is difficult. Further, when inert inorganic or organic particles are added to and blended with the polyester, the particles are likely to peel off from the film surface to produce a white powdery substance. It causes deterioration and frequent dropouts.

As described above, it has been the actual situation that a polyester film having a high degree of surface uniformity and abrasion resistance has not been obtained so far.

[Means for solving the problem]

As a result of intensive studies in view of such problems, the present inventors have found that a film containing crosslinked polymer particles having a specific shape has excellent properties, and completed the present invention.

That is, the gist of the present invention is that the average particle size is 0.05 to 3 μm,
Ratio (Dw / D) of weight average particle diameter (Dw) to number average particle diameter (Dn)
n) is 1.3 or less, and the ratio of minor axis to thickness (flatness)
0.01 to 4% by weight of flat cross-linked polymer particles having a content of 1.5 to 15
It exists in the biaxially oriented polyester film characterized by containing.

 Hereinafter, the present invention will be described in more detail.

In the present invention, polyester means terephthalic acid, 2,6
An aromatic dicarboxylic acid such as naphthalenedicarboxylic acid or its ester, and a polyester obtained by using ethylenegtacol as a main starting material, but may contain other third component. For example, as the dicarboxylic acid component, one type such as isophthalic acid, terephthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid and sebacic acid can be used. As the glycol component, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexanedimethanol, neopentyl glycol and the like can be used. In any case, the polyester of the present invention refers to a polyester in which 80% or more of repeating structural units have ethylene terephthalate units or ethylene-2,6-naphthalate units.

Further, the polyester film of the present invention refers to a polyester film having such a polyester as a starting material and oriented in at least a uniaxial direction, and a known method can be used as a manufacturing method thereof. For example, usually, after melt extruding into a sheet at 270 to 320 ℃, 40 to 80
Chilled and solidified at ℃ to form an amorphous sheet, then 80-130
A method of biaxially stretching at a temperature of 4 to 20 times in the machine direction in the machine direction and in the transverse direction at a temperature of 160 to 250 ° C. and heat-treating at 160 to 250 ° C. (for example, the method described in JP-B 30-5639) is used. be able to. When stretching in the machine and transverse directions, each may be stretched in one stage, or may be stretched in multiple stages or a heat treatment section for orientation relaxation may be provided between the multi-stage stretches, if necessary. Further, after biaxial stretching, it may be stretched again before being subjected to the heat treatment step of the next step. This re-stretching can be carried out in any of the longitudinal and lateral directions, or in both directions.

The greatest feature of the present invention is that monodispersed flat crosslinked polymer particles are used as particles to be blended in the polyester film.

The method for producing such particles is not particularly limited, but as a typical production example, there can be mentioned a method in which monodisperse spherical crosslinked polymer particles are first obtained, and then the particles are deformed into a flat shape by applying an external force. The monodisperse spherical crosslinked polymer particles can be produced by one or more monovinyl compounds (A) having only one aliphatic unsaturated bond in the molecule and two or more fats in the molecule as a crosslinking agent. A method in which one or more compounds (B) having a group unsaturated bond are used and an emulsion polymerization method (broadly defined emulsion polymerization including concepts such as soap-free emulsion polymerization and seed emulsion polymerization) is applied is preferred.

The compound (A) used for obtaining the monodisperse spherical crosslinked polymer particles includes acrylic acid, methacrylic acid and their alkyl or glycidyl esters, maleic anhydride and its alkyl derivatives, vinyl glycidyl ether, vinyl acetate, styrene. , Alkyl-substituted styrene, and the like.

Further, examples of the compound (B) include divinylbenzene, divinylsulfone, ethylene glycol dimethacrylate and the like. One or more compounds (A) and (B) are used, but a compound having a nitrogen atom or ethylene may be copolymerized.

One embodiment of the production of monodisperse spherical crosslinked polymer particles in the present invention is as follows. That is, after dissolving a predetermined amount of a water-soluble polymerization initiator such as hydrogen peroxide or potassium persulfate in an aqueous medium, a predetermined amount of a mixed solution of the compounds (A) and (B) is added. Thereafter, the temperature is not lower than the decomposition start temperature of the polymerization initiator, preferably at 30 to 90 ° C under stirring.
Perform the reaction for about 10 hours. At that time, depending on the monomer composition, some aggregated particles may be generated, and in this case, a dispersion stabilizer such as an emulsifier may be added in order to maintain the dispersion stability of the particles. In any case, the particles are obtained as a uniformly dispersed water slurry.

Then, an external force is applied to the obtained monodisperse spherical crosslinked polymer particles so as to crush the particles. At this time, external force may be directly applied to the particles, water, ethylene glycol,
External force may be applied in a state of being dispersed in a matrix of polyester oligomer, polyester or the like. Examples of the external force imparting means include, but are not limited to, a compressor such as a roller mill, a ball mill, and a medium stirring mill, and a crusher.

More specific conditions for particle flattening are as follows.
That is, the monodisperse spherical crosslinked polymer particles obtained as an aqueous slurry are treated with a sand grinder, which is a kind of medium stirring mill, at a peripheral speed of 1 to 15 m / sec for 5 to 60 minutes to obtain flat crosslinked polymer particles. In this case, since the flat particles are obtained as a uniformly dispersed water slurry, it is preferable that the flat particles are replaced with an ethylene glycol slurry for blending with the polyester or taken out as dried particles.

In the present invention, monodisperse flat crosslinked polymer particles obtained under special emulsion polymerization conditions may be added directly to the polyester or the production process thereof.

The flat crosslinked polymer particles used in the present invention have an average particle size of 0.05 to 3 μm, preferably 0.1 to 1 μm.
When the average particle size is less than 0.05 μm, the running property and abrasion resistance of the film are insufficient. Further, if the average particle size exceeds 3 μm, the surface roughness of the film becomes too large, which is not preferable.

The ratio (Dw / Dn) of the weight average particle diameter (Dw) and the number average particle diameter (Dn) of the flat crosslinked polymer particles is 1.3 or less,
It is preferably 1.2 or less, more preferably 1.1 or less.
If this ratio exceeds 1.3, a uniform film surface cannot be obtained, which is not preferable. Further, the ratio of the minor axis to the thickness (flatness) of the flat crosslinked polymer particles is in the range of 1.5 to 15, preferably 2.0 to 7.0. When the particles having such a shape are used, the particles are arranged substantially parallel to the film surface in the biaxially oriented film, so that the particles can be prevented from falling off due to abrasion. If the flatness is less than 1.5, the shape of the particles becomes close to a sphere, and the abrasion resistance becomes insufficient, which is not preferable. On the other hand, if the flatness exceeds 15, protrusions on the film surface are not sufficiently formed by particles and the running property of the film is deteriorated, which is not preferable. Further, the flat particles may or may not be porous, but the former is preferred because it has a better affinity with polyester.

The glass transition temperature of the flat crosslinked polymer particles used in the present invention is usually 90 ° C or higher, preferably 110 ° C or higher. Particles having a glass transition temperature of less than 90 ° C are not preferable because they are easily deformed by a strong stress during stretching and a sharp protrusion cannot be formed on the film surface.

The particles used in the present invention may be those which are somewhat deformed by stretching, but if the particles have a flat shape in the film, that is, particles that can maintain a shape close to a columnar shape or an elliptic cylinder, the abrasion resistance of the film The effect of can be further improved.

The amount of flat crosslinked polymer particles in the biaxially oriented polyester film of the present invention is in the range of 0.01 to 4% by weight, preferably 0.05 to 0.8% by weight. 0.01% by weight
When it is less than 4, the slipperiness and abrasion resistance of the film are insufficient, and conversely, when it exceeds 4% by weight, the surface roughness of the film becomes too large, and for example, when it is used for a magnetic tape, the electromagnetic characteristics deteriorate. It is not preferable.

The method of blending the flattened crosslinked polymer particles used in the present invention with the polyester as the film-forming raw material is not particularly limited, and a known method can be adopted. For example, when the flat particles are obtained as an ethylene glycol slurry dispersion, at any stage of the polyester production process,
It is preferable to add the polycondensation reaction at the stage before the start of the polycondensation reaction at the end of the esterification or transesterification reaction to advance the polycondensation reaction. Alternatively, the polyester containing spherical cross-linked polymer particles may be melted and rolled with a roll to obtain a film-forming raw material containing flat particles.

As described above, in the present invention, it is possible to obtain a film having excellent properties that could not be achieved hitherto by stretching a polyester containing specific flattened crosslinked polymer particles. According to the above, other particles, for example, particles of kaolin, talc, calcium carbonate, silicon dioxide, aluminum oxide and the like can be used in combination within the range not impairing the gist of the present invention.

In the present invention, when the obtained polyester film satisfies certain physical properties, the running property and abrasion resistance of the film can be improved to a higher degree, and the mechanical strength and the slit property can also be improved. Achievable, making it more suitable, for example, as a base film for magnetic tape. One preferable physical property of such a polyester film is that the refractive index in the film thickness direction is 1.492 or more. When this value is less than 1.492, slipperiness and abrasion resistance are often insufficient even when the flat particles of the present invention are used. This value is preferably in the range 1.494 to 1.505. In order to obtain a film having such physical properties, for example, in the case of sequential longitudinal-transverse biaxial stretching, the longitudinal stretching temperature may be set to about 105 to 115 ° C, which is 5 to 30 ° C higher than the normal stretching temperature. Alternatively, such a film can also be obtained by subjecting the film to a substantial lateral relaxation after the biaxial stretching and before the heat treatment.

The film of the present invention can be suitably used especially as a base film for a magnetic recording medium by taking advantage of its high abrasion resistance, but its characteristic is that it exhibits particularly high strength and thin high recording density. You can Specifically, the F-5 value in the vertical direction is 12.0 kg / mm ² or more, preferably 14.0 kg / mm ²
Above, the film thickness is 12.0 μm or less, preferably 10.0 μm or less. It is particularly effective in applications where abrasion resistance is required.

The polyester film of the present invention takes advantage of its excellent running property and abrasion resistance, and is used as a base film of a magnetic recording medium such as a magnetic tape or a floppy disk, for capacitors, for photoengraving, for thermal transfer, for packaging. It is extremely useful as a base film in various fields such as for applications, transfer marks, and gold and silver threads.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded. The measuring methods and definitions of various physical properties and characteristics in the examples are as follows. In Examples and Comparative Examples, “part” means “part by weight”.

(1) Average particle size and particle size distribution Shimadzu's centrifugal sedimentation type particle size distribution measuring device (SA-CP3
Type) 50% integrated weight fraction in equivalent spherical distribution
The particle size of was taken as the average particle size.

Although this value is the weight average particle size (Dw), the number average particle size (Dn) was also determined at the same time, and the ratio (Dw / Dn) between them was used as an index of the particle size distribution.

(2) Flatness The minor axis in the plane of the flat particles and the thickness in the direction perpendicular to the plane were measured by a photographic method using an electron microscope, and determined by the following formula.

Flatness = Short diameter of particle / Thickness of particle (3) Glass transition temperature Differential scanning calorimeter (DSC-Thermal manufactured by Du Pont
The glass transition temperature was defined as the starting point of the calorific value change of the DSC curve when the temperature was raised at a heating rate of 16 ° C / min using Analyst 200 type).

(4) Number of Coarse Protrusions Aluminum was vapor-deposited on the film surface, and the number was measured using a two-beam interference microscope. The measurement wavelength was 0.54 μm, and the number showing the interference fringes of the third order or higher was converted and shown per 10 cm ² .

(5) Runnability The sliding property of the film was evaluated. The slipperiness was measured by the device shown in Fig. 1 and the film was brought into contact with a fixed hard chrome-plated metal roll (diameter 6 mm) at a wrapping angle (θ) of 135 ° and a load of 53 g (T ₂ ) was applied at one end to 1 m / min. The frictional force (μd) during running was determined by the following equation by running the test piece at the speed of 2 and measuring the resistance force (T _{1 (g)} ) at the other end.

(6) Friction characteristics Friction characteristics were evaluated by two methods. The first method is a method of quantifying the number of particles dropped out. That is, the film surface is subjected to gold vapor deposition, and a photograph is taken with a scanning electron microscope at a magnification of 20,000, and the number of projections that are thought to be formed by particles disappeared and the number of depressions was measured, and the unit area ( Converted per 1 mm ² ). The smaller this value is, the better.

The second method is evaluation of the amount of white powder generated. That is, the film was run for 20,000 m in the running system shown in FIG. 2, and the amount of wear white powder adhering to the 6 mm hard chrome fixing pin was visually evaluated and evaluated according to the ranks shown below. The film speed was 13 m / min and the tension was about 200.
g, θ = 135 °.

Rank A: No abrasion white powder adheres at all Rank B: A small amount of abrasion white powder adheres Rank C: A small amount of abrasion white powder adheres (more than Rank B) Rank D: Very much abrasion white powder adheres (7) Electromagnetic characteristics Evaluation First, a magnetic tape was manufactured. That is, magnetic fine powder 20
0 parts, polyurethane resin 30 parts, nitrocellulose 10 parts,
Vinyl chloride-cellulose acetate copolymer 10 parts, lecithin 5
Part, cyclohexanone 100 parts, methyl isobutyl ketone 1 part
After mixing and dispersing 00 parts and 300 parts of methyl ethyl ketone in a ball mill for 48 hours, 5 parts of a polyisocyanate compound was added to form a magnetic paint, which was applied to a polyester film, and then magnetically oriented before the paint was sufficiently dried and solidified. After drying, a magnetic layer having a thickness of 2 μm was formed on the polyester film. This magnetic layer-coated film was surface-treated with a super calendar and slit into a 1/2 inch width to obtain a video tape. The obtained magnetic tape was wrapped around a hard chrome-plated metal bottle (diameter 6 mm, surface roughness 3S) at a winding angle of 135 ° and a tension of 50 g was brought into contact with the base film surface, and the tape was rubbed for 200 m at a running speed of 4 m / min. The electromagnetic characteristics were measured using a Matsushita Electric NV-3700 type video deck.

○ S / N (VTR head output) The VTR head output was measured at a measuring frequency of 4 MHz with a synchroscope, and the relative value was expressed in decibels with the blank as 0 decibel.

○ Number of dropouts A videotape recording a signal of 4.4 MHz was played back, and the number of dropouts was measured with a dropout counter of Okura Industry Co., Ltd. for about 20 minutes and converted to the number of dropouts per minute.

Example 1 [Production of flat cross-linked polymer particles] 1500 parts of demineralized water were added with water-soluble polymerization initiator potassium persulfate 3.
After adding 2 parts and 0.004 part of sodium lauryl sulfate as a dispersion stabilizer and dissolving them uniformly, 60 parts of styrene, 20 parts of ethylene glycol dimethacrylate and vinylbenzene
20 parts of mixed solution was added. Then, polymerization was carried out at 70 ° C. for 8 hours while stirring under a nitrogen gas atmosphere. The reaction rate was 98%, and the obtained particles had an average particle size of 0.50 μm and a Dw / Dn value of 1.07. When the obtained particles were observed with an electron microscope, they were almost spherical. Next, the obtained particle water slurry was treated with a sand grinder at a peripheral speed of 6 m / sec for 20 minutes.

After the treatment, the particles were measured by an electron microscope photographic method, and the flatness was 2.2, the average particle size was 0.55 μm, and the Dw / Dn value was 1.07.
The glass transition temperature was 120 ° C.

Then 2000 parts of ethylene glycol was added to the obtained water slurry of the flat particles, and the mixture was heated and the water was distilled off under reduced pressure.

[Production of polyester]

Dimethyl terephthalate 100 parts, ethylene glycol 6
0 part and 0.09 part of magnesium acetate tetrahydrate were placed in a reactor, heated and heated, and methanol was distilled off to carry out an ester exchange reaction. It took 4 hours from the start of the reaction to reach 230 ° C.
The temperature was raised up to substantially complete the transesterification reaction. Next, the above-mentioned flat particle-containing ethylene glycol slurry was added to
After addition of 0.04 part of ethyl acid phosphate and 0.04 part of antimony trioxide, polycondensation reaction was carried out for 5 hours to obtain an intrinsic viscosity of 0.65 polyethylene terephthalate. After drying the obtained polyester, 290 ℃
Melt-extrudes to form an amorphous sheet, then 110
The film was stretched 3.5 times at ℃, 3.7 times at 120 ℃ in the transverse direction and heat-treated at 210 ℃ for 3 seconds to obtain a film having a thickness of 15µ.

[Manufacture of magnetic tape]

A magnetic layer is applied to the obtained film to obtain a magnetic tape,
Its properties were measured.

Example 2 A film and magnetic tape were prepared in the same manner as in Example 1 except that the monomer composition used in the production of the flat crosslinked polymer particles was changed to 70 parts of styrene, 20 parts of ethylene glycol dimethacrylate and 10 parts of divinylbenzene. Was obtained and its characteristics were measured.

Example 3 In Example 1, the monomer composition at the time of producing the flat cross-linked polymer particles was changed to 0.4% by mixing the film composition of the particles obtained with 60 parts of methyl methacrylate, 20 parts of ethylene glycol dimethacrylate and 20 parts of divinylbenzene. Otherwise, a film and a magnetic tape were obtained in the same manner as in Example 1 and their characteristics were measured.

Comparative Example 1 A film and a magnetic tape were obtained in the same manner as in Example 1 except that the flattening treatment was not performed, and the characteristics thereof were measured.

Comparative Example 2 0.50μ average particle size as particles to be blended with polyester
Using only spherical silica having m and Dw / Dn of 1.02, a film and a magnetic tape were obtained in the same manner as in Example 1 and the characteristics thereof were measured.

Comparative Example 3 Average particle size of 0.52μ as particles to be blended with polyester
Using only kaolin having m and Dw / Dn of 1.35, a film and a magnetic tape were obtained in the same manner as in Example 1, and the characteristics thereof were measured.

 The results obtained above are summarized in Table 1 below.

As shown in Table 1, Example 1 which is a category of the present invention
Films Nos. 3 to 3 all have excellent running properties and abrasion properties, and are extremely useful as, for example, base films for magnetic tapes, while Comparative Examples 1 and 2 have a spherical particle shape with a high resistance. Inferior in wear. Further, Comparative Example 3 shows the case of kaolin having an average particle diameter of 0.52 μm as an example of the inorganic flat particles. However, in addition to being inferior in wear characteristics, the particle size distribution is wide and coarse projections frequently occur.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The film of the present invention has a flat and uniform surface, is excellent in running properties and abrasion properties, can be applied to various applications, and has a high industrial value.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a running system for evaluating a dynamic friction coefficient with a metal. In the figure, (I) shows a 6 mmφ hard chrome plated fixing pin, (II) shows an entrance tension meter, (III) shows an exit tension meter, and θ is 135 °. FIG. 2 is a diagram showing a running system for evaluating wear resistance.
(IV) is a 6 mmφ hard chrome plated fixing pin, (V) is a tension meter, and θ is 135 °.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuhiro Kabahara 1000 Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa Inside the Central Research Laboratory, Diafoil Co., Ltd. (56) Sho 63-178144 (JP, A) JP-A-2-182730 (JP, A)

Claims (1)

[Claims] 1. The average particle size is 0.05 to 3 μm, the ratio (Dw / Dn) of the weight average particle size (Dw) to the number average particle size (Dn) is 1.3 or less, and the ratio of the minor axis to the thickness. A biaxially oriented polyester film containing 0.01 to 4% by weight of flat crosslinked polymer particles having a (flatness) of 1.5 to 15.