JPH047336A - Biaxially oriented polyester film - Google Patents

Abstract

PURPOSE:To provide a biaxially oriented polyester film having a uniform surface and excellent running properties, abrasion resistance, etc., by using a specified amount of titanium dioxide particles having a specified mean particle diameter and surface-coated with a crosslinked organic polymer. CONSTITUTION:Titanium dioxide particles surface-coated with a crosslinked organic polymer and having a mean particles diameter of 0.05-3mum are produced by,for example, emulsion-polymerizing a monovinyl compound (e.g. methacrylic acid) with a compound having a plurality of unsaturated bonds in the molecule (e.g. divinylbenzene) in an aqueous slurry of the titanium dioxide particles. A specified amount of the titanium dioxide particles are added to the reaction system in a polyester production process, and the obtained polyester is formed into a film, which is biaxially oriented to produce a biaxially oriented film containing 0.001-4wt.% titanium dioxide particles. This film can be desirably used as, e.g. a base film for a magnetic recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a biaxially oriented polyester film having a uniform surface and excellent slip properties and abrasion resistance.

More specifically, the present invention relates to a polyester film imparted with excellent surface properties by incorporating particles having titanium dioxide particles as cores and whose surfaces are coated with an organic crosslinked polymer.

[Prior art and problems to be solved by the invention] Polyester films, especially biaxially oriented films represented by polyethylene terephthalate, have excellent physical and chemical properties and are used as base films for magnetic recording media and capacitor dielectrics. It is used all over the body. Furthermore, due to its excellent transparency, it is widely used in fields such as graphic arts, displays, and packaging materials.

Incidentally, film runnability and abrasion resistance are particularly required in terms of process passability in the molding process to obtain the above product, post-processing processes such as coating and vapor deposition, and handling of the product itself, but conventionally, this has not been possible. It was not always fully achieved.

For example, when films come into contact with each other or a film and a base material at high speed, friction and abrasion between the two increases, and abrasion powder is often generated.

For example, in magnetic recording applications, this abrasion powder causes loss of recording signals, that is, dropouts, and significantly reduces the quality of the film.

It is generally known that in order to improve the runnability and abrasion characteristics of a film, it is sufficient to roughen the film surface appropriately.

In order to achieve this, a method has been adopted in which fine particles are present in the raw material polyester, and although this method has been put into practical use in some cases, it has not necessarily been successful in satisfying these characteristics to a high degree.

For example, when so-called precipitated particles from catalyst residues during polyester production are used as fine particles, the fine particles are easily destroyed by stretching, resulting in poor runnability and wear resistance.
It is also difficult to recycle and use.

In addition, when inert inorganic compound particles are added to polyester such as silicon oxide, calcium carbonate, titanium dioxide, calcium phosphate, etc., the particles are not destroyed or deformed by stretching, and relatively steep protrusions are formed. Although running properties are improved, the particles tend to detach from the film surface due to their poor affinity with polyester, resulting in the production of white powdery substances.

On the other hand, when heat-resistant organic particles are used as additive particles,
These particles generally have excellent affinity with polyester, and although they often deform as they are stretched and are less likely to come off from the film surface, on the other hand, the protrusions tend to be gentle, and combined with the elasticity of the particles themselves, they do not have sufficient runnability. I can't say that.

Of course, there is also a method of using an appropriate blend of inorganic particles and organic particles, but this only provides an average effect and cannot be a fundamental solution.

[Means to solve the problem]

The inventors of the present invention have conducted extensive studies in order to provide an excellent film that satisfies both running properties and abrasion resistance to a high degree, and also fully satisfies the mechanical properties necessary for a film. The present inventors have discovered that such required characteristics can be met by incorporating particles whose surfaces are coated with an organic crosslinked polymer, and have completed the present invention.

That is, the gist of the present invention is to provide a biaxially oriented polyester film containing 0.001 to 4% by weight of titanium dioxide particles having an average particle size of 0.05 to 3 μm and whose surface is coated with an organic crosslinked polymer. exists in

The present invention will be explained in more detail below.

The polyester referred to in the present invention refers to terephthalic acid, 2.6
- It refers to a polyester obtained using an aromatic dicarboxylic acid such as naphthalene dicarboxylic acid or its ester and ethylene glycol as the main starting materials, but it may contain other third components. In this case, the dicarboxylic acid component includes, for example, isophthalic acid, phthalic acid, 2.
6-naphthalene dicarboxylic acid, terephthalic acid, adipic acid, sebacic acid, and oxycarboxylic acid components such as p
-Oxyethoxybenzoic acid or the like can be used alone or in combination of two or more. As the glycol component, one or more of diethylene glycol, propylene glycol, butanediol, 1,4-cyclohexane dimetatool, neopentyl glycol, etc. 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-naphthalene units.

Further, the polyester film of the present invention refers to a polyester film that is at least uniaxially oriented using a polyester as a starting material, and any known method can be used for its production.

For example, it is usually melt-extruded into a sheet at 270-320°C, then cooled and solidified at 40-80°C to form an amorphous sheet, and then heated at 80-130°C with an area magnification of 4-20 in the vertical and horizontal directions.
Biaxially stretching or simultaneously stretching to double the amount of 16
Methods such as heat treatment at 0 to 250°C (for example,
The method described in Japanese Patent No.-5639) can be used. When stretching in the longitudinal and transverse directions, the stretching may be carried out in one stage, or in multiple stages as necessary, or a heat treatment section for orientation relaxation may be provided between the multi-stage stretching. Further, after the two-wheel stretching, the film may be stretched again before being subjected to the next heat treatment step.

This re-stretching can be carried out in either the longitudinal or lateral directions, or in both directions.

A feature of the present invention is the use of inorganic and organic composite particles. Inorganic particles that are commonly used as additives for polyester inherently have poor affinity with the polyester matrix, and when strong stress is applied during stretching, they do not deform and create voids around the particles. If voids are created, particles will easily separate from the film using these voids as starting points when the film surface is abraded.

In addition, in recent years, as the field of magnetic recording media has become more dense and precise, there has been a strong demand for films that are flat and have excellent running properties. Hardness particles are used. Titanium dioxide particles are known as such particles, but when such particles are used, although they have excellent running properties, they lack affinity with polyester, which causes particles to detach from the film, which is typical of inorganic particles, making them difficult to use. That is the reality.

The present inventors decided to improve the wear characteristics of titanium dioxide particles while taking advantage of their characteristics, and by coating their surfaces with an organic crosslinked polymer that has good affinity with polyester. The above issues were resolved.

The titanium dioxide particles that form the core of the composite particles used in the present invention may be either commercially available anatase titanium or rutile titanium, and preferably have a particle size distribution (r).
value (ratio of the diameter at a point with a weight fraction of 25% and the diameter at a point with a weight fraction of 75% when integrated from the large particle side) is 2.5 or less, more preferably an (r) value of 2.0 or less. They are titanium dioxide particles.

Such particles are generally lumpy and have high hardness, but in the present invention, the surfaces of the particles are coated with an organic crosslinked polymer.

The organic crosslinked polymer is a monovinyl compound (A) having only one aliphatic unsaturated bond in the molecule, and the crosslinking agent is a compound (B) having two or more aliphatic unsaturated bonds in the molecule. An example is a copolymer with In this case, such copolymers may have groups capable of reacting with the polyester.

The compound (A) which is a component of the copolymer includes acrylic acid, methacrylic acid, and their methyl or glycidyl esters, maleic anhydride and its alkyl derivatives,
Examples include vinyl glycidyl ether, vinyl acetate, styrene, and alkyl-substituted styrene. Furthermore, examples of the compound (B) include divinylbenzene, divinyl sulfone, ethylene glycol dimethacrylate, and the like. One or more types of each of compounds (A) and (B) are used, but a compound having ethylene or a nitrogen atom may be copolymerized.

In order to polymerize these organic components on the surface of titanium dioxide, it is preferable to apply, for example, an emulsion polymerization method.

Emulsion polymerization here refers to emulsion polymerization in a broad sense, including concepts such as so-called soap-free emulsion polymerization and seed emulsion polymerization. Therefore, although this emulsion polymerization uses titanium dioxide particles as a nucleus, it can be carried out with or without the addition of an emulsifier.

Although it depends on the type of monomer used, it is advantageous to keep the amount of emulsifier as low as possible because it can suppress the generation of only organic particles.

One embodiment of the production of composite 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, potassium persulfate, or sodium persulfate-thiosulfate in a water slurry in which titanium dioxide particles are dispersed, compounds (A) and (B) are dissolved. Add a mixed solution of After that, the temperature is higher than the decomposition start temperature of the polymerization initiator,
The reaction is preferably carried out under stirring at a temperature of 40 to 90°C for about 3 to 10 hours. In this case, since the composite particles are obtained as a uniformly dispersed water slurry, it is preferable to replace the composite particles with an ethylene glycol slurry for blending with polyester, or to take them out as dry particles.

In addition, since agglomerated particles are likely to be formed depending on the bath ratio and the composition of the polymer, a dispersion stabilizer may be used in combination during the polymerization. In any case, any method of coating with an organic component may be used as long as it satisfies the spirit of the present invention.

The coating component needs to be thermally stable, and for this purpose, the crosslinking density, that is, the ratio of compound (B) to the total weight of compound (A) and compound (B), must be 1 to 40.
%, preferably about 2 to 30%. In this case, the degree of heat resistance varies depending on the type of monomer, but
Specifically, the weight loss rate after heat treatment at 300° C. for 2 hours in nitrogen gas is preferably 20% by weight or less, more preferably 10% by weight or less.

Further, it is preferable that the coating component of the present invention contains a group that can react with polyester, such as an ester group, a carboxyl group, a hydroxyl group, an epoxy group, etc., but if the coating component has excellent dispersibility in the polyester. There are no particular restrictions,
Further, the component may or may not be porous, and the coating layer may have a multilayer structure as required.

The thickness of the coating is usually 1/100 to 1/100 of the diameter of the core particle.
1/2, preferably 1) 50 to 1/2, more preferably 1/30 to 1/2. If this value is less than 1/100, the elastic effect of the organic component is insufficient, and just like a single-layer coating treated with a silane cuff pulling agent, it will not absorb the force when strong stretching stress is applied. However, peeling is not improved. Moreover, if this value exceeds 1/2, the elastic effect becomes too strong (too much) and running properties become insufficient, which is not preferable.

The thickness of the coating layer can be easily determined by performing sedimentation separation treatment in a solvent with a higher specific gravity than the organic crosslinked polymer of the coating layer, and then measuring the particle size before and after coating, using a centrifugal sedimentation type particle size distribution analyzer, for example. You can ask for it. Furthermore, it can be easily confirmed that the particles actually have a multilayer structure, for example, by measuring the infrared absorption spectrum of the particles after coating.

The average particle diameter of the composite particles coated with an organic crosslinked polymer used in the present invention is 0.05μ to 3μ, preferably 0.05μ to 3μ.
．． It is selected from the range of 1 to 1μ.

If the average particle diameter is less than 0.05 μm, the running properties and abrasion resistance of the film will be insufficient, and if it exceeds 3 μm, the surface roughness will become too large, which is not preferable. In addition, the amount of the particles blended into the polyester film is 0.001 to 4% by weight,
It is preferably selected from the range of 0.01 to 1% by weight.

If the amount is less than 0.001% by weight, the running properties and abrasion resistance of the film will be insufficient, and if the amount exceeds 4% by weight, the surface roughness will become too large, which is not preferable.

The method for blending the composite particles used in the present invention with the polyester as a raw material for film formation is not particularly limited, and any known method may be employed. For example, it may be added as an ethylene glycol slurry at any stage of the polyester manufacturing process, preferably after the end of the esterification or transesterification reaction but before the start of the polycondensation reaction, to advance the polycondensation reaction, or the particles and polyester chips may be may be blended directly.

As described above, in the present invention, by stretching polyester containing specific composite particles in which titanium dioxide particles are coated with an organic crosslinked polymer, it is possible to obtain a film with excellent properties that have not been achieved before. However, if necessary, other particles, such as particles of kaolin, talc, calcium carbonate, silicon dioxide, aluminum oxide, etc., may be used in combination without departing from the spirit of the present invention.

In addition, in the present invention, when the resulting polyester film satisfies certain physical properties, the running properties and abrasion resistance of the film can be improved to a higher degree, and further improvements in mechanical strength and slitting properties can also be achieved. This makes it more suitable as a base film for magnetic tape, for example.

One preferable physical property of the polyester film is that its refractive index in the thickness direction is 1.492 or more. If this value is less than 1.492, even if the particles of the present invention are used, slipperiness and abrasion resistance will often be insufficient. This value preferably ranges from 1.494 to 1.505. In order to obtain a film having such physical properties,
For example, in the case of sequential longitudinal and transverse biaxial stretching, the longitudinal stretching temperature may be set to about 105 to 1)5°C, which is 5 to 30°C higher than the normal stretching temperature. Alternatively, after two-wheel stretching and before heat treatment, significant lateral relaxation can be performed to obtain a film that will flop.

Furthermore, one of the preferred embodiments of the polyester film containing the specific composite particles of the present invention is a biaxially oriented film that is strongly oriented in the longitudinal direction and has a film thickness of 12.0 μm or less. In other words, the film of the present invention can be particularly suitably used as a base film for magnetic recording media by taking advantage of its high abrasion resistance properties, but its characteristics are particularly exhibited when used for high strength, thin, and high recording density applications. be able to. Specifically, the F-5 value in the longitudinal direction is 12.0 kg/Tsuru 2 or more, especially 14.0 kg/Tsuru 2 or more, and the film thickness is 12.0 μm or less, especially 10.
It is particularly effective in applications requiring wear resistance properties of 0μ or less.

The polyester film of the present invention has particularly excellent running properties, especially the ability to maintain a low coefficient of friction even when running repeatedly, and wear resistance, and can be used for magnetic recording media such as magnetic tapes and floppy disks. It is extremely useful as a base film for various fields such as capacitors, photolithography, electric power, thermal transfer, packaging, transfer marks, gold and silver thread, etc.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof. The measurement methods and definitions of various physical properties and characteristics in Examples are as follows.

In Examples and Comparative Examples, "parts" indicate "parts by weight."

(1) Average particle size and particle size distribution Shimadzu-manufactured fracture centrifugal sedimentation 2 particle size distribution measuring device (SA-CF
Cumulative weight fraction 5 in equivalent spherical distribution measured with type 2)
The particle size of 0% was taken as the average particle size. At the same time, the ratio (r) value of the diameter at a point with a weight fraction of 25% and the diameter at a point with a weight fraction of 75%, integrated from the large particle side, was used as an index of particle size distribution.

(Excellent) Running performance Evaluated by the slipperiness of the film. The slipperiness was measured using the apparatus shown in FIG. In other words, the film is wrapped around a fixed hard chrome-plated metal roll (diameter 6m) at corner 13.
5” or 2.356 rad(θ),
A load of 3 g (T2) was applied to one end, and it was run at a speed of 1 m/sin, the resistance force (TI, g) at the other end was measured, and the coefficient of friction (μd) during running was determined using the following formula.

(3) Wear characteristics Wear characteristics were evaluated using two methods. The first method is to quantify the number of traces of particles falling off. In other words, gold is deposited on the surface of the film, a photograph is taken with a scanning electron microscope at a magnification of 2000 times, and the number of protrusions that are thought to have been formed by particles that have disappeared and become depressed is measured. It was converted into (1■2) per unit. The smaller this value is, the better.

The second method is to evaluate the amount of white powder generated.

That is, the film was run for 1000 m using the running system shown in FIG. 2, and the amount of abrasion white powder adhering to a fixed pin made of hard chrome with a diameter of 6 cranes was visually evaluated and evaluated according to the ranks shown below. The film speed was 13 m/sin, the tension was about 200 g, and θ=135''.

Rank A: Does not adhere at all Rank C: A small amount adheres Rank C: A small amount (more than rank B) adheres Rank D: Extremely much adheres (4) Evaluation of electromagnetic properties 200 parts of magnetic fine powder, 30 parts of polyurethane resin, 10 parts of nitrocellulose, 1 part of vinyl chloride-vinyl acetate copolymer
0 parts of lecithin, 100 parts of cyclohexanone, 100 parts of methyl isobutyl ketone, and 300 parts of methyl ethyl ketone were flow-dispersed in a ball mill for 48 hours. 5 parts of a polyisocyanate compound was added to make a magnetic paint, and this was applied to a polyester film. Before the paint was sufficiently dried and solidified, it was magnetically oriented and then dried to form a magnetic layer with a thickness of 2 μm. Further, this coated film was subjected to surface treatment using a Suher calender, and was slit into 1/2 inch width to prepare a videotape.

Next, attach the obtained magnetic tape to a hard chrome-plated metal pin (
The base film surface was brought into contact with the base film (diameter 6m, surface roughness 3S) at a wrapping angle of 135° and a tension of 50g, and the running speed was 4m/
It rubbed 200m in seconds.

Next, the electromagnetic properties of the wound tape were measured using Matsushita Electric's N
Measurements were made using a V-3700 video deck.

○ VTR head output was measured at a measurement frequency of 4 MHz using a VTR head output synchroscope, and the relative value was expressed in decibels with a blank as O decibels.

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

(5) Number of coarse protrusions Aluminum was deposited on the film surface and measured using a three-beam interference microscope. The measurement wavelength was 0.54 .mu.m, and the number of interference fringes of third order or higher order was calculated per 10 parts m''.

Example 1 [Manufacture of composite particles] 100 parts of titanium dioxide particles having an average particle size of 0.3 μm and an (r) value of 1.70 were dispersed in 3000 parts of demineralized water.

Next, 0.00 potassium pergate was added as a water-soluble polymerization initiator.
6 parts and sodium lauryl sulfate o as a dispersion stabilizer,
After adding oos part and melting it uniformly, 4 parts of methyl methacrylate and 14 parts of ethylene glycol dimethacrylate were added.
A homogeneous solution of 1 part and 2 parts of divinylbenzene was added. Next, polymerization was carried out at 70° C. for 6 hours with stirring under a nitrogen gas atmosphere. The reaction rate was 99%, the average particle size of the newly obtained particles was 0.41 μm, and the (r) value was 1.66.

Substantially no particles other than these particles were observed in the reaction system, and the infrared absorption spectrum of the particles that were the starting material and the particles obtained was 1725 cm-' and 1300-1)50
It is clear that the titanium dioxide particles are uniformly coated with the organic crosslinked polymer since al-' shows absorption based on the ester bonds of ethylene glycol dimethacrylate and methyl methacrylate. Note that the weight loss of the organic component upon heating was 5.9%.

[Production of polyester film]

100 parts of dimethyl terephthalate, 60 parts of ethylene glycol, and 0.09 parts of magnesium acetate tetrahydrate were placed in a reactor, heated to an elevated temperature, and methanol was distilled off to perform a transesterification reaction, which took 4 hours from the start of the reaction. 2
The temperature was raised to 30°C to substantially complete the transesterification reaction.

Next, 0.04 part of ethyl acid phosphate was added, then 0.30 part of the above composite particles having an average particle size of 0.41 μm were added, and further 0.04 part of antimony trioxide was added.
A time polycondensation reaction was carried out to obtain polyethylene terephthalate having an intrinsic viscosity of 0.65°.

After drying the obtained polyester, it was melt extruded at 290°C,
After forming an amorphous sheet, it was stretched 3.5 times in the machine direction at 90°C and 3.7 times in the transverse direction at 1) 0°C, and heat treated at 210°C for 3 seconds to obtain a film with a thickness of 15μ. Ta.

[Manufacture of magnetic tape]

A magnetic layer was applied to the obtained film to obtain a magnetic tape, and its properties were measured.

Example 2 A film and magnetic tape were obtained in the same manner as in Example 1, except that the production of composite particles was changed as shown in Table 1, and the amount added to the film was changed to 0.20% by weight. , its characteristics were evaluated.

Example 3 A film and a magnetic tape were obtained in the same manner as in Example 1 except that the organic component to be coated was changed to methyl methacrylate/divinylbenzene = 9/1, and their properties were evaluated.

Comparative Example 1 A film and a magnetic tape were obtained in the same manner as in Example 1, except that titanium dioxide not coated with an organic crosslinked polymer was used as particles to be blended with polyester, and their properties were evaluated.

Comparative Example 2 In Example 1, the surface treatment of titanium dioxide was performed by replacing the organic crosslinked polymer coating with γ-glycidoxyprobyltrimethoxysilane. Next, films and magnetic tapes were obtained using the particles in the same manner as in Example 1, and their properties were evaluated.

Comparative Example 3 The titanium dioxide particles used in Example 1 had an average particle size of 0.
．． The particles were replaced with 30μ styrene/divinylbenzene=9/1 particles, and the surface layer was coated with methyl methacrylate/ethylene glycol dimethacrylate/divinylbenzene. Next, films and magnetic tapes were obtained using the particles in the same manner as in Example 1, and their properties were evaluated.

Comparative Example 4 Average particle size of particles added to polyester: 0°52μ
A film and a magnetic tape were obtained in the same manner as in Example 1 using kaolin with m and (r) values of 2.6, and their properties were evaluated.

The results obtained above are summarized in Table 1 below.

As shown in Table 1, Examples 1-
All three films have excellent running properties and abrasion characteristics,
For example, while it is extremely useful as a base film for magnetic tape, when it is not coated with an organic component as in Comparative Example 1, it has poor abrasion resistance.

Further, as shown in Comparative Example 2, no effect can be expected from surface treatment using a silane coupling agent.

Furthermore, as shown in Comparative Example 3, when the particles are composed only of organic components, the wear characteristics are excellent, but the running properties are poor.

In addition, Comparative Example 4 has an average particle size of 0.52 as an example of inorganic particles.
This shows the case of μ-〇 kaolin, which not only has poor wear characteristics but also has a wide distribution and frequent occurrence of coarse protrusions.

〔Effect of the invention〕

The film of the present invention has a flat and relatively uniform surface, has excellent running properties and abrasion resistance, can be applied to various uses, and has high industrial value.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram showing a running system for measuring the coefficient of dynamic friction of a film, where (1) shows a fixed bin, (II) shows an entry rotance meter, (1) shows an exit tension meter, and θ is 135°. be. FIG. 2 is a diagram showing a running system for evaluating the abrasion resistance of the film, where (mV) indicates a fixed pin, (V) indicates a tension meter, and θ is 135@.

Claims (1)

[Claims] (1) Surface coated with organic crosslinked polymer, average particle size 0
．． A biaxially oriented polyester film containing 0.001 to 4% by weight of titanium dioxide particles having a diameter of 0.05 to 3 μm.