JP2990709B2 - Laminated polyester film - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a laminated polyester film having improved surface properties, and more particularly to a laminated polyester film for high density magnetic recording media.

[Conventional technology]

Biaxially oriented polyester films are widely used for magnetic tapes, electrics, packaging, etc. because of their excellent mechanical and electrical properties.

2. Description of the Related Art Conventionally, a polyester film has a slippery surface by making the surface of the film rough to improve workability and handleability. However, information recording materials, especially magnetic recording materials, have been required to improve the electromagnetic conversion characteristics with the recent increase in recording density, and it has been strongly required that the base film surface for providing the magnetic layer be as smooth as possible. I have.

From the viewpoint of the electromagnetic conversion characteristics, it is desirable to use a base film having a flat mirror surface without protrusions on the surface, but such a film is extremely poor in slipperiness, running property when formed into a tape, and winding characteristics, and is practical. It is customary to lose the character. Generally, in order to improve the slip properties, running properties, winding characteristics, and the like of a film, a method of reducing the contact area between the film and the roll, between the film and the film, and the like by providing fine projections on the surface of the film is adopted. Generally, the larger the size of the film surface projections, the greater the effect of improving the slipperiness.However, a base film for a magnetic recording medium such as a magnetic tape requires a high degree of slipperiness.
The large protrusions themselves cause serious defects such as dropout of magnetic recording signals, so-called dropouts, and thus have the disadvantage that the electromagnetic conversion characteristics are significantly deteriorated.

Therefore, there is a demand for a film that does not have coarse projections but satisfies a high degree of slippage only with fine surface projections.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems in the biaxially oriented polyester film, that is, it is difficult to obtain a film having particularly excellent surface flatness and good workability and handleability.

[Means for solving the problem]

The present invention relates to spherical silica (A) having an average particle size of 0.05 to 0.5 μm.
And the surface roughness is center line average roughness Ra
Is a polyester film in which a resin layer containing 2,000 to 800,000 ppm of spherical silica (B) is laminated on at least one surface of a polyester film substrate having a thickness of 0.007 μm or less, wherein the spherical silica (A) and (B) have the following formula: At the same time.

_{D B: D A = 1:} 60~4: 1 ...... (1) ( wherein D _A is the average particle diameter of the spherical silica (A), D _B is the average particle diameter of the spherical silica (B) ), C _A : C _B = 1: 20,000 to 1: 1 (2) (where C _A is the concentration of spherical silica (A) and C _B is the concentration of spherical silica (B)).

As the polyester constituting the polyester film substrate of the present invention, any polyester conventionally used as a film can be used.For example, polyalkylene terephthalate, a crystalline polyester represented by polyalkylene naphthalate, etc., and especially polyethylene Polyester containing terephthalate or polyethylene naphthalate as a main component is suitable. In particular, at least 80 mol% of the repeating unit is composed of ethylene terephthalate or ethylene naphthalate. The component is an aliphatic glycol having 3 to 8 carbon atoms or 6 carbon atoms.
~ 12 alicyclic glycols, specifically 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-cyclohexane Dimethanol, p-xylylene glycol, diethylene glycol, triethylene glycol and the like, and polyether glycols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol and the like may be contained. Also, when included, aromatic, aliphatic and alicyclic dicarboxylic acids can be used as the dicarboxylic acid component in the remaining copolymer components, and examples of the aromatic dicarboxylic acid include isophthalic acid, orthophthalic acid and 2,6- Examples of aliphatic and alicyclic dicarboxylic acids such as naphthalenedicarboxylic acid include succinic acid, adipic acid, sebacic acid, oxalic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and p-hydroxybenzoic acid. A part of oxyacids such as an acid can be arbitrarily selected and used.

A small amount of a compound containing an amide bond, a urethane bond, an ether bond, a carbonate bond or the like may be contained as a copolymer component other than the above.

As the method for producing the polyester, any conventionally known production method such as a so-called direct polymerization method in which a dicarboxylic acid and a glycol are directly reacted, and a so-called transesterification method in which a dimethyl ester of a dicarboxylic acid and a glycol are transesterified are applied. can do.

The polyester film substrate in the present invention has an average particle size.
The spherical silica (A) of 0.05 to 0.5 μm is added in an amount of 30 to 2000 ppm.
And a film having surface protrusions based on the catalyst residue and having a roughness of not more than 0.007 μm in center line average roughness Ra.

According to the present invention, a surface layer made of a specific spherical silica (B) and a resin to be described later is provided on at least one surface of the above-mentioned polyester film base material during or after its formation.

Examples of the method of laminating the surface layer include a method in which a resin layer containing silica particles (B) is co-extruded on one or both sides of the base polyester, a method such as an extrusion coating method, or a method in which water or organic resin of the surface resin is used. A method of mixing and dispersing spherical silica (B) in a solution or dispersion of a solvent and applying the mixture is used. The coating method can be performed using a reverse roll coater, a gravure coater, a rod coater, an air doctor coater, or another known coating device. In particular, spherical silica (B) is applied to an unstretched film after the polyester is melt-extruded or a polyester film substrate after uniaxially stretching in the longitudinal or transverse direction.
A coating method comprising applying a coating liquid composed of a silica particle (B) and a resin described below is applied, followed by stretching in a biaxial or other uniaxial direction, followed by heat treatment to obtain a biaxially oriented laminated film. Contribution of projection formation to the film surface,
It is preferable in terms of cost and the like.

Further, before the surface layer composed of the spherical silica (B) and the resin is provided, the polyester substrate is subjected to a pretreatment such as a corona discharge treatment, an electron beam irradiation treatment, an ultraviolet irradiation treatment, a plasma treatment, and a coating of an anchor agent. The adhesion between the surface layer and the polyester substrate may be improved.

Also, by applying a corona discharge treatment, an ultraviolet irradiation treatment, an electron beam irradiation treatment, a plasma treatment, etc. to the laminated surface to which the magnetic layer is provided after the surface layer is provided, the wettability and adhesion of the surface film surface can be improved. Good.

As the resin constituting the surface layer, it is preferable to use a thermoplastic polyester resin when coextrusion or extrusion coating is used. In this case, the polyester may be the same as or different from the polyester substrate described above.

The other resin constituting the surface layer is not particularly limited as long as it is an organic polymer compound that can be a solution or a dispersion when the coating is carried out by a coating method, but is not limited to an ester, a vinyl, an acrylic, a styrene, Alkyd-based, urethane-based, vinylidene-based, diene-based, olefin-based, amide-based, epoxy-based, amino-based, other addition-condensation type, polycondensation-type condensation systems, unsaturated polymerization types, ring-opening polymerization-type polymerization systems, etc. Such as various synthetic resins, rubber-based resins, semi-synthetic and natural-based resins such as protein-based resins, and copolymers thereof, and preferably those having good adhesiveness with the base material,
One or more polymer compounds are selected from the group consisting of ester, vinyl, acrylic, urethane, epoxy, melamine and the like.

Further, if necessary, additives such as a sticking property improver, a thickener, an ultraviolet absorber, an antioxidant, an antistatic agent, a lubricant, and a dye may be contained.

The shape of the spherical silicas (A) and (B) may be spherical, but is preferably spherical silica having an area ratio to the circumscribed circle defined by the following formula of 80% or more.

The projection morphology on the film surface using particles having an area ratio of spherical silica of less than 80% tends to be non-uniform, and cannot provide a high degree of slipperiness, which is not preferable.

Further, the degree of variation of the average particle diameter of the spherical silica is preferably 25% or less.

The average particle diameter mentioned here is the average of the particle diameters observed with a scanning electron microscope, and the degree of dispersion of the particle diameter is defined by the following equation.

Further, the production method of the spherical silicas (A) and (B) is not limited at all. For example, it is produced by a hydrolysis and condensation reaction using an alkoxysilane as a starting material and an amine catalyst.

The alkoxysilane compound has a general formula (CnH _{2n + 1} O)
_This is a compound represented by 4Si (n = 1 to 8), for which tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like are used. Ammonia, trimethylamine and the like can be used as the amine catalyst. The above alkoxysilane compound is hydrolyzed by adding an amine-based catalyst [(Si (O
H) ₄ ] Make monodisperse spheres. Furthermore, this hydrated silica is dehydrated and three-dimensionally bonded There is a way to grow. In addition, cation exchange is performed on the aqueous sodium silicate solution to obtain de-sodium activated silicic acid. When the pH of the activated silicate is set to be neutral to alkaline, a so-called alkali silicate decomposition method in which dehydration condensation proceeds in a three-dimensional direction to form spherical silica, and the like can be mentioned.

The particle size of the polyester film substrate in the present invention is 0.
A spherical silica (A) having a particle size of from 0.5 to 0.5 μm is contained in an amount of from 30 to 2,000 ppm, and the surface roughness is 0.007 μm as a center line average roughness Ra
It must be:

When the average particle size D _A of the spherical silica (A) is less than 0.05 .mu.m, unfavorably poor can on GaTsuta film also slip properties and slip properties of the base material is laminated extremely poor. When the particle diameter of the spherical silica (A) is larger than 0.5 μm, the base material has good slipperiness, but a large number of coarse projections are formed, and the projections remain undesirably on the laminated film. Particularly preferably D _A is 0.07～0.2Myuemu.

If the concentration C _A is 30ppm or less slipperiness of the film substrate of the spherical silica (A) it is extremely poor, since the poor also slidability can on GaTsuta film laminated undesirable. The slipperiness of the film substrate when the concentration C _A exceeds 2000ppm of spherical silica (A) is good generates many coarse surface protrusions, the protrusions remains undesirable to be on GaTsuta film laminated.
Particularly preferred is C _A is 50 to 1000 ppm.

The center line average roughness Ra of the film substrate is preferably 0.007 μm or less, and if it exceeds 0.007 μm, coarse surface projections of the substrate remain after lamination and the desired film cannot be obtained, which is not preferable.

The concentration C _B of the spherical silica (B) contained in the surface layer 2000 to
800000 ppm. If it is less than 2000 ppm, the effect on the slip of the surface layer is small, which is not preferable. On the other hand, if the content exceeds 800,000 ppm, it is not preferable because the adhesion of the particles is poor and the durability is poor. More preferably, it is 5000 ppm to 300,000 ppm.
Particularly preferably, it is from 10,000 ppm to 200,000 ppm.

It is necessary that the spherical silica (B) contained in the surface layer and the spherical silica (A) contained in the film substrate satisfy the following formulas at the same time.

The average particle diameter D _B ratio of spherical silica (B) to the average particle size D _A of the spherical silica (A), i.e., D _B: the D _A 1: sixty to four: 1.

Spherical silica substrate concentration C _A of the spherical silica (A) (B)
Is C _B 1:: the ratio of surface concentration C _B, i.e. C _A 20000~1: 1
It is.

Particle size ratio D _B / D _A is smaller and the projection of the relatively film substrate is larger than 1/60, almost no unfavorable effect on the surface of the slip. The particle size ratio D _B / D _A is effective with little undesirable surface protrusions for sliding relatively increased and film substrate than the projection of the larger the film substrate than 4.

The concentration ratio C _A / C _{B of the} spherical silica (A) and (B) is 1/200.
If it is less than 00, the projections on the film substrate are less than the projections on the surface layer, and there is almost no effect on the sliding of the film substrate, which is not preferable. When the concentration ratio C _A / C _B is larger than 1, the number of projections on the film substrate is smaller than the projections on the surface layer, and there is almost no effect on the sliding of the surface layer.

〔Example〕

Next, the present invention will be described more specifically with reference to examples.
The methods for measuring the coefficient of static friction, the number of surface projections, and the like of the film were as follows.

(1) Static friction coefficient (μs) A static friction coefficient (μs) between films was measured using a thread type slip tester (DAVENPORT) in accordance with ASTM D-1894-63. The measurement environment was 23 ° C,
The relative humidity was 65%.

(2) Non-contact three-dimensional roughness Ra (μm) of the laminated film The film surface was measured in the longitudinal direction of the film using a non-contact three-dimensional surface roughness meter (ET-30HK) manufactured by Kosaka Laboratory Co., Ltd.
Measured in a 45 ° direction with a cut-off value of 0.08 mm over a length of 0.25 mm, divided into 500 points with a 0.5 μm pitch, and the height of each point was taken into a three-dimensional roughness analyzer (SPA-11). . Perform the same operation 150 times at 0.5 μm intervals, that is, 0.075 mm width
The data was imported into the analyzer. Next, the center line average roughness SRa (μm) was determined by an optical non-contact roughness meter using an analyzer.

(3) Number of coarse protrusions (number of protrusions with a height of 0.54 μ or more) After thinly depositing aluminum on the film surface, use a two-beam interference microscope manufactured by Natsuha Corporation to enlarge the length to 20 m at 800 times magnification.
The entire area of m ² was scanned, and the number of projections having interference fringes of 2.0 order or more was obtained, and the number of projections per cm ² was converted to the number of coarse projections (pieces / mm ² ).

(4) Contact-type three-dimensional roughness of film substrate without laminating
Using -3AK), the measurement was performed in the direction of 45 ° with respect to the longitudinal direction of the film under the conditions of a needle radius of 2 μm and a load of 30 mg.
This data was taken into a three-dimensional roughness analyzer (SPA-11) to determine the average roughness Ra (μm).

(5) Electromagnetic conversion properties After coating a magnetic layer having a thickness of 3 μm on the surface lamination surface of the obtained laminated film (or any surface if the surface layer is provided on both surfaces of the base film), The tape was slit to a half inch width to obtain a VHS standard video tape.
The chroma S / N of the obtained tape with respect to the standard tape (Comparative Example 1) was measured using a TG-7 type NTSC TV test signal generator and a 925D / 1 type NTSC color video noise meter manufactured by Shibasoku Co., Ltd. And evaluated according to the following three ranks.

×: less than −1 dB…: −1 dB or more and less than +1 dB…: +1 dB or more In the following examples, parts and% are by weight unless otherwise specified.

Example 1 (Production of coating liquid for lamination) 5 parts of an organosol (SiO ₂ content: 20%) in which spherical silica having an average particle size of 0.08 μm was uniformly dispersed in isopropyl alcohol as spherical silica (B) was mixed with 50 parts of water. And 50 parts of isopropyl alcohol. Then, 80 parts of this dispersion was mixed with 20 parts of an aqueous dispersion of a polyester copolymer resin, and the mixture was stirred well until uniform to obtain a coating liquid. The solid content of the coating solution was 10% for SiO _{2 and} 90% for the copolyester resin.

(Production of Laminated Film) As spherical silica (A), polyethylene terephthalate containing 1500 ppm of spherical silica having an average particle size of 0.18 μm is 290.
Extrusion at 15 ° C, cooling with 15 ° C chill roll, thickness 12
An unstretched film of 0 μm was obtained. This unstretched film was stretched 3.5 times in the longitudinal direction between a pair of rolls at 85 ° C. having different peripheral speeds. Next, the coating solution was applied by a roll coater method, dried with hot air at 70 ° C., stretched 3.5 times in the transverse direction at 98 ° C. with a tenter, and further heat-fixed at 210 ° C. to a thickness of 10 μm.
To obtain a laminated polyester film comprising a biaxially stretched film substrate and a surface layer. Surface layer coating amount is 0.04 after biaxial stretching
g / m ² . Table 1 shows the evaluation results of the obtained films.

 A film with few coarse projections and slippery was obtained.

Example 2 In Example 1, the average particle size was 0.3 as the granular silica (B).
The coating amount was 02 μm, the content of SiO ₂ in the coating solution solid content was 30%, the content of the copolymerized polyester resin was 70%, and the coating amount of the surface layer was 0.02 g / m ² after biaxial stretching. Laminate biaxially stretched in the same manner as in Example 1 using the same film substrate as in Example 1 except that spherical silica having an average particle size of 0.2 μm was used as 100 ppm as the granular silica (A) of the film substrate. A polyester film was obtained. Table 1 shows the evaluation results of the obtained films. A film with few coarse projections and slippery was obtained.

Example 3 In Example 1, the average particle size was 0.3 as the granular silica (B).
The thickness of the coating solution was 12 μm, the content of SiO ₂ in the coating solution solid content was 1%, the content of the copolymerized polyester resin was 99%, and the coating amount of the surface layer was 0.08 g / m ² after biaxial stretching. Further, the same film substrate as in Example 1 was used except that spherical silica having an average particle size of 0.08 μ was 2000 ppm as the granular silica (A) of the film substrate,
A biaxially stretched laminated polyester film was obtained in the same manner as in Example 1. Table 1 shows the evaluation results of the obtained films. A slippery film without coarse projections was obtained.

Example 4 In Example 1, the average particle size of the particulate silica (A) was 0.3.
Polyethylene terephthalate containing 12 μm spherical silica at 1000 ppm was melt-extruded at 300 ° C. and cooled with a cooling roll at 15 ° C. to obtain an unstretched film having a thickness of 120 μm. Then, the same surface coating solution as in Example 1 was rolled. Apply with a coater method, dry with hot air of 70 ° C,
The film was stretched 3.2 times, further stretched 4.7 times in the longitudinal direction between a pair of rolls having different peripheral speeds at 85 ° C., and heat-set at 210 ° C. to obtain a biaxially stretched laminated polyester film having a thickness of 8 μm. The surface layer coating amount was 0.05 g / m ² after biaxial stretching. Table 1 shows the evaluation results of the obtained laminated films. A film with few coarse projections and slippery was obtained.

Comparative Example 1 A biaxially stretched laminated polyester film was obtained in the same manner as in Example 1 except that a liquid containing no spherical silica (B) was used in the coating liquid.
Table 1 shows the evaluation results of the obtained films. The obtained film was excellent in flatness but poor in slipperiness and lacked practicality.

Comparative Example 2 A biaxially stretched laminated polyester film was obtained in the same manner as in Example 1, except that polyethylene terephthalate containing no spherical silica (A) was used as the film substrate in Example 1. Table 1 shows the evaluation results of the obtained films. The obtained film had particularly good flatness, but lacked slipperiness and lacked practicality.

Comparative Example 3 The procedure of Example 1 was repeated except that the coating liquid had a spherical silica (B) having an average particle diameter of 0.08 μm and the solid content of SiO ₂ in the coating liquid was 0.1%. A biaxially stretched laminated polyester film was obtained in the same manner. Table 1 shows the evaluation results of the obtained films. The obtained film had particularly good flatness, but lacked slipperiness and lacked practicality.

Comparative Example 4 Example 1 was repeated except that polyethylene terephthalate containing 20 ppm of spherical silica (A) having an average particle size of 0.18 μm was used as the film substrate in the method of Example 1.
A biaxially stretched laminated polyester film was obtained in exactly the same manner as described above. Table 1 shows the evaluation results of the obtained films. The resulting film is particularly excellent in flatness, but has poor slipperiness and lacks practicality.

Comparative Example 5 Example 1 was repeated except that polyethylene terephthalate containing 1500 ppm of spherical silica (A) having an average particle diameter of 0.4 μm was used as the film substrate in Example 1.
A biaxially stretched laminated polyester film was obtained in exactly the same manner as described above. Table 1 shows the evaluation results of the obtained films. The obtained film had good slipperiness, but did not have the desired electromagnetic conversion characteristics due to many coarse projections.

Comparative Example 6 In the method of Example 1, polyethylene terephthalate containing 2000 ppm of spherical silica (A) having an average particle diameter of 0.02 μm was used as a film substrate, and the average particle diameter of the spherical silica (B) was Exactly the same as Example 1 except that 0.02 μm, 10% of SiO ₂ in the coating liquid solid component, 90% of copolymerized polyester resin, and the coating amount of the surface layer was set to 0.02 g / m ² after biaxial stretching. A biaxially stretched laminated polyester film was obtained by the above method. Table 1 shows the evaluation results of the obtained films.
Shown in Although the obtained film had excellent surface flatness, it was poor in slipperiness and was not practical.

Comparative Example 7 In Example 1, polyethylene terephthalate containing 3000 ppm of spherical silica (A) having an average particle diameter of 0.18 μm was used as a film substrate, and the average particle diameter of spherical silica (B) was 0.08 μm in the surface coating solution. And the solid content of the coating liquid
A biaxially stretched laminated polyester film was obtained in exactly the same manner as in Example 1, except that SiO _{2 was} 5% and copolyester resin was 95%, and the coating amount of the surface layer was 0.04 g / m ² after biaxial stretching. . Table 1 shows the evaluation results of the obtained films. The obtained film was excellent in slipperiness, but had many coarse projections, and the desired electromagnetic conversion characteristics could not be obtained.

[Effects of the Invention] From the data shown in Table 1, the laminated film of the present invention has very excellent flatness, excellent electromagnetic conversion characteristics when formed into a magnetic tape, excellent slipperiness, and workability and running when formed into a tape. It is understood that it is possible to obtain a base film having excellent properties. On the other hand, when the surface roughness of the substrate and the average particle size concentration of the particles are out of the range of the present invention (Comparative Examples 1 to 5).
5) shows that the slipperiness is good but the electromagnetic conversion characteristics are poor (Comparative Examples 3 and 5), or that there are few coarse protrusions and the flatness is good but the slip is extremely poor (Comparative Examples 1, 2, and 4). .

Continued on the front page (72) Katsuro Kuze, Inventor 10-24, Toyo-cho, Tsuruga-shi, Fukui Prefecture Toyobo Co., Ltd. Tsuruga branch room, Research Laboratory Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 1 / 00-35/00 G11B 5/704

Claims (1)

(57) [Claims] 1. A polyester film base material containing 30 to 2000 ppm of spherical silica (A) having an average particle size of 0.05 to 0.5 μm and having a surface roughness of 0.007 μm or less in center line average roughness Ra on at least one surface of a substrate. 2000 to 800,000 spherical silica (B)
surface layer of ppm including resin is a polyester film that is laminated by a coating method, the spherical silica (A) and (B), the following formula _{D B: D A = 1:} 60~4: 1 ...... (1) ( D _a where is the average particle diameter of the spherical silica (a), D _B is the average particle diameter of the spherical silica (B)), and _{C a: C B = 1:} 20000~1: 1 ...... ( 2) (C _a where spherical silica (a) is the concentration of, C _B is laminated polyester film which satisfies the spherical silica is the concentration of (B)).