JPH05208476A - Composite oriented polyester film - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and running properties by a method wherein a resin forming at least one of outermost layers is composed of a specific polyester composition. CONSTITUTION:A resin forming at least one of outermost layers is composed of a polyester composition, which is obtained by mixing a thermoplastic resin in a molten state with a polyester substantially not containing inactive particles. The thermoplastic resin has Tg lower than the glass transition temperature of the polyester and contains inactive particles. A layer adjacent to the outermost layer does not contain particles acting to form substantial projections, or contain particles having an average particle diameter which is 3/2 or less of the average particle diameter of the maximum diameter particles in the particles contained in the outermost layer. The outermost layer has a thickness Ta which is 1/4 or less of the overall thickness Tf of the film 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a composite oriented polyester film suitable as a base film for magnetic tape.

[0002]

2. Description of the Related Art Generally, polyester such as polyethylene terephthalate has excellent physical and chemical properties, and therefore, in addition to fibers, molded articles, magnetic tapes, photographs, capacitors, packaging, etc. It is also widely used for various kinds of applications. When used for these films, their slipperiness and abrasion resistance are major factors that affect the workability of the film manufacturing process and the processing process in each application, and further the quality of the product. Especially when a magnetic layer is coated on the surface of a polyester film and used as a magnetic tape,
Friction and abrasion between the coating surface and the film surface of the coating roll and the calendar roll during coating of the magnetic layer are extremely severe, and wrinkles and scratches on the film surface are likely to occur. Also, even after slitting the film after coating the magnetic layer and processing it into audio, video or computer tape, etc., when pulling out from the reel, cassette, etc., winding up and other operations, many guide parts, playback heads etc. Friction and wear occur remarkably between the two, and scratches and distortions are generated, and as a result of depositing white powdery substances due to abrasion of the polyester film surface, it often becomes a major cause of loss of magnetic recording signals, that is, dropout. .. Generally, in order to improve the slipperiness and abrasion resistance, a method of reducing the contact area with the guide roll etc. by giving unevenness to the film surface is adopted, and from the catalyst residue of the polymer used as the film raw material, A method of precipitating insoluble particles, a method of adding inactive inorganic particles, and the like are used. However, the roughening of the film is not preferable because it causes deterioration of electromagnetic conversion characteristics.

Further, due to the rapid speeding up of the working process in recent years, the phenomenon in which the projections provided to improve the slidability are scraped off and appear as white powder has become remarkable. In particular, when a magnetic layer is applied to the polyester film surface and used as a magnetic tape, friction and abrasion between the calendar roll and the film surface during application of the magnetic layer are extremely severe, and white powder-like substances due to abrasion of the polyester film surface protrusions are removed. As a result of the precipitation, it often causes a dropout of the magnetic recording signal, that is, a dropout.

The precipitation of the white powder substance is particularly remarkable in the case of the method of adding the inert inorganic particles. Since the affinity with the polyester, which is an organic component, is not sufficient, the projection skin is easily scraped off and the inert inorganic particles are dropped off in the calendar step when coating the magnetic layer. The inert inorganic particles are deposited on the surface of the film and are a major cause of dropout. As means for avoiding such dropout of surface protrusions and improving wear resistance, (1) a method in which glycol is grafted on the surface of inorganic particles to improve the affinity between polyester and the surface of the inorganic particles (JP-A-63- 280763), and (2) those having improved abrasion resistance by controlling the crystallization coefficient of the film surface layer (Japanese Patent Laid-Open No. 62-201938). However, it cannot be said that these improvements have reached a sufficient range, and there is a strong demand for improvements in this respect.

[0005]

DISCLOSURE OF THE INVENTION In view of the actual state of the prior art described above, the present invention is excellent in both runnability and electromagnetic conversion characteristics and is resistant to film processing steps, especially in the calendar step when applying a magnetic layer of a magnetic tape. The present invention provides an oriented composite polyester film for magnetic recording, which is excellent in abrasion resistance.

[0006]

That is, the present invention is a composite oriented polyester film comprising at least two layers, wherein the resin constituting at least one of the outermost layers (A layer) contains substantially inactive particles. To polyester not containing,
A polyester composition having a Tg lower than the glass transition temperature (Tg) of the polyester and melt-mixing a thermoplastic resin containing inert particles with the polyester, which is adjacent to the outermost layer (A layer). The layer (B layer) does not contain particles having a substantial protrusion-forming effect, or the outermost layer (A layer) contains the largest average particle diameter of the particles, and is ⅔ of the average particle diameter of the particles. It contains particles having the following average particle diameter, and the thickness (Ta) of the outermost layer (A layer) and the thickness (Tf) of the entire film satisfy the following relationship Ta <(1/4) Tf. It is a composite oriented polyester film characterized by the following. The composite oriented polyester film of the present invention is composed of at least two polyester layers.
Any number of layers may be used as long as the structure has two or more layers.

When the composite oriented polyester film of the present invention is used as a base film for a magnetic tape, a magnetic layer is formed on either surface of the film. The magnetic layer may be formed on either side of the film, but when the surface of the layer A is used as the running surface and the magnetic layer is provided on the opposite side, the effect of the present invention is most remarkable, which is preferable. .. Further, a back coat may be or may not be provided on the surface opposite to the magnetic surface (traveling surface), but when the A layer surface is used as the traveling surface, it is excellent without providing a back coat. Excellent running performance can be obtained.

The polyester used in the present invention is a crystalline polyester such as polyethylene terephthalate or polyalkylene naphthalate, and is not particularly limited, but one in which the main component of its repeating unit is ethylene terephthalate is preferable. Other copolymerization components include isophthalic acid, p-β-oxyethoxybenzoic acid, 2,6
-Naphthalenedicarboxylic acid, 4,4'-dicarboxyl diphenyl, 4,4'-dicarboxyl benzophenone, bis (4-carboxyphenyl) ethane, adipic acid, sebacic acid, 5-sodium sulfoisophthalic acid, Dicarboxylic acid components such as cyclohexane-1,4-dicarboxylic acid, propylene glycol, butanediol,
Neopentyl glycol, diethylene glycol, cyclohexanedimethanol, ethylene oxide adduct of bisphenol A, glycol components such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and oxycarboxylic acid components such as p-oxybenzoic acid can be optionally used. Can be used selectively. In addition, a compound containing a small amount of an amide bond, a urethane bond, an ether bond, a carbonate bond or the like may be contained as a copolymerization component.

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

In the composite oriented polyester film of the present invention, inert particles are contained in the resin constituting at least one of the outermost layers (A layer). Then, by forming protrusions on the surface of the film based on the particles added to the A layer, excellent running property can be imparted. Here, as the inert particles that can be added to the layer A, Ca, M
Carbonates of g, Sr and Ba, Na, K, Mg, Ca, B
a and Al sulfate, Na, K, Mg, Ca, Sr, B
Phosphates of a, Al, Ti and Zr, silicon dioxide, alumina, complex silicate compounds (amorphous or crystalline clay minerals, aluminosilicate compounds, etc.), asbestos (zircon, fly ash, etc.), Zr And oxides of Ti, C
terephthalates of a, Ba, Zn and Mn, Ba and P
Inorganic particles such as chromate of b, carbon (carbon black, graphite, etc.), glass (glass powder, glass beads, etc.), fluorspar, and ZnS, and crosslinked polystyrene resin,
Examples of organic particles include crosslinked acrylic resins, benzoguanamine resins, silicone resins, and crosslinked polyester resins. Among these, calcium carbonate, anhydrous silicic acid, hydrous silicic acid, aluminum oxide, aluminum silicate, barium sulfate, calcium phosphate, zirconium phosphate, titanium oxide, lithium benzoate, glass powder, clay (kaolin, bentonite, clay etc.) , Talc, and diatomaceous earth are particularly preferable. These inert particles may be natural products or synthetic products. These inert particles may be used alone or in combination of two or more kinds. It may also be used in the form of a complex salt.

In the present invention, when the resin constituting the layer A is prepared, the inert particles are preliminarily treated with T of the substrate polyester.
It has an important feature in that it is dispersed in a thermoplastic resin having a Tg of less than g and then blended in a matrix polyester. However, it is important that the abrasion resistance in the film processing step is remarkably improved. The T of the substrate polyester is formed on the protrusions of the film surface generated by the active particles.
It is presumed that a layer having a Tg of less than g can be provided, and that the presence of this layer relieves the shear stress applied to the protrusions during the film processing process. The thermoplastic resin has a Tg less than that of the film-forming substrate polyester.
It is not particularly limited except that it has, and any resin can be used, and resins such as polyester, polyether, polyamide, polycarbonate, polyurethane, polyester urethane, polyether urethane, vinyl polymer, and polysiloxane can be used. It is illustrated. In particular, polyester, polyamide, polyurethane, polyesteramide, polyesterurethane and the like which are well compatible with polyester are preferable, and polyester resin is particularly preferable. It is also possible to introduce a functional group into the resin in order to improve the adhesion with the inert particles, such as hydroxyl group, carboxyl group, sulfone group, phosphoric acid group, amino group, silyl group, phosphonic acid group and oxazoline. A group etc. are illustrated.

The method of dispersing the inert particles in the thermoplastic resin is not particularly limited, but the addition method during polymerization is preferably used. In particular, when it is added in the production process of polyester, it may be added in either a slurry state or a powder state, but it is added after being dispersed in a slurry state from the viewpoints of particle splash prevention, improvement of supply accuracy and uniformity. It is preferable to add it as a slurry of ethylene glycol (EG). In the case of dispersion in a slurry form, it is necessary to carry out uniform dispersion so as to reproduce the original primary particles of each particle as much as possible. Further, in order to obtain particles having a predetermined average particle diameter, means such as classification and filtration of commercially available particles may be used. In addition, a small amount of another compound (containing compound) may be used in combination to increase the binding property between the thermoplastic resin and the inert particles during the addition during polymerization, or the surface of the inert particles may be subjected to physical or chemical treatment. May be given. Further, conventionally known silane coupling agents, titanate coupling agents and the like may be used in combination.

The amount of the inert particles contained in the thermoplastic resin is preferably 0.01 to 2 in weight ratio with respect to the thermoplastic resin. 0.1 to 1 is particularly preferable.

The average particle diameter of the inert particles is preferably 0.05 μm or more and 5.0 μm or less, but 0.1 μm or more and 2.5.
A range of μm or less is particularly preferable. Average particle size is 0.05
If it is less than μm, the effect of improving the slipperiness is insufficient, which is not preferable. On the contrary, if it is 5.0 μm or more, coarse projections may occur on the surface when formed into a film, which is not preferable.

The amount of the thermoplastic resin containing the inert particles added to the polyester is not particularly limited, but is 0.1% by weight or more and 20.0% by weight based on the polyester.
The following is preferable. 0.5 to 10.0% by weight is more preferable.

As a method of adding the thermoplastic resin to the polyester in the present invention, a method of mixing the heat-melted thermoplastic resin and the polyester with a twin-screw extruder, a Brabender, a roll kneader or the like can be used. However, the present invention is not limited to these, and can be arbitrarily selected as long as the object of the present invention is achieved.

In addition, as long as the effects of the present invention are not impaired, inert particles other than the inert particles contained in the thermoplastic resin, such as inorganic particles of silica, titanium oxide, kaolinite, calcium carbonate, etc., or crosslinked styrene. Organic particles such as polymer beads and acrylic acid polymer beads may be used in combination. Further, a so-called internal particle method for precipitating particles in the polyester manufacturing process may be used in combination. Further, for example, additives for improving electrostatic adhesion, stabilizers for preventing side reactions such as coloration prevention, colorants, antistatic agents, and ultraviolet absorbers may be used in combination without any problem.
Further, there is no limitation on the combined use of an anti-aggregation agent for suppressing aggregation of the inert particles.

In the composite oriented polyester film of the present invention, the layer (B layer) adjacent to the A layer does not contain particles having a substantial projection forming action, or has the largest average particle size among the particles contained in the A layer. It is necessary to contain particles having an average particle size of one third or less of the average particle size of the particles. When the film has a two-layer structure, in order to impart slipperiness to the surface (magnetic surface) opposite to the surface of the A layer,
It is preferable to add particles to the B layer. Examples of the particles that can be added to the B layer include particles having the same composition as the particles exemplified as the inert particles that can be added to the A layer.
Then, by limiting the average particle size of the particles that can be added to the B layer within the above range, it is possible to substantially prevent the formation of protrusions on the surface of the A layer by the particles added to the B layer. .. Therefore, the protrusions formed on the surface (traveling surface) of the A layer are essentially only those particles added to the A layer, and have uniform and high density protrusions, and both the electromagnetic conversion characteristics and the traveling property are obtained. It is possible to obtain an excellent film surface. On the contrary, when particles having an average particle diameter outside the above range are added to the B layer, the particles added to the B layer form protrusions on the surface (traveling face) of the A layer, and the protrusions on the traveling face are The non-uniformity or the roughness of the magnetic surface (the surface on the side opposite to the surface of the A layer) becomes large, which deteriorates the running property and the electromagnetic conversion characteristic.

In the polyester film of the present invention, the thickness (Ta) of the A layer and the total thickness (Tf) of the film must satisfy the following relationship Ta <(1/4) Tf. Generally, when the tape running surface is roughened, the running property is improved, but the electromagnetic conversion characteristics are deteriorated due to the transfer of the running surface roughness to the surface of the magnetic layer. However, by setting Ta within the above range, it is possible to obtain a running surface (A layer surface) with a very small transfer effect, and a film having both excellent electromagnetic conversion characteristics and running characteristics can be obtained. On the other hand, when Ta exceeds the above range, transfer of the running surface (A layer surface) roughness to the magnetic surface becomes remarkable,
The magnetic surface is roughened, resulting in poor electromagnetic conversion characteristics. Therefore, from the viewpoint of electromagnetic conversion characteristics, the thinner the A layer, the better. However, in order to satisfy the excellent running property, the product of the concentration of particles added to the A layer and Ta is 100 to 20000 p.
It is preferable that it is pm · μm. The thicknesses of the A layer and the B layer are determined by the secondary ion mass spectrometry (SIM
S) etc. can be evaluated.

The surface roughness of the composite oriented polyester film for magnetic recording of the present invention is not limited and is arbitrary, but the average roughness of one surface is not more than 2/3 of the average roughness of the other surface. Is preferred. In particular, the rough surface is the surface of the layer A, and the average roughness is 0.010 to 0.030.
It is preferably μm. This is because by forming the magnetic layer on a flat surface, it is possible to suppress the surface roughening of the magnetic layer due to the underlayer effect, and the surface A is extremely roughened due to the transfer effect. This is because it has the property of being hard to cause, and it is possible to further improve the electromagnetic conversion characteristics.

The production method for producing the composite oriented polyester of the present invention is not limited. The compounding method may be a co-extrusion method of laminating resins in soybean or a method of laminating separately prepared films with an adhesive. Further, it may be a uniaxially oriented film or a biaxially oriented film. Further, in the case of a biaxially oriented film, it may be oriented in two directions at the same time or sequentially. When they are sequentially aligned, they may be aligned in the vertical direction first and then in the horizontal direction, or vice versa. Further, it may be stretched and oriented in multiple stages of two or more stages.

Since the composite oriented polyester film of the present invention has the outermost layer (A layer) in which particles having a substantial protrusion forming action are added to the resin for relieving the shearing force, it can be used in the calendering process. Only the projections that are not easily scraped off are uniformly and densely formed on the film surface. Therefore,
It is possible to provide a film which is excellent in both electromagnetic conversion characteristics and running properties, and in which white powder is remarkably generated in the calendar processing step.

Various measuring methods adopted in the present invention will be described below.

(1) Particle Size of Inert Particles The particle size distribution in the slurry obtained by sufficiently dispersing the powder in the EG slurry by high-speed stirring is shown by Shimadzu's light-transmitting centrifugal sedimentation type particle size distribution analyzer SA. -Use the value of 50% accumulated in the distribution measured using CP3 type.

(2) Calendering characteristics A film with a width of 30 cm is struck with a super calender of 4 stages (line pressure 300 Kg / cm, running speed 300 m / min).
After processing for 000 m, the amount of white powder adhering to the elastic roll was visually observed and ranked as follows. 1 ... White powder is not recognized at all 2 ... A slight amount of white powder is recognized, but it is extremely small amount 3 ... A small amount of white powder is recognized 4 ... A large amount of white powder is recognized

(3) Running property Tests were carried out using the apparatus of FIG. 1 under the conditions of a temperature of 23 ° C. and a relative humidity of 65%. In FIG. 1, 1 is a crank having a length of 40 mm, 2 is a rotatable guide roller, 3 is a tension detecting device, 4 is a metal guide post of a commercially available VTR for home use (maximum roughness Rt = 0.15 μm, average roughness). Ra = 0.008
.mu.m) and a film 5 having a width of 12.5 mm is provided on the guide roller 2, the tension detecting device 3, and the guide post 4 as shown in the drawing.
The contact angle to the guide post 4 by 3π /
The film 5 is set to 4 radians, one end of the film 5 is connected to the crank 1, the weight 6 having a weight of 50 g is hung at the other end, and the crank 1 is rotated at a speed of 8 rpm to set the film 5 to 1
The friction coefficient (μk) was obtained by reciprocating 00 times, and evaluated and ranked in three stages as described below. ○ ・ ・ ・ μk ≦ 0.25 △ ・ ・ ・ 0.25 ≦ μk ≦ 0.35 × ・ ・ ・ 0.35 <μk

(4) Electromagnetic conversion characteristics Chroma S / N for a standard tape was measured using a TG-7 / 1 type NTSC-TV test signal generator manufactured by Shibasoku Co., Ltd. and a 925D / 1 type NTSC color video noise measuring instrument. Then, the following three grades were evaluated and ranked. ○ ・ ・ ・ S / N> +3 dB △ ・ ・ ・ S / N> +1 dB × ・ ・ ・ S / N <+1 dB The magnetic tape was prepared by using a magnetic paint of the following composition on the base film 1) Magnetic powder (γ -Fe ₂ O ₃ ) 2) Binder (polyurethane / nitrocellulose) 3) Hardener (trifunctional isocyanate) 4) Carbon black 5) Abrasive (alumina) 6) Lubricant (stearic acid / isobutyl stearate) 7) Solvent (Methyl ethyl ketone / toluene / cyclohexanone) was dried and then applied and dried so as to have a thickness of 5 μm. After supercalendering, it was heat-cured. The obtained film was slit into a width of 1/2 inch to prepare a VHS video tape.

(5) Average roughness (Ra) Using a surface roughness meter Surfcom 300A manufactured by Tokyo Seimitsu Co., Ltd., needle diameter 2 μm, load 0.07 g, measurement reference length 0.8 m
The center line average roughness measured under the conditions of m and cutoff of 0.08 mm.

[0029]

EXAMPLES Next, examples and comparative examples of the present invention will be shown. All parts in the examples mean parts by weight unless otherwise specified.

(1) Method for producing thermoplastic resin containing inert particles An esterification reaction vessel was charged with the compounds shown in Table 1, and further 0.055 parts of zinc acetate and 0.03 of antimony trioxide were added.
5 parts and 0.040 part of sodium acetate are charged, the temperature is raised by heating, and the esterification reaction is carried out at 240 ° C. for 90 minutes at a gauge pressure of 3.5 kg / cm ² . The reaction product was transferred to a polymerization vessel together with 32 parts of a 30 wt% EG slurry of calcium carbonate having an average particle size of 0.6 μm, and the temperature was raised to 285 to reduce the pressure.
Polycondensation reaction was performed for 3 hours at 0.1 ° C. and 0.1 mmHg to obtain copolyester resins (TPE1 to 3). The Tg of these copolyesters was measured by DSC manufactured by Rigaku Denki Co.,
It shows in Table 1. TPA: terephthalic acid IPA: isophthalic acid SA: sebacic acid AA: adipic acid EG: ethylene glycol NPG: neopentyl glycol BD: butanediol

(2) Method for producing polyester In polymerizing polyester by a conventional method, each particle shown in Table 2 was added at the time of polymerization so as to have the addition amount shown in the same table, and a polyethylene having an intrinsic viscosity of 0.620 was added. Terephthalate (PET-1 to PET-3) was created.

Examples 1 to 3 and Comparative Examples 1 to 4 The polyesters constituting the layers A and B shown in Table 3 were individually dried and then fed to respective extruders. Then, the ratio of the discharge amount of each extruder is adjusted so as to be the thickness ratio of each layer shown in Table 3, and 2
It was melted at 90 ° C., laminated using a T-die and coextruded on a cooling drum adjusted to 30 ° C. to obtain a 220 μm-thick unstretched composite polyester film. The film was then heated to a roll heated to 75 ° C. and a surface temperature of 60.
The film was heated using an infrared heater at 0 ° C. (installed at a position 20 mm away from the film) and stretched 3.3 times in the machine direction between the low speed roll and the high speed roll. Further, this film was introduced into a tenter, stretched 4.4 times in the transverse direction at 100 ° C., and heat-treated at 220 ° C. for 5 seconds to give a thickness of 15 μm.
A biaxially oriented polyester film of was obtained.

[0033]

[Table 1]

Example 4 The polyesters constituting the layers A, B and C shown in Table 3 were separately dried and then fed to respective extruders. Then, the ratio of the discharge amount of each extruder was adjusted so as to be the thickness ratio of each layer shown in Table 3, melting was performed at 290 ° C., lamination was performed using a T die, and 30 ° C.
Co-extruded on the cooling drum adjusted to
An unstretched composite polyester film of μm was obtained. Subsequently, the film was heated using a roll heated to 75 ° C. and an infrared heater having a surface temperature of 600 ° C. (installed at a position 20 mm away from the film), and the film was heated in a longitudinal direction between the low speed roll and the high speed roll to 3.3. The film was stretched twice. Further, this film was introduced into a tenter, stretched 4.4 times in the transverse direction at 100 ° C, and heat-treated at 220 ° C for 5 seconds to give a thickness of 15
A biaxially oriented polyester film of μm was obtained. Table 4 shows the properties of the oriented polyester films obtained in Examples 1 to 4 and Comparative Examples 1 to 4 above.

[0035]

As shown in Table 4, the composite oriented polyester film of the present invention is excellent in both electromagnetic conversion characteristics and running property and is also excellent in calendering, and is particularly suitable as a base film for magnetic recording. Met.

[Brief description of drawings]

FIG. 1 shows an outline of an apparatus used for evaluating the runnability of a film.

[Explanation of symbols]

 1 crank 2 guide roller 3 tension detector 4 guide post 5 film 6 weight

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI technical display location // G11B 5/704 7215-5D B29K 67:00 B29L 9:00 4F

Claims (2)

[Claims] 1. A composite oriented polyester film comprising at least two layers, wherein the resin constituting at least one of the outermost layers (A layer) contains substantially no inert particles, and a glass of the polyester. A layer (B) which is composed of a polyester composition having a Tg lower than the transition temperature (Tg) and which is melt-mixed with a thermoplastic resin containing inert particles and which is adjacent to the outermost layer (A layer). Layer) does not contain particles having a substantial protrusion forming effect, or the average particle size of the particles contained in the outermost layer (A layer) is the average particle size of two thirds or less of the average particle size of the largest particles. The outermost layer (A
A composite oriented polyester film characterized in that the thickness (Ta) of the layer) and the total thickness (Tf) of the film satisfy the following relationship Ta <(1/4) Tf. 2. The composite oriented polyester film according to claim 1, wherein the average roughness of one surface is 2/3 or less of the average roughness of the other surface.