JPS63202451A - Easily adhesive polyethylene terephthalate film - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an easily adhesive polyethylene terephthalate film, and more particularly to an easily adhesive polyethylene terephthalate film suitable primarily for a base material of a videotape.

[Prior Art] In order to improve the adhesion of the surface of a polyethylene terephthalate film, films whose surfaces are thinly coated with vinyl resin, polyester resin, acrylic resin, etc. have been well known (Japanese Patent Publication Publication No. 30-3-1989).
437.41-8470, etc.). Among these coating resins, there are many polyethylene terephthalate films coated with coating layers mainly composed of polyester copolymers, and many patent applications have been filed recently (Japanese Patent Publication No. 61-39658).
Publication No. 58-191156.58-19625
2.61-2528.61-149353.61-20
5137, etc.).

[Problems to be Solved by the Invention] However, when the above-mentioned conventional easily adhesive polyethylene terephthalate film is made into a videotape by providing a magnetic layer on the easily adhesive layer, the chroma S/N ratio ( The problem is that parameters indicating the quality of color display) and skew (parameters indicating image distortion) do not reach satisfactory levels. This tendency becomes even clearer in the case of so-called metal tapes that use ferromagnetic metal powder as the magnetic material in the magnetic layer.

SUMMARY OF THE INVENTION An object of the present invention is to provide an easily adhesive polyethylene terephthalate film which can improve the above problems and has a high chroma S/N ratio and a small skew when used as a video tape.

[Means for Solving the Problems] The present invention provides an easily adhesive film in which at least one side of a polyethylene terephthalate film is coated with an easily adhesive coating, in which the filtering center line waviness on the surface of the coating layer is zero. .08 μm or less, and the secondary elastic modulus of the film in the longitudinal direction is 6×109 to 2×10 N
The gist of the invention is an easily adhesive polyethylene terephthalate film characterized by having a polyethylene terephthalate film having a polyethylene terephthalate content in the range of /TIi.

Polyethylene terephthalate (hereinafter referred to as PET) in the present invention
(abbreviated as) is one in which 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more of ethylene terephthalate is a repeating unit, but within this limited amount range, the acid component and /Or a portion of the glycol component may be replaced with a third component as described below.

-Acid component- Isophthalic acid, 2,6-naphthalene dicarboxylic acid, 1.
5-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4゜4゛-diphenylsulfonedicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, Kano β-hydroxyethoxybenzoic acid, Adipic acid, azelaic acid, sepatic acid, hexahydroterephthalic acid, hexahydroisophthalic acid, ε-oxycaproic acid, trimellitic acid, trimesic acid, pyromellitic acid, α,β-bisphenoxyethane-4,4゛dicarboxylic acid , α, β-bis(2-chlorophenoxy)ethane-4,4° dicarboxylic acid, 5-sodium flufoisophthalic acid, etc.

- Glycol components - Propylene glycol, butylene glycol, hexamethylene glycol, decamethylene glycol, neobenzene gelicol, 1,1-cyclohexane dimetatool, 1,4-cyclohexane dimetatool, 2,2-bis(4-β -hydroxyethoxyphenyl)propane,
Bis(4-β-hydroxyethoxyphenyl)sulfone, diethylene glycol, triethylene glycol, pentaerythritol, trimethylolpropane, polyethylene glycol, etc.

Also. This PET contains known additives, such as heat stabilizers, oxidation stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, and mold release agents. , an antistatic agent, a nucleating agent, etc. may be added.

The intrinsic viscosity of PET as described above (measured in orthochlorophenol at 25°C) is from 0.40 to 1.20, preferably from 0.50 to 0.80, more preferably from 0.5
Those in the range of 5 to 0.75 dα/g are suitable for the content of the present invention.

Furthermore, the PET film referred to in the present invention refers to unoriented PE film.
It is a biaxially oriented PET film obtained by stretching a T-sheet in two wheel directions, that is, in both the longitudinal direction and the width direction. The presence or absence of biaxial orientation can be confirmed by the appearance of a pattern unique to biaxial orientation in the X-ray diffraction pattern.

The thickness of the PET film referred to in the present invention is not particularly limited, but from the viewpoint of its use, it is preferably in the range of 4 to 30 μm, particularly 5 to 20 μm.

The easily adhesive coating layer as used in the present invention means that the thickness of the coating layer is 0.01 to 1 μm, preferably 0.01 μm.
~0.5μm, more preferably 0.02~0.2μm
It is within the range of . If the thickness of this coating layer becomes thicker than the above range, not only will the rigidity of the entire film decrease, but it will also be disadvantageous in terms of film manufacturing cost.

Conversely, if this coating layer thickness is thinner than the above range,
This is not preferable because it causes uneven adhesion.

Since the thickness of this coating layer is extremely small as described above, it is not very advisable to coat a pre-manufactured biaxially oriented PET film with a coating liquid. A coating method suitable for the present invention includes unstretched or uniaxially stretched P
This is a method in which an ET film is coated with a coating liquid and then stretched biaxially or uniaxially. With this method,
Since the coating layer becomes thinner by an amount corresponding to the stretching ratio, it is easy to form a thin coating layer. In addition, it has the advantage of increasing the adhesive strength between the base PET film and the coating layer, and it also has the advantage of reducing film production costs because coated films can be made all at once on the film production line. be.

The polymer constituting the highly adhesive coating layer in the present invention is preferably one as shown below.

(1>, polyester copolymer sulfonic acid A mixed dicarboxylic acid or its ester containing 0.5 to 40 mol% of a dicarboxylic acid containing a metal group and 60 to 99.5 mol% of a dicarboxylic acid or its ester not containing this) A polyester copolymer obtained by reacting an ester with a glycol component.Sulfonic acid metal base-containing dicarboxylic acids include sulfoterephthalic acid,
5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 2-sulfo-
1,4-bis(hydroxyethoxy)benzene, 5(4
Alkali metal salts such as -sulfophenoxy)isophthalic acid and ester-forming derivatives thereof are used.

Also, other dicarboxylic acids or esters thereof)
As the component and the glycol component, one or more of the acid components and glycol components described in the above-mentioned PET section are used in appropriate combination.

(2) Acrylic copolymer A copolymer whose main component is an acrylic component such as acrylic acid, methacrylic acid, acrylamide, acrylonitrile, or a derivative thereof. In addition to acrylic components, vinyl components such as vinyl chloride, vinyl acetate, and vinylidene chloride may be copolymerized. Also included are so-called thermosetting acrylic copolymers crosslinked with compounds such as melamine, urea, and isocyanate.

(3), polyvinylidene chloride copolymer (4), polyurethane copolymer (5), polyvinyl acetate copolymer (6), polyolefin copolymer (7), condensation of thermosetting resin products (e.g. condensation products of melamine, urea, diazine or their derivatives with formaldehyde).

Various polymers such as those described above can be used in the easily adhesive coating layer of the present invention, but among these, polyester copolymers and acrylic copolymers are preferred, especially those with good adhesiveness to the base PET film. Polyester copolymers are preferred for the present invention because of their ease of recovery and reuse when a defective film is broken into pieces and returned to PET raw materials for recovery and reuse.

In addition, known additives such as inorganic or organic fine particles, lubricants, surfactants, antistatic agents, plasticizers, etc. may be added to the coating layer made of the above-mentioned polymer.

Next, the filter centerline waviness (WCA) of the coating layer surface of the film of the present invention needs to be 0.08 μm or less, preferably 0.06 μm or less, and more preferably 0.04 μm or less. When this W ratio is larger than the above, when a magnetic layer is applied to the surface to make a videotape, the chroma S/N ratio (hereinafter referred to as C-3) of this videotape is
/N) worsens. Filter center line waviness (Wo
A) is a measure that indicates surface unevenness (waviness) with a much longer period than the average surface roughness (Ra), and conventionally, no attention has been paid to the waviness of the film surface. The inventors have determined W to indicate the degree of this waviness. The present invention was based on the finding that the value of A greatly influences C-3/N. Note that the lower limit of the WCA value is not particularly limited, but since it is very difficult to set this value completely to O, it is considered that approximately 0.005 μm is substantially the lower limit value.

Next, the secondary elastic modulus of the film of the present invention in the longitudinal direction is 6X
109-2 X 101G, preferably 7X109
~1.8X10'N, more preferably 8X109~1.
It is necessary to be in the range of 5×1010N/Td.

If the value of the secondary elastic modulus is smaller than the above range, a videotape based on this film will have a large skew. On the other hand, if the value of the secondary elastic modulus is larger than the above range, there will be a drawback that the film or tape is likely to be cut when slitting it into narrow widths.

As is clear from the measurement method described in detail, the value of the second-order elastic modulus indicates the magnitude of the elastic term of the Voigt model in a four-element model in which the Maxwell model and the Voigt model are arranged in series, which are commonly used as dynamic models. Conventionally,
Although not much attention has been paid to this value, the inventors discovered that this value greatly affects the skew of a videotape, leading to the present invention.

In order to make the film of the present invention suitable as a base material for video tapes, especially metal tapes, the average surface roughness Ra of the coating layer surface should be 0.003 to 0.020 μm.
, preferably in the range of 0.004 to 0.015 μm, more preferably in the range of 0.01 to 0.012 μm.

If the value of Ra is larger than the above range, the video output of the videotape using this as the base material will decrease;
If the value is smaller than the above range, the film tends to block, resulting in poor handling and workability.

In order to make the film of the present invention more suitable as a base material for videotape, among the minute projections on the surface of the coating layer, the number of projections with a height of 0.54 μm or more (high projection density) should be reduced to 60. /s2 or less, preferably 40 pieces/mm
It is preferable that the number of dropouts be less than 20, more preferably less than 20 pieces/rnm2.By doing this, when a videotape is made using this film as a base material, the number of signal dropouts (dropouts) on the videotape can be reduced. can be significantly reduced.

Next, an example of a method for manufacturing the film of the present invention will be shown. Manganese acetate is added as a catalyst to dimethyl terephthalate and ethylene glycol, and transesterification is carried out while methanol is distilled off using a conventional method. Next, inorganic particles that have been sufficiently dispersed and filtered (for example, an average particle size of 0.20
After adding an ethylene glycol slurry of colloidal silica spherical particles (μm) to a colander and adding trimethyl phosphate and antimony trioxide as a polymerization catalyst, 1st-
A polycondensation reaction is carried out while heating under a vacuum of 1 g or less to obtain a pellet-like polymer having an intrinsic viscosity of 0.63. The inorganic particles are contained in this polymer in an amount of 0.2 to 0.8% by weight. After fully vacuum drying this pellet at 170 to 200°C, it was fed to an extruder and melted and extruded at 280 to 290°C, and after passing through a gear pump to suppress flow rate fluctuations,
The mixture is passed through a filter that can capture 99% or more of solids of 3 μm or larger, and introduced into a T-type nozzle, from which it is discharged as a sheet-like melt. This sheet-like melt is heated to a surface temperature of 20
The film is wound around a cooling drum at ~50°C, brought into close contact using electrostatic charge, and cooled and solidified to produce an unstretched film.

This unstretched film is heated to 75 to 95°C and stretched 3 to 4 times in the longitudinal direction to form a uniaxially stretched film. This-
After corona discharge treatment is applied to one side of the axially stretched film, a solution or dispersion containing an easily adhesive polymer is coated on the treated surface. The solvent of the coating liquid may be water, a mixture of water and an organic solvent, or an organic solvent.
Further, the coating method may be any of various known methods, such as reverse coating, gravure coating, fountain coating, die lip coating, air knife coating, and metering bar method coating. After drying the coated surface of the coated uniaxially stretched film by blowing hot air, the film is passed through a super calendar roll to smooth the coating layer, and then the film is sent to a stick where it is heated to 95-120°C. It is stretched 3.5 to 4.2 times in the width direction while being heated, and then guided out of the stick while slowly cooling. Next, the film temperature is heated to 120 to 160°C, and the film is heated again in the longitudinal direction.
．． The film is stretched 4 to 1.8 times, sent to the stenter again, and heat treated at 180 to 225°C for 1 to 10 seconds, then slowly cooled and led out of the stenter. This film is transported under low tension and wound onto a core while dielectrically heating the film winding section with microwaves. The film roll wound around the core is left in a temperature-controlled room at 40 to 60°C for 10 to 30 hours, and then placed in a room temperature atmosphere for 10 to 2 hours.
After allowing it to cool for 0 hours, it is rewound using a slitter or C-roll to form a film product roll of an appropriate width. The thus obtained PET film having an easily adhesive coating layer fully satisfies each physical property value required by the present invention, and is extremely excellent as a base material for video tapes, especially metal tapes. After applying an anchor coating agent to one side of this film as necessary, apply magnetic paint (any of heat cure type, radiation cure type, electron beam cure type, etc.) on top of it to a thickness of 1 to 4 μm after drying. After coating it so that Make pancakes. By winding up an appropriate length of this pancake onto a reel and storing it in a cassette, a cassette-packed videotape that can be put to practical use can be obtained.

[Methods for Measuring Characteristics and Methods for Evaluating Effects] The methods for measuring each characteristic and the methods for evaluating effects used in the present invention are summarized below.

(1) Filtered centerline waviness (woA) using a universal surface profile measuring instrument model 5E-3Ef manufactured by Koita Seisakusho, JIS-
80610-'1976. The measurement conditions are as follows.

Height magnification: 50,000x Measurement plane magnification: 20x Measurement length: 8Nr1 (measured in the longitudinal direction of the film) Low cutoff: 0.8Al11 High cutoff: 8m (2) Secondary elastic modulus width A sample slit into 12.5#l111 (the longitudinal direction of the sample is made to match the longitudinal direction of the film. The thickness of this sample is d (μm), and the heat shrinkage rate in the longitudinal direction is Hl (%)), 1. (Apply a load equivalent to the stress of Jf/nwn2 and place it in a forced circulation hot air oven (volume 0.09 m) at 100°C for 5 seconds in this state,
After that, quickly remove the load and move it to an atmosphere of 23° C. and 60% RH. The longitudinal heat shrinkage rate of the sample subjected to this load treatment is defined as H2 (%). Then, the quadratic elastic modulus can be approximately determined by the following equation.

Secondary elastic modulus (N#) = 1.57xlO1G (1-exp(-1/2)) d(
H2+H1(1-exp (-1/2))) In addition, Hl
, H2 is measured as follows.

A sample to be measured with a size of 300 m x 12.5 m and whose longitudinal direction matched the longitudinal direction of the film was placed in an atmosphere of 23°C and 60% RH for 30 minutes.
The film was left to stand for a minute, and in that atmosphere, two marks were made in the longitudinal direction of the film at an interval of about 20011111, and the interval between the marks was measured with a micrometer, and the measured value was designated as A.

Next, the sample to be measured was left in a tension-free atmosphere at 70°C for 48 hours, and then at 23°C and 60% R
1) After cooling for 1 hour, measure the interval between the marks made earlier, and let the measured value be A'.

The thermal contraction rate H1 or H2 is determined from the above measured values using the following formula.

100 (A-A-)/A (3) Average surface roughness Ra> Measurement was carried out by connecting a signal analyzer (both manufactured by Koita Institute) to a high-precision thin film step measuring device ET-10 model. The Ra brightening principle is based on JIS-80601-1976. The measurement conditions are as follows.

Height direction magnification: 100.000 times Measurement surface direction magnification: 500 times Measurement length = 4 m (measured in the film width direction) Cutoff value: 0.08 #1 (4> High protrusion density Nippon Kogaku vA'!! Using a surface finishing microscope, the number of interference fringes of second order or higher is counted by multiple interference method, and this is calculated based on the film area of 11TIIT1.
Convert and display the number per 2 pieces.

The wavelength of the light used for measurement is 0.54 μm 1 mirror reflectance 6
5%, and the microscope magnification is 200x.

(5) Manufacture of videotape and evaluation of its properties A black ferromagnetic metal powder was produced by thermally decomposing acicular α-FeOOl-( containing 5% cobalt) and reducing α-Fe203 with hydrogen. 300 parts by weight of this ferromagnetic metal powder and the following composition were mixed and dispersed in a ball mill for about 12 hours.

Urethane-modified saturated polyester resin = 35 parts by weight PVC/vinyl acetate copolymer resin: 30 α-alumina: 15 Carbon black:
: 3 Butyl acetate: :30
0 Methyl isobutyl ketone: 300 Next, 3 parts by weight of oleic acid, 3 parts by weight of valmitic acid and 4 parts by weight of aluminum stearate are added thereto, and kneaded for an additional 30 minutes. Next, 75% of the triisocyanate compound
Add 22 parts of ethyl acetate solution and perform high-speed shear dispersion treatment for 1 hour to prepare a magnetic paint. This magnetic paint is made into PET
It is coated on the surface of the easily adhesive coating layer of the film to a thickness of 3 μm after drying, subjected to magnetic field alignment treatment, dried, and supercalendered.

Next, the following composition was applied to the opposite side (back side) to a thickness of 1 μm after drying, dried, calendered, and cured.

Carbon black = 50 parts by weight Polyisocyanate: 20 Stearic acid:
4 〃Butyl stearate゛ 2 〃Nitrified cotton: 40 〃PVC φVinyl acetate/vinyl alcohol copolymer: 30 〃Polyurethane elastomer: 30 〃Mixed solvent (MI
BK/Toluene): 250 The coated sheet thus obtained was slit into 8m wide pieces,
Incorporate it into the BJllllIVTR cassette.

The videotape thus obtained was evaluated for the following characteristics.

■ Video output Using 8 rttm VTR for home use, 4MH2
A single signal was recorded and its playback output was measured. In addition,
The standard is the one with the lowest output among each experimental level.
Expressed relatively as dB.

■ Chroma S/N ratio (C-3/N) Measured using a home-use 8 rum VTR and Shibaku 925C color video noise meter. In addition,
The standard is relatively displayed with the lowest C-3/N among each experimental level as OdB.

■ Using a skew home 8am VTR, measure the degree of distortion of the straight line image that appears at the top of the monitor screen after 300 bus runs in 90 minutes mode at 40℃ and 80%RH, and calculate this in terms of time (μ5ec). Convert and display.

■ Record a single 4MH2 signal using a dropout home-use 8 as VTR, and calculate the number of times per minute that the signal drops by 12 dB or more from the average playback level for 5 μsec or more. Count with

[Example] Examples and comparative examples of the present invention are shown below. It goes without saying that the present invention is not limited to these Examples.

Example 1 Preparation of ethylene glycol slurry of solid particles> 10 parts by weight of silica particles with an average particle size of 0.20 μm, 1 part by weight of ethylene glycol, and 0 parts of ammonium salt
．． 4 parts were mixed and stirred with a homogenizer to prepare an ethylene glycol slurry of silica particles. In 100 parts of this slurry, the average particle diameter is 0.0971! I11
100 parts by volume of glass beads were added thereto, and the mixture was stirred at 3000 rpm for 2 hours using a cross blade with a blade diameter of 16 rm. After the dispersion was completed, the glass beads were removed by filtration through a 400-mesh wire mesh, and the slurry of silica particles obtained by dispersion was further filtered through a 3μ filter. The slurry thus obtained was used to produce PET polymer.

<Production of PET Polymer> To 100 parts by weight of dimethyl terephthalate, 60 parts by weight of ethylene glycol and 0.04 parts by weight of manganese acetate were added, and transesterification reaction was carried out at 150 to 240°C for 4 hours while removing methanol. Then phosphoric acid 0
．． After adding 0.02 parts by weight and 0.03 parts by weight of antimony trioxide, and further adding a slurry of solid particles, 1MIIH
A polycondensation reaction was carried out in a high vacuum of Q or lower for 3 hours to obtain a PET polymer containing 0.3% by weight of silica particles. The intrinsic viscosity of this polymer was 0.635.

<Preparation of polymer solution for coating> 165 parts of dimethyl terephthalate, 44.5 parts of dimethyl 5-sodium sulfoisophthalate, 124 parts of ethylene glycol, 0.106 parts of manganese acetate tetrahydrate, 0.07 part of calcium acetate dihydrate. were mixed, methanol was distilled off at 140 to 220°C, and a transesterification reaction was carried out. Then, 0.09 parts of trimethyl phosphate, 7.2 parts of diethylene glycol, and 0.06 parts of antimony trioxide were added.
The temperature was raised to ~280°C over 1 hour and 30 minutes, and the pressure was gradually lowered from normal pressure to 0.5 sHg to remove the generated ethylene glycol from the system, and this state was maintained for an additional 40 minutes to react, until the intrinsic viscosity was 0. A polymer of .57 was obtained.

Analysis of the copolymerization components of the produced polyester ether revealed that the diethylene glycol component was 17 mol% of the total diol component, including by-products during the reaction, and the 5-sodium sulfoisophthalic acid component was 14 mol% of the total dicarboxylic acid component.
It contained mol%.

The obtained copolyester ether was dissolved in 85° C. hot water to make a 5% by weight aqueous solution. Colloidal silica with an average particle size of 0.3 micrometers was added to this, and the composition ratio of the solids was 95% by weight of copolyester and 5% by weight of colloidal silica.
This was determined in weight percent and used as a coating polymer solution.

After vacuum drying the above polymer pellet at 180°C for 6 hours, it was fed to an extruder and melt-extruded at 285°C. The molten polymer was passed through a gear pump to suppress flow rate fluctuations, and then After filtering through a metal fiber sintered filter capable of capturing 99% by weight or more of solids, the mixture was introduced into a T-type nozzle and discharged as a sheet-like melt from this nozzle.

This sheet-like melt was wound around a cooling drum with a surface temperature of 30° C., and was cooled and solidified while imparting an electrostatic charge to improve the adhesion between the drum and the molten sheet, thereby producing an unstretched film. This unstretched film was heated to 85° C. and stretched 3.2 times in the longitudinal direction to form a uniaxially stretched film. One side of this film was subjected to corona discharge treatment, and the above-mentioned coating was applied on the treated surface. A polymer solution was applied.

The thickness of the coating layer is determined at the time it becomes the final product film.
The coating conditions were adjusted so that the thickness was 0.08 μm. After drying the coated surface of the coated uniaxially stretched film by blowing hot air on it, the film is passed through a set of super calender rolls to smoothen the coating layer, and then the film is sent to a stenter and
The film was stretched 3.8 times in the width direction while being heated to 00°C, and then led out of the stenter while being slowly cooled.

Next, this film is heated again to 140°C, and using the speed difference between the two sets of nip rolls, the film is heated to 1.6°C in the longitudinal direction.
Stretched twice, sent it to the stenter again, and heated it to 210°C.
The sample was heat-treated for 5 seconds.

Next, while maintaining tension, the hot air was introduced into a zone with a temperature of 120°C for intermediate cooling to this temperature, and then heated to a temperature of 120°C.
℃ zone where it was allowed to relax 1% of its original length in the longitudinal direction, and then the film was slowly cooled to room temperature. The thickness of this film was approximately 10 μm. This film 2. The film was transported with a tension of 1 m width and wound around a core while dielectrically heating the film winding part with microwaves.

A large diameter film roll wound with approx. 60'OOm (winding hardness: 65° shore. Film temperature inside the roll is approx. 70°C)
) was placed in a temperature-controlled room at 70°C and left for 24 hours, then placed in an air-temperature atmosphere for 24 hours to slowly cool it.
I11 film product roll (rolling hardness 90' shore)
And so.

Table 1 shows the properties of the film thus obtained and the properties of a videotape made using this film as a base material. These results show that when a film having the characteristics of the present invention is used as a base material, a videotape with extremely excellent characteristics can be obtained.

Example 2.3 In Example 1, films with different filter centerline waviness (WCA) values were produced by changing the conditions when supercalendering the coated uniaxially oriented film. Table 1 shows the properties of this film and the videotape made using it as a base material. From this result, as the value of filter centerline waviness (WcA) increases, C
It can be seen that -3/N is decreasing.

Comparative Example 1 In Example 1, by changing the type of solid particles added to PET, the processing method thereof, and the supercalendering conditions of the coated uniaxially stretched film, the average surface roughness (Ra) and the filter center line waviness were improved. (WcA)
Films with both high and high protrusion density values were produced. Table 1 shows the properties of this film and the properties of a videotape using it as a base material. Video output, C-3
/N1 It can be seen that this example is inferior to Examples 1 to 3 in terms of dropout.

Example 4 and Comparative Example 2 In Example 1, heat treatment of the biaxially stretched film,
By changing the winding and storage conditions, films with different secondary elastic modulus values were produced.

Table 1 shows the properties of this film and the properties of a videotape using it as a base material. It can be seen that as the value of the secondary elastic modulus of the film decreases, the skew of the videotape worsens.

[Effects of the Invention] The present invention has the following effects: The present invention has succeeded in improving the C-3/N and 1-characteristics of video tapes, particularly metal tapes, based on this film. Since these effects are not necessarily limited to video tapes, the film of the present invention can also be effectively used in other applications, such as as a base material for computer memory tapes, digital audio tapes, and the like.

Claims (1)

[Claims] An easily adhesive film formed by applying an easily adhesive coating on at least one side of a polyethylene terephthalate film, wherein the filter center line waviness on the surface of the coating layer is 0.08 μm or less, and the film has a secondary elasticity in the longitudinal direction. The rate is 6×10^9 to 2×10^10N/m
An easily adhesive polyethylene terephthalate film characterized by being in the range of ^2.