DE2424466A1 - BIAXIAL ORIENTED POLYAETHYLENE-2,6NAPHTHALATE FILMS - Google Patents

Description

With regard to the progress of the information on recording methods and the reduction in size of recording equipment in recent years an increased tendency that the base sheets for the magnetic recording tapes are made thinner and therefore there is a need for films with a high Yourig module in the longitudinal direction. Stretched Polyethylene terephthalate foils and polyethylene-2,6-naphthalate foils are available as commercial foils for fulfillment known for this task «Many of these gang

509831/0758

have conventional stretched polyethylene terephthalate films however, a remarkably decreased Young's modulus in the transverse direction due to the increased Young's modulus in in the longitudinal direction and none of these has a sufficiently high Young's modulus and at the same time a sufficient one reduced thickness unevenness. on the other hand outperform commercially available polyethylene-2,6-naphthalate foils In general, the stretched Polyäthylenterephtha la tf olien with regard to Young's modulus and unevenness of strength. However, those with a very high Young's modulus in the longitudinal direction show the failure easy distortion in the transverse direction, in other words, a low tear strength in the longitudinal direction, or a large unevenness in thickness in the transverse direction.

It is therefore an object of the invention to provide a new biaxially oriented polyethylene-2,6-naphthalate film with a very high Young's modulus in the longitudinal direction, equal to or greater than the value in the transverse direction is, although the P-olie has a high tear strength in in the longitudinal direction and reduced unevenness in thickness in the transverse direction.

Another object of the invention is a biaxially oriented polyethylene-2,6-naphthalate film, which has a high Young's modulus in the longitudinal direction, a high tear strength in the longitudinal direction and a reduced Has unevenness in thickness and others for a base film of a magnetic recording tape required physical properties, such as high impact resistance and high voltage stress owns in the longitudinal direction.

It has been found that biaxially oriented polyethylene-2,6-naphthalate films, which fulfill these tasks, can be produced if one of a polymer which

509831/0758

consists essentially of Äthylen ^ jö-naphthalate structural units and has an inherent viscosity, measured in o-chlorophenol as solvent of 36 ⁰ C, of at least 0.35, in a stretching ratio of 2.5 to 5.0 in the longitudinal direction at a temperature im Range of 10 ⁰ C higher than the temperature transition point of the second order of the polymer is ^{stretched up to 17O 0} C, whereupon the film in a stretching ratio of 2.5 to 4.5 in the transverse direction at a temperature in the range of a temperature of 3 ⁰ C higher than the temperature transition point of the second order of the polymer is ^{stretched up to 160 0} C and further the film is stretched in the longitudinal direction at a temperature of 50 to 200 ⁰ C with a stretching ratio of 1.1 to 2.0 and then the film is heat set at a temperature of 160 to 25O ⁰ C.

With "polymer that consists practically of ethylene-2,6-naphthalate structural units consists ", is a Pclyäthylen-2,6-naphthalat or a modified polyethylene-2,6-naphthalate, which consists of at least 90 mol%, preferably at least 95 mol-76, ethylene-2,6-naphthalate structural units and at least 10 mol- #, preferably at least 5 mol- #, of structural units at least one further comonomers is built up.

The polyethylene-2,6-naphthalate is made by polymerization of naphthalene-2,6-dicarboxylic acid or functional Derivatives thereof and ethylene glycol or functional derivatives thereof in the presence of a catalyst manufactured. The modified polyethylene-2,6-naphthalate can, for example, by melting a mixture of Polyethylene-2,6-naphthalate and polyethylene terephthalate to initiate an ester exchange reaction or by Addition of at least one comonomer as a modifier to the polymerization system before the end of the polymerization

509831/0758

of ethylene-2,6-naphthalates are produced. Suitable, Widely useful monomers for such modifiers are compounds having two ester-forming functional groups Typical group examples include dicarboxylic acids such as oxalic acid, adipic acid, phthalic acid, isophthalic acid, Terephthalic acid, liaphthalene-2,7-dicarboxylic acid and diphenyl ether dicarboxylic acid, lower alkyl esters of these Dicarboxylic acids, hydroxycarboxylic acids, such as p-hydroxybenzoic acid, p-Hydroxyethoxybenzoic acid, lower alkyl esters of these hydroxycarboxylic acids and dihydric alcohols such as Propylene glycol, trimethylene glycol or diethylene glycol.

The polyethylene-2,6-naphthalate or the modified ones Polyethylene-2,6-naphthalate can also consist of materials whose terminal hydroxyl and / or Carboxyl groups with a monofunctional compound such as benzoic acid, benzyloxybenzoic acid, benzyloxybenzoic acid or methoxypolyalkylene glycols are substituted or from such compounds that continue with a very small amount, this amount leading to the formation of practically linear copolymers, a trifunctional Compound such as glycerol or pentaerythritol are modified. Of course, the polyethylene-2,6-naphthalate or modified polyethylene-2,6-naphthalate as well Gloss breaking agents such as titanium dioxide, stabilizers such as phosphoric acid, phosphorous acid, esters of the same Contains acids or hindered phenols or lubricants such as finely divided silica or bauxite.

The ethylene-naphthalate, 2,6-or the modified ethylene-2,6-naphthalate should have an inherent viscosity, determined with an o-chlorophenol solution of 35 ^r 'C, hold of at least 0.35. Polymers with an inherent viscosity of 0.45 to 0.80 are particularly preferred because the films obtained therefrom have superior physical properties and permit a good extrusion operation.

509831/0758

Polymers with an inherent viscosity of less than 0.35 cannot be used in accordance with the invention because they do not produce useful films because of their too low degree of polymerization.

The starting unstretched film used in the present invention can be obtained by processing the above polymers in accordance with customary processes, for example by a melt extrusion process, getting produced.

In the method according to the invention, this unstretched PiIm is successively passed through the following stages subject to:

(1) Stretching stage in the longitudinal direction:

The unstretched PiIm is stretched in the longitudinal direction in a stretching ratio of 2.5 to 5.0 at a temperature in the range of a ^{temperature which is 10 °} C. higher than the transition temperature of the second order of the polymer forming the film up to 170 ^° C. Preferably, the unstretched film is stretched in the Längsrichtung.in a draw ratio of 3.0 to 4.5 at a temperature of 125-150 ⁰ C.

(2) Stretching stage in the transverse direction:

The film stretched in the longitudinal direction of step (1) is then stretched in the transverse direction at a stretching ratio of 2.5 to 4.5, preferably 3.0 to 4.0, at a temperature in the range from a temperature higher ^{by 3 ° C. than} the transition temperature of the door of the second order, the film-forming polymers of up to 160 ⁰ C stretched. In view of the flatness of the film obtained as the end product, it is favorable that the stretching ratio in this transverse stretching should not exceed that value in the longitudinal direction in step (1). The most favorable stretching ratio in the transverse stretching is 50 to 90 io of the stretching ratio in the longitudinal direction in step (1).

509831/0758

- * "'■ 2A2A466

Alterna can tiwerfahren than the transverse stretching and at a temperature in the range of 4O ⁰ C, ie a lower temperature to a temperature of 3 ⁰ C higher than the polymer are carried out the transition point of the second order. In this method, the draw ratio is set in a range from 2.5 to 4.5. It goes without saying that a suitable stretch ratio which does not cause breakage of the film must be selected within this range.

(3) Heat treatment stage:

The film was subjected to the steps 1 and 2 in this manner is then heat-treated at a temperature of 170 to 25O ⁰ C. This heat treatment step is not essential according to the invention. This stage is preferred, however, since the heat treatment of the film helps to reduce the occurrence of kinks when the film is re-stretched in the longitudinal direction in stage (4) to be described below.

(4) Longitudinal re-stretching stage:

The film which has been subjected to stages 1 and 2 or stages 1, 2 and 3 is then in the longitudinal direction in a stretching ratio of 1.1 to 2 * .0, preferably 1.2 to 1.6 at a temperature of 50 to 200 ⁰ C stretched. In order to achieve the objects of the invention, it is most favorable if the stretching ratio at this re-stretching stage is such that the product thereof, multiplied by the stretching ratio of the longitudinal stretching in stage (1), is at least 4 »0, in particular at least 4.5 amounts to.

(5) Heat setting stage:

The film, which was subjected to Step 4, is then at a temperature of 160 to 25O ⁰ C, preferably a temperature of 170 to 24O ^C C wärmeverfeatigt.

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The biaxially oriented polyethylene-2,6-naphthalate film produced in the series of the above step has a Young's modulus in the longitudinal direction, determined at a peeling speed of $ 100 / min., Of at least 100,000 kg / cm ² and at least 120,000 kg / cm ² if the manufacturing conditions are appropriately chosen. It should be pointed out that the hitherto known highest Young's modulus values known for conventional polyethylene-2,6-naphthalate films, determined at a take-off speed of $ 100 / min., Are 93,000 kg / cm ² .

The film according to the invention thus has a Young's modulus in the longitudinal direction equal to or higher than that usual value and at the same time has a high tear strength in the longitudinal direction. According to the invention The determinations carried out indicate the Young's modulus in the longitudinal direction and the tear strength in the longitudinal direction in a relationship represented by the following equation:

(A - 15600) (B + 0.165) = 43600

where A is Young's modulus (kg / cm ·) in the longitudinal direction and B indicate the tensile strength (kg / mm) in the longitudinal direction,

if the film is 25 microns thick. With regard to to the fact that a high Young's modulus in the longitudinal direction of polyethylene-2,6-naphthalate films according to the usual processes can be granted, but no higher tear strength in the longitudinal direction at the same time can be achieved, it is surprising that according to the present invention films with a Young's modulus in the longitudinal direction and a tensile strength in the longitudinal direction given in the equation given by the above Relate, can be preserved.

509831/0758

The films according to the invention have a very reduced non-uniformity of thickness in the transverse direction, which is shown by the fact that they have an R value of at most 0.050 at any desired point own in the transverse direction. The value R is obtained by taking a sample with a length of at least 10 cm in the transverse direction and any desired length in the longitudinal direction from any location on the film is cut, marking lines in the longitudinal direction of the sample are formed at a distance of 2.5 cm, the thickness of the sample continuously in the transverse direction determines the average thickness and the difference between the maximum thickness and the minimum Thickness in each area defined by two adjacent display lines can be determined and the average value dividing these differences by the average strength.

The accompanying drawings are graphical representations of the variations in thickness in the transverse direction of the slides, where

1 shows that obtained in Example 3 below

Film shows
2 shows that obtained in Example 4 below

Film shows, and
3 shows the comparison example 2 below

shows obtained film.

In each of these figures, the axis of the abscissa corresponds to the actual length of the film in the transverse direction. A comparison of FIGS. 1 to 3 clearly shows that the films according to the invention reduced a very great deal Have unevenness of thickness in the transverse direction compared to the usual films.

509831/0758

The films of the invention are further characterized by impact resistance up to at least 200 kg-cm / ram and an F-5 value in the longitudinal direction of at least 2300 kg / cm and a satisfactory breaking strength and elongation at break are excellent. The F-5 value in the Longitudinal direction denotes the tension when the film is stretched by 5 $ in the longitudinal direction.

As the biaxially oriented polyethylene-2,6-naphthalate foils according to the invention possess the superior properties set forth above, they will advantageously for applications such as magnetic recording tapes, metallized foils, adhesive tapes, strip tapes, Ropes and the like are used. They are particularly well used as materials for audio tapes, video tapes or computer tapes.

The properties of the films for the above and following were determined by the following methods measured:

Toung modulus, F-5 value, breaking strength and elongation at break

The determinations were made on film samples of 15 cm in length and 1 cm in width using a determination instrument made by Shimazu Seisakusho Co., Ltd. The determination conditions were: clamping distance 10 cm, pulling speed $ 100 / min., Room temperature and 65 % relative humidity.

Tear resistance

The determination was carried out for a sheet according to the method according to ASTM D689-62 using a determination instrument (Elmendorf.) From Toyo Seiki Mfg. .. Co ·, Ltd. at room temperature and a relative humidity of 65 9 &. .......: _; .

5 0 9 8 317 0 7 5 8

- ¹⁰ - 2A24466

The measured tear strength per unit thickness is influenced by the strength of the polie. In the pail from polies with different strengths, but which were produced under the same conditions, there is a proportional relationship between the tensile strength per unit thickness and the thickness. from the tensile strength values given in the following examples and comparative examples are those of Films with a thickness of 25 microns actually measured values. Those of films with other thickness values were derived from the value of a film with one thickness of 25 microns using this proportional relationship.

Impact resistance

The determination was made according to ASTM D781-59T using a Toyo Tester Industry measuring instrument Go., Ltd.

R value

The thickness of the sample sheets was continuously measured on a recording paper using an automatic Recording Electron Micrometer (K-313A) of Anritsu Denki Co., Ltd. and the R value based on this record by the above specified procedure calculated.

The following examples and comparative examples explain the invention in detail without affecting the invention is limited to this.

Examples 1 to 5 and Comparative Examples 1 and 2

An unstretched film by melt-extruding polyethylene-2,6-naphthalate having an intrinsic viscosity of 0.62 at a temperature of 295 ⁰ C manufacturing

50 9 831/0758

posed. The obtained unstretched film was then successively stretched in the Longitudinal direction, stretching in the transverse direction, heat treatment, re-stretching in the longitudinal direction and Subjected to heat setting under the conditions given in Table I. The characteristics of each of the The films obtained in this way are shown in Table II.

509831/0758

Table I.

cn σ co co co

-J cn co

example
and Ver
equal
example
No. ■ elongation Relationship
nis
(X) Transverse stretching Relationship
nis
(X) Heat treatment Time
(Sec.) Re-stretching in
the longitudinal direction Relationship
nis
(X) Heat supply
consolidation Time
(Sec.) Example 1
Example 2
Example 3
Example 4
Example 5
Cf. 1
Cf. 2 Temp.
( ⁰ C) 3.1
3.5
4.0
4.0
4.5
5.0
5.7 Temp.
( ⁰ C) 3.5
3.8
3.1
3.1
2.8
2.9
• 1.4 Temp.
( ⁰ C) 15th
15th
15th
15th
15th
15th
15th Temp.
( ⁰ C) 1.6
1.5
1.25
1.4
1.3 Temp.
( ⁰ C) 15th
15th
15th
15th
15th
15th
15th 134
137
138
133
145
143
141 122
128
125
127
90
132
118 205
230
200
200
190
200
225 160
125
95
137
130 200
. 230
235
190
215

Table II

err ex co CO. ' co

-J CT?

Ex.
u.Ver-
same me> -
ex.
: ■■ Kr :. Young
Module r,
(£ 1o4k / em-) TD F-5-
Value
in MD
(10 ³ kg / cm ² ) Break-proof
keit r, '
(lO ^ kg / cnr) TD fracture
strain
W ' TD Tear
firm
speed in
Maschi
nenrich
tion
(kg / mm) Blow
firm
speed
(kg «cm / mm) R value
in
Cross
rich
tion Length d.
Sample in
Querrich
tion to
Calc
tion of the
R value by
cut
licher
strength
(Micron) Be is.p .. 1
Be is p. 2
Be. is p. 3
Be isp. 4th
Example 5
Cf. 1
VIergl. 2 'MD 4.3
5.3
4.7
4.3
4.7
4.8
3.1 3.3
2.7
3.2
3.6
3.7
1, 8
3.2 MD 2.3
3.0
2.4
2.0
1.8
2.0
0.7 MD 133
1 30.
165
126
123
97
9 0.47
0.53
0.37
0.32
0.28
0.15
0.07 318
295
258
264
283
63
247 0.032
0.017
0.021
0.022
0.028
0.071
0.131 15th
22.5 ^v
15th
15th
12.5
15th
22.5 26th
25th
25th
27
24
25th
40 13.7
14.0.
12.8
14.8
15.6
9.4
13.8 ' 4.5
4.8
4.1
4.5
5.8
4.7
6.3 19th
22nd
29
25th
23
23
16

MD ■ = machine direction; (Longitudinal direction); TD = cross direction

■ ^u "242U66

It can be seen from the values in Table II that, according to the invention, films with a high Young's modulus in the longitudinal direction, high tensile strength in the longitudinal direction, reduced unevenness of the strength in the transverse direction, high impact strength and high tensile strength at break in the longitudinal direction can be obtained. That the Films according to the invention have reduced thickness unevenness in the transverse direction likewise visually by comparing FIGS. 1 (example 3) and 2 (example 4) with FIG. 3 (comparative example 2) determine.

Example 6

An unstretched film was prepared by melt extrusion of a copolymer having an inherent viscosity of 0.59, which mole 56 ethylene naphthalateinneiten 2,6-97 and 3 Mo1- $ isophthalate units was established at a temperature of 293 ⁰ C. The obtained unstretched film was subjected to the various treatments under the same conditions as in Example 3. The physical properties of the film obtained are shown in Table III.

Example 7

An unstretched film was produced by melt-extruding a copolymer with an inherent viscosity of 0.59, which consisted of 97 mol- # Ethylene-2,6-naphthalate units and 3 Kol-fo ethylene-2,7-naphthalate units, at a temperature of 293 ^° C manufactured. The obtained unstretched film was subjected to the respective treatments under the same conditions as in Example 4.

The physical properties of the film obtained are shown in Table III.

50 9831/0758

Example 8

An unstretched film was composed by melt extruding a mixture containing polyethylene-2,6-naphthalate of 96.7 wt .- ^ having an inherent viscosity of 0.64 and polyethylene terephthalate having an intrinsic viscosity of 0.75 ·, hei a temperature of 295 ⁰ C manufactured. The obtained unstretched film was subjected to the various treatments under the same conditions as in Example 3.

The physical properties of the obtained Films are listed in Table III.

509 8 31/07 58

Table III

cn O co OO co

-J cn OO

at
game
No. Young
Module «
(104kg / cnT ) TD F-5-
worth
MD ₀
(103kg / cnT) Break-proof
ability ₂ TD fracture
strain TD Tear
firm
speed in
MD
(kg / mm) Blow
firm
speed
(kg cm / mm) R value
in TD Along
rich
tion d.
sample
in TD
to Be
invoice
of the R-
Worth By
cut
strength
(Micron) 6th
7th
8th MD 5.1
5.3
5.3 3.4
3.4
3.5 MD 2.5
3.1
2.5 MD 161
141
137 0.47
0.56
0.39 280
281
275 0.031
0.029
0.035 15th
15th
15th 12th
12th
12th 13.0
13.8
14.3 4.6
4.9
4.7 35
26th
28

MD = machine direction (longitudinal direction)
TD = cross direction

-F-CD CJ)

Claims (16)

Patentan's claims Mj Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm and an R value at any Place the transverse direction of at least 0.050, the R-value being obtained by cutting a sample with a Length of at least 10 cm in the transverse direction and any length in the longitudinal direction of any desired location of the film, formation of indicator lines in the longitudinal direction of the sample at a distance of 2.5 cm, determination of the thickness of the sample continuously in the transverse direction, determination of the average thickness and the difference between the maximum thickness and the minimum thickness in each by two adjacent ones Indicator lines limited the range and dividing the average value of these differences by the average Thickness was obtained. 2. Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm, if the thickness of the film is 25 microns, the Young's modulus in the longitudinal direction and the tensile strength in the longitudinal direction have the relationship given by the following equation own: . (A - 15600) (B + 0.165) = 43,600 where A is Young's modulus (kg / cm) in the longitudinal direction and B indicate the tensile strength (kg / mm) in the longitudinal direction. 3. Biaxially oriented polyethylene-2,6-naphthalate film with a Young module · in the longitudinal direction and O- at least 100,000 kg / cm and an impact strength of at least 200 kg-cm / mm. 509831/07 58 4. Biaxially oriented polyethylene ^^ naphthalate foil with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm and an R-value at any desired location in the transverse direction of at most 0.050, the R-value being obtained by cutting a sample having a length of at least 10 cm in the transverse direction and any length in the longitudinal direction from any desired location of the film, formation of indicator lines in the longitudinal direction of the sample at a distance of 2.5 cm, determination of the thickness of the sample continuously in the transverse direction, determination of the average thickness and the difference between the maximum thickness and the minimum thickness in each by two Adjacent indicator lines limited area and division of the average value of these differences by the average thickness was obtained, the film forming polymer from at least 90 MoI- ^ Ethylen-2,6-naphthalate structural units and at most 10 Mol- $ of units of at least one further comonomer , the polymer having an inherent viscosity, determined in o-chloropheno Oil solution of 35 ⁰ C, of at least 0.35 possesses. 5. Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm, the thickness of the film Is 25 microns, the Young's modulus in the longitudinal direction and the tear strength in the longitudinal direction, which is by have the following equation (A - 15600) (B + 0, -165) = 43 600 ρ
where A is Young's modulus (kg / cm) in the longitudinal direction and B is the tensile strength (kg / mm) in the longitudinal direction indicate, wherein the polymer forming the film of at least 90 mol% ethylene-2,6-naphthalate structural units and at most 10 mole units of at least one more 509831/07 58 Gomonomeren is constructed, the polymer a
Intrinsic viscosity, determined in o-chlorophenol solution, of 35 ⁰ C, has at least 0.35.
6. Biaxially oriented polyethylene-2,6-naphthalate foil with a Young's modulus in the longitudinal direction of ο
at least 100,000 kg / cm and an impact resistance of at least 200 kg · cm / mm, the polymer forming the polie being built up from at least 90 mol% ethylene-2,6-naphthalate structural units and at most 10 mol% of units of at least one further comonomer, the polymer having an inherent viscosity in o-chlorophenol solution of 35 ⁰ C, of at least 0.35. 7. Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction of at least 10 000 kg / cm and an R-value at any desired point in the transverse direction of at most 0.050, the R- ¥ ert by cutting a sample with a length of at least 10 cm in the transverse direction and any length in the longitudinal direction from any desired point of the eolia, formation of indicator lines in the longitudinal direction of the sample at a distance of 2.5 cm, determination of the thickness of the sample continuously in the transverse direction, determining the average thickness and the difference between the maximum thickness and the minimum thickness in each area bounded by two adjacent indicator lines and dividing the average value of these differences by the average thickness, the polymer forming the film being at least 95 mol- $ Ethylene-2,6-naphthalate structural units and at most 5 mol- $ structural units at least e is constructed ines other comonomers, wherein the polymer has an inherent viscosity, determined in o-chlorophenol solution at 35 ⁰ C, of 0.45 to 0.80 has. 509831/0758 8- Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction 'von at least 100,000 kg / cm, if the thickness of the The film is 25 microns, the Young's modulus in the longitudinal direction and the tear strength in the longitudinal direction have the relationship given by the following equation (A - 15600) (B + 0.165) = 43,600 where A is Young's modulus (kg / cm) in the longitudinal direction and B is the tensile strength (kg / mm) in the longitudinal direction indicate, wherein the polymers of the Polie forming-2,6-naphthalatstruktureinheiten ethylene of at least 95 llol-fo and at most 5 Fiol-% of structural units of a further comonomer is at least constructed, wherein the polymer has an inherent viscosity, determined in o-chlorophenol solution of 35 ⁰ C, of 0.45 to 0.80. 9. Biaxially oriented polyethylene-2,6-naphthalate film with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm and an impact strength of at least 200 kg «cm / mm, the polymer forming the film of at least 95 MoI- ^ ethylene-2,6-naphthalatstruktureinheiten and? S structural units of a further comonomer is constructed at least at most 5 mol, wherein the polymers have an intrinsic viscosity, determined in o-chlorophenol phenollös ung yon 35 ⁰ C, of 0.45 to 0.80 has. 10. Biaxially oriented polyethylene ^ -2,6-naphthalate- foil with a Young's modulus in the longitudinal direction of at least 100,000 kg / cm and an R-value at any desired Place in the transverse direction of at most 0.050, the R-value being obtained by cutting a sample with a length of at least 10 cm in the transverse direction and any length in the longitudinal direction from .any-. 509831/0758 a desired location on the film, formation of indicator liaises in the longitudinal direction of the sample at a distance of 2.5 cm, determining the thickness of the sample continuously in the transverse direction, determining the average thickness and the difference between the maximum Thickness and the minimum thickness in each area bounded by two adjacent indicator lines and dividing the Average value of these differences by the average Thickness was obtained where, if the thickness of the film is 25 microns, the Young's modulus in the longitudinal direction and the tensile strength in the longitudinal direction are given by the following equation Have relationship (A - 15600) (B + 0.165) = 43600 where A is Young's modulus (kg / cm) in the longitudinal direction and B is the tensile strength (kg / mm) in the longitudinal direction indicate, wherein the film furthermore has an impact strength of at least 200 kg «-cm / mm and a tension at 5 % stress (F5 value) in the longitudinal direction of at least 2300 kg / cm, the polymer forming the film being made up of at least 90 mol% ethylene-2,6-naphthalate structural units and at most 10 mol% units of at least one further comonomer, the polymer having an inherent viscosity determined in o-chlorophenol solution at 35 ⁰ Cj of at least 0.35. 11. Biaxially oriented polyethylene ^^ naphthalate film with a Young's modulus in the longitudinal direction of at least 120,000 kg / cm and an R value at any desired Place in the transverse direction of 0.050 or less, the R-value being obtained by cutting a sample with a Length of at least 10 cm in the transverse direction and any length in the longitudinal direction of any desired location of the film, formation of indicator lines in the longitudinal direction of the sample at a distance 509831/0758 of 2.5 cm, determination of the thickness of the sample continuously in the transverse direction, determining the average thickness and the difference between the maximum thickness and the minimum thickness in each by two adjacent ones Indicator lines limited area and division of the Average value of these differences was obtained by the average thickness, if the thickness of the film is 25 microns, the Young's modulus in the longitudinal direction and the tear strength in the longitudinal direction is have the relationship represented by the following equation, (A - 15600) (B + 0.165) = 4-3600 where A is Young's modulus (kg / cm) in the longitudinal direction and B is the tensile strength (kg / mm) in the longitudinal direction indicate, wherein the film furthermore has an impact strength of at least 200 kg »cm / mm and a tension at 5% stress (F5 value) in the longitudinal direction of at least 2300 kg / cm, the polymer forming the film being composed of at least 95 mol- ^ ethylene -2,6-naphthalatetruktureinheiten and at most 5 mol $ structural units of a further comonomer is constructed at least, wherein said polymer has an inherent viscosity, determined in o-chlorophenol solution of 35 ⁰ C, has 0.45 to 0.80. 12. A magnetic recording tape containing a film according to claim 1. 13. A magnetic recording tape containing a film according to claim 2. 14. Magnetic recording tape containing a film according to Claims 1 to 11. . 15. Process for producing a biaxially oriented Foil made of polyethylene-2,6-naphthalate, thus marked 509831/0758 242U66 draws that (1) an unstretched film which was * made of a essentially of ethylene-2,6-naphthalatstruktureinheiten existing polymers having an intrinsic viscosity, determined in o-chlorophenol solution at 35 ⁰ C of at least 0.35, in the longitudinal direction in a draw ratio is stretched from 2.5 to 5.0 at a temperature in the range of 10 ⁰ C higher than the temperature transition point of the second order of the polymer up to 17O ⁰ C, (2) the polymer is stretched up to 16O ⁰ C, the film in the transverse direction at a stretch ratio of 2.5 to 4.5 at a temperature in the range of 3 ⁰ C higher than the temperature transition point of the second order, (3) the film is stretched in the longitudinal direction in a stretching ratio of 1.1 to 2.0 at a temperature of 50 to 20O ⁰ C and (4) Then, the film is heat set at a temperature of 160 to 25O ⁰ C. 16. Process for producing a biaxially oriented Foil made of polyethylene-2,6-naphthalate, characterized in that (1) an unstretched film, which was produced from a polymer consisting essentially of ethylene-2,6-naphthalate structural units and having an intrinsic viscosity, determined in o-Cblorphenolösung at 35 ⁰ C ₁ of at least 0.35, in the longitudinal direction at a Temperature is stretched from 125 to 15O ⁰ C, (2) then the film is stretched in the transverse direction at a stretching ratio of 3.0 to 4.0 at a temperature in the range of a temperature 3 ^° C. higher than the temperature transition point of the second order of the polymer, the stretching ratio being the value of the stretching ratio does not exceed in the longitudinal direction of the step (1), 509831/0758 (3) the polie is heat-treated at a temperature of 170 to 25O ^{0 C,} (4) the pile is further stretched in the longitudinal direction at a stretching ratio of 1.2 to 1.6 at a temperature of 50 to 20O ⁰ C, the product of this stretching ratio multiplied by the stretching ratio in the longitudinal direction during the stretching of the step ( 1) is at least 4.0 and (5) then the Polie is heat set at a temperature of 170 to 24O ⁰ C. 17 · Process for producing a biaxially oriented Polie made of polyethylene-2,6-naphthalate, characterized that (1) an unstretched Piim, which comprises a substantially from ethylene-2,6-naphthalatetruktureinheiten existing polymers having an intrinsic viscosity, determined in o-chlorophenol solution at 35 ⁰ C, was prepared from at least 0.35, in the longitudinal direction in a draw ratio is stretched 3.0 to 4.5 at a of temperature of 125 to 15O ⁰ C, (2) the Polie of the polymer is in the transverse direction at a stretch ratio of 2.5 to 4.5 up to a temperature 3 ⁰ C higher at a temperature in the range of 4O ⁰ C than the transition temperature door of the second order stretched, wherein the draw ratio selected so is that no breakage of the polie is caused, (3) the polie is heat-treated at a temperature of 170 to 25O ^{0 C,} • (4) the polie is further stretched in the longitudinal direction at a stretching ratio of 1.2 to 1.6 at a temperature of 50 to 200 ^° C., the product of this stretching ratio being multiplied by the stretching ratio in the longitudinal stretching Level (1) is at least 4.0 and 509831/0758 (5) then the Polie is heat set at a temperature of 170 to 24O ⁰ C. 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