DE2924159A1 - MAGNETIC RECORDING TAPE - Google Patents

Description

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• PATENT LAWYERS ·

VIERING & JENTSCHURA 2924159

Authorized representative at the European Patent Office Dipl.-Ing. Hans-Martin Viering · Dipl.-Ing. Rolf Jentschura · Steinsdorfstrasse 6 · D-8000 Munich 22

Attorney's file 3 545

Magnetic recording tape

The invention relates to a magnetic recording tape having a substrate made of polyethylene terephthalate (hereinafter also referred to by the abbreviation "PET").

Polyethylene terephthalate is commonly used as the substrate material in magnetic recording tapes such as audio tapes and video tapes is used on which a magnetic material layer is to be formed. Sound and picture quality characteristics and other physical properties of magnetic recording tapes vary depending not only on the magnetic material layer but also depending on the ■ J substrate.

J According to the invention it has been found that the physical egg \ properties of a magnetic recording tape, which is made of a PET substrate from '\, and in particular the increase in the signal-to-failure figure, which is observed during repeated recording and playback of the tape, strongly influenced by the size of the PET crystals and the surface roughness of the PET substrate can be influenced.

The invention makes a magnetic recording tape such designed that there is a reduced increase in the number of signal dropouts during repeated playing and playing of the Has band.

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StelnsdortstrafJe 6 Telex: S 212 306 jepa d Postscheck Munich 3067 26-601 D-8000 Munich 22 Telegram: Stelnpat Munich Bayerische Vereinsbank Munich S67 895 Telephone: (0 89) »34 13 Fax: (0 89) 222 066 RalftoHenbank Munich 032 16 18

(0 89) 29 34 14 (Siemens CCITT Norm Group 2) Deutsche Bank Munich 2 711 687

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According to the invention, a magnetic recording tape having an I.

Polyethylene terephthalate substrate and a magnetic ι

Material-containing layer which closely adheres to the substrate;

is bound, in particular characterized in that the poly ν

Ethylene terephthalate substrate of formula (1) is sufficient: -

(5.0A-586.7) A-1.04H ₁ - (0.027H ₂ -7.46) H ₂ + 16971.8 <20.0. (1) ;

where A is the mean particle size of the polyethylene terephthalate

lat crystals according to the definition given below, H ₁ the mean number of projections in

a unit area of 1 mm ² on the surface of the substrate \

are present and have a height ranging from 0.27 to ι,

0.53 microns, and H ^ is the mean number of protrusions ϊ as for H ₁ , but with a height in the range of
0.54 to 0.80 microns rather than 0.27 to 0.53 microns.

Fig. 1 is a coordinate diagram showing the relationship
between the increase in the signal failure number (ordinate), the
is observed during the repeated playing and playing of the tape, and represents the Y ₄ ~ value (abscissa) obtained from
the formula (2) is calculated:

Y ₄ = (5.0A-586.7) A-1.04H ₁ - (0.027H ₂ -7.46) H ₂ +16971.8 (2)
wherein A, H- and H _{2 have} the meanings given above.

In the preferred embodiment, the PET substrate is
Magnetic recording tape according to the invention characterized by having the crystal particle size A and the surface roughness both of those given above
Formula (1) suffice.

The term "crystal particle size A" as used here
is used, refers to the crystal particle size,
which is calculated from the following equation:
A = (0.9 χ A) /B.cose

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where A is the particle size of the crystal in Angstroms, B the Half width in radians in the definition below, θ the Bragg angle and Λ the value of 2.2896 (Angstrom) mean.

The half width is on the PiOOj plane of a crystal sample determined by using an X-ray diffraction apparatus (Model 4011-B2 from RIGAKU ELECTRIC CO.). At this Determination is a line drawn between two points corresponding to the scatter intensities at 29 = 50 ° and 26 = 20 ° is used as the baseline.

The crystal particle size, A, is usually in the range of approximately 45 to 75 angstroms. The crystal particle size A can be varied by appropriately selecting the conditions under which the PET film is produced. In particular, the crystal particle size varies greatly depending on the temperature at which the biaxially stretched PET film is heat set. The higher the heat-setting temperature, the larger the crystal particle size. In general, the desired crystal particle size can be obtained in that the heat set temperature in the range of 180 to 23O ⁰ C is appropriately set.

The PET substrate has the surface roughness which is determined by the values H ₁ and H ₂ given above and which satisfies the formula (1) given above. The PET substrate having surface protrusions can be made as follows:

(a) Dialky terephthalate and ethylene glycol become mutually exclusive in the presence of calcium acetate as an ester exchange catalyst esterified, after which the interester product is subjected to polycondensation under normal conditions, in order to thereby make particles of the calcium compounds produced by the

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the following formula are shown, i.e. Calcium stearate or a calcium salt of a PET oligomer, during the To precipitate polycondensation:

CaOOC- { \ -C00 - (- CH ₀ CH ₀ OOC

\ ^{2 2}

where η is a number from 0 to 3.

Alternatively, particles of the aforementioned calcium compounds previously prepared can be added to the polycondensation reaction mixture be included.

(b) particles of inorganic substances such as kaolin and calcium carbonate, are included in the polycondensation reaction mixture or in the molten PET in the process stage, at which the film is formed.

The aforementioned methods (a) and (b) can be used alone or in combination. The height and density of the Projections that are present on the substrate surface can be varied by adjusting the amount and particle size the particles to be formed or the particles involved in the aforementioned processes (a) and (b) are suitable to get voted.

The points entered in FIG. 1 correspond to the data for the increase in the number of failures given in the table below. It can be seen from Fig. 1 that the increase in the failure number of the magnetic recording tape is in good agreement with the value Y. given by the formula (2). The correlation coefficient in Fig. Is 0.89. Therefore, the PET substrate with a Y ₄ value of 20 or less exhibits a failure number increase of approximately 20 or less.

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The Y. value can generally be reduced to approximately zero. That is, the Y, value of the PET substrate according to the invention can generally be varied in the range from 0 to 20. However, it is more preferably in the range of 0 to 10.

The magnetic material layer formed on the PET substrate can be of conventional composition. The magnetic material layer can thus be composed of approximately 60 to 80% by weight of a finely divided magnetic material such as magnetic hematite (JS-FeJO-), CrO ₂ , Fe-Co alloy, magnetite (Fe ₃ O ₄ ) and Co-impregnated or CO adsorbed containing tf - Fe ₃ O ₃ , and approximately 20 to 40% by weight of a binder resin. The binder resin contains, for example, a thermoplastic resin such as a vinyl chloride / vinyl acetate copolymer, a styrene / butadiene copolymer, nitrocellulose, cellulose acetate or cellulose butyrate, or a thermosetting resin such as a polyurethane resin, an epoxy resin or a melamine resin. Additives such as a plasticizer, a dispersant, a lubricant and a coloring agent can be included in the magnetic material layer.

The formation of the magnetic material layer on the substrate can be accomplished in a conventional manner, with a Magnetic material, a binder resin and other additives are slurried in a suitable solvent, after which the Substrate is coated with the slurry and the Drying and heat treatment follows.

The invention is further illustrated by the following Example in which the percentages and parts are by weight unless otherwise specified.

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example

100 parts of dimethyl terephthalate and 70 parts of ethylene glycol were heated in the presence of 0.035 part of manganese acetate to cause an ester interchange reaction. The reaction Sprodukt were 0.04 parts of antimony trioxide, 0.15 parts of lithium acetate (dissolved in ethylene glycol), calcium acetate and Calcium carbonate (dispersed in ethylene glycol) added. The amounts of calcium acetate and calcium carbonate were in varies in the ranges from 0 to 0.20 parts and from 0 to 0.06 parts, respectively. The mean particle size of the calcium carbonate was varied in the range of 0.01 to 3 microns. Thereafter, 0.13 part of trimethyl phosphate was added to the mixture. Then the resulting mixture was heated to effect polycondensation. The one made in this way Polyethylene terephthalate had an intrinsic viscosity of 0.620.

The PET was melt extruded in a conventional manner and thereafter the extrudate was stretched first in the longitudinal direction and then in the transverse direction. The stretching ratio was varied in the range of 2 to 5 times the original length in both the longitudinal direction and the transverse direction. Each stretched film was heat set at various temperatures from 180 ° to 230 ⁰ C. The heat set film was about 15 microns thick.

The crystal particle size, the amount of birefringence and the surface roughness of those produced in this way PET films are given in the table below.

Each PET film was corona discharge at 10 watts min / m * surface treated and then with a magnetic

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Coating slurry containing table material in a knife coating process. The layer thickness was 5.5 microns, expressed in terms of the dry layer thickness. The coating slurry was composed of 70 parts of Co adsorbed <p -Fe ₃ O ₃ , parts of a binder resin (15 parts of a urethane rubber, 10.5 parts of nitrocellulose and 4.5 parts of polyvinyl chloride) and 270 parts of methyl ethyl ketone. The coating slurry also contained an isocyanate hardener ("Desmodul L" from Bayer AG) in an amount of 15% of the weight of the binder resin. The coated film was air-dried and then heat treated at a temperature of 6O ⁰ C for 24 hours.

The physical properties of those produced in this way Magnetic recording tapes are shown in the table.

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No. ι particle size
(Angstrom) TAB E L L. E. 153 9 3.8 S / N
(dB) Envelopes
modification (%) - adhesion
(G) Increase in
Signal failure .!.eel • - NJ
CD
IS)
-tr- » 1* 62.7 Birefringence
(Δη) ]
^H l 30, 8th 0 -ο, ι 32.9 30.5 76.0 cn
CD 2 * 71.0 -8.4 306 35, 9 0 1.1 21.3 42.0 766.9 > ι 1.11 3 58.4 -6.7 133 Roughness 156 4th 3.8 1.1 29.5 26.7 19.6 4th 61.3 +20.4 59 , 4 33, 3 0 0.5 34.1 30.6 0 β 5 66.8 -3.9 269 , 3 50, 0 0 0.6 25.0 25.0 0 ». 6 * 64.4 -31.4 152 , 0 66 7th 0 - - 27.5 95.8 .... 7 * 67.2 +2.5 106 , 2 296, 2 1.8 1.1 20.9 27.0 298.0 8th* 69.8 -7.8 185 6th 78 2 0 - - 42.0 75.7 co
O 9 * 64.4 -6.6 157 4th 50, 0 0 - 22.4 33.5 301.5 co
CD 10 * 67.9 +7.5 138 9 51, 3 0 1.4 18.4 22.7 394.5 cn 11 * 67.9 +8.6 73, 7th 59, 0 1.3 - 23.2 33.5 240.9 12 * 60.7 -1.2 80, 5 6 ', 3 7.7 1.7 10.8 22.7 134.4 O
CD 13th 55.8 -45.7 56, 1 67, 9 2.6 1.0 24.6 25.0 5.0 CO 14th 53.5 -9.9 187, 8th 0.5 34.5 17.5 9.9 * Comparison trial -9.4 159 4th 2 0 O

The physical properties of the PET substrates and the Magnetic recording tapes according to the table were made as follows certainly:

Birefringence [A n)

Using a polarizing microscope (model POH from Nippon Kogaku KK), a path difference R (µm) is measured, with white light projected by the light source being sent through a green filter (546.1 μπ \) and a compensator. The birefringence (An ₁ ) is obtained from the path difference R measured in this way according to the equation:

An ₁ = R / d

calculated, where d is the thickness of the film sample in μΐη. The birefringence (An ₁ ) calculated in this way is corrected according to the following equation:

corrected birefringence Λ η = 1,000 Δ n ₁ / (0.009X ³ -0.113X ² + 2.114X + 1Q0.229) where X is the deflection angle, measured in degrees, of the molecular orientation direction from the longitudinal direction.

The corrected birefringence Δη is expressed by a positive number when ny -nß 0, and in a negative number, if η y -nß <O, where ηi "and NSS corrected birefringence are, in the longitudinal direction of the film sample or whose transverse direction has been determined.

Surface roughness

The surface roughness of the film is expressed in terms of the height and density of protrusions formed on the film surface available. Film samples are thinly metallized with aluminum and then the height and density are determined of protrusions measured. The protrusion height is with a

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Surface condition microscope (NIKON model BFM from \

Nippon Kogaku K.K.) using a visible green measured with monochromatic light. The protrusion heights obtained are divided into the following 3 groups:

H ₁ : from 0.27 to 0.53 microns

H ₂ : from 0.54 to 0.80 microns

H ₃ : from 0.81 to 1.07 microns'

The protrusions with heights that fall under the respective groups are ^{counted in randomly selected samples with an area of 1.28 mm 2} , and the protrusions f

are classified into the appropriate group H ₁ , H ₃ or H ₃ . | The ledges with. Heights falling below the corresponding | Groups falling can be counted as follows. The microscope f with 240-fold magnification is adjusted so that a photo- <graphical Shoo "" is obtained, in which χ 6 to 7 Inter-, are ferenz ribbons vorhcinden. The protrusions with heights that | under group I ₁ . are single ring figures with |

Lengths of at least 2 mm measured parallel to the inter | reference tapes. The projections with heights that fall under the groups Η »and H ₃ are double ring figures and triple ring figures, respectively. The number of protrusions in each group is expressed in terms of the number of protrusions existing ^{in the unit area of 1.0 mm 2.}

Signal to Noise Ratio (S / N in dB)

With a commercially available VHS tape recorder, a 50% white value signal is recorded on a tape sample recorded at optimal recording current and then reproduced. When reproduced, the ratio (S / N) of the demodulated video signal becomes that contained therein Noise determined with a video noise meter (model 925C by Shibasoku K.K.). A reference S / N ratio is given in

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similarly determined on a TDK standard tape (manufactured by TDK Electronics Co., Ltd.). The S / N ratio is expressed in terms of the difference between the S / N ratio from the tape sample and the reference S / N ratio.

Envelope curve variation (in%)

With a commercially available VHS video tape recorder, a sine wave signal having a frequency of 4 MHz is recorded on a tape sample at an optimal recording current and then played back. When reproducing, an output signal from the head amplifier is observed using an oscilloscope having a bandwidth of 100 MHz. The envelope curve variation "y" is determined from the peak-to-peak value 'W (mV · PP) and the valley-to-valley value ⁿ ß' (mV · PP) according to the equation: γ (%) = {joi- ß) / oc] χ 100

η λ Ii

Adhesion (in grams)

A double-coated adhesive tape is applied to a backing paper approximately 200 microns thick. One Tape sample in the form of a strip with a width of 12.65 mm is applied to the adhesive tape so that the strip is perpendicular to the adhesive tape and the layer of magnetic material having the strip side is brought into contact with the adhesive tape. The sample prepared in this way is immediately used in Put in an Instron tensile tester and it gets the force determined in grams, which is required to peel off the tape at an angle of 180 °.

Increase in the number of signal dropouts

With a commercially available VHS video tape recorder a three-step staircase signal is recorded on a tape sample at the optimum recording current, and then reproduced. During playback, the number of

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Loss of signal in the output of the video head amplifier counted in 15 minutes with a loss of signal counter (manufactured by NJS). The term "signal dropout" as used here refers to an output reduction of at least 18 dB over a period of at least 20 μ seconds. The number of signal failures is determined at different points on the tape sample. The mean number of dropouts is ^{denoted by 11} V ₁ ". The above recording-reproducing operation is repeated three times at the same points on the tape sample. v. ". The increase in the number of dropouts is the difference between v ₁ and V 1, expressed by the equation:
Increase in the number of signal failures = V ₄ -V ₁

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Claims (2)

PATENT CLAIMS Magnetic recording tape with a substrate made of polyethylene terephthalate and a layer containing a magnetic material which is closely adhered is applied to the substrate, characterized in that the polyethylene terephthalate substrate the following condition is sufficient: (0.5A-586.7) A-1.04H ₁ - (0.027H ₂ -7.46) H ₂ + 16971.8 <20.0 where A is the mean particle size of the polyethylene terephthalate crystals, determined by X-ray diffraction from the half width, H _{1 is} the mean number of protrusions in a unit area of 1 mm ^a on the surface of the substrate with a height of the protrusions in the range of 0.27 to 0.53 microns, and H ~ the mean number of protrusions as for H ₁ , however with a height in the range of 0.54 to 0.80 microns rather than 0.27 to 0.53 microns. 2. Magnetic recording tape according to claim 1, characterized in that that the polyethylene terephthalate substrate satisfies the following condition: (5.0A-586.7) A-1.04H ₁ - (0.027H ₂ -7.46) H ₂ +16971.8 f: 10.0 909851/0890 i / w -2- St «! N« dorfstraB · 6 Τ · Ιβ *: 6 21230β | · ρ · d PottlCheck Munich 3067 28-801 D-MOO Munich 22 Telegram: 81 · 1πρι | Munich Bayorliche Verelnibank Munich M7 BOi Telephone: (0 β «) ίβ M 13 Telekoplerer: (0 M) 222 086 F, al (lel» enbank Munich 0321 »18 (089) »3414 (Slemeni CCtTT Norm Qruppt 2) Deultche Bank Munich 2 711 887