KR19990000209A - Manufacturing method of base film for magnetic recording medium - Google Patents

Abstract

The present invention relates to a method for producing a base film for a magnetic recording medium. On both sides of the first polyester film containing carbon black and containing light-blocking properties, a second polyester film containing inert particles having an average particle size of 0.001 to 1 µm and an inert particle having an average particle diameter of 0.01 to 3 µm are contained. In the manufacturing method of the film in which the said 3rd polyester film is laminated | stacked, the said 1st polyester film grind | pulverizes a polyester resin chip, and then knead | mixes with carbon black and contains a master polyester resin containing a high concentration of carbon black When using the manufacturing method, and the method of manufacturing through the step of mixing the master polyester resin with the polyester resin, as well as excellent light shielding as a whole can be made thin film excellent in activity. Thus, the film produced according to the present invention is suitable for use as a base film for magnetic recording media.

Description

Manufacturing method of base film for magnetic recording medium

The present invention relates to a method of manufacturing a base film for a magnetic recording medium, and more particularly, to provide a thin film suitable for use as a base film for a magnetic recording medium because of its excellent light blocking property and excellent activity. It is about how.

Saturated linear polyester films represented by polyethylene terephthalate have excellent mechanical properties, heat resistance, weather resistance, electrical insulation, chemical resistance, and the like, and are widely used in packaging, photographic films, insulating materials, magnetic recording media, and the like.

In particular, with the increase in the popularity of video tape recorders (VTRs), the demand for video base films is greatly increased. With the progress of science and technology, information and communication media are becoming smaller, and recording density is required for magnetic recording media. In accordance with this trend, the demand for polyester films suitable for use as the base film of magnetic recording media is constantly increasing.

Currently, when employing a VHS system in video, a method of detecting the start and end of a cassette tape by the light transmittance of the tape is used. At the beginning and the end of the tape, a leader tape without a magnetic layer is connected so that light passes through when the leader tape passes through the sensor. In the VHS system, the video tape is automatically stopped in response to the signal output by the light-sensitive sensor.

Therefore, the video tape must be kept at a light transmittance below a certain degree. If the light transmittance is too high, the sensor may mistake the video tape as the leader tape and stop the operation. This malfunction can occur if the tape is defective. For example, when a part of the magnetic layer is peeled off or the thickness of the magnetic layer is thin, more than a certain amount of light passes through the tape, and a malfunction may occur in which the sensor detects the light and stops the video tech in operation.

In order to solve the problem that the sensor detects light, a method of coating the base film with a magnetic material of about 3-5 μm, and mixing a colorant with a magnetic material to block light is proposed. However, according to this method, since the purity of the magnetic material is reduced, and the coating layer must be thick, it is not preferable in terms of cost reduction.

In view of this problem, Patent Publication No. 90-6334 proposes a method of laminating a polyester film containing inert particles on both sides of a polyester film containing carbon black to block light. Here, inert particles or carbon black contained in the film of each layer to be laminated are added in the polyester resin production step. Such a film has an advantage of obtaining excellent light blocking effect while reducing the thickness of the magnetic layer.

Despite these advantages, there is a problem in that the thickness of the film itself is inevitably increased when the method is used. When inorganic particles or carbon black are added during the polymerization reaction, the dispersibility is not good and the film thickness of each layer must be increased. For example, in a film containing carbon black, the film may have a large light transmittance locally because the carbon black is not evenly dispersed. For this reason, in order to lower light transmittance, a film should be thickened. For example, according to the conventional method, the thicknesses of the intermediate layer and the two layers on both sides thereof are 3-5 mu m, 4-7 mu m and 5-8 mu m, respectively, and it is difficult to lower the minimum thickness to 12 mu m or less. Therefore, the film according to the conventional method has a problem that the thickness is large and unsuitable for the film of the video tape for long time driving.

SUMMARY OF THE INVENTION The present invention has been made in an effort to solve the above problems and to provide a method for manufacturing a base film for a magnetic recording medium having a small thickness and excellent light blocking property.

The technical problem of this invention is the 2nd polyester film which contains the carbon black, and the 2nd polyester film which contains inert particle whose average particle diameter is 0.001-1 micrometer on both surfaces of a 1st polyester film which has light blocking property, and 0.01-0.05 in average particle diameter. In the method for producing a base film for a magnetic recording medium, on which a second polyester film containing 3 μm inert particles is laminated, the first polyester film is kneaded with carbon black after grinding the polyester resin chip. Producing a master polyester resin containing a high concentration of carbon black, and mixing the master polyester resin with the polyester resin to produce a base film for a magnetic recording medium. Is provided.

According to the present invention, by uniformly dispersing carbon black in the polyester resin, it is possible to produce a thin film required to have the required light barrier property.

The polyester resin is a polycondensation of an aromatic dicarboxylic acid component and a glycol component, and there is no particular limitation as long as it is usually used for a base film for magnetic recording media. In particular, it is preferable that the repeating unit consists of ethylene terephthalate or ethylene naphthalate.

In the present invention, the base film for the magnetic recording medium includes the carbon black and the second and third polyesters having inactive particles on both sides of the film made of the first polyester resin having light blocking properties and containing the inert particles. The film made of resin is laminated. Here, the size of the inert particles contained in the second polyester film is relatively small compared to the size of the inert particles contained in the third polyester film. This is because the second polyester film is coated with a magnetic material, so the roughness needs to be small, and the third polyester film needs to have a large roughness because a large amount of active activity is required without coating the magnetic material.

There is no particular limitation on the kind of carbon black added to have light blocking properties, and it is preferable to be used as a conventional colorant. For example, there are channel carbon, Fannes carbon, and the like.

Inert particles include inorganic particles or organic particles which are inert to polyester. For example, the inorganic particles include calcium carbonate, dolomite, glass spare, fiberglass, talc, kaolin, mica, silica, barium sulfate, aluminosilicate, alumina, titanium dioxide, and the like, but are not limited thereto. In addition, organic particles insoluble in polyester include a copolymer of a monovinyl compound having one aliphatic unsaturated bond in a molecule and a compound having two or more aliphatic unsaturated bonds in a molecule with a crosslinking agent, a thermosetting phenol resin, a thermosetting epoxy resin, One or two or more kinds of fine powders of thermosetting urea resins, benzoguanamine resins and fluorine-based resins may be used, but are not limited thereto.

Hereinafter, the present invention will be described in detail through a manufacturing process of a base film for magnetic recording media.

The base film for magnetic recording media of the present invention is produced by co-extruding the second and third polyester resins on both sides of the first polyester resin produced as described below.

In the present invention, in order to manufacture the first polyester resin, first, the polyester resin chip is pulverized, and then kneaded with carbon black to prepare a master polyester resin containing a high concentration of carbon black. Then, the master polyester resin is mixed with the polyester resin not containing carbon black to prepare a first polyester resin containing an appropriate content of carbon black. The content of carbon black is preferably 0.01 to 30% with respect to the polyester resin. When the carbon black content is less than 0.01% by weight, the light blocking effect is insignificant, and when the content of the carbon black exceeds 30% by weight, the difference in physical properties between layers is large, and when the external force is applied to the base film, layer separation may occur.

The second and third polyester resins can be prepared by conventional methods except for the size and content of the inert particles. That is, it can be prepared by adding inert particles of the size and content required during the polycondensation process for producing the polyester resin. Alternatively, as in the manufacturing process of the first polyester resin containing carbon black, the polyester resin chip may be ground and then kneaded with the inert particles.

Specifically, the size of the inert particles contained in the second polyester resin is, respectively, 0.001 to 1 ㎛ average particle diameter. If less than 0.001 μm, this activity is poor, and if more than 1 μm, the surface of the film is roughened, and when the magnetic material is applied, dropout may occur. In addition, the content of the inert particles is preferably 0.001 to 0.5% by weight relative to the polyester resin in the second polyester resin. This is because if the content of the particles is less than 0.001% by weight, this activity is very poor, and if the content of the particles is more than 0.5% by weight, the surface of the film is roughened, making it unsuitable for applying the magnetic material.

The average particle diameter of the size of the inert particle contained in 3rd polyester resin is 0.01-3 micrometers, respectively. If the thickness is less than 0.01 µm, it is difficult to have the required activity in the magnetic recording medium. If the thickness is greater than 3 µm, the surface of the film is too roughened, and the surface irregularities are transferred to the magnetic layer while the magnetic tape is wound, causing dropout. Because it can. In addition, the content of the inert particles is preferably 0.01 to 2.0% by weight relative to the polyester resin in the third polyester resin. This is because when the content of the particles is less than 0.01% by weight, it is difficult to have the diactivity required in the magnetic recording medium, and when the content of the particles exceeds 2.0% by weight, the surface of the film is too rough.

In the present invention, when each of the above-mentioned resins are produced, they are first produced in a multilayer sheet by a coextrusion method. For example, each molten resin is extruded through a multi-manifold die or feed block die so that the first polyester resin is in the middle layer and the second and third polyester resins are in both, and then cooled Solidification produces a layered sheet. Then, when longitudinal stretching, lateral stretching, or biaxial stretching, a stretched film is produced. The obtained film is composed of a middle layer serving as a light blocking layer, one outer layer suitable for applying a magnetic substance, and another outer layer having excellent activating properties, and are suitable for use as a base film for magnetic recording media.

In the present invention, the thickness of the first polyester film containing carbon black may be relatively thin compared to the thickness of the film produced according to the conventional method. This is because the carbon black is evenly dispersed, so that light can be evenly shielded over the entire surface even by a thin thickness. That is, in the conventional film, the thickness of the polyester film containing carbon black needs to be 3 micrometers or more, but 0.5 micrometer or more is enough in this invention. When the thickness is less than 0.5 µm, it is difficult to uniformly adjust the thickness, and even a slight thickness variation causes variation in the light blocking effect and the film appears to be stained. Therefore, the minimum thickness needs to be 0.5 µm.

Moreover, the thickness of a 2nd polyester film and a 3rd polyester film also needs to be 1 micrometer or more. This is because when the thickness of the second and third polyester films is less than 1 μm, the surface may be roughened under the influence of the first polyester film layer, which is the middle layer.

As can be seen from the above, if the thickness of the base film for a magnetic recording medium of the present invention is 2.5 탆 without considering the tensile strength, it can have the required light transmittance and activity. Compared to the conventional method, the thickness of the film can be made very thin, and when the magnetic recording medium is manufactured using the film, the tape wound in a case of a certain size can be very long. On the other hand, in order to satisfy the tensile strength of the film required in a magnetic recording medium such as a video tape, the thickness of the film produced according to the present invention needs to be 5 µm or more, preferably 5 to 15 µm.

Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to this.

Evaluation of the physical properties of the film in the present invention was performed by the following method.

1) layer thickness

After cutting the film with a microtop, the cross section was observed under an electron microscope.

2) light transmittance

It was measured using Murakami Color Co., Ltd. Clarity Meta T, M-1D.

3) Average particle diameter

Using a scanning microscope, the size of the particles was magnified by 50,000 times, and then the arithmetic average of the values obtained by measuring the particle size of each part by an image analyzer.

4) active activity

Using the TBT-300D (manufactured by Yokohama Systems Research Institute, Japan), a running tester, the tape slitting the film ½ inch in width was 3.3 (cm / sec), the pulling force was 30 g, and the contact angle with the pin was 135 °. The running friction coefficient was measured using the following equation 1 from the winding tension after passing the fixed guide pin (material SUS303) by 90 m.

[Equation 1]

μK = [2.303 / θ] × log [Ti / To]

Where θ is the contact angle between the film and the guide pin, and Ti and To are the pulling and winding tensions, respectively.

5) wear resistance

After completion of the activity measurement, the degree of the amount of powder deposited on the surface of the fixed guide pin was evaluated by dividing it into four grades as follows.

◎: Almost no powder on guide pin

(Circle): When the powder adheres to 5% or less of guide pin area

(Triangle | delta): When a powder adheres to the area of 10% or less of the guide pin area.

X: When powders are deposited in an area exceeding 10% of the guide pin area

6) Electronic property

A video tape was prepared using a polyester film, and then the size (S / N ratio) of the noise signal to the signal output at a measurement frequency of 4 MHz was measured using a BR6400U VTR deck made by Nippon VIC.

Example 1

1) Polyester manufacture

In the reactor, dimethyl terephthalate, ethyleneglycone and calcium acetate (70 and 0.05% by weight relative to dimethyl terephthalate, respectively) were transesterified. After 4 hours, trimethyl phosphate and antimony trioxide (0.06 and 0.04% by weight relative to dimethyl terephthalate) were added to the reactor and polycondensation was carried out for 5 hours to prepare polyester (polyester a).

2) Preparation of Polyester Containing Inorganic Particles

After the transesterification reaction, polyester (each poly) was added in the same manner as in step 1, except that 5 wt% of calcium carbonate having an average particle diameter of 0.5 µm and calcium carbonate having 0.8 µm were further added to dimethyl terephthalate. Esters b and b ') were prepared.

3) Preparation of polyester containing carbon black

The polyester a prepared in the above step was pulverized into a powder having a size of about 1 mm, and then kneaded in a compounder with carbon black to prepare a master polyester (polyester c) containing 50% by weight of carbon black.

4) film manufacturing

The outer layer resin (A layer) in which polyester a and polyester b were mixed, the middle layer resin (B layer) and poly in which polyester a and polyester c were mixed so that it may become a ratio as shown in Table 1. Another outer layer resin (C layer) in which ester a and polyester b 'were mixed was prepared. An amorphous sheet consisting of three layers was produced through a die provided with a feed block so that the resin for the B layer was located in the outer layer of the B layer in the middle layer. At this time, each resin temperature extruded was 290 ° C. The obtained sheet was stretched 3.5 times at 90 ° C. in the longitudinal direction and 4.3 times at 110 ° C. in the lateral direction, and then heat-treated at 210 ° C. for 3 seconds to prepare a film having a thickness as shown in Table 1 below. The physical properties of the prepared film were measured in the same manner as described above, and the light transmittance, the activity, and the wear resistance were excellent.

Finally, the magnetic tape was prepared by applying a magnetic paint on the A layer of the prepared film, and then the S / N ratio was measured. The electronic characteristics were excellent as 1.3 dB.

Example 2-7

As shown in Table 1, except that the content of the carbon black contained in the B layer, and the type, content and size of the inorganic particles contained in the A and C layers are different within the scope of the present invention, Films and magnetic tapes were prepared in the same manner as in Example 1. The properties of the produced film and magnetic tape were evaluated and shown in Table 1. As shown in Table 1, not only the overall light transmittance, the activity, the wear resistance, etc. of the physical properties of the film were excellent, but also the electronic properties were excellent.

Comparative Example 1-8

The polyester containing carbon black is the same as the conventional method, except that the method for producing polyester containing inorganic particles is used, and the content and content of the inorganic particles contained in the A and C layers. And the size was kept within the scope of the present invention to produce a film and magnetic tape. The properties of the produced film and magnetic tape were evaluated and shown in Table 1, but at least one of physical properties and electronic properties of the film was poor.

Comparative Example 9

As shown in Table 1, the film was prepared in the same manner as shown in Example 1, except that the content of carbon black (40% by weight) in the B layer resin was out of the range of the present invention. The produced film has the advantage that the light transmittance is very low as 1.90%, but there is a problem that the magnetic tape can not be produced by using the drop off of the carbon black layer by layer separation.

TABLE 1

division A floor B floor C floor Properties Layer thickness (㎛) Inorganic particles Layer thickness (㎛) Carbon black Layer thickness (㎛) Inorganic particles Light transmittance (%) Activity Wear resistance Electronic characteristic (dB) Comprehensive Evaluation Kinds Average particle size (㎛) Content (wt%) Content (wt%) Kinds Average particle size (㎛) Content (wt%) Example One 3 Calcium carbonate 0.5 0.3 2 10 3 Calcium carbonate 0.8 0.3 35 0.36 ◎ 1.3 ◎ 2 One Silica 0.7 0.2 0.5 0.01 3 Calcium carbonate 0.8 0.3 80 0.35 ◎ 1.5 ◎ 3 One Kaolin 0.3 0.1 3 0.5 One Silica 0.9 0.2 63 0.34 ◎ 2 ◎ 4 One Kaolin 0.3 0.1 3 30 One Silica 0.9 0.2 2.70 0.32 ◎ 0.5 ○ 5 3 Calcium carbonate 0.5 0.3 5 10 One Calcium carbonate 0.80.03 0.10.3 16 0.34 ◎ 1.4 ◎ 6 3 Silica 0.15 0.1 5 10 One Calcium carbonate 0.8 0.1 17 0.32 ◎ 3 ◎ 7 3 Silica 0.15 0.1 5 10 One Alumina 0.03 0.3 18 0.42 ○ 3 ○ Comparative example One 0.5 Calcium carbonate 0.5 0.3 2 10 3 Calcium carbonate 0.8 0.3 33 0.34 ◎ -0.5 △ 2 3 Silica 2 0.3 2 10 3 Calcium carbonate 0.8 0.3 34 0.32 ◎ -2.1 × 3 3 Calcium carbonate 0.5 0.6 2 10 3 Calcium carbonate 0.8 0.3 33 0.35 ◎ -1.1 × 4 3 Calcium carbonate 0.5 0.3 0.3 10 3 Calcium carbonate 0.8 0.3 85 0.34 ◎ 1.3 × 5 3 Calcium carbonate 0.5 0.3 4.5 10 0.5 Calcium carbonate 0.8 0.3 18 0.34 ◎ -0.6 △ 6 0.5 Calcium carbonate 0.5 0.3 2 10 3 Silica 5 0.1 33 0.32 ◎ -1.1 × 7 3 Calcium carbonate 0.5 0.3 2 10 0.5 Calcium carbonate 0.8 3 31 0.31 ◎ -0.8 × 8 3 Calcium carbonate 0.5 0.3 2 10 3 - - - 33 0.85 × -0.3 × 9 3 Calcium carbonate 0.5 0.3 2 40 3 Calcium carbonate 0.3 0.3 1.90 - - - ×

Using the method according to the invention, it is possible to produce a thin film not only excellent in light blocking property but also excellent in activity. Thus, the film produced according to the present invention is suitable for use as a base film for magnetic recording media.

Claims (6)

On both sides of the first polyester film containing carbon black and containing light-blocking properties, a second polyester film containing inert particles having an average particle size of 0.001 to 1 µm and an inert particle having an average particle diameter of 0.01 to 3 µm are contained. In the manufacturing method of the base film for magnetic recording media in which the said 3rd polyester film is laminated, The first polyester film, Grinding the polyester resin chip, and then kneading with carbon black to prepare a master polyester resin containing a high concentration of carbon black; And And producing the master polyester resin by mixing the master polyester resin with the polyester resin. The method of claim 1, wherein the polyester has at least one main repeating unit selected from the group consisting of ethylene terephthalate and ethylene naphthalate. The method of claim 1, wherein the second and third polyester film, Grinding the polyester resin chip, and then kneading with each of the inert particles to prepare a master polyester resin containing a high concentration of inert particles; And And producing the master polyester resin by mixing the master polyester resin with the polyester resin. The method of manufacturing a base film for a magnetic recording medium according to claim 1, wherein the content of the carbon black is 0.01 to 30% by weight based on the polyester resin contained in the first polyester film. The magnetic recording medium according to claim 1, wherein the content of the inert particles contained in the second polyester film is 0.001 to 0.5% by weight based on the polyester resin contained in the second polyester film. Method for producing a base film. The magnetic recording medium according to claim 1, wherein the content of the inert particles contained in the third polyester film is 0.01 to 2.0 wt% based on the polyester resin contained in the third polyester film. Method for producing a base film.