FR2723863A1 - Extrusion coating device for magnetic recording medium manufacture - Google Patents

Abstract

The device includes an extrusion die (1) with an emulsion store (2) which is supplied with emulsion through inlet orifices (6,7). The emulsion is extruded through a slot (4), between 0.01 and 2 mm in width, which is positioned at one end (1a) of the die. The emulsion is applied on a continuously unwinding flexible polyester film base. The emulsion store includes a porous cylindrical strainer (3) with a pore inside diameter between 1 and 200 micrometres. The emulsion is fed to the slot while passing through the porous body.

Description

 This invention relates to an extrusion coating device, also called a matrix coating device.

 In general, a coating type magnetic recording medium, in which a magnetic layer is formed by depositing on a base film, such as a polyester film, a magnetic paint composed of magnetic powders, a binder, a A dispersant or lubricant dispersed and kneaded in an organic solvent is used as an audio tape or video tape.

 As a method of coating the base film of the magnetic paint in such a coating-type magnetic recording medium, a roller coating method using a roll, illustrated by an engraving roll method or a method of reverse roller, is mainly used.

However, these roller coating processes have certain problems. For example, a defect in the transfer of paint from the roll to the base film generates irregularities in the thickness of the deposit by causing output fluctuations and splinters of paint, resulting in a loss of signal. Similarly, when excess paint is returned to the paint mixing process, the quality of the paint is deteriorated. These problems tend to be more complicated, especially during high speed coating.

 A (matrix) extrusion process has recently been noted and partially implemented as a new coating method for solving the above problems. The extrusion process uses a matrix having a wide slot on the distal end thereof adjacent the distal end formed with a scraping edge, so that a paint extruded continuously to the surface of the a scrolling support is applied to the support with a uniform coating thickness thanks to the scraping edge.

 Normally, in this extrusion coating device, the paint is delivered to a supply of paint called the die pocket by means of paint feed ports provided on both side sides of the paint stock, and the paint is extruded from the paint supply to the slot under a predetermined pressure.

 With such a coating device, it is possible to easily form a deposited film with a relatively uniform thickness. Likewise, the coating device is advantageous in reducing the manufacturing costs and the size of the device because it does not use a large roll. Moreover, because all the paint delivered in the die is applied, problems such as the deterioration of the quality of the paint caused by the reuse of a paint delivered in excess can be avoided.

 However, when a high flocculation paint such as a magnetic paint is applied by the extrusion coating device, small lines in the direction of travel of the carrier may appear on the surface of the coated film. These small lines formed on the surface of the magnetic film deposited in the magnetic recording medium cause irregularities in the electromagnetic conversion characteristics.

As a measure to prevent these small lines, a fluidification technique by circulation of the paint in the matrix to limit the lines on the surface of the deposited film has been proposed by
Fuji Film and Konika. However, it is difficult to generate the fluidification by circulating the paint uniformly in the matrix. Therefore, with this technique, although it is effective in preventing lines on the deposited film, the preventive effect itself is not uniform and lines appear partially on the surface of the film. More particularly, when the high flocking paint such as magnetic paint is applied, the lines appear in an obvious manner.

 In view of the above, it is an object of the present invention to provide a coating device which is capable of forming a deposited film of satisfactory surface property having no small lines, even when the paint has high flocculation characteristics.

 According to the present invention, there is provided an extrusion coating device having a matrix having a paint supply in which paint is supplied to extrude the paint through a slot provided on a distal end of the die so as to to apply the paint on a flexible support running continuously. A porous body with a pore diameter of 1 to 200 ssm is provided in the paint supply, and the paint is delivered to the slit through the porous body.

 Similarly, the pore diameter of the porous body is 20 to 100 ssm.

 In addition, the porous body is a porous sintered body.

 In addition, the porous body is a wound filter.

 With the extrusion coating device having a matrix having a supply of paint in which the paint is fed to extrude the paint through a slot provided on a distal end of the die so as to apply the paint to a flexible support continuously scrolling, because a porous body is provided in the paint supply so as to extrude the paint to the slit through the porous body, a shearing force acts on the paint as the paint passes through the porous body . The paint is then extruded to the slot and applied to the support to form a deposited film. Because the shearing force acts on the paint, a deposited film of satisfactory surface property having no small lines can be formed even when the high flocculation paint is used.

 Figure 1 is a sectional view showing an exemplary structure of a coating device according to the present invention.

 Figure 2 is a perspective view showing the coating device according to the present invention.

 Figure 3 is a sectional view showing another example of the coating device according to the present invention.

 A preferred embodiment of the present invention will now be described with reference to the accompanying drawings.

 A coating device of the present embodiment is used to deposit a magnetic paint or a nonmagnetic carrier paint in a process of manufacturing a coated type magnetic recording medium.

With this coating device, a magnetic paint fed into a pocket 2 (paint supply) of a matrix 1 (extruder) and is extruded through a porous body 3 to a slot 4 in order to be applied to a base film 5 which is scrolled by means of a guide roller, as shown in FIG. 1 and 2.

The matrix is a substantially rectangular parallelepipedal metal block having a predetermined width, and has its wedge-shaped oblique cut distal end, as shown in FIG. 2. A distal end surface 1a, made of super alloy, is shaped scraping edge. The die 1 has the slot 4 formed on the distal end surface 1a as a function of the coating width. The slot 4, defined as a space through which the magnetic paint is extruded, is normally narrow with a size of 0.01 to 2
On the rear side of the slot 4, the bag 2 which communicates with the slot 4 is in the form of a cylindrical space with a length equal to the width of the slot 4. At both ends of the bag 2, orifices 6, 7 with a diameter smaller than that of the pocket 2 are designed to open on the two lateral sides 1b, 1c of the matrix 1, and thanks to which the magnetic paint is brought into the pocket 2 The pocket 2 thus serves as a space for receiving the magnetic paint fed under pressure from a paint supply unit, and performs an accumulator function.

 In the present embodiment, the porous cylindrical body 3 is provided in the pocket 2 of the matrix 1 having the above structure, as shown in FIG. 2. The porous body 3 has an outside diameter smaller than the inside diameter of the 2, and an inner diameter greater than the inside diameter of the paint supply ports 6, 7. Similarly, the porous body 3 is in the form of a cylindrical body with a height substantially equal to the width of the slot 4. The porous body 3 is placed in the pocket 2 so that the paint supply orifices 6, 7 are in the internal diameter of the porous body 3.

Thus, the magnetic paint supplied by the paint supply ports 6, 7 enters first inside the porous body 3, and then flows from the outer surface of the porous body 3 into the pocket 2. The magnetic paint is then extruded towards the slot 4.

 When the magnetic paint flows from the outer surface of the porous body 3, a shearing force acts on the magnetic paint.

The magnetic paint is then extruded to the slot 4 as described above, and is applied to the base film 5 to form a deposited film. Because the shear force acts on the magnetic paint, a deposited film of satisfactory surface property having no small lines can be formed.

 As a porous body 3, a porous sintered body made of a metal such as stainless steel or copper, or plastic particles, or a coiled filter produced by winding a wire several times can be used.

 The pore diameter of the porous body 3 must be from 1 to 200 ssm. When the pore diameter of the porous body 3 exceeds 200 μm, the shear force can not act satisfactorily on the magnetic paint. When the pore diameter of the porous body 3 is less than 1 ssm, the porous body is clogged with solid components of the magnetic paint, which reduces the service life of the porous body 3. It is preferable that the pore diameter of the porous body 3 is 20 to 100 ssm. The pore diameter of the porous body 3 can be determined by a bubble test, that is to say by immersing the porous body 3 in a liquid in order to pass air through the pores and measuring the size. resulting air bubbles with a light scattering technique.

 Although the porous body 3 is made with the cylindrical shape and is in the cylindrical pocket 2 in the coating device of the present invention, the shape and location of the porous body 3 is not limited to the above.

Any shape and location of the porous body may be used as long as the magnetic paint delivered by the paint supply ports 6, 7 is extruded to the slot 4 through the porous body 3.

 For example, the bag 2 of the matrix 1 is hollow consisting of a cylindrical chamber 2a and a rectangular chamber 2b in the extension thereof, as shown in FIG.

The cylindrical chamber 2a is provided such that the paint supply ports 6, 7 are in the inner diameter thereof. The rectangular chamber 2b is located between the cylindrical chamber 2a and the slot 4 so that these spaces are continuous. A porous body in the form of a plate 3 having a width equal to the slot 4 and slightly smaller than the rectangular chamber 2b is provided in the rectangular chamber 2b.

 In such a matrix, the magnetic paint delivered by the paint supply ports 6, 7 enters firstly into the cylindrical chamber 2a of the bag 2, and then passes through the porous plate-shaped body 3 provided in FIG. the rectangular chamber 2b so that the magnetic paint is extruded to the slot 4. When the magnetic paint passes through the porous body 3, the shear force acts on the magnetic paint. With this shear force, a deposited film of satisfactory surface property having no small lines can be formed even when the high flocculation paint is used.

 A deposited magnetic film was actually formed using the coating device described above, and the surface property of the film was evaluated.

Example 1
Magnetic paint components were measured according to the following composition, and the measured components were kneaded and dispersed to prepare a magnetic paint.

Composition of the magnetic paint
Magnetic powder (CO - Fe203)
100 parts by weight
Bonding resin
Polyurethane polyester resin 20 parts by weight
nitrocellulose
Abrasive material: Al203
3 parts by weight
Additive agent: carbon powder
2 parts by weight
Lubricant: Butyl stearate
1 part by weight
Solvent
Butanone 100 parts by weight
Toluene 100 parts by weight
Cyclohexanone 50 parts by weight
The magnetic paint thus prepared was applied to a base film using the coating device shown in Fig. 2 to produce a deposited magnetic film.

The porous body 3 provided in the pocket 2 of the coating device is a cylindrical stainless steel sintered body having a pore diameter of 20.
Crm.

 The running speed of the base film 5 is 200 m / min, and the dry thickness of the deposited magnetic film is 3 ssm.

Comparative Example 1
A deposited magnetic film was formed in the same manner as in Example 1, except using a coating device having no porous body provided in the pocket to apply the magnetic paint to the base film.

 The surfaces of the deposited magnetic films formed in Example 1 and Comparative Example 1 were observed using a Nomarski differential interference microscope, and the surface properties were evaluated. The film surfaces were observed in three observation positions, i.e. positions corresponding to both edges of the slot (position Sl and position S2 in Fig. 2) and a position corresponding to the center (position C in Figure 2).

 The results are shown in Table 1.

TABLE 1

<tb><SEP> Sl <SEP> C <SEP> S2
<tb> Example <SEP> 1 <SEP> with <SEP> porous <SEP> body <SEP> 0 <SEP> 0 <SEP> 0
<tb><SEP> (diameter <SEP> of <SEP> pore <SEP> 20
<tb><SEP> ssm) <SEP>
<tb> Example <SEP> without <SEP> body <SEP> porous <SEP> x <SEP> x <SEP>
<tb> comparative <SEP> 1
<Tb>
In Table 1, 0 indicates that no line is observed on the surface of the deposited film. A indicates that although a small number of lines have been observed on the surface of the deposited film, these lines are at a level which does not affect the reproduction waveform. X indicates that a large number of lines have been observed on the surface of the deposited film and are at a level which causes the reproduction waveform to be unsatisfactory.

 As shown in Table 1, several lines are observed in all Sl, S2 and C positions on the deposited magnetic film of Comparative Example 1 formed using the coating device which does not have the porous body provided. in the pocket.

 On the contrary, no line is observed in any position on the deposited magnetic film of Example 1 formed using the coating device having the porous body provided in the pocket.

The deposited magnetic film of Example 1 has a satisfactory surface property.

 Thus, providing the porous body in the pocket of the coating device is effective to prevent the generation of lines on the surface of the deposited film in the case where the high flocculation paint such as magnetic paint is applied.

Optimum pore diameter of the porous body
A deposited magnetic film was formed in the same manner as in Example 1, except for the use of a stainless steel sintered body with pore diameters as shown in Table 2 as a porous body provided in the pocket of coating device. The surface properties were then evaluated. The results are shown in Table 2 with pore diameters.

TABLE 2

<tb><SEP> diameter of <SEP><SEP> pore <SEP> of porous <SEP> body <SEP> Sl <SEP> C <SEP> S2
<tb><SEP> l <SEP> ssm <SEP> 0 <SEP> 0 <SEP> 0
<tb><SEP> 10 <SEP> ssm <SEP> 0 <SEP> 0 <SEP> 0
<tb><SEP> 20 <SEP> ssm <SEP> o <SEP> 0 <SEP> 0
<tb><SEP> 40 <SEP> ssm <SEP> 0 <SEP> 0 <SEP> 0
<tb><SEP> 70 <SEP> ssm <SEP> o <SEP> 0 <SEP> 0
<tb><SEP> 100 <SEP> m <SEP> o <SEP> o <SEP> A
<tb><SEP> 200 <SEP> ssm <SEP> A <SEP> A
<tb><SEP> 250 <SEP><SEP> A <SEP> x <SEP> x
<Tb>
As can be seen from Table 2, with the pore diameter of the porous body provided in the pocket of the coating device greater than 200 μm, stripes are observed on the surface of the deposited film.

 The upper limit of the pore diameter of the porous body must thus be 200 ssm. When the pore diameter of the porous body is excessively low, the porous body can be clogged, and it is difficult to obtain a practical life. The lower limit of the pore diameter is therefore 1 ssm. A more preferred pore diameter of the porous body is from 20 to 100 ssm.

 The evaluation results have been described above in the case where the cylindrical sintered stainless steel body is provided in the coating device of Figure 1. However, similar results are found in a case where a porous cylindrical body consisting of a copper sintered body or polypropylene particles is used in place of the cylindrical stainless steel sintered body, or when a plate-shaped stainless steel sintered body is provided in the coating device of the figure 3.

Claims (4)

An extrusion coating device comprising a matrix (1) having a supply of paint (2) into which paint is supplied to extrude the paint through a slot (4) provided on a distal end (1a). of the matrix (1) so as to apply the paint on a flexible support (5) moving continuously, characterized in that a porous body (3) with a pore diameter of 1 to 200 μm is provided in the reserve of paint (2), the paint being delivered to the slot (4) passing through the porous body (3). 2. Coating device according to claim 1, characterized in that the pore diameter of the porous body (3) is 20 to 100 ssm. 3. Coating device according to claim 2, characterized in that the porous body (3) is a porous sintered body. 4. Coating device according to claim 2, characterized in that the porous body (3) is a wound filter.