JP2530202B2 - Application method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating method, and more particularly to an improved coating method for a coating type magnetic recording medium.

(Prior Art) The coating type magnetic recording medium referred to in the present invention means that a non-magnetic and flexible strip-shaped support (hereinafter referred to as "web") is continuously transferred along a predetermined traveling path. The coating liquid is applied to the surface of the web in a desired thickness according to the purpose and dried, and ion plating, sputtering,
The manufacturing process is remarkably different from the so-called non-coating type magnetic recording medium based on the method such as vacuum deposition.

Most of the audio, video or data magnetic recording media are still produced and sold as the above-mentioned coating type, and they are generally manufactured by a coating method such as gravure, reverse roll, doctor blade, extrusion and the like. It was

However, it has been difficult for each of the above-mentioned conventional coating methods to significantly increase the coating speed due to the demand for increased production lamps.

The factors that make it difficult to increase the coating speed are mainly that the thickness of the support is extremely thin, and that among the coating liquids, especially the coating liquid for the ferromagnetic layer has a great influence on the electromagnetic conversion characteristics. The thixotropic property to give, what is called thixotropic property, etc. are mentioned.

Further, in the coating method in which the flow path of the coating liquid for the ferromagnetic layer has a relatively large number of stagnant portions, abnormal viscosity increase or aggregation due to the thixotropic property is likely to occur, and as a result, the ferromagnetic layer The electromagnetic conversion characteristics of, etc., may vary greatly. This problem is that in the conventional extrusion type coating device, as the amount of coating liquid discharged from the extruder slit (discharging port) is reduced, the amount of coating liquid on the side opposite to the supply port that supplies liquid to the extruder sump is reduced. Agglomeration is likely to occur, and vertical streaks in the coating layer frequently occur due to this liquid agglomeration. On the contrary, the vertical streaks tend to decrease as the amount of liquid supplied increases, but the color unevenness (thickness unevenness) of the coating layer
Tended to spread over the entire coating width.

Furthermore, regarding the cause of the color unevenness and the vertical stripes, the flow velocity in the longitudinal direction of the liquid reservoir extruder largely controls the thixotropic, specifically, the application in the vicinity of the liquid supply side where the flow velocity is relatively large. It is judged that the liquid is liable to decrease in viscosity due to shearing action, causing color unevenness, and the coating liquid on the side opposite to the liquid supply side where the flow velocity drops to almost zero easily aggregates, causing vertical stripes. ing.

As a result of such analysis, a proposal as shown in Japanese Patent Publication No. 60-53674 is proposed. In this method, a thin film of the coating liquid is layered on the surface of the support by continuously discharging the coating liquid from a slit tip portion opposed to the surface of a flexible strip-shaped support that is continuously moving. In the coating method, in which the coating liquid is supplied to the liquid pool of the Listruder communicating with the slit in an amount larger than a desired coating amount on the support, and part of the coating liquid in the liquid pool is the liquid. The coating method is characterized in that the liquid is made to flow from a position farthest from the liquid supply position of the pool in the width direction of the support or in the vicinity thereof without passing through the slit.

By the method disclosed in Japanese Patent Publication No. 60-53674, vertical streaks and color unevenness can be considerably improved, and the electromagnetic conversion characteristics of the ferromagnetic layer can be improved. However, there remains a problem to be further studied and improved on the relationship between thixotropic property at the time of applying the coating liquid and the liquid supply flow rate to the liquid reservoir in the extruder.

The above-mentioned problem is a certain liquid supply amount (amount supplied to the liquid reservoir) in the outflow type extruder in which the coating liquid flows out from the discharge port other than the coating nozzle disclosed in Japanese Patent Publication No. 60-53674.
On the other hand, the balance between the coating amount and the outflow amount (outflow amount from the discharge port) is determined by the pressure balance generated in the coating liquid at the coating nozzle of the extruder and the discharge port. That is, the allowable range for setting the coating amount and the outflow amount is easily restricted by various conditions such as the shape of the extruder, the liquid feeding system, the physical properties of the coating liquid, the coating work, etc. in order to reduce color unevenness and vertical stripes. There is a problem that the adjustment range of the outflow amount based on the opening degree of the outlet is narrow. Also, during the coating process, the physical properties of the coating liquid fluctuate in a strict sense, for example, depending on the production lot, and it is thought that this fluctuation causes fluctuations in the pressure of the coating liquid and changes in the flow velocity. To be

(Object of the Invention) The present invention has been made in view of the above problems, and coating capable of stably producing a magnetic recording medium having excellent electromagnetic conversion characteristics, which can be applied to a wide range of production conditions such as occurrence of color unevenness and vertical stripes. It is intended to provide a method for applying a liquid.

(Structure of the Invention) An object of the present invention is to continuously discharge the coating liquid from a slit tip portion opposed to the surface of a continuously moving flexible strip-shaped support member, thereby continuously In the coating method of layering the coating liquid on the surface, while supplying the coating liquid to the extruder communicating with the slits in excess of the coating amount on the support, the support from the liquid supply port Is achieved by an external draining means forcibly withdrawing an excessive amount of the coating liquid supplied into the liquid storage through the drainage port farthest in the width direction or in the vicinity thereof. It

Hereinafter, embodiments of the method of the present invention will be described with reference to the accompanying drawings.

FIG. 1 and FIG. 2 show an extruder for carrying out the method of the present invention, in which a small gap (below) is formed on the surface of the support 4 supported by the backing roll 7 and transferred at a constant speed. The tip of the slit 2 of the extruder 40 is vertically opposed to the coating liquid with a supply amount Q _0, which is larger than the coating amount Q ₁ on the surface of the support 4, and is usually 5 mm or less). Three
When the coating liquid 3 is continuously fed under pressure into the liquid reservoir 10, the coating liquid 3 fills the entire liquid reservoir 10 and then its liquid pressure distribution is made substantially uniform in the width direction of the support 4 while part of the liquid is distributed. Is a position farthest from the liquid supply nozzle 12 in the width direction of the support body 4, that is, a liquid discharge nozzle 41 attached to the other end of the liquid reservoir 10 to the outside of the device, and a pulling pump P which is an external liquid discharge means described later. by ₂ to withdraw forces excess coating liquid in the reservoir 10.

The extruder 60 shown in FIG. 3 is different from the extruder 40 shown in FIGS.
The position of and the shape of the liquid reservoir 61 are slightly different.

The extruder 60 is of a so-called central supply type, in which the liquid supply nozzle 62 is located substantially in the center, and the vertical stripes and color unevenness are less likely to occur than the one-sided supply type extruder 40 described above. However, due to the physical properties of the coating liquid 3, there is a tendency that vertical stripes and color unevenness that cause the above-mentioned variations in electromagnetic conversion characteristics near the both ends and the center of the boat bottom type liquid pool 61 tend to occur. By attaching drainage nozzles 63 and 64 to both ends of the liquid pool 61 and allowing a part of the coating liquid 3 to flow out as described above, a coating film of uniform quality in the width direction can be obtained.

The drainage nozzles 41, 63, 64 are the liquid reservoirs 10, 61.
The flow path may be provided through the extruder block in the vicinity of the end portion as well as the end portion.

In FIG. 2, the extruder 40 is provided so as to face upward, but it is possible to make the extruders 40 and 60 vertically face the support body 4 if necessary. Of course.

Further, the extruders 40 and 60 have the slit 2
The front end of the backing roller 7 so as to directly contact the surface of the support 4 located away from the backing roller 7,
It is also possible to apply the liquid such that the support 4 is slightly separated from the tip of the slit 2 by the liquid pressure of the applied coating liquid 3.

FIG. 4 shows a schematic diagram of the liquid delivery system of the present embodiment using the extruders 40 and 60 configured as described above.

The coating liquid 3 stored in the stock tank 20 is sent out by the liquid supply pump P ₁ , and at this time, the extruder 4 is passed through the filter f while being calculated by the flow meter FM ₁ .
It is sent to 0, 60. At the same time, a part of the coating liquid 3 in the extruder from the drainage nozzle 41 (63, 64) is an external drainage means of a system different from the liquid supply system.
Withdrawn while being metered by the flow meter FM ₂ by P _2. Therefore, the amount (Q ₁ ) of the coating liquid 3 flowing out from the slit 2 is the amount represented by the flow rate difference (Q ₀ −Q ₂ ) between the flowmeters FM ₁ and FM ₂ on the support 4. Will be applied. Then, the liquid feed amount can be controlled by the control panel 21 based on the measured value measured by the flow meter FM ₁ so as to control the rotation of the liquid feed pump P ₁ . On the other hand, the amount of liquid drawn from the drainage nozzle 41 (63, 64) is determined by the flowmeter.
Based on the value measured by FM ₁ , the rotation of the drawing pump P ₂ by the control panel 22 can be controlled to change the drawing amount appropriately.

The liquid feed pump P ₁ and the withdrawal pump P ₂ are preferably those that feed the liquid smoothly and stably, and any type of pump may be used without any particular limitation. Particularly, in the extraction pump P ₂ , the drain nozzle 41
A pump for circulating the coating liquid 3 may be used as long as it has a function of extracting the coating liquid 3 from (63, 64), or another liquid feeding means may be used.

According to the coating method as described above, the amount of the liquid discharged from the nozzle 2 of the extruder 40 (60) is equal to that of the drawing pump P ₂
Since it can also be controlled by means of a conventional extruder, the liquid feed pressure by the liquid feed pump P ₁ and the valve V attached to the drain nozzle 41 (63, 64) as in the conventional extruder (see FIG. 9)
As compared with the case where it is determined by adjusting the opening degree, the amount of application can be adjusted stably and reliably in a wide range, and the range in which color unevenness and vertical stripes are less likely to occur can be widened. That is, the drawing force of the drawing pump P ₂ makes the flow velocity of the coating liquid 3 in the liquid reservoirs 10 and 61 uniform over the entire area, and causes pressure fluctuations and excess pressure generated in the coating liquid 3 in the liquid reservoir 10. It is possible to suppress the above, and to maintain a state in which the effective fluidity of the coating liquid 3 is enhanced, and the behavior of the coating liquid 3 discharged from the slit 2 can be stabilized. From a different point of view, even when the same coating amount is obtained, the liquid feeding conditions of the coating liquid 3 are made different by appropriately changing the operating states of the liquid feeding pump P ₁ and the drawing pump P _2. Therefore, the degree of freedom in setting conditions such as the amount of liquid to be sent can be increased.

In the embodiment shown in FIG. 4, the liquid feeding side and the drawing side are separately controlled by the control panels 21 and 22, but both pumps P _{1 and} P ₁ can be controlled by other control means which can be set so as to obtain a desired flow rate difference. , P ₂ may be controlled simultaneously. Further, the method of the present invention is not limited to this, and may be modified as shown in FIGS. 5 to 8, for example.

Case shown in Fig. 5, the liquid feed pump P ₁ leave operated at a constant rotation, feed volume based on the measured value of the flow meter FM ₁ and FM ₂ (Q ₀₎ and withdrawal amount (Q ₂ In order to maintain a desired flow rate difference with the above), the control panel 23 controls only the drawing pump P ₂ .

In the case shown in FIG. 6, contrary to the case shown in FIG. 5, the drawing pump P ₂ is operated at a constant rotation, and the control panel 23 controls only the liquid feed pump P ₁ .

In the case shown in FIG. 7, the control panel 21, 22 similar to that shown in FIG. 4 appropriately controls the liquid feeding amount and the drawing liquid amount, but the liquid feeding route is different from that shown in FIG. Differently, the drawn-out coating liquid 3 is returned again between the flow meter FM ₁ and the extruder 40 (60). Therefore, the coating liquid 3 passing through the inside of the extruder 40 (60)
The closely-circulated circulation system is formed by the drawing pump P _2, and the coating liquid 3 is always subjected to stable stress and the viscosity and fluidity are kept stable. In this case, if a highly quantitative pump is used as the drawing pump P ₂ , the flow meter
It is also possible to omit FM ₂ .

In the case shown in FIG. 8, similar to the method shown in FIG.
The drawing pump P ₂ is operated at a constant rotation, the liquid feed pump P ₁ is controlled by the control panel 23, and the coating liquid 3 drawn by the drawing pump P ₂ and the liquid feed pump P ₁ and the flow rate are set. It is designed to form a circulatory system for returning to the meter.

(Effect of the Invention) As described above, according to the method of the present invention, the excess amount of the coating liquid is supplied to the liquid pool of the extruder under pressure and the liquid is discharged from the drain port provided at a proper position of the liquid pool. Since a part of the coating liquid is forcibly drawn out, the coating amount is adjusted on the feeding side of the coating liquid as compared with the conventional coating method in which the coating amount largely depends on the liquid feeding amount on the feeding side. This can be done by controlling the flow rate on both the drawing side and, for example, even if the same coating amount is set, the flow rate flowing through the entire feeding system can be changed while maintaining the desired difference between the feeding amount and the drawing amount. As described above, the selection range of setting conditions is widened, and the coating conditions can be more stable and more accurate than in the past. Further, from the viewpoint of thixotropy of the coating liquid, as in the present invention, by forcibly withdrawing from the discharge port with a pump or the like, the flow velocity in the extruder can be made uniform, and the viscosity and fluidity can be improved. Since it is possible to create a stable state of liquid physical properties such as, it is possible to improve the effect of preventing color unevenness and vertical streaks due to fluctuations in the liquid physical properties.

Next, the novel effects of the method of the present invention will be further clarified by Examples and Comparative Examples.

(Example) After putting each component having the composition shown in Table 1 in a ball mill and thoroughly mixing and dispersing, an epoxy resin (epoxy equivalent 50
0) was added and uniformly mixed and dispersed in 30 parts by weight to obtain a magnetic coating liquid.

When the equilibrium viscosity of the magnetic coating liquid thus obtained was measured with a Shimadzu Rheometer RM-1 manufactured by Shimadzu Corporation, the shear rate was
It showed 7 poise at 10 sec ^-1 .

The above magnetic coating liquid was applied to a polyethylene terephthalate film support by the method shown in FIG. 4 using the extruder 40 shown in FIGS. Table 2 shows the application conditions.

Under the above-mentioned coating conditions, 500 m of coating was applied, the operation of the apparatus was once stopped, and after 3 hours, 500 m of coating was applied again under the same conditions. The results are shown in Table 3.

(Comparative Example) The same magnetic coating solution as shown in Table 1 was coated by the coating method shown in FIG. 9 according to the conditions shown in Table 2. In the method shown in FIG. 9, the coating liquid 3 delivered by the liquid supply pump P ₁ is weighed by the flow meter FM ₁ and enters the extruder 40. Drainage nozzle of this extruder 40
A variable valve V whose flow rate can be changed by manual operation is provided on the 41 side, and a part of the coating liquid 3 flows out. And this outflow is measured by the flow meter FM ₂ .

500m under the same conditions as in the above example
After the application, the operation of the apparatus was once stopped, and after 3 hours, application of 500 m was performed again under the same conditions. The result is the third
It was as in the table.

For the measurement of the average film thickness shown in Table 3, a Tokyo Seimitsu Co., Ltd. minicom contact type film thickness meter (E-M43K) was used. As a measuring method, after measuring the film thickness of the applied sample sample,
The coating thickness of the measurement part is peeled off using a solvent, and the support thickness is measured. Then, the difference between the two is obtained and the coating film thickness is calculated. The above measurement was carried out at 5 positions in the width direction and 4 positions every 2 m in the longitudinal direction, for a total of 20 positions, and the average film thickness was obtained.

 The vertical stripes were visually observed.

As is clear from Table 3, with respect to the average coating thickness and the vertical streak at the time of initial setting, the comparative example and the example show similar good results, but by stopping the coating process for a certain time, the coating liquid When a change in liquid physical properties due to thixotropy occurs, in Comparative Examples, changes in viscosity and fluidity appear as deterioration of direct coating accuracy, but in Examples based on the present invention, stable coating is always performed. Could be done.

[Brief description of drawings]

1, 2 and 3 are schematic views showing the main part of an apparatus for carrying out the coating method of the present invention, and FIGS. 4 to 8 are liquid feeding control by the coating method of the present invention. And FIG. 9 is a schematic view showing a conventional coating method. 2 ... Slit, 3 ... Coating solution, 4 ... Support, 7 ...
Backing roll, 10, 61 …… Liquid reservoir, 12, 62 …… Supply nozzle, 20 …… Stock tank, 21, 22, 23 …… Control panel, 40, 60 …… Extruder, 63, 64 …… Drainage nozzle .

Claims (1)

(57) [Claims] 1. A thin film of the coating liquid on the surface of the support by continuously discharging the coating liquid from a slit tip portion opposed to the surface of a continuously moving flexible strip-shaped support. In the coating method of layering, while supplying the coating liquid to the liquid reservoir of the extruder communicating with the slit in excess of the coating amount on the support, from the liquid supply port of the liquid reservoir of the support A coating method, characterized in that an excess amount of the coating liquid supplied into the liquid reservoir is forcibly withdrawn by an external drainage means through a drainage port that is farthest from or in the vicinity of the width direction.