JPH04209664A - Production of magnetic coating material - Google Patents

Abstract

PURPOSE:To prepare the title material having an increased solid content and an improved degree of dispersion in a short time by a simple process by mixing a compsn. having a specified solid content in the first mixing step, increasing the solid content in a drying step, and mixing further in the second mixing step. CONSTITUTION:A process for preparing a magnetic coating material by mixing a compsn. mainly comprising a magnetic powder, a binder, and a solvent on a twin-shaft continuous mixer, wherein the mixer is one having screws 5 and paddles 6 on the shafts 3 and 4 and the compsn. having a specified solid content is mixed in the first mixing step (region (b)). Then, the compsn. is transferred to a drying step (region (c)) where a part of the solvent is removed to increase the solid content to another specified value. Finally, the compsn. having the increased solid content is mixed further in the second mixing step (region (d) and region (f)).

Description

[Detailed description of the invention]

[00011

[Industrial Field of Application] The present invention relates to a method for producing magnetic paint, and more particularly to a technique for dispersing magnetic powder as uniformly as possible in as short a time as possible, in as simple a process as possible. [0002] Conventionally, as methods for producing magnetic paints, there are the following methods. That is, JP-A-2-17836
As shown in Publication No. 4, when producing magnetic paint, first, a twin-screw continuous kneading mixer is used to obtain a solid content concentration of 6.
A mixture of 5 to 95% by weight of an organic solvent solution containing a binder and magnetic powder is kneaded, and then an organic solvent is added to make the solid content concentration 30 to 60% by weight. There is another kneading mixer in which the gaps between the paddle members and between the paddle members and the barrel are smaller than that of the mixer to knead and produce magnetic paint. [0003] Furthermore, as shown in JP-A No. 62-41274, when producing a magnetic paint using a twin-screw continuous kneading mixer, first, a compound having a solid content concentration of 65 to 85% by weight is prepared. Next, an organic solvent solution is further added to form a blend with a solid content concentration of 40 to 65% by weight, and this is kneaded, and finally, an organic solvent solution is further added,
There is a mixture with a solid content concentration of 25 to 60% by weight, which is kneaded to produce a magnetic paint. [0004]

[Problems to be Solved by the Invention] Magnetic recording media such as magnetic tapes for audio and video are produced by coating a base material such as a plastic film with a magnetic paint containing magnetic powder, a binder, an antistatic agent, etc. It is manufactured by drying. In order to obtain a magnetic recording medium with excellent magnetic properties, electromagnetic conversion properties, etc., it is important to improve the degree of filling and dispersion of magnetic powder in the magnetic paint. [0005] To achieve this, dispersing magnetic powder by kneading rather than mere stirring is an effective method, and this includes a twin-screw continuous kneading mixer that can obtain high shearing force. is suitable to use. In addition, in order to obtain a high kneading effect, it is considered better to knead using a compound with a high solid content concentration, but if the solid content concentration is high, parts of the kneading machine (paddle, shaft, etc.)
There is a risk that an excessive load will be applied to the machine and smooth kneading will not be achieved. [0006] However, if the solids concentration of the formulation is reduced by the addition of a solvent, as in the conventional method shown above, the viscosity may in turn become too low to provide sufficient shear during kneading. There is a problem that the magnetic powder cannot be added, resulting in poor dispersion of the magnetic powder. SUMMARY OF THE INVENTION In view of the above-mentioned problems, an object of the present invention is to provide a method for producing a magnetic coating material that can sufficiently disperse magnetic powder using a twin-screw continuous kneading mixer. [0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a magnetic paint formulation containing a solvent and containing magnetic powder and a binder as main components, using a twin-screw continuous kneading mixer. When producing magnetic paint by kneading materials, in the first step of mixing and purification, a compound having a solid content at a first predetermined concentration is kneaded, and then the mixture is transferred to a drying step, and in the drying step, By removing a portion of the solvent, the solid content in the blend is increased to a second predetermined concentration, and in the second stage of mixing, the solid content is increased to the second predetermined concentration. The blended mixture is then kneaded further. [0008]

[Operation] According to the above method, in order to sufficiently disperse the magnetic powder, it is first necessary to mix the magnetic powder with the solvent. In the first step, the magnetic powder and the solvent can be made to blend together by kneading a compound having a relatively low solid content at a first predetermined concentration. [0009] If the mixture at the same concentration is continued to be kneaded, the dispersion of the magnetic powder will be insufficient, so in order to improve the kneading effect, it is necessary to increase the solid content concentration and apply high shear. You need to gain strength. Therefore, a part of the solvent is removed from the blend in the drying stage to make the solid content concentration of the blend a relatively high second predetermined concentration, and a high shear force is obtained in the second stage of kneading. The degree of filling of magnetic powder can be improved. [00101

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. The composition of the magnetic paint is as follows:
This has a solid content concentration of about 65%, which corresponds to the first predetermined solid content concentration (unit: parts by weight). Magnetic powder-metal powder 1
00 binder - polyvinyl chloride resin
10 Polyurethane resin
10 Antistatic agent - carbon black (average single particle size 25
rm) 5 Organic solvent - methyl ethyl ketone/cyclohexanone (mixture of weight ratio 1:1) 67 This was transferred to the twin-screw continuous kneading mixer shown in Figure 1, and 10 kg
/Hr feed rate and kneading. [00111 This kneading machine 1 has two shafts 3 and 4 extending in parallel inside the barrel 2.
．． 4 is a screw rotation speed of 12 by a motor (not shown).
It is driven to rotate at 0 rpm, and the compound is supplied from the left in the figure, and the kneaded magnetic paint is discharged from the right in the figure. The shaft 3.4 has a region a, a region b, a region C, a region d, and a region C in this order in the axial direction.
It is divided into seven regions: A region, F region, 7G region, A region, and C region. In the e region 9g region, a screw 5 is provided around the shafts 3 and 4 to have a feeding function. [0012] Also, in the b region, d region, and f region, the shaft 3
．． It is equipped with paddles 6 around 4 and has a kneading function. Incidentally, the paddle 6 is constituted by a combination of so-called S-type double thread screw type discs. Incidentally, the barrel temperature is maintained at approximately 50°C in each zone, but only zone C is heated to approximately 70°C. [0013] Further, the L/D (ratio of the total length of the shaft of the portion having the screw and paddle to the diameter of the screw or paddle) of the present device is 40, and the L/D of each region is:
4. Starting from area a. 4. 4.10. 4.12. 2
It is. The effects in each area will be explained. Zone a is a feed section and the above blend is transferred to the kneading section of Zone b. [00141b area is a kneading section where the magnetic powder and the solvent are blended. Zone C is a feed section where the blend is transferred to zone d, where drying is performed as a drying stage. That is, in this region C, the formulation is heated to about 70°C, while the rest of the region is kept at about 50°C,
A vacuum is then applied to remove some of the solvent (dry up) and increase the formulation to a second predetermined concentration of about 80%. ** [0015] Area d is a kneading section where the compound is kneaded, but the solid content of the compound here is a concentration sufficient to obtain a high shear force, so the compound does not receive a high shear force. obtained and thoroughly kneaded. After passing through the feed section in area C, it is further kneaded in the kneading section in area f, and the kneaded magnetic paint is discharged out of the system via the feed section in area a. [0016] Here, region b corresponds to the first stage of kneading,
Area C corresponds to the drying stage, and areas d and f correspond to the second stage of kneading. The magnetic paint produced in this way is
For comparison, a magnetic tape was manufactured using the method shown below. The same type of solvent as above was added to this magnetic paint to dilute the solid content to approximately 35%, and the mixture was passed through a sand mill for 4 baths, and a small amount of solvent was added to reduce the solid content to approximately 30%.
and add a curing agent (polyisocyanate compound),
It was coated on a polyethylene terephthalate film using a test coater so that the dry film thickness was 3 μm, and after drying, it was calendered. Note that the calender treatment was performed by passing a roll heated to 80° C. six times under a linear pressure of 200 kg/cm. [0017] Thereafter, a back coat containing polyurethane resin, nitrocellulose, and carbon black as main components was applied to the film surface opposite to the magnetic layer surface, stored at 60° C. for 4 days, cut into 8 mm width, and magnetically coated. Got the tape. In addition, as a comparative example, with the solid content concentration unchanged at 65%,
That is, the same magnetic tape was produced without going through the drying step in area C, but by performing the other steps in the same manner. [0018] The light reflectance (gross, unit %), electromagnetic properties, etc. of these magnetic tapes were investigated. The results are shown below. Example Comparative example Gloss after coating (%) 150
138 center line surface roughness (nm)
16 18 Gloss after calendering 162 160 Surface roughness after calendering (nm) 11
11 Holding force Hc (unit; Oe)
1520 1530 Saturation magnetization Bs
(Unit; Gauss) 3520
3005 Video S/N [:dB)
+1.5 0In this way, at the beginning,
The magnetic powder and solvent are mixed with each other in a state where the concentration of solids is low, and then through a drying stage, the concentration of solids is increased to a state where a high shearing force can be obtained, and then kneaded. It was found that the magnetic tape of this example produced using magnetic paint was generally better. [00191] In other words, it is considered that the present example was able to improve the degree of filling and the degree of dispersion of the magnetic powder. [0020] [Effects of the Invention] As explained above, according to the present invention,
It is possible to obtain the effect that the filling degree and the dispersion degree of the magnetic coating material can be improved, and a magnetic coating material that can obtain a good magnetic recording medium can be manufactured.

[Brief explanation of the drawing]

[Fig. 1] Diagram of an apparatus showing one embodiment of the present invention

[Explanation of symbols]

1 Kneading machine 2 Barrel 3 Shaft 4 Shaft 5 Screw paddle

Claims (1)

[Claims] [Claim 1] When producing a magnetic paint by kneading a magnetic paint composition containing a solvent and having magnetic powder and a binder as main components, using a two-screw continuous kneading mixer, A blend having a first predetermined concentration of solids is kneaded in the step, and then transferred to a drying step, in which a portion of the solvent is removed to reduce the solid content in the blend. The proportion is increased to obtain a second predetermined concentration formulation, and the second
A method for producing a magnetic coating material, which comprises further kneading the mixture whose solid content has been increased to a second predetermined concentration in the step.