JPH0773871B2 - Melt film formation method of polyester containing carbon black - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a melt film-forming method for carbon black-containing polyester, and more specifically, it reduces the amount of agglomerated particles in carbon black and remarkably improves the roughness of the film surface. The present invention relates to a melt film forming method for carbon black-containing polyester.

[Prior Art and its Problems] Polyester films have excellent physical and chemical properties and are used in a wide variety of applications. For example, it is used as a base film of a magnetic recording medium.

A magnetic recording medium needs to record or detect two signals, a magnetic signal and an optical signal. Conventionally, a magnetic paint having a light-shielding property is applied to the surface of a base film to give a magnetic signal, and a small hole is formed in the base film itself. Optical signals were detected by punching or attaching a leader tape that allows light to easily pass through.

However, such a conventional magnetic recording medium has the following drawbacks.

That is, since a transparent base film coated with a magnetic agent cannot provide sufficient light-shielding properties only by coating the magnetic agent, it is necessary to mix a light-shielding agent such as carbon black into the magnetic agent. There is a drawback that the density is lowered by that amount and that the light-shielding property is lowered when the coated surface of the magnetic agent is scratched. Further, a tape using a base film containing a dye such as carbon black can obtain a sufficient light-shielding property, but unevenness due to the dye etc. occurs on the surface of the base film so that the magnetic agent cannot be uniformly applied, and therefore the tape However, there are drawbacks such as loss of magnetic recording (dropout) and reduction of magnetic output.

Therefore, as a method for eliminating these drawbacks, for example, a film in which a polyester film A containing no light-shielding agent is laminated on at least one surface of a polyester film B containing carbon black as a light-shielding agent (Japanese Patent Application Laid-Open No. Sho.
No. 56-83841) has been proposed. However, even with this method, when the film thickness is thin, it is necessary to increase the amount of carbon black in the polyester film B in order to improve the light-shielding property. In this case, the film surface is very rough due to the agglomeration of carbon black, and the magnetic tape When converted into a magnetic layer, the rough surface of the layer B is transferred to the magnetic layer applied to the layer A, and there is a problem that sufficient magnetic characteristics cannot be obtained.

As a countermeasure against this, there is a method of laminating A layer not containing a light shielding agent on both surfaces of polyester B mixed with carbon black. In this case, it is necessary to further reduce the thickness of polyester B, and the light transmittance is reduced. In order to make the polyester film B sufficiently low, it is necessary to further increase the concentration of carbon added to the polyester film B. Therefore, the surface of the layer B mixed with carbon is very rough, and even if the polyester A containing no light-shielding agent is laminated, the unevenness of the layer B stands out on the surface of the layer A after lamination, and the magnetic agent is formed on the surface of the film. Can not be applied uniformly, and defects such as a decrease in magnetic output occur.

[Object of the Invention] The present inventor focused on the fact that the drawback of the prior art lies in the agglomeration of carbon black, and as a result of diligent research into a method of eliminating this agglomeration, as a result, a specific amount of shear was imparted to the molten polyester containing carbon black. Then, they have found that the amount of aggregated carbon black particles can be significantly reduced, and have reached the present invention.

Therefore, it is an object of the present invention to provide a melt film forming method of a carbon black-containing polyester which reduces the amount of aggregated particles in carbon black and remarkably improves the roughness of the film surface.

[Structure / Effects of the Invention] According to the present invention, the object of the present invention is to add carbon black having an average primary particle size of 20 to 100 mμm to 0.01
When melt-forming a polyester containing 20% by weight, the shear deformation rate as a shear amount is
It is achieved by a melt film-forming method of carbon black-containing polyester, which is characterized by imparting a residence time of 70 seconds- ^{1 to} 200 seconds- ¹ and a residence time of 20 seconds to 60 seconds.

Here, the shear deformation rate (S) is defined as the following equation S = when two planes sandwiching polyester and having a distance of dx are relatively displaced laterally (parallel) by dz per unit time (dt). It is defined by d (dz / dx) / dt. For example, in the case of the simplest single-screw extruder,
When the outer diameter is φD, the depth of the screw groove in the zone to which shear is applied is X, and the screw rotation speed is Y (rpm), the shear deformation speed S is represented by S = πDY / 60 · X (sec ⁻¹ ).

The residence time is the time (seconds) during which the polyester passes through the shearing zone.

As the polyester in the present invention, a thermoplastic aromatic polyester, particularly polyethylene terephthalate is suitable. Such a polyester has a usual intrinsic viscosity, and unless the object of the present invention is impaired, it may be one in which a bond other than an ester bond is introduced or another polymer is mixed in an amount of 30% by weight or less. Further, additives such as an antistatic agent can be contained as required.

The carbon black added and contained in the polyester in the present invention has an average primary particle size of 20 to 100 m. Further, although the content of addition is 0.01 to 20% by weight,
The light transmittance of the film is preferably 50% or less, more preferably 10% or less, and particularly preferably 1% or less when the light source wavelength is 9,000 Å.

In the present invention, the melt-film formation is performed using the polyester containing the carbon black added, but this film formation method may be basically a conventionally known method. However,
A shear deformation rate of 70 seconds ^-1 or more, preferably 90 seconds ^-1 or more and a residence time of 20 seconds or more, preferably 30 seconds or more, must be applied to the melt of the above polyester. By imparting such a shear amount to the molten polymer, carbon black agglomerated particles such as secondary agglomerated particles, 3
The secondary agglomerated particles and the like can be destroyed to make the particles finer.
However, if the shear deformation rate is too high, deterioration of the molten polymer (for example, heat deterioration, breakage of polymer molecules, etc.) increases, so the shear deformation rate is preferably 200 sec ^-1 or less. Further, if the residence time is too long, the deterioration of the molten polymer will increase, so the residence time is preferably 60 seconds or less.

In the present invention, the melt film formation can be performed using only the carbon black-containing polyester, but using the carbon black-containing polyester and the polyester containing no carbon black or the polyester having a low carbon black concentration, a coextrusion method is used. A melt-deposited film may be formed into a laminated film. A laminated film is preferable for some applications. In the laminated film, it is preferable that a polyester containing no carbon black or a polyester having a low carbon black concentration forms the surface layer,
For example, in a three-layer laminated film, it is preferable to use the polyester as both surface layers.

When the above-mentioned shear amount is applied to the carbon black-containing polyester, the melt viscosity of the polyester is
It is preferably 1000 to 4000 poise, more preferably 1000 to 2000 poise. Further, when the laminated film is formed into a film, it is preferable that the melt viscosity of the co-extrusion component is also within the above viscosity range.

The thus melt-extruded melt is rapidly solidified into an unstretched film. As this cooling means, a conventionally known one can be used, and for example, it can be rapidly cooled and solidified by using a cooling rotary drum. The unstretched film is preferably further stretched to obtain a stretched film. As the means for stretching treatment, conventionally known ones can be used, and the stretching temperature, the stretching ratio, the heat setting conditions, etc. may be selected according to the application of the film. The stretching may be uniaxial stretching or biaxial stretching, and the biaxial stretching may be single-stage stretching or multi-stage stretching.

According to the present invention, it is possible to obtain a polyester film containing a small amount of agglomerated particles and containing uniformly finely dispersed carbon black. The film has excellent surface flatness and light shielding properties. For this reason, for example, the magnetic tape based on the film is remarkably improved in the loss of magnetic recording and the decrease in magnetic output due to the surface irregularities of the base film. Also, if the base film has a light-shielding property with a light transmittance of 10% or less, it is not necessary for the magnetic layer to have almost a light-shielding property. Therefore, the magnetic layer can be made thinner and the magnetic agent can be further miniaturized. Therefore, higher output and higher density of magnetic recording can be achieved.

[Examples] The present invention will be further described with reference to Examples.

Example 1 and Comparative Example 1 Polyethylene terephthalate mixed with 2% by weight of carbon black having an average primary particle size of 24 mμ was melt-extruded at a temperature of 280 using an extruder having an outer diameter of 65 mm and a screw groove depth of 2.98 mm.
After applying a shear deformation rate of 80 sec- ¹ and a shear residence time of 30 sec at a temperature of 70 ° C and a rotational speed of 70 rpm, the mixture was passed through a filter, extruded from a slit-shaped die, and rapidly cooled to obtain an unstretched film having a thickness of 150 µ. This unstretched film was sequentially biaxially stretched 3.5 times in the longitudinal direction and 3.5 times in the transverse direction by a conventional method and heat-set at 200 ° C. to obtain a stretched film having a final thickness of 14 μm.

On the other hand, for comparison, a stretched film having a thickness of 14 μm was obtained in the same manner as described above, except that the rotation speed of the extruder was set to 40 rpm and a shear rate of 45 sec ⁻¹ and a shear residence time of 45 sec were applied.

Using these as base films, magnetic tape was formed by a conventional method, and the characteristics were measured by a VHS video coder manufactured by Matsushita Electric Co., Ltd. The results are shown in Table 1.

From the above table, the stretched film of Example 1 has a small surface roughness and excellent light-shielding properties and magnetic recording characteristics. On the other hand, the stretched film of Comparative Example 1 has agglomerated carbon black. Markedly, the unevenness of the film surface becomes abnormal, a uniform coating of the magnetic layer cannot be obtained, and the unevenness of the base film on the side opposite to the magnetic layer is transferred to the magnetic layer, resulting in missing magnetic recording (dropout) or magnetic It can be seen that the output is reduced and the noise is increased.

Example 2 and Comparative Examples 2 and 3 Polyethylene terephthalate mixed with 2.5% by weight of carbon black having an average primary particle size of 40 mμ was melt-extruded at the same extruder as in Example 1 at a temperature of 280 ° C. and a rotational speed of 80 rpm. 90 seconds- ¹ and 20 seconds of shear residence time, and carbon-free polyethylene terephthalate were melt-extruded using a 50φ extruder at a temperature of 280 ° C and a rotation speed of 6
The mixture was extruded at 0 rpm, and each molten polymer was separately passed through a filter, laminated with a slit-shaped die and coextruded to obtain an unstretched two-layer film having a thickness of 150 μm. The thickness constitution was 1: 2, and the carbon mixed polymer layer was thickened. This unstretched film was biaxially stretched 3.5 times in the longitudinal direction and 3.5 times in the transverse direction and heat-set at 200 ° C. to obtain a biaxially stretched laminated film having a final thickness of 14 μm.

On the other hand, as Comparative Example 2, 2.5% by weight of carbon black
Except that the rotational speed of the mixed polyethylene terephthalate 65φ extruder is 50 rpm, the shear deformation speed is 60 seconds- ¹ and the shear residence time is 45 seconds, and the rotational speed is 38 rpm in the polyethylene terephthalate 50 φ extruder that does not contain carbon. A biaxially stretched laminated film having a final thickness of 14 μ was obtained in the same manner as in 2.

In addition, as Comparative Example 3, 1.5% by weight of carbon black was used.
A biaxially stretched laminated film having a thickness of 14 μm was obtained in the same manner as in Comparative Example 2 except that the mixed polyethylene terephthalate and polyethylene terephthalate containing no carbon black were used.

Using these films as base films, a magnetic coating was applied to the layer side not containing carbon black by a conventional method to form a magnetic tape, and the characteristics were measured by a VHS video coder manufactured by Matsushita Electric Co., Ltd. The results are shown in Table 2.

From the above table, it can be seen that the base film of the stretched film of Example 2 has an excellent effect of achieving high output, while the base film of the stretched film of Comparative Example 2 winds the magnetic tape. In this state, there is magnetic transfer of the back surface layer, and a sufficient output cannot be obtained. Also, in the case where the stretched film of Comparative Example 3 is used as the base film, the surface unevenness of the back surface layer is relatively small, and therefore the transfer to the magnetic layer is also possible. It can be seen that high output can be obtained with almost nothing, but signal trouble occurs due to insufficient light transmittance.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B29L 7:00 (56) References JP 62-122734 (JP, A) JP 62- 51420 (JP, A) JP 62-95216 (JP, A)

Claims (3)

[Claims] 1. When melt-forming a polyester containing 0.01 to 20% by weight of carbon black having an average primary particle size of 20 to 100 mμm, a shear deformation rate as a shear amount of the molten polyester is 70 seconds ^{-1 to} 200 seconds. ^-1 or less and residence time is 2
A melt film forming method of carbon black-containing polyester, which is characterized by imparting 0 seconds or more and 60 seconds or less. 2. The melt film forming method according to claim 1, wherein a polyester containing carbon black added and another polyester are used to form a melt film by a coextrusion method. 3. A method for drawing a film formed by melting and forming a film according to claim 1 to obtain a film for a magnetic recording medium.