JPH0568007B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic tape or other magnetic recording medium comprising a base film provided with a magnetic layer on its main surface and a back coat layer provided on the back surface. In general, magnetic tape such as videotape
In order to improve the output and SN ratio in the high frequency region,
A magnetic layer is provided on a smooth base film to give it a smooth surface, but the surface of the base film is too smooth, making it difficult to use in video tape recorders (VTR).
The coefficient of friction with tape guides, etc. increases,
Driving stability deteriorated, making it difficult to record and reproduce signals correctly. For this reason, conventional efforts have been made to roughen the surface by providing a back coat layer made by dispersing and bonding non-magnetic powder in a suitable binder on the back surface of the base film, which has a smooth surface, thereby improving running stability. There is. However, the provision of such a back coat layer causes problems such as deterioration of video characteristics and abrasion of members such as tape guides with which the back coat layer comes into contact. In other words, if the back surface of the tape is too roughened, the surface condition of the back coat layer will be transferred to the surface of the magnetic layer when the tape is wound, resulting in a decrease in video characteristics. The particles fall off and are transferred to the surface of the magnetic layer, resulting in a loss of video characteristics. On the other hand, if the back coat layer is too hard, it will cause abrasion of the tape guide and other objects that come into contact with it, and will not produce good results in improving running stability. From the above viewpoint, various proposals have been made to date regarding the material of the back coat layer, especially the type of nonmagnetic powder, particle size, etc. However, driving stability,
The reality is that a back coat layer that can highly satisfy both the video properties and the non-abrasion properties of objects in contact has not yet been found. As a result of intensive studies in view of the above-mentioned circumstances, the inventors used an inorganic pigment as the non-magnetic powder, and constructed this inorganic pigment by a hard inorganic pigment with a specific hardness and a soft inorganic pigment with a specific hardness, so that both pigments could be combined. We learned that when the usage ratio is set within a specific range and the particle size of the hard inorganic pigment is specified, it is possible to achieve high levels of running stability, video characteristics, and non-abrasion of objects in contact. , completed this invention. That is, the present invention provides a magnetic recording medium in which a back coat layer formed by dispersing and binding non-magnetic powder in a binder is provided on the back side of a base film having a magnetic layer on the main surface, and the non-magnetic powder has a Mohs hardness of 3. Contains an inorganic pigment consisting of a soft inorganic pigment with a particle size of less than ~4.5 and a hard inorganic pigment with a Mohs hardness of 5 to 6 and an average particle size of 0.2 μm or less, which accounts for 1 to 50% by weight in the total amount. The present invention relates to a magnetic recording medium characterized by the following. In this invention, since hard inorganic pigments and soft inorganic pigments are used together in a specific ratio, the back coat layer has appropriate flexibility and hardness, and its abrasion resistance and non-abrasion properties against objects are improved. Together, we can achieve good results. On the other hand, when only one of the hard inorganic pigment and the soft inorganic pigment is used, or even when they are used in combination, if the ratio is outside the scope of the present invention, good results may not be obtained in either or both of the above properties. do not have. In addition, in this invention, by setting the average particle diameter of the hard inorganic pigment to a small value of 0.2 μm or less, it is possible to prevent the deterioration of video characteristics caused by the surface condition of the back coat layer, and furthermore, it is possible to prevent the aforementioned abrasion of the contact material. You can get even better results in terms of sex, etc. In other words, the inventors found that when the particle size of the inorganic pigment included in the back coat layer is increased to increase the surface roughness and thereby reduce frictional resistance and improve running stability, the pigment is hard. In contrast, the deterioration of the video characteristics due to the above-mentioned surface roughness is noticeable and the non-abrasion property of the contact object is impaired, whereas the soft material does not cause any problem in the non-abrasion property of the contact object, and of course the video characteristics deteriorate. It was found that the decrease was also small. Therefore, as mentioned above, by setting only the particle size of the hard inorganic pigment to be small, it is possible to improve the video characteristics over a relatively wide particle size range of the soft inorganic pigment used together, and also to improve the non-abrasion property of the contact object. It was also found that good results could be obtained. As described above, according to the present invention, it is possible to form a back coat layer which has good abrasion resistance and non-abrasion property against contact objects, and has little negative effect on video characteristics due to surface roughness, thereby improving running stability and video characteristics. In addition, good results can be obtained in preventing damage to objects such as tape guides. The soft inorganic pigment used in this invention has a Mohs hardness of 3 to 4.5, because if the hardness is too low, it will impair wear resistance and will not give good results in terms of running stability. Examples include barium sulfate powder, calcium silicate powder, calcium carbonate powder, calcium sulfate powder, magnesium carbonate powder, zinc carbonate powder, zinc oxide powder, and the like. The hard inorganic pigment used in the present invention is made of
The Mohs hardness range is 5 to 6, and a typical example thereof is α-Fe ₂ O ₃ powder. In this invention, among the above pigments, the hard inorganic pigment has an average particle diameter of 0.2 μm.
The average particle size mentioned above means that the particle size distribution forms a uniform normal distribution, with the upper limit of the distribution being 0.35 μm and the lower limit being 0.05 μm. As mentioned above, the particle size of the soft inorganic pigment is not particularly limited. However, if the particle size becomes too large, the adverse effects on video characteristics caused by surface roughness cannot be ignored. Therefore, preferably the average particle diameter is 0.5 μm or less, particularly preferably
It is preferably 0.2 μm or less. In the present invention, the ratio of the two pigments used in combination is set so that the hard inorganic pigment accounts for 1 to 50% by weight, preferably 5 to 30% by weight.
This is because if the amount of the hard inorganic pigment becomes too large or too small, the effects of the present invention will be impaired. In this invention, by configuring the inorganic pigment used as the non-magnetic powder as described above, it is possible to achieve both running stability and video characteristics, and also to obtain good results in non-abrasion of objects in contact with the VHS. In particular, for VHS video tapes, by making at least one of the soft inorganic pigment and the hard inorganic pigment a light-resistant inorganic pigment, it is possible to create a videotape that is suitable for the VHS system. It becomes possible to produce sex videotapes. In other words, in order to detect the end of the video tape in the video cassette, VHS format video tapes have leader depths installed at the front and rear ends of the cassette that have a high light transmittance to determine the difference between the video tape and the video tape inside the recorder. 9000 to the driving route within
The tape is irradiated with light of .ANG., and if the transmittance of this light is high, it is determined that it is a leader tape, and if it is low, it is determined that it is a videotape. Therefore, this type of tape is required to have a high optical resistance of 9000 Å, but in recent years, the particle size of the magnetic powder is often reduced in order to improve the characteristics in the high frequency range of video tapes. In this case, the light resistance is small and the above discrimination becomes difficult. Therefore, in the present invention, by configuring at least one of the hard and soft inorganic pigments contained in the back coat layer from a light-resistant pigment, the back coat layer can provide a light-resistant effect, and therefore the magnetic The above-mentioned discrimination can be easily made without paying particular attention to the light resistance and resistance of the layer. Therefore, by using the above-mentioned light-resistant pigment composition, good results can also be obtained in video characteristics. Furthermore, in the present invention, the above-mentioned α-Fe ₂ O ₃ powder exemplified as a hard inorganic pigment is conveniently a dark pigment with light-resistance properties, and therefore most of the above-mentioned soft inorganic pigments are Even if it is a light-transmitting white pigment, this α-
By selecting and combining Fe ₂ O ₃ powder,
It should be noted that the advantage is that it is possible to obtain a back coat layer having good light and resistance properties suitable for video tapes in the VHS system. Among the above combinations, a particularly preferred embodiment is such that the hard inorganic pigment consists of a light-resistant α-Fe ₂ O ₃ powder with a Mohs hardness of 5 to 6, and the soft inorganic pigment has a Mohs hardness of 3 to 4.5. This is a case where the combination consists of at least one light-transmitting white inorganic pigment selected from barium sulfate powder, calcium carbonate powder, and zinc oxide powder within the range. Each of the above pigments has excellent dispersibility in the binder and gives particularly good results in terms of surface roughness, abrasion resistance, coefficient of friction, etc. of the back coat layer. The magnetic recording medium of the present invention is produced by preparing a paint in which the above-mentioned inorganic pigment is dispersed as a non-magnetic powder in a suitable binder, and applying this paint to a polyester film or other base with a magnetic layer on the main surface. It can be made by coating and drying the film to a thickness of about 1 μm after drying to form a back coat layer. In preparing the above paint, conventionally known carbon black may be added as a non-magnetic powder other than the inorganic pigment. This carbon black gives good results in improving the mechanical strength of the back coat layer and preventing static electricity, and also gives good results in light resistance. The amount used is 3 to 50% of the total amount including inorganic pigments.
% by weight, preferably in the range from 5 to 40% by weight. The average particle diameter of carbon black is generally about 10 to 100 mμ (nm). Further, a lubricant such as a higher fatty acid or a higher fatty acid ester may be added to the above paint for the purpose of adjusting the friction coefficient of the back coat layer and further improving the running stability of the tape. The amount added is generally 0.5 to 5.0 parts by weight per 100 parts by weight of non-magnetic powder (inorganic pigment or inorganic pigment or carbon black). Other known additives other than those mentioned above may also be added. The binder for dispersing and binding the non-magnetic powder is not particularly limited. Polyurethane resin, vinyl chloride-vinyl acetate copolymer, polybutyral resin,
Any conventionally known resins such as fiber-based resins, polyacetal resins, and polyester resins can be used. Examples of the present invention will be described below in comparison with comparative examples. In addition, in the following, parts shall mean parts by weight. Example 1 After drying, a magnetic paint consisting of the following composition was applied to the main surface of a polyester base film with a thickness of 14 μm and a centerline average roughness (Ra) of 0.03 μm or less (cutoff 0.25 mm) with good surface smoothness. A magnetic layer was formed by coating and drying to a thickness of about 5 μm and calendering. Co-containing acicular magnetic iron oxide powder 250 parts Carbon black 12 parts Powdered α-Fe ₂ O ₃ powder 10 parts Nitrified cotton 22 parts Polyurethane resin 19 parts Trifunctional low molecular weight isocyanate 7 parts n-butyl stearate 3 parts Myristic acid 6 parts Cyclohexanone 340 parts Toluene 340 parts Next, on the back side of the polyester base film with the magnetic layer formed on the main surface, apply a back coat paint having the following composition to a dry thickness of approximately
A back coat layer was formed by coating and drying to a thickness of 1.0 μm, and then cutting to a predetermined width to produce a videotape of the present invention. Barium sulfate powder with an average particle size of 0.08 μm (Mohs hardness 3.5) 400 parts α-Fe ₂ O ₃ powder with an average particle size 0.10 μm (Mohs hardness 5-6) 100 parts Nitrified cotton 135 Polyurethane resin 94 parts Low trifunctionality Molecular weight isocyanate 40 parts n-butyl stearate 5 parts Myristic acid 10 parts Cyclohexanone 1000 parts Toluene 1000 parts Examples 2 to 9 and Comparative Examples 1 to 3 Non-magnetic powder (barium sulfate powder and α - Fe ₂ O ₃ powder), the 8 types of this invention were prepared in exactly the same manner as in Example 1, except that the non-magnetic powder shown in Table 1 below was used in the proportions shown in the same table. This videotape and three types of videotapes for comparison were made.

[Table] Regarding the video tapes of the above examples and comparative examples, the light resistance, the surface roughness of the back coat layer,
The results of examining video characteristics (color SN ratio), abrasion resistance of the back coat layer, running stability, and abrasion of the tape guide are shown in Table 2 below. In addition, each characteristic was measured and evaluated as follows. <Light resistance> Using a VHS type VTR (video tape recorder), the sample tape was exposed to light with a wavelength of 9000 Å, and its transmittance was measured. <Surface Roughness> The center line average roughness (Ra) of the sample tape was measured using a stylus type surface roughness meter. <Color SN ratio> Using a VHS system VTR, record and play back the one-color chroma signal of a color video noise measuring device on the sample tape, measure the AM noise component, calculate the color SN ratio, and calculate the relative value with the reference tape. It was shown in <Abrasion resistance and tape guide wear> Using a VHS VTR, a practical running test was repeated 100 times on a sample tape recording a 50% gray signal, and the video SN ratio after running was compared to that before running. The amount of decrease was measured. Also, at the same time, VTR
The state of wear of the tape guide and the tape guide of the cassette was visually determined. <Running Stability> Using a VHS-type VTR, run the sample tape 500 times, then observe the deformation of the tape. If no tape deformation is observed, the tape is considered good; if only a little is observed, the tape is considered poor. Cases where the deformation was significant were evaluated as poor.

[Table] As is clear from the results in Table 2 above, the videotape of the present invention has excellent running stability and video characteristics, has less wear on the tape guide, and is also good in light sensitivity and resistance. It turns out that it is excellent.

Claims (1)

[Scope of Claims] 1. A magnetic recording medium in which a back coat layer formed by dispersing and bonding non-magnetic powder in a binder is provided on the back side of a base film having a magnetic layer on the main surface, wherein the non-magnetic powder has a Mohs hardness. A soft inorganic pigment with a hardness of 5 to 6 and a Mohs hardness of 5 to 6, with an average particle size of 1 to 50% by weight in the total amount of soft inorganic pigments
A magnetic recording medium characterized by containing an inorganic pigment consisting of a hard inorganic pigment of 0.2 μm or less. 2. The magnetic recording medium according to claim 1, wherein at least one of the soft inorganic pigment and the hard inorganic pigment comprises a light-resistant inorganic pigment. 3. The hard inorganic pigment is a light-transparent α-Fe ₂ O ₃ powder, and the soft inorganic pigment is a light-transparent powder of at least one kind selected from barium sulfate powder, calcium carbonate powder, and zinc oxide powder. The magnetic recording medium according to claim 2, which is a white inorganic pigment. 4. The magnetic recording medium according to any one of claims 1 to 3, wherein the soft inorganic pigment has an average particle diameter of 0.2 μm or less. 5. The magnetic recording medium according to any one of claims 1 to 4, which contains carbon black in addition to the inorganic pigment as the non-magnetic powder.