JPS59193535A - Magnetic recording body - Google Patents

Abstract

PURPOSE:To improve the durability by using modified nitrocellulose in combination with polyisocyanate and carbon black. CONSTITUTION:The back layer of this magnetic recording body contains carbon black of 50-150mmu average particle size, nitrocellulose and polyisocyanate. The nitrocellulose is prepd. by droping nitrocellulose hydrate by the substitution of a nitrocellulose dissolving solvent other than alcohol for water by azeotropy. The preferred average particle size of the carbon black is 90-100mmu, and the carbon black is used by 5-500pts.wt. per 100pts.wt. binders in the back layer. The back layer contains polyisocyanate besides the nitrocellulose so as to form three-dimensional network structure. The preferred weight ratio between nitrocellulose ad polyisocyanate is 1:10-10:1.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording body provided with a back layer, and particularly to a magnetic recording body having excellent durability.

In recent years, small-sized video tape recorders (hereinafter referred to as VTRs) have become extremely popular and widely used among general amateurs, and video cassettes have come to be used under harsh conditions. Therefore, there was a particular need to improve the durability of magnetic tapes. In order to improve this durability, attempts have been made to improve the winding characteristics of magnetic tape by providing a back layer and incorporating carbon black with a particle size of 10 to 20 mμ into the entire pack layer (especially Kimiaki!λ
-17110/issue). However, such measures did not provide sufficient durability.

On the other hand, various studies have been made regarding the binder used for the back layer.

Conventionally, nitrified cotton has been used as the L-shibinder because of its good wettability. However, since nitrified cotton is flammable, it is necessary to always take precautions against fire when handling it.
In order to maintain the safety of storage and handling, it is required by law to impregnate nitrified cotton with 30 to 30% of isopropyl alcohol, and when the fine particles of nitrified cotton dry, they will be released into the air as feces and explode. are required to prevent it.

On the other hand, when nitrated cotton is combined with a polyisocyanate compound, the non-nitrated hydroxyl groups in the cellulose chains react with the isocyanate groups, forming a partial crosslinking structure. The improvement in mechanical strength due to binding is extremely effective in improving the abrasion resistance required of magnetic tapes. However, when using the reaction with isocyanate groups, polyinsyanate is added so that the hydroxyl groups in the isozorobyl alcohol that is impregnated with the above-mentioned nitrified cotton will crosslink with the nitrified cotton. It reacts with the isocyanate groups of urethane compounds and lowers the degree of crosslinking, reducing the effect of improving the wear resistance, running friction characteristics, etc. of the magnetic recording medium.

In order to overcome all of these drawbacks, nitrified cotton impregnated with isopropyl alcohol is kneaded with a plasticizer such as dibutyl phthalate or dioctyl phthalate or a resin such as salt-vinyl acetate in a kneader, and then mixed with hot twin rolls. After volatilizing the inopropyl alcohol, make a chip of nitrified cotton with the isopropyl alcohol substituted behind a plasticizer or salt-vinyl acetate resin, and place this on a MA with polyurethane resin, etc.
It has also been proposed that a crosslinking agent containing active incyanate groups is added to this to effectively react the isocyanate groups with the main binder to improve mechanical properties.

However, the durability of the 7ζ recording material created using this binder is affected by plasticizers such as dibutyl phthalate, resins such as salt and vinyl acetate, and isopropyl alcohol that remains without being completely removed. This was not sufficient, and there were drawbacks such as poor running due to increased friction during running, squeaks, and dirt on the running system such as falling powder. Nitrified cotton kneaded with salt, vinyl acetate, etc., has little room for choice when considering the binder composition.

Therefore, the inventors of the present invention made extensive studies on improving the binder used in the back layer and on the particle size of carbon black, and as a result, they used improved nitrified cotton.

The present invention was achieved by discovering that durability can be significantly improved by using a combination of polyisocyanate and carbon black.

A first object of the present invention is to provide a magnetic recording medium with improved durability.

The purpose of the λth is to provide a magnetic recording medium that is less prone to dropouts and scratches.

That is, the object of the present invention is to provide a magnetic recording medium in which a magnetic layer is provided on one side of a non-magnetic support and a back layer is provided on the other side.
The back layer has (1) average particle size! O-′-l! Om
μ carbon black, (2) nitrified cotton ↓ and (3) polyisocyanate, and the nitrated cotton is doped by azeotropically replacing water with a nitrified cotton-soluble solvent other than alcohol from water-wet nitrified cotton. Ll) is achieved by using .

The carbon black used in the present invention has an average particle size of 60. /101rLμ, especially? θ~10
Preferably, θmμ.

If the size is small, the durability tends to be poor, while if the size is too large, the unevenness on the surface of the pack layer becomes thick and may be transferred to the surface of the magnetic layer, resulting in deterioration of electromagnetic conversion characteristics.

For carbon black, the total amount of binder in the pack layer is ioo
J-500 parts by weight is preferred, and 10-2 parts by weight.
00 parts by weight is Lp preferably L<,t.

~/jO parts by weight is a particularly preferred range.

The nitrified cotton used in the present invention is prepared by mixing the nitrified cotton with a nitrified cotton-soluble solvent other than the alcohol containing nitrified cotton moistened with water, and azeotropically distilling the mixture to replace the water content to form a nitrified cotton dope (hereinafter referred to as NC dope). ). Such solvents include methyl ethyl ketone, methyl isobutyl ketone, ethylseron rub acetate, cyclohexanone, ethyl acetate, butyl acetate, toluene, xylene, and the like.

Nitrified cotton that is mainly used for paints can be used.

It is defined as JIS Kb7os-19Au'i "Standard for industrial nitrocellulose". The nitrogen content is divided into two grades: rLJ and rHJ, and the former is [10.7 or higher].

The latter is defined as "less than 11.!/2 degrees, up to 2 degrees". This is because high nitrogen content increases the danger of handling.

This is not preferable, and if the amount is too low, the solubility in organic solvents will be poor and the effects of the present invention will not be obtained.

The viscosity is also determined by the above-mentioned JIS, and the falling time (seconds) is from 17i4 to 2004. Although any one can be used, 1iit-aθ is preferable in order to obtain the effects of the present invention, and / /1. II O is well-crafted, 174
t-20 is more preferred.

The type of nitrified cotton is "L, 20" which contains nitrogen content and viscosity.
, rl-J//2J.

In addition to the above-mentioned nitrified cotton, the back layer of the present invention contains polyisocyanate in order to form the components of this layer into a three-dimensional network structure. The weight ratio of nitrified cotton and polyisocyanate is /:1
0 to lθ:l is preferred.

l:! ~! :L is preferably rainbow.

The polyisocyanates used in the present invention include, for example, tolylene diisocyanate, xylylene diisocyanate,
Diisocyanate 3 such as hexamelene diocyanate
reaction product of 7371 moles of trimethylolpro, biuret adduct of 3 moles of hexamethylene diisocyanate, isocyanurate adduct of 3 moles of tolylene diisocyanate and comol of hexamethylene diisocyanate, polymer of diphenylmethane diisocyanate Compounds, etc.

These compounds are from Nippon Polyurethane KK.

``Desmodule L'' is produced by Sumitomo Bayer Urethane KK under trade names such as ``Coronate L'', ``Coronate HLJ'', ``Coronate 2030'', ``Millionay'' MRJ, and ``Millionay) MTLJ''.

"Takene" D-102, manufactured by Takeda Pharmaceutical Co., Ltd. under the trade names of "Tesmodule NJ,""DesmoduleILj,""Desmodule HL 10, etc."

"Takenate D-iioN", [Takenate D-202
Each is commercially available under the trade name J.

tx and inphorone diisocyanate are also excellent in terms of pot life, dispersibility, etc.

For information on polyisocyanates, please refer to Tokkai Sho! Ko 1orro
It is stated in item a etc.

Additives for the back layer include inorganic pigments such as magnesium silicate, calcium carbonate, aluminum silicate, barium sulfate, and clay; organic particles such as benzoguanamine resin; abrasives and surfactants used in the magnetic layer described below. agent,
Can be used with lubricants etc. as required.

The magnetic recording medium of the present invention is published by JPO! Call lθrt.

It can be prepared by using the material described in No. μ-jM method or the like.

The present invention will be explained below using Examples, but the present invention is not limited to these Examples.

In the following examples, all parts are by weight.

Example I Co biasing force 0γFe zQ 3 3θO part (
Particle size 0.3! μ, axial ratio /:, l', anti-boring force jjjOOel salt vinyl acetate co-weight saving 55 parts (vinyl chloride vinegar bead 7 = / 3; degree of polymerization ≠, 20) polyester polyurethane 30 parts (butylene acetate is one ton) , sweetened from Hiro'-diphenylmethane diisocyanate, styrene equivalent molecular weight approximately 130,000) α-A120a /- 1 part lecithin 3 parts liquid paraffin 3 parts butyl acetate
100 parts of the above composition were placed in a ball mill, and after qt hours, 30 parts of a linear prepolymer with terminal isocyanate was added and dispersed for 30 minutes, followed by passing through a filter with an average pore diameter of lμ to obtain a magnetic paint.

This was coated with a back layer having the following composition on a polyethylene terephthalate film with a thickness of 'fC/Hiromu using a doctor method, oriented in a magnetic field in the length direction, calendered, and then slit to a width of 172 inches to form a videotape. . (Sample flat) Carbon black 300 parts ("Furnace black" average particle size ≠ mμ) Nitrified cotton dope ago part frH/
733 parts (1 mol) of polyisocyanate (solid content 7I of an adduct of 1 methylolpro/gum and 3 mol of toluylene diynonate) Ethyl acetate solution #) Methyl ethyl ketone, 200 parts Methyl isobutyl ketone, zooo parts Dispersion of pack layer composition 1d Silk composition excluding polyisocyanate O
H-boru mill treatment, addition of polyisocyanate 2,
After adjusting the viscosity, it was filtered by kg (3μ filter) and coated.

The coating thickness of the magnetic layer is 1.5 mm, and the coating thickness of the back layer is 1.5 mm.
jμ.

Comparative Example 1 A comparative sample was prepared using the following nitrified cotton in place of the nitrified cotton in the back layer composition of Example 1 (also.

(11R8//2 seconds, samples obtained using nitrified cotton impregnated with 30 parts of isopropyl alcohol are sample A, 2
shall be.

(2) R8172 seconds, sample A was obtained by completely replacing the contained isopropyl alcohol with 30 times dibutyl phthalate.
3.

(3) R8z/x seconds, nitrification in which 30 g of isopropyl alcohol was replaced with salt-vinyl acetate copolymer! The sample obtained by using the 87θ type is used as a sample plate.

Comparative Example 2 Sample &j was prepared by removing the polyisocyanate from the 1-pack layer composition in Example IK and increasing the amount of NC dope having the same solid content weight.

Comparative Example 3 In Example IK, a sample &t was prepared in which the particle size of carbon black in the composition of Bag 10 was λθmμ.

Example 2 In Example 1, the size of carbon black was changed to sample &7 (Y01rLμ), 5g (l!Omμ)
was prepared.

Example 3 In Example 1, the binder of the back layer was polyurethane (average molecular weight lθ 1,000, butanediol/adipic acid/
In order to introduce 0 parts of Ir (toluene diisocyanate) and to keep the total amount of binder (solid content) constant, a sample plate was prepared in which the weight was reduced in proportion to the nitrified cotton dope.

Tape Sample Edition/~AA was incorporated into a video cassette and its durability was evaluated. The VTR used was a VH8 system V 1'R, which was used to examine the durability of the pack layer from the viewpoint of differences in running system.
J:9 also has a harsh rating Betaformatsu) VTR'
It was used for. The results are shown in Table 1.

The evaluation method will be briefly explained below.

The dropout was left in the low-temperature thermo room of the VTRt-j'C dry, and the evaluation tape was repeatedly run through f200 passes, then the signal was recorded/played and displayed on the monitor.
The number of pieces per minute was visually measured for H or higher. Less tape has superior durability.

The number of scratches was determined by running the VTR under the conditions of go 'C and go% RH and observing the puncture layer surface of the tape with a microscope with a magnification of 2 to after running the VTR for -200 passes.
) There were a lot of scratches. The fewer the number, the more durable it is.

Table/L#) As is clear, the durability of the fresh example sample 4/ according to the present invention is significantly superior to that of the other comparative examples.

Claims (1)

[Claims] In a magnetic recording medium in which a magnetic layer is provided on one side of a nonmagnetic support and a back layer is provided on the other side, the back layer has (1) an average grain size of 30-/! 0rrLμ carbon black, (2
) nitrified cotton and (3) polyisocyanate, the nitrified cotton is doped by azeotropically substituting xp water from wet nitrified cotton with a nitrified cotton-soluble solvent other than alcohol. body.