JPH0359486B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a magnetic recording medium, and more particularly to a magnetic recording medium with excellent running characteristics in which the back layer on the opposite side to the side where the magnetic layer is formed is made of a specific resin. (Prior Art) Conventionally, magnetic recording media such as magnetic tapes used in audio equipment, video equipment, computers, etc. are made of magnetic powder and binder resin on one side of a non-magnetic support such as a polyester film. This is achieved by forming a magnetic layer and also forming a back layer for improving running stability of these tapes, reducing frictional resistance between the tapes, or improving charging characteristics. As a resin for forming the back layer of such a magnetic recording medium, vinyl chloride resin, polyurethane resin, polyester resin, nitrocellulose resin, epoxy resin, etc. are generally used. In addition, in the magnetic recording medium as described above, the surfaces of the magnetic layer and the back layer are smooth in order to increase the recording speed, increase the recording density, and reduce the size and weight of the device.
In addition, it is required to be wear resistant so that it can withstand repeated use many times. (Problems to be Solved by the Invention) However, the back layer formed using the above-mentioned resin has a friction coefficient of approximately
0.4 or higher, when the magnetic recording medium is for video tape or audio tape, the slip properties of these tapes are poor and irregular winding may occur when winding or rewinding the tape. ,the result,
This causes deformation and damage to the tape, causing dropouts. In order to solve these drawbacks, attempts have been made to reduce the coefficient of friction of the back layer by adding lubricants such as fatty acids, wax, and silicone oil to the back layer. The greater tendency to bleed onto the surface creates another problem: clogging of the recording head. As another method, it has been proposed to form the back layer using a polyurethane resin having siloxane bonds in the molecule as the resin (for example, JP-A-57-176536, JP-A-58-222436, JP-A-59 −
(See Publication No. 82636, etc.) However, the back layer formed using such a resin is susceptible to frictional heat generated between the tapes during high-speed use such as during rewinding or fast forwarding.
The back layer tends to soften, and therefore, when used continuously for a long time, the softening increases the coefficient of friction, causing the above-mentioned problems. In order to solve these drawbacks, it has been proposed to add a cross-linking agent such as polyisocyanate to the paint for forming the back layer when forming the back layer. , they tend to change over time, causing problems with their pot life. The present inventor has conducted intensive research to solve the above-mentioned drawbacks of the prior art and to obtain a magnetic recording medium that has a high softening point, a low coefficient of friction, and can therefore be used at high speeds and repeatedly used many times. The present invention was completed based on the finding that the above-mentioned drawbacks of the prior art can be solved by using a specific resin as the resin forming the back layer of a magnetic recording medium. (Means for solving the problems) That is, the present invention consists of a non-magnetic support, a magnetic layer provided on one side of the support, and a back layer provided on the other side of the support, The magnetic recording medium is characterized in that the resin forming the back layer is a polyurea resin having a siloxane bond in the molecule. Next, to explain the present invention in more detail, the resin used in the present invention and which mainly characterizes the present invention was developed for the first time by the present inventor, and is a polyurea resin having a siloxane bond in its molecule. The above polyurea resin can be easily produced from a polysiloxane polyamine having two or more amino groups in one molecule and a polyisocyanate compound having two or more isocyanate groups in one molecule according to conventional polyurea resin manufacturing methods. Obtainable. Preferred as the above polysiloxane polyamine is polydialkylsiloxane diamine, which can be represented by the following general formula. R in the above formula is an aliphatic, aromatic, or aliphatic divalent group, and preferred in the present invention is a C ₁ to C ₆ alkyl group or a C ₆ to _{C 10} aromatic group. . Further, R' is an alkyl group, and a methyl group is preferred in the present invention. m is a value such that the average molecular weight of the polysiloxane diamine of the above general formula is about 500 to 10,000, and particularly preferred in the present invention is a value where the average molecular weight is about 500 to 10,000.
1000-5000. Incidentally, such polysiloxane diamine can be used alone or as a mixture, and furthermore, in order to adjust various physical properties such as breaking strength, breaking elongation, hardness, etc. of the resulting polyurea resin, other general diamine or more functional compounds may be used. A polyamine can be used in combination as a copolymerization component. Other common polyamines such as
1 per mole of the above polysiloxane polyamine
Preferably, it is used in submolar amounts. The polyisocyanate compound to be reacted with the polysiloxane polyamine is a general polyisocyanate compound conventionally used in the production of polyurethane resins, such as toluene-2,4-diisocyanate, 4-methoxy-1,3-phene, etc. Nylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 4-butoxy-1,3-phenylene diisocyanate, 2,4-diisocyanate-diphenyl ether, mesitylene Diisocyanate, 4,4-methylenebis(phenyl isocyanate), diylylene diisocyanate, 1,5-naphthalene diisocyanate, benzidine diisocyanate, o-nitrobenzidine diisocyanate, 4,4-dibenzyl diisocyanate, 1,4-tetramethylene diisocyanate, Examples include 1,6-tetramethylene diisocyanate, 1,10-decamethylene diisocyanate, 1,4-cyclohexylene diisocyanate, xylylene diisocyanate, 4,4-methylenebis(cyclohexyl isocyanate), and 1,5-tetrahydronaphthalene diisocyanate. The polyurea resin used in the present invention can be obtained by reacting the above-mentioned polysiloxane and polyisocyanate by a conventionally known method. Preferably, the amount is about 5 to 50% by weight in 100 parts by weight. The amount of silicon atoms can be adjusted by adjusting the average molecular weight of the polysiloxane polyamine to be used. Further, there is a method of using other polyols such as ethylene glycol, propylene glycol, polyether polyol, polyester polyol, etc. in combination. When the amount of silicon atoms in the resulting polyurea resin is less than about 5% by weight, when the back layer is formed, the coefficient of friction of the surface of the back layer can be adjusted to a desired value, that is, about 0.3.
On the other hand, if the amount of silicon atoms exceeds 50% by weight, the solubility and flexibility of the resulting polyurea resin in organic solvents will decrease, making it undesirable as a resin for forming the back layer. It disappears. The production of the polyurea resin as described above can be carried out according to a conventionally known method for producing polyurea resin. For example, the above components are mixed with an organic solvent and/or
or in the presence or absence of a catalyst, from about 0 to
The polyurea resin used in the present invention is obtained by reacting at a temperature of 100° C. for about 0.5 to 3 hours. A preferred method is a method in which the polyurea resin to be produced is dissolved in an organic solvent. The magnetic recording medium of the present invention has the following features except that the specific polyurea resin as described above is used to form the back layer.
All methods may be conventionally known. For example, the magnetic layer can be formed by adding a conventionally known binder resin for magnetic layer formation into an organic solvent together with magnetic powder, and preparing a dispersion using a dispersant as necessary. , can be obtained by coating this dispersion on a support and drying it to form a magnetic layer. Conventionally known materials and methods may be used for the organic solvent, magnetic powder, support, coating, drying method, etc. used in this case. For example, as binder resins, vinyl chloride-vinyl acetate copolymers, cellulose resins, epoxy resins, polyvinyl butyral resins, polyurethane resins, synthetic rubber resins, acrylic resins, polyester resins, etc. are used. Ru. In addition, preferred organic solvents include:
For example, methyl ethyl ketone, methyl-n-propyl ketone, methyl isobutyl ketone, diethyl ketone, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, butyl acetate, acetone, cyclohexane, tetrahydrofuran, dioxane, methanol, ethanol, isopropyl alcohol , butanol, methyl cellosolve,
Butyl cellosolve, cellosolve acetate, dimethyl formamide, dimethyl sulfoxide, pentane, hexane, cyclohexane, heptane, octane, mineral spirits, petroleum ether, gasoline, benzene, toluene, xylene, chloroform, carbon tetrachloride, chlorobenzene, perchloroethylene, trichlor Examples include ethylene. In addition, examples of magnetic powder include γ-Fe ₂ O ₃ ,
Cobalt-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ Cobalt-containing
Any conventionally known magnetic powder such as Fe ₂ O ₃ , CrO ₂ , Fe, Fe-Ni alloy, Co-Ni-P alloy, Fe-Co-Ni alloy can be used. For these magnetic powders, binder resin is used at a ratio of about 10 to 40 parts by weight per 100 parts by weight of magnetic powder, and the solid content of the resulting coating liquid is about 20 to 40 parts by weight.
The amount is preferably 40% by weight. In addition, any conventionally known support can be used, such as polyester film, polypropylene film, etc. with a thickness of 5 to 50 μm,
Cellulose triacetate film, cellulose diacetate film, polycarbonate film, etc. can be used arbitrarily. The magnetic layer is formed by applying the above-mentioned coating solution onto one side of the above-mentioned support to a dry thickness of about 5.
It can be formed by coating by any method to a thickness of ~20 μm and then drying. The magnetic recording medium of the present invention can be obtained by forming a back layer using the above-mentioned specific polyurea resin on the back side of the magnetic recording medium obtained by the conventionally known method as described above. Formation of such a back layer is carried out by dissolving the above-mentioned polyurea resin in the above-mentioned organic solvent to a concentration of about 10 to 50% by weight to prepare a coating solution, applying this coating solution to the back side of the support, and drying. This is done by applying the coating to a thickness of about 5 to 50 μm and drying it. Various conventionally known coating methods can be used as they are, and drying is performed at about 50 to 120°C for about 0.5 to 2 hours. In addition to the polyurea resin used above, conventionally used resins such as polyurethane resin and polyester may be used in combination to adjust the Young's modulus and improve adhesion, and antistatic agents may also be used. Various additives such as these can also be used in combination. In the above description, the magnetic layer is first formed and then the back layer is formed, but the same effect can be obtained by forming the back layer first and then forming the magnetic layer. (Function/Effect) In the magnetic recording medium of the present invention obtained as described above, the back layer is formed from a polyurea resin containing siloxane bonds in its molecules. As demonstrated in the examples, the coefficient of friction of the material is very low, and the softening point is very high. This remarkable effect is thought to be due to the fact that the polyurea resin used in the present invention has stronger hydrogen bonds between urea bonds than conventional polyurethane resins containing siloxane bonds. There is. Therefore, the magnetic recording medium of the present invention exhibits extremely superior tape running properties compared to conventional magnetic recording media, and even when used continuously for a long time, the back layer does not soften due to frictional heat. It can be used extremely stably without causing any damage. The present invention will be explained in more detail with reference to the following Examples and Comparative Examples. In the text, parts and percentages are based on weight. Example 1 (Synthesis of polyurea resin) 150 parts of dimethylpolysiloxane diamine (average molecular weight 3880) of the above formula and 10 parts of 1,3-propylene diamine were added to 250 parts of dimethylformamide, and the mixture was mixed with a stirrer, a reflux condenser,
Charge into a reactor equipped with a dropping funnel and gas introduction tube. Cool the contents externally to bring the internal temperature to 0 to -5℃
Then, while maintaining this temperature, carbon dioxide gas continues to flow through the gas introduction pipe. Next, a solution of 15 parts of hydrogenated MDI dissolved in 65 parts of dimethylformamide was dropped into the reactor through the dropping funnel to cause a reaction. After dropping, the internal temperature was gradually raised, and when it reached 50℃, it was kept for 1 hour.
Stirring was continued at 50°C. The resulting polyurea resin solution has a solids content of 35%.
It had a viscosity of 15,000 cps (25°C). The breaking strength (Kg/cm) of the film formed from this solution was 450℃, the breaking elongation (%) was 550,
Moreover, the softening point was 150°C or higher. Example 2 (Synthesis of polyurea resin) 150 parts of the polysiloxane diamine in Example 1 having an average molecular weight of about 1000 were mixed with 100 parts of dimethylformamide and 150 parts of methyl ethyl ketone.
A polyurea resin solution was obtained in the same manner as in Example 1 except that 39 parts of hydrogenated MDI was added to 100 parts of methyl ethyl ketone. The solids content of this solution is 35% and 10000cps (25
℃). The film formed from this solution had a breaking strength (Kg/cm) of 210, a breaking elongation (%) of 650, and a softening point of 150°C or higher. Comparative Example 1 (Synthesis of conventionally known binder resin) Adding 150 parts of polydimethylsiloxane diol and 10 parts of 1,3-propanediol represented by the above formula and having an average molecular weight of about 3200 to a mixed organic solvent consisting of 200 parts of methyl ethyl ketone and 50 parts of dimethylformamide, Further, a solution of a polyurethane resin having siloxane bonds was obtained in the same manner as in Example 1 except that a solution of 47 parts of hydrogenated MDI dissolved in 134 parts of dimethylformamide was used. The solids content of this solution is 35% and 13000cps (25
℃). The film formed from this solution had an elongation at break (Kg/cm) of 200, a strength at break (%) of 560, and a softening point of 100°C or less. Comparative Example 2 (Synthesis of conventionally known binder resin) Same structure as Comparative Example 1, but with an average molecular weight of approx.
150 parts of 1000 polydimethylsiloxane diol
Dissolved in 250 parts of methyl ethyl ketone and also 39
A polyurethane resin solution having siloxane bonds was obtained in the same manner as in Comparative Example 1 except that 1 part of hydrogenated MDI was dissolved in 100 parts of methyl ethyl ketone. The solid content of this solution is 35% and 11600 cps (25
℃). The film formed from this solution had a breaking strength (Kg/cm) of 90, a breaking elongation (%) of 700, and a softening point of 100°C or less. Comparative Example 3 (Synthesis of conventionally known polyurethane resin) Polybutylene adipate with an average molecular weight of approximately 2000
150 parts of 1,3-propanediol are dissolved in a mixed organic solvent consisting of 120 parts of methyl ethyl ketone and 130 parts of dimethyl formamide, and 55 parts of hydrogenated MDI are dissolved in 150 parts of methyl ethyl ketone. However, a polyurethane resin solution was obtained in the same manner as in Example 1. The solid content of this solution is 35% and 14500 cps (25
℃). A film formed from this solution had a breaking strength (Kg/cm) of 250, a breaking elongation (%) of 500, and a softening point of 100°C or less. The softening point above was determined by cutting the film into strips, attaching an awl to the bottom end of the film to give a weight of 450 g/ ^cm2 , hanging it in a gear oven, and then raising the temperature at a rate of 2°C/min. , the temperature at which the elongation of the film suddenly increases or when the film is cut. Examples 3 to 4 and Comparative Examples 4 to 6 Paints consisting of the following ingredients were prepared, and the thickness
It was applied to one side of a 15 μm polyester film to a dry thickness of 1 μm, and the solvent was dried to form a back layer. Next, Co-containing γ-
A magnetic layer is formed on the opposite surface using a binder resin consisting of Fe ₂ O ₃ , ordinary polyurethane resin, and vinyl chloride copolymer resin, and cut to a predetermined width to form the video magnet of the present invention. A recording medium and a video magnetic recording medium for comparison were prepared. Example 3 100 parts of the resin solution of Example 1 Vylon-200 (polyester resin manufactured by Toyobo Co., Ltd.)
5 parts Methyl ethyl ketone 1200 parts Example 4 Resin solution of Example 2 100 parts Vylon-200 (Polyester resin manufactured by Toyobo Co., Ltd.)
5 parts Methyl ethyl ketone 1200 parts Comparative example 4 Resin solution of Comparative example 1 30 parts Vylon-200 (Toyobo polyester resin)
5 parts Methyl ethyl ketone 1200 parts Comparative example 5 Resin solution of Comparative example 2 30 parts Vylon-200 (Polyester resin manufactured by Toyobo Co., Ltd.)
5 parts Methyl ethyl ketone 1200 parts Comparative example 6 Resin solution of Comparative example 3 30 parts Vylon-200 (Toyobo polyester resin)
5 parts Methyl ethyl ketone 1200 parts Evaluation The friction coefficients and running characteristics of the tapes obtained in Examples 3 to 4 and Comparative Examples 4 to 6 were as follows.

[Table] In the above, the friction coefficient is a measured value between the surface of each magnetic layer and the support (base film). Other performance tests were carried out as a videotape, and observations were made of the tape's squeal, jitter, lateral wobbling, tape winding during fast forwarding, and wear of the magnetic layer during 200 runs. From the above results, it is clear that the magnetic recording medium of the present invention has a lower friction coefficient of the back layer and a significantly higher softening point than conventional magnetic recording media, and thus has excellent running characteristics. It is.

Claims (1)

[Claims] 1 Consists of a non-magnetic support, a magnetic layer provided on one side of the support, and a back layer provided on the other side of the support, and the resin forming the back layer has siloxane bonds in its molecules. A magnetic recording medium characterized by being made of a polyurea resin.