JPS6216231A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium which is improved in the dispersion of a nonmagnetic solid additive in a back coat layer and has excellent running stability and electromagnetic conversion characteristic by forming the back coat layer contg. at least the above-mentioned additive and prescribed org. compd. on the rear surface of a base having a magnetic layer on the main surface. CONSTITUTION:The back coat layer contg. the nonmagnetic powder such as TiO2 powder, ZnO powder, Al2O3 powder or others having about 0.05-2mum particle size and 3-8 Mohs' hardness and a silane coupling agent for incorporation of the org. compd. contg. the group expressed by the formula (where R1 is an alkyl group, R' is an alkylene group, m is >=1 integer, n is 0-5 integer) is formed on the rear surface of the base having the magnetic layer on the main surface. The org. compd. expressed by the formula is stuck and formed on the surface of the solid additive by the hydrolysis of the silane coupling agent. The dispersibility and dispersion stability of the solid additive are thereby improved and the running stability and electromagnetic characteristic are improved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magnetic recording medium such as a magnetic tape, which is formed by providing a back coat layer containing a non-magnetic solid additive on the back side of a base having a magnetic layer on the main surface. Regarding.

[Prior art] In order to improve the running stability of a magnetic tape, a back coat layer containing a non-magnetic solid additive is provided on the back side of a smooth-surfaced base such as a polyester film that has a magnetic layer on its main surface. The method used is to roughen the surface. Various inorganic powders such as titanium oxide (TiO2) powder, zinc oxide (ZnO) powder, and alumina (AI!203) powder are used as the above additives, but these additives are generally combined with binder resin. Due to poor affinity and poor dispersion within the bank coat layer, the surface of the back coat layer may become excessively rough, and particles tend to fall off during running, which may result in poor running performance. There were drawbacks such as not being able to sufficiently improve stability and impairing electromagnetic conversion characteristics.

By the way, as a means to improve the dispersibility of the magnetic powder in the magnetic layer, it is common practice to surface-treat the magnetic powder with a surface-treating agent.A particularly effective surface-treating agent is a silane coupling agent. is known (Japanese Unexamined Patent Publication No. 59-129938, No. 58-155703)
Publications, etc.). If such a surface treatment agent is applied to the solid additive for the back coat layer, that is, if the additive is surface treated with the treatment agent, the dispersibility of the additive in the back coat layer will be improved. It is expected that

[Problem to be Solved by the Invention J] However, the above-mentioned conventionally known silane coupling agents all have amino groups and epoxy groups in their molecules.

Most of them have reactive groups such as incyanate groups, and such reactive groups are polar groups normally contained in binder resins, such as carboxyl groups.

Because a chemical reaction occurs with hydroxyl groups, etc., the viscosity of the paint for the back coat layer increases abnormally, which may actually impair the dispersibility of the solid additive.

Therefore, the present invention improves the dispersibility of this additive in the back coat layer by applying a specific silane coupling agent that is different from the above-mentioned conventionally known surface treatment agents to the solid additive in the back coat layer. An object of the present invention is to obtain a magnetic recording medium such as a magnetic tape which has improved running stability and excellent electromagnetic conversion characteristics.

[Means for solving problems]

As a result of intensive studies to achieve the above object, the inventors found that when a specific silane coupling agent having an alkylene oxide group in the molecule was used as a surface treatment agent for solid additives in the back coat layer, , a back coat layer containing the above additive and an organic compound containing a specific group derived from the above silane coupling agent is obtained, and in this case, thickening of the paint for the back coat layer due to reaction with the binder resin is obtained. The inventors discovered that the affinity and dispersibility of the additive for the binder resin were significantly improved without causing any damage to the binder resin, and that a magnetic recording medium with excellent running stability and electromagnetic conversion characteristics could be obtained. It was completed.

That is, this invention provides at least a non-magnetic solid additive on the back side of a base having a magnetic layer on its main surface and the following formula: % formula % [) (wherein R1 is an alkyl group, R' is an alkylene group m is an integer of 1 or more, and n is an integer of O to 5). .

[Structure and operation of the invention] In the present invention, the silane coupling agent used to include the organic compound containing the group represented by the formula (+) in the back coat layer together with the non-magnetic solid additive is as follows. Formula; % Formula % C In the formula, R,, R2, R3 are an alkyl group, R' is an alkylene group, e is an integer of 1 to 3, m is an integer of 1 or more, n is 0
This silane coupling agent does not have a reactive group that reacts with the binder resin, such as an amine group, an epoxy group, or an incyanate group, in its molecule.
Even when a binder resin containing a reactive group such as a hydroxyl group, a carboxyl group, or an incyanate group is used, there is no risk of thickening of the paint for the back coat layer.

Moreover, the above-mentioned silane coupling agent has the property of easily reacting and adsorbing onto the surface of the solid additive due to the hydroxyl group generated by hydrolysis of the alkoxy group (OR2 group) contained in its molecule, and this adsorption causes the above-mentioned A small amount of an organic compound (containing a group represented by formula +11 above) is deposited on the surface of the additive.

By adjusting the type of alkylene oxide and the number of moles added in the alkylene oxide structural part represented by RO in this deposit, good affinity for the binder resin and organic solvent can be imparted to the solid additive. be able to.

Therefore, even when various binder resins are used, the dispersibility of the solid additive and its dispersion stability are significantly improved.

Among the above-mentioned silane coupling agents that exhibit such effects, dialkoxy type agents in which 1 in formula (2) is 2 or trialkoxy type agents in which 1 is 3 are preferred.

In addition, R' in the above formula 〇), +21 is an alkylene group usually having 2 to 4 carbon atoms, and the repeating unit represented by R'0 is an ethylene oxide group and a propylene oxide group.
It may be composed of a mixture of at least two of -oxide groups and butylene oxide groups. When it is composed of a salt compound, each unit may be randomly assigned or may be a block, and the order in which the blocks are added is not particularly limited. In addition, m indicates the number of repeating units, usually 1 to 30. The number is preferably 5 to 15.

In addition, R,, R2, R3 in the above formula fl+, +2)
is an alkyl group having 1 to 3 carbon atoms, and the number of carbon atoms in each alkyl group may be the same or different.

n represents the repeating number of methylene group (-CH2-) and is 0
It can be arbitrarily selected from the integers of ~5. n=
=o, the alkylene oxide group (R'O) is S
It has a structure in which it is directly bonded to the i atom.

Such silane coupling agents are also available as commercial products, and the method for producing them is not particularly well-known. For example, an alkoxysilane compound can be prepared by adding an alkylene oxide and then converting it into an alkyl ether, or by using method C, such as introducing an alkylene group that directly bonds to Si molecules by an appropriate means before adding the alkylene oxide. can be obtained easily.

) In this invention, the amount of the silane coupling agent used is preferably 01 to 20 parts by weight, preferably 2 to 10 parts by weight, per 100 parts by weight of the nonmagnetic solid additive. If the amount used is too small, a sufficient effect of improving dispersibility cannot be obtained, and if it is too large, the surface roughness of the back coat layer cannot be made to an appropriate level or durability may be lowered, which are both undesirable.

In this invention, as a means for incorporating an organic compound containing a group represented by the above formula (!) into the back coat layer using the above silane coupling agent, a non-magnetic solid additive, a binder resin and an organic A method is adopted in which a silane coupling agent is added to the back coat layer paint containing a solvent, and this back coat layer paint is applied to the back of the base, which has a magnetic layer on the main surface, to form the back coat layer. However, in general, a non-magnetic solid additive is treated in advance with a run coupling agent to attach an organic metal compound containing a group represented by the above formula t1 to the particle surface of the additive. It is preferable to prepare a coating material for a back coat layer using the powder of this powder, and then form a bank coat layer in the same manner as described above.

The latter method has been found to be particularly effective in improving dispersibility, since a more uniform layer of the organic compound can be deposited on the surface of the solid additive. In this latter method, a solution is prepared by dissolving the silane coupling agent in an appropriate solvent, the solid additive is added to this solution, mixed and dispersed using a homomixer, etc., and then heated and dried to remove the solid additive. A predetermined amount of the organic compound derived from the silane coupling agent is attached to the surface of the particles.

Examples of solvents for dissolving the above silane coupling agent include water, alcohols having 1 to 5 carbon atoms, acetone, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, benzene, toluene, etc. Examples include aromatics and ethers such as tetrahydrofuran and dioxane. Among these, alcohols having 1 to 5 carbon atoms give particularly good results to the dispersibility of the final target non-magnetic solid additive.

The concentration of the silane coupling agent in these solvents is as follows:
Although it varies considerably depending on the type of solvent, generally 0,1
The content is preferably about 2.0% by weight, particularly preferably about 0.5% to 1% by weight.

Next, the non-magnetic solid additive applied to this invention has a particle size of about 0.05 to 2μ and a Mohs hardness of 3 to 2μ.
No. 8 non-magnetic inorganic powder is used.

For example, titanium oxide (TiO□) powder, zinc oxide (ZnO
) powder, alumina (AI!203) powder, chromium oxide (c
r203) powder, mullite (3AI!203・2 S 1
02) Powder, aluminum titanate (Al2O3・Ti0
2) Powder, α-Fe203 powder, zircon (Zr02・5i
O2) powder, forsterite (2MgO-3ioz)
powder, beryl (3BeO-A1203・6SiO□) powder,
Spodumene (Li20-A1203・4SiO,1
Powder, eucryptite (Li20・Ag2O,・2Si
O□) powder, barium sulfate (BaSO<) powder, calcium carbonate (CacO3) powder, cordierite (2Mg0
2A1203・5S 1o2) powder, enstatite (
MgO・SiO□) powder, Saphirin (4Mg0-5A7
7203-25i02) powder, Celsian (BaO・Al
2O3・25102) powder, Petalite (Li20・A7
? 203.8SiO2) powder, which has been conventionally added to the back coat layer for the purpose of improving running stability, is widely included. Among these, from the viewpoint of exhibiting a strong bonding force with the silane coupling agent,
Particularly preferred are barium sulfate powder, calcium carbonate powder, zinc oxide powder, alumina powder, titanium oxide powder, α-Fe203 powder, and the like. This solid additive is binder resin 10
It is usually used in a ratio of 50 to 200 parts by weight to 0 parts by weight.

The binder resin for dispersing and binding the above-mentioned solid additives is preferably one that has excellent adhesion to the base and abrasion resistance, such as vinyl chloride-vinyl acetate copolymer, polyvinyl butyral resin, Any conventional binder resin such as cellulose resin, polyurethane resin, polyester resin, polyisocyanate compound, etc. can be used. Further, various electron beam curable resins can also be used.

Furthermore, organic solvents for preparing the paint for the back coat layer include cyclohexanone, methyl ethyl ketone,
Ketone solvents such as methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, aromatic hydrocarbon solvents such as benzene, toluene, and xylene, alcohol solvents such as isopropyl alcohol, and acid amide solvents such as dimethylformamide. There are no particular restrictions on the solvents suitable for dissolving the binder resin used, such as sulfoxide-based solvents such as dimethyl sulfoxide, and ether-based solvents such as tetrahydrofuran and dioxane.
Used alone or in combination of two or more.

Needless to say, the back coat layer paint containing such non-magnetic solid additives, binder resin, organic solvent, and the silane coupling agent may contain commonly used additives, such as A lubricant, an antistatic agent in the form of ultrafine particles such as carbon black, etc. may be added as appropriate. Also, amine groups and hydroxyl groups that react with the binder resin in some cases.

A silane coupling agent containing a functional group such as an isocyanate group or an unsaturated bond group can also be used in combination without significantly impairing the characteristics of the present invention.

The magnetic recording medium of the present invention is generally produced by coating a backcoat layer paint made of such components on the back side of a base such as a polyester film having a magnetic layer on the main surface.
, by forming a back coat layer of about 2 to 2 pm, and the surface treatment (mirror finish treatment) that is usually adopted after that.
It can be obtained by performing a cutting process and the like.

The magnetic layer provided on the main surface of the base may be a vapor-deposited metal magnetic thin film, or a magnetic coating film formed by applying a magnetic paint containing magnetic powder and binder resin. good. Examples of the magnetic powder in the latter magnetic coating include T-Fe203 powder, Fe50. Powder, Co
In addition to oxide-based magnetic powders such as T-Fe203 powder, Co-containing Fe3O4 powder, hexagonal ferrite powder such as barium ferrite and strontium ferrite, metal powders such as Fe powder, Co powder, and Fe-Ni powder, etc. Can be mentioned.

Further, the binder resin and the organic solvent for preparing the magnetic paint can be appropriately selected from those listed for the back coat layer.

〔Effect of the invention〕

As detailed above, in this invention, the specific organic compound derived from the silane coupling agent is contained in the back coat layer using the specific silane coupling agent. Even when various binder resins are used in the preparation of paints, the dispersibility of non-magnetic solid additives can be greatly improved without causing the problem of agglomeration. Since it is possible to form a back coat layer with excellent abrasion resistance and less powder falling, it is possible to provide a magnetic recording medium that can improve running stability and electromagnetic conversion characteristics.

〔Example〕

Next, examples of the present invention will be described in more detail. In addition, in the following, parts shall mean parts by weight. Moreover, the silane coupling agents A to D used in the following examples and comparative examples are as follows.

<Silane coupling agent A> CH30÷EO←PO←CH2urS i (-0CR
3) 3EO: Ethylene oxide PO: Propylene oxide (silane coupling agent B) CH30+PO什CH2-+-8i+0CH3)3PO
: Propylene oxide silane coupling agent C> CH30 (-EO廿→CH2-+VS i÷0CH3)
3EO: Ethylene oxide (silane coupling agent D) H2N + CH2Sr + QC2Hs)a Example 1 Titanium oxide powder (average particle size 0.07p) 100 parts Zinc oxide powder (average particle size 0.27") 100 parts Silane coupling agent A 2Cl isopropyl alcohol 2,000 parts The dispersion containing the above components was mixed and dispersed in a homomixer for 4 hours, allowed to stand still for 24 hours, and then filtered.Then, the surface was dried for 15 hours in SO'C. A treated mixed solid additive was obtained. On this treated additive, 1 to 6 parts of an organic compound derived from silane coupling agent A per 100 parts of each powder was uniformly adhered.

Using the above-mentioned surface treatment mixed solid additive, a paint for a back coat layer was prepared by mixing and dispersing in a ball mill for about 100 hours with the following formulation composition.

Surface treatment mixed solid additive 200 parts Nitrified cotton 100 parts Polyurethane resin 70 parts Trifunctional low molecular weight incyanate compound 30 parts n-butyl stearate
3 parts myristic acid 2 parts liquid paraffin 3 parts cyclohexanone 750 parts
On the other hand, 750 copies
Prepare a magnetic paint consisting of the following composition and apply it to 1
A magnetic layer was formed by coating on a 4 μm thick polyester film with good surface smoothness to a dry thickness of 5 μm, drying, and mirror-finishing.

Co-containing magnetic iron oxide powder 250 parts Carbon black 12 parts Granular α-iron oxide
10 parts nitrified cotton
22 parts polyurethane resin 1
9 parts trifunctional low molecular weight incyanate compound 7
Part cyclohexanone 340 parts
Le en
340 parts n-butyl stearate
3 parts liquid paraffin 2 parts myristic acid 2 parts The above paint for the back coat layer was applied to the back side of the polyester film on which the above magnetic layer was formed to a dry thickness of 0.
After coating and drying to a thickness of 8 μm, mirror treatment was performed and the magnetic tape was cut to a predetermined width.

Example 2 Titanium oxide powder and zinc oxide powder were not surface-treated with silane coupling agent A in advance, but surface-treated mixed solid additive 2 was used in the formulation of the back coat layer paint of Example 1.
A magnetic tape was produced in the same manner as in Example 1, except that 100 parts of untreated titanium oxide powder, 100 parts of untreated zinc oxide powder, and 10 parts of silane coupling agent A were used instead of 0 parts. .

Comparative Example 1 No surface treatment with silane coupling agent A was performed, and 100 parts of untreated titanium oxide powder was used instead of 200 parts of the surface treatment mixed solid additive in the formulation of the back coat layer paint of Example 1. A magnetic tape was produced in the same manner as in Example 1, except that 100 parts of untreated zinc oxide powder was used.

Comparative Example 2 A magnetic tape was produced in the same manner as in Example 1, except that the same amount of silane coupling agent A was used instead of silane coupling agent A. In this case 1. When preparing the paint for the back coat layer, the viscosity clearly increased compared to those of Examples 1 and 2.

Example 3 Alumina powder (average particle size 0.3/'') 200 parts Silane coupling agent B 20 parts Inpropyl alcohol 2,001 A dispersion consisting of the above components was mixed and dispersed in a homomixer for 4 hours, and left to stand still for 24 hours. It was then dried at 80'C for 15 hours to obtain a surface treated solid additive. Organic compounds were uniformly attached.

200 parts of this surface-treated solid additive was added to 200 parts of the surface-treated mixed solid additive in the back coat layer paint of Example 1.
A magnetic tape was produced in the same manner as in Example 1, except that the sample was used in place of the sample.

□) Example 4 A magnetic tape was produced in the same manner as in Example 3, except that the same amount of silane coupling agent C was used instead of silane coupling agent B.

Comparative Example 3 No surface treatment with silane coupling agent B was performed, and 20 parts of untreated alumina powder was used in place of 200 parts of the surface treatment solid additive in the formulation of the back coat layer paint of Example 3.
A magnetic tape was produced in the same manner as in Example 3 except that 0 parts were used.

Regarding each of the magnetic tapes of Examples 1 to 4 and Comparative Examples 1 to 3, the surface roughness of the back coat layer (surface roughness by centerline average), abrasion resistance (S before and after running in 100 running tests) /Decrease in N ratio), color S/
N ratio (relative value to standard tape) and running stability (
The results of the investigation (wow and flutter) were as shown in the table below.

As is clear from the above table, the magnetic tape of the present invention has a back coat layer with excellent abrasion resistance and appropriate surface properties, and can satisfy both running stability and electromagnetic conversion characteristics. It turns out that there is something.

Claims (1)

[Claims] (1) On the back side of the base having a magnetic layer on the main surface, there is at least a non-magnetic solid additive and the following formula; ▲Mathematical formula, chemical formula, table, etc.▼...(1) group, R' is an alkylene group, m
is an integer of 1 or more, and n is an integer of 0 to 5.