JPH02220221A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain good kneading property and dispersibility even when magnetic powder of fine particles is used by incorporating magnetic powder and polymers having the unit composition expressed by the specified formula into the magnetic layer. CONSTITUTION:The magnetic recording medium has a magnetic layer containing magnetic powder and the polymer having the unit composition expressed by formula I. In formula I, R1 is an alkyl group and X is a hydrophilic group which contains at least one of -COOM, -SO3M, -OSO3M, -PO(OM)2, formula II (wherein R represents an alkyl group and M is one of H, Li, Na and K), tertiary amine, quaternary ammonium salt and betaine. l, m, n and p are molar ratios (%), satisfying l>=60, m<=6, 0.01<=p<=5 and l+m+n+p=100.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to magnetic recording media such as magnetic tapes, and particularly to improvements in the binder contained in the magnetic layer.

[Summary of the invention]

The present invention provides a so-called coated magnetic recording medium in which a magnetic layer mainly composed of magnetic powder and a binder is formed on a non-magnetic support, in which a wood-philic group is added to polyvinyl acetal resin as the binder. By using a polyvinyl acetal-based resin into which a fourth unit is introduced, the kneadability and bidispersity of the magnetic powder is improved.

[Conventional technology]

In so-called right-handed magnetic recording media, ferromagnetic powder and binder 1 are deposited on a nonmagnetic support such as a polyester film.
The magnetic layer is formed by applying a magnetic paint made by dispersing and kneading a dispersant, lubricant, etc. in an organic solvent.

The binder contained in the magnetic layer has properties such as excellent dispersibility of magnetic powder, ability to impart good electromagnetic conversion characteristics to the magnetic recording medium, and ability to form a magnetic layer with excellent wear resistance and heat resistance. is required.

Conventionally, binders that have such properties and are relatively hard include chlorinated vinyl chloride-vinyl acetate copolymers, vinyl chloride-propionic acid copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, etc., as in the magnetic layer. Vinyl binders are widely used.

Furthermore, acetal resins have also come to be used as binders that achieve better dispersibility than the vinyl chloride binders mentioned above; for example, JP-A No. 61-22722
No. 4 discloses a polyvinyl butyral-based polyvinyl mixed acetal.

[Problem to be solved by the invention]

However, in response to the recent increase in the recording density of magnetic recording media, magnetic powder tends to be made into finer particles, and a material with better kneadability and zero dispersibility is desired as a binder.

Therefore, the present invention has been proposed in view of the conventional situation, and an object of the present invention is to provide a magnetic recording medium containing a binder having excellent kneadability and monodispersity in a magnetic layer.

[Means for solving problems]

As a result of repeated studies aimed at achieving the above-mentioned purpose, the present inventors discovered that good results could be obtained by actively introducing a unit containing a hydrophilic group into the polyvinyl acetal resin. This led to the completion of the invention.

That is, the magnetic recording medium according to the present invention is characterized by comprising a magnetic layer containing a polymer whose unit composition is represented by the following general formula and magnetic powder.

[However, in the formula, R represents an alkyl group, and X is -COO
M,-3o,M,-03O,M,-PO(OM)! .

(M represents any one of H, Li, Na, etc.)
, tertiary amine, quaternary ammonium salt, and betaine.

Also, l, m, n, p represent the molar ratio as a percentage, and! ≧6
0. m≦6.0.01≦p≦5. j! +m+n10P-
The polymer used in the present invention can be structurally considered to be a polyvinyl acetal resin, which is a copolymer of vinyl acetal, vinyl acetate, vinyl alcohol, and a monosubstituted ethylene. . For convenience, the above general formula is
The composition is shown by arranging the various types of constituent units in random order, and the actual partial structure of the above polymer is expressed, for example, by the following formula.

In the above formula, 22 is an acetal type or an acetate type.

Each of the three types of alcohol type units is a constituent component contained in a general polyvinyl acetal resin, and the unit having the hydrophilic group X at the right end is the fourth unit newly introduced according to the present invention.

As a method for synthesizing the above polymer, the following (A) and (
B) is possible.

(A) A method in which a unit having a hydrophilic group X is allowed to coexist in advance during the formation of the main chain.

Generally, polyvinyl acecool resin is synthesized by condensing polyvinyl alcohol obtained by saponifying polyvinyl acetate with an aldehyde. At this time, if the saponification degree or acetalization degree is selected appropriately, a corresponding amount of acetoxyl groups or hydroxyl groups will remain, and a polyvinyl acetal resin consisting of three types of units: acetal type, acetate ester type, and alcohol type will be synthesized. That is why it is done. Therefore, in order to introduce a unit having a hydrophilic group X as the fourth unit into such a polyvinyl acetal resin, an ethylene monosubstituted product by the hydrophilic group X must be subjected to addition polymerization during the synthesis of polyvinyl acetate. That's a good thing.

Of course, in this case, the hydrophilic group X needs to be a group or atomic group that does not take part in the saponification and acetalization that will be carried out later. Groups that impart hydrophilicity to such hydrophilic group X include -COOM, SOsM,
OS OsM, P O (OM)! .

Examples include tertiary amines, quaternary ammonium salts, and betaines. However, M represents any one of H, Li, and Na. For example, examples of mono-substituted ethylene by hydrophilic group X containing -3o and M include the following compounds (1) to (2).

■ CH! -CHS Os M ■ CH, -CI-CH OSO3M ■ Cu-CH-CH□-0-CH-CHI-503MH ■ CHI-CH-go-〇 (CHz)-S OsM
(B) A method of introducing a hydrophilic group X using the water group of the alcohol type unit after the main chain is formed.

As representative examples of this method, the following (B-1) and (B
-2) is possible.

(B-1) A method using a halogen substituted product.

For example, when the following compounds ① to ＠ are reacted with the hydroxyl group of an alcohol type unit, a hydrophilic group X is introduced as hydrogen chloride is eliminated.

■ CI CHz CHt SO3M@ CI C
Hz CHOO3O,M■ C/ICH,C00M @ CI CH! The P (OM)z reaction is carried out in a solvent such as dimethylformamide or dimethyl sulfoxide, and in order to neutralize by-produced hydrogen chloride, amines such as pyridine, picoline, triethylamine, or epoxides such as ethylene oxide or propylene oxide are used. As an example, the reaction when the above compound (1) is used is shown below.

1+CH1-CH)-+ Cl CH2CH2SO3
MH (B-2) A method using a difunctional isocyanate.

In this method, the hydroxyl groups remaining after saponification and the terminal hydroxyl groups of the following compounds @~[phase] are separated using a bifunctional isocyanate such as 4°4'-diphenylmethane diisocyanate, tolylene diisocyanate, hexamethylene diisocyanate, etc. It is used for crosslinking.

@ HOCH, CH, 0303M ■ HOCHlCOOM To perform crosslinking, first react equimolar amounts of the above compound @~■ with a bifunctional isocyanate in dimethylformamide or dimethyl sulfoxide, and then react the hydroxyl group of the above compound with the 2-functional isocyanate.
A urethane bond is formed between one -N=C-0 group of the functional isocyanate, and then a urethane bond is formed between the remaining -N=C=O group of the bifunctional isocyanate and the hydroxyl group in the acetal resin. to be generated. - As an example, the reaction using the above compound (1) and hexamethylene diisocyanate is shown below.

0CN-(CHi) b-NCO+ HOCIIz
CHtSQ3j1-1 → OCN-(CL)i-NH
CO-CHzCHtSO3MCONH-(Cut) *
-NHCO-CHtCHzSOJ■ HOCHz CH
t S Os M The method for introducing the hydrophilic group X has been described above, and R8 contained in the acetal type unit is an alkyl group, particularly a short-chain alkyl group. The number of carbon atoms is not particularly limited, but is generally desirably selected to be 5 or less.

Therefore, it is sufficient to use an aldehyde having 2 to 6 carbon atoms in the acetalization reaction. In particular, the above acetal type unit is converted into vinyl acetal (R+ -C84
) or vinyl butyral (R,=C,H,) is highly practical.

Number 1 expressing the molar ratio as a percentage. ．． The conditions regarding m, n, and p are set from the viewpoint of optimizing the properties of the resulting polymer as a binder.

First, the molar ratio l of the acetal type unit is selected to be 60% or more. If it is less than 60%, the glass transition point may be lowered, leading to a risk of deterioration of heat resistance or reduction of mechanical strength.

The molar ratio m of acetate type units is selected to be 6% or less. If it exceeds 6%, there is a risk that solvent resistance and strength will decrease.

The molar ratio p of the unit having the hydrophilic group X is 0.01 to
Selected by 5%. This unit also greatly contributes to the kneading and dispersibility of the magnetic powder. If it is less than the above range, the effect of introducing the unit will not appear, and if it exceeds the above range, the moisture resistance will decrease.

After l, m, and p are determined in this way, the remaining portion is the molar ratio n of alcohol-type units, which is usually 27
It is in the range of ~40%.

The polyvinyl acetal resin having the above unit composition exhibits excellent kneadability and dispersibility with respect to magnetic powder. It is a measure to evaluate the ease of dispersing magnetic powder in a mixture. This is a measure to evaluate the ease of dispersion.

The mixing ratio of this polyvinyl acetal resin and magnetic powder is
The amount is 4 to 7 parts by weight per 100 parts by weight of magnetic powder.

Furthermore, the above-mentioned polyvinyl acetal resin may be mixed with other resins conventionally used as general binders within a range that does not impair kneadability and dispersibility. The amount is 20 to 60 parts by weight per 100 parts by weight of the resin.

The magnetic recording medium of the present invention may have a bank coat layer mainly composed of nonmagnetic powder and a binder on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed. ,
The above-mentioned polyvinyl acecool resin can also be used as a binder for such a back coat layer.

In addition, any conventionally known materials can be used for the nonmagnetic support, magnetic powder, nonmagnetic powder, and various additives used in the magnetic recording medium of the present invention.

[Effect]

The polyvinyl acecool resin used in the present invention contains an optimal range of acetal type units, acetate type units, and alcohol type units, so it has good heat resistance, mechanical strength, solvent resistance, and magnetic properties. It has the ability to disperse and knead powder. Furthermore, by including a unit containing a hydrophilic group, the dispersibility of the magnetic powder, which has conventionally been mainly achieved by an alcohol-type unit, is further improved, and excellent magnetic properties are achieved.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

Example 1 This example is an example of a magnetic tape using a polyvinyl acetal resin having -3O, Na as the hydrophilic group X as part of the binder.

Here, the polyvinyl acetal resin used as the binder has the following general formula: 1=10°m=3. n=
26.5. It has a composition of P"0.5.

Using this resin, a magnetic paint for forming a magnetic layer was prepared. That is, 100 g of magnetic powder (pure Fe powder, specific surface area 50 m''/g) and 10 g of the above polyvinyl acetal resin were mixed, cyclohexanone was added as a solvent so that the solid content concentration was 80%, and the mixture was kneaded for 1 hour. Further, 5 g of vinyl chloride resin and 5 g of urethane resin were added as binders to this mixture, and a mixed solvent of methyl ethyl ketone/toluene/cyclohexanone (2:2:1) was added so that the solid content concentration was 35%. The mixture was kneaded in a sand mill for 4 hours.

The magnetic paint thus prepared was coated with a 14 μm thick P.
The film was coated on an ET (polyethylene terephthalate) film so that the dried coating film had a thickness of 6 μm.The film was then subjected to a magnetic field orientation treatment, and then dried and rolled up. It was further calendered and cut into 1 inch pieces to create magnetic tapes.

Example 2 The composition of the polyvinyl acetal resin was 1=70,
m=3. n=26. A magnetic tape was prepared in the same manner as in Example 1, except that p-1,0 was used.

Comparative Example This comparative example is an example of a magnetic tape prepared in the same manner using a polyvinyl acetate resin without the hydrophilic group X as a binder. The composition of this polyvinyl acetal resin was 1-70, m=3°n-27, p-0.

Example 1 above. Example 2. Regarding the magnetic tape created in the comparative example, the saturation magnetic flux density, the squareness ratio of the magnetization curve, and the S/
The N ratio was measured. The results are shown in Table 1.

The S/N ratio was determined by recording a 4MHz sine wave signal on each magnetic tape using the optimum recording current for the reference tape, and measuring the frequency distribution of modulation noise centered around this frequency.
It was determined as the ratio (dB) between the reproduction output level and the noise level at 3.9MHz. Table 1 shows relative values when the S/N ratio of the magnetic tape of Comparative Example 1 is OdB.

Table 1 Procedures (Hoshosho (voluntary) August 29, 1999 Yoshi, Commissioner of the Patent Office 1) Takeshi Moon 1.Display of the incident As is clear from this result, the saturation magnetic flux density.

In both the squareness ratio and the S/N ratio, the magnetic tape according to the example exhibited better characteristics than the magnetic tape according to the comparative example.

3. Relationship with the case of the person making the amendment Patent applicant address: 6-7-35, Kitashinyo, Tokyo Parts Store Name (2)
18) Sony Corporation [Effect of the invention] As is clear from the above explanation, if the present invention is applied, good kneading properties can be achieved even when finely divided magnetic powder is used.
Dispersibility is obtained. As a result, it is possible to provide a magnetic recording medium that is suitable for high-density recording and has excellent magnetic properties.

6. Each column of "Claims" and "Detailed Description of the Invention J" of the specification to be amended.

7. Contents of correction (1) Amend the claims as shown in the attached sheet.

(2) From the first line to the fourth line of the text following the general formula on page 5 of the specification: ``[In the formula, R1 represents an alkyl group, and X represents -COOM, -So, M.

-OS OsM, P O(OM)2. (MhaH,
L represents any one of rNa, ),'' was changed to ``[In the formula, R1 is an alkyl group, R represents an alkyl group, and M represents any one of H, LiNa, "represents the alkyl group to be corrected, M is H, Li
, Na. ),” is corrected.

(3) From line 8 to line 12 on page 7 of the specification' C00M, 505M, 0305M,
PO(OM)1+ Tertiary amine and quaternary ammonium salt betaine can be mentioned. However, M is H, LiN
4 Ammonium salts and betaine are examples. The appended claim ``A magnetic recording medium comprising a magnetic layer containing a polymer whose unit composition is represented by the following general formula and magnetic powder.

[However, in the formula, R1 represents an alkyl group, and X is Li, N
Represents one of a. ), tertiary amine, quaternary
Represents a hydrophilic group containing at least one of ammonium salt and betaine. Also l.

m, n, p represent the molar ratio as a percentage, and! ≧605m≦6
．． 0.01≦p≦5. The relationship ffi+m+n+P=100 is satisfied. 〕”

Claims (1)

[Scope of Claims] A magnetic recording medium comprising a magnetic layer containing a polymer whose unit composition is represented by the following general formula and magnetic powder. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [However, in the formula, R_1 represents an alkyl group, and X represents -CO
OM, -SO_3M, -OSO_3M, -PO(OM)
_2, (M represents any one of H, Li, Na, or K), represents a hydrophilic group containing at least one of a tertiary amine, a quaternary ammonium salt, and betaine. In addition, l, m, n, and p represent the molar ratio as a percentage, and l≧6
0, m≦6, 0.01≦p≦5, l+m+n+p=10
satisfies the relationship 0. ]