JPS61162818A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility and durability by forming a magnetic layer on a nonmagnetic base by dispersing ferromagnetic particulates in a copolymer consisting of vinyl chloride, a specific monomer, and a vinyl monomer with a univalent organic group including a specific group. CONSTITUTION:The magnetic layer is formed on the nonmagnetic base by dispersing ferromagnetic particulates in the copolymer consisting of a vinyl chloride unit (a), a monomer unit shown by a formula (b), a vinyl monomer (c) having a univalent organic group including a hydroxyl group as a side chain, and a vinyl monomer unit having a -SO3M group or a univalent group (d) with a -SO3M as a side chain. In this case, the copolymer consists of the 60-95wt% unit (a), 5-25wt% unit (b), 1-15wt% unit (c), and 0.5-15wt% unit (d), and the mean degree of polymerization is 200-800. Consequently, the superior dispersibility, filling performance, compatibility, and heat stability of the ferro magnetic particulates are obtained, and consequently this magnetic recording medium has excellent durability and superior secular stability.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a magnetic Q' recording medium, and is particularly characterized by vinyl chloride, which exhibits excellent performance as a binder for ferromagnetic fine powder. This invention relates to an improved magnetic recording medium using a special quaternary copolymer.

Magnetic recording media such as magnetic tapes are generally held together by providing a coating film made of magnetic powder and a binder (synthetic resin) on the surface of a support such as a polyester film.

Examples of magnetic powders include r -Fe, ○, -FeO, those obtained by adsorbing or doping cobalt ions, or 0r02, as well as Fe-Co, Fe-
00 or 6) Depending on the case, acicular fine particle materials containing N1, etc. are used, but in recent years, with the improvement in the performance of video tapes and audio tapes, 1) High signal density and high playback in short wavelength MIF recording have been used. A way is needed.

In order to cope with these trends, magnetic powders have been made into 1) finer particles and have a very large magnetic moment, making it difficult for the particles to agglomerate with each other. It is becoming more difficult than ever to achieve uniform dispersion.

In order to address these technical issues, a wide range of studies are being conducted from the viewpoint of improving the affinity for magnetic powder as a property of the binder resin. For example, binders with carboxyl groups or hydroxyl groups r Although the resin has been put into practical use, 1) the dispersibility of the ferromagnetic powder is still insufficient;
3. As a result, the residual magnetic flux density and squareness ratio are unsatisfactory, and furthermore, powder is likely to fall off and durability is poor.

On the other hand, there is also a sulfonic acid group or the gold WA in the molecular structure.
It is also known that very good results can be obtained in terms of dispersibility of ferromagnetic fine powders when using binder resins into which salts have been introduced, such as vinyl chloride-vinyl acetate-vinyl into which vinyl alcohol units have been introduced. -803M for the purpose of improving the dispersibility of OH groups in alcohol copolymers,
Binder resins have been proposed in which a hydrophilic group containing a group such as -080,M (M is a gold atom) is introduced.

Although this binder resin has been improved in terms of dispersibility and powder shedding, it does not easily cause dehydrochlorination and has poor long-term durability (stability). However, there is a major drawback in that magnetic properties such as residual magnetic flux density deteriorate over time. The cause of this is that a vinyl chloride copolymer containing vinyl alcohol units is used as a starting material, and the vinyl alcohol units are modified by reacting with a compound having a sulfonic acid group and a sulfonic acid gold base in one molecule. Busy exposure) Gold sulfonate +
A binder resin with an S base introduced and one polymerization - saponification -
This is thought to be because the polymer is manufactured under harsh reaction conditions consisting of three steps of introducing a sulfonic acid base and the deterioration of the polymer occurs. Therefore, vinyl chloride units, vinyl ester units, and polymerizable unsaturated sulfonic acid units It is possible to use a copolymer consisting of OH or its metal salt, but in this case, when used as a coating film and then used as an OH that causes a crosslinking reaction with an isocyanate group-containing urethane prepolymer, there are problems with durability. be.

Therefore, it can be obtained by copolymerizing vinyl chloride units, vinyl ester units, and polymerizable unsaturated sulfonic acid units or gold salts thereof, and saponifying this copolymerized resin by a known method. It is conceivable to use a copolymer resin consisting of a vinyl chloride unit, a tohinyl ester unit, a vinyl alcohol unit, and a polymerizable unsaturated sulfonic acid unit or a gold salt thereof. However, in this case, many of the polymerizable unsaturated sulfonic acids or their gold salts have an ester structure, so the sulfonic acids or their gold salts are removed during the saponification reaction, and the harsh saponification reaction is difficult. The reaction causes deterioration of the resin, and Sarak cannot exhibit the expected performance because the saponification reaction catalyst remains in the resin.

(Structure of the Invention) The inventors of the present invention have developed a bonded mJ resin with further improved L-4+ stability and obtained a high-performance magnetic recording medium (as a result of intensive research).

We have arrived at the present invention.

That is, in the present invention, each of the following structural units (vinyl chloride unit) (wherein R is a hydrogen atom or a methyl group) is formed on a non-magnetic support.

R represents a -valent hydrocarbon group)
(hereinafter referred to as ester unit or ether unit) (c) A vinyl spinning wheel whose side chain is a hydroxyl group-containing -valent organic group (hereinafter simply referred to as hydroxyl group-containing unit).

and) having one 8o M group or one 8o M group in the side chain -
A vinyl monomer unit (hereinafter simply referred to as S!O,M group-containing unit) that is a valent organic group (M in the formula is a hydrogen atom or a metal atom).

The present invention relates to a magnetic recording medium having a magnetic layer formed by dispersing ferromagnetic fine powder in a copolymer comprising:

The copolymer (binder resin) used in the present invention has excellent dispersibility and high filling properties of the ferromagnetic powder, and has sufficient compatibility with polyurethane resin and the like used in combination as appropriate. Furthermore, reactive crosslinking with urethane prepolymers containing isocyanate groups is possible. By using it as a binder, a high-performance magnetic recording medium with improved long-term durability can be obtained.

The present invention will be explained in detail below.

The copolymer used as the binder resin conveniently used in the present invention is characterized by being composed of each of the units 1-f) to 4 described above, and particularly U) units 60 to 4. 95% by weight, (b) unit 5-25% by weight, (/→ unit l-ls
It is preferable that the polymer has a proportion of 0.5 to 0.1 m%, and an average degree of polymerization of 200 to 800.

(a) If the amount of vinyl chloride units is too small, the physical strength will decrease, while if it is too soft, the solubility will decrease, which is disadvantageous in use.

(The ester unit or ether unit at position 111 is used to improve the solubility, flexibility, etc. of the copolymer, and the monomer corresponding to this (b) unit is - (1) (fi)
Examples include [■]. R in the formula is a hydrogen atom or a methyl group, and R2 is a monovalent hydrocarbon group.

Desirable vinyl esters corresponding to the above formula (1) include vinyl acetate and vinyl propionate.

Vinyl versatate (manufactured by Shell Chemical).

Examples include vinyl stearate and vinyl benzoate. Examples of preferable (meth)acrylic esters corresponding to formula [■] include ethyl monoacrylate, butyl acrylate, 2-ethylhexyl acrylate, and propyl medalylate.

Desirable vinyl ethers corresponding to the C111 formula include ethyl vinyl ether, inbutyl vinyl ether, etc., and maleic acid diesters and fumaric acid diesters corresponding to the [1v] formula include diethyl maleate, dibutyl maleate-diptyll fumarate, etc. is exemplified.

(b) As an ester unit or ether unit.

Any of the formulas CI) to (ff) described above may be used alone or in combination of two or more thereof, but if the weight ratio in the copolymer is too small, the solubility in organic solvents will deteriorate, and if it is too large If the resin is soft, the durability of magnetic recording media (magnetic tape, etc.) will decrease.
As mentioned above, it is desirable that the weight is in the range of 5 to 25%.

→ As a fluorophore corresponding to a hydroxyl group-containing unit.

Examples include the following:

OH2=C8-C-00H20H20H.

CH2=CH-C-0CR, OHOH.

0H2=OB-(1-0(OH2)40R.

OOH OR,=CH-0-00! (20HCH, 01.

H3O CH2=CH-C-OCH, C)l, OH.

OH,=C-0-00H2CHO)i.

CH2=CH-004H80I(.

0H2=CH-C! -NHOH,OH.

OOH 0H2=CH-C-700HOH20C,H,.

0H2=CH-aH2o (OH2CH2 leaf iH-CH3 blind 0) I27fFH-OH,O(CH2C)]O sweet H se O
H.

CH2=CH-0H20(CH,C)(20SOH,O
HO÷iH.

I CH,=C! H-C-0(OH2CIH20→iH.

OOH3 C3E, =('ju -0-0(OH2CHO-Fuku-
H-OH,0 0)12=0- o-0(O)12aR,O force in.

OH OF[2=C)T-00-OH0H3-OOH 0H2=OH-00-(CH2), CH2CHOH,0
)l(C3H,),OH.

In the above, m and n represent numbers from 2 to 9.

These single 1. If the weight ratio of the hydroxyl group-containing unit introduced into the copolymer is too small, the dispersibility of the ferromagnetic fine powder will only decrease.

The compatibility with the appropriately used polyurethane resin etc. decreases, and on the other hand, if too much is used, the isocyanate prepolymer'? When combined, the viscosity increases significantly, causing difficulties in bot life,
Magnetic recording media (8A tape, etc.) due to decreased physical strength
Because the durability of is reduced.

As mentioned above, the content is preferably in the range of 1 to 15% by weight.

) SQ, , M The monomers corresponding to the group-containing units are exemplified by those listed below.

0H2=OH-8o, M, CH2=CtH-OH
,803M.

Oh.

0H2=OH-06H4-803M, CH=0-C
H280,M.

CH3 CH=CH-Co-NH=(:j-0)12S03M
.

■ 0H2=○H-0)(, -oa-aH-8o3M.

C1i, 0OOR CH3 ■ 0H2=O-Coo-0□! (4So1M.

OH,=OH-000-02H4S03M In the above, gold IPJI of Ml hydrogen atoms or alkali residual dust, etc.
The atom and R represent an alkyl group having 6 to 18 carbon atoms.

In copolymer neutralization) the weight proportion of So3M group-containing units is preferably in the range of 0.5 to 10 tlt%,
If this amount is too small or too large, the dispersibility of the magnetic powder will deteriorate.

In a copolymer composed of such unit components, if the average degree of polymerization is too low, the physical strength of the magnetic layer will decrease, and the durability of magnetic tapes will also decrease; If it is too high, the solution viscosity at a predetermined fragility will be high and the workability will be extremely poor, so it is desirable that the average degree of polymerization is in the range of 200 to 800.゛In addition, this copolymer can be produced using the general suspension polymerization method, emulsion polymerization method,
It can be produced by a solution polymerization method, a bulk polymerization method, or the like.

When using the above copolymer as a binder resin, other resins may be used in equal or less amounts as necessary, and examples of resins that can be used in combination include polyurethane resins, nitrocellulose, epoxy resins, and polyamide resins. , phenolic resin, or acrylic acid ester-methacrylic ester, styrene.

Examples include polymers or copolymers of acrylonitrile, butadiene, ethylene, propylene, vinylidene chloride, acrylamide, vinyl ethers, and the like. Among these, polyurethane resins and nitrocellulose are particularly preferred.

In addition to this, it is desirable to use a polyisocyanate curing agent in combination.11. Examples of this curing agent include tolylene diisocyanate, diphenylmethane diisocyanate,
Bifunctional isocyanate such as hexane diisocyanate,
Examples include trifunctional isocyanate or urethane prepolymers containing incyanate groups at both ends, such as Furonate L (trade name, manufactured by Nippon Polyurethane Industries) and Dismodur L (trade name, manufactured by Bayer). In addition.

The amount of these curing agents used is 4 parts per 100 parts by weight of binder resin.
0! It should be below Isobe.

The ferromagnetic powder used in the present invention includes:

r-Fe, o3. Fe5Q4 and these adsorbed or doped with cobalt ions, or Or
Examples of O□TK and K include acicular fine particle materials containing Fe, Co, Fe-0O, or 11Ni as the case may be, and various other conventionally known magnetic powders. What is the mixing ratio of ferromagnetic fine powder and binder resin?

100 parts by weight of ferromagnetic fine powder t) Binder resin 8-3ON
It is desirable to use it as a leisure area.

Furthermore, a lubricant commonly used in the past is used to uniformly disperse the ferromagnetic powder and the binder resin.

The addition of abrasives, antistatic agents, dispersion aids, rust preventives, etc., and the use of various other organic solvents such as methyl ethyl ketone, methyl isobutyl ketone, and toluene as coating media are the same as in the past. There are no special restrictions on points.

The support is polyester or polyolefin.

Synthetic resins such as cellulose acetate and polycarbonate, other non-magnetic metals, and ceramics are used.
Forms are film, tape, and sheet.

Used in plate-shaped bodies, etc.

The coating means for forming the magnetic layer on the support may be any conventionally known method, and a smoothing treatment such as calendaring treatment may be applied as appropriate.

A high-performance magnetic recording medium, which is the object of the present invention, can be obtained.

Next, examples of synthesis of a copolymer as a binder resin and specific examples using this copolymer will be given.

Synthesis Example 1 (Synthesis of Polymer ■) In an autoclave equipped with a heating device, 400 parts by weight of methanol after room replacement, 68 parts by weight of vinyl chloride, 36 parts by weight of vinyl acetate, and 16 parts by weight of hydroxypropyl acrylate. -Allyldodecyl sulfosuccinate'Na
12 parts by weight of salt, 6 parts by weight of di(2-ethylhexyl) peroxydicarbonate and 2 parts by weight of partially saponified polyvinyl alcohol were charged, and the reaction was started by raising the temperature by 50'cK while stirring under a nitrogen gas atmosphere. A 68 t Flit portion of vinyl chloride was continuously press-injected over a period of 8 hours to cause a copolymerization reaction.

Autoclave internal pressure is 0.5Ky/I:I after 12 hours
Since it became TiG, remove the residual pressure, cool it, and filter it.

The mixture was washed twice with 400 parts by weight of methanol, filtered and dried to obtain a copolymer powder (Polymer ■) 133.

Synthesis Example 2 (Synthesis of Polymer ■) ρ・(In an autoclave equipped with a heating device, 400 parts by weight of nitrogen-substituted ionized water, 61 parts by weight of vinyl chloride, 52 parts by weight of vinyl propionate, and 18 parts by weight of tomato diethyl methacrylate) Parts by weight, 8 parts by weight of Na 2-acrylamido-2-methylpropanesulfonate, 9 parts by weight of ammonium persulfate, and 6 parts by weight of polyoxyethylene-polyoxybutylene block polymer were added, and while stirring under a nitrogen gas atmosphere, 55 parts by weight Start the reaction by raising the temperature to ℃,
Furthermore, 61 parts by weight of vinyl chloride was continuously fed under pressure for 6 hours to cause a copolymerization reaction, followed by an aging reaction for 1 hour to obtain an emulsicon.

To this emulsion, 50 parts of sodium chloride,
20 parts by weight of 5% diluted hydrochloric acid and 500 parts by weight of hot water were added, and the resulting slurry was passed through a V to form a cake.
The dispersion was washed in 00 parts by weight of deionized water and filtered. After repeating this water washing and filtration operation 5 times, the copolymer 120
Parts by weight were obtained.

Synthesis Example 3 (Synthesis of Polymer (Ffi)) Polymerization was carried out under the same polymerization conditions as in Synthesis Example 1 with the following charges.

Methanol 400 parts by weight Vinyl chloride 72 I isophthyl vinyl ether 28 N-methylolacrylamide 24
I Sodium vinyl sulfonate 4 I di(2-ethylhexyl) peroxydicarbonate) 61 Partially saponified polyvinyl altu/E/ 2 1 Additional vinyl chloride
72 1 In this way, a copolymer powder (Polymer ■) 1501r was obtained.

Synthesis Example 4 (Synthesis of Polymer ①) Polymerization was carried out under the same polymerization conditions as in Synthesis Example 1 with the following charges.

Methanol 400! Parts by weight Vinyl chloride 68 1 Beopa φ10 (vinyl versatate, trade name manufactured by Shell Chemical Co., Ltd.) 36 I hydroxypropyl acrylate) 16 1 Allylsulfonic acid Na salt 12 1 Di(2-ethylhexylcoperoxydicarbonate) 61 parts Saponified polyvinyl alcohol 21 additional vinyl chloride 68 liters #C was carried out in this way to obtain 130 parts of copolymer powder (polymer ■).

Synthesis Example 5 (Synthesis of Polymer ①) Polymerization was carried out under the same polymerization conditions as in Synthesis Example 1 with the following charges.

Methanol 400 parts by weight Vinyl chloride 78N Butyl acrylate
36 I hydroxyethyl methacrylate 4I 2-acrylamido-2-methylgusepanesulfonic acid 41 Di(2-ethylhexylume peroxydicarbonate 6 #Partially saponified polyvinyl alcohol 21 Additional vinyl chloride
78 #Synthesis Example 6 (Synthesis of Polymer ○) Polymerization was carried out under the same polymerization conditions as in Synthesis Example 1 except that the same bt was used instead of vinyl acetate, and 1301 parts by weight of copolymer powder (Polymer ■) was obtained. I got it.

Comparative Synthesis Example 1 (Synthesis of Polymer (1)) Polymerization was carried out with the following charges under the same polymerization conditions as in Synthesis Example 1, and post-treatment was carried out to obtain 172 pieces of co-merged powder (polymer (2)).

Methanol 400 parts by weight Vinyl chloride 78 1 Vinyl acetate
32 I Allyldodecyl sulfosuccinate Na salt 12 I Di(2-ethylhexyl) peroxydicarbonate 61 Partially saponified polyvinyl alcohol 21 Additional vinyl chloride 78 l Comparative synthesis example 2 (synthesis of polymer ○) Polymerization similar to comparative synthesis example 1 Polymerization was carried out under the same conditions and with the same recipe, followed by post-treatment to obtain 154 parts of a copolymer.

This copolymer 154 is blind! ! methanol 900 parts
1i'Rt parts, 100 parts by weight of acetone.

Boil 8 parts by weight of sodium hydroxide, let the saponification reaction take place at 40°C for 6 hours, then boil vinegar and 16 parts by weight.

Washed three times with 1000 parts of methanol, and then washed with 1000 parts of methanol. [Washing twice with 1 part of deionized water and over-drying to obtain 133 parts of copolymer powder (Polymer 2).

Comparative Synthesis Example 3 (Synthesis of Polymer ①) Synthesis! Polymerization was carried out with the following charges under the same polymerization conditions as A1, and then post-treated to obtain 160 parts of copolymer powder.

Methanol 400 parts by weight Vinyl chloride 78 I Vinyl propionate
34 l Sodium vinyl sulfonate 10
〃Di(2-ethylhexyl) peroxydicarbonate 6 〃 Partially saponified polyvinyl alcohol 2 parts by weight additional vinyl chloride 78 1 This copolymer 140! l
900 parts by weight of methanol, 10 parts by weight of acetone based on it part
0 parts by weight and 5N parts by weight of sodium hydroxide were added, and after a saponification reaction was carried out at 40°C for 6 hours, 10 parts by weight of acetic acid was added to the mixture.
Washed 3 times with 0 parts by weight of methanol, and then washed with 1000 parts by weight of methanol.
The mixture was washed twice with ionized water (parts by weight), filtered and dried to obtain 130 parts by weight of copolymer powder (polymer ①).

When we measured the polymer composition and various physical properties of the polymers ① to ② synthesized above, we found that the results were as follows:
It was as shown in Part 2).

However, the following abbreviations were used in the same table.

VAc: Vinyl acetate.

vA: Polyvinyl alcohol.

VPr: Vinyl propionate.

rBvE: Isobutyl vinyl ether.

T3BM: Dibutyl malate.

HPA: Hydroxypropyl acrylate-[
A: Hydroxyethyl methacrylate.

NMAM: N-methylol acrylamide.

AD88Na: Allyldodecyl sulfosuccinate sodium salt - AMP8Na: 2-acrylamido-2-methylpropanesulfonic acid sodium salt.

SV8: Sodium vinyl sulfonate.

88A: Sodium allylsulfonate.

AMP8: 2-acrylamide-2-methylpropanesulfonic acid N-2304: Polyurethane resin manufactured by Nippon Polyurethane Co., Ltd. N-5032: Polyurethane resin manufactured by Nippon Polyurethane Co., Ltd. NO: Nitrocellulose or Table III (Part 2) ), 'compatibility' and 'Ho
/, the occurrence I' was investigated by the following method.

[compatibility]

Sample polymer-5 inguinal region and target resin (polyurethane resin)
5 parts by weight were dissolved in a mixed solvent consisting of 30 parts by weight of methyl ethyl lactone, 30 parts by weight of methyl isobutyl ketone and 30 M parts of toluene.

A coating film was prepared from this solution and examined for the presence of 4J insoluble particles.

0: Completely transparent coating film △: Transparent coating film ×: Opaque coating film (RCt generation observed) Sample polymer "-" was heated at 100°C for 1 hour and 1 HC was generated.
l @0. IN-KO! '! The amount was determined by absorption with a solution and back titration, and expressed as a percentage of the sample polymer.

Examples 1-6. Comparative Examples 1 to 3 300 parts by weight of ferromagnetic alloy powder (major axis 0.
5μ. Long axis/short axis ratio 7゜Saturation magnetization fil 30 emu15L specific surface area 50tr
//! ! , coercive force 1400 oersted) Polymer ((0~■) 40 parts by weight N-23
0420# Silicone oil KF-963/I (4rg manufactured by Etsu Kagaku Kogyo) Methyl ethyl ketone 300 l Methyl isobutyl ketone 150 l Toluene
150 N The above composition was mixed and dispersed in a ball mill for 48 hours.

After filtration, 10 parts by weight of Coronate L was added and mixed. Table 2 shows the viscosity of this magnetic paint at 25°C.

This magnetic nutrient was applied to a polyester film having a thickness of 21 microns at a coating thickness of 6 microns, subjected to magnetic field orientation treatment, and dried. After that, the surface is treated with a super calender, and
I cut it into half-width pieces.

For each magnetic tape produced in this way.

The squareness ratio, gloss (%), and powder shedding were evaluated. The results are shown in Table 2.

Squareness ratio: Measured using a vibrating sample magnetometer (Toei Kogyo Exhibition).

The 60' reflectance of the jar before cicalendering was compared with that of a standard glass slope using a gloss meter (Murakami Color Giken).

Powder falling: After running the Qi 130 times, the state of powder falling onto the guide rolls, etc. was compared, and a 3-level evaluation was performed.

A: Excellent B: Fair C: Poor As can be seen from the results in Tables 1 and 2, the present invention provides excellent dispersibility, filling properties, compatibility, and thermal stability of the ferromagnetic fine powder 1. Therefore, magnetic recording media (LI
(a-air tape, etc.) has good durability and excellent stability over time.

Claims (1)

[Claims] 1. On a non-magnetic support, there are the following structural units (a) vinyl chloride unit, (b) formula ▲ mathematical formula, chemical formula, table, etc. ▼・▲ mathematical formula, chemical formula,
There are tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ or ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (However, R^1 in the formula is a hydrogen atom or a methyl group, R^
2 represents a monovalent hydrocarbon group). (c) a vinyl monomer unit whose side chain is a hydroxyl group-containing monovalent organic group, and (d) a monovalent organic group whose side chain is a -SO_3M group or a -SO_3M group (M in the formula is a hydrogen atom or A magnetic recording medium formed by forming a magnetic layer in which fine ferromagnetic powder is dispersed in a copolymer consisting of vinyl monomer units (metal atoms). 2. The copolymer contains (a) 60 to 95% by weight of units, (
b) Units 5 to 25% by weight, (c) Units 1 to 15% by weight,
(d) The magnetic recording medium according to claim 1, which comprises 0.5 to 10% by weight of units and has an average degree of polymerization of 200 to 800.