JPH0432017A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve dispersibility and electromagnetic conversion characteristics by using an amino group-contg. comb type acrylic resin formed by bonding an amino group-contg. acrylic resin by either or both of an urethane bond and urea bond in combination with metallic magnetic powder having specific pH. CONSTITUTION:The amino group-contg. comb type acrylic resin formed by bonding the amino group-contg. acrylic resin by either or both of the urethane bond and urea bond is used in combination with the metallic magnetic powder having <=7 pH. Since the amino group-contg. acrylic chain of the amino group-contg. comb type acrylic resin used as the binder component is of the comb shape, the degree of freedom near the amino group is high and the affinity to the metallic magnetic powder having <=7 pH is improved. This resin is thus adsorbed extremely well to the surface of the magnetic powder. Particularly the polar group is the amino group and, therefore, if this resin is used in combination with the acidic metallic magnetic powder having <=7 pH, the affinity to the particle surface is improved and the amt. of the resin to be adsorbed on the surface of the metallic magnetic powder is increased, by which the dispersibility of the metallic magnetic powder is additionally improved. The dispersibility and electromagnetic conversion characteristics are improved in this way.

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 in which magnetic powder has good dispersibility and excellent electrical properties.

[Conventional technology]

Magnetic recording media are usually made by applying a magnetic paint consisting of magnetic powder, a binder component, an organic solvent, and other necessary components onto a substrate such as a polyester film, and drying the coating.
As recording density increases, further improvements in electromagnetic conversion characteristics such as output and S/N ratio are required.

For this reason, ultrafine metal magnetic powder with excellent magnetic properties and S/N ratio is used as the magnetic powder, but the finer the metal magnetic powder is, the more likely it is to agglomerate. Dispersibility decreases, resulting in S/
Electromagnetic conversion characteristics such as N ratio deteriorate.

Therefore, in order to improve the dispersibility of this finely divided metal magnetic powder, binder resins with polar groups are used. For example, carboxyl groups, sulfonic acid It is common practice to use those into which polar groups such as phosphoric acid groups, phosphoric acid groups, and tertiary amino groups have been introduced. (JP-A-55-38693, JP-A-57-9
(No. 2422, JP-A-59-30235) (Problems to be Solved by the Invention) However, with polyurethane resins in which various polar groups are introduced into the main chain, it is still difficult to sufficiently disperse finely divided metal magnetic powder. In particular, when using ultrafine metal magnetic powder with a pH of 7 or less, the dispersibility of the magnetic powder may be adversely affected depending on the type of polar group contained in the main chain of the polyurethane resin. Therefore, it is not possible to sufficiently improve the electromagnetic conversion characteristics.

[Means to solve the problem]

The present invention was made as a result of various studies in view of the current situation, and it is possible to create an amine group-containing comb-shaped acrylic resin in which an amino group-containing acrylic resin is bonded with either or both of a urethane bond and a urea bond. is 7
In particular, p
The dispersibility of ultrafine metal magnetic powder with H of 7 or less is sufficiently improved, and the electromagnetic conversion characteristics are further improved.

In this invention, the amino group-containing comb-shaped acrylic resin used as a binder component is made by bonding the amino group-containing acrylic resin with either or both of a urethane bond and a urea bond. Therefore, compared to polyurethane resins in which the polar groups are in the main chain, the degree of freedom near the amino groups is higher, and the affinity with metal magnetic powders with a pH of 7 or less is further improved.
Adsorbs extremely well to the surface of magnetic powder. In particular, since the polar group is an amino group, when used together with acidic metal magnetic powder with a pH of 7 or less, the affinity with the particle surface increases, the amount of adsorption on the metal magnetic powder surface increases, and the pH increases to 7. The dispersibility of the following metal magnetic powders is further improved. Therefore, when this type of amino group-containing comb-shaped acrylic resin is used in combination with metal magnetic powder with a pH of 7 or less, the dispersibility of the metal magnetic powder with a pH of 7 or less is sufficiently improved, and the electromagnetic conversion characteristics are sufficiently improved. be done.

An amino group-containing comb-shaped acrylic resin in which such an amino group-containing acrylic resin is bonded by either or both of a urethane bond and a urea bond can be produced by any method, but for example, (a) (b) Organic diisocyanate (c) Chain extender (d) At least (a) and (b) of polyols having hydroxyl groups at both ends, such as polyester and polyether, are reacted and the necessary Depending on the conditions, those obtained by further reacting (c) or (d) are preferably used. Here, the ratio of each component (a), (b), (c), and (d) is adjusted as necessary, and as each of these components, for example, the following are preferably used.

(a) As the acrylic resin containing a diol-amino group at one end, one manufactured by any method can be used. For example, one manufactured by a typical manufacturing method such as radical polymerization of an acrylic monomer together with a chain transfer agent can be used. It will be done. Then, an acrylic monomer containing an amino group is added to the acrylic monomer so that the amino group is introduced into the acrylic resin obtained at this time.

Here, examples of the acrylic monomer include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, lauryl methacrylate, and stearyl methacrylate, which may be used alone or in combination of two or more. In addition, dimethylaminoethyl methacrylate is an example of the amino group-containing acrylic monomer added to the acrylic monomer, and a monomer having a reactive functional group such as glycidyl methacrylate is further copolymerized, and other reactive functional groups are added to these reactive functional groups. It is also possible to introduce new amino groups by reacting compounds. As an initiator, α, α′-
Azobisisobutyronitrile, benzoyl peroxide, etc. are used, and examples of the chain transfer agent include 1,000-glycerin.

(b) As the organic diisocyanate, tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, hexamethane diisocyanate, etc. are preferably used.

(C) As the Slit extender, ethylene glycol,
1,3-propanediol, 1,4-butanediol,
Diols such as neopentyl glycol, diamines such as ethylenediamine and tolylene diamine, substances without polar groups such as water, 2,2-dimethylolpropionic acid, sodium bis(4-hydroxybutyl)5-sulfoisophthalate, β -Those having polar groups such as sodium glycerophosphate, N-methyljetanolamine, and potassium 2,3-dihydroxy-1-propanesulfonate are used.

(d) As the polyol, polyethylene glycol,
polyether diols such as polypropylene glycol,
Preferably used are polyester diols such as polybutylene adipate and polyphthylene phthalate, polylactone diols such as poly ε-caprolactone, and polycarbonate diols such as poly 1,6-hexane carbonate.

When the acrylic resin content of the amino group-containing comb-shaped acrylic resin obtained by reacting each component is less than 10% by weight, the properties of the acrylic resin cannot be expressed.
If the amount exceeds 0% by weight, the resin becomes brittle and the durability decreases, so it is preferably within the range of 10 to 90% by weight, and more preferably within the range of 20 to 80% by weight. In addition, if the number average molecular weight is less than 1000, the mechanical properties will deteriorate, and if it is larger than 1000, the viscosity will be high when dissolved in an organic solvent etc., making it difficult to make magnetic paint. is preferably used, and has a number average molecular weight of 10,000 to 60,000.
are more preferably used. In addition, if the amino group-containing acrylic resin before being bonded into a comb shape by a urethane bond or a urea bond has a number average molecular weight of less than 500, it will not be able to exhibit the properties of an acrylic resin;
If it is larger than 0, the degree of freedom of the acrylic resin will decrease, and the dispersibility of the magnetic powder will decrease when it is made into a magnetic paint.
Those with a number average molecular weight of 500 to 30,000 are preferably used, and those with a number average molecular weight of 1,000 to 10,000 are more preferably used.

Furthermore, if the amount of amino groups introduced into the amino group-containing comb-shaped acrylic resin is less than 0.05 mmol/g, the dispersibility of the metal magnetic powder with a pH of 7 or less cannot be sufficiently improved; If the amount exceeds mmol/g, the viscosity increases when dissolved in an organic solvent etc. due to aggregation of amino groups, making it difficult to make magnetic paint, so 0.05 to 1
It is preferably within the range of 0 mmol/g, and from 0.2 to
More preferably, it is within the range of 5 mmol/g.

Such amino group-containing comb-shaped acrylic resin may be used in combination with other binder resins, such as polyurethane resins, vinyl chloride-vinyl acetate copolymers, cellulose resins, polyvinyl butyral resins, It is compatible with and used in combination with commonly used binder resins such as polyester resins, phenolic resins, and polyisocyanates.

The binder component using such an amino group-containing comb-shaped acrylic resin has a pH of 10 to 35% relative to the metal magnetic powder in order to sufficiently improve the dispersibility of the metal magnetic powder with a pH of 7 or less.
It is preferably used within the range of 15 to 30% by weight.
It is more preferable to use it within a range of % by weight.

The magnetic recording medium of the present invention may be manufactured according to a conventional method. For example, the above-mentioned amino group-containing comb-shaped acrylic resin may be used with or without other binder resin, magnetic powder, organic A magnetic paint may be prepared by mixing and dispersing the magnetic paint with a solvent and other additives, and this magnetic paint may be applied onto a substrate by any method such as spraying or roll coating, and dried. At this time, a magnetic layer may be provided on the surface of the substrate and a back coat layer may be provided on the opposite surface, or magnetic layers may be provided on both surfaces of the substrate. When a back coat layer is provided in this way, this amino group-containing comb-shaped acrylic resin is also suitably used as a binder resin for the back coat layer.

Examples of the magnetic powder used here include Fe powder, CO powder, Fe-Ni-
A wide variety of conventionally known metal magnetic powders are included, such as Cr alloy powder.

Further, as the organic solvent, those commonly used in magnetic recording media, such as methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, toluene, ethyl acetate, tetrahydrofuran, dioxane, and dimethyl formamide, are used alone or in a mixture of two or more.

Furthermore, as a substrate, polyethylene terephthalate,
Various synthetic resin films such as polypropylene, polycarbonate, polyethylene naphthalate, polyamide, polyamideimide, polyimide, etc., and metal foils such as aluminum foil and stainless steel foil, which are commonly used as substrates, are all suitable for use. be done.

In addition, magnetic paint contains myristic acid, stearic acid,
Lubricant such as stearic acid ester, silicone oil, paraffin, alumina, 0r20. If necessary, those commonly added to magnetic paints, such as abrasives such as red iron, carbon black, or dispersants such as lecithin, may be used.

[Example〕 Next, embodiments of the invention will be described.

Example 1 Methyl methacrylate 90 parts by weight Diethylaminoethyl methacrylate 21〃Rate α,α'-azobisisobutyro 1.5〃Nitrile thioglycerin 3.2〃Tetrahydrofuran 100〃This composition was placed in a flask equipped with a condenser. After replacing with nitrogen thoroughly,
The reaction was carried out at 60°C for 2 hours while stirring.

Next, the obtained reaction product was purified by reprecipitation in petroleum ether and water, and dried under reduced pressure at 60°C for 48 hours to obtain an acrylic resin.

The acrylic resin thus obtained had a molecular weight of 5.0×10' as measured by vapor pressure osmosis.

Next, using the acrylic resin obtained in this way, 150 parts by weight of acrylic resin 1.4-
Butanediol 4.8〃PolyL6-hexane carbonate 65〃Todiol (number average molecular weight 4.4'-diphenylmethane 33〃Socyanate tin octylate 0.05s Tetrahydrofuran 100〃Toluene
A composition of 100% was heated to 80% under a nitrogen atmosphere.
The reaction was carried out at °C for 10 hours, and after the reaction, the mixture was diluted to 20% by weight with tetrahydrofuran to obtain an amino group-containing comb-shaped acrylic resin solution.

The comb-shaped acrylic resin thus obtained has an acrylic resin content of 59% by weight, an amino group content of 1 mmol/g, and a number average molecular weight of 30. It was OX 10'.

Using the amino group-containing comb-shaped acrylic resin thus obtained, tx-Fe magnetic powder (pH 6.5, 100 parts by weight, coercive force 1500 oersted, saturation phase 120 emu/g), amino group-containing comb-shaped acrylic resin Resin 12 Resin polyurethane resin 10 Polyfunctional isocyanate 3 Carbon black
3 α-AIZO3 powder 1
〃Myristic acid 2 〃N-Butyl stearate 2.5〃Cyclohexanone
130〃Toluene
A magnetic coating material was prepared by mixing and dispersing the composition No. 130 in a ball mill for 72 hours. This magnetic paint is applied onto a polyethylene terephthalate film with a thickness of 20 μm so that the thickness after drying is 5 μm, and is dried to form a magnetic layer.
After calendering, the tape was cut into 1/2 inch width to produce a magnetic tape.

Example 2 In the synthesis of the acrylic resin in Example 1, the amount of diethylaminoethyl methacrylate used was changed from 21 parts by weight to 15.5 parts by weight, and the amount of αα゛-azobisisobutyronitrile used was changed to 1.5 parts by weight. parts by weight to 1.6 parts by weight, and the amount of thioglycerin used from 3.2 parts by weight to 8 parts by weight.
．． Same as Example 1 except that the amount was changed to 6 parts by weight,
An amino group-containing acrylic resin having a molecular weight of 2.0×10' was obtained by vapor pressure osmosis.

Next, in the synthesis of the amino group-containing comb-shaped acrylic resin in Example 1, the same procedure as in Example 1 was used except that the same amount of the acrylic resin obtained in Example 2 was used instead of the acrylic resin obtained in Example 1. Similarly, the content of acrylic resin was 59% by weight, and the content of amino groups was 0.3 mmol/
g, to obtain an amino group-containing comb-shaped acrylic resin having a number average molecular weight of 40.0×10 3 in terms of polystyrene measured by GPC.

The procedure of Example 1 was repeated except that the amino group-containing comb-shaped acrylic resin thus obtained was used in the same amount in place of the amino-group-containing comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1. A magnetic tape was manufactured using the following steps.

Example 3 In the synthesis of the amino group-containing comb-shaped acrylic resin in Example 1, the content of the acrylic resin was The amount is 60% by weight, the content of amino groups is 1 mmol/g, and the number average molecular weight is 30. A comb-shaped acrylic resin containing an amino group of OX 10'' was obtained.

The procedure of Example 1 was repeated except that the amino group-containing comb-shaped acrylic resin thus obtained was used in the same amount in place of the amino-group-containing comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1. A magnetic tape was produced using the following steps.

Example 4 A magnetic paint was prepared in the same manner as in Example 1, except that the polyurethane resin was omitted and the amount of amine group-containing comb-shaped acrylic resin was changed from 12 parts by weight to 65 parts by weight. A tape was made.

Example 5 In the composition of the magnetic paint in Example 1, 12 parts by weight of vinyl chloride-vinyl acetate vinyl alcohol copolymer was used instead of polyurethane resin, and the amount of amino group-containing comb-shaped acrylic resin was changed from 12 parts by weight. A magnetic tape was produced in the same manner as in Example 1 except that the amount was changed to 10 parts by weight.

Comparative Example 1 In the synthesis of the amino group-containing comb-shaped acrylic resin in Example 1, the acrylic resin was omitted, 5.7 parts by weight of ethylenediamine was used in place of 1,4-butanediol, and 5.7 parts by weight of ethylenediamine was used. The same procedure as in Example 1 was carried out, except that the amount of carbonate diol used was changed from 65 parts by weight to 100 parts by weight, and the amount of 4,4'-diphenylmethane diisocyanate was changed from 33 parts by weight to 47.4 parts by weight. An amino group-containing polyurethane resin having a number average molecular weight of 30 and OX 103 in terms of polystyrene by GPC measurement was obtained.

The magnetic coating was carried out in the same manner as in Example 1, except that the amino group-containing polyurethane resin thus obtained was used in the same amount in place of the amino group-containing comb-shaped acrylic resin used in the composition of the magnetic paint in Example 1. A tape was made.

Comparative Example 2 The composition of the magnetic paint in Example 1 was the same as in Example 1, except that the same amount of vinyl chloride-vinyl acetate-vinyl alcohol copolymer was used instead of the amino group-containing comb-shaped acrylic resin. A magnetic tape was produced using the following steps.

Regarding the magnetic tapes obtained in each example and comparative example,
Chroma S/N ratio, C/NPc and RF specific output were measured by the following methods.

<Chroma S/N ratio> Using a VH3 system VTR, a chroma signal of 3.58 MHz was applied to each obtained magnetic tape at 0.714 V p-P.
The signal was recorded on a brightness modulated signal, and the noise portion of the reproduced signal was measured using a chroma noise measuring device to determine the chroma S/N ratio. Note that the chroma S/N ratio is expressed as a relative value with the magnetic tape of Comparative Example 2 as a reference (OdB).

<C/N ratio> Using a VH3 system VTR, the obtained magnetic tape was
5± when recording a MHz signal and reproducing this signal.
Measure the noise generated within the IMHz range, and calculate the ratio of the reproduced signal to this noise using the Matsushita Electric Industrial Co., Ltd.; NV-8.
Measurements were made using a 70HD output level measuring device. In addition,
The C/N ratio is expressed as a relative value with the magnetic tape of Comparative Example 2 as a reference (OdB).

<RF specific output Using a VTR for measuring RF output, the obtained magnetic tape was
After recording a MHz signal at a constant level, the output when played back was measured, and the magnetic tape of Comparative Example 2 was used as a reference (OdB).
) is expressed as a relative value.

Table 1 below shows the results.

Table 1 shows that the dispersibility of metal magnetic powders with a pH of 7 or less is good, and the electromagnetic conversion characteristics are further improved.

Claims (1)

[Claims] 1. Comprising an amino group-containing comb-shaped acrylic resin in which an amino group-containing acrylic resin is bonded by either or both of a urethane bond and a urea bond, together with a metal magnetic powder having a pH of 7 or less. In the magnetic recording medium 2 having a magnetic layer, the amino group-containing acrylic resin has a number average molecular weight of 500.
3. The magnetic recording medium 3 according to claim 1, wherein the amino group-containing acrylic resin has a number average molecular weight of 1,000 to 100,000. Magnetic recording medium 4, amino group-containing comb-shaped acrylic resin has 0 amino groups.
．． The magnetic recording medium according to claims 1 and 3, which is an amino group-containing comb-shaped acrylic resin containing 05 to 10 mmol/g.