JPS6399276A - Coating composition for magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled composition outstanding in magnetic powder dispersibility, low in the porosity of the coating film formed, outstanding in both the strength and elongation of said film, by polyurethane synthesis in the presence of low molecular weight pyroxylin and/or carboxylated pyroxylin. CONSTITUTION:A polyurethane composite is prepared by incorporating (A) a polyurethane formed by reaction between (i) a polyol with a molecular weight 500-3,000 and (ii) equimolar amount or more of an organic isocyanate compound with (B) a low molecular weight pyroxylin (e.g., with a nitrogen content <=8.0wt%) and/or carboxylated pyroxylin each having an average polymerization degree <=30 followed by chain extension using a diol having two primary OH groups with a molecular weight <=200. This composite is incorporated as the binder to obtain the objective composition capable of giving outstanding adhesiveness between the substrate and the coating film formed and also high tensile modulus of said film without impairing the dispersibility of the magnetic powder preset in the pyroxylin.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides magnetic powder with good dispersibility and magnetic #!
The present invention relates to a coating composition for a magnetic recording medium that provides a magnetic recording medium with a low film porosity, excellent strength and elongation, and high tensile modulus.

(Prior art and problems to be solved by the invention) Currently, as coating compositions for magnetic recording media, γ-Fe,
It consists of a mixture of magnetic powder such as O., a binder, a dispersant, a lubricant, an antistatic agent, a solvent, etc. The binder is selected from vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinylidene chloride copolymer, butyral resin, epoxy resin, polyurethane resin, nitrified cotton, etc. Examples include combinations of two or more types. Among them, nitrified cotton has advantages such as improving the dispersibility of magnetic powder, so it is used in combination with other resins. In particular, it is common to combine it with polyurethane, which has excellent heat resistance, cold resistance, oil resistance, solvent resistance, durability, adhesion to other surfaces, and rubber elasticity.
Examples include combinations such as polyurethane/isocyanate group-containing resin/nitrified i4, or polyurethane/vinyl chloride-vinyl acetate copolymer/incyanate group-containing resin.

However, the film of nitrified cotton has low elongation and high Young's modulus, so when applying a coating solution containing nitrified cotton to form a coating,
The drying process tends to create large internal stresses in the paint film,
For this reason, there are problems such as poor adhesion between the wall film and the base, and if the base is flexible, the paint film may peel off or crack. In particular, poor interlayer bonding between binder and substrate can occur in chemically inert and highly crystalline plastic films, e.g.

This is noticeable when applied to polyethylene terephthalate film.

Therefore, DB
Plasticizers or dispersants such as P, fatty acids, and surfactants are added. However, in this case, there is a problem of changes in physical properties over time (decrease in adhesion, decrease in blocking resistance, etc.) due to bleed-out of these additives.
It was difficult to obtain a coating film with excellent overall physical properties.

In addition, various methods of modifying nitrified cotton itself have been studied.For example, there is a method of modifying nitrified cotton using low-molecular diisocyanate, but the reaction product does not have a high crosslink density, The film becomes too hard. Even when using a relatively flexible urethane prepolymer made by reacting low-molecular diisocyanate at both ends of polyester polyol or polyether polyol, if it is mixed with enough IT nitrified cotton to improve the adhesion of the coating, it will be difficult to apply the coating. Unless it is mixed immediately before, gelation occurs, making it difficult to store for a long time, which poses a practical problem.

In addition, a method has been proposed for producing urethane resin with good solvent solubility by adding a chain extender and cellulose resin to NGO-terminated urethane prepolymer and heating the mixture (Japanese Patent Laid-Open No. 54-43299 ).

However, in this case, cellulose resin is used for the purpose of preventing gelation or abnormal thickening during the synthesis reaction process of urethane resin, and for this purpose, a low molecular chain extender is first added to the chain. The best method is to add cellulose resin and heat it after it has been extended. When considering the urethane resin produced by the method based on the invention as a magnetic paint binder, if a cellulose resin other than nitrified cotton is used, the dispersibility of the magnetic powder is opaque, making it unusable for practical use. Unfortunately, the prepolymer having NCO at both ends crosslinks the nitrified cotton molecules, increases the molecular weight, increases the viscosity of the solution, and in severe cases results in gelation. In order to prevent this, as described in the invention, it is necessary to reduce the NCO content of the reaction system after carrying out the chain extension reaction to a certain degree.

However, as described in the invention, the polyurethane obtained in this way has improved solubility in solvents, but basically the nitrified cotton is softened, so it has poor rigidity or blocking resistance. In fact, after dissolving a urethane prepolymer having isocyanate groups at both ends in a solvent and partially extending the chain with an active hydrogen compound, the remaining inocyanate By reacting the base and nitrified M at a relatively low temperature, by adding modified nitrified cotton that softens the nitrified cotton while leaving most of the hydroxyl groups in the nitrified cotton, polyester films, etc. There have also been proposals for magnetic coating compositions for magnetic recording media that have improved adhesion to magnetic particles and maintain the dispersibility of magnetic powder, etc.
161132), the modified nitrified cotton molecules obtained in this method are crosslinked by polyurethane containing incyanate groups at both ends, and as the molecular weight increases, the viscosity of the solution increases, and in severe cases, gelation occurs. There is a problem with doing so.

To prevent this, it is necessary to reduce the NCO content in the reaction system to the O of the nitrified cotton.
It is preferable to maintain it in the range of 1/2 to 1/100 with respect to the number of moles of H group. Although this certainly improves the adhesion, it basically aims to soften the nitrified cotton. Because of this effect, the properties of nitrified cotton, such as imparting rigidity and imparting anti-blocking properties, are lost. Therefore, in practical use, it is necessary to use nitrified cotton or the like together.

In order to improve the dispersibility of the modified nitrified cotton, a modified nitrified cotton in which a hydroxyl group-containing urethane resin is addition-polymerized has also been proposed (Japanese Unexamined Patent Application Publication No. 1931-132).

However, even in this method, the obtained modified steel cotton is soft, so it is basically the same as the modified JX nitrified cotton and is not preferable.

(Means for Solving the Problems and Their Effects) Therefore, as a result of extensive research in order to improve these drawbacks, the present inventors have found that a solution system containing low molecular weight nitrified cotton and/or carboxylated nitrified cotton. When the chain extension reaction of polyurethane is carried out in The present invention was completed by devising a method to provide a coating M having a low resistance and excellent strength and elongation.

The reason for this is that the hydroxyl groups of low molecular weight nitrified cotton and/or carboxylated nitrified cotton are secondary, and also due to structural factors, the molecules used as chain extenders have a molecular weight of 1200 or less.
Compared to the primary OH of diols with N
Since the reactivity with CO is low, in the reaction system of the present invention, the polyurethane production reaction proceeds preferentially, while the low molecular weight nitrified cotton and/or carboxylated nitrified cotton in the solution react during the urethane synthesis reaction. It is presumed that this molecular association is dissociated, and as a result, low molecular weight nitrified cotton molecules or carboxylated nitrified cotton molecules and polyurethane molecules reach a very micro-dispersed state. Moreover, when polyurethane synthesis was performed using the method of the present invention using ordinary nitrified cotton, gelation occurred and a stable polyurethane solution could not be obtained.

The present invention will be explained in more detail below.

The organic diisocyanate used in the production of the invention is as follows:
There are no particular limitations, and any organic diisocyanate normally used for producing polyurethane can be used. That is, as the aromatic diisocyanate, 2.6-tolylene diinocyanate, 2.4-
) lylene diisocyanate), 4,4'-diphenylmethane diisocyanate, 1,5-s7tale diisocyanate, p-xylene diisocyanate, m-xylene diisocyanate, p-phenyl diisocyanate $-), m
-Fini diisocyanate, tolylene diisocyanate, aliphatic or alicyclic diisocyanate, 1.6-hexamethylene diisocyanate, 1.
Examples include 10-decamethylene diisocyanate, inlon diisocyanate, bis(isocyanate, methylcocyclohexane, dicyclohexylmethane diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, etc.).

As a polyol with a molecular weight of 500 to 3000.

The most common ones include polyester polyols such as polyethylene adipate, polyethylene propion oxynit, polycaprolactone, and polyethylene ether glycol, polypropylene ether glycol,
Examples include polyether polyols such as polytetramethylene ether glycol, silicone polyols, and polycarbonate polyols.

As the chain extender, diols such as ethylene glycol, propylene glycol, and butylene glycol, glycerin, and dihydroxycarboxylic acids having two li&on groups such as 2,2-dimethylolpropionic acid can be used.

The low molecular weight nitrified cotton used in the present invention has a nitrogen content of a, O
S or higher) means nitrified cotton with an average degree of polymerization of 30 or less. The average degree of polymerization is determined by the method described in "1 Industrial Nitrified Cotton" published by Asahi Kasei Co., Ltd., pages 48-50.
34872, which has a nitrogen content of 8.0 or more and a carboxyl group content of 2 mmot/10 o y or more. The amount of carboxyl groups is determined by the following measurement method. Weigh accurately about 1.51 grams of carboxylated nitrified cotton, put it into a 100 d Erlenmeyer flask together with about 50 sd of 0.1 N net aqueous solution, shake it, and let it stand for about 2 hours. Next, the contents were filtered, and the carboxylated nitrate was thoroughly washed with ion-exchanged water until the washing solution became completely neutral.
After confirming that this is the case, stop cleaning. Place the washed carboxylated nitrified cotton in a beaker with a small amount of water, and add 0.
Add 50 g of 0.5 M acetic acid and water bath solution to a beaker, shake, and leave overnight. Remove the upper layer from the beaker and use phenolphthalein as an indicator in a 01N NaOH water bath solution. blank test,
The amount of carboxyl groups is calculated using the following formula.

Carboxyl fund position = (NaOH dripping amount (rnl)
-Blank test NaOH dripping 1 (Tnt)), /20
x ((Water amount + 50) / (Sample weight - 1)) When using ordinary nitrified cotton, which is generally used as a binder for magnetic paint and has an average filtration capacity of more than 30'7', H, the detailed mechanism is Although it is unclear, gelation occurs during the reaction, making it impossible to obtain a sufficient solution.

Furthermore, cellulose derivatives other than nitrified cotton are not generally used because they do not have sufficient dispersibility for magnetic powder. For the reaction of polyurethane, there is a so-called one-shot method in which the reaction components are reacted all at once, or a so-called prepolymer method in which a prepolymer having an incyanate terminal is produced and a chain extender is used to pick up the polymer. Although there are known methods such as the polymer method, it is preferable to use the prepolymer method1.For the b0 reaction, commonly used catalysts may be used to shorten the reaction time or improve the yield. can. Examples of this catalyst include triethylamine, dimethylethanolamine, N, N,
Tertiary amines such as N', N'-tetramethyl-1,6-butanediamine and tin compounds such as dibutyltin dilaurate and dibutyltin di(2-ethylhexoate) can be used.

Further, during the reaction, it is preferable to use an organic solvent that is inactive to incyanate and can dissolve low molecular weight nitrified cotton and carboxylated nitrified f8. Examples of these solvents include methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone. Single or mixed solvents of ketones such as esters such as ethyl acetate, butyl acetate, and amyl acetate can be used. Furthermore, it is of course possible to use these solvents by adding a diluent such as benzene, toluene, or xylene.

The method for producing the composite composition of low molecular weight nitrified cotton and/i or carboxylated nitrified cotton and polyurethane of the present invention will be described below. An inocyanate inert solvent solution of a urethane prepolymer with terminal isocyanates, which is a reaction product of a polyol and a diisocyanate in an amount equal to or more than the same mole thereof, requires an inocyanate inert solvent solution of low molecular weight nitrified cotton and/or carboxylated nitrified cotton. The chain extension reaction is carried out in a system containing a chain extender, a chain extender, and a catalyst. At this time, the molar ratio between the terminal incyanate of the urethane prepolymer and the active hydrogen-containing group of the chain extender is maintained at 1 or less.

The magnetic coating composition for atmospheric recording media of the present invention includes a magnetic powder, a composite composition of the above-mentioned low molecular weight nitrified cotton and/or carboxylated nitrified cotton and polyurethane, an antistatic agent, a lubricant, and a dispersing agent as necessary. , a wetting agent, etc. are added. As the magnetic powder, any commonly used Fi may be used, such as r-Fe, Os, Fe, etc.
3O41Crom, Cod-Fe, 031CO-γ
-FelO, and barium ferrite or a mixture thereof. As a binder, in addition to the composite composition of low molecular weight nitrified cotton and/or carboxylated nitrified cotton and polyurethane according to the present invention, vinyl chloride-
Examples include combinations of one or more selected from vinyl acetate copolymers, vinyl chloride-vinyl acetate-vinyl alcohol copolymers, epoxy resins, polyurethanes, isocyanate-containing resins, cellulose derivatives, and the like.

The method for producing the magnetic coating composition of the present invention is based on a conventional method for producing magnetic coating compositions. For example, 1. the composite composition of low molecular weight nitrified cotton and/or carboxylated nitrified cotton and polyurethane according to the present invention, magnetic powder, lubricant, antistatic agent, and solvent are mixed in a kneader, ball mill, sand mill, attritor, etc. It can be obtained by mixing with K.

(Examples) Next, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

Hereinafter, parts and units are by weight, unless otherwise specified.

Reference example 1 Nitrified cotton HIG 1/16 manufactured by Asahi Kasei Industries, Ltd.
00 times the amount of water, stir well, and then dehydrate using a centrifuge. After repeating this 5 times, add 5 times the amount of water,
The average degree of polymerization of the nitrified cotton obtained by heating at 150C for 30 minutes in an autoclave was 28, and the carboxyl group content was 0.47 mmot/100. The nitrified cotton thus obtained was dried and dissolved in methyl ethyl ketone to obtain a 30% solution.

On the other hand, polyester polyol (Poly 2 manufactured by Dainippon Ink)
Weigh out 100 t of 0DX240) into a reactor with a capacity of 1000α and equipped with a stirrer and a flux condenser, and heat to 85C to dissolve while thoroughly purging with N and gas. 4゜4'-diphenylmethane diisocyanate (CMDI) 51.3 F was heated to 1091 by passing cooling water through it.
The mixture was dissolved in toluene and reacted for 4 hours. After 4 hours, methyl ethyl ketone 1 B 6. S P, methyl ethyl ketone solution of the low molecular weight nitrified cotton 49.7f, diptyltin dilaurate 0.10? , 2.52% of 1,4-butanediol were added, and the reaction was further carried out for 9 hours to obtain a composite composition A of low molecular weight nitrified cotton and polyurethane having a solid content of about 30 inches. Thereafter, compositions B to C were obtained in the same manner with the low molecular weight nitrified cotton content and polyurethane composition shown in Table 1.

Reference Example 2 100 parts of silk linters were placed in a desiccator, 30% of liquid nitrogen dioxide was added thereto, and the mixture was left to stand at room temperature for 30 hours, washed with water, and dried to obtain partially oxidized cellulose.

This is HgSO4/HNOs/H2O=59
React for 40 minutes in a mixed acid consisting of / 23 / 18,
Carboxylated nitrified cotton was obtained. The amount of nitrogen is 10.50 inches,
Carboxyl group content is 2.5 mmot/100
f Nitrified cotton, average degree of polymerization was 50. In the same manner, partially oxidized cellulose was obtained by changing the amount of nitrogen dioxide and the oxidation time, and nitrified with the above mixed acid to obtain carboxylated nitrified cotton of each strain as shown in the following table.

The carboxylated nitrified cotton thus obtained was dried and dissolved in methyl ether ketone to make a 30-line bath solution.
'j 6# In the same manner as in Example 1, low molecular weight nitrified AJB was applied to carboxylated nitrified cotton, and compositions D to H were prepared using the carboxylated nitrate-containing container and polyurethane composition shown in Table 1.
I got it.

Reference Example 3 A polyurethane The composition is as shown in Table 1.

Example 1 Using the composite composition A of low molecular weight nitrified cotton and polyurethane produced in Reference Example 1, it was dispersed in a ball mill for 48 hours according to the formulation shown in Table 2, and the obtained magnetic paint was mixed with polyethylene. Coated on terephthalate film, 20C
, dried at RH 65 for 24 hours, and measured the surface gloss (a measure of dispersibility) using a surface gloss meter (manufactured by Suga Test Instruments).
It was determined by measuring G-60 specular reflection "4. Also, the porosity of the coating film was determined by the following formula.

In addition, the magnetic paint was coated on paper and 20C1651
After drying at RH for 24 hours, heat treating at 60C for 24 hours,
A coating film with a film thickness of 20 to 30 μm was obtained. Tensilon tensile tester (manufactured by Toyo Bold Line) K, strength and elongation of coating film,
The tensile modulus of elasticity was determined (grip length Bo 1 m, tensile speed B II 7 minutes). Table 3 shows the results of the various physical properties determined.

Examples 2 to 3 Using the composite composition B-C of low molecular weight nitrified cotton and polyurethane produced in Reference Example 1, the compound composition shown in Table 2 was dispersed in a ball mill for 48 hours, and the resulting magnetic Apply the paint onto the polyethylene Tele 7 tallate film,
After drying at 0.65% RH for 24 hours, the surface gloss and porosity of the coating film were determined in the same manner as in Example 1. Further, the magnetic paint was applied onto a release paper, dried at 20C, 65% RH for 24 hours, and then heat treated at 60C for 24 hours to change the strength and elongation and tensile modulus of the coating film in the same manner as in Example 1. I asked for it. The results are shown in Table 5.

Examples 4 to 8 Using the composite composition D-J'fc of carboxylated nitrified cotton and polyurethane produced in Reference Example 2, the compositions shown in Table 2 were dispersed for 48 hours using a ball mill. The magnetic material was coated on a polyethylene terephthalate film and the physical properties were measured in the same manner as in Example 1. The results are shown in Table 3.

Comparative Examples 1 to 3 Using a magnetic paint prepared by adding low molecular weight nitrified #ll manufactured in Reference Example 1 to the polyurethane X synthesized in Reference Example 3 at the ratio of the magnetic paint formulation shown in Table 2, Example 1
Various physical properties were determined using the procedures and methods shown below. The results are shown in Table 5.

Comparative Examples 4 to 8 Examples were prepared by adding the carboxylated nitrified f4 produced in Reference Example 2 to the polyurethane X synthesized in Reference Example 3 in the ratio of the magnetic coating formulation shown in Table 2. Various physical properties were determined using the procedures and methods shown in 1. The results are shown in Table 3.

Comparative Example 9 Cellulose acetate butyrate and cellulose acetate butyrate (CAB 381-0.1 manufactured by Eastman Co., Ltd.) were used in the same manner as in Reference Example 1, with the composition shown in Table 1, except that the low molecular weight nitrified cotton was changed to cellulose acetate butyrate (CAB 381-0.1 manufactured by Eastman). A polyurethane composite composition 1' was prepared. Various physical properties were determined using the procedure and method shown in Example 1 using a magnetic paint prepared using the product 1' according to the formulation shown in Table 2. Table 3 shows the results.
Shown below.

Comparative Example 10 In the same manner as Reference Example 1, in an autoclave at 150C.
The average degree of polymerization obtained by heating for 10 minutes at 35, carboxyl group content i 0.23 mmoυ'1o o P Using nitrified cotton, which is nitrified cotton, the composition shown in Table 1 was prepared in the same manner as in Reference Example 1. When a composite composition J' of nitrified cotton and polyurethane was produced, it gelled during the reaction and a stable polyurethane solution could not be obtained.

Comparative Example 11 Low molecular weight nitrified cotton with polymerization degree of 50 and carboxyl group-containing fl
O, 27 mmoL/100 with normal nitrified cotton (
A composite composition of nitrified cotton and polyurethane was prepared in the same manner as in Reference Example 1, except that the composition was changed to HIG 1/8 (manufactured by Asahi Kasei Kogyo Co., Ltd.), as shown in Table 1.
Gelation occurred during the reaction, and a stable polyurethane solution could not be obtained.

Comparative Example 12 Using polyurethane solution X produced in Reference Example 2, Table 2
The procedure shown in Example 1 was carried out using the magnetic paint obtained by dispersing for 48 hours in a ball mill with the formulation shown in
Various physical properties were determined using the method. The results are shown in Table 5.

Table 3 List of Measurement Results (Effects of the Invention) As is clear from the above results, the magnetic dispersibility, the strength of the coated and dried coating film, the 11 degrees, the It is clear that in all respects of the elastic modulus, this material is far superior to the TLX material produced by the usual method using the same materials. If a nitrified χ3 with an average degree of unity exceeding 30 or a carboxylated nitrified cotton with a carboxyl group content of less than 2 mmot is used as the primary cellulose derivative, gelation will occur during the reaction, resulting in the formation of the desired cellulose 164. A polyurethane composite cannot be obtained, and when cellulose acetate butyrate is used, sufficient dispersibility of magnetic powder cannot be obtained.

Claims (1)

[Claims] During polyurethane synthesis, a prepolymer obtained by reacting a polyol with a molecular weight of 500 to 3000 with an equimolar or more organic diisocyanate compound is chain-extended with a diol having two primary OHs with a molecular weight of 200 or less, during the chain extension reaction. The binder is a composite of low molecular weight nitrified cotton and/or carboxylated nitrified cotton and polyurethane, which is produced in the presence of one type or a mixture of low molecular weight nitrified cotton and carboxylated nitrified cotton with an average degree of polymerization of 30 or less in the reaction system. A coating composition for magnetic recording media comprising the following: