JPH06157450A - Isocyanate-based crosslinking agent and magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide an isocyanate-based crosslinking agent composed of a blocked polyisocyanate blocked by using a fluorinated alcohol having a specific carbon chain length as a masking agent, having low regeneration temperature and free from problems caused by the masking agent. CONSTITUTION:A blocked polyisocyanate is produced by blocking the isocyanate groups of a polyisocyanate compound having >=2 isocyanate groups in one molecule with a fluorinated alcohol of the formula HO-CH2CnF2n+1-mHm or formula ((n) and (i) are 1-7; (m) is 0-2n; (j) is 0-2i) as a masking agent. The blocked polyisocyanate can be used as an isocyanate-based crosslinking agent having low regeneration temperature and free from the safety problems caused by the masking agent and the lowering of the physical properties of the crosslinked product. A magnetic recording medium such as magnetic disk and magnetic tape having excellent magnetic properties and durability can be produced by using the blocked polyisocyanate as a crosslinking agent for the magnetic layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an isocyanate cross-linking agent and a magnetic recording medium such as a magnetic disk or a magnetic tape using the same.

[0002]

2. Description of the Related Art Polyisocyanate compounds having two or more isocyanate groups in one molecule, for example, a 3 mol adduct of tolylene diisocyanate with trimethylolpropane, have a high activity of two or more active hydrogens. It is widely used as a crosslinking agent for molecular compounds. However, since this polyisocyanate compound has too high reactivity, it has the inconvenience that it is inactivated by reacting with moisture in the atmosphere or moisture contained in other materials. .

Therefore, in the blocked polyisocyanate obtained by temporarily blocking the highly reactive isocyanate group with various masking agents, for example, in the above-mentioned 3 mol tolylene diisocyanate adduct of trimethylolpropane, There has been an attempt to use a product obtained by blocking three isocyanate groups by using phenol as a masking agent as the crosslinking agent.

This blocked polyisocyanate regenerates the isocyanate group by thermal decomposition upon use, but in the case of using the above-mentioned phenol as a masking agent, the phenol is It is necessary to heat to a high temperature of 170 ° C. or higher in order to eliminate and regenerate the isocyanate group. Therefore, it is not suitable for the purpose of use where it cannot be exposed to high temperatures.

For example, in a magnetic recording medium, when a magnetic layer containing magnetic powder and a binder is provided on a non-magnetic support, a polymer resin having two or more active hydrogens is used as the binder, and an isocyanate is used as the crosslinking agent. -A magnetic layer with good solvent resistance and mechanical strength is formed using a genotype cross-linking agent, but in the process of forming such a magnetic layer, in order to prevent deterioration of the non-magnetic support and deterioration of magnetic properties. It should be performed at 100 ° C. or lower, more preferably 60 ° C. or lower. Therefore, the blocked polyisocyanate using the above-mentioned phenol as a masking agent cannot be used for this kind of purpose.

As a masking agent capable of regenerating the isocyanate group at a low temperature, a blocked polyisocyanate using hydrogen cyanide, acidic sodium sulfite or the like is also known. However, hydrogen cyanide is highly toxic and not practical. Also, with sodium acid sulfite, it remains in the reaction system even after the isocyanate group is regenerated, which adversely affects the physical properties of the cross-linked product.For example, in a magnetic layer containing magnetic powder and a binder, magnetic properties and durability There is a problem that deteriorates.

[0007]

As described above, the conventionally known blocked polyisocyanate has a too high regeneration temperature of the isocyanate group, or has a safety problem due to the masking agent after regeneration or cross-linking formation. Since it has a problem of physical property deterioration, it cannot be effectively used as an isocyanate cross-linking agent, particularly as a cross-linking agent for magnetic recording media.

In view of the above-mentioned conventional circumstances, the present invention provides an isocyanate-based crosslinking agent which has a low regeneration temperature and is free from the problems of safety caused by the masking agent and of the physical properties of the crosslinking product. It is intended to provide a polyisocyanate and a magnetic recording medium using the same.

[0009]

[Means for Solving the Problems] The present inventors first considered the mechanism of the regeneration reaction of blocked polyisocyanate for the above purpose. Although the details of this mechanism are unknown, it is generally considered to be the following thermal decomposition reaction.

[0010]

Here, in order to lower the regeneration temperature,
It is important to reduce the bond energy of the C—X bond to facilitate the above reaction and to facilitate the reaction to the right because the boiling point of the masking agent HX is low.
Further, the low boiling point of the masking agent HX is also important in that the masking agent does not remain in the final cross-linked product.

From such a viewpoint, as a result of examining various masking agents, it was found that fluorinated alcohols are suitable. Although ordinary alcohols have a lower boiling point than phenols, they have high C—O bond energy when bonded to an isocyanate group, and the regeneration temperature is 200 ° C.
That is all. However, in the case of alcohol fluoride, the C—O bond becomes weak because the fluorine atom attracts an electron.
Further, the fluorocarbon chain has a small intermolecular force, and the perfluoro compound generally has a low boiling point. Therefore, polyisocyanate blocked with a fluorinated alcohol of an appropriate chain length is
The isocyanate group can be regenerated at 60 ° C or lower.

As described above, the present inventors have found that a blocked polyisocyanate using a fluorinated alcohol having a specific chain length as a masking agent is more effective than a conventional one using a phenol as a masking agent. When the isocyanate group can be regenerated at a lower temperature, and the masking agent does not cause the problem of safety or deterioration of the physical properties of the crosslinked product after regeneration, particularly when used as a crosslinking agent for a magnetic recording medium, The inventors have found that a magnetic layer having excellent magnetic properties and durability can be formed, and have completed the present invention.

That is, the first aspect of the present invention is
Polyisocyanate having two or more isocyanate groups
The above isocyanate group of the compound is blocked with a masking agent.
Isocyanate Consisting of Blocked Polyisocyanate
-In the cross-linking agent, the above masking agent has the following formula
(1) or (2); HO-CH₂C_nF_{2n + 1-m}H_m … (1) (In the formula, n, an integer of i = 1 to 7, m = 0 to 2n, j = 0
Is a fluorinated alcohol represented by
A second aspect of the present invention relates to a isocyanate-based cross-linking agent.
A magnetic layer containing magnetic powder and a binder is provided on a non-magnetic support.
In the magnetic recording medium, the cross-linking agent of the above-mentioned binder
As the isocyanate-based cross-linking agent of the first invention,
The present invention relates to a magnetic recording medium.

[0015]

The fluorinated alcohol used as a masking agent in the present invention has one or two fluorinated carbon chains represented by the above formula (1) or (2) in one molecule. Compounds, and in both formulas, n and i = 1 to 7 are fluorinated alcohols that are eliminated when the number is 8 or more.
This is because the boiling point of hydrogen increases.

The polyisocyanate compound used in the present invention may be any compound having two or more isocyanate groups in one molecule, and any of aliphatic, aromatic and alicyclic compounds can be used. Can be used. The tolylene diisocyanate 3 mol adduct of trimethylolpropane described above can also be used as a typical polyisocyanate compound, and its chemical structure is as shown in the following formula (3).

[0017]

[Chemical 1]

In the present invention, the above polyisocyanate compound and the fluorinated alcohol represented by the above formula (1) or (2) as a masking agent are combined with an isocyanate group and a hydroxyl group. Blocked polyisocyanate in which the isocyanate group is blocked by the urethanization reaction.
To This reaction may be carried out using a known urethanization catalyst such as tin octylate at a reaction ratio such that the hydroxyl group is equivalent to or slightly larger than the isocyanate group.

The blocked polyisocyanate thus obtained has two or more urethane structure moieties represented by the following formula (11) or (12) in one molecule,
This part is thermally decomposed at a temperature of 100 ° C. or lower, preferably 60 ° C. or lower to regenerate the isocyanate group,
The fluorinated alcohol represented by the formula (1) or (2) is eliminated. The thus desorbed fluorinated alcohol has a low boiling point and can be easily removed, so that it does not adversely affect the cross-linked product and does not cause toxicity such as hydrogen cyanide.

[0020] (In the formula, n, i, m and j are the same as above)

As an example of such a blocked polyisocyanate, a block product obtained by urethane-reacting 3 mol of trifluoroethanol as a masking agent with 3 mol of the tolylene diisocyanate tolylene diisocyanate adduct described above. The chemical structure thereof is as shown in the following formula (4).

[0022]

[Chemical 2]

The magnetic recording medium of the present invention comprises the above-mentioned blocked polyisocyanate in a magnetic paint containing a magnetic powder, a binder, and usually an organic solvent and other additives.
Is added to the non-magnetic support such as polyester film, or it is applied onto the non-removable support and then onto the non-magnetic support. It is manufactured by transferring to.

In this manufacturing process, a heat treatment for regenerating the isocyanate group in the above-mentioned cross-linking agent is usually carried out after the coating on the non-magnetic support or the releasable support, and the binder by the regenerated isocyanate group is changed. By sufficiently causing the cross-linking, it is possible to form a magnetic layer having a three-dimensional network structure having excellent durability and the like.

Magnetic powders include γ-Fe ₂ O ₃ and Co.
In addition to the oxide-based magnetic powder such as γ-Fe ₂ O ₃ and barium ferrite contained, conventionally known ones such as metal-based magnetic powder such as Fe, Co, Mn or alloys thereof can be widely used. As the binder, polyurethane resins, polyester resins, vinyl chloride-vinyl acetate copolymers, fibrin resins, etc., which are conventionally known for magnetic layers, can be used alone or in combination of two or more kinds. For at least one of them, those having two or more active hydrogens in the molecule are preferably used.

The present invention is characterized in that the above-mentioned blocked polyisocyanate is used as an isocyanate cross-linking agent, particularly as a cross-linking agent for a magnetic layer in a magnetic recording medium, as described above. Apart from this cross-linking agent, for example, it can be used as a polymer raw material by mixing with polyols to directly synthesize polyurethane having a three-dimensional network structure.

[0027]

As described above, according to the present invention, by using a fluorinated alcohol having a specific carbon chain length as a masking agent, an isocyanate-based crosslinking agent having a low regeneration temperature and a masking agent is used. It is possible to obtain a blocked polyisocyanate free from the problems of safety caused by the above and deterioration of the physical properties of the crosslinked product, and by using this blocked polyisocyanate as a crosslinking agent for the magnetic layer, A magnetic recording medium having excellent characteristics and durability can be obtained.

[0028]

EXAMPLES Next, examples of the present invention will be described to explain more specifically. In the following, "parts" means "parts by weight".

Example 1 As a polyisocyanate compound, Coronet L (3 mol addition product of tolylene diisocyanate of trimethylolpropane) manufactured by Nippon Polyurethane Industry Co., Ltd. was used. 90 parts of a 25 wt% ethyl acetate solution of this coronet L,
Trifluoroethanol 10 parts and tin octylate 0.
02 parts were placed in a flask equipped with a condenser, and after sufficiently substituting with nitrogen, the mixture was reacted for 20 hours at room temperature with thorough stirring to obtain a blocked polyisocyanate A.

This blocked polyisocyanate A is
^{By 13} C-NMR analysis, the isocyanate group (128 ppm) in the molecule was completely disappeared, and instead, 151 ppm
The following formula near; Since a characteristic absorption represented by C of the * mark in the urethane structure portion represented by the following appears, it was found to be a blocked polyisocyanate having the chemical structure represented by the above formula (4).

The blocked polyisocyanate A thus obtained was used as the isocyanate crosslinking agent of the present invention. Since the crosslinker has a low regeneration temperature of the isocyanate group of 50 ° C, it is easy to regenerate the isocyanate group that contributes to the crosslinking, and the trifluoroethanol released at that time has a boiling point of 77 ° C. Since it is low, it can be easily removed if necessary.

Example 2 As a polyisocyanate compound, a coroneate HL (a hexamethylene diisocyanate 3 mol adduct of trimethylolpropane) manufactured by Nippon Polyurethane Industry Co., Ltd. was used. 92 parts of a 25 wt% ethyl acetate solution of this coronet HL, 8 parts of trifluoroethanol, and 0.02 part of tin octylate were placed in a flask equipped with a condenser, and after thoroughly purging with nitrogen. , Reacting at room temperature for 20 hours with good stirring to obtain blocked polyisocyanate B
Got

The blocked polyisocyanate B is
NMR analysis confirmed that the isocyanate group in the molecule was completely
Disappears, and instead the following formula; As a characteristic absorption indicating the urethane structure part represented by
Characteristic absorption similar to that of locked polyisocyanate A
Was seen.

The blocked polyisocyanate B thus obtained was used as the isocyanate cross-linking agent of the present invention. Since the crosslinker has a low regeneration temperature of the isocyanate group of 50 ° C, it is easy to regenerate the isocyanate group that contributes to crosslinkage, and the trifluoroethanol that is released at that time is as described above. Since it has a low boiling point, it can be easily removed if necessary.

Example 3 Barium ferrite powder 300 parts Phosphoric acid-modified vinyl chloride-vinyl acetate-vinyl alcohol copolymer 30 parts Polyester polyurethane 8 parts Carbon black 12 parts Alumina powder 45 parts Cyclohexanone 395 parts Toluene 395 parts

The above composition was mixed and dispersed by a sand grinder mill for 2 hours, and 16 parts of blocked polyisocyanate A as an isocyanate cross-linking agent was added thereto, and further mixed for 15 minutes to prepare a magnetic paint. did.

Next, this magnetic paint was applied to a thickness of 70 μm.
On the polyethylene terephthalate film of, the coating was dried to a thickness of 0.6 μm, dried, calendered, and further heat-treated at 50 ° C. for 96 hours, and then punched into a disk shape. A magnetic disk was produced.

The magnetic disk was immersed in tetrahydrofuran for 2 hours while being irradiated with ultrasonic waves, and the solvent resistance of the magnetic layer was examined. As a result, almost no dissolved component was found and very good solvent resistance was obtained. showed that. From this result, 5
It was found that a sufficiently crosslinked magnetic layer was obtained by heat treatment at a low temperature of 0 ° C. It was also confirmed that the magnetic characteristics were good and that excellent electromagnetic conversion characteristics were obtained by the recording / reproducing apparatus.

Example 4 Blocked polyisocyanate B was used in place of blocked polyisocyanate A as the isocyanate cross-linking agent.
A magnetic disk was produced in the same manner as in Example 1 except that 16 parts were used. The solvent resistance of this disk was examined in the same manner as in Example 3. As a result, almost no dissolved components were found, the disk showed very good solvent resistance, and a magnetic layer sufficiently crosslinked by heat treatment at a low temperature of 50 ° C. was found. I was able to get it. It was also confirmed that the magnetic characteristics were good and that excellent electromagnetic conversion characteristics were obtained by the recording / reproducing apparatus.

Comparative Example 1 In the same manner as in Example 1 except that as the isocyanate cross-linking agent, 10 parts of Coroneate L manufactured by Nippon Polyurethane Industry Co., Ltd. was used in place of the blocked polyisocyanate A. A magnetic disk was prepared. When the solvent resistance of this disk was examined in the same manner as in Example 3, a considerable proportion of solvent-extracted components was found, and the solvent resistance was very poor.

The solvent-extracted component was estimated by IR analysis to be the binder component and the urea compound in the magnetic layer, and the latter urea compound was presumed to be a reaction product of coronate L and water. Further, from the result of IR analysis at the stage of the magnetic paint, it was found that 99% or more of the isocyanate groups of the coroneto L had already reacted with the water in the air or on the surface of the barium ferrite powder. Therefore, it is considered that the crosslinking reaction of the magnetic layer hardly occurred and the solvent resistance became poor.

Comparative Example 2 Instead of blocked polyisocyanate A as an isocyanate type cross-linking agent, 3 mol of Torenylene diisocyanate of coroneate Ap [trimethylolpropane] manufactured by Nippon Polyurethane Industry Co., Ltd. was added. Pheno as a masking agent for objects
A magnetic disk was produced in the same manner as in Example 1 except that 10 parts of a block obtained by subjecting a urethane to a urethane reaction was used.

The solvent resistance of this disk was examined in the same manner as in Example 3. As a result, a considerable proportion of the solvent-extracted components was found and the disk resistance was poor. From the IR analysis, the above solvent-extracted components were found to be the binder component in the magnetic layer and the coroneate Ap. From this, it was found that the heat treatment at a low temperature of 50 ° C. did not regenerate the isocyanate group of the coronate Ap, resulting in insufficient crosslinking of the binder.

Claims (2)

[Claims] 1. Two or more isocyanate groups per molecule
The above-mentioned isocyanate group of the polyisocyanate compound having
Blocked polyisocyanate blocked with masking agent
In the isocyanate-based cross-linking agent consisting of a net, the above
Is a masking agent of formula (1) or (2) below; HO-CH₂C_nF_{2n + 1-m}H_m … (1) (In the formula, n, an integer of i = 1 to 7, m = 0 to 2n, j = 0
Is a fluorinated alcohol represented by
Sociate crosslinking agent. 2. A magnetic recording medium comprising a magnetic layer containing a magnetic powder and a binder provided on a non-magnetic support, and the isocyanate as claimed in claim 1 as a crosslinking agent for the binder.
A magnetic recording medium using a cross-linking agent.