JP2596541B2 - Manufacturing method of magnetic recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention forms a coating layer containing a specific polyurethane resin on a nonmagnetic support, and then cures the coating layer by electron beam irradiation. More particularly, the present invention relates to a method for manufacturing a magnetic recording medium having excellent durability such as mechanical strength, moisture and heat resistance, and heat resistance.

[Conventional technology]

Magnetic recording media such as magnetic tapes and floppy disks are manufactured by applying a magnetic paint consisting of magnetic powder, a binder, an organic solvent, and various additives as necessary onto a non-magnetic support such as a polyester film and drying. Is done.
A method is known in which an electron beam-curable resin composition is used as the binder, and the magnetic coating film is irradiated with an electron beam to be cured. For example, Japanese Patent Publication No. 47-12423, Japanese Patent Publication No. 53-3
2123 JP, JP-A-47-15104, JP-A-50-77433
No. 6,086,045.

As described above, the method for producing a magnetic recording medium using an electron beam curable resin as a binder is advantageous in terms of improving the pot life of a magnetic paint, improving the properties of a magnetic coating film, simplifying the production process, saving energy, and the like.

Acrylic modified resins such as polyester acrylate, urethane acrylate and epoxy acrylate are used as the electron beam curing resin, but urethane acrylate, which has excellent mechanical strength and flexibility, is mainly used for magnetic recording media. I have. However, in order to obtain a magnetic recording medium with excellent durability, mechanical strength and elastic modulus are high,
A well-balanced binder having an appropriate flexibility is required, and conventional urethane acrylates cannot sufficiently satisfy the performance.

[Object of the invention]

In order to obtain a magnetic recording medium with excellent durability, the present inventors cure with an electron beam, have a high mechanical strength, a high elastic modulus, a moderate flexibility, a well-balanced, excellent heat and moisture resistance, and excellent heat resistance. As a result of intensive studies on the polyurethane resin used for the coating film layer, the present invention was found.

That is, the gist of the present invention is that a nonmagnetic support has 1 to 3 polyether polyol skeletons obtained by adding propylene oxide and / or ethylene oxide to sorbitol in one molecule, and 3 to 15 acryl or methacryl groups. To form a coating film layer containing a polyurethane resin having a number average molecular weight of 1,000 to 50,000, and then apply the accelerating voltage of 150 to 3 to the coating film layer.
A method for manufacturing a magnetic recording medium characterized by curing by irradiation with an electron beam under conditions of 00 KV and an absorbed dose of 0.5 to 20 Mrad.

[Configuration of the invention]

(1) Polyurethane resin The polyurethane resin used for the coating layer of the present invention has a polyether polyol skeleton obtained by adding propylene oxide and / or ethylene oxide to sorbitol in one molecule.
It is preferable that the number of the acryl or methacrylic groups is 3 to 15, and the number average molecular weight is in the range of 1,000 to 50,000.

In the polyurethane resin used in the present invention, the polyether polyol portion obtained by adding propylene oxide and / or ethylene oxide to polyfunctional sorbitol represented by the following formula is used to improve the mechanical strength, elastic modulus, wet heat resistance and heat resistance of the magnetic layer. However, if the number of sorbitol-based polyether polyol skeletons is 4 or more in one molecule, the coating film becomes too hard, which is not preferable. In addition, it is not preferable because the resin is easily three-dimensionally formed into a gel when producing the resin.

Resins having 16 or more acrylic or methacrylic groups in one molecule are not preferred because they tend to gel during resin production or storage. If the number is less than 2, the mechanical strength and the elastic modulus of the coating film layer become low, which is not preferable.

If the number average molecular weight of the resin is more than 50,000, the dispersibility of the magnetic powder is inferior and the surface smoothness of the magnetic recording medium deteriorates, which is not preferable.

The polyurethane resin used in the present invention has a specific structure as described above, whereby a magnetic coating film using the present resin is cured with an electron beam at a low dose, and the mechanical strength and elastic modulus of the cured coating film are moderately high. It becomes a flexible and well-balanced resin.

The method for producing the polyurethane resin used in the present invention is appropriately selected from known production methods in consideration of the desired degree of polymerization of the polyurethane resin, the type of raw materials used, and the like.

For example, a polyvalent isocyanate compound (a) or a urethane prepolymer (b) having an isocyanate group at a terminal and a compound (c) having an active hydrogen and an acryl or methacryl group are optionally added to the isocyanate group, if necessary. Using an inert organic solvent, a vinyl monomer or a vinyl oligomer, and further using a usual urethanization catalyst and a thermal polymerization inhibitor if necessary, reacting at a temperature of 10 to 150 ° C, preferably 20 to 100 ° C. Obtained by 1
0.3 to 1.2 isocyanate groups and 1
It is obtained by reacting a modified isocyanate having two or more acrylic or methacrylic groups with a sorbitol-based polyether polyol.

In addition, a sorbitol-based polyether polyol, a polyol compound having at least two hydroxyl groups, and a compound (c) having active hydrogen and an acryl or methacryl group are added to an organic solvent inert to an isocyanate group, a vinyl monomer. Alternatively, it can also be obtained by mixing a vinyl oligomer, and dropping and reacting a polyvalent isocyanate compound (a) or a urethane prepolymer (b) having an isocyanate group at a terminal.

Examples of the polyvalent isocyanate compound (a) include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 1,3-xylylene diisocyanate, 1,4-xylylene diisocyanate, and diphenylmethane-4,4'-diisocyanate. Diphenylmethane-2,4'-diisocyanate, 3-methyldiphenylmethane diisocyanate, hexamethylene diisocyanate, isifolone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, dicyclohexylmethane-2,4'-diisocyanate, W, W ' -Diisocyanate dimethylcyclohexane, lysine diisocyanate and the like.

As the urethane prepolymer (b) having an isocyanate group at the terminal, the above-mentioned polyvalent isocyanate compound (a) and a compound having at least two hydroxyl groups are used in an amount of the isocyanate compound of more than 1 equivalent per equivalent of the polyol compound, preferably It is prepared by reacting 1.5 to 2 equivalents.

Examples of the polyol compound having at least two hydroxyl groups include those having a molecular weight of 50 to 10,000, and known polyhydroxy compounds generally used for producing a polyurethane resin, such as low molecular weight polyol, polyether polyol, and polyester polyol. , Polybutadiene polyol, hydrogenated polybutadiene polyol, silicon-containing polyol, phosphorus-containing polyol and the like can be used.

Examples of low molecular weight polyols include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, pentaethylene glycol, hexamethylene glycol, neopentyl glycol, and 2-ethyl. Glycols such as 1,3-hexanediol and bisphenol A and polyhydric alcohols such as trimethylolpropane and glycerin can be used.

Examples of the polyether polyol include polymerization products such as ethylene oxide, propylene oxide, and tetrahydrofuran, and copolymers. Further, polyethers or mixed ethers obtained by condensation of the low-molecular glycol, and products obtained by addition-polymerizing ethylene oxide and propylene oxide to these polyethers and the low-molecular glycol can also be used.

Examples of the polyester polyol include a polyester polyol obtained by a dehydration condensation reaction from a low molecular glycol and a dibasic acid, and a lactone polyol obtained by ring-opening polymerization of a lactone such as ε-caprolactone in the presence of the low molecular glycol or the like. .

The compound having an active hydrogen and an acryl group or a methacryl group to be reacted therewith may be one kind or a mixture of two or more kinds, for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, -Hydroxypropyl methacrylate, N-methylolacrylamide, N-
Methylol methacrylamide, N-hydroxyacrylamide, polyethylene glycol monomethacrylate,
Examples include polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, polypropylene glycol monomethacrylate, and trimethylolpropane diacrylate. Among these, 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate are preferred.

The sorbitol-based polyether polyol which is a feature of the present invention includes sorbitol and propylene oxide and / or sorbitol.
Alternatively, a polyol having a number average molecular weight of 400 to 3,000 obtained by addition polymerization of ethylene oxide can be used, and as a commercially available product, Adeka polyether SP-60 manufactured by Asahi Denka Kogyo KK
0, SP-690 (trademark) or Exenol 40 manufactured by Asahi Glass Co., Ltd.
0SO, 451SO, 550SO (trademark) and the like.

As the solvent, an organic solvent inert to an isocyanate group, a vinyl monomer or a vinyl oligomer can be used.

Examples of the organic solvent inert to the isocyanate group include acetone, methyl ethyl ketone, methyl isobutyl ketone, dioxane, dimethylformamide, toluene, cyclohexanone, tetrahydrofuran, and ethyl acetate.

Examples of the vinyl monomer inert to the isocyanate group include acrylic acid and methacrylic acid ester such as tetrahydrofurfuryl acrylate, 2-ethylhexyl acrylate and methyl methacrylate, and N-vinylpyrrolidone.

Examples of the vinyl oligomer inert to the isocyanate group include diethylene glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, and trimethylolpropane trimethacrylate.

 These can be used alone or as a mixture.

A urethanization catalyst used in the reaction, for example, a catalyst used in a urethanization reaction of a general isocyanate compound such as a tertiary amine (triethylamine, triethylenediamine, etc.) or an organotin compound (stanner octoate, dibutyltin dilaurate, etc.) May be used if necessary.

Further, a polymerization inhibitor such as o-nitrotoluene, 2,4-dinitrotoluene, sulfur, copper chloride, methylhydroquinone, hydroquinone monomethyl ether to suppress a polymerization reaction of a carbon-carbon double bond of an acryl group or a methacryl group, For example, p-quinone may be used. The use amount of the polymerization inhibitor is preferably in the range of 50 to 5000 ppm based on the resin. If the polymerization inhibitor is added in an amount of more than 5000 ppm, the electron beam curing rate is reduced, and the advantage of fast curing is lost.

(2) Polyurethane Resin-Containing Coating In the case where the electron beam-curable polyurethane resin used in the present invention is used as a binder for a magnetic recording medium, a reactive diluent for electron beam curing and another electron beam curing resin are mixed. It is also possible to use it.

Reactive diluents include vinylpyrrolidone, tetrahydrofurfuryl acrylate, 2-ethylhexyl acrylate, hydroxyethyl acrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol hexaacrylate, and the like.

Urethane acrylate as other electron beam curing resin,
Examples include epoxy acrylate, polyester acrylate, and acrylic group-containing vinyl chloride-vinyl acetate copolymer.

It is also possible to use a mixture of a vinyl chloride-vinyl acetate copolymer, a thermoplastic polyurethane resin, a nitrocellulose, an epoxy resin, a phenoxy resin or the like, which is used as a binder component of an ordinary magnetic recording medium.

Also, a low molecular weight polyisocyanate can be mixed and used in a combined system of heat curing and electron beam curing.

The electron beam-curable polyurethane resin used in the present invention is preferably used in an amount of not less than 10% by weight, preferably not less than 15% by weight, based on the whole binder for a magnetic recording medium. Below this, a magnetic recording medium having excellent durability such as mechanical strength, which is a feature of the present invention, cannot be obtained.

The magnetic recording medium using the polyurethane resin used in the present invention is obtained by applying a magnetic paint comprising a binder, a magnetic powder, a solvent and various additives as necessary onto a non-magnetic support, and then heating and drying the solvent. , And cured by irradiation with an electron beam.

As the solvent, considering the solubility of the binder, the boiling point, etc., acetone, methyl ethyl ketone, methyl isobutyl ketone, dioxane, dimethylformamide, toluene,
Cyclohexanone, tetrahydrofuran, ethyl acetate and the like can be mentioned, and these can be used alone or in combination.

As the magnetic powder used in the magnetic recording medium of the present invention,
It is a known substance conventionally used, for example, γ
-Iron oxide, cobalt coated γ-iron oxide, cobalt doped γ
- iron oxide, CrO _2, alloy magnetic powder, and a metal magnetic powder and the like.

As the additive, for example, an antistatic agent, carbon black, a lubricant, a non-magnetic inorganic pigment, or the like can be used.

(3) Non-magnetic support As the non-magnetic support, polyester (for example, polyethylene terephthalate), polyamide, polyolefin, cellulose derivative, non-magnetic metal, paper, etc. are used, and the shape is tape, disk, sheet, Cards, films and the like can be used.

(4) Curing Method of Coating Layer As the electron beam irradiating device used for curing the coating layer of the magnetic recording medium, a low-output type electron beam accelerator is preferable because the coating layer is thin. The electron beam curing is preferably performed by irradiating an electron beam in an inert gas stream under the conditions of an acceleration voltage of 150 to 300 KV and an absorbed dose of 0.5 to 20 Mrad.

(5) Others The polyurethane resin used in the present invention can also be used as an ultraviolet curable resin by adding a few percent by weight of a commercially available photopolymerization initiator such as benzoin alkyl ether and benzophenone.

In the above, the case where the polyurethane resin is used as the magnetic layer of the magnetic recording medium has been described,
In addition to the magnetic layer, the polyurethane resin of the present invention comprises a so-called top coat layer (upper layer of the magnetic layer), a back coat layer (lower layer of the base film), and an undercoat layer (an intermediate layer between the magnetic layer and the base film) of the magnetic recording medium. Is also applicable.

〔Example〕

Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the present invention.

Synthesis Example 1 A four-necked flask equipped with a thermometer, a stirrer, a dropping funnel, and a condenser with a drying tube was charged with 870 g of 2,4-tolylene diisocyanate, 967 g of methyl ethyl ketone, and 0.3 g of hydroquinone monomethyl ether. Thereafter, 580 g of 2-hydroxyethyl acrylate was added dropwise. After the completion of the dropwise addition, the reaction was further performed at 50 ° C. for 5 hours to obtain a modified isocyanate having an acryl group and an isocyanate group. Subsequently, the reaction product was added dropwise to a mixed solution of 690 g of sorbitol-based polyether polyol SP-690 ^* 690 g and methyl ethyl ketone 460 g. After the completion of the dropwise addition, the reaction is further carried out at 60 ° C. for 4 hours.
I got ^* SP-690: manufactured by Asahi Denka Co., Ltd. Synthesis Example 2 Isophorone diisocyanate was used in the same device as in Synthesis Example 1.
1110 g, methyl ethyl ketone 1173 g, dibutyltin dilaurate 0.85 g, hydroquinone monomethyl ether 0.3 g
And the internal temperature was adjusted to 40 ° C., and 650 g of 2-hydroxyethyl methacrylate was added dropwise. After dropping, add 50 ° C
For 4 hours to obtain a modified isocyanate having a methacryl group and an isocyanate group. Subsequently, the reaction product was subjected to sorbitol-based polyether polyol SP-
It was dropped into a mixed solution of 600 ^* 612 g and 408 g of methyl ethyl ketone. After the completion of the dropwise addition, the reaction was further carried out at 60 ° C. for 4 hours to obtain a methacryl group-containing polyurethane resin. ^* SP-600: Synthetic Example 3 manufactured by Asahi Denka Co., Ltd. 696 g of 2,4-tolylene diisocyanate, 1337 g of methyl ethyl ketone and 0.06 g of hydroquinone monomethyl ether were charged in the same apparatus as in Synthetic Example 1, and the internal temperature was adjusted to 40 ° C.
1100 g of caprolactone glycol having a number average molecular weight of 550 and 1,
A mixed solution of 90 g of 4-butanediol was added dropwise. After completion of the dropwise addition, an aging reaction was performed at 50 ° C. for 5 hours, and 116 g of 2-hydroxyethyl acrylate was added dropwise. After completion of the dropwise addition, the mixture was further reacted at 60 ° C. for 5 hours to obtain a modified isocyanate having an acryl group and an isocyanate group. Subsequently, the reaction product was dropped into a mixed solution of sorbitol-based polyether SP-600 ^* 122 g, methyl ethyl ketone 82 g and dibutyltin dilaurate 0.2 g. After the completion of the dropwise addition, the mixture is further reacted at 60 ° C. for 5 hours to obtain a polyurethane resin containing an acrylic group.
I got ^* SP-600: Asahi Denka Synthetic Example 4 Isophorone diisocyanate in the same device as in Synthetic Example 1
444 g, 1125 g of methyl ethyl ketone and 0.3 g of dibutyltin dilaurate were added to adjust the internal temperature to 60 ° C., and then the molecular weight was 1000.
Of polybutylene adipate was gradually added dropwise and allowed to react for 5 hours. To this was added 0.12 g of hydroquinone monomethyl ether, the internal temperature was brought to 40 ° C, and 244 g of 2-hydroxyethyl acrylate was gradually added dropwise.
The reaction was carried out for a time to obtain a polyurethane resin containing an acrylic group and a urethane bond.

Synthesis Example 5 To the same apparatus as in Synthesis Example 1, 850 g of trifunctional polycaprolactone polyol having a molecular weight of 850, 365 g of 2-hydroxyethyl acrylate, 1158 g of methyl ethyl ketone and 0.18 g of hydroquinone monomethyl ether were added, and the internal temperature was lowered to 6%.
After the temperature was reduced to 0 ° C., 522 g of 2,4-tolylene diisocyanate was gradually added dropwise, and the mixture was reacted for 7 hours to obtain a polyurethane resin containing an acryl group and a urethane bond.

Example 1 The mixture having the above composition was dispersed in a sand glide mill for 6 hours and filtered to obtain a magnetic paint. This magnetic paint is applied on a polyethylene terephthalate film so that the film thickness after drying becomes 5 μm. After the solvent is removed by a hot air drier, electron beam irradiation is performed so that the accelerating voltage becomes 180 KV and the absorbed dose becomes 10 Mrad. A recording medium was obtained.

Example 2 A magnetic recording medium was manufactured in the same manner as in Example 1, except that a polyurethane resin was used in place of the polyurethane resin of Example 1.

Example 3 A magnetic recording medium was manufactured in the same manner as in Example 1 except that a polyurethane resin was used instead of the polyurethane resin of Example 1.

Comparative Example 1 A magnetic recording medium was manufactured in the same manner as in Example 1 except that a polyurethane resin was used in place of the polyurethane resin of Example 1.

Comparative Example 2 A magnetic recording medium was manufactured in the same manner as in Example 1 except that a polyurethane resin was used instead of the polyurethane resin of Example 1.

Comparative Example 3 A magnetic recording medium was manufactured in the same manner as in Example 1 except that trimethylolpropane triacrylate was used instead of the polyurethane resin of Example 1.

The following tests were performed on the magnetic recording media obtained in Examples 1 to 3 and Comparative Examples 1 to 3.

(I) Scratch resistance The pencil hardness was measured according to the method of JIS K 5400. The measured value was represented by the hardness of a pencil from which the magnetic coating film was peeled off from the base film surface.

(Ii) Wear resistance According to the method of JIS K 7204, wear wheel CS-10, load 250g
The disk is rotated 500 times on the magnetic recording medium. The abrasion resistance was relatively evaluated in terms of the amount of abrasion of the coating film.

(Iii) Adhesiveness of the support and the magnetic coating film After the cellophane tape is adhered to the magnetic coating film, the tape is strongly peeled off. What was done was evaluated as x.

Examples 4 to 7 and Comparative Examples 4 to 6 Also, a mixed binder of the resin obtained in Synthesis Examples 1 to 5, a vinyl chloride-vinyl acetate copolymer (VAGH) and a thermoplastic urethane resin (Nitsuporan 2304) was dried. The solution was applied so as to have a thickness of 50 μm, and after removing the solvent with a hot air drier, electron beam irradiation was performed so that the accelerating voltage was 180 KV and the absorbed dose was 6 Mrad to obtain a transparent film containing no magnetic powder. Table 2 shows the mechanical properties of the cured film.

[Effect of the Invention] The electron beam-curable polyurethane resin used in the present invention is a resin having a specific structure having a sorbitol-based polyether polyol residue and an acrylic group or a methacryl group in a molecule, and is a conventional urethane acrylate or acrylic resin. Compared to oligomers, the elastic modulus, mechanical strength, and heat and humidity resistance are high, and the magnetic recording medium on which a coating layer containing such a polyurethane resin is formed has durability such as scratch resistance, abrasion resistance, and adhesion. Excellent effects are observed.

Claims (1)

(57) [Claims] 1. A nonmagnetic support comprising, in one molecule, 1 to 3 polyether polyol skeletons obtained by adding propylene oxide and / or ethylene oxide to sorbitol, and 3 to 15 acrylic or methacrylic groups in one molecule, And forming a coating layer containing a polyurethane resin having a number average molecular weight of 1,000 to 50,000, and then curing the coating layer by electron beam irradiation under the conditions of an acceleration voltage of 150 to 300 KV and an absorbed dose of 0.5 to 20 Mrad. A method for manufacturing a magnetic recording medium.