JPS6346885B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic recording medium such as a magnetic tape having a back coat layer on the side opposite to the magnetic layer. Conventionally, in magnetic tapes where charging performance, durability, winding characteristics, etc. are important, a back coat layer containing carbon is formed on a non-magnetic base on the side opposite to the magnetic surface. This back coat layer is generally a coating film formed from a thermosetting resin in order to improve durability and heat resistance (blocking resistance). However, thermosetting materials based on chemical reactions are difficult to cure in-line due to the slow reaction time, and therefore, until now, the materials have been cured while being wound into a roll. In this case, the surface roughness required for the back coat layer is reduced due to the influence of temperature and pressure near the winding core. As a result,
Variations in surface roughness result in non-uniform coefficients of friction along the length of the tape, significantly impairing the effectiveness of the backcoat layer on winding. Furthermore, when the magnetic layer is also thermally cured at the same time, the roughness of the back coat layer is transferred to the magnetic surface, which worsens the surface roughness of the magnetic layer and significantly deteriorates the S/N and C/N of the tape. become. The present invention was made to correct the above-mentioned defects, and in the magnetic recording medium mentioned at the beginning, CH ₂ =CHCOO−,

[Formula] CH ₂ = CHCH ₂ COO−, CH ₂ = CHCH ₂ −CH ₂ COO−,
CH ₂ = CHCH ₂ −CH ₂ CH ₂ COO−,

【formula】

[Formula] CH ₂ = CHCONH−,

A compound having in one molecule at least two groups selected from the group consisting of [Formula] is used for the back coat layer, and the back coat layer is subjected to radiation irradiation treatment so that the compound forms a crosslinked structure. The present invention relates to a magnetic recording medium characterized by: According to the present invention, since radiation is applied to the back coat containing a compound having a radiation-sensitive double bond together with carbon and inorganic pigments, the curing speed by radiation is fast and the curing reaction can be carried out in-line. be able to. That is, among the ionized products generated from the compound itself or from the thermoplastic compound used in combination with the radiation irradiation, free radicals mainly act as the initiating species and act on the double bonds of the above compound, resulting in so-called radical polymerization. A reaction occurs and a complex network-like three-dimensional crosslinked structure is formed. This cross-linked structure allows carbon etc. to form a durable coating film with interfacial reinforcement.
Therefore, there is no need for conventional heat curing treatment, and the surface roughness and coefficient of friction do not change over the entire length, resulting in a highly cross-linked back coat layer with excellent blocking resistance, durability, and good winding properties. It does not have any negative effect on magnetic surfaces. Moreover, radical bonding with the carbon surface is also considered, and the carbon is further reinforced at the interface. The number of double bonds in the above compound used in the present invention is preferably 2 or more, and the molecular weight of the compound is preferably 200 to 10,000 per double bond. The higher the number of double bonds, the more efficiently the above crosslinked structure is formed,
If the molecular weight is less than 200, the curing reaction will proceed too much and the reaction product will become brittle, while if it exceeds 10,000, crosslinking will be insufficient. The above compound is preferably a reactive acrylic oligomer or oligoacrylate having two or more double bonds, preferably three or more. Specific examples of the acrylic compounds include acrylic esters and methacrylic esters,
There are polyacrylates and polymethacrylates (herein, "poly" refers to diacrylate or higher) of polyhydric alcohols. Examples of the polyhydric alcohol include polyethylene glycol, polypropylene oxide, polybutylene oxide, polycyclohexene oxide, polyethylene oxide, propylene oxide, polystyrene oxide, polyoxetane, polytetrahydrofuran, cyclohexanediol, xylylene diol, di-(β-hydroxyethoxy )benzene,
Glycerin, diglycerin, neopentyl glycol, trimethylolpropane, triethylolpropane, pentaerythritol, dipentaerythritol, sorbitan, sorbitol, butanediol, butanetriol, 2-butene-1,
4-diol, 2-n-butyl-2-ethyl-propanediol, 2-butyne-1,4-diol, 3-chloro-1,2-propanediol,
1,4-cyclohexanedimethanol, 3-cyclohexene-1,1-dimethanol, decalin diol, 2,3-dibromo-2-butene-1,4
-diol, 2,2-diethyl-1,3-propanediol, 1,5-dihydroxy-1,2,
3,4-tetrahydronaphthalene, 2,5-dimethyl-2,5-hexanediol, 2,2-dimethyl-1,3-propanediol, 2,2-diphenyl-1,3-propanediol, dodecanediol, meso Erythritol, 2-ethyl-1,
3-hexanediol, 2-ethyl-2-(hydroxymethyl)-1,3-propanediol, 2
-ethyl-2-methyl-1,3-propanediol, heptanediol, hexanediol, 3-
Hexene-2,5-diol, hydroxybenzyl alcohol, hydroxyethylresorcinol, 2-methyl-1,4-butanediol, 2-
Methyl-2,4-pentanediol, nonanediol, octanediol, pentanediol, 1
-phenyl-1,2-ethanediol, propanediol, 2,2,4,4-tetramethyl-1,
3-cyclobutanediol, 2,3,5,6-tetramethyl-p-xylene-α,α′-diol,
1,1,4,4-tetraphenyl-1,4-butanediol, 1,1,4,4-tetraphenyl-
2-butyne-1,4-diol, 1,2,6-trihydroxyhexane, 1,1'-bi-2-naphthol, dihydroxynaphthalene, 1,1'-methylenedi-2-naphthol, 1,2,4 -benzenetriol, biphenol, 2,2'-bis(4-hydroxyphenyl)butane, 1,1-bis(4-
hydroxyphenyl)cyclohexane, bis(hydroxyphenyl)methane, catechol, 4-chlorresorcinol, 3,4-dihydroxyhydrocinnamic acid, hydroquinone, hydroxybenzyl alcohol, methylhydroquinone, methyl-2,4,6-tri hydroxybenzoate, phloroglucinol, pyrogallol,
resorcinol, glucose, α-(1-aminoethyl)-p-hydroxybenzyl alcohol,
2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol, 3-amino-1,2-propanediol, N-(3-aminopropyl)- Diethanolamine, N,N'-bis-(2-hydroxyethyl)piperazine, 2,2-bis(hydroxymethyl), 2,2',2''-nitrilotriethanol, 2,
2-bis(hydroxymethyl)propionic acid, 1,3-bis(hydroxymethyl)urea, 1,2-bis(4-pyridyl)-1,2-ethanediol, N-n-butyldiethanolamine, diethanolamine , N-ethyldiethanolamine, 3-mercapto-1,2-propanediol, 3-piperidino-1,2-propanediol, 2-(2-pyridyl)-1,3-propanediol, triethanolamine, α-( 1-aminoethyl)-p-hydroxybenzyl alcohol,
Examples include 3-amino-4-hydroxyphenyl and sulfone. Among these acrylic esters and methacrylic esters, preferred ones are:
Due to its ease of availability, ethylene dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, polyethylene glycol diacrylate, pentaerythritol triacrylate, pentaerythritol dimethacrylate, dipentaerythritol pentaacrylate, glycerin triacrylate, diglycerin dimethacrylate, 1,3-propanediol diacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate, 1,5-pentanediol diacrylate, neopentyl glycol diacrylate, ethylene oxide-added trimethylol These include propane triacrylate ester. Acrylamides and methacrylamides that can be used as acrylic compounds include methylenebisacrylamide, methylenebismethacrylamide, ethylenediamine, diaminopropane, diaminobutane, pentamethylenediamine, hexamethylene, and bis(2-aminopropyl). amines, diethylenetriaminediamine, heptamethylenediamine, octamethylenediamine, polyamines interrupted by heteroatoms, polyamines containing rings [e.g. phenylenediamine,
Xylylene diamine, β-(4-aminophenyl)
Ethylamine, diaminobenzoic acid,
diaminotoluene, diaminoanthraquinone, diaminofluorene, etc.] and polymethacrylamide. In addition, two or more different addition-polymerizable unsaturated bonds, such as N-β-hydroxyethyl-β-(methacrylamide)ethyl acrylate, N,N-bis(β-methacryloxyethyl)acrylamide, acle methacrylate, etc. Compounds having the above are also suitable as the acrylic compound of the present invention. Further, as acrylic compounds that can be used, there are polyester copolymers of various degrees of polymerization obtained by the reaction of trimethylolpropane monoacrylate, hexanediol, and adipic acid. In this case, diacrylate of aliphatic polyol such as pentaerythritol, diacrylate of alicyclic diglycidyl ether, etc. may be used instead of trimethylolpropane monoacrylate. Also, instead of hexanediol, ethylene glycol, propylene glycol, 1,3
-propanediol, 1,4-butanediol,
1,5-pentanediol, neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol A and propylene oxide adducts, ethylene oxide adducts and propylene oxide adducts of hydrogenated bisphenol A, polyethylene glycol,
Polypropylene glycol, polytetramethylene glycol, etc. may be used. Small amounts of tri- and tetraols such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be used in combination. Furthermore, in place of adipic acid, terephthalic acid, isophthalic acid, orthophthalic acid,
Aromatic dicarboxylic acids such as 1,5-naphthalic acid; p
-oxybenzoic acid, p-(hydroxyethoxy)
Aromatic oxycarboxylic acids such as benzoic acid; aliphatic dicarboxylic acids such as succinic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, etc. may be used. In this case, when aromatic carboxylic acid and aliphatic carboxylic acid are used together, their molar ratio is 50/
50 to 100/0 and preferably at least 30 mole % of the aromatic carboxylic acid is terephthalic acid. Small amounts of tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid, and pyromellitic acid may be used in combination. Note that the acid component such as adipic acid may be replaced with an aromatic or aliphatic diisocyanate such as tolylene diisocyanate to form a polyurethane.
In addition, the ratio of the above acrylate and polyol is
The molar ratio is preferably 80/20 to 10/90 when the acrylate is a monoacrylate, and 40/60 to 5/95 when the acrylate is a diacrylate. These radiation-sensitive compounds may be used in combination with thermoplastic resins such as polyurethane, polyester, rubber-based (eg AB), specifically to improve flexibility and adhesion. This thermoplastic resin may or may not be acrylic modified (introducing a double bond). Furthermore, among the above radiation-sensitive compounds, those having an active hydrogen group (for example, -OH, -COOH, _-NH2 ) are compounds having -NCO, -OH, -COOH, epoxy group, etc. at the terminal and/or -OH at the end
The reaction products obtained with various molecular weights may be used. The reaction product may be a polyurethane, polyester, polyether, etc. having active terminals at both ends, to which an acrylic compound is bonded. This reaction product can be added to the back coat paint as it is, or both components can be added to the back coat paint before the above reaction and then applied, so that the above reaction and the radical polymerization reaction can be carried out simultaneously. The radiation-sensitive compounds having active hydrogen groups include 2-hydroxyethyl ester, 2-hydroxymethyl ester, 2-hydroxybutyl ester of acrylic acid or methacrylic acid; acrylamide, methacrylamide, N-methylolacrylamide, acrylic acid, Methacrylic acid, glycidyl (meth)acrylate, etc. are preferable. In addition, the terminals of ethylene glycol, propylene glycol, etc.
Polyfunctional polyols with OH; polyfunctional polyisocyanates with terminal NCO such as 2,4-toluene diisocyanate; combinations of glycidyl (meth)acrylate homopolymers or copolymers, homopolymers or copolymers such as acrylic acid, methacrylic acid or maleic anhydride; Thus, radiation-sensitive compounds of various molecular weights are obtained. Ionizing radiation such as an electron beam, neutron beam, or gamma ray is used as the above-mentioned radiation to be irradiated to the back coat layer of the present invention, and the irradiation amount is preferably 1 to 10 Mrad, more preferably 2 to 7 Mrad. The energy (acceleration voltage) is preferably 100KV or more. This irradiation amount is sufficient to cause the above-mentioned radical reaction. It is desirable that the back coat layer be irradiated with radiation after coating and drying and before winding up, but it may also be done after winding up. In the back coat layer of a magnetic recording medium according to the present invention, such as a magnetic tape, this radiation-sensitive compound may be used in combination with other resins commonly used as binders, if necessary. Other resins include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride copolymer, Vinyl-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer,
Acrylic acid ester-vinylidene chloride copolymer,
Methacrylic acid ester-vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer,
Thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-acrylic acid copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral , cellulose derivative, styrene-butadiene copolymer,
Examples include polyester resins, phenolic resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and mixtures thereof.
However, even in this case, the molecular weight per double bond is preferably 200 to 10,000. The back coat layer is
Carbon (for example, classified according to manufacturing method such as furnace, channel, acetylene, thermal, lamp, etc., but furnace carbon and thermal carbon are preferable), inorganic pigments (added to control surface roughness and improve durability) γ-
FeOOH, α-Fe ₂ O ₃ , Cr ₂ O ₃ , TiO ₂ , ZnO,
SiO, _SiO2・_2H2O , _Al2O3・_2SiO2・_{2H2O ,}
3MgO・4SiO ₂・H ₂ O, MgCO ₃・Mg(OH) ₂・
3H ₂ O, Al ₂ O ₃ , Sb ₂ O ₃ , etc.).
Further, the composition of the magnetic layer and the material of the non-magnetic base may be those conventionally known. Examples of the present invention will be described below. Example A back coat paint having the following composition was prepared. Carbon (#35 manufactured by Asahi Carbon Co., Ltd.) 100 parts FeOOH 10 parts Oligoacrylate (M manufactured by Toagosei Chemical Industry Co., Ltd.)
-8030: 3 double bonds, molecular weight 2000) 30 parts Estane 5702 (thermoplastic polyurethane manufactured by B.F. Gutdrich) 40 parts Methyl ethyl ketone 300 parts Cyclohexanone 200 parts After mixing this composition in a ball mill for 48 hours , passed through a 3μ filter, and then applied the paint to a thickness of 3μ on the back side of a calendered 21μ thick polyester film (the side facing the magnetic layer), and after drying it was installed in-line. The material was then guided to an electron beam irradiation (hardening) device, where it was irradiated with a dose of 150 V and 5 Mrad. After winding it up, it was cut into 1-inch widths. Comparative Example Instead of the oligoacrylate in the above example,
30 parts of VAGH (vinyl chloride-vinyl acetate-vinyl alcohol copolymer manufactured by UCC) and newly added Desmodyur.
A back coat paint containing part L7 was prepared in the same manner as in the above example, and after coating, drying and winding, it was heated at 60℃.
It was cured for 48 hours and then cut to 1 inch width. Using the tapes in each of the above examples, FF is recorded on the VTR.
When winding in this mode, the results shown in the following table were obtained. It can be seen that the results of this example are good.

【table】

Claims (1)

[Claims] 1. In a magnetic recording medium having a back coat layer on the side opposite to the magnetic layer, CH ₂ =CHCOO-, [Formula] CH ₂ = CHCH ₂ COO-, CH ₂ =CHCH ₂ -CH ₂ COO−,
CH ₂ = CHCH ₂ −CH ₂ CH ₂ COO−,
[Formula] [Formula] CH ₂ = CHCONH-, [Formula] A compound having in one molecule at least two groups selected from the group consisting of [Formula] is used for the back coat layer, and the back coat layer is subjected to radiation irradiation treatment. A magnetic recording medium characterized in that the compound is coated to form a crosslinked structure.