JPS64426B2 - - Google Patents

Description

[Detailed description of the invention]

A typical magnetic recording substrate has a support member having a layer of magnetizable particles contained in a polymeric binder. To apply the magnetizable layer, the binder is usually dissolved in an organic solvent, which pollutes the atmosphere if it is not recovered after volatilization. Recovery of organic solvents involves explosion and fire hazards. This issue is discussed in U.S. Patent No. 3023123 and U.S. Patent No.
3795539 and 3901816;
-borne binder).
Among these patents, US Patent No. 3901816
No. only discloses a crosslinkable water-borne binder. It is currently believed that crosslinking is necessary to obtain completely satisfactory physical properties such as blocking and abrasion resistance of magnetic recording tape. The inventor is not aware of any magnetic recording tape on the market that uses a water-based binder. The present invention relates to what is believed to be the first commercially viable magnetic recording medium having a coating of magnetizable particles contained in a cross-linked binder applied from water. The water-borne latex used in applying this coating is self-crosslinking, but both this latex and its dispersion with magnetizable particles are common in the market. Can be stored and transported at ambient temperature. Magnetizable particles dispersed in an aqueous latex are coated with an organic solvent-based binder.
It can be applied at least as conveniently and economically as a solvent-borne binder. Raw materials for latex are readily available commercially at reasonable prices. The resistance of the coating to abrasion and blocking is very good. Furthermore, surprisingly smooth recording surfaces can be easily obtained.
Furthermore, when using the widely used biaxially oriented polyethylene terephthalate film support, the physical properties of waterborne latex coatings are considerably improved over solventborne latex coatings. This is because, in the case of solvent-mediated coating, low molecular weight components extracted from the support film by the organic solvent can migrate and crystallize on the surface of the recording layer. Aqueous latexes exhibit little or no tendency to extract low molecular weight components from such polyethylene terephthalate film supports. Non-magnetic particles such as carbon black and aluminum oxide, which are commonly used in coating magnetic recording substrates, are also effectively dispersed in the aqueous latex of the present invention. Dispersions containing stable, coatable inorganic particles in aqueous latexes are believed to be new. This latex contains the following monomers (1) 100 parts by weight of alkyl acrylates and/or alkyl methacrylates having from 1 to 8 carbon atoms in the alkyl group or an average of up to 8 carbon atoms in the alkyl group. (2) 1 to 20 parts of acrylic acid, methacrylic acid and/or itaconic acid and (3) 1 to 15 parts of glycidyl acrylate and/or glycidyl methacrylate. Contains a self-crosslinking copolymer. The production of a coating for a magnetic recording substrate includes the steps of dispersing inorganic particles in the aqueous latex, coating the resulting dispersion on a support member, and heating and drying the resulting coating. The copolymer of the latex crosslinks during the drying process of the coating. The monomers of the copolymer are selected such that the copolymer has a secondary glass transition temperature Tg of -5 to 60 DEG C. after crosslinking in the coating. Crosslinking may begin during emulsion polymerization of the latex and may proceed to an undesirable extent when the latex is exposed to high temperatures. In order to avoid this, it is preferable to copolymerize the monomers at 50 to 60°C. When there is no further evidence of reaction, add additional initiator to ensure substantially complete conversion of monomer, followed by
It can also be heated at 80°C for about 1 hour. When preparing the copolymer using less than 2 parts of copolymerizable acid or less than 2 parts of glycidyl acrylate and/or glycidyl methacrylate, the copolymer may be unsuitably crosslinked during drying of the coating. It may therefore be desirable to use additional crosslinking agents. The use of more than about 11 to 13 parts of glycidyl acrylate and/or glycidyl methacrylate can create problems with the stability of the aqueous latex when mixed with iron oxide particles, especially when mixed with iron particles. Other amounts can be expected to maintain the aqueous latex effectively and stably for several months at normal storage temperatures, both before and after mixing with the inorganic particles. 5
Amounts of ~10 parts are preferred. The use of more than about 16 to 18 parts of copolymerizable acid can create difficulties in manufacturing and handling the aqueous latex. Best results were achieved with 10-15 parts of acrylic acid and/or methacrylic acid. Good quality coatings are obtained using methyl acrylate, ethyl acrylate and n-butyl acrylate as alkyl acrylates, preferably by using a mixture of two of these alkyl acrylates to optimize the properties of the tape. Ta. Isobutyl acrylate, t-butyl acrylate and propyl acrylate are also effective as the alkyl acrylates mentioned above, but propyl acrylate is not easily available. Alkyl methacrylates tend to give a higher Tg than alkyl acrylates and tend to be brittle. Therefore, methacrylates are preferred only when used with acrylates. It has been experienced and believed that by mixing two copolymers with significantly different Tg's, the resulting magnetic recording tape exhibits less change in performance with changes in temperature. When using such mixtures, the Tg after crosslinking in the coating of one copolymer
is substantially lower than -5°C, e.g. as low as about -20 to -50°C, if the other copolymer has a relatively high Tg after crosslinking, e.g. about 40 to 60°C. It is. Blends of such low Tg and high Tg copolymers gave tapes exhibiting very good blocking resistance. Alkyl acrylates and/or alkyl methacrylates can be substituted up to about 50% by weight with acrylonitrile, and this substitution tends to improve toughness and therefore wear resistance. The amount of acrylonitrile substituted is preferably 10 to 40%.
Methacrylonitrile is also effective. However, the toxicity of acrylonitrile and methacrylonitrile imposes additional costs on equipment to protect the workers making the tape. Another preferred copolymerizable monomer is 2-
Hydroxyethyl acrylate. 25% by weight
When substituted with alkyl acrylates and/or alkyl methacrylates, there is a tendency to improve the friction properties of the recording layer. 2-Hydroxyethyl methacrylate and 2-hydroxypropyl acrylate and the same methacrylates are also readily available and have the same beneficial effects. Other copolymerizable monomers such as vinyl chloride, vinyl acetate, butadiene, styrene, isoprene, diallyl phthalate and acrylamide can also be used in limited amounts so as not to provide significantly altered properties. Methacrylic acid esters of polyethylene glycol having an average molecular weight of 400 to 750 could also be used to replace up to about 12% by weight of alkyl acrylates and/or methacrylates without observable differences in the results. Dispersions of inorganic particles in aqueous latexes can be applied in the same manner as organic solvent-based coatings. This dispersion is self-thickening and gives a dense, uniform coating without the need for defoamers. Crosslinking of the copolymer tends to be substantially complete as a result of drying of the latex. Depending on the extent to which the crosslinking is incomplete, crosslinking will proceed gradually during storage of the roll of finished tape at room temperature, which may occur if the roll of finished tape is kept at an elevated temperature, such as 60-70°C, for about two weeks. It can be accelerated by exposure. As long as the glycidyl acrylate or glycidyl methacrylate and the copolymerizable acid are within the above ranges, the copolymer will not become too highly crosslinked. As soon as the magnetizable coating is dry, a second aqueous latex coating can be applied without risk of damaging the underlying coating. The particle size of the copolymer in the aqueous latex is preferably less than 0.25 μm to ensure good agglomeration. In the following Preparations, all parts are given by weight. Aqueous Latex A The following premixes were prepared under nitrogen in a mixing kettle. Parts by weight Deionized water 400 Emulsifier 16 n-butyl acrylate 100 Methyl acrylate 180 2-hydroxyethyl acrylate 56 Methacrylic acid 40 Glycidyl methacrylate 24 t-dodecyl mercaptan 0.2 In a glass-lined polymerization reaction vessel under nitrogen
200 parts of the premix and 400 parts of water were charged. This was stirred, heated to 35°C, and 0.32
1 part of potassium persulfate and 0.24 part of isomeric sodium bisulfite were charged. Once the exotherm raises the temperature to 60°C, the batch is then cooled to 55°C and the temperature maintained between 55°C and 60°C at a rate of approximately 10°C.
Premix was added to the remainder at a rate of 50%/min). When all the premixes were added, 0.08 parts of potassium persulfate and 0.04 parts of isomeric sodium bisulfite were charged and the batch was heated at 70°C for 1 hour, then cooled and filtered. The resulting aqueous latex A had a solids content of 33.6%, a pH of 4.8 and a pH of 0.15.
It had an intrinsic viscosity of 1.2 dl/g in dimethylformamide of g/dl. This latex is 0.1%
It contained the following unreacted monomers. Gel swelling tests in dimethylformamide showed that the latex A copolymer was self-crosslinking. The calculated Tg of this copolymer was 4°C. Aqueous Latex B The following premixes were prepared in a mixing kettle under nitrogen. Parts by weight Ethyl acrylate 144 Acrylonitrile 40 Acrylic acid 10 Glycidyl methacrylate 6 T-dodecyl mercaptan 0.1 Under nitrogen, 100 parts of the above premix were added.
A polymerization reaction vessel was charged with 400 parts of deionized water and 8 parts of emulsifier. After stirring and heating to 30℃,
0.4 part potassium persulfate, 0.134 part isomeric sodium bisulfite and 0.001 part ferrous sulfate pentahydrate were added. After heating up to 66-70℃, heat this batch to 50℃.
The remaining premix was added and the temperature was increased to 65-70°C. The batch was steam distilled to remove unreacted monomers, cooled and filtered. The resulting aqueous latex B had a solids content of 38%, a pH of 3.4 and an intrinsic viscosity of 1.4 dl/g in methyl ethyl ketone of 0.15 g/dl. This latex contained less than 0.5% unreacted monomer. Gel swelling tests similar to those for Latex A showed that the copolymer of Latex B was self-crosslinking. Calculated Tg of this copolymer
The temperature was 3°C. An additional aqueous latex was prepared in the same manner as Aqueous Latex B, except that no steam distillation was performed and the following monomers were used:

[Table] Example 1 In a mill, 100 parts of acicular γ-Fe ₂ O ₃ particles with an aspect ratio of 5:1 and an average length of 0.4 μm, 2 parts of dispersant, 2 parts of aluminum oxide, 2 parts of N,N
-Dimethylaminoethanol and 117 parts deionized water were charged. After kneading the resulting slurry until well mixed, 91.7 parts (diluted to 32.43% solids)
Aqueous latex B and 3 parts of lubricant were added to obtain a dispersion, which was filtered, defoamed, and knife coated onto a support member of biaxially oriented polyethylene terephthalate film. The wet coating was passed through a magnetic field to longitudinally orient the acicular particles and heated in an oven to a temperature not exceeding 95° C. to drive off the volatiles. After unloading, the coated support member was cut to standard tape width. This magnetizable coating is 9.65 μm thick and has a square
0.75, Br930 Gauss and Hc325 Oersted. The blocking resistance was excellent. Blocking resistance was tested at 66°C/80% relative humidity as per GSA-17 March 1972.
FSS Interim Federal Standard (GSA-FSS)
Interim Federal Specification)WT-
001572, determined by the procedure of Section 4.4.8. This excellent blocking resistance indicates that the latex B copolymer was crosslinked. This tape is also used on the Sony U-Mateik video deck.
-Matic vidio deck) showed excellent abrasion resistance, as evidenced by a signal loss of only 2.7dB even after more than 6.75 hours of stop motion. Example 2 100 parts of acicular γ-Fe ₂ O ₃ particles of Example 1 in a mill;
Charged were 2 parts dispersant, 2 parts N,N-dimethylaminoethanol, and 120 parts deionized water. After kneading these until well mixed, 75.5 parts (solid content 33.6%) of aqueous latex A and 3 parts of lubricant were added to obtain a dispersion, which was then defoamed, filtered, and corona discharge treated. Gravure coated onto axially oriented polyethylene terephthalate film, magnetically oriented, dried, elongated, and cut to standard tape width. This magnetizable coating has a thickness of 6 μm, a squareness of 0.79,
It had Br1000 Gauss and Hc347 Oersted. Blocking resistance was excellent at 66°C/80% relative humidity when tested according to the method of Example 1. This tape exhibited abrasion resistance that was at least as good as the best audio recording tapes on the market, and much better than many of these tapes. Example 3 After storing a portion of aqueous latex A at room temperature for approximately one month, a dispersion of acicular γ-Fe ₂ O ₃ particles was prepared as in example 2 except that only 73.75 parts of latex A were used. It was prepared using This dispersion
After storage for 124 days, it was coated as in Example 2.
The resulting magnetizable coating is approximately 7.8 μm thick and square
0.77, Br1225 Gauss, Hc308 Oersted, and had excellent blocking and abrasion resistance.
This tape was completely equivalent in quality to the tape of Example 2. Example 4 Instead of aqueous latex A, 30 parts (solid content 33.6
%) of aqueous latex C and 45 parts (solids content 34.1
A magnetic recording tape was prepared as in Example 2, except that a mixture of aqueous latex D of 1.0%) was used. This magnetizable coating has a thickness of 5.4 μm, a squareness of 0.77,
It had Br1175 Gauss and Hc322 Oersted. Blocking resistance and abrasion resistance were acceptable. Example 5 The magnetizable material of this example was acicular fine iron particles with an average length of 0.3 μm, an average diameter of 0.05 μm, and 187 emu/g. A 4 ounce (120 ml) Quickie mill was charged in an inert atmosphere with 100 parts of the acicular fine iron powder, 4 parts of dispersant, and 87 parts of deionized water. After kneading for about 1 hour to obtain a well-mixed ground paste, the mill was opened to the atmosphere and
86 parts of deionized water, 43 parts of Aqueous Latex A, and 4 parts of lubricant were added, then kneading was resumed for about 1 minute to obtain a coatable dispersion. After this,
Degassed and air plasma treated biaxially oriented polyethylene terephthalate film was knife coated, magnetically oriented, dried, stripped and then cut to standard tape widths. This magnetizable coating has a thickness of 3.7 μm, a squareness of 0.69,
It had Br2960 Gauss and Hc900 Oersted. It also had excellent blocking resistance and abrasion resistance. The acicular fine powder iron in the tape of this example is
It had 163 emu/g. This indicates an oxidation rate of 17% during treatment. Oxidation rates on the same order of magnitude are experienced when finely divided iron is used in solvent-borne binder formulations. Example 6 As in Example 5, except that before coating the coatable dispersion was left in a covered glass jar with 90% air space for 4 days. A tape was prepared. The acicular fine powder iron in the tape has 158 emu/g, which has an additional oxidation rate of 3%.
It shows that. This indicates that this coatable dispersion can be stored during production for at least several days without significant deterioration. Example 7 A mill was charged with 100 parts conductive carbon black, 20 parts dispersant, and 360 parts deionized water. After kneading until well mixed, the charge was transferred to a blade type mixer and 990 parts of aqueous latex A and 2400 parts of deionized water were added. After thorough mixing, it was filtered, defoamed and gravure coated onto a corona discharge treated biaxially oriented polyethylene terephthalate film and then dried to obtain a 2 μm thick conductive subbing layer. A magnetizable coating similar to Example 2 was applied over this subbing layer. Testing of the resulting magnetic recording tape showed that the subbing layer was effective in dissipating static electricity. Despite the relatively high heat of vaporization of water, the coating drying process requires less energy than conventional solvent recovery systems, which require large amounts of air to minimize fires and explosions. The hot air used in the final stage of drying to drive out the water only absorbs a limited amount of water and can therefore be further heated and reused in the first stage. That heat can be stored in a heat exchanger for further use without risk of fire or explosion.

Claims (1)

[Scope of Claims] 1. A dispersion containing stable and coatable inorganic particles in an aqueous latex suitable for making a coating for a magnetic recording substrate, the dispersion comprising the following monomers: (a) 100 parts by weight of at least one of alkyl acrylates and alkyl methacrylates having 1 to 8 carbon atoms in the alkyl group, and (b) about 1 to 20 parts by weight of acrylic acid or methacrylic acid. and at least one of itaconic acid, and (c) about 1 to 15 parts by weight of at least one of glycidyl acrylate and glycidyl methacrylate.
A self-crosslinking copolymer with a seed, said monomers being selected such that the copolymer has a Tg of -5 to 60°C after crosslinking. 2. The dispersion according to claim 1, wherein the monomer (a) is selected from methyl acrylate, ethyl acrylate, and n-butyl acrylate. 3. A patent in which the monomers (b) and (c) contain 5 to 15 parts of at least one of acrylic acid and methacrylic acid and 3 to 8 parts of at least one of glycidyl acrylate and glycidyl methacrylate. The dispersion according to claim 1. 4. The dispersion according to claim 1, wherein the inorganic particles are magnetizable. 5. A dispersion containing stable and coatable inorganic particles in an aqueous latex suitable for making a coating for a magnetic recording substrate, the dispersion containing 100% by weight of the following monomers (a): (b) about 1 to 20 parts by weight of at least one of alkyl acrylates and alkyl methacrylates having 1 to 8 carbon atoms in the alkyl group; and (b) about 1 to 20 parts by weight of at least one of acrylic acid, methacrylic acid, and itaconic acid. (c) about 1 to 15 parts by weight of at least one of glycidyl acrylate and glycidyl methacrylate.
about 50% of the alkyl acrylates and alkyl methacrylates, including self-crosslinking copolymers with species;
% by weight is substituted with at least one of acrylonitrile and methacrylonitrile, and the monomers are selected such that the copolymer has a Tg of -5 to 60°C after crosslinking. liquid. 6. The dispersion according to claim 5, wherein the monomer (a) is selected from methyl acrylate, ethyl acrylate, and n-butyl acrylate. 7 A patent in which the monomers (b) and (c) contain 5 to 15 parts of at least one of acrylic acid and methacrylic acid and 3 to 8 parts of at least one of glycidyl acrylate and glycidyl methacrylate. The dispersion according to claim 5. 8. The dispersion according to claim 5, wherein the inorganic particles are magnetizable. 9. A dispersion containing stable and coatable inorganic particles in an aqueous latex suitable for making a coating for a magnetic recording substrate, the dispersion containing 100% by weight of the following monomers (a): (b) about 1 to 20 parts by weight of at least one of alkyl acrylates and alkyl methacrylates having 1 to 8 carbon atoms in the alkyl group; and (b) about 1 to 20 parts by weight of at least one of acrylic acid, methacrylic acid, and itaconic acid. (c) about 1 to 15 parts by weight of at least one of glycidyl acrylate and glycidyl methacrylate.
about 25% of the alkyl acrylates and alkyl methacrylates, including self-crosslinkable copolymers with species;
% by weight of 2-hydroxyethyl acrylate, and the monomers are selected such that the copolymer has a Tg of -5 to 60°C after crosslinking. 10. The dispersion according to claim 9, wherein the monomer (a) is selected from methyl acrylate, ethyl acrylate, and n-butyl acrylate. 11 The monomers (b) and (c) are 5 to 15 parts of at least one of acrylic acid and methacrylic acid and 3 to 8
9. The dispersion according to claim 9, which contains at least one of glycidyl acrylate and glycidyl methacrylate. 12. The dispersion according to claim 9, wherein the inorganic particles are magnetizable. 13 Suitable for making coatings for magnetic recording substrates,
A dispersion containing stable and coatable inorganic particles in an aqueous latex, wherein the dispersion contains 100 parts by weight of the following monomer (a) having 1 to 8 carbon atoms in the alkyl group. (b) about 1 to 20 parts by weight of at least one of acrylic acid, methacrylic acid, and itaconic acid; (c) about 1 to 15 parts by weight of glycidyl acrylate; and at least one of glycidyl methacrylate.
a self-crosslinkable copolymer (first copolymer) with a species, said monomer is -5 after crosslinking of the first copolymer.
The latex is selected to have a Tg of ~60°C and the latex has a Tg of -5 to -50°C after self-crosslinking.
The dispersion liquid further comprises a second self-crosslinking copolymer obtained by copolymerizing the monomers (a) to (c) above selected to have a Tg. 14 The first copolymer has a Tg of 40-60℃ after crosslinking.
and the second copolymer has -20 to -20 after crosslinking.
Claim 13 having a Tg of -50°C
The dispersion liquid described in Section. 15. The dispersion according to claim 13, wherein the monomer (a) is selected from methyl acrylate, ethyl acrylate, and n-butyl acrylate. 16 The monomers (b) and (c) are 5 to 15 parts of at least one of acrylic acid and methacrylic acid and 3 to 8
14. The dispersion according to claim 13, which contains at least one of glycidyl acrylate and glycidyl methacrylate. 17. The dispersion according to claim 13, wherein the inorganic particles are magnetizable.