Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
  • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
  • G11B5/62—Record carriers characterised by the selection of the material
  • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
  • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
  • G11B5/702—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer characterised by the bonding agent
  • G11B5/7026—Radiation curable polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/67—Unsaturated compounds having active hydrogen
  • C08G18/671—Unsaturated compounds having only one group containing active hydrogen
  • C08G18/672—Esters of acrylic or alkyl acrylic acid having only one group containing active hydrogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
  • C08G18/67—Unsaturated compounds having active hydrogen
  • C08G18/671—Unsaturated compounds having only one group containing active hydrogen
  • C08G18/672—Esters of acrylic or alkyl acrylic acid having only one group containing active hydrogen
  • C08G18/673—Esters of acrylic or alkyl acrylic acid having only one group containing active hydrogen containing two or more acrylate or alkylacrylate ester groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
  • C08G18/72—Polyisocyanates or polyisothiocyanates
  • C08G18/77—Polyisocyanates or polyisothiocyanates having heteroatoms in addition to the isocyanate or isothiocyanate nitrogen and oxygen or sulfur
  • C08G18/78—Nitrogen
  • C08G18/7806—Nitrogen containing -N-C=0 groups
  • C08G18/7818—Nitrogen containing -N-C=0 groups containing ureum or ureum derivative groups
  • C08G18/7831—Nitrogen containing -N-C=0 groups containing ureum or ureum derivative groups containing biuret groups
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G18/00—Polymeric products of isocyanates or isothiocyanates
  • C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
  • C08G18/70—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the isocyanates or isothiocyanates used
  • C08G18/72—Polyisocyanates or polyisothiocyanates
  • C08G18/77—Polyisocyanates or polyisothiocyanates having heteroatoms in addition to the isocyanate or isothiocyanate nitrogen and oxygen or sulfur
  • C08G18/78—Nitrogen
  • C08G18/79—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates
  • C08G18/791—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates containing isocyanurate groups
  • C08G18/792—Nitrogen characterised by the polyisocyanates used, these having groups formed by oligomerisation of isocyanates or isothiocyanates containing isocyanurate groups formed by oligomerisation of aliphatic and/or cycloaliphatic isocyanates or isothiocyanates
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
  • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
  • C09D175/04—Polyurethanes
  • C09D175/14—Polyurethanes having carbon-to-carbon unsaturated bonds
  • C09D175/16—Polyurethanes having carbon-to-carbon unsaturated bonds having terminal carbon-to-carbon unsaturated bonds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G2270/00—Compositions for creating interpenetrating networks
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L2205/00—Polymer mixtures characterised by other features
  • C08L2205/04—Polymer mixtures characterised by other features containing interpenetrating networks

Definitions

• the present invention relates to a novel class of radiation curable oligomers containing a plurality of urethane and/or urea moieties and a plurality of radiation crosslinkable moieties.
• the present invention also relates to magnetic recording media incorporating such oligomers.
• Magnetic recording media generally comprise a magnetizable layer coated on at least one side of a nonmagnetizable support.
• the magnetizable layer comprises a magnetic pigment dispersed in a polymeric binder.
• the magnetizable layer may also include other components such as lubricants; abrasives; thermal stabilizers; antioxidants; dispersants; wetting agents; antistatic agents; fungicides; bacteriocides; surfactants; coating aids; nonmagnetic pigments; and the like.
• Some forms of magnetic recording media such as flexible magnetic recording tape, also have a backside coating applied to the other side of the nonmagnetizable substrate in order to improve the durability, conductivity, and tracking characteristics of the media.
• the backside coating typically comprises a polymeric binder, but may also include other components such as lubricants; abrasives; thermal stabilizers; antioxidants; dispersants; wetting agents; antistatic agents; fungicides; bacteriocides; surfactants; coating aids; nonmagnetic pigments; and the like.
• the magnetizable layer and the backside coating, if any, of a majority of conventional magnetic recording media are derived from materials which require curing in order to provide magnetic recording media with appropriate physical and mechanical properties.
• the uncured components of the magnetizable layer or the backside coating are dissolved in a suitable solvent and milled to provide a homogeneous dispersion.
• the resulting dispersion is then coated onto the nonmagnetizable substrate, after which the coating is dried, calendered if desired, and then cured.
• Curing can be achieved in a variety of ways.
• the polymeric binder of the magnetizable layer or the backside coating is derived from hydroxy functional polymers which rely upon a chemical reaction between the hydroxy functionality and an isocyanate crosslinking agent to achieve curing.
• the isocyanate crosslinking agent is typically added to the dispersion just prior to the time that the dispersion is coated onto the substrate.
• the coating will have poor green strength until the cure reaction has progressed sufficiently.
• the coating will be susceptible to damage during subsequent processing unless an inconvenient and expensive time delay is incorporated into the manufacturing process.
• the viscosity of the solution begins to gradually increase as crosslinking reactions take place. After a certain period of time, the viscosity of the dispersion becomes sufficiently high such that it is then extremely difficult to filter and coat the dispersion onto the nonmagnetizable support.
• Radiation curable dispersions have been used as an alternative to isocyanate curable formulations.
• the dispersion is coated onto the substrate, dried, calendered if desired, and then irradiated with ionizing radiation to achieve curing.
• Radiation curable dispersions are capable of providing, fast, repeatable, controlled crosslinking, thereby eliminating the inconvenient and expensive delays associated with isocyanate curable formulations.
• IPN interpenetrating polymer network
• a semi- interpenetrating polymer network i.e., "semi-IPN”
• IPN's and semi-IPN's have been described in R.A. Dickie et al., editors, Cross-linked Polymers: Chemistry. Properties, and Applications. American Chem. Society, pages 244-268 and 311-323 (1988) .
• Magnetic recording media incorporating semi-IPN compositions have been described in the art.
• L.B. Lueck Radiat. Phys. Chem., Vol. 25, Nos. 4-6, pp. 581-586 (1985) discusses radiation cured magnetic media.
• Lueck proposes that
• the present invention concerns a novel class of radiation curable oligomers having the formula: 0 0 0 0 0
• each R is independently an organic moiety comprising at least one radiation curable moiety; each n is independently at least 1; each is independently an organic moiety having a valence of n+1;
• the present invention concerns a process for making the radiation curable oligomers described above.
• a multifunctional isocyanate, or mixture of multifunctional isocyanates, of the formula W—(NC0) n+1 is reacted with a dinucleophile of the formula
• H—X—Z—X—H such as a diamine or a diol, wherein the molar ratio of the multifunctional isocyanate(s) to the dinucleophile is about 2:1.
• the reaction product of this first step is an oligomer precursor of the formula o o ( OCN ) n -W-NO II-X— Z— X-C IIN-W- ( NCO ) n
• a second step the oligomer precursor is reacted with at least one alcohol of the formula R-OH in amounts such that the molar ratio of the alcohol to the oligomer precursor is at least 2n:l.
• the reaction product of this second step is a radiation curable oligomer of the present invention as is described above.
• n, , X, R, and Z are as defined above.
• the present invention concerns a magnetic recording medium incorporating the radiation curable oligomers described above.
• Magnetic recording media of the present invention comprise a magnetic layer provided on a nonmagnetizable support.
• the magnetic layer comprises a magnetic pigment dispersed in a polymeric binder.
• the polymeric binder is an irradiated blend of components comprising the radiation curable oligomer described above and a secondary polymer component.
• the secondary polymer component comprises a polymer that is miscible with the radiation curable oligomer.
• radiation curable moiety means a moiety that undergoes a crosslinking reaction upon irradiation.
• An example of a radiation curable moiety is a carbon-carbon double bond such as is found in (meth)acrylate materials.
• ( eth)aerylate” includes acrylates and methacrylates.
• glass transition temperature is determined using DSC techniques. DESCRIPTION OF THE PREFERRED EMBODIMENTS
• Magnetic recording media of the present invention comprise a magnetic layer provided on a nonmagnetizable support.
• the particular nonmagnetizable support of the present invention is not critical and may be any suitable support known in the art.
• suitable support materials include, for example, polyesters such as polyethylene terephthalate (“PET”) ; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate or cellulose diacetate; polymers such as polycarbonate, polyvinyl chloride, polyimide, polyphenylene sulfide, polyacrylate, polyether sulphone, polyether ether ketone, polyetherimide, polysulphone, aramid film, polyethylene 2,6-naphthalate film, fluorinated polymer, liquid crystal polyesters, polyamide; metals such as aluminum, or copper; paper; or any other suitable material.
• PET polyethylene terephthalate
• polyolefins such as polypropylene
• cellulose derivatives such as cellulose triacetate
• the components of the magnetic layer comprise a magnetic pigment dispersed in a polymeric binder.
• the type of magnetic pigment used in the present invention is not critical and may include any suitable magnetic pigment known in the art including iron oxides such as gamma Fe 2 0 3 and Fe 3 0 4 ; cobalt-modified iron oxides; chromium dioxide, hexagonal magnetic ferrites such as BaCo ⁇ Ti x Fe 12 _ 2X 0 19 and the like; and metallic pigments such as Fe and- the like.
• the magnetic layer of the present invention generally contains from about 50 to 90, preferably about 65 to 90, and more preferably about 70 to 85 percent by weight of magnetic pigment. The percent by weight of magnetic pigment is based on the total weight of the magnetic layer.
• the polymeric binder of the present invention is an irradiated blend of components comprising a novel radiation curable oligomer and a secondary polymer component.
• the novel radiation curable oligomers of the present invention may be prepared according to a two-step reaction scheme.
• a multifunctional isocyanate, or mixture of multifunctional isocyanates, of the formula W—(NCO) n+1 is reacted with a dinucleophile selected from the group consisting of a diol and a diamine.
• n is at least l.
• n is in the range from 1 to 4. More preferably, n is 1 or 2. Most preferably, n is 2.
• the multifunctional isocyanate(s) and the dinucleophile are used in amounts such that the molar ratio of the multifunctional isocyanate(s) to the dinucleophile is about 2:1.
• W is an organic moiety having a valence of n + 1.
• the nature of the moiety W is not critical in the practice of the present invention, so long as W is substantially unreactive to isocyanate groups, a ine groups, and OH groups under the reaction conditions employed to react the dinucleophile with the multifunctional isocyanate(s) . It is also preferred that W is stable upon exposure to ionizing radiation. "Stable” means that the moiety W undergoes substantially no scission or crosslinking reactions when exposed to radiation. Examples of structures suitable for W include straight chain, branched chain, or cyclic alkylene, arylene, aralkylene, alkoxy, or acyloxy moieties, and the like.
• the term "multifunctional isocyanate” shall mean a multifunctional isocyanate, or mixture of such isocyanates, as described above.
• Examples of preferred multifunctional isocyanates include a cyclic triisocyanate of the formula
• each of R 2 and R 3 is a divalent, organic linking group.
• the nature of the linking groups R 2 and R 3 is not critical in the practice of the present invention, so long as each of R 2 and R 3 is substantially unreactive to isocyanate groups, amine groups, and OH groups under the reaction conditions employed to react the dinucleophile with the multifunctional isocyanate. It is also preferred that the linking group is stable upon exposure to ionizing radiation. "Stable" means that the linking group undergoes substantially no scission or crosslinking reactions when exposed to radiation. Examples of structures suitable for R 2 and R 3 include straight chain, branched chain, or cyclic alkylene, arylene, aralkylene, alkoxy, acyloxy, and the like.
• R 2 is preferably alkylene.
• a specific example of such a cyclic triisocyanate for which R 2 is -(CH 2 ) 6 - is commercially available as Desmodur N3300 from Miles, Inc.
• a specific example of a branched triisocyanate for which R 3 is -(CH 2 ) 6 - is commercially available as Desmodur N100 from Miles, Inc.
• diols and/or diamines may be used as the dinucleophile.
• diols and diamines suitable in the practice of the present invention may be represented by the formula
• H-X—Z-X-H wherein each X is independently selected from -O- and -N(R°)-, wherein R° is H; a straight-chain, branched, or cyclic alkyl group of 1 to 10, preferably 1 to 2 carbon atoms; or a divalent organic moiety bridging the two nitrogens of the diamine, e.g., piperazine.
• Z is a divalent, organic linking group.
• X is oxygen when the corresponding hydrogen active moiety of the dinucleophile is -OH
• X is -N(H)- when the corresponding hydrogen active moiety of the dinucleophile is -NH 2 .
• linking group Z is not critical in the practice of the present invention, so long as Z contains no NCO or OH moieties. It is also desirable that Z is substantially unreactive to isocyanate groups, amine groups, and OH groups under the reaction conditions employed to react the dinucleophile with the multifunctional isocyanate. It is also preferred that Z is stable upon exposure to ionizing radiation. “Stable” means that the linking group undergoes substantially no scission or crosslinking reactions when exposed to radiation.
• Examples of structures suitable for Z include straight chain, branched chain, or cyclic alkylene, arylene, aralkylene, alkoxy, or acyloxy moieties, and the like.
• suitable polydiols and diamines include polyester, polycaprolactone, polycarbonate, polydimethylsiloxane, polyether, and polyolefin diols and diamines, and the like.
• Preferred diols have a molecular weight in the range from about 100 to about 3000.
• One class of preferred dinucleophiles include diols in which Z is an alkylene moiety.
• a particularly preferred alkenyl diol is 1,6-hexane diol.
• dinucleophiles include polyether diols, and more preferably polyether diols having a molecular weight of in the range from about 1000 to 6000, preferably 1000 to 3000.
• Representative polyether diols are essentially hydroxy- containing compounds having ether linkages.
• polyether diols examples include hydroxy-terminated poly(propylene oxide) , hydroxy-terminated poly(tetramethylene oxide) , hydroxy-terminated poly(pentamethylene oxide) , hydroxy-terminated poly(hexamethylene oxide) , hydroxy-terminated poly(ethylene oxide) , hydroxy-terminated poly(1,2-propylene oxide) , hydroxy-terminated poly(1,2-butylene oxide), tetrahydrofuran, ethylene oxide copolyethers, and the like.
• Particularly preferred polyether diols have the formula HO-(CH 2 CH 2 0) p -H, wherein the subscript p has an average value in the range from 20 to 25.
• the reaction product is an oligomer precursor of the formula
• W is the residue remaining after removal of NCO groups from the multifunctional isocyanate.
• the multifunctional isocyanate is the cyclic triisocyanate described above,
• W when the multifunctional isocyanate is a mixture of the cyclic and branched isocyanates described above, W may be
• Z is the residue remaining after removal of the hydrogen active moieties from the dinucleophile.
• the dinucleophile is HO-(CH 2 ) 6 -OH
• Z is -(CH 2 ) 6 -.
• the oligomer precursor is reacted with at least one alcohol of the formula R-OH, wherein R is an organic moiety comprising at least one radiation curable moiety.
• the alcohol, R-OH is used in an amount such that there is a stoichiometric excess of OH groups from the alcohol relative to the number of NCO groups from the oligomer precursor.
• "Stoichiometric excess" means that the molar ratio of the (meth)acrylate functional alcohol to the oligomer precursor is greater than 2n:l, wherein n is as defined above. Using such an excess ensures that substantially all of the NCO groups from the oligomer precursor are converted into urethane linkages in the reaction with the alcohol. In the practice of the present invention, it is preferred to use no more than a 5% stoichiometric excess of the alcohol relative to the oligomer precursor.
• the alcohol of the present invention is a (meth)acrylate functional alcohol comprising a single OH group and one or more (meth)acrylate groups.
• Representative (meth)acrylate functional alcohols of the present invention may be selected from the group consisting of
• each of R 5 and R 7 is independently a divalent aliphatic moiety of 1 to 24 carbon atoms; and each of R 6 and R 7 is independently -H or -CH 3 .
• the use of hydroxyethyl (meth)acrylate and pentaerythritol tri(meth)acrylate have been found to be particularly suitable for use as the (meth)acrylate functional alcohol in the practice of the present invention.
• Hydroxyethyl (meth)acrylate has a structure according to formula (7) in which R 5 is -CH 2 CH 2 -, and R 6 is -H or -CH 3 .
• Pentaerythritol tri(meth)acrylate has a structure according to formula (8) in which R 7 is -CH 2 - and R 8 is hydrogen or methyl.
• the reaction product is a radiation curable oligomer of the formula
• R is the residue remaining after removal of the -OH moiety from the alcohol R-OH.
• R-OH is hydroxyethyl (meth)acrylate
• R is hydroxyethyl (meth)acrylate
• R 6 may be -H or -CH 3 .
• R-OH pentaerythritol triacrylate
• R 8 may be -H or -CH 3 .
• Particularly preferred radiation curable oligomers of the present invention are selected from the group consisting of
• the secondary polymer component of the present invention may be any polymer, or combination of polymers, known in the art to be suitable as a binder material for magnetic recording media.
• the secondary polymer component is miscible with the radiation curable oligomer.
• polymers suitable for use as the secondary polymer component include thermoplastic or thermosetting polyurethanes, polyureas, nitrocellulose polymers, vinyl chloride copolymers, phenoxy resins, combinations of such polymers, and the like.
• the secondary polymer component may contain one or more pendant functional groups to enhance the performance of the magnetic recording medium.
• the secondary polymer component may contain carbon-carbon double bonds and/or hydroxy groups to facilitate crosslinking of the secondary polymer component if desired.
• the secondary polymer component may contain pendant dispersing moieties such as -S0 3 M; quaternary ammonium moieties; -COOM; 0 0
• the vinyl chloride copolymer may have pendant epoxy groups to help prevent degradation of such copolymers due to outgassing of HC1.
• the secondary polymer component comprises at least one hydroxy functional polymer and an isocyanate cross-linking agent, wherein the hydroxy functional polymer has no radiation crosslinkable moieties.
• the weight percent of the oligomer is desirably in the range from 10 to 90 percent, preferably 15 to 70 percent, and more preferably 20 to 50 percent based on the total weight of the oligomer and the hydroxy functional polymer.
• the isocyanate crosslinking agent if any, is a polyfunctional isocyanate having an average functionality of at least 2 isocyanate groups per molecule. Examples of specific polyfunctional isocyanate useful as the isocyanate crosslinking agent in the practice of the present invention include materials commercially available as Mondur CB-601 and CB-701 from Miles, Inc.
• the isocyanate crosslinking agent is preferably used in an amount such that the molar ratio of NCO groups from the isocyanate crosslinking agent to the total number of hydroxy groups from the hydroxy functional polymer is greater than 0.
• the molar ratio of the NCO groups from the isocyanate crosslinking agent to the total number of hydroxy groups from the hydroxy functional polymer is in the range from 0.3 to 3.0, more preferably 1.2 to 1.8, and most preferably is about 1.5.
• the NCO groups of the isocyanate crosslinking agent will begin to react with the hydroxy groups of the hydroxy functional polymer.
• a catalyst e.g., dibutyltin dilaurate
• suitable catalytic amounts may also be added in suitable catalytic amounts in order to facilitate this crosslinking reaction.
• the secondary polymer component is a thermoplastic polymer which does not crosslink with itself or with the radiation curable oligomer.
• Suitable thermoplastic materials include polymers having no radiation crosslinkable moieties and, preferably no chemically crosslinkable moieties.
• thermoplastic polymers of the present invention may include chemically crosslinkable moieties so long as substantially no chemical crosslinking agent is present.
• the thermoplastic polymer may be a hydroxy functional polymer so long as substantially no isocyanate crosslinking agent or other free isocyanate moieties available for crosslinking are present.
• the weight percent of the radiation curable oligomer is desirably in the range from 10 to 90 percent, preferably 30 to 70 percent, more preferably 30 to 50 percent based on the total weight of the oligomer and the thermoplastic polymer.
• the radiation curable oligomer is blended with a secondary polymer component comprising at least one radiation curable polymer containing a plurality of radiation curable moieties and, optionally, a thermoplastic material as described above.
• the radiation curable oligomer is used in an amount effective to induce crosslinking of the radiation curable polymer when the blend is irradiated.
• a secondary polymer component comprising at least one radiation curable polymer containing a plurality of radiation curable moieties and, optionally, a thermoplastic material as described above.
• the radiation curable oligomer is used in an amount effective to induce crosslinking of the radiation curable polymer when the blend is irradiated.
• 25 to 50 parts by weight of the radiation curable oligomer based on 100 parts by weight of the radiation curable polymer would be suitable in the practice of the present invention.
• the radiation curable oligomer When the radiation curable oligomer is blended with a secondary polymer component comprising a radiation curable polymer and a suitable thermoplastic material, it is believed that irradiation of the blend provides a semi-IPN composition in which the radiation curable oligomer and the radiation curable polymer crosslink only with themselves to form a 3-dimensional, crosslinked matrix.
• the thermoplastic material undergoes no crosslinking reactions, but rather becomes entangled in the crosslinked matrix formed by the radiation curable oligomer and the radiation curable polymer.
• Semi-IPN compositions of the present invention have better resilience and better toughness than irradiated compositions of only the radiation curable oligomer alone or only the secondary polymer component alone. Our investigations have also shown that preferred semi-IPN compositions of the present invention have better toughness than semi-IPN compositions based on previously known radiation curable oligomers.
• the radiation curable oligomers of the present invention are miscible with a wide variety of polymer materials, including both acidic and polymeric materials. It is believed that the excellent miscibility characteristics of the oligomers is attributable to the urethane and/or urea content of the oligomers. Inasmuch as urethane and urea moieties are both donor and acceptor groups for hydrogen bonding, it is believed that such moieties enhance the intermolecular interactions between the oligomers and other polymers.
• the radiation curable oligomers are particularly miscible with polyurethanes and polyureas since the oligomers are polyurethanes and/or polyureas themselves.
• the magnetic layer of the present invention may also comprise one or more conventional additives such as lubricants; abrasives; thermal stabilizers; antioxidants; dispersants; wetting agents; antistatic agents; fungicides; bactericides; surfactants; coating aids; nonmagnetic pigments; and the like in accordance with practices known in the art.
• lubricants such as lubricants; abrasives; thermal stabilizers; antioxidants; dispersants; wetting agents; antistatic agents; fungicides; bactericides; surfactants; coating aids; nonmagnetic pigments; and the like in accordance with practices known in the art.
• a preferred class of dispersants comprises novel monomeric, oligomeric, or polymeric dispersants comprising at least one dispersing moiety and at least one radiation curable moiety selected from
• Such dispersants shall be referred to hereinafter as " ⁇ -methylstyrene functionalized" dispersants.
• suitable dispersing moieties include -S0 3 M; 0 0 quaternary ammonium -C00M; -P »(0M) 2 ; -0P II(0M) 2 ; and the like, wherein M is H + Na + , K + , Li + , NH 4 +, and the like.
• these ⁇ -methylstyrene functionalized dispersants are capable of crosslinking with the other radiation curable binder materials when exposed to ionizing radiation in the presence of the radiation curable oligomer.
• One example of a preferred ⁇ -methylstyrene functionalized dispersant may be prepared by reacting an ⁇ -methylstyrene functionalized isocyanate selected from
• metal-TMI metal-TMI
• para-TMI para-TMI
• m is an integer from 1 to 5.
• Phosphorylated polyoxyalkyl polyols are described in U.S. Pat. No. 4,889,895. All or only a portion of the hydroxy groups of the phosphorylated polyoxyalkyl polyol may be reacted with NCO groups of the isocyanate.
• the isocyanate is reacted with the polyol in an amount such that the ratio of NCO groups to OH groups is about 0.6.
• a preferred difunctional dispersant may be prepared by reacting the ⁇ -methylstyrene functionalized isocyanate with a polyoxyalkylated quaternary ammonium polyol such as the Emcol brand dispersing agents commercially available from Witco Chemical, New York, New York.
• the Emcol materials are exemplified by the formula
• A is a monovalent, anionic counterion.
• A typically is phosphate, acetate, or chloride. All or only a portion of the hydroxy groups of such polyols may be reacted with the NCO groups of the isocyanate.
• the Emcol materials typically contain other free polyols.
• the isocyanate is reacted with such polyols in an amount such that the ratio of NCO groups to OH groups of the polyoxyalkylated quaternary ammonium polyol is about 2.2:1. In this way, all of the hydroxy groups of the other polyols and the polyoxyalkylated quaternary ammonium polyol are reacted with the isocyanate.
• the magnetic pigment, the secondary polymer component (except for (meth)acrylate functional materials and the isocyanate crosslinking agent if any are used) and a suitable solvent are milled in a first step to form a magnetic dispersion.
• a suitable solvent may also be milled in this first step.
• using about 60 percent by weight of solvent based on the total weight of the magnetic pigment, the secondary polymer component, and any other additives has been found to be suitable in the practice of the present invention.
• the radiation curable oligomer, the (meth)acrylate functional materials of the secondary polymer component if any, the isocyanate crosslinking agent if any, and additional solvent are blended into the magnetic dispersion just prior to coating the dispersion onto a nonmagnetizable support.
• additional solvent may be added to the dispersion during this second step as well as during the first step.
• suitable solvents for preparing the magnetic dispersion may include ketones such as acetone, methyl ethyl ketone ("MEK”) , methyl isobutyl ketone, or cyclohexanone; alcohols such as methanol, ethanol, propanol, or butanol; esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, or glycol diacetate; tetrahydrofuran; glycol ethers such as ethylene glycol dimethyl ether, or ethylene glycol monoethyl ether; dioxane or the like; aromatic hydrocarbons such as benzene, toluene, or xylene; aliphatic hydrocarbons such as hexane or heptane; nitropropane or the like; and mixtures thereof.
• ketones such as acetone, methyl ethyl ketone (“MEK”) , methyl is
• a particularly preferred solvent is a solvent blend containing 50 parts by weight of toluene and 50 parts by weight of methyl ethyl ketone. Use of such a solvent blend tends to provide a magnetic layer with very little solvent retention. Low solvent retention is desirable, particularly when the solvent interferes with hydrogen bonding between the radiation curable oligomer and the secondary polymer component. Such interference can reduce the toughness of the resulting polymeric binder.
• the magnetic dispersion is then coated onto the nonmagnetizable substrate.
• the dispersion may be applied to the nonmagnetizable substrate using any conventional coating technique, such as gravure coating techniques or knife coating techniques.
• the coated substrate may then be passed through a magnetic field to orient the magnetic pigment, after which the coating is dried, calendered if desired, and then irradiated with ionizing radiation to cure the radiation curable binder components.
• Irradiation i.e., curing of the radiation curable materials
• curing is achieved using any type of ionizing radiation, e.g., electron beam radiation or ultraviolet radiation, in accordance with practices known in the art.
• curing is achieved with an amount of electron beam radiation in the range from l to 20 Mrads, preferably 4 to 12 Mrads, and more preferably 5 to 9 Mrads of electron beam radiation having an energy in the range from 100 to 400 kev, preferably 200 to 250 keV.
• electron beam irradiation can occur under ambient conditions or in an inert atmosphere, it is preferred to use an inert atmosphere as a safety measure in order to keep ozone levels to a minimum and to increase the efficiency of curing.
• Inert atmosphere means an atmosphere comprising flue gas, nitrogen, or a noble gas and having an oxygen content of less than 500 parts per million (“ppm") .
• a preferred inert atmosphere is a nitrogen atmosphere having an oxygen content of less than 75 parts per million.
• polyisocyanate (Desmodur N3300, Miles, Inc., NCO equivalent weight 195) and 5.9 g 1,6-hexane diol (Aldrich) were dissolved in 350 g of toluene in a one liter resin flask equipped with a mechanical stirrer, a reflux condenser fitted with a drying tube filled with anhydrous calcium sulfate, an additional funnel, and a glass thermowell containing a thermometer with a Thermo-O-Watch sensor/controller connected to two 250 watt infra-red lamp heaters. The diol did not completely dissolve.
• Dibutyl tin dilaurate (Aldrich, 2 drops) was added and the mixture was heated with stirring to 50°C. The diol dissolved on heating. After five hours at 50°C, 26 g of hydroxyethyl methacrylate (Rohm and Haas, Rocryl 400) was added. After one-half hour at 50°C another 2 drops of dibutyl tin dilaurate was added. After 2 hours the temperature of the mixture was increased to 60°C and held there for 5 hours. On cooling, the solution become cloudy but cleared on the addition of 30 g of a 50:50 by weight blend of methyl ethyl ketone and toluene.
• Functionalized Dispersant 133.33 parts by weight of a 75% solution of a phosphorylated polyoxyalkyl diol (0.238 equivalents OH) in toluene, 0.03 parts by weight BHT, and 0.28 parts by weight dibutyltindilaurate were dissolved in 38.37 parts by weight toluene.
• 28.70 parts by weight meta-TMI (0.143 equivalents NCO) was slowly added at room temperature.
• the resulting reaction mixture was stirred for 30 minutes. After 30 minutes, stirring was stopped, and the reaction was allowed to proceed.
• the reaction was complete after 2 days when an IR absorption for NCO at 2250 cm" 1 could no longer be detected.
• Six hours after the meta-TMI had been added a 10,000 gram batch showed a maximum exotherm of 37°C.
• a radiation curable polymer sample was prepared under ambient conditions by reacting 100 parts by weight of a hydroxy functional polymer (PKHH UCAR phenoxy resin commercially available from Union Carbide Corporation) with 42.46 parts by weight of meta-TMI.
• the hydroxy-functional polymer was first dissolved in 233 parts by weight methyl ethyl ketone. Next, 200 ppm (based on total weight of the hydroxy functional polymer and the meta-TMI) of BHT gellation inhibitor and 0.15 weight percent (based on the total weight of the hydroxy functional polymer and the meta-TMI) of dibutyltindilaurate catalyst were added to the solution with mixing. The meta-TMI was then slowly added with mixing.
• PKHH UCAR phenoxy resin commercially available from Union Carbide Corporation
• the reaction between the hydroxy-functional polymer and the meta-TMI was monitored by measuring the IR absorption peak of the NCO group (2250 cm" 1 ) from the meta-TMI. The reaction was deemed to be complete when an IR absorption peak for the NCO group could no longer be detected.
• the dispersion was also diluted to 20% solids with methyl ethyl ketone and cyclohexanone, wherein the cyclohexanone was used in an amount such that the total amount of solvent in the dispersion was comprised of 18% by weight of cyclohexanone.
• a backside dispersion was prepared in accordance with Example 12A, except that no myristic acid was blended into the dispersion.
• a backside dispersion was prepared in accordance with Example 12B, except that the dispersion was diluted to 20% solids with MEK and toluene, wherein the toluene was used in an amount such that the total amount of solvent in the dispersion contained 20 weight percent toluene.
• Example 13
• Example 12A The backside dispersion of Example 12A was coated onto one side of a thin gauge, pre-primed polyester substrate. The coated substrate was then dried at 140°F. Next, the magnetic dispersion was coated onto the other side of the pre-primed polyester substrate. The coated substrate was then passed through a magnetic field (3000 gauss) to orient the magnetic pigment. After this, the coated substrate was again dried at 140°F, and then the magnetic and backside coating were calendered. The backside coating and the magnetic coating were then cured with 8 megarads of electron beam radiation in a N 2 atmosphere containing no more than 50 ppm 0 2 .
• the resulting magnetic medium showed a squareness of 0.791, a coercivity of 1461, and a remanence of 2659 gauss. All bulk magnetic measurements were made with a vibrating sample magnetometer ("VSM”) at 12.3 KOe.
• VSM vibrating sample magnetometer
• Example 12B The backside dispersion of Example 12B was coated onto one side of a thin gauge, pre-primed polyester substrate. The coated substrate was then dried at 140°F. Next, the magnetic dispersion was coated onto the other side of the pre-primed polyester substrate. The coated substrate was then passed through a magnetic field (2500 gauss) to orient the magnetic pigment. After this, the coated substrate was again dried at 140°F, and then the magnetic and backside coating were calendered. The backside coating and the magnetic coating were then cured with 8 megarads of electron beam radiation in a N 2 atmosphere containing no more than 50 ppm 0 2 .
• the resulting magnetic medium showed a squareness of 0.752, a coercivity of 1427, and a remanence of 2704 gauss. All bulk magnetic measurements were made with a vibrating sample magnetometer ("VSM”) at 12.3 KOe.
• VSM vibrating sample magnetometer
• Example 12C The backside dispersion of Example 12C was coated onto one side of a thin gauge, preprimed polyester substrate. The coated substrate as then dried at 140°F. Next, the magnetic dispersion was coated onto the other side of the pre-primed polyester substrate. The coated substrate was then passed through a magnetic field (3000 gauss) to orient the magnetic pigment. After this, the coated substrate was again dried at 140°F, and then the magnetic and backside coating were calendered. The backside coating and the magnetic coating were then cured with 8 megarads of electron beam radiation in a N 2 atmosphere containing no more than 50 ppm 0 .
• the resulting magnetic medium showed a squareness of 0.723 and a coercivity of 1444 and a remanence of 2304 gauss. All bulk magnetic measurements were made with a vibrating sample magnetometer ("VSM”) at 12.3 KOe.
• VSM vibrating sample magnetometer
• Example 12C The backside dispersion of Example 12C was coated onto one side of a thin gauge, preprimed polyester substrate. The coated substrate was then dried at 140°F. Next, the magnetic dispersion was coated onto the other side of the pre-primed polyester substrate. The coated substrate was then passed through 2 magnetic fields to orient the magnetic pigment. The first magnetic field (2000 gauss) was located just after the coating head, and the second magnetic field (3400 gauss) was coated 47" into the drying oven. After this, the coated substrate was again dried at 140°F, and then the magnetic and backside coating were calendered. The backside coating and the magnetic coating were then cured with 8 megarads of electron beam radiation in a N 2 atmosphere containing no more than 50 ppm 0 2 .
• the resulting magnetic medium showed a squareness,of 0.662 and a coercivity of 1498 and a remanence of 1804 gauss. All bulk magnetic measurements were made with a vibrating sample magnetometer ("VSM”) at 12.3 KOe.
• VSM vibrating sample magnetometer
• a magnetic recording medium was prepared according to the procedure of Example 15, except that Ebecryl 220 (Trademark) radiation curable oligomer commercially available from Radcure Specialties, Inc. was used instead of the radiation curable oligomer of the present invention.
• Ebecryl 220 Trademark radiation curable oligomer commercially available from Radcure Specialties, Inc. was used instead of the radiation curable oligomer of the present invention.
• a magnetic recording medium was prepared according to the procedure of Example 16, except that Ebecryl 220 (Trademark) radiation curable oligomer was used instead of the radiation curable oligomer of the present invention.
• DMTA modulus was measured at 1 N (newton) , 10 Hz, using the DMTA device commercially available from Polymer Laboratories, Ltd. Percent strain to microfracture was measured using a Miniature Materials Tester by Polymer Laboratories, Ltd. Slit edge quality of the coatings was visually observed at a magnification of 500X.

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