Classifications

• • 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
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
  • C09D183/04—Polysiloxanes
• • 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
  • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
  • C09D183/04—Polysiloxanes
  • C09D183/06—Polysiloxanes containing silicon bound to oxygen-containing groups
• • 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
  • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
• • 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
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/65—Additives macromolecular
• • 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
  • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
  • C09D7/40—Additives
  • C09D7/70—Additives characterised by shape, e.g. fibres, flakes or microspheres
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J7/00—Adhesives in the form of films or foils
  • C09J7/40—Adhesives in the form of films or foils characterised by release liners
  • C09J7/401—Adhesives in the form of films or foils characterised by release liners characterised by the release coating composition
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
  • C09J2483/00—Presence of polysiloxane
  • C09J2483/005—Presence of polysiloxane in the release coating

Definitions

• Microparticle Containing Silicone Release Coatings having Improved Anti- Block and Release Properties
• the invention relates generally to silicone release coating compositions, the use of such silicone release coating compositions to coat a substrate, and a release coated substrate formed thereof. More particularly, the invention relates to thermal curable, radiation curable, and UV-cationic solventless silicone release coatings having improved slip/shear, transfer, anti-block, and lower release properties.
• Silicone release coatings or compositions are well known and the subject of many publications and patents. They are useful in many applications where one requires a relatively non-adherent surface. In such applications release compositions are coated onto a substrate, and are caused to be cured. A particularly useful application is the coating of paper, polyethylene films, and other materials that are used among other applications for providing non-stick surfaces, pressure sensitive adhesive labels, decorative laminates, and transfer tapes. Silicone polymers and copolymers have been used extensively in release compositions because they are inherently low in surface energy. The silicone polymers and copolymers (sometimes referred to as polyorganosiloxanes) used in the prior art for making release compositions can be radiation cured or thermally cured. Solventless silicone release compositions are also well known.
• Non-radiation cure silicone-release compositions release performance in such coatings is characteristic of the base silicone polymer.
• Thermal cure versions of these polymers are generally standard polydimethylsiloxanes, which have been terminated with either vinyl or silanic hydrogen reactive groups, or they are copolymers of polydimethyl and methylvinylsiloxane. These copolymers can also be terminated with vinyl reactive groups as in the case of the standard polydimethylsiloxanes.
• Solventless compositions generally do not include any organic solvent such as toluene or xylene.
• release-coated papers and films have a release force which is low enough to enable the release backing sheet to be easily removed from a coated substrate, but not so low that the release backing sheet will become separated from the coated surface prior to when desired by forces normally encountered in handling and processing.
• Release force is defined as the amount of force required to peel or separate the release-coated substrate from the adhesive. While various release compositions have been provided that limit an increase in release force, there has not been such success in lowering the release force below that which is the normal minimum of the silicone release composition. Often the force below the normal minimum release force is known in the art as the premium release level and accordingly, a release coating which exhibits a low release force, is referred to in the art as a "premium release".
• silicone layers also referred to as sheets or films
• blocking also generally refers to the sticking of one layer, for example a silicone layer, to another layer, for example a non-silicone side of another layer.
• anti-block is used to describe preventing such adhesion and when referring to materials coated onto film sheets,
• antiblocking agents and “antifriction agents” all refer to materials which are used to prevent two sheets from adhering together.
• free silicone oil is inevitably released from the coated sheet onto the surface of another coated sheet leaving discrete patches of free silicone oil on the sheet surface. This creates what is referred to as high "slip". Free silicone oil can also be transferred easily to the non-silicone-coated back side of the sheet.
• the coated sheet is stored in a front surface to back surface contact manner, as in a typical roll, some of the free silicone oil (typically low molecular weight silicones) on the front silicone coated surface of the sheet will be transferred to the back (typically uncoated) surface of the roll.
• this free silicone oil contamination can be a drawback.
• the idler rolls can slip and lose contact with the sheet. This can result in uneven tension on the sheet web or loss of alignment.
• Related problems arise when printing on the resulting silicone-coated sheet or when labels are applied to the sheet.
• the ability of printing inks and solvents to adhere is impaired by the presence of free silicone oil on the surface to be printed.
• loss of alignment due to the sheet's high slip can lead to a high reject rate during printing, particularly where multiple printing passes are used and in cases where proper alignment is critical for formation of an integrated image.
• the invention is directed to a silicone release composition containing polymeric microparticles, preferably microspheres.
• the invention is directed to a radiation curable solventless silicone release composition containing polymeric microparticles.
• the invention is directed to a UV-cationic or free radical silicone release composition containing polymeric microparticles.
• the invention is directed to a thermal curable silicone release composition containing polymeric microparticles.
• a further aspect of the invention comprises a method for producing a release coating on a substrate by applying the aforedescribed release composition containing microparticles to a substrate and curing the coating on the substrate. The coating may be cured by exposing the coating to radiation or heat.
• a still further aspect of this invention comprises a release coated article comprising a substrate which has been coated with the release composition containing microparticles and has optionally been cured by exposure to radiation or heat.
• FIG. 1A is a photograph of a silicone release composition without microparticles.
• FIG. 1 B is a photograph of a silicone release composition having microparticles therein in accordance with the invention. Detailed Description of Invention and Preferred Embodiments
• a first subject of the invention is a release coating, characterized in that it comprises, as a mixture: (1 ) at least one heat or radiation curable organopolysiloxane polymer (2) a catalytically effective amount of at least one initiator, and (3) polymeric microparticles.
• the addition of polymeric microparticles in combination with the other silicone components makes it possible to achieve the desired properties. Thanks to the slight protrusion of the microparticles, silicone contact is slightly minimized to reduce the coefficient of friction thereby improving release, transfer, and slip/shear properties of the release composition.
• FIG. 1A shows a silicone release composition without microparticles
• FIG. 1B shows a silicone release composition having microparticles therein, in accordance with the invention.
• the slight protrusions of the microparticles helps impart improved release coating properties.
• the microparticles also contribute to lowering the density of the release composition. As such, less silicone will be required to coat a particular surface.
• the polymeric microparticles maybe of any suitable shape, and are preferably spherical, e.g., microspheres.
• the microparticles may be in solid or hollow form. Hollow microspheres do not have the crush resistance exhibited by solid spheres and cannot be used in systems requiring high-shear mixture or high-pressure molding.
• the polymeric microparticles may be formed of any suitable polymeric material, and preferably is formed of a polyethylene material and more preferably polytetrafluoroethylene (PTFE) or combinations of polyethylene and PTFE materials.
• Preferred microparticles are sold under the name Polyfluo® by Micro Powders Inc and Ceraflour® by BYK-Cera bv.
• the microparticles preferably have a softening or melting point of at least about 100°C, and more preferably of at least about 300°C.
• the microparticles may also be expandable organic microparticles comprising, as is known in the art, a polymer wall having a liquid or a gas formed therein.
• microparticles are expanded by heating them beyond the softening point of the polymer and to a temperature sufficient to vaporize the liquid or suitably expand the gas, which can be, for example, an alkane, such as isobutane or isopentane.
• the wall can be composed, of polymers or copolymers, for example prepared from vinyl chloride, vinylidene chloride, acrylonitrile, methyl methacrylate or styrene monomers, or mixtures of polymers and/or copolymers, for example, in particular, acrylonitrile/methacrylonitrile copolymer or acrylonitrile/vinylidene chloride copolymer. (See in particular U.S. Pat. No.
• a preferred expandable organic microparticle is sold under the name Dualite® by UCB Chemicals. Expandable organic microparticles can be incorporated in the composition without distinction in the expanded state or before their expansion, which can be induced by appropriate heating. It may be advantageous for the microparticles or microspheres to be surface treated, as is known in the art, in order to promote dispersion in the composition. Suitable surface treatment materials include silica or salts or hydroxides of metals such as Ca, Mg, Ba, Fe, Zn, Ni, Mn, as is described for example in EP-A-486,080, or else carbonates, for example calcium carbonate.
• the polymeric microparticles may be any suitable size, and are preferably slightly larger than the required release composition thickness, in order to allow a slight protrusion.
• the expandable organic microparticles are present for example, in a proportion of about 0.1% to about 30% by weight, preferably about 0.5% to about 10% by weight and more preferably about 2% to about 4% by weight with respect to the total composition.
• the microspheres will preferably have a diameter of between about 0.5 ⁇ m and about 15 ⁇ m and more particularly between about 1 ⁇ m and about 4 ⁇ m.
• the microspheres are preferably present in an amount of for example about 0.5% to about 30% by weight, preferably from about 0.5% to about 10% by weight, and more preferably from about 0.5% to about 3% by weight with respect to the total composition.
• Pre-expansion microspheres will preferably have a diameter of between about OJ ⁇ m and about 10 ⁇ m and more preferably between about 0.5 ⁇ m and about 3 ⁇ m.
• a composition according to a first aspect of the invention advantageously comprises a radiation curable solventless release composition. Any suitable radiation curable solventless release composition may be used.
• a preferred polymeric microparticle containing radiation curable solventless release composition as described in the aforesaid mentioned patent comprises:
• the polymeric microparticles containing radiation-curable solventless silicone release compositions in accordance with the invention are produced by mixing microparticles in an amount of from about 0J to about 5 parts by weight of the total composition with the silicone components of the aforementioned components of the composition.
• the microparticles may be mixed into any of the components (a), (b), (c) or (d) or any combination thereof.
• the microparticle and component(s) may be mixed at room temperature with stirring.
• the main silicone components and microparticles are very compatible when blended into one another and generally do not require them to be maintained under continuous stirring and heat to keep the system homogeneous.
• the polymeric microparticles containing radiation-curable solventless silicone release compositions of the invention can be stabilized against premature polymerization during storage by the addition of conventional polymerization inhibitors, such as hydroquinone, monomethylether of hydroquinone, phenothiazine, di-t-butyl paracresol, and the like. Amounts of about 0J weight percent or less of the stabilizers are generally effective.
• the polymeric microparticles containing radiation-curable solventless silicone release compositions of the invention generally are applied to a substrate prior to curing.
• the compositions may be applied to a substrate as a coating by any conventional means known in the coating art, such as roller coating, curtain coating, brushing, spraying, reverse roll coating, doctor knife, dipping, die coating and the like.
• a wide variety of substrates can be coated with the polymeric microparticles containing radiation-curable solventless silicone release compositions of the invention. These compositions can be applied to any suitable substrate when it is desirable to modify the release properties of a surface of the substrate.
• compositions of the invention can be employed to form release coatings on substrates, such as paper, vinyl, polyvinyl chloride, and polyester polyolefin films, non-woven fabrics, glass, steel, aluminum, and the like.
• substrates such as paper, vinyl, polyvinyl chloride, and polyester polyolefin films
• substrates such as paper, vinyl, polyvinyl chloride, and polyester polyolefin films
• substrates such as paper, vinyl, polyvinyl chloride, and polyester polyolefin films
• substrates such as paper, vinyl, polyvinyl chloride, and polyester polyolefin films, non-woven fabrics, glass, steel, aluminum, and the like.
• clay coated paper such as clay coated paper, polymer coated paper, paperboard from straw, bark, wood, cotton, flax, cornstalks, sugarcane, bagasse, bamboo, hemp, and similar cellulose materials prepared by such processes as the soda, sulfite or sulfate (Kraft) processes, the neutral sulfide cooking
• Examples of papers which can be utilized as substrates in preparing the composite laminates of the invention include Kraft papers such as 40-pound and 50-pound bleached Kraft papers, 41 -pound offset grade bleached Kraft paper, and the like.
• the amount of radiation-curable solventless silicone release compositions of the invention applied to the various substrates will vary depending upon the characteristics of the substrate, the properties desired in the release coating, the radiation source utilized, and the particular formulation of the release composition. Generally, it is desired to apply the least amount of coating to obtain the desired result. Thus, applied coating weights may range from about 0J to about 10 or more grams/m 2 depending on the substrate and intended use.
• the polymeric microparticles containing radiation curable solventless silicone release compositions of the invention can be cured by exposure to known forms of radiation, especially ultraviolet light or ionizing radiation, such as electron beam radiation.
• ultraviolet radiation especially ultraviolet light or ionizing radiation, such as electron beam radiation.
• One of the advantages of using ultraviolet radiation to effect cure of the composition is that polymerization takes place rapidly at ambient temperature, and heating is not necessary.
• the preferred ultraviolet radiation used has a wavelength of from about 0J5 ⁇ m to about 0.4 ⁇ m, preferably from about 0.20 ⁇ m to about 0.35 ⁇ m.
• the duration of irradiation can be short and it is generally less than 1 second and is on the order of a few hundreds of a second for very thin coatings.
• a preferred curing process would be a high speed cure of about 200m/min at 240W/cm using two radiation lamps.
• a composition according to another aspect of the invention advantageously comprises a radiation curable cationic silicone release composition, commonly referred to as a "UV-cationic" silicone release composition and microparticles.
• UV-cationic silicone release compositions are generally based on epoxy-silicone copolymer technology that is blended with a cationic curing agent or photoinitiator.
• the epoxy-silicone copolymer technology generally has the following composition, as described in US Patent No. 5,340,898 which is herein incorporated by reference: a curable epoxypolyorganosiloxane having a linear or a substantially linear polymer of recurring structural units of formula (IV) and end groups of formula (V); or are cyclic and comprise recurring structural units of formula (IV)
• R represents a C1-C6 linear or branched alkyl radical; a C5-C8 cycloalkyl radical, an aryl radical; or a substituted aryl radical.
• At least 60 molar % of the radical R" is preferably a methyl radical.
• Z is preferably from a group as defined by R" or a cationically crosslinkable functional organic radical being bonded to an atom of the silicone chain via a divalent bridge having from about 2 to about 20 carbon atoms whereby at least one of the Z components is a crosslinkable functional epoxy containing organic radical.
• Z may be identical or vary for each of the recurring structural units.
• a polymeric microparticle containing UV-cationic silicone release composition may comprise: (a) a curable epoxypolyorganosiloxane having a linear or a substantially linear polymer of recurring structural units according to formula (IV) and end groups of formula (V) as described in US Patent No.
• a suitable polymeric microparticle containing UV- cationic silicone release composition may comprise: (a) at least a liquid polyorganosiloxane having a viscosity of about 10 to 10,000 mPa's at 25°C and bearing a crosslinkable/polymerisable function Z on at least an M and/or T unit, and /or at least a crosslinkable/polymerisable function on at least a D unit (b) a cationic photoinitiator of onium borate type; and (c) microparticles.
• Another suitable UV-cationic silicone release composition is a "premium release" composition. As discussed above, premium release, relates to a release composition that has low release properties.
• Preferred premium release compositions are commercially available under the name Silcolease® by Rhodia Inc.
• One such UV-cationic premium release composition comprises: aJ) about 50 to about 99 parts by weight and preferably about 70 parts of a curable epoxypolyorganosiloxane formula (VI)
• n is between about 10 to about 100, and preferably about 20; bJ) about 1 to about 50 parts by weight and preferably about 30 parts by weight of the polyorganosiloxane having formula (VII),
• r is between about 150 to about 300, and preferably about 220; c.1) about 0J to about 5 parts by weight and preferably about 2.5 parts by weight of a cationic initiator; and dJ) about 0J to about 5 parts by weight and preferably about 1 part by weight microparticles.
• the cationic initiator is preferably of an onium salt. Suitable onium borate initiators are discussed in U.S. Pat. Nos. 5,340,898 and 5,468,902, which are herein incorporated by reference. Other cationic curing agents or photoinitiators can alternatively be selected for use.
• Another preferred polymeric microparticle containing UV-cationic silicone premium release composition comprises: a.2) about 50 to about 99 parts by weight and preferably about 60 parts of a curable epoxypolyorganosiloxane of formula (VI), wherein n is between about 10 to about 100, and preferably about 20; b.2) about 1 to about 50 parts by weight and preferably about 30 parts by weight of the polyorganosiloxane of formula (VII), wherein r is between about 150 to about 300, and preferably about 220; c.2) about 1 to about 20 parts by weight and preferably about 10 parts by weight of a polyorganosiloxane of a formula (VIII),
• p is between about 0 to about 300 and preferably 70 and further wherein q is between about 1 to about 20 and preferably 8; d.2) about 0J to about 5 parts by weight and preferably about 2.5 parts by weight of a cationic initiator; and e.2) about 0J to about 5 parts by weight and preferably about 1 part by weight microparticles.
• Yet another preferred polymeric microparticle containing UV- cationic silicone premium release composition comprises: a.3) about 60 to about 99 parts by weight and preferably about 65 parts of the formula (VI) curable epoxypolyorganosiloxane, wherein n is between about 10 to about 100, and preferably about 20; b.3) about 1 to about 40 parts by weight and preferably about 30 parts by weight of the formula (VII) polyorganosiloxane, wherein r is between about 150 to about 300, and preferably about 220; c.3) about 1 to about 20 parts by weight and preferably about 5 parts by weight of the formula (VIII) polyorganosiloxane, wherein p is between about 100 to about 300 and p is preferably 200; and further wherein q is between about 1 to about 20 and q is preferably 3; d.3) about 0J to about 5 parts by weight and preferably about 2.5 parts by weight of a cationic initiator; and e.3) about 0J to about 5 parts by weight and
• the microparticles in accordance with this aspect of the invention are preferably microspheres.
• the microspheres may be mixed into any of the individual components or any combination thereof.
• the microspheres are mixed in with formula (VI) or (VII) and are more preferably mixed in with formula (VII).
• the microparticles are preferably mixed in at a percentage by weight of between about 10% to about 50% of the formula, and more preferably between about 25 and about 40% by weight of the formula.
• the microparticle and component(s) may be mixed at room temperature with stirring. In some instances, it may be desirable to employ mild heating to facilitate mixing.
• the main silicone components and microparticles are very compatible when blended into one another and generally do not require them to be maintained under continuous stirring and heat to keep the system homogeneous.
• UV-cationic silicone release compositions can be used as such or in solution in an organic solvent. They are useful for providing anti-adherent coatings on cellulosic materials, films, paints, encapsulation of electrical and electronic components, coatings for textiles and for sheathing optical fibers.
• the invention also features a process for the production of articles, comprising coating an amount of the UV-cationic silicone release composition of the invention, generally from about 0J to about 5 g/m 2 , onto at least one face surface thereof, and cross linking the composition by supplying radiation (i.e., visible light, ultraviolet or electron beam radiation).
• radiation i.e., visible light, ultraviolet or electron beam radiation.
• the type of radiation source utilized is directly correlated to the curing agent selected.
• the radiation source selected should be an ultraviolet wave source.
• the preferred ultraviolet radiation used has a wavelength of from about 0.2 ⁇ m to about 0.4 ⁇ m and preferably from about 0.23 ⁇ m to about 0.3 ⁇ m.
• the duration of irradiation can be short and it is generally less than 1 second and is on the order of a few hundreds of a second for very thin coatings.
• a preferred curing process is a high speed cure of about 200m/min at 240W/cm using two radiation lamps. Curing may be performed in the absence of any heating. However, it should be appreciated that heating at a temperature of from about 25° C to about 100°C is also within the scope of the invention.
• UV-cationic silicone release composition deposited onto the substrates are variable and typically range from about 0.1 to about 5 g/m 2 of treated surface. These amounts depend on the nature of the substrates and on the desired anti-adherent or anti-block properties. They usually range from about 0.5 to about 3 g/m 2 for nonporous substrates.
• UV-cationic silicone release compositions in accordance with the invention are for single or double coated release liners for tapes, labels or personal care items (e.g., diapers), other applications include: embossing strip release liners, protective release surfaces for floor tiles and wall coatings, release papers for low pressure plastic laminates, release materials for interleaves, release materials for self-sealing roofing, bakery tray liners, and like applications where a release surface of some definite value exists.
• a composition according to a third aspect of the invention advantageously comprises a thermal curable solventless release composition. Any suitable thermal curable solventless release composition may be used.
• a preferred polymeric microparticle containing thermal curable solventless silicone release composition may comprise: (a) from about 0 to about 50 parts by weight of an organopolysiloxane of formula (IX) wherein the Brookfield viscosity of formula (IX) is about 50 cps to about 45,000 cps at room temperature, and is more preferably about 180 cps;
• crosslinkable polymer may be any suitable polymer. Suitable crosslinkable polymers include, a homopolymer crosslinker having a general formula (XI) of for example:
• y is from about 0 to about 300 and t is from about 1 to 100.
• the composition may include from about 0 to about 15 parts of a flow modification agent which serves to enhance or otherwise control the viscosity or flow-ability of the final composition.
• the composition comprises microparticles in an amount of about 1 part by weight of the total composition. The microspheres may be mixed into any of the silicone components (a), (b), (c) or (d) or any combination thereof.
• the microparticles and silicone component(s) may be mixed at room temperature with stirring. It may also be desirable to employ mild heating to facilitate mixing.
• the thermal curable solventless silicone release compositions of the invention can also be stabilized against premature polymerization during storage by the addition of conventional polymerization inhibitors, such as hydroquinone, monomethylether of hydroquinone, phenothiazine, di-t-butyl paracresol, and the like. Again, amounts of about 0J weight percent or less of the stabilizers are generally effective.
• the polymeric microparticles containing thermal curable solventless silicone release compositions of the invention generally are applied to a substrate prior to curing.
• the compositions may be applied to a substrate as a coating by any conventional means known in the coating art, such as roller coating, curtain coating, brushing, spraying, reverse roll coating, doctor knife, dipping, die coating and the like.
• a wide variety of substrates can be coated with the thermal curable solventless silicone release compositions of the invention.
• These compositions can be applied to any suitable substrate when it is desirable to modify the release properties of a surface of the substrate.
• thermal curable silicone release compositions are widely used in the graphic arts sheet label market.
• the amount of polymeric microparticle containing thermal curable solventless silicone release compositions of the invention applied to the various substrates will vary depending upon the characteristics of the substrate, the properties desired in the release coating, the heat source utilized, and the particular formulation of the release composition. Generally, it is desired to apply the least amount of coating to obtain the desired result. Thus, applied coating weights may range from about 1.3 g/m 2 to about 1.8 g/m 2 for most paper and clay coated substrates and from about 0.65 g/m 2 to about 1J5 g/m 2 for poly coated Kraft substrates and will vary widely depending on the substrate and intended use.
• the thermal curable solventless silicone release compositions of the invention can be cured by exposure to known forms heat.
• the combination of microparticles in the silicone release composition provides surprisingly unexpected synergies.
• the addition of the microparticles to silicone release compositions have shown improved slip/shear and anti-block properties.
• the addition of the microparticles to silicone release compositions has also shown lower release properties. Another benefit exhibited by the invention is lower transfer.
• the microparticles are believed to act as an effective anti-blocking agent.
• the compositions are able to provide release values on the order of between about 3 to about 25 grams per linear inch at pull rates of about 12 inches to 600 inches per minute. ln order to further illustrate the invention and the advantages thereof, the following non-limiting examples are given.
• Example I The starting formulations of the release coatings were:
• the photoinitiator employed in the test compositions was Silcolease® UV Cata211 available from Rhodia Inc., a cationic photoinitiator activated by UV radiation.
• the polymeric microparticles were polytetrafluoroethylene (PTFE) microsphere sold under the name FLUO HT® commercially available from Micro Powders Inc.
• the polymeric microspheres were prepared as a dilution in formula (VII) at 33% by weight of the formula.
• the components were thoroughly mixed, applied to a polypropylene film at a coat weight of about 0.9 g/m 2 using a Dixon coater, and cured under two 240 W/cm ultraviolet lamps at a line speed of 200 meters per minute.
• Table 1 shows the results of the testing of the standard formulations and the standard formulations with 3 part's by weight of the total composition polymeric microspheres FLUO HT.
• Adhesives evaluated were acrylic adhesive tapes (commercial designations TESA4970 and TESA7475 available from Rhodia Inc.) and natural rubber adhesive tape (commercial designation TESA4651 available from Rhodia Inc.).
• the photoinitiator is commercially designated PC-702 and is available from Rhodia Inc.
• the microsphere are commercially designated XF-523 and are commercially available from Micro Powders Inc.
• standard UV-cationic silicone release compositions with and without polymeric microparticles were prepared, coated on a suitable substrate, cured by exposure to focused UV light, and the release values determined.

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• Chemical Kinetics & Catalysis (AREA)
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• Adhesive Tapes (AREA)

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• 2004
  • 2004-06-30 EP EP04756367A patent/EP1644431A4/de not_active Withdrawn

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