FIELD OF THE INVENTION
The present invention relates to the use of microfibers and/or microflakes as receptor media for a printable substrate. The printable substrate includes an oriented film with at least one microfibrillated, ink receptive surface. Printing on such receptor media with inkjet printers provides fine-resolution images with good solid fill. This type of printable substrate can be used with many types of inkjet inks.
BACKGROUND OF THE INVENTION
Image graphics are omnipresent in modern life. Images and data that warn, educate, entertain, advertise, etc. are applied on a variety of interior and exterior, vertical and horizontal surfaces. Nonlimiting examples of image graphics range from advertisements on walls or sides of trucks, to posters that advertise the arrival of a new movie, warning signs near the edges of stairways, and the like.
The use of thermal and piezoelectric inkjet inks has greatly increased in recent years with accelerated development of inexpensive and efficient inkjet printers, ink delivery systems, and the like.
Inkjet printers have come into general use for wide-format electronic printing for applications such as engineering and architectural drawings. Because of the simplicity of operation and economy of inkjet printers, this image process holds a superior growth potential promise for the printing industry to produce wide format, image on demand, presentation quality graphics.
Therefore, the components of an inkjet system used for making graphics can be grouped into three major categories:
1. Computer; software, printer
3. Receptor medium
The computer, software, and printer will control the size, number and placement of the ink drops and will transport the receptor medium through the printer. The ink will contain the colorant which forms the image and carrier for that colorant. The receptor medium provides the repository which accepts and holds the ink. The quality of the inkjet image is a function of the total system. However, the compositions and interaction between the ink and receptor medium are most important in an inkjet system.
Image quality is what the viewing public and paying customers will want and demand to see. From the producer of the image graphic, many other obscure demands are also placed on the inkjet media/ink system from the print shop. Also, exposure to the environment can place additional demands on the media and ink (depending on the application of the graphic).
Media for inkjet printers are also undergoing accelerated development. Because inkjet imaging techniques have become vastly popular in commercial and consumer applications, the ability to use a personal computer to print a color image on paper or other receptor media has extended from dye-based inks to pigment-based inks. The media must accommodate that change. Pigment-based inks provide more durable images because of the large size of colorant as compared to dye molecules , which results in superior fade resistance and improved water fastness.
Inkjet printing is emerging as the digital printing method of choice due to its good resolution, flexibility, high speed, and affordability. Inkjet printers operate by ejecting, onto a receiving substrate, controlled patterns of closely spaced ink droplets. By selectively regulating the pattern of ink droplets, inkjet printers can produce a wide variety of printed features, including text, graphics, holograms, and the like. The inks most commonly used in small inkjet printers, such as those used in the small office and home office (SOHO) markets, are water based. Industrial type wide format inkjet printers can use water based inks such as the Novajet printers from Encad Inc. (San Diego, Calif.), oil based inks such as piezo print 5000 from Raster Graphics Inc. (San Jose, Calif.), solvent based inks such as the PressVu printers from VUTEk, Inc. (Meredith, N.H.), or UV curable inkjet inks such as the SIAS printer from Siasprint Group (Novara, Italy). This wide variety of inks typically requires specialized substrates, where each specific substrate is optimized to work with a specific type of inkjet ink. For example, water based inks require porous substrates or substrates with special hydrophilic coatings that absorb the large quantities of water contained in these inks. Oil based inks are similar to water based inks in that they require the use of either porous substrates or substrates coated with a receptor that is oil absorbing.
On the other hand, solvent based inks typically contain about 90% organic solvents. These inks work well on substrates that have high affinity to the solvents, where the solvents can quickly penetrate the polymeric film preventing the printed ink layer from running down the film. In high speed inkjet printing, there is a need to drive off large quantities of solvent so that the substrate is dry enough to be rolled without blocking in a relatively short period of time. Therefore, typical solvent based inkjet inks consist of aggressive solvents such as cyclohexanone and acetates that penetrate quickly into typical films such as vinyl giving the printed graphic a “dry” feel within a short period of time from printing. As a consequence, the quickly penetrating solvents tend to remain in the film (as well as in the PSA backing if present) resulting in deteriorated film properties, reduced PSA performance, and strong odor when the graphic is unrolled and applied to a flat surface.
In particular, most wide format solvent based piezo inkjet inks require a very low viscosity for jetting, resulting in a very high ratio of solvent to binder/pigment. Large amounts of ink must be jetted onto the desired substrate to produce a graphic with acceptable image density. Polyvinyl chloride (PVC) is typically used for producing large format durable graphics. The solvents used in the inks are quickly absorbed into the vinyl film and adhesive layers, leaving the pigment and binder on the surface of the film and resulting in acceptable image quality. The piezo ink solvents are very compatible with the PVC and adhesive layers, and also have relatively high boiling points so it is difficult to fully dry all of the solvent from a printed sample, especially with the constraints typical of a graphic production shop. The presence of the retained solvent negatively affects product performance in three ways: 1) the solvents migrate through the PVC and plasticize the adhesive which results in very poor adhesive performance, 2) the solvents are retained in the PVC film layer resulting in decreased film properties, and 3) the retained solvents in the film and adhesive have an objectionable odor which is very noticeable especially on large format graphics, and has been noted as objectionable by a number of customers. Traditional olefin-based graphic films can work well for screenprint and flexographic printing, but have problems with solvent based piezo inks because the large amount of solvents jetted cannot be absorbed into the film. When large amounts of piezo inkjet inks are printed onto traditional olefin based graphic films the inks pool on the surface of the film and readily run, producing a poor quality, distorted image. There is a need for a substrate that is receptive to solvent based piezo inkjet inks, does not allow running of the inks, provides good adhesion of the inks when dry, and dries quickly to prevent objectionable odors.
In order to avoid the challenges associated with the above-described inks, there is a drive in the marketplace to move towards UV curable inkjet inks. These inks are expected to provide an “instant dry” feature when exposed to UV radiation. However, the use of UV curable inkjet inks requires redesigning the printer to accommodate curing lamps. This increases the cost of the printer. Additionally, there is an inherent problem with UV curable inkjet inks: in order to obtain fine line resolution, the inks should be cured within a relatively short time from printing, which results in poor ink flow and leveling compromising the quality of the solid fill areas of the graphic. But to obtain good solid fill, the inks should be allowed to flow and level before curing, which results in the loss of fine line resolution.
Therefore, a need exists for a universal substrate that can be used with all types of inkjet inks, and that does not require a special receptor coating or UV curing conditions.
We have discovered that microfibrillated films provide good ink receptive properties for various types of inkjet inks.
SUMMARY OF THE INVENTION
The present invention concerns the finding that certain polymeric films, which are not good receptors for inkjet inks can produce good inkjet printed articles when they are microfibrillated. For example, polypropylene and polylactic acid films can be microfibrillated using a hydroentangling process described in U.S. Pat. No. 6,110,588 which patent is incorporated herein by reference. This process produces a microfibrillated substrate with very fine microfibers or microflakes having a very large surface area. When printed with solvent based piezo and water based inkjet inks much of the ink adsorbs onto the large surface area of the microfibers or microflakes, eliminating ink puddling and running. Due to the microscale of the microfibers and microflakes, the solvent in the ink remains close to the air interface (e.g., from microfibrillated, oriented polypropylene films) compared with PVC films, the microfibrillated substrates feel dry to the touch after printing and do not have a significant solvent odor, which the PVC films often have. The dried images also have little residual odor resulting from solvent because the solvents remain close to the surface of the microfibers resulting in faster evaporation of the solvents from the receptor media. PVC films that absorb large amounts of the ink solvents typically have residual odors because evaporation of the solvents from the film is very slow. Upon drying, the inks bond very well to the microfibrillated structures and are difficult to abrade off, resulting in a durable image. This is surprising because the microfibers and microflakes are composed of materials that the ink systems do not bond to as well when printed on the unfibrillated film form. For example, ink solvents (including water) have a very low rate of diffusion into films of polypropylene (PP), polyester (PET) and polylactic acid (PLA), and ink in the printed images pools and runs severely with solvent based inkjet inks, and beads up and runs with water based inkjet inks. When dry, the beaded-up areas of ink have poor adhesion to any of these materials in film form. When these films are microfibrillated the inks are adsorbed onto the microfibers and microflakes and do not run or puddle. Upon drying the image is well bonded to the substrate and extremely difficult to abrade without abrading the fibers. The dried images also have little residual odor resulting from solvent because the solvents are held to the surface of the microfibers resulting in faster evaporation of the solvents from the receptor media. PVC films, which absorb large amounts of the ink solvents typically, have residual odors because evaporation of the solvents from the film is very slow. The excellent adhesion of the inks to microfibrillated substrates is believed to occur because the very small microfibers are coated with ink binder/pigment producing a physical interlock of the inks to the substrate; this is very different from the chemical bonding mechanism that occurs when the inks are printed onto a relatively smooth film.
Accordingly, the present invention is directed to a receptor medium including an oriented film having at least one microfibrillated surface with a depth of microfibrillation of greater than 10 microns.
One embodiment of the present invention includes a uniaxially oriented film with a microfibrillated surface containing melt-processed polymer microfibers having an average effective diameter of less than 20 microns and a transverse aspect ratio of 1.5:1 to 20:1.
Another embodiment of the present invention is directed to a receptive medium including a biaxially oriented film containing a mixture of a melt-processed polymer or polymer blend and a void initiating component.
The present invention also includes a method of producing an image which includes the step of printing a jettable material through an inkjet printing head onto the above defined receptor medium.
The present invention further includes an imaged graphics film including the above defined receptor medium having an inkjettable material on a surface of the receptor medium.
Another embodiment of the present invention includes a multiple component receptor medium containing:
(a) a biaxially oriented film having at least one microfibrillated surface;
(b) an adhesive layer on a major surface opposite the microfibrillated surface;
(c) a release liner protecting the adhesive layer; and
(d) an inkjettable material, such as an ink, deposited on the microfibrillated surface.
A particular embodiment of the present invention includes a receptor medium and an imaged graphics film containing the receptor medium where the receptor medium contains a biaxially oriented film having at least one microfibrillated surface, the surface including:
(b) a void initiating component comprising solid particles and/or an immiscible polymer.
“Immiscible” refers to polymer blends with limited mutual solubility and non-zero interfacial tension, i.e. a blend whose free energy of mixing is greater than zero:
ΔG m ≅ΔH m>0
Still another particular embodiment of the present invention includes a multiple component receptor medium containing
(a) a biaxially oriented film having at least one microfibrillated surface, said surface comprising:
(i) polypropylene; and
(ii) a void initiating component comprising inorganic solid particles, copolymers of ethylene selected from the group consisting of acid/acrylate modified ethylene vinyl acetate resin, terpolymer of ethylene/vinyl acetate/carbon monoxide/ethylene, poly(isobutyl)methacrylate and combinations thereof;
(b) an adhesive layer on a major surface opposite the microfibrillated surface;
(c) a release liner protecting the adhesive layer; and
(d) an inkjet ink deposited on the microfibrillated surface.
Advantageously, the present invention allows printing with solvent-based, water-based, oil based, or radiation curable inkjet inks onto receptor media containing microfibers and/or microflakes to provide fine-resolution images with good solid fill.
These microfibrillated materials are comprised of microfibers or microflakes, which are physically unique in their microscopic dimensionality. The microfibers are ribbon like in contrast to standard melt blown microfibers, which are generally cylindrical in shape, and the microflakes are flake-like structures that are physically bound to the polymer film. The microflakes may have a thickness from 1 to 20 micrometers depending on the nature of orientation, preferably from 1 to 10 micrometers and most preferably from 1 to 5 micrometers. The aspect ratio of the surface of a microflake may range from 1:1 to 1:20 depending on how balanced the orientation is. If the orientation is unbalanced (machine direction orientation does not equal transverse direction orientation), the microflakes have an increased dimension in the dominant orientation direction, and when the uniaxial orientation limit is reached, only microfibers are produced from microfibrillation. The use of the microfibrillated polymers also allows for the preparation of materials into fibrous substrates that are not easily made into microfibers of this size by other means, e.g. high molecular weight resins, incompatible blends, highly filled systems, and the like. Due to the surface texture comprising microfibers and microflakes, the present microfibrillated polymeric materials allow for printing on poor inkjet-receptive materials (e.g. low surface energy polyolefins) without surface treatments (i.e. print receptive coatings, corona discharge, etc.), preventing the inks from feathering and beading up as they do on the films that have not been microfibrillated. In addition, this surface texture helps to control dot gain. Dots printed on the present microfibrillated materials show an immediate finite dot gain which does not change significantly with time as is common with most inkjet receptive materials. Thus, microfibrillation improves resolution, by better controlling the bleeding together of print lines.
Because of the presence of microfibers or microflakes in their surface, the present microfibrillated materials provide a number of advantageous properties. For example these materials prevent the inks from running even with high solvent loading and also minimize intercolor ink bleed. Inkjet printed inks feel dry to the touch quickly after printing so that they may be transferred immediately after printing without smudging and may be rolled up without causing surface impressions or blocking of the image. They do not retain solvent for long periods of time as PVC based films do. Thus, they do not tend to emanate an undesirable solvent odor when unrolled and displayed. Microfibrillated materials can also provide a moderate degree of waterfastness to water-based inks. The microfibrillated surfaces may be embossed after printing to provide other properties, including special optical effects.
The degree of surface microfibrillation of an oriented polymer may be selected, controlled, and used as a way to affect printing quality. Thus, a printed sheet can be generated from a single precursor film (no lamination or coating or binders required) when only partial microfibrillation is employed. The receptor medium has a microfibrous or microflake surface that has a high surface area but the film itself may not be permeable or have low permeability to solvents in the ink. Therefore, the receptor medium of the present invention may comprise both a receptor layer (the microfibrillated surface) and a solvent barrier layer (the unmicrofibrillated base film) preventing the solvent in the inkjet inks from adversely affecting any adhesives located on the unmicrofibrillated side. This also eliminates curling problems, which occur when the coatings dry due to swelling and de-swelling of solvent sensitive materials. Because significant amounts of the ink solvents are not absorbed into the material comprising the microfibers or microflakes and do not penetrate into the base film, there is no need for a carrier liner as is required for printing on thin (4 mil) PVC-based graphics films which tend to absorb solvent and curl up.
Through this microfibrillated film making process it is possible to incorporate one or more additives that may improve printing quality directly into the melt instead of having to solvent coat the additive(s) onto the surface. This eliminates the need for an extra coating step and the use of solvents which may be environmentally unfriendly. These print quality improvement additives tend to improve the color density of inkjet ink on both the microfibrillated material and the unfibrillated material, but they do not substantially enhance the image resolution on the precursor (unfibrillated) film, which still suffers from ink bleeding and mottling.
When microfibrillated materials are prepared from low surface energy polymers (e.g., polyolefins), color density tends to be low. This low color density does not appear to be due to the lack of ink absorption into the microfibrillated materials, but rather due to insufficient ink spreading on the surfaces of the microfibrillated material. To improve color density, blends of one or more polymers with print quality improvement additives selected from the group consisting of polymers, surfactants, and mordants may be used. These polymers and surfactants are selected for their ability to increase surface energy of the microfibrillated material or for their affinity for the binders in the ink to promote spreading of the ink on the surface. The mordants are selected for their ability to shorten drying time by complexing with the colorant in the ink making make the inkjet printed image smudge-free and/or water fast.
The present invention provides a receptor medium which includes an oriented film having at least one microfibrillated surface with a depth of microfibrillation of greater than 10 microns. The films may be uniaxially oriented to produce a fibrous surface having polymeric microfibers of average effective diameter of less than 20 microns, generally from 0.01 to 10 microns, and a substantially rectangular cross-section, having a transverse aspect ratio (width to thickness) of from 1.5:1 to 20:1. Such microfiber uniaxially oriented films and methods of making them, including microfibrillation, are described in U.S. Pat. No. 6,110,588, which patent is incorporated herein by reference. Alternatively, the films may be biaxially oriented to produce a microfibrous surface of microflakes that are thin in cross-section, in comparison to the width and lengths, and irregular in shape. Such microflake biaxially oriented films and methods of making them, including microfibrillation, are described in U.S. Pat. No. 6,331,433, which patent is incorporated herein by reference. The microflakes are flake-like structures that are physically bound to the polymer film. The microflakes may have a thickness from 1 to 20 micrometers depending on the nature of orientation, preferably from 1 to 10 micrometers and most preferably from 1 to 5 micrometers. The aspect ratio of the surface of a microflake may range from 1:1 to 1:20 depending on how balanced the orientation is. If the orientation is unbalanced (machine direction orientation does not equal transverse direction orientation), the microflakes have an increased dimension in the dominant orientation direction, and when the uniaxial orientation limit is reached, only microfibers are produced from microfibrillation. Both the microfibers and the microflakes impart a large surface area to the film, which in combination with a high density of microfibers or microflakes, can minimize ink wicking or bleeding and provide high resolution in inkjet images.
Polymers useful in undergoing the microfibrillation process are single polymers or blends. A first polymer component or single polymer component includes any melt-processible crystalline, semi-crystalline or crystallizable polymer or copolymer, including block, grafted, and random copolymers. Semi-crystalline polymers consist of a mixture of amorphous regions and crystalline regions. The crystalline regions are more ordered, and segments of the chains actually pack in crystalline lattices. Some crystalline regions may be more ordered than others. If crystalline regions are heated above the melting temperature of the polymer, the molecules become less ordered or more random. If cooled rapidly, this less ordered feature is “frozen” in place and the resulting polymer is said to be amorphous. If cooled slowly, these molecules can repack to form crystalline regions and the polymer is said to be semicrystalline. Some polymers remain amorphous and show no tendency to crystallize. Some polymers can be made semicrystalline by heat treatments, stretching or orienting and by solvent inducement, and these processes can control the degree of true crystallinity.
Semicrystalline polymers useful in the present invention include, but are not limited to, polyethylene, polypropylene, copolymers of polypropylene and polyethylene, poly(alpha)olefins, polyoxymethylene, poly(vinylidine fluoride), poly(methyl pentene), poly(ethylene-chlorotrifluoroethylene), poly(vinyl fluoride), poly(vinyl alcohol), poly(ethylene oxide), poly(ethylene terephthalate)(PET), poly(butylene terephthalate)(PBT), polylactide, nylon 6, nylon 66, nylon 610, nylon 612, polybutene, syndiotactic polystyrene and thermotropic liquid crystal polymers. Examples of suitable thermotropic liquid crystal polymers include aromatic polyesters, which exhibit liquid crystal properties when melted, and which are synthesized from aromatic diols, aromatic carboxylic acids, hydroxycarboxylic acids, and other like monomers. Typical examples include a first type consisting of parahydroxybenzoic acid (PHB), terephthalic acid, and biphenol; a second type consisting of PHB and 2,6-hydroxynaphthoic acid; and a third type consisting of PHB, terephthalic acid, and ethylene glycol. Preferred polymers are polyolefins such as polypropylene and polyethylene and polyethylene/polypropylene copolymers, that are readily available at low cost and can provide highly desirable properties in the fibrillated articles such as high modulus and high tensile strength.
The semicrystalline polymer component may further comprise, as a blend, a second polymer to impart desired properties to the microfibrillated film of the invention. The second polymer of such blends may be semicrystalline or amorphous and is generally present in less than 40 weight percent, based on the weight of the semicrystalline polymer component. For example, small amounts of polyethylene may be added to polypropylene, when used as the semicrystalline polymer component, to improve the softness and drapability of the microfibrillated film. Other polymers may be added as print quality improvement additives, for example, to enhance print color density. Still other polymers may be added to improve film stiffness, crack resistance, Elmendorff tear strength, elongation, tensile strength and impact strength, as is known in the art. Examples of particularly useful polymer blends include polypropylene with poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), polyvinylpyrrolidone and an ionomer copolymer of ethylene and (meth)acrylic acid, ethylene vinyl acetate, polystyrene/polyisoprene copolymers, acid modified ethylene vinyl acetate, acid/acrylate modified ethylene vinyl acetate, polyether-ester elastomers, terpolymers of ethylene/vinyl acetate/carbon monoxide/ethylene without and with poly(isobutyl methacrylate), and thermoplastic polyurethanes. Other secondary polymers may include, for example, polycarbonates; polymethylpentene; nylons; acrylate and methacrylate homopolymers and copolymers; polystyrenes; vinylchloride/vinyl acetate copolymers; vinyl chloride/vinyl acetate/vinyl alcohol terpolymers; polyethyleneimines; acrylate and maleic anhydride modified ethylene vinyl acetate copolymers; copolymers of ethylene and methyl acrylate; ethylene/octene copolymers; blends of polyvinylpyrrolidone with polyvinylalcohol: copolymers or terpolymer of N-vinyl-2-pyrrolidinone with acrylic acid, dimethylaminoethyl acrylate, trimethoxysilylethylmethacrylate, and/or poly(ethylene oxide) acrylate; poly(cyclic olefins); and rubbers. When a secondary polymer is used as a print quality improvement additive, it may be combined with the microfibrillated film, not only by melt processing, but also by coating the microfibrillated film with a solution or dispersion of the additive.
The void-initiating component is chosen so as to be immiscible in the semicrystalline polymer component. It may be an organic or an inorganic solid particulate component having an average particle size of from about 0.1 to 10.0 microns and may be any shape including amorphous, needle-like, spindle, plate, diamond, cube, and sphere shapes. Inorganic solids useful as void initiating components include solid or hollow glass, ceramic or metal particles, microspheres or beads; zeolite particles; inorganic compounds including, but not limited to metal oxides such as titanium dioxide, alumina and silicon dioxide; metal, alkali- or alkaline earth carbonates or silicates, metasilicates, sulfates; kaolin, talc, carbon black and the like. Typically useful is calcium carbonate or wollastonite, i.e. calcium metasilicate. Inorganic void initiating components are chosen so as to have little surface interaction, due to either chemical nature or physical shapes, when dispersed in the semicrystalline polymer component. In general the inorganic void initiating components should not be chemically reactive with the semicrystalline polymer component, including Lewis acid/base interactions, and have minimal van der Waals interactions.
The void initiating component may be a thermoplastic polymer, including semicrystalline polymers and amorphous polymers, to provide a blend immiscible with the semicrystalline polymer component. An immiscible blend shows multiple amorphous phases as determined, for example, by the presence of multiple amorphous glass transition temperatures. As used herein, “immiscibility” refers to polymer blends with limited solubility and non-zero interfacial tension, i.e. a blend whose free energy of mixing is greater than zero:
ΔG m ≅H m>0
Miscibility of polymers is determined by both thermodynamic and kinetic considerations. Common miscibility predictors for non-polar polymers are differences in solubility parameters or Flory-Huggins interaction parameters. For polymers with non-specific interactions, such a polyolefins, the Flory-Huggins interaction parameter can be calculated by multiplying the square of the solubility parameter difference with the factor (V/RT), where V is the molar volume of the amorphous phase of the repeated unit, R is the gas constant, and T is the absolute temperature. As a result, the Flory-Huggins interaction parameter between two non-polar polymers is always a positive number indicating that the two polymers do not mix spontaneousely and the blend is considered “immiscible”.
Polymers useful as the void-initiating component include the above described semicrystalline polymers, as well as amorphous polymers, selected so as to form discrete phases upon cooling from the melt. Useful void-initiating polymers include, but are not limited to, polyesters, vinyl resins, copolymers of ethylene, polystyrene resins and copolymers thereof, polycarbonates, polyisobutylene, acrylates and methacrylate homopolymers and copolymers thereof, cyclic polyolefins, maleated polypropylene block copolymers, rubbers, sulfonated poly(ethylene terephthalate), polyvinylpyrrolidone and vinylpyrrolidinone copolymers, epoxies, thermoplastic polyurethanes, and combinations thereof. Examples of polystyrene copolymers include poly(styrene-co-acrylonitrile), poly(styrene-co-maleic anhydride), and poly(acrylonitrile-butadiene-styrene). Examples of useful acrylates and methacrylates include polymers of butyl acrylate, ethyl acrylate, isopropyl acrylate, methylacrylate, benzyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, ethyl methacrylate, hexyl methacrylate, isobutyl methacrylate, isopropyl methacrylate, methyl methacrylate, phenyl methacrylate and propyl methacrylate. Examples of useful methacrylate copolymers include copolymers of methyl methacrylate with butyl methacrylate, ethyl methacrylate, isobutyl methacrylate, isobornyl methacrylate, and lauryl methacrylate, and butyl methacrylate with isobutyl methacrylate. Examples of cyclic polyolefins include polynorbornene and copolymers thereof. Examples of vinyl resins include poly(vinyl chloride), poly(vinyl acetate), and poly(vinyl alcohol). Examples of ethylene copolymers include acid modified ethylene vinyl acetate, metal ion neutralized copolymers of ethylene and methacrylic or acrylic acid, maleic anhydride grafted polyethylene, acid modified ethylene/acrylate/carbon monoxide terpolymers, ethylene/n-butyl acrylate/carbon monoxide terpolymer, ethylene/glycidyl methacrylate/carbon monoxide terpolymer, ethylene acrylic elastomers, ethylene/vinyl acetate/carbon monoxide terpolymer, and copolymers of ethylene and butyl-, ethyl-, and methyl acrylate. Typically useful are poly(ethylene terephthalate) or poly(butylene terephthalate), copolymers of methyl methacrylate with butyl acrylate, butyl methacrylate, isobutyl methacrylate or isobornyl methacrylate, copolymers of isobutylmethacrylate and butyl methacrylate; butyl methacrylate resins, or copolymers of ethylene, such as acid/acrylate modified ethylene vinyl acetate resin, terpolymer of ethylene/vinyl acetate/carbon monoxide/ethylene, and combinations thereof. Preferred void initiating components include a mixture of an inorganic solid particulate component and a polymer component as defined above.
When using an immiscible polymer blend, the relative amounts of the semicrystalline polymer component and void initiating polymer component can be chosen so the first polymer forms a continuous phase and the second polymer forms a discontinuous phase, or that the second polymer forms a continuous phase and the first polymer forms a discontinuous phase, or each polymer forms a continuous phase; as in an interpenetrating polymer network. The relative amounts of each polymer can vary widely, from 99:1 to 1:99 weight ratio. Preferably, the semicrystalline polymer component forms the continuous phase while the void initiating component forms a discontinuous, or discrete phase, dispersed within the continuous phase of the first polymer. In such constructions, the amount of void initiating component will affect final film properties. In general, as the amount of the void initiating component increases, the amount of voiding in the final film also increases. As a result, properties that are affected by the amount of voiding in the film, such as mechanical properties, density, light transmission, etc., will depend upon the amount of added void initiating component. When the void initiating component is a polymer, as the amount of void initiating polymer in the blend is increased, a composition range will be reached at which the void initiating polymer can no longer be easily identified as the dispersed, or discrete, phase. Further increase in the amount of void initiating polymer in the blend will result in a phase inversion wherein the void initiating polymer becomes the continuous phase.
Preferably, whether the void initiating component is organic, inorganic or both, the amount of the void initiating component in the composition is from 1% by weight to 65% by weight, more preferably from 20% by weight to 50% by weight, most preferably from 30% by weight to 45% by weight. In these composition ranges, the first semicrystalline polymer forms a continuous phase, while the void initiating component forms the discrete, discontinuous phase.
Additionally, the selected void initiating component must be immiscible with the semicrystalline polymer component selected. In this context, immiscibility means that the discrete phase does not dissolve into the continuous phase in a substantial fashion, i.e., the discrete phase must form separate, identifiable domains within the matrix provided by the continuous phase.
The molecular weight of each polymer should be chosen so that the polymer is melt processible under the processing conditions. For polypropylene and polyethylene, for example, the molecular weight may be from about 5000 to 500,000 and is preferably from about 100,000 to 300,000.
In order to obtain the maximum physical properties and render the polymer film amenable to microfibrillation, the polymer chains need to be oriented along at least one major axis (uniaxial) in one or more stages, and may further be oriented along two major axes (biaxial) either simultaneously or sequentially. The degree of molecular orientation is generally defined by the draw ratio, that is, the ratio of the final length or width to the original length or width, respectively. This orientation may be effected by a combination of techniques in the present invention, including the steps of calendering, length orienting, and tentering.
Processes for uniaxially orienting a film and microfibrillating the film are described in U.S. Pat. No. 6,110,588, which patent is incorporated herein by reference. Processes for biaxially orienting films and microfibrillating the films to prepare microfibers and microfibrous flakes (microflakes) are described in U.S. Pat. No. 6,331,433, which patent is also incorporated herein by reference.
Generally, greater void initiating content enhances the subsequent microfibrillation, and subsequently for uniaxially oriented films, the greater the yield of microfibers and for biaxially oriented films, the greater the yield of microflakes. Preferably, when preparing an article having at least one microfibrillated surface, the polymer film should have a void content in excess of 5%, more preferably in excess of 10%, most preferably in excess of 30%, as measured by density, i.e., the ratio of the density of the voided film with that of the starting film. The degree of voiding or void content in the oriented films is strongly dependent on the temperature and degree of orientation achieved during processing. To achieve higher void contents, it is preferred to keep the temperature just high enough to allow flow of the polymer(s) and to orient the film to the greatest extent possible without breaking the film.
In practice, the films first may be subjected to one or more processing steps to impart the desired degree of crystallinity to the semicrystalline polymer component, and further processed to impart the voids, or the voids may be imparted coincident with the process step(s), which impart crystallinity. Thus the same calendering or stretching steps that orient the polymer film and enhance the crystallinity (and orientation) of the polymer may concurrently impart voids.
In the present process the degree of microfibrillation can be controlled to provide a low degree to a high degree of microfibrillation, whether from a uni- or biaxially oriented film. In either microfibrillation process most of the microfibers or microflakes stay attached to the web due to incomplete release from the polymer matrix. Advantageously the microfibrillated article, having microfibers or microflakes secured to a web, provides a convenient and safe means of handling, storing and transporting the microfibrillated article without contamination due to nonbonded microfibers or microflakes. For many printing applications it is desirable to retain the microfibers or microflakes secured to the web.
The receptor medium of the present invention may also have an adhesive layer on the major surface of the sheet opposite the microfibrillated surface that is also optionally but preferably protected by a release liner. After imaging, the receptor medium can be adhered to a horizontal or vertical, interior or exterior surface to warn, educate, entertain, advertise, etc.
The choice of adhesive and release liner depends on usage desired for the image graphic.
Pressure-sensitive adhesives can be any conventional pressure-sensitive adhesive that adheres to both the polymer sheet and to the surface of the item upon which the inkjet receptor medium having the permanent, precise image is destined to be placed. Pressure-sensitive adhesives are generally described in Satas, Ed., Handbook of Pressure Sensitive Adhesives, 2nd Ed. (Von Nostrand Reinhold 1989). Pressure-sensitive adhesives are commercially available from a number of sources. Particularly preferred are acrylate pressure-sensitive adhesives commercially available from Minnesota Mining and Manufacturing Company and generally described in U.S. Pat. Nos. 5,141,790; 4,605,592; 5,045,386; and 5,229,207; and EPO Patent Publication No. EP 0 570 515 B1 (Steelman et al.).
Release liners are also well known and commercially available from a number of sources. Nonlimiting examples of release liners include silicone coated craft paper, silicone coated polyethylene coated paper, silicone coated or non-coated polymeric materials such as polyethylene or polypropylene, as well as the aforementioned base materials coated with polymeric release agents such as silicone urea, urethanes, and long chain alkyl acrylates, such as defined in U.S. Pat. Nos. 5,957,724; 4,567,073; 4,313,988; 3,997,702; 4,614,667; 5,202,190; and 5,290,615; and those liners commercially available as Polysilk brand liners from Rexam Release of Oakbrook, Ill., and EXHERE brand liners from P. H. Glatfelter Company of Spring Grove, Pa.
The receptor media of the present invention have utility for the production of image graphics using inkjet printers. The present receptor media unexpectedly solve common inkjet image quality problems as feathering, banding and mud cracking (mud cracking where pigmented, binderless water based inks are used) in inkjet printing systems and also provide an adsorptive surface for the inks to prevent running and help bind the inks to the substrate. Because of the high surface area of the microfibrillated structures, the solvents of the ink are able to evaporate quickly, are not absorbed into the bulk of the fibers, and there is no residual odor from retained solvents during use as is common with current PVC-based products. Another advantage of the receptor media of the present invention is the usefulness of the microfibrillated surface with organic solvent-based, oil-based, water-based, or radiation polymerizable inks. The inks used on the receptor medium can further include either dye- or pigment-based colorants.
Inkjet receptor media of the present invention can be employed in any environment where inkjet images are desired to be precise, stable, rapid drying, handled immediately after printing, and abrasion resistant.
Inkjet receptor media of the present invention can accept a variety of inkjet ink formulations to produce rapid drying and precise inkjet images. The topography of the microfibrillated surface of the inkjet receptor medium can be varied for optimum results, depending on several factors, such as: ink droplet volume; ink liquid carrier composition; ink type (pigment or blend of pigment and aqueous or non-aqueous dye); and manufacturing technique (machine speed, resolution, roller configuration); etc.
The formation of precise inkjet images is provided by a variety of commercially available printers. Nonlimiting examples include thermal inkjet printers such as Deskjet brand, Paintjet brand, Deskwriter brand, DesignJet brand, and other printers commercially available from Hewlett-Packard Corporation of Palo Alto, Calif. Also included are piezo type inkjet printers such as those from Seiko-Epson, Raster Graphics, VUTEk, Scitex, Idanit, and Xerox, spray jet printers and continuous inkjet printers. Any of these commercially available printers introduces the ink in a jet spray of a specific image into the medium of the present invention. Apparent drying time is much more rapid under the present invention than if the imaging layer were to be applied to a similar non-microfibrillated media.
The media of the present invention can be used with a variety of inkjet inks obtainable from a variety of commercial sources. It should be understood that each of these inks has a different formulation, even for different colors within the same ink family. Nonlimiting sources include Minnesota Mining and Manufacturing Company, Encad Corporation, Hewlett-Packard Corporation, DuPont, Inkware, Prizm, NuKote, and the like. These inks are preferably designed to work with the inkjet printers described immediately above and in the background section above, although the specifications of the printers and the inks will have to be reviewed for appropriate drop volumes and resolution in order to further refine the usefulness of the present invention.
Media of the present invention can also be employed with other jettable materials; that is, those materials capable of passing through an inkjet printing head. Nonlimiting examples of jettable materials include adhesives, particulate dispersions, waxes, electrically, thermally, or magnetically modifiable materials, biological fluids, chemical reagents, and combinations thereof.
The media of the present invention may contain, as desired, other print quality improvement additive materials, including mordants and surfactants, to improve printing or other additives to protect the media. These materials may be blended with the above defined polymers and processed to form microfibrillated materials as described above, or coated as a solution or dispersion onto the microfibrillated materials.
Thus, for example, an inkjet receptor medium of the present invention may contain mordants which can act as drying agents for dye-containing inks and pigment management agents for pigmented inks. Drying agents include an aromatic or aliphatic acid having sulfonic, carboxylic, phenolic, hydroxyl functional groups or a mixture of these functional groups. The drying agent, when combined with a multivalent inorganic salt and a surfactant, is capable of drying the medium to obtain a smudge-free rapidly dried image onto and in the medium when the image is printed.
Typical salts are alkali metal salts of aromatic acids such as, for example, sulfosalicylic acid, disulfosalicylic acid, sulfophthalic acid, sulfoisophthalic acid, sulfoterephthalic acid, disulfophenyldicarboxylic acid, sulfophenolic acid, hydroquinone sulfonic acid, hydroquinone disulfonic acid, sulfocarboxyphenolic acid, hydroxy-phthalic acid and combinations thereof.
Pigment management agents may also include multivalent metal salts which destabilize dispersants surrounding pigment particles and are not soluble in water after complexing with the dispersing aid that surrounds the pigment particles to provide a water fast image. Typical multivalent cations employed are those of Group IIA of the periodic table with counter ions such as sulfate, nitrate, bisulfate, chloride, aromatic carboxylates, and sulfocarboxylates. Particularly useful are aluminum sulfate and aluminum sulfophthalate.
A further additive for the receptor medium of the present invention is an organometallic salt of a multivalent metal cation and an organic acid anion. The metallic salt simultaneously releases the multivalent metal cation and the organic acid anion for both pigment management and ink drying. The metallic salt includes a multivalent metal derivative of an aromatic carboxylic, sulfocarboxylic, sulfophenolic acid, or combination thereof. The aromatic moiety can be a simple aromatic, a condensed aromatic, a heterocyclic aromatic or a combination thereof. The multivalent metal ion can be derived from Group IIA to VIA and Group IB to VIIIB of the periodic table. Typical metal ions include, but are not limited to, Al, Mg, Zn, Fe, Bi, Ga, Sr, Ca, Ti and Zr.
Surfactants can also be used as a print quality improvement additive, alone or in combination with one or more polymer or mordant additives. For example, the above salts may be combined as mentioned above with a surfactant. Surfactants may also, for example, be used to improve inkjet ink wetting on the microfibrillated material, and include non-ionic, anionic, cationic, zwitterionic or combinations thereof. Non-ionic surfactants may be fluorocarbon, hydrocarbon, or silicone based. Preferred surfactants increase the hydrophilicity of the microfibrillated materials and are particularly useful when water-based inkjet inks are employed. Examples of useful surfactants are described in U.S. Ser. No. 09/314,034, filed on May 18, 1999, and entitled “Ink-Jet Printable Macroporous Material”.
In addition to the above, the receptor medium of the present invention may also contain free-radical scavengers, heat stabilizers, ultraviolet light stabilizers and inorganic fillers.
Free-radical scavengers can be present in an amount from about 0.05 to about 1.0 weight percent of the total microfibrillated material composition. Typically, scavengers include hindered amine light stabilizers (HALS), hydroxylamines, sterically hindered phenols, and the like. HALS compounds are commercially available from Ciba Specialty Chemicals under the trade designation “Tinuvin 292” and Cytec Industries under the trade designation “Cyasorb UV3581”.
Heat stabilizers may be used to protect the resulting image graphic against the effects of heat. These are commercially available from Witco Corp., Greenwich, Conn. under the trade designation “Mark V 1923” and Ferro Corp., Polymer Additives Div., Walton Hills, Ohio under the trade designation “Synpron 1163”, “Ferro 1237” and “Ferro 1720”.
Ultraviolet light stabilizers may be present in small amounts ranging from about 0.1 to about 5 weight percent of the total microfibrillated material. Benzophenone type UV-absorbers are commercially available from BASF Corp., Parsippany, N.J. under the trade designation “Uvinol 400”; Cytec Industries, West Patterson, N.J. under the trade designation “Cyasorb UV1164” and Ciba Specialty Chemicals, Tarrytown, N.Y. under the trade designations “Tinuvin 900”, “Tinuvin 123” and “Tinuvin 1130”.
Inorganic fillers may be used in the microfibrillated material as a preferred additive to impart one or more of desirable properties such as improved solvent absorption, improved dot gain and color density, and improved abrasion resistance. Typical fillers include silicates, e.g. amorphous silica, clay particles, aluminates, e.g. aluminum silicate, feldspar, talc, calcium carbonate, titanium dioxide, and the like. The particle size of these fillers is preferably less than one micron and may typically range from 0.5 to 0.2 microns.
The following examples further disclose embodiments of the invention: