US20200199823A1 - Glass Interleaver Paper Produced With Coarse Fibers - Google Patents

Glass Interleaver Paper Produced With Coarse Fibers Download PDF

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US20200199823A1
US20200199823A1 US16/622,167 US201816622167A US2020199823A1 US 20200199823 A1 US20200199823 A1 US 20200199823A1 US 201816622167 A US201816622167 A US 201816622167A US 2020199823 A1 US2020199823 A1 US 2020199823A1
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paper
sheet
fibers
glass
fiber
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US16/622,167
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Zachary L. Leimkuehler
Christopher L. Williams
Christopher R. Jansen
Joel J. Neuville
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Expera Speciality Solutions, LLC
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Priority to US16/622,167 priority Critical patent/US20200199823A1/en
Publication of US20200199823A1 publication Critical patent/US20200199823A1/en
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    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
    • D21H27/08—Filter paper
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H5/00—Special paper or cardboard not otherwise provided for
    • D21H5/12—Special paper or cardboard not otherwise provided for characterised by the use of special fibrous materials
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F11/00—Processes for making continuous lengths of paper, or of cardboard, or of wet web for fibre board production, on paper-making machines
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21F—PAPER-MAKING MACHINES; METHODS OF PRODUCING PAPER THEREON
    • D21F9/00—Complete machines for making continuous webs of paper
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
    • D21H13/10—Organic non-cellulose fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H15/00—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution
    • D21H15/02—Pulp or paper, comprising fibres or web-forming material characterised by features other than their chemical constitution characterised by configuration
    • D21H15/10—Composite fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
    • D21H17/20—Macromolecular organic compounds
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
    • D21H21/50—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by form
    • D21H21/52—Additives of definite length or shape
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H5/00—Special paper or cardboard not otherwise provided for
    • D21H5/26—Special paper or cardboard manufactured by dry method; Apparatus or processes for forming webs by dry method from mainly short-fibre or particle material, e.g. paper pulp
    • D21H5/2607—Pretreatment and individualisation of the fibres, formation of the mixture fibres-gas and laying the fibres on a forming surface
    • D21H5/2628—Formation of a product from several constituents, e.g. blends of various types of fibres, fillers and/or binders or formation from various sources and/or streams or fibres
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
    • D21H5/00—Special paper or cardboard not otherwise provided for
    • D21H5/26—Special paper or cardboard manufactured by dry method; Apparatus or processes for forming webs by dry method from mainly short-fibre or particle material, e.g. paper pulp
    • D21H5/265—Treatment of the formed web
    • D21H5/2657—Consolidation
    • D21H5/2664—Addition of a binder, e.g. synthetic resins or water

Definitions

  • This disclosure relates to interleaver sheets for the separating sheets of glass in order to protect the glass from breakage and surface damage.
  • Glass sheet products are commonly packaged in packs or stacks with an interleaving sheet separating the sheets of glass.
  • the purpose of the interleaver sheet is to protect the glass from breakage, surface damage such as scratches or stain spots, and to allow for ease of handling and separation of the glass during unpacking.
  • the interleaver ideally protects the glass from developing even tiny surface defects caused by contaminants in the interleaver or from contaminants created during the glass making, packing, transporting, and use processes.
  • Such interleaver paper should be free of contaminants such as hard particles, which can cause a scratch or abrasion spot in the glass surface, free of contaminants that will transfer to the glass and are not easily removed, and cause loose particles or a “stain” on the glass.
  • the protection of the glass for the display has become increasingly difficult because as the resolution of such displays increases (e.g., from 720 to 1080 to 4K to beyond in future generations of displays), the size constituting a defect in the glass decreases in proportion to the resolution. Therefore, as the quality demands on glass continue to increase, especially on LCD/OLED glass, higher performing interleaver paper is required.
  • interleaver papers Conventionally, to inhibit the presence or impact of contaminants, interleaver papers have been designed with northern softwood ‘soft’ fibers to have low bulk, to have very fine smooth surface texture, and to minimize particle generation and migratable materials.
  • interleaver paper This disclosure presents a different and counter-intuitive approach to production and composition of interleaver paper which has been found to have improved protection performance over the conventional paradigm that interleaver paper should have exceptionally smooth contact surfaces.
  • the interleaver paper disclosed herein employs coarse, long fibers with optimized refining to produce a sheet with uniform thickness, with reduced density, and with a higher roughness surface suitable as a high performance glass interleaver.
  • the pulp containing coarse fibers can be refined to provide a high percentage of short length fiber fractions. Production of paper with these fibers has resulted in a uniform thickness sheet with even higher bulk, higher but more uniform surface micro-roughness, high surface strength, and good physical properties that have been discovered to be well-suited for a high performing glass interleaver.
  • the newly-disclosed interleaver paper is especially suitable for LCD glass protection during shipping and use because it is posited that, among other things, the greater bulkiness cushions the glass layers and minimizes scratching, the roughness (smoothness) minimizes scratching, and the internal bonds prevent fiber transfer and particle generation. Based on the current state of the art, it is counter-intuitive to prevent scratching by making the sheet with coarse fibers and high micro roughness. In practice, it has been found that the uniform (but comparably higher) surface micro-roughness provides a multitude of support peaks separated by valleys. Thus, when contacting the glass, the micro-roughness is akin to laying on a bed of one thousand nails rather than on a surface with only two or three contact points.
  • a paper that is used as a slip sheet interleaver for the protection of glass surfaces.
  • the paper comprises a sheet with a basis weight of 15-60 lb/3,000 ft 2 , having a bulk density less than 0.75 g/cm 3 , and an average fiber coarseness greater than 0.18 mg/m.
  • the sheet may comprise at least 20%, 80%, or 100% coarse fibers, for example.
  • the coarse fibers may comprise a set of fibers selected from a group consisting of southern softwood kraft, southern hardwood kraft, mercerized fibers, Coastal Douglas Fir, Radiata Pine, and synthetic polymeric fibers. Still further in some specific forms, the sheet may comprise southern softwood and comprise 20, 80, or 100% fluff pulp.
  • the sheet may comprise at least 10% coarse fibers and those coarse fibers may include one or more of southern softwood kraft, southern hardwood kraft, mercerized fibers, Coastal Douglas Fir, Radiata Pine, Fluff Pulp, and synthetic polymeric fibers.
  • the sheet may comprise at least 80% coarse fibers and those coarse fibers may include one or more of southern softwood kraft, southern hardwood kraft, mercerized fibers, Coastal Douglas Fir, Radiata Pine, Fluff Pulp, and synthetic polymeric fibers.
  • the sheet may have a basis weight of 25-40 lb/3000 ft 2 , a bulk density less than 0.65 g/cm 3 , and an average fiber coarseness greater than 0.20 mg/m.
  • the sheet may have a Scott Bond strength greater than 200 g, 250 g, or 300 g.
  • the sheet may have a Parker smoothness greater than 7.5 ⁇ m on both sides or a Parker smoothness greater than 8.5 ⁇ m on both sides.
  • the sheet may have a surface roughness (Sa) greater than 4.5 ⁇ m on both sides or a surface roughness (Sa) greater than 5.0 ⁇ m on both sides.
  • the sheet may have a void volume greater than 1.30 g/g or 1.40 g/g.
  • the sheet may have an average fiber length (LWFLA) less than 1.9 mm or an average fiber length (LWFLA) less than 2.1 mm.
  • LWFLA average fiber length
  • LWFLA average fiber length
  • the sheet may have a short fiber and fines content greater than 10% (in which the short fibers and fines are less than 0.5 mm).
  • the sheet may also have a long fiber content greater than 5% (in which the long fibers are greater than 3.5 mm).
  • the sheet may have a short fiber and fines content greater than 10% (in which the short fibers and fines are less than 0.5 mm) and simultaneously have a long fiber content greater than 5% (in which the long fibers are greater than 3.5 mm).
  • the sheet may have a content of medium length fibers between 0.9 mm and 2.7 mm of less than 55%.
  • the sheet may have a short fiber and fines content greater than 15% (in which the short fibers and fines are less than 0.5 mm).
  • the sheet may have less than 0.5 parts per million (ppm) poly dimethyl siloxane fluid (PDMS) content.
  • ppm parts per million
  • the sheet has less than 0.35% ash content.
  • the paper may comprise a binding agent.
  • the binding agent may be selected from the group of adhesives including acrylic latex, styrene butadiene copolymer, butadiene acrylonitrile copolymer, polyurethane, polyvinyl acetate, polyvinyl alcohol, natural rubber or other nature-based adhesive, polyvinyl chloride, polychloroprene, epoxy, phenol, urea-formaldehyde, and thermal melt adhesive.
  • the binding agent may be fiber including at least one polymer selected from the group of polymers consisting of polyolefin, polyester, polyamide, polylactide, polycaprolactone, polycarbonate, polyurethane, polyvinyl acetate, polyvinyl chloride, polyvinyl alcohol, polyacrylate or polyacrylonitrile, and ionomer.
  • a method of making the paper described above includes the use of refining equipment, refining energy level, and fiber types to produce the paper comprising fibers having a wide fiber length distribution in which the sum of short fibers and fines and long fibers is greater than 20% of the fiber mix in which the short fibers and fines are less than 0.5 mm and in which the long fibers are greater than 3.5 mm.
  • a method of making the paper described above includes the step of using of a paper machine forming section to make the paper, in which the forming section includes at least one of a Fourdrinier, Inclined Wire Former, Cylinder Former, Twin Wire Former, Gap Former, Top Former, Multi-layer Former, and Tanmo.
  • a method of separating sheets of glass using the paper described above comprising the step of separating two sheets of glass by positioning the paper therebetween.
  • FIG. 1 illustrates the paper surface roughness profile of paper made from Northern bleached softwood kraft pulp (NBSK).
  • NBSK Northern bleached softwood kraft pulp
  • FIG. 2 illustrates the paper surface roughness profile of paper made from Coarse Pulp.
  • the basis weight is a measure of the weight of a paper per area. Typical units are pounds per 3000 ft 2 or grams per square meter (gsm).
  • Sheets with low density are said to have high bulk.
  • Calendering is a process of exposing a sheet of paper to pressure and heat in order to further densify, smooth, and consolidate the sheet.
  • Caliper is thickness of a paper. Typical units are mils (thousandths of an inch) or microns.
  • a defoamer is a chemical used in the pulping process to reduce/minimize foam. Most commonly these contain poly dimethylsiloxane (PDMS) oil as the base for the defoaming capability.
  • PDMS poly dimethylsiloxane
  • Density is a measure of the mass per unit volume of a paper. Density can be calculated by dividing the basis weight by the thickness of a paper. Typical units of density are grams per cubic centimeter.
  • the felt side is the surface of paper which is opposite the side facing the forming fabric during the drainage process (with the opposite side being referred to as the wire side).
  • Fiber coarseness is the measure of the mass of fibers expressed in units of mass per length (mg/m). Fiber coarseness is dependent upon fiber wall thickness.
  • Fiber length (arithmetic mean) is the sum of all the fiber lengths divided by the number of fibers. Arithmetic mean fiber length is typically expressed in millimeters.
  • Fiber length is a fiber length calculation which reduces the significance of shorter fibers in the distribution—which is typically not uniform. Length weighted average fiber length is typically expressed in millimeters.
  • Fiber wall thickness is the thickness, typically measured in microns, of the outer wall of a wood fiber.
  • Fines are fibers or portions of fibers less than 0.2 mm in length.
  • Fluff pulp is long, coarse fibers, typically softwood kraft, more specifically, slash pine. Fluff pulp is commonly used in absorbent products and airlaid application.
  • Glassine is a highly densified sheet of paper which is typically produced using high levels of fiber refining and supercalendering.
  • Lumen diameter is the width of the round center hollow portion of a wood fiber.
  • Mercerized pulp is a wood pulp which has been treated with a strong alkali such as caustic soda, which results in a fiber with a high degree of kinks or bending. Mercerized pulp is typically used in high bulk, highly breathable applications such as filtration papers.
  • Micro-roughness is a measure of the sheet surface roughness. Micro-roughness may be measured using Vertical Scanning Interferometer (VSI) technique.
  • VSI Vertical Scanning Interferometer
  • MorFi fiber analyzer is an instrument which determines fiber properties of a mix of fibers by using optical methods as described by standard test method ISO 16065-2.
  • NBSK Northern bleached softwood kraft pulp
  • Parker smoothness is a measure of surface smoothness and is also known as Parker Print Surf (PPS), standard Tappi method T555. Units of Parker smoothness are in microns with higher values indicating less smooth surfaces.
  • Percent ash is amount of ash remaining after paper is placed in oven higher than 525 degrees C. according to standard method Tappi T211.
  • Refining is a process of applying energy to develop wood pulp fibers for papermaking. Effects of refining include cutting of fibers, bruising of fibers, collapsing of fibers, creating fines, and creating fibrils.
  • Refining energy is a measure of the amount of energy applied during the refining process to a stream of wood pulp, typically expressed at units of horsepower-days per ton. Most papers are produced using a refining energy of up to 10 hp-day/ton.
  • SBHK Southern bleached hardwood kraft pulp
  • SBSK Southern bleached softwood kraft pulp
  • Scott Bond strength is paper sheet strength measured in the direction of the thickness (z direction) of the sheet.
  • the method of measurement involves placing two-sided tape on the surfaces of the sheet and measuring the force required to split the sheet.
  • the method of testing is also known as Internal Bond and is standard method Tappi T569.
  • Silicone refers to synthetic polymers whose structure is based on repeating units of siloxane, which is a chain of alternating silicon and oxygen atoms, such as poly dimethyl siloxane fluids. Silicone backbone polymers may also be polymerized with, have side chains or other functional groups added for specific chemical or performance in use properties.
  • Supercalendering is an extreme method of calendaring utilizing high heat and pressure and a number of nips. Supercalendering is typically used in the manufacture of pressure sensitive release liners and glassines.
  • Sa Surface roughness
  • Void volume is a measure of the volume of empty space within a paper sample, as measured by saturation with a standard wetting agent. This test method is described in detail in U.S. Pat. No. 7,794,566, which is incorporated herein by reference. In pertinent part, U.S. Pat. No. 7,794,556 explains that void volume is determined by saturating a sheet with a nonpolar liquid and measuring the volume of liquid absorbed. The volume of liquid absorbed is equivalent to the void volume within the sheet structure. The void volume is expressed as grams of liquid absorbed per gram of fiber in the sheet.
  • each single-ply sheet sample to be tested eight sheets are selected and 1 inch by 1 inch squares are cut out (1 inch in the machine direction and 1 inch in the cross-machine direction).
  • each ply is measured as a separate entity. Multi-ply samples should be separated into individual single plies and eight sheets from each ply position are used for testing. The dry weight of each test specimen is weighed and recorded to the nearest 0.001 gram. The specimens are placed in a dish containing POROFIL® pore wetting liquid of sufficient depth and quantity to allow the specimen to float freely following absorption of the liquid.
  • POROFIL® liquid having a specific gravity of 1.875 grams per cubic centimeter, is available from Quantachrome Instruments, 1900 Corporate Drive, Boynton Beach, Fla. 33426. After 10 seconds, the specimen is grasped at the very edge (1-2 millimeters in) of one corner with tweezers and is removed from the liquid. The specimen is held with that corner uppermost and excess liquid is allowed to drip for 30 seconds. The lower corner of the specimen is lightly dabbed (less than 1 ⁇ 2 second contact) on filter paper in order to remove any excess of the last partial drop. The specimen is immediately weighed within 10 seconds, and the weight is recorded to the nearest 0.001 gram. The void volume for each specimen, expressed as grams of POROFIL® per gram of fiber, is calculated as follows:
  • Void Volume [( W 2 ⁇ W 1 )/ W 1 ]
  • W 1 is the dry weight of the specimen in grams and W 2 is the wet weight of the specimen, in grams.
  • Wire side is the surface of a sheet of paper which is facing the forming fabric (the wire) during the drainage process.
  • Pulps with high coarseness fibers tend to be used in absorbent products and are not typically refined, as this reduces the bulk and thus absorbency properties.
  • PCT Application Publication No. WO 01/57313 explains the difficulty in producing sheets with high levels of fluff pulp due to the lack of bonding with coarse fibers.
  • the best fibers, according to the current state of the art, to produce a bulky, soft sheet such as a bath tissue or toweling are Eucalyptus bleached kraft, or NBSK fibers with low coarseness. See, for example, U.S. Patent Application Publication No. 2106/0244916.
  • JP4313415B1 states that fibers less than 1.0 mm result in poor cushioning effect with any cushioning effect resulting from fiber lumens that are easily collapsed (i.e., thin wall, wide lumen).
  • pulps containing high coarseness fibers were not deemed suitable for production of glass interleaver sheets because of their poor ability to form a uniform sheet and to form a smooth sheet surface to prevent damage of the glass and further because they were not believed to be particularly cushioning.
  • Handsheets were made prior to refining, and after 1500, 2250, and 3000 revolutions. Properties of the handsheets were tested to determine the suitability of each pulp for the manufacture of glass interleaving paper. These properties include Density, Parker Smoothness, Scott Bond, Void Volume, and Surface Roughness. The results of the study are shown in Table 1.
  • Southern Bleached Hardwood Kraft is shown to have good void volume and low density at lower refining levels, but low Scott bond and sheet strength makes the paper prone to fiber transfer to the glass or tearing when removed from the glass respectively.
  • Northern Bleached Softwood Kraft can be used to make paper with good internal bond, but paper from NBSK is more dense, has low void volume, but is too smooth to be a high performing glass interleaver since the surface valleys are too shallow to keep particles from contacting the glass.
  • Southern Bleached Softwood Kraft is the second best performing pulp, but is outperformed by fluff pulp in levels of Density, Parker Smoothness, Surface Roughness, and Void Volume.
  • the trial interleaver papers were produced from pulps including high coarseness fibers including “fluff” pulp and a mercerized pulp.
  • Fluff pulps are typically used in absorbent products such as air-laid nonwovens and other absorbent type pads.
  • Mercerized pulps are typically used in filtration applications due to their extreme bulkiness and ability to create high air or liquid flow through a substrate. These fibers were chosen based on superior cleanliness as well as bulking abilities. It is contemplated that other coarse fibers might also be employed in formulations including southern hardwood kraft (from southeastern United States), Radiata pine (from South America), and Chinese red pine (Southeast Asia and China).
  • coarse fibers such as in fluff pulp, specifically from pine species growing in the southeast United States, including slash, loblolly, longleaf pine, or other coarse fibered softwood species, have not been known to be used in pulp formulations for glass interleaver sheets and the current state of the art suggest that low coarseness fibers are better in such applications for cushioning/scratch prevention because they result in a smoother surface.
  • Table 2 below, various comparative data is provided detailing various paper compositions and trial results.
  • Table 2 the following formulations are compared: (1) a benchmark formulation of a competitive paper A; (2) NBSK [Northern bleached softwood kraft pulp], high refined; (3) NBSK [Northern bleached softwood kraft pulp], moderate refining; (4) NBSK, moderate refining, less uniform; (5) Coarse pulp, moderate refining; (6) Coarse pulp, high refining; (7) Coarse pulp (90%) and mercerized pulp (10%), moderate refining; and (8) Coarse pulp (90%) and mercerized pulp (10%), high refining.
  • condition produced with Coarse Fiber and moderate refining produced a slip sheet for glass interleaver which is a preferred embodiment of the invention with a superior combination of Density, Parker Smoothness, Surface Roughness, Void Volume, and Scott Bond versus currently useful approaches.
  • Fiber coarseness is a result of the thickness of the fiber wall and the overall fiber diameter. Fibers with thick walls and narrow lumens (hollow area in center) have high coarseness while fibers with thin walls and wide lumens have low coarseness.
  • Mercerized pulps are produced with a chemical process that creates “kinks” in the fiber, which creates a high coarseness measurement. It was also surprisingly learned that the coarse pulps when refined using the same conditions as the northern fibers resulted in a similar average fiber length after refining than the less coarse, northern fiber pulps.
  • This difference is a result of increased cutting in the refining process, rather than effects that just cause fibrillation and collapse of the fibers.
  • the refining equipment and intensity produced a broad fiber distribution of fiber fractions with a high percentage of low fiber length fractions compared to northern fiber sheets. There is also a surprisingly large percentage of long fibers remaining. This broad distribution of fiber lengths containing a higher percentage of long and short fiber fractions results in a well formed sheet with high bulk, anti-linting, and roughness properties that provide superior glass protection.
  • an improved paper for slip sheet interleavers for contacting glass surfaces for separating glass sheets in which the paper is produced using fibers with high coarseness could be as high as 18 hp-day/ton but would likely be more specifically in the range of 7-16 hp-day/ton, and the sheet would retain bulk properties due to the coarseness of the pulps.
  • the pulp length distribution in the superior performing sheet may contain greater than 5% of fibers in the 0.2 to 0.5 mm range, greater than 5% fines (i.e., less than 0.5 mm), and greater than 5% of the fibers greater than 3.5 mm.
  • the pulp used could be produced without the use of a PDMS oil containing defoamer.
  • the sheet may preferably be produced with one pulp source but multiple pulp sources could be used to achieve the fiber length distribution and sheet properties. Unlike many existing interleaver sheets, the improved sheet would not be calendered in order to retain high bulk properties.
  • the bulky, soft, high number of contact point sheet properties result in reduced scratching of glass due to contaminants from the paper or the glassmaking process [especially when packing unfinished LCD glass having contaminants from the bottom of draw (BOD) of the glassmaking process].
  • This improvement is especially valuable in view of the increasing demands for interleaver paper that reduces the number and size of scratching and abrasions packaging for display glass identified above for displays of increased resolution where there is increasingly less tolerance for damage to the glass.
  • the increased bulk and micro roughness in the newly disclosed interleaver formulations translate to a reduction in scratches on glass packed with the new paper.
  • High levels of internal bond and surface strength will result in reduced particle generation.
  • Reduction in scratching and particle generation reduces pixel loss when producing LCD/OLED device screens, improves glass sheet yield, reducing overall costs of the glass, and improving customer satisfaction from glass manufacturers as well as LCD/OLED panel manufacturers.
  • FIGS. 1 and 2 surface roughness profiles are shown in FIGS. 1 and 2 .
  • the charts in FIGS. 1 and 2 show the roughness of the paper surface, with the height of peaks and depth of valleys shown on the Y-axis in microns for a 1.2 mm span, shown along the X-axis in the cross direction of the paper. Simulated contaminants were included on the sheet surface profile and are shown as circles approximately 5 microns in diameter. Also in each figure, a simulated glass plate is shown against the paper surface to illustrate the number of touch points with the paper as well as contact points with the contaminants.
  • FIG. 1 shows the surface of glass interleaver paper produced with standard NBSK pulp. This figure clearly shows the high rate of occurrence of contact with a contaminant. This high number of contaminant contact points increases the number of defects on the glass surface, including scratches and stains.
  • FIG. 2 shows the surface of glass interleaver paper produced with standard Coarse Pulp. This figure clearly shows the reduced number of contact points with a contaminant as compared to the NBSK paper. This lower number of contaminant contact points reduces the number of potential defects on the glass, including scratches and stains.

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US16/622,167 2017-06-14 2018-12-12 Glass Interleaver Paper Produced With Coarse Fibers Abandoned US20200199823A1 (en)

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US201762519698P 2017-06-14 2017-06-14
PCT/US2018/037056 WO2018231792A1 (en) 2017-06-14 2018-06-12 Glass interleaver paper produced with coarse fibers
US16/622,167 US20200199823A1 (en) 2017-06-14 2018-12-12 Glass Interleaver Paper Produced With Coarse Fibers

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