FIELD AND BACKGROUND

The present disclosure relates to an abrasive backing with improved strength properties.

When using an abrasive backing for sanding applications, a common problem is the tearing of the backing after a certain number of sanding cycles. It is also a common issue that after a certain number of folds, the backing tears and is no longer usable. When abrasive backings are used for sandpaper on power equipment, a high amount of internal heat buildup can negatively impact the rate of material removal when using the equipment. Additionally, sandpaper is softened or rejuvenated in water to wash the sanded material out of the grit and in doing so, the sandpaper loses some of its strength properties from being soaked or cleaned.

Thus, there is a need for an abrasive backer that has improved strength properties. Specifically, there is a need for an abrasive backer that allows for an increased number of sanding cycles or folds before the backing tears. There is also a need for an abrasive backer that increases the rate of material removal and retains its strength properties when soaked or cleaned.

SUMMARY

An abrasive backing is generally provided. In some embodiments, the abrasive backing includes a base sheet, comprising wood fibers, synthetic fibers, cellulose filaments, a saturant, wherein the saturant includes two or more latex polymers and a crosslinking agent, and a first surface and opposing second surface, a barrier coating adjacent the first surface of the base sheet, and a backside coating adjacent the opposing second surface of the base sheet. The barrier coating can be impervious to liquid water and allow transmission of gas. In some embodiments, the abrasive backing can have two or more barrier coatings applied adjacent the first surface of the base sheet. The abrasive backing can have grit applied adjacent to the surface of the barrier coating opposing the first surface of the base sheet. The backside coating can be waterproof. In further embodiments, the abrasive backing can have a layer including a plurality of loops or a plurality of hooks on a surface of the backside coating opposing the second surface.

In some embodiments, the base sheet can include wood fibers that include hardwood fibers, softwood fibers, or a combination thereof. In some embodiments, the base sheet can include wood fibers in the base sheet that include a blend of softwood fibers and hardwood fibers, for example, a blend of 30-70% softwood fibers and 70-30% hardwood fibers by weight, each based on the weight of the wood fibers and the cellulose filaments in the base sheet. The base sheet can further include jute fibers, straw fibers, cotton fibers, hemp fibers, bagasse fibers, bamboo fibers, reed fibers, sisal fibers, abaca fibers, kenaf fibers, flax fibers, or a combination thereof.

In further embodiments, the base sheet can have two or more latex polymers in an amount of from 55% to 99.9% by weight of the saturant based on the weight of the dry solids in the saturant. In some embodiments, the two of the two or more latex polymers can be crosslinkable. The saturant can include a third latex polymer. The two or more latex polymers can include copolymers prepared from monomers including styrene and butadiene. In some embodiments, the latex polymers are selected from latex polymers having a Tg of from -40°C to -20°C and a Tg of from -12°C to 8°C. The latex polymers can further include a latex polymer having a Tg of 32°C to 52°C. The latex polymers can include 10% to 50% by weight of a latex polymer having a Tg of from -40°C to -20°C, 50% to 90% by weight of a latex polymer having a Tg of from -12°C to 8°C, and 10% to 50% by weight of a latex polymer having a Tg of 32°C to 52°C, based on total dry weight of the latex polymers. In further embodiments, the saturant can include the cross-linking agent in an amount of from 0.25% to 1.5% by weight of the saturant based on the weight of the dry solids in the saturant. The cross-linking agent can include an aziridine crosslinking agent, a glyoxal-based crosslinking agent, ammonium zirconium carbonate, a carbodiimide, an aliphatic polyglycidyl ether, hexamethoxymethylmelamine, zinc di ethyldithiocarbamate, or a combination thereof. For example, the crosslinking agent can include an aziridine crosslinking agent.

In some embodiments, the base sheet can include cellulose filaments in an amount of from 1% to 5% by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet. The cellulose filaments can have an aspect ratio of from 200 to 5000 and a width of from 30 to 500 nm. Further, the base sheet can have synthetic fibers of from 2% to 8% by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet. The synthetic fibers can include polyester fibers such as polyethylene terephthalate (PET) fibers. The abrasive backing can have a basis weight of 75 to 155 gsm.

Methods are also generally provided for forming an abrasive backing. In one embodiment, the method includes providing a base sheet comprising wood fibers, synthetic fibers, cellulose filaments, and a saturant comprising two or more latex polymers and a crosslinking agent, applying a barrier coating to a first surface of the base sheet, and applying a backside coating to a second surface of the base sheet opposing said first surface of the base sheet. The method may also include providing a base sheet made of wood fibers, synthetic fibers, and cellulose filaments, saturating the base sheet with a saturant comprising two or more latex polymers and a crosslinking agent, and drying the saturated base sheet. The method may also include providing a base sheet by forming a base sheet from a fiber matrix comprising wood fibers, synthetic fibers, and cellulose filaments, and drying the base sheet. The base sheet can then be calendered after saturating the base sheet with a saturant. The method of making an abrasive backing can include the other features described above with regard to the abrasive backing.

The details of one or more embodiments are set forth in the description below and accompanying drawing. Other features, objects, and advantages will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF DRAWINGS

The application includes reference to the accompanying figures, in which:

FIG. 1A shows an exemplary abrasive backing; and

FIG. IB shows an expanded view of the exemplary abrasive backing of Fig. 1 A along line IB.

FIGS. 2A and 2B provide data from the examples demonstrating the abrasive backing described herein.

Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.

DETAILED DESCRIPTION

The present disclosure generally provides an abrasive backing, as well as methods of its formation. In certain embodiments, the abrasive backing includes a base sheet comprising wood fibers, synthetic fibers, cellulose filaments and a saturant, wherein the saturant includes two or more latex polymers and a crosslinking agent. The base sheet includes a first surface and an opposing second surface. Adjacent the first surface of the base sheet is a barrier coating and adjacent the opposing second surface is a backside coating.

Referring to Fig. 1A, an exemplary abrasive backing 10 is shown, formed from a base sheet 12 having a first surface 11 and a second surface 13. A barrier coating 22 is adjacent the first surface 11 of the base sheet. A backside coating 20 is adjacent the second surface 13 of the base sheet 12.

Fig. IB illustrates an expanded view of the abrasive backing 10 of Fig. 1A. In the embodiment shown, the base sheet 12 includes a plurality of fibers including softwood fibers 14, hardwood fibers 16, and synthetic fibers 24. The base sheet 12 also includes cellulose filaments 26. The base sheet 12 also includes latex particles 18 that are provided from the two or more polymers in the saturant.

Each of the components of the abrasive backing 10 provided herein is discussed in greater detail below with respect to the abrasive backing and the method of forming the abrasive backing.

The base sheet 12 includes a plurality of fibers that includes wood fibers, synthetic fibers, and cellulose filaments that are bound together by a polymeric matrix formed by the reaction of the two or more latex polymers and the crosslinking agent. As discussed herein, the polymeric matrix is provided by the saturant that saturates the plurality of fibers in the base sheet. In some embodiments, the hydroxyl groups present in the fibers and the cellulose filaments can hydrogen bond with pendant groups present in the latex polymers provided in the saturant (for example, when the latex polymers are carboxy lated).

The wood fibers in the base sheet can include softwood fibers 14, hardwood fibers 16, or blends thereof. In certain embodiments, the wood fibers can include a blend of softwood and hardwood fibers. The base sheet can include 5-95%, 10-90%, 20-80%, or 30-70% softwood fibers by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet. The base sheet can include 5-95%, 10-90%, 20-80%, or 30-70% hardwood fibers by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet.

Examples of softwood fibers include Northern Bleached Softwood Kraft (NBSK) and examples of NBSK are provided in Table 1. In some embodiments, the softwood fibers can have a length weighted average fiber length from 1.99 to 2.30 mm. Examples of hardwood fibers include Northern Bleached Hardwood Kraft (NBHK) and examples of NBHK are provided in Table 2. In some embodiments, the hardwood fibers can have a length weighted average fiber length from 0.58 to 1.11 mm. In some embodiments, it is also possible to substitute a Eucalyptus

Bleached Kraft (EuBK) for NBHK.

In some embodiments, the plurality of fibers can include additional fibers. The additional fibers can include jute fibers, straw fibers, cotton fibers, hemp fibers, bagasse fibers, bamboo fibers, reed fibers, sisal fibers, abaca fibers, kenaf fibers, flax fibers, or a combination thereof. The additional fibers can replace 1% or greater, 5% or greater, 10% or greater, 20% or greater,

30% or greater, or 40% or greater, or 50% or greater, or 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, or 5% or less by weight of the wood fibers in the base sheet. For example, straw fibers can be used to replace all or a portion of the hardwood fibers that would be used in a hardwood/softwood fiber blend.

The base sheet 12 can include cellulose filaments. The cellulose filaments can be formed, for example, from unraveling of wood fibers to provide single filaments. The cellulose filaments can have an aspect ratio of from 200 to 5000 and a width of from 30 nm to 500 nm. One exemplary source of cellulose filaments is FILOCELL™ CF, which is commercially available from Kruger Biomaterials Inc. The cellulose filaments can be provided in the base sheet in an amount of from 0.1% to 10%, 0.5% to 7.5%, or 1% to 5% by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet.

The plurality of fibers can include synthetic fibers to provide additional properties to the base sheet. For example, the synthetic fibers can work in conjunction with the wood fibers to increase the tear resistance of the base sheet. The synthetic fibers can be formed of any suitable material and to any suitable size and shape as long as the resulting synthetic fibers serve as high tensile strength fibers. Examples of such synthetic fibers can include polyolefins (e.g., polyethylene, polypropylene, polybutylene, etc.); polytetrafluoroethylene; polyesters (e.g., polyethylene terephthalate); polyvinyl acetate; polyvinyl chloride acetate; polyvinyl butyral; acrylic resins (e.g., polyacrylate, polymethylacrylate, polymethylmethacrylate, etc.); polyamides (e.g., nylon 6, nylon 6/6, nylon 4/6, nylon 11, nylon 12, nylon 6/10, and nylon 12/12); polyvinyl chloride; polyvinylidene chloride; polystyrene; polyvinyl alcohol; polyurethanes; polylactic acid; and combinations thereof. In certain embodiments, the synthetic fiber includes a polyester such as polyethylene terephthalate (PET) 24. Synthetic PET fibers include those commercially available from Toray Industries, Inc. In some embodiments, the synthetic fibers have a length from 1 mm to 10 mm or from 2 mm to 8 mm. In some embodiments, the synthetic fibers can have a denier of from 0.5 dpf (denier per filament) to 6.0 dpf or from 3.0 dpf to 6.0 dpf. The synthetic fibers are provided in the base sheet in an amount of from 0.5% to 15%, 1% to 12%, 2% to 10%, or 2% to 8% by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet.

Various additives can be applied to the plurality of fibers during formation of the fibrous web or after formation of the base sheet 12 (e.g., to the dried fiber). For example, wet-strength agents can be used to improve the strength properties of the web during formation. The wetstrength agents can be present in an amount from 0.001% to 5% or 0.01% to 2% by weight based on the weight of the wood fibers and the cellulose filaments in the base sheet. Wet strength agents are typically water soluble, cationic oligomeric or polymeric resins that are capable of bonding with the cellulosic fibers. For example, some suitable wet-strength agents are polyamine-epichlorohydrin, polyamide epichlorohydrin, or polyamide-amine epichlorohydrin resins (collectively “PAE” resins). Other wet strength agents can also be employed in certain embodiments. For example, other suitable wet strength agents can include dialdehyde starches, polyethyleneimines, mannogalactan gum, glyoxal resins, polyisocyanates, and dialdehyde mannogalactan. In some embodiments, the wet-strength resin includes a polyamideepichlorohydrin (PAE) resin.

Various other additives can also be employed in the base sheet 12. The additives can be provided with the fibers during formation of the base sheet or applied to the base sheet with the saturant. Suitable additives can include antifoaming agents, processing aids, surfactants, and dispersing agents. For example, kaolin pigments can be included in the base sheet to increase opacity. A wide range of pigments and dyes can also be added to impart color to the base sheet. Pigments and dyes can be added during formation of the base sheet, can be provided with the saturant when the base sheet is saturated, or can be provided as a separate coating onto the base sheet after saturation.

As discussed herein, the plurality of fibers are provided in a polymeric matrix in the base sheet 12. The polymeric matrix is provided by a saturant or saturating composition that is used to saturate the fibers in the formation of the base sheet or after the base sheet is formed. In certain embodiments, the saturant is provided after the base sheet is formed by saturating the base sheet. As discussed herein, the polymeric matrix is formed by the use of at least two latex polymers and a crosslinking agent. In certain embodiments, two or more of the at least two latex polymers are crosslinkable so they can react with the crosslinking agent or with other latex polymers in the saturant. The reaction of the latex polymers and the crosslinking agent can occur through heat or by the removal of water from the saturant in the base sheet. In addition to physically bonding the plurality of fibers in the base sheet, one or more of the latex polymers and the crosslinking agent can additionally bond with the plurality of fibers or the cellulose filaments, for example, through hydrogen bonding.

The saturant includes at least two latex polymers 18, at least three latex polymers, or more. In some embodiments, the saturant includes three latex polymers. In some embodiments, two or more of the latex polymers are crosslinkable to form a polymeric matrix when reacted with the crosslinking agent. In some embodiments, all three of the latex polymers are crosslinkable. Suitable latex polymers include styrene butadiene copolymers (formed primarily from the reaction of styrene and butadiene monomers), styrene acrylic copolymers (formed primarily from the reaction of styrene and (meth)acrylic and/or (meth)acrylate monomers), pure acrylic copolymers (formed primarily from the reaction of (meth)acrylic and/or (meth)acrylate monomers), or mixtures thereof. For example, the pure acrylic copolymer can be a polyacrylate salt such as a zinc polyacrylate. Other suitable latex polymers include N-methylolacrylamides, ethylene- vinyl acetate copolymers, nitrile rubbers, acrylonitrile-butadiene copolymers, poly(vinyl chloride) copolymers, poly(vinyl acetate) copolymers, ethylene-acrylate copolymers, vinyl acetate-acrylate copolymers, neoprene rubbers or trans- 1,4-poly chloroprenes, cis- 1,4- polyisoprenes, butadiene rubbers, cis- and trans- 1,4-poly butadienes, ethylene-propylene copolymers, or mixtures thereof. In certain embodiments, the latex polymers can be crosslinkable and can include functionalized groups configured to allow crosslinking of the latex polymer either with the crosslinking agent, another latex polymer, or both. For example, the latex polymer can include crosslinkable groups such as carboxyl groups, amine groups, pyridyl groups, or combinations thereof. In some embodiments, the crosslinkable latex polymers can include one or more carboxylated styrene butadiene copolymers. In some embodiments, the particle size of the latex polymer particles can range from 100 nm to 300 nm or from 140 nm to 210 nm.

In some embodiments, the saturant can include the two or more latex polymers 18 in an amount of from 55% to 99.9% or 70% to 99.75% by weight based on the weight of the dry solids in the saturant. The at least two latex polymers can include latex polymers having a Tg of from -40°C to -20°C and latex polymers having a Tg of from -12°C to 8°C. In certain embodiments, the latex polymers can have a Tg of from 32°C to 52°C. For example, the latex polymers can include 10% to 50% by weight of a latex polymer having a Tg of from -40°C to -20°C, 50% to

90% by weight of a latex polymer having a Tg of from -12°C to 8°C, and 0% (or 10%) to 50% by weight of a latex polymer having a Tg of from 32°C to 52°C based on total dry weight of the latex polymers in the saturant. Certain properties can be imparted to the base sheet 12 by using different polymeric latexes depending on the particle size, gel content, glass transition temperature, and number of crosslinking groups (e.g., the degree of carboxylation).

The saturant can include a crosslinking agent. In certain embodiments, the crosslinking agent can include an aziridine crosslinking agent, a glyoxal-based crosslinking agent, ammonium zirconium carbonate, a carbodiimide, an aliphatic polyglycidyl ether, hexamethoxymethylmelamine, zinc diethyldithiocarbamate, or a combination thereof. In certain embodiments, the crosslinking agent can include an aziridine crosslinking agent. The saturant can include the crosslinking agent in an amount of from 0.1% to 2.5%, 0.2% to 2%, or 0.25% to 1.5% by weight based on the weight of the dry solids in the saturant. A crosslinking agent with an aziridine backbone achieves both wet and dry properties as it covalently bonds with molecules having carboxylic acid groups, such as carboxylated styrene butadiene latex, thereby forming a crosslinked network.

Other components can be included in the saturant composition, as desired. For example, an antioxidant compound can be included in the saturating composition. Antioxidants help inhibit oxidation of the saturating composition during the curing process. Oxidation can discolor the saturating composition and degrade its final physical properties. Examples of antioxidants include substituted phenolic compounds such as butylated dihydroxyanisole, di-tert-butyl-p- cresol, and propyl gallate. Additional examples of antioxidants include aromatic amines, such as, di-beta-naphthyl-para-phenylenediamine and phenyl-beta-naphthylamine. If used, the antioxidants can be included in the formulation at a concentration of less than 10%, less than 5%, less than 2%, less than 1%, or less than 0.5% by weight based on the weight of the dry solids in the saturant. In one particular embodiment, a phenol-type antioxidant can be included in the saturating composition.

Additional materials such as fillers, emulsifying agents, water repellants, and film forming resins can be included in the saturating composition, if desired. Suitable fillers can include silica or silicates, clays, and borates. The filler can be included in the saturant in an amount of greater than 0% to 45% or 5% to 30% by weight based on the weight of the dry solids in the saturant. The filler (e.g., a clay) can act to reduce the moisture and air penetration of the base sheet. Examples of suitable clays include No. 1 high brightness kaolin clays, as provided in Table 3, No. 1 High Brightness Ultrafine Clays, No. 2 High Brightness Clays, No. 1 Regular Brightness Ultrafine Clays, No. 1 Regular Brightness Clays, No. 2 Regular Brightness Clays, and combinations thereof.

The saturant can also include other additives for providing the saturating composition with desirable qualities. Examples can include chemicals for pH adjustment or surfactants. Trisodium phosphate can be included in the saturating composition to help control the pH of the emulsion, as an emulsifier, and/or as a thickening agent.

The barrier coating 22 can be applied onto the base sheet 12 following saturation. The barrier coating 22 can be applied from a composition that can include, independently, any of the materials discussed above with respect to the saturant composition. A suitable latex polymeric binder for the barrier coating can include an acrylic latex binder. Suitable polyacrylic latex binders can include polymethacrylates, poly(acrylic acid), poly(methacrylic acid), and copolymers of the various acrylate and methacrylate esters and the free acids; ethylene-acrylate copolymers; and vinyl acetate-acrylate copolymers

The latex polymeric binders for the saturant and the barrier coating can be the same or different. The latex polymer of the barrier coating is typically selected to adhere or bond well to the surface of the saturated base sheet. Additionally, the latex polymeric binder of the barrier coating can be configured to flow sufficiently well during any subsequent calendering (e.g., soft nip calendering or supercalendering). For example, latex polymeric binders having viscosities ranging from 10-100 centipoise can be expected to flow sufficiently well.

The thickness of the barrier coating 22 can vary according to the intended use for the resulting adhesive backing. For example, a thinner barrier coating can be utilized for coarse grit abrasive products, e.g., abrasives having particle sizes of 200 mesh or greater (the term "mesh" is used herein to mean U.S. Standard Sieve mesh). On the other hand, a thicker barrier coating can be used for finer grit products which are to be used for polishing or fine surface finishing. A practical minimum layer thickness is 10 micrometers, whereas the practical maximum layer thickness is 250 micrometers. However, thinner or thicker layers can be employed, if desired, provided that the layers are continuous. Thermoplastic polymeric compositions which are inherently stiff will be more useful for coarse grit products, while softer or elastomeric thermoplastic polymeric compositions like ethylene-vinyl acetate copolymers and polyurethanes will be more useful for such fine grit products as fine sanding and polishing cloths.

In another exemplary barrier coating, a bond layer can be on the first surface and a barrier coating on the bond layer, as disclosed in U.S. Patent Application Serial No. 14/245,342 titled “Super Smooth Paper Backing for Fine Grit Abrasives and Methods of Their Application and Use” of Vervacke filed on April 4, 2014, which is incorporated by reference herein.

In certain embodiments, the barrier coating 22 can be impervious to liquid water and allows transmission of gases. In certain embodiments, the barrier coating 22 allows for transmission of gases and liquids. In some embodiments, the abrasive backing can have two or more barrier coatings applied adjacent to the first surface of the base sheet. An exemplary abrasive backing can include a make coating applied adjacent to the barrier coating and a grit coating applied adjacent to the make coating. In some embodiments, the make coating can include a liquid phenolic resole resin, a hydroxyl-bearing polyester, a polyester polyol, an aromatic polyisocyanate, a butyl acetate, a sorbitan laurate, or a combination thereof. In some embodiments, the make coating includes a liquid phenolic resole resin. The make coating anchors the grit to the base sheet 12 of the abrasive backing 10.

The backside coating 20 can be any suitable layer of or coating on the second surface that is not configured to have a layer of abrasive particles thereon. Any such backside coating can be utilized and tailored for a specific application, as known in the art. Such a backside coating can be applied from a composition that can include, independently, any of the materials discussed above with respect to the saturant. In some embodiments, the backside coating 20 can be waterproof and, in some embodiments, can include a layer comprising a plurality of loops or a plurality of hooks (such as Velcro®). The layer comprising a plurality of loops or a plurality of hooks can be discontinuous and only be provided where needed to match with a sanding device that has a corresponding plurality of loops (in the event the backside coating 20 has a plurality of hooks) or a plurality of hooks (in the event the backside coating has a plurality of loops). The backside coating 20 can include latex polymers as well as various other additives. Suitable additives can include antifoaming agents, pigments, processing aids, dispersing agents, and matting agents. In some embodiments, the backside coating 20 can include a filler such as diatomaceous earth. The diatomaceous earth can increase the tactile feel of the backside coating 20 when used in hand sanding applications.

An exemplary abrasive backing 10 can be formed from a method that includes providing a base sheet 12 comprising wood fibers, synthetic fibers, and cellulose filaments and a saturant comprising two or more latex polymers and a crosslinking agent, applying a barrier coating 22 to a first surface 11 of the base sheet 12, and applying a backside coating 20 to a second surface 13 of the base sheet 12 opposing said first surface 11 of the base sheet 12. For certain embodiments of the abrasive backing, providing the base sheet 12 can include providing a base sheet 12comprising wood fibers, synthetic fibers, and cellulose filaments, saturating the base sheet 12 with a saturant comprising two or more latex polymers and a crosslinking agent, and drying the saturated base sheet 12. In other embodiments, providing a base sheet 12 can include forming a base sheet 12 from a fiber matrix comprising wood fibers, synthetic fibers, and cellulose filaments, and drying the base sheet. In some embodiments of the abrasive backing 10, the method of formation can include calendaring the base sheet 12.

In certain embodiments, the abrasive backing 10 is formed by a method that includes a barrier coating 22 that is impervious to liquid water and allows transmission of gases. The method can also include a barrier coating 22 that allows transmission of gases and liquids. There can also be two or more barrier coatings 22 applied adjacent to the first surface 11 of the base sheet 12. The abrasive backing 10 can also be formed by a method that includes applying grit adjacent to the surface of the barrier coating 22 opposing the first surface 11 of the base sheet 12. In some embodiments, the abrasive backing 10 is formed by a method that includes a layer comprising a plurality of loops or a plurality of hooks provided on a surface of the backside coating 20 opposing the second surface 13.

In certain embodiments, the abrasive backing 10 includes an abrasive backing base paper with a basis weight of from 75 to 155 gsm, which encompasses between A-C weight abrasive papers.

To form the base sheet 12, the plurality of fibers including the wood fibers, the optional additional fibers, the cellulose filaments, and the synthetic fibers are mixed together. The plurality of fibers is generally placed in a conventional papermaking fiber stock prep beater or pulper containing water. The fibrous material stock is typically kept in continued agitation such that it forms a suspension. If desired, the cellulose filaments and/or the wood fibers can also be subjected to one or more refinement steps to provide a variety of benefits, including improvement of the tensile and porosity properties of the base sheet. Refinement results in an increase in the amount of intimate contact of the fiber surfaces and can be performed using devices well known in the art, such as a disc refiner, a double disc refiner, a Jordan refiner, a Claflin refiner, or a Valley-type refiner.

The resulting fibrous suspension can then be diluted and readied for formation into a fibrous web using conventional papermaking techniques. For example, the web can be formed by distributing the suspension onto a forming surface (e.g., wire) and then removing water from the distributed suspension to form the web. This process can involve transferring the suspension to a dump chest, machine chest, clean stock chest, low density cleaner, headbox, etc., as is well known in the art. Upon formation, the fibrous web can then be dried using any known technique, such as by using convection ovens, radiant heat, infrared radiation, forced air ovens, and heated rolls or cans to produce the base sheet. Drying can also include centralized steam drying followed by contact drying. Drying can also be performed by air drying without the addition of thermal energy.

In some embodiments, the components of the saturant are provided as a beater add so they are present in the fiber suspension used to produce the base sheet. In some embodiments, the saturant can be used to saturate an already formed base sheet. Any known saturation technique can be employed, such as brushing, flooded nip saturation, doctor blading, spraying, and direct and offset gravure coating. For example, the plurality of fibers can be exposed to an excess of the solution and then squeezed. The squeezing of excess saturant from the plurality of fibers can be accomplished by passing the plurality of fibers between rollers. If desired, the excess saturant can be returned to the supply for further use. After squeezing out excess material, the saturated plurality of fibers can then be dried. Other suitable techniques for saturating a plurality of fibers with a saturant are described in U.S. Patent No. 5,595,828 to Weber and U.S. Patent Application Publication No. 2002/0168508 to Reed, et al., which are incorporated herein in their entirety by reference thereto for all purposes.

The amount of the saturant applied can vary depending on the desired properties of the plurality of fibers, such as the desired permeability. Typically, the saturant is present at an addon level of 10% to 40% by weight, and in some embodiments, from 10 to 25% by weight “parts pick up” or PPU. The PPU add-on level is calculated by dividing the dry weight of the saturant applied by the dry weight of the plurality of fibers before treatment and multiplying the result by

100. PPU can be calculated according to the formula: 100 wherein BWfiber+saturant and BWfiberare both bone dry (no moisture) measurements of the basis weight of the base sheet and BWaber is the measurement at the stage before the size press and BWfiber+saturant is the measurement after the size press when the sheet has been saturated.

In one particular embodiment, the saturated base sheet 12 is calendered after saturation. Calendering the saturated base sheet can increase the softness and smoothness of the sheet. When desired, the saturated base sheet 12 can be calendered according to any process. Calendering generally involves pressing the saturated base sheet in a nip formed by a first and second calendering rolls. The effect of calendering on the saturated base sheet depends upon the temperature, the pressure applied, and the duration of the pressure. For purposes herein, calendering can be carried out at either ambient or elevated temperatures. Suitable calendering pressures can be from 50 to 2000 pounds-force per linear inch (ph), 100 to 1600 pli, 300 to 1000 pli, or 400 to 600 ph. Suitable temperatures can be from 20°C to 240°C, 20°C to 140°C, or 20°C to 90°C.

The duration of calendering can be varied in conjunction with the nip pressure and/or the composition of the calender rolls to produce the desired smoothness of the paper backing for the sheet. For example, softer calender rolls such as fiber-filled rolls tend to compress to form a larger contact area in the nip, thus increasing the duration of the calendering. Hard steel rolls compress more, thus decreasing the duration of the calendering. In one arrangement, the calender nip comprises a steel roll and a soft fiber-filled roll. In another arrangement, for example, a production supercalender stack can include more than two rolls, desirably from nine to eleven rolls, stacked upon each other in a vertical arrangement. Desirably the stacked rolls alternate between steel and fiber-filled rolls. With such an arrangement, the paper can be exposed to various pressures, up to 1600 ph, and a number of nips, for example from one to eight, to develop the desired smoothness level.

The saturated, calendered base sheet 12 can be dried to remove the solvent from the saturating composition. For example, the saturated base sheet 12 can be heated to a temperature of at least 100° C, and in some embodiments at least 150° C, such as at least 200° C. Suitable drying techniques can include heating with a conventional oven, microwave, forced air, heated roll, can, or thru-air drying. Drying can also include centralized steam drying followed by contact drying.

Additionally, the saturated, calendered base sheet 12 can be cured such that the latex polymer reacts with the crosslinking agent of the saturating composition to crosslink and form a three-dimensional polymeric structure. Thus, the crosslinked latex polymer can help bind the fibers of the base sheet together, either mechanically and/or chemically.

No matter the particular processing steps of the base sheet, the base sheet 12 is kept at temperatures below that of the softening point or melting point of the synthetic fibers such that the synthetic fibers keep their as-laid shape and physical construction in the final ply sheet orientation (and resulting abrasive backer laminate). Thus, the structural and physical integrity of the synthetic fibers is kept intact in the individual ply sheets to allow the synthetic fibers to provide strength properties to the ply sheet.

The backside coating 20 and the barrier coating 22 can be applied to the base sheet 12.

The backside coating 20 can be customized to provide particular properties. Specifically, the backside coating 20 can be printed on, can have a tactile feel for hand sanding, or can be precoated for pressure sensitive adhesives.

The abrasive backing 10 also has demonstrated improvements of 100% to 200% in wet properties, which allows a sandpaper product made of the abrasive backing 10 to retain the strength properties while being soaked or cleaned to wash the sanded material out of the grit. Although not wishing to be bound to a particular theory, it is believed that the improvements are due to use of a combination of the two or more latex polymers, the crosslinking agent, the wood fibers, the cellulose filaments, and the synthetic fibers. The latex polymers provide reinforcement to the fibers thereby increasing the strength properties and durability of the abrasive backing 10. The improvements in wet sanding properties are also due to the barrier coating and backside coating, which decrease the permeability as sheet tightness is improved with the use of the saturant.

The abrasive backing 10 can withstand harsh usage in both hand sanding and power tool application in both wet and dry sanding applications. The strength improvements in the abrasive backing 10 are exhibited in both in-plane and out-of-plane strength properties. This is demonstrated by a root mean square (RMS) tensile index of greater than 95 Nm/g (e.g., from 95- 100 Nm/g). The out-of-plane delamination force is from 150 grams force to 1000 grams force or from 450 grams force to 750 grams force. It is believed that the cellulose filaments and synthetic fibers provide additional tear strength by entangling and bonding with the wood fibers.

The abrasive backing 10 has a high delamination force in the wet state after both 1 hour or 24-hour soaking cycles, which allows for the abrasive backing to better retain its strength properties after being soaked or cleaned. Because the abrasive backing 10 maintains the strength properties when periodically cleaned in an appropriate polar cleaning solvent like water, the wet sanding longevity is in turn improved. The improved backing retains 40% to 60% of the dry tensile strength after a one-hour soak in water. The improved backing does not require any increase in refining energy to the base sheet, therefore allowing for the same level of refining that increased the densification and strength properties of the backing.

Sandpaper using the improved abrasive backing 10 is more durable in both hand and power sanding applications. When used in power equipment, the improved sandpaper will have a reduced internal heat buildup, causing the energy transfer from the power equipment into the material to improve. Thus, the rate of material removal will also improve when the same grit and make coat are applied to the abrasive backing.

The abrasive backing will now be further described by the following non-limiting examples. Parts and percentages are on a per weight basis unless noted otherwise.

TEST METHODS

Sample Conditioning

Samples were conditioned using TAPPI T402 sp-13 prior to any of the following test methods with the additional step of pulling conditioned air through the specimens for a minimum of 20 minutes.

Basis Weight

Basis weight was measured using TAPPI T410, however, the specimen was four sheets with a total area of 412.3 in ² instead of the minimum of 800 in. ² .

Caliper

Caliper was measured using TAPPI T411 om-15. Tensile Strength. Tensile Energy of Absorption (TEA), Stretch %, and RMS Tensile Index

Tensile strength, TEA, and Stretch % were measured using TAPPI T494-om-01. The RMS Tensile is the square root of the MD Tensile squared plus CD Tensile.

MD Aged Wet Tensile Strength and MD Aged Wet Stretch

MD aged wet tensile strength and MD aged wet stretch were measured using TAPPI T456 om-15, however, the specimens were aged for 5 minutes at 145°F before measurement. Tear

Tear was measured using TAPPI T414 om-21, however, the results are in grams force to tear sixteen plies instead of one ply.

Guriev Porosity

Gurley porosity was measured using TAPPI T460 using either one sheet or four sheets.

Wire Smoothness

Wire smoothness was measured using TAPPI T538 om-16. Delamination

Delamination was measured using the following procedure:

The Twing- Albert Vantage NX EJA Series testing machine was a properly calibrated test machine that can be operated in a displacement control mode with a constant displacement rate of 30.5 cm/min. The testing machine was equipped with two opposing grips to hold the two ends of heat seal tape bonded to the abrasive backing specimen. The testing machine load-sending device was capable of indicating the total load carried by the test specimen and in this case a 500N load cell was used. This device was essentially free from inertia lag at the specified rate of testing and indicated the load with an accuracy over the load range(s) of interest of within ± 1 % of the indicated value. The data was stored digitally and post-processed. At least five specimens were tested per test condition. The accuracy of all measuring equipment had certified calibrations that were current at the time of use of the equipment. Specimens were stored and tested at standard laboratory atmosphere of 23 ± 3 °C and 50 ± 10% relative humidity.

1. The width of each abrasive backing specimen and heat seal tape was 15 mm.

2. A cloth heat seal tape was laminated at 312°F ± 12°F to both sides of the abrasive backing by applying the heat seal tape at a pressure of 45.5 gm/cm ² for 20 seconds and was used to bond opposing sides of the abrasive backing specimen so that the delamination force was measured along the center plane of the specimen.

3. After the abrasive backing specimen was heat sealed and before it was loaded into the grip blocks, the delamination was initiated by hand by pulling the two strips of heat seal tape away from each other at 180° until at least 2.54 cm was pre-delaminated.

4. The two ends of the heat seal tape on the pre-delaminated specimen were mounted in the grips of the loading machine, making sure that the specimen was aligned and centered.

5. The specimen was loaded at a constant crosshead rate of 30.5 cm/min.

6. The load and displacement values were recorded continuously.

7. The test loading was stopped after a test distance of 5.08 cm.

8. The specimen was unloaded at a constant crosshead rate of 30.5 cm/min.

9. After the specimen was unloaded, the average force in grams was calculated over the 5.08 cm test distance.

One Hour Wet Delamination

The equipment, test method and instrument parameters were exactly the same as the Delamination method provided above, except with the addition of a soaking step. Specimens were soaked in an immersion solution of 10 g. per liter of a non-ionic surfactant (Ci4H22O(C2H4O) _n ) for 1 hour prior to testing.

1. The sample was blotted with paper towels to remove any excess water.

2. The pre-delamination steps and the loading steps as provided in the Delamination method were performed on the one hour soaked specimen.

3. After the test was completed, the average delamination force of the one hour soaked specimen was calculated over the 50.8 cm test distance as performed in the Delamination method.

4. The 1 hr. wet delamination force was reported in grams and the ratio of the one hour wet/dry test was reported as a percentage.

24 Hour Wet Delamination

Twenty-four hour wet delamination was measured using the same test as the one hour wet delamination, except that the specimens were soaked in the immersion solution for 24 hours instead of one hour.

Sheffield Porosity

Sheffield Porosity was measured using TAPPI T547 om-18.

Felt Smoothness

Felt smoothness was measured using TAPPI T538 om-16.

Felt Gloss

Felt gloss was measured using TAPPI T480 om-15.

Turpentine Penetration

Turpentine penetration was measured using the following test: 1. Xylene was combined with heptane at a volume ratio of 3 to 1 and 0.25 g of Sudan Red IV was added per 400 ml of total xylene/heptane to create a solvent.

2. This solvent was brushed on the barrier coat side of the sample with a 2” wide paint brush.

3. The sample sat for 10 seconds while coated with solvent and was then wiped off.

4. The level of penetration was the rate on a scale of 1, 3, or 4, wherein 1 represents the least amount of penetration and 4 represents solvent penetration to the side opposite the barrier coat.

Density

Density was calculated by using basis weight as measured above and caliper as measured above.

EXAMPLES

Example 1

Eight different samples of coated, saturated base sheet were prepared and then the properties compared between the samples. For each of the prepared samples, the same process was performed, but the materials used in both the base sheet and saturant were altered.

The samples of coated, saturated base sheet were prepared according to the following method:

Unsaturated base sheets with compositions according to Table 4 were refined for 15 minutes. Table 4

The dried sheets were saturated to the appropriate pickup with saturants of a composition according to Table 5.

Table 5 Barrier and backside coatings were provided on opposing sides of the base sheet with compositions according to Table 6.

Table 6

Properties for the different abrasive backings are provided in FIGS. 2A and 2B.

As shown in FIGS. 2A and 2B, there are improved properties when comparing control samples A B30 and A B35 with the abrasive backings provided herein. For example, there is an increase in root mean square (RMS) tensile index from approximately 80 Nm/g in A B30 to a range as high as 95-100 Nm/g as shown in samples B_P30 and B_P35. This shows the abrasive backing can withstand harsh usage in both hand sanding and power tool application in both wet and dry sanding applications. There are also 15% to 30% improvements in strength properties such as in-plane tensile strength and tear and 100% improvement in out of plane properties such as z-directional tensile and out of plane delamination force on saturated sandpaper product.

The abrasive backing allows for an increased number of sanding cycles before either tensile or tear failure of the abrasive backing. This improvement is demonstrated by the increase in tensile energy of absorption (TEA) from 219.8 J/m ² in sample A B30 to 311.9 J/m ² in sample B P35, as provided in FIG. 2A. This improvement is also demonstrated by the average fold endurance of 4,194 folding cycles for conditioned and unaged B 35P and the average fold endurance of 6,513 for conditioned B 35P that was aged for 30 minutes at 120°C, as provided in Table 7.

Table 7

Example 2

The properties of sample B P35 was tested on a commercial 3.15 meter wide paper machine. This embodiment of the abrasive backing had a base sheet with a composition according to Base Sheet B in Table 4 and a saturant with a composition according to saturating formula P in Table 5. The components of the base sheet according to Table 4 were supplied to the paper machine stock delivery system, formed on the Fourdrinier table, wet-pressed, dried, and saturated with the saturant according to Table 5 at a PPU of 28. The barrier coating was applied commercially on the 3.15 meter paper machine and has a composition according to Table 6. The backside coating was applied offline to sample B P35 BC and has a composition according to Table 6.

The property measurements resulting from the trial are provided in Table 8. The property improvements are based on the current corresponding commercial control grade. Table 8

The property measurements of the abrasive backing sample and corresponding abrasive backings manufactured by Neenah® Performance Materials and Monadnock Paper Mills, Inc. are provided in Table 9. The corresponding abrasive backings were manufactured on a commercial scale and the data provided is published and publicly available.

Table 9

As shown in Table 9, there is improved RMS Tensile Index when comparing sample

B P35 with the corresponding products of Neenah® Performance Materials and Monadnock

Paper Mills, Inc. For example, there is an increase in RMS tensile index from 63.8 Nm/g in the Monadnock Paper Mills, Inc. product in Table 9 to 106.1 Nm/g in B P35. The difference in the RMS Tensile Index between B P35 BC in Table 8 and B P35 in Table 9 is due to the backside coating applied to B P35 BC, which increases its basis weight to 115 gsm from the basis weight of 108.7 gsm ofB_P35.

The compositions and methods of the appended claims are not limited in scope by the specific compositions and methods described herein, which are intended as illustrations of a few aspects of the claims and any compositions and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the compositions and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative compositions and method steps disclosed herein are specifically described, other combinations of the compositions and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated. The term “comprising”, and variations thereof as used herein is used synonymously with the term “including” and variations thereof and are open, non-limiting terms. Although the terms “comprising” and “including” have been used herein to describe various embodiments, the terms “consisting essentially of’ and “consisting of’ can be used in place of “comprising” and “including” to provide for more specific embodiments of the invention and are also disclosed. Other than in the examples, or where otherwise noted, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood at the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, to be construed in light of the number of significant digits and ordinary rounding approaches.