Paper mats

Abstract: A paper mat is made from an aqueous slurry or dispersion of kraft wood pulp, a large amount of finely divided inorganic pigments and as a binder an anionic latex of a copolymer of at least one conjugated diene monomer, at least one vinyl substituted aromatic monomer, at least one acrylic-­ type monomer and at least one monomer having a vinyl group and an activatable methyl, ethyl, propyl or butyl ester group.

Description: This invention relates to methods of forming paper mats, and paper mats made thereby. Paper mats are generally formed from an aqueous slurry of kraft wood pulp, a predominant amount of finely divided inorganic pigments, a latex binder and other ingredients such as antioxidants, biocides and flocculants. The slurry is cast onto a fourdrinier machine from a head box where the water is largely removed, roll pressed to form a sheet which is then passed over drying cans, cooling cans, calendered and wound on a reel. See Encyclopedia of Polymer Science and Technology , Interscience Publishers, l968, Vol. 9, pages 718 to 747. Kraft paper pulp may be made from wood chips boiled in an alkaline solution containing sodium sulfate. Such mats may be used e.g. in the manufacture of flooring tiles. To form a flooring tile, the mat is unwound from the reel, passed to a conveyor where the top layer of the mat is coated with a vinyl plastisol which is fluxed and cooled to form a vinyl coating which is then printed to form a design on the vinyl coating of the mat sheet. The design is then overcoated with a hot melt vinyl coating composition and cooled to form an abrasion-resistant top coating. The back side or opposite side of the mat sheet or layer is provided with a peelable foil of paper or plastic sheet. The resulting composite is then cut into appropriate sizes for use as flooring tiles. They are then assembled and placed in boxes for shipping. The problem addressed herein is to provide novel processes for making a paper mat, and paper mats made thereby. Preferably it is sought to enable manufacture of paper mats of improved strength. According to the present invention, a method of making an improved paper mat is provided according to claim 1 wherein the latex binder used in the paper making method comprises an anionic emulsion of a copolymer of at least one conjugated diene monomer, at least one vinyl substituted aromatic monomer, at least one acrylic-type monomer and at least one monomer having a vinyl group and an activatable methyl, ethyl, propyl or butyl ester group. The invention also includes a paper mat obtainable by said method. The conjugated diene monomers have from 4 to 6 carbon atoms. Butadiene-1,3 is preferred. Examples of other diene monomers include isoprene, piperylene, 2,3-dimethyl-1,3-butadiene, pentadiene, hexadiene and the like. Mixtures of the dienes can be used. The vinyl substituted aromatic monomers utilized in forming the latex copolymer have from 8 to 10 carbon atoms. Examples of such monomers include alpha methyl styrene, para methyl styrene, methyl vinyl toluene, p-vinyl toluene, 3-ethyl styrene and the like with styrene being preferred. In lieu of a single vinyl substituted aromatic type monomer, a plurality of such monomers can be utilized. The acrylic-type monomer used has from 3 to 6 carbon atoms. Examples are acrylamide, methacrylamide, acrylic acid, methacrylic acid and itaconic acid. Mixtures of these acrylic type monomers can be used. The monomer having a vinyl group and an activatable methyl, ethyl, propyl or butyl ester group is at least one monomer selected from the group consisting of methyl acrylamidoglycolate, ethyl acrylamidoglycolate, butyl acrylamidoglycolate, methyl acrylamidoglycolate methyl ether, butyl acrylamidoglycolate butyl ether, methyl methacryloxyacetate, ethyl acrylamido-N-oxalate (N-ethyloxalyl acrylamide), N,N′-Bis(ethyloxalyl)acrylamide, N-isopropyl, N-ethyloxalyl-3-propylamino methacrylamide, N-ethyloxalyl-N′-methyleneaminoacrylamide, ethyl N-2-ethyloxamatoacrylate, ethyl 3-pyruvylacrylate, ethyl methylenepyruvate, methyl acrylthiocarbonyloxyacetate (Methyl thiacryloxyacetate), methyl thiacrylthiogylcolate, methyl acryl-2-thioglycolate, methyl thiacrylamidoacetate, methyl acrylamidoglycolate thioether, methyl acrylamido-N-methylenethioglycolate andd p-ethyl oxalyl styrene. In the anionic latex disclosed herein the copolymer contains the diene monomer in an amount by weight of from about 30 to 60%, the vinyl substituted aromatic monomer in an amount by weight of from 36 to 66% by weight, the acrylic type monomer in an amount of from 1 to 4% by weight and the monomer having a vinyl group and an activatable methyl, ethyl, propyl or butyl ester group in an amount of from 3 to 6% by weight. All percentages of monomers add up to 100%. The copolymer is usually made in an aqueous alkaline medium containing an anionic surfactant or emulsifier such as an alkyl sulfate, an alkyl sulfosuccinate and the like. Free radical initiators are usual, such as the persulfates and peroxides and the like. Chain transfer agents e.g. alkyl mercaptans are suitable. Other materials which may if desired be used in the process are shortstops, chelating agents, antioxidants, biocides and the like. Polymerization is preferably to above 60% conversion, more preferably above 90% conversion of monomers to copolymer and to provide a latex with a total solids content of from about 40 to 60% by weight. For methods of making latices, reference may usefully be made to US-A-4,788,008 and US-A-4,808,660. On a dry weight basis the aqueous slurry to form the mat preferably comprises (parts by weight): Kraft wood pulp 5. to 20. Polyethylene particles 0.5 to 3.0 to improve pulping Finely divided clay 60. to 85. or talc (clay preferred) Glass fibers, chopped 1. to 2. Antioxidant 0.01 to 0.25 Water clarifier 0.01 to 0.02 Latex copolymer 8. to 16. Flocculants, surfactants and defoamers also may be added to the slurry. The following examples will serve to illustrate the present invention with more particularity to those skilled in the art. Examples Aqueous slurries were prepared from, on a dry parts-by-weight basis Kraft wood pulp 13.0 Pulpex P, Grade A-DC polyethylene particles 1.00 NARVON R F-3 clay 15.70 Afton clay 36.60 Digalite (not clay) 18.00 Glass fibers 1.50 Antioxidant 0.1 Water clarifier, KYMENE R 0.0125 Latex copolymer (various) 14.0 The slurries were flocculated with cationic flocculant and then cast onto wire screens to remove the water to form sheets which were compressed, heated and cooled to form mats which were then tested. The anionic latices used were the following copolymers (parts by weight of monomers): A. Copolymer of 40 butadiene, 51.5 styrene, 1.5 itaconic acid, 2 acrylamide and 5 methyl acrylamidoglycolate methyl ether B. Copolymer of 42 butadiene-1,3, 54 styrene, 0.5 itaconic acid, 3 acrylamide and 0.5 methacrylic acid. C. Copolymer of 45 butadiene, 51 styrene, 0.5 itaconic acid, 3 acrylamide and 0.5 methacrylic acid. D. Copolymer of 51 butadiene and 49 styrene. E. Copolymer of 48.75 butadiene-1,3, 44.25 styrene, 1.5 itaconic acid, 2.5 acrylamide, 2.5 N-methylolacrylamide and 0.5 divinylbenzene. F. Same as E but from a larger batch of latex. G. Blend of 30% of a copolymer of 30 butadiene-1,3, 65.25 styrene, 0.75 methacrylic acid, 1.75 hydroxyethylacrylate and 2.25 itaconic acid and 70% of a copolymer of 45 butadiene-1,3, 51 styrene, 0.5 itaconic acid, 3 acrylamide and 0.5 methacrylic acid. H. Commercial latex. I. Same as copolymer B. Three mats were prepared for each latex sample and each tested for a specific property. An explanation of terms used in the table of mat properties is given below. Cold Plasticizer Tensile - A sample of mat is soaked in a plasticizer (dioctyl phthalate) at ambient temperature. This sample is then tested for tensile strength at ambient temperature. This test is an indication of strength loss when plasticized polyvinyl chloride resin is applied to the mat. Hot Plasticizer Tensile - This is the same as cold plasticizer tensile except that the sample is tested for strength properties at elevated temperatures. Again this test indicates the "runability" under commercial manufacturing conditions. Pocket Heat Age - Samples of mats were placed in an oven at 215°C (420°F). The time for complete degradation of the latex was recorded. This test is an indication of the product performance when produced on a commercial line. % Plasticizer PU - Percent Plasticizer Pick-Up - The sample mat was soaked in a plasticizer and reweighed. This test indicates how much plasticiser is absorbed into the mat. Drain Time - This test is carried out on the flocculated slurry before the mat is formed. The time for the water to drain from the slurry is recorded. This test is an indication of how quickly the slurry will dewater when it is being manufactured on a commercial line. Sheet Thickness Units - wt. = weight in grams per 645 mm² (64 inch square) mat N.B. The Table appears twice: the second appearance is in imperial units as originally filed, the first appearance is a conversion to metric units. The results show that mats made from copolymer A gave better results than mats from copolymers B to I (the controls). Further runs of mats made from copolymer A exhibited a general overall improvement in ambient tensile, hot tensile, ambient plasticizer tensile, hot plasticizer tensile and split strength, regarded in combination, over mats made from other copolymers.

Claims: A method of forming a paper mat, in which a latex binder is included in a slurry subsequently formed into the mat, characterised by using as the latex binder an anionic emulsion of a copolymer of: (i) 30-60 wt% conjugated C₄₋₆ diene monomer; (ii) 36-66 wt% C₈₋₁₀ vinyl-substituted aromatic monomer; (iii) 1-4 wt% C₃₋₆ acrylic monomer, and (iv) 3-6 wt% vinyl monomer with an activated C₁₋₄ alkyl ester group. A method according to claim 1 in which the slurry contains from 5 to 20 parts (dry weight) of kraft wood pulp to 8 to 16 parts (dry weight) of the latex binder, the latex binder having a solids content of from 40 to 60%, a predominant amount of finely divided clay or talc, and minor amounts of additives selected from polyethylene particles, glass fibres, antioxidants, biocides, water clarifiers and flocculants. A method according to claim 2 in which the paper mat is formed by applying the slurry to a screen, removing water using the screen to form a sheet, and compressing, drying and cooling the sheet to form the paper mat. A method according to any one of claims 1 to 3 in which the conjugated diene monomer is selected from butadiene-1,3, isoprene, piperylene, 2,3-dimethyl-1,3-butadiene, pentadiene and hexadiene; the vinyl substituted aromatic monomer is selected from styrene, alpha methylstyrene, paramethyl styrene, methyl vinyl toluene, p-vinyl toluene and 3-ethylstyrene; the acrylic-type monomer is selected from acrylamide, methacrylamide, itaconic acid, acrylic acid and methacrylic acid; the monomer having a vinyl group and an activatable methyl, ethyl, propyl or butyl ester group is selected from methyl acrylamidoglycolate, ethyl acrylamidoglycolate, butyl acrylamidoglycolate, methyl acrylamidoglycolate methyl ether, butyl acrylamidoglycolate butyl ether, methyl methacryloxyacetate, ethyl acrylamido-N-oxalate (N-ethyloxalyl acrylamide), N,N′-Bis(ethyloxalyl)acrylamide, N-isopropyl, N-ethyloxalyl-3-propylamino methacrylamide, N-ethyloxalyl-N′-methyleneaminoacrylamide, ethyl N-2-ethyloxamatoacrylate, ethyl 3-pyruvylacrylate, ethyl methyienepyruvate, methyl acrylthiocarbonyloxyacetate (Methyl thiacryloxyacetate), methyl thiacrylthioglycolate, methyl acryl-2-thioglycolate, methyl thiacrylamidoacetate, methyl acrylamidoglycolate thioether, methyl acrylamido-N-methylenethioglycolate and p-ethyl oxalyl styrene. A method according to any one of claims 1 to 3 in which the conjugated diene monomer is butadiene-1,3, the vinyl substituted aromatic monomer is styrene, the acrylic-type monomer is a mixture of itaconic acid and acrylamide and the monomer having a vinyl group and an activatable vinyl, ethyl, propyl or butyl ester group is methylacrylamidoglycolate methyl ether. A paper mat obtainable by a method according to any one of claims 1 to 4. A paper mat according to claim 6, and obtainable by a method according to claims 2 and 3, comprising on a dry-weight basis a predominant amount of finely divided clay or talc particles, minor amounts of polyethylene particles, glass fibers, antioxidants and biocides, from 5 to 20 parts of kraft wood pulp and from 8 to 16 parts of a copolymer of from about 30 to 60% by weight of at least one conjugated diene monomer of from 4 to 6 carbon atoms, from about 36 to 66% by weight of at least one vinyl substituted aromatic monomer having from 8 to 10 carbon atoms, from about 1 to 4% by weight of at least one acrylic-type monomer having from 3 to 6 carbon atoms, and from about 3 to 6% by weight of at least one monomer having a vinyl group and an activatable methyl, ethyl, propyl or ester group.

Inventors: NEUBERT TERRY C, NEUBERT, TERRY C.
Applicants: GENCORP INC, GENCORP INC.
Application year: 1990
Main classification: D21H17
IPC codes: D21H17