Classifications

• • 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
  • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H13/26—Polyamides; Polyimides
• • 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
  • D21H27/30—Multi-ply

Definitions

• This invention relates to an improved layered aramid paper having a smooth surface and good tensile and tear strengths.
• the smooth surface provides for better print clarity and makes such papers particularly useful for high temperature label applications.
• Prior art techniques that improve on surface smoothness often lead to a reduced level of mechanical strength and/or thermal stability.
• synthetic papers which have been pressed or calendered at high temperature and pressure will generally have fibers on the surface which cause roughness or snagging when the surface of the paper is worked during end use processing.
• US-A-5,076,887 describes a multi-layered, high temperature resistant pressboard. All layers have the same uniform distribution of polyaramid fibrids and floc. The surface smoothness is not sufficient for the purpose of the present invention.
• US-A-5,089,088 describes flash expansion of moist multi-layered boards, wherein each layer comprises the same uniform composition comprising aramid floc bonded by aramid fibrid.
• This invention provides a multi-layered calendered aramid paper having a surface suitable for high quality printing characterized in that the paper contains from 40 to 55% by weight of fibrids and comprises a substrate layer which consists essentially of aramid fibrids and floc and one or two surface layers, each bonded to the substrate layer to form a single consolidated sheet, said surface layer(s) comprising from 10 to 67% of the weight of the paper and consisting essentially of from 65 to 90% by weight aramid fibrids and from 10 to 35% by weight aramid floc and wherein the entire surface of the paper is calendered and the sheet has a density of from 0.8 to 1.0 g/cc and a thickness of from 1 to 30 mils (0.0254 to 0.762 mm).
• the multi-layered aramid papers of the invention are comprised of layers of different compositions to provide desired properties.
• the surface layer(s) provide a smooth surface and contain from 65 to 90% aramid fibrid and from 10% to 35% of aramid floc.
• the surface layer(s) constitutes from 10 to 67% of the weight of the paper.
• the substrate layer provides high tear strength. In order for the multi-layered paper to behave as a unitary structure, it is preferred that the fibrous materials at the interface between layers be intermingled.
• a layer of furnish i.e., a papermaking aqueous dispersion of floc and fibrid on an undried, previously formed layer of furnish in a paper making machine or by simultaneously depositing the layers of different composition on the screen of the paper making machine using a 2 or 3 layer hydraulic type headbox.
• the paper coming off the machine is dried and calendered, to a thickness of from 1 to 30 mils.
• the density of the layered paper is from 0.8 to 1.0 g/cc for use as labels.
• the multi-layered papers of this invention have excellent mechanical properties.
• the smooth surface retains a high degree of smoothness even after the necessary working to prepare it for end use applications. This quality is important if print clarity and color density is to be achieved.
• Aramid floc is high temperature resistant floc or short fiber cut from longer aramid fiber, such as those prepared by processes described in U.S.-A-3,063,966; 3,133,138; 3,767,756 and 3,869,430. It refers to short fibers typically having a length of 2 to 12 mm and a linear density of 1-10 decitex, made of aromatic polyamide which is non-fusible.
• the aramid fibrids can be prepared using a fibridating apparatus where a polymer solution is precipitated and sheared in a single step as described in U.S. -A-3,756,908.
• the tensile break strength of paper is determined based on ASTM method D 828-87 for "Standard Test Method for Tensile Breaking Strength of Paper and Paperboard". Specimens are 2.54 cm wide and 20.3. cm long and the jaws of the tensile testing machine are initially separated by 12.7 cm. Ten paper samples are tested in the machine direction (MD) and ten are tested in the cross direction (CD) and the values for each direction are averaged. The total of the MD and CD strengths is divided by paper density and paper basis weight to obtain the Total Break Strength.
• MD machine direction
• CD cross direction
• Thickness of papers is determined using calipers in accordance with ASTM D 374-79 (1986).
• Density of papers is determined by determining the weight per unit area of the paper (Basis Weight) in accordance with ASTM D 646-86 and dividing by the thickness.
• a two layered structure was made by combining fibrids of poly(m-phenylene isophthalamide) prepared as described in Example 1 of U.S. Pat. No. 3,756,908 and floc prepared by dry spinning poly(m-phenylene isophthalamide) from a solution containing 67% dimethyl acetamide (DMAc), 9% calcium chloride and 4% water.
• the spun filaments were flooded with an aqueous liquid and contained about 100% DMAc, 45% calcium chloride and 30-100% water based on dry polymer.
• the filaments were washed and drawn 4X in an extraction-draw process in which the chloride and DMAc contents were reduced to about 0.10% and 0.5%, respectively.
• the filaments had a denier of 2 (2.2 dtex) and typical properties were: elongation to break, 34%, and tenacity, 4.3 grams/denier (3.8 dN/tex). The filaments were then cut to floc length of 0.27 inch (0.68 cm) and slurried in water to a concentration of about 0.35%.
• Blends of fibrids and floc were separately fed to a 2-layer hydraulic type headbox which maintains each blend as a distinct layer until the slice exit where limited mixing of the layers occurs. This allows good bonding between the layers while still maintaining the individual nature of each layer.
• the formed sheet is then processed as is normally done on a fourdrinier paper machine by pressing and drying.
• the papers are dried completely using infrared heaters before being calendered at 320°C at a line speed of 30 feet per minute (9 meters per minute) using a pressure of 725 pounds per linear inch (130 kg/cm).
• the composition of the layers varied from 35 to 65% fibrid, the remainder being floc.
• the basis weight of each layer was adjusted so that the high fibrid layer (65% fibrid) ranged from 33 to 67% of the total basis weight of the final sheet.
• the total fibrid content of the test papers ranged from 45 to 55% of the sheet versus 53% for the single layer control papers (C1-1).
• Table 1 gives the basis weight of each layer and its composition.
• Layered structures, 4.0-4.5 oz/yd 2 (135.6-152.6 g/m 2 ) were produced with high fibrid layers on both top and bottom of the structure.
• the top and bottom plies (outer layers) had equal basis weight.
• the top and bottom layers contain 65% fibrid and 35% floc.
• the top layer was applied using a secondary headbox jetting the furnish onto an already formed sheet which was prepared using the headbox of Example 1.
• the control (C2-1) was a single layer paper.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Paper (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (3)

Publications (2)

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Family Applications (1)

Country Status (7)

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Family Cites Families (3)

• 1994
  • 1994-12-20 DE DE69408170T patent/DE69408170T2/de not_active Expired - Lifetime
  • 1994-12-20 WO PCT/US1994/014672 patent/WO1995017549A1/en active IP Right Grant
  • 1994-12-20 RU RU96115279A patent/RU2125131C1/ru not_active IP Right Cessation
  • 1994-12-20 ES ES95907233T patent/ES2111394T3/es not_active Expired - Lifetime
  • 1994-12-20 EP EP95907233A patent/EP0736120B1/en not_active Expired - Lifetime
  • 1994-12-20 UA UA96062487A patent/UA37254C2/ru unknown
  • 1994-12-20 JP JP51755495A patent/JP3673277B2/ja not_active Expired - Fee Related

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