Classifications

• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/14—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing calcium sulfate cements
• • E—FIXED CONSTRUCTIONS
  • E04—BUILDING
  • E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
  • E04C2/00—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels
  • E04C2/02—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials
  • E04C2/04—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials of concrete or other stone-like material; of asbestos cement; of cement and other mineral fibres
  • E04C2/043—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials of concrete or other stone-like material; of asbestos cement; of cement and other mineral fibres of plaster
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00612—Uses not provided for elsewhere in C04B2111/00 as one or more layers of a layered structure
  • C04B2111/0062—Gypsum-paper board like materials

Definitions

• This invention relates to a method of manufacturing wallboard having a protective decorative surface coating on a paper cover sheet over a set cementitious core. It relates particularly to a method of forming board with a wet set-gypsum core, applying a wet decorative coating of low permeability to the board, rapidly increasing the permeability of the coated cover sheet and then quickly drying the board.
• a face cover sheet is passed face down over a work surface, an aqueous slurry of calcined gypsum is deposited upon the paper, a back sheet is added over the slurry, the edges of the face sheet are folded up and secured to the back sheet and the board formed to desired dimensions.
• the board is supported until the core sets; it is then cut to size and passed through a kiln to drive the excess moisture from the core.
• the paper cover sheets are manufactured with a carefully controlled porosity which may be determined by methods such as TAPPI T460 m-49, or ASTM D726- 58.
• the test method determines the number of seconds required to pass 100 ml. of air through 1 sq. inch of the paper; thus a high value indicates a tight paper having few and/or small pores as compared with a loose or highly permeable paper.
• Paper for boardmaking operations usually will pass 100 ml. of air in 250 seconds but paper requiring somewhat longer time, about 500 seconds, can be used in special circumstances or with additional caution to prevent blows.
• Gypsum board obviously is not a homogeneous material and the problems of producing it are unique to this product.
• the bond between the paper cover and the set gypsum core may be extremely weak so that even at normal rates of drying, an irregularity in core formation may deteriorate an already weak bond so that during the drying step, the moisture driven from the core can blow the cover sheets free of the core.
• a jam may occur and the loose paper cover sheets, separated from the core, sometimes catch fire and further disrupt the drying operation.
• a process for manufacturing a decorated wallboard had long been sought but it had previously been thought that the application of a wet decorative coating to only one side of the wet board would produce a warping tendency and accompanying kiln jams during the drying operation.
• a previously decorated sheet has been laminated to the paper cover of 3,507,684 Patented Apr. 21, 1970 ice a dried board as a separate operation. This is an expensive procedure because of the extra labor involved in handling the board for the extra process step.
• an aqueous coating is applied to a porous paper cover sheet of a wet gypsum board as it proceeds along the board machine.
• the coating which is preferably applied to the upper surface of the board and may contain sand grains to assist the development of a textured surface, initially renders the coated cover sheet substantially non-porous. Re moval of moisture from the coating by wicking into the underlying paper sheet or by evaporation, desirably at a temperature about 250 F. and preferably about 450 F.
• the coating comprises a polyvinyl acetate emulsion as the binder ingredient andmay use an acrylic emulsion to achieve a higher viscosity where such is indicated as for a textured finish.
• the amount of material applied may be as low as 5 lbs. of solids per thousand square feet of board although coverage may be marginal at this low rate. Smooth coatings in excess of about ten pounds per thousand square feet tend to have low permeability, but textured coatings may employ about lbs. or more per thousand square feet to achieve the desired surface effect and yet develop adequate permeability.
• a suitable polyvinyl acetate is a homopolymer emulsion with a large particle size (0.5-3 microns) such as that sold by Borden Chemical Company under the designation Polyco 117-H.
• the clay was a water washed white clay with a particle size larger than about 0.7 micron and preferably with a size of about 4.8 microns.
• the clay with larger particles tended to produce a more porous coating.
• Formula A is simpler but its viscosity was somewhat sentitive to pH changes.
• the acrylic emulsion thickener of Formula B provided more stability.
• a suitable acrylic thickner was Acrysol ASE 60, an acid-containing, cross linked acrylic emulsion copolymer manufactured by Rohm and Haas. The viscosity of the coating material was adjusted by neutralizing the batch with the 10 parts of triethanolamine which gave a viscosity of 220 to 250 Brabender units (measured with the paddle) or 120 to 124 ku.
• Viscosity of the coating desirably is from 190 to 260 Brabender but for a sharper texture it may be adjusted to more than 400.
• Cellulosic thickners such as methyl cellulose, were unsuitable.
• a suitable wetting and dispersing agent was an anionic polymer type dispersing agent, the sodium salt of a polymeric carboxylic acid sold by Rohm and Haas under the mark Tamol 731.
• a suitable defoamer was Nopco NDW, a nonionic liquid product sold by Nopco Chemical Co.
• the sand was a white silica sand with the following approximate particles size as measured by U.S. Standard Sieves.
• a coating prepared according to Formula B was applied to the back (upper) paper with a coating roll at a rate of 45-50 pounds of solids per 1000 square feet of board. By the time the board was cut to length the coating had lost its gloss but was still soft.
• the coated board was then passed into a dryer which had three zones. In the entrance zone which occupied about one quarter of the total length the air temperature was about 485 F., in the middle zone (about one half 4 the drier length) it was 480-500 F. and in the outlet zone it was 255-260 F. Drying took about 45 minutes for this board but thicker board may take up to minutes. In some instances it was desirable to pin perforate the uncoated paper sheet with a porcupine roll to aid drying.
• the dried coating was so water and abrasion resistant that it withstood a standard washability test of over 500 strokes on a Gardner Heavy Duty Wear Tester with an estimated removal of less than 1% of the coating material in the scrubbed area.
• EXAMPLE 1 Samples of coating materials according to Formulas A and B (for some tests the sand was omitted) were prepared and applied to board paper with a wire wound Meyer coating rod. All of the coatings applied without sand produced a smooth flat white finish on the paper. Two base paper materials were used, one each for samples 1 and 2, and 21 to 26. Each sample of coated paper was cut into halves, one of which was dried in an oven at 300 F. for 15 minutes while the other was dried in a room maintained at 70 F. and 50% relative humidity. The dried coated papers were weighed to determine the weight of dry solids applied. The porosity of the dried samples was measured using a soft rubber gasket to insure an adequate seal between the sample and the apparatus. Results are shown in Table II. The slight differences in porosity between the air-dried and oven-dried samples are not significant when determinations are performed on so few samples because of the low sensitivity of the test method.
• sample 1 The effect of sand on the permeability of a coated paper is illustrated by sample 1 in which instance the coating was prepared according to Formula A, and by sample 25 coated with material according to Formula B. Note that for sample 25 a weight of coating material was applied which was nearly ten times as great as that applied to sample 22 with but a moderate, if any, increase in resistance to air passage.
• Thickness of the dried coating was determined microscopically on samples 21 and 25.
• the coated paper was in one instance cut with a shears, which undoubtedly produced some compression; a second specimen was sliced transversely with a knife, which possibly produced a small amount of expansion. These samples were then mounted on edge on a microscope stage and the film thickness determined optically. Results are shown in Table III. The value shown for sample 2.5 is the coating thickness generally between sand particles. Where the coating included sand particles, the total thickness was 800 to 1200 microns.
• Example 2 A portion of the water may be removed from the coating by wicking the moisture into the paper substrate if the paper has not been highly sized. Development of permeability of the coated paper by this mechanism is illustrated in Example 2.
• EXAMPLE 2 A coating prepared according to Formula B (but without the sand) was applied with sufiicient thickness to deposit from about 6 to 8 pounds of solid per thousand square feet over a regular manila board paper having a porosity of 154 seconds per 100 mls. of air. The paper with the wet coating was immediately placed in the porosity measuring apparatus and a determination of its porosity begun. The quantity of air passed through the sample was recorded at one minute intervals and the increment for each one minute period noted. In this procedure there was virtually no opportunity for water to evaporate from the coating.
• the amount of moisture which a paper sheet can absorb without reducing its permeability is quite limited.
• the permeability of the face paper of sample 26 (see Table II) was sharply reduced when its moisture content was in excess of the air dry condition by more than 15 pounds per 1000 square feet. This paper had a basis weight of 70 pounds per 1000 square feet.
• the moisture in the paper exceeded this amount and no air had passed through the sheet in a period of 45 minutes after which time the test was terminated.
• permeability was obtained by evaporative removal of the water. The effect of oven drying coated paper was shown in Table II.
• thermocouples mounted in the middle of the gypsum core, at the interface between the core and a paper cover sheet and against the outer paper surface. This board was inserted into a kiln in which drying gas at 500 F. was circulated over the surface of the board at a rate of 50 pounds per minute per square foot of board. The temperatures indicated by the thermocouples in response to this drying treatment are shown in Table V.
• the improvement comprising the steps of applying to the surface of a cover sheet an aqueous decorative textured coating in an amount sufiicient to deposit from about 5 pounds to about 75 pounds of solids per thousand square feet of board area whereby the coated sheet becomes substantially less permeable, absorbing a portion of the moisture of the coating into the paper and evaporating moisture from the coating to render the coated sheet not substantially less permeable than the uncoated paper and subsequently passing the coated board into a gaseous atmosphere above the boiling point of water to drive moisture from the core and through the coated sheet.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Structural Engineering (AREA)
• Ceramic Engineering (AREA)
• Architecture (AREA)
• Inorganic Chemistry (AREA)
• Materials Engineering (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Organic Chemistry (AREA)
• Civil Engineering (AREA)
• Laminated Bodies (AREA)
• Paper (AREA)
• Producing Shaped Articles From Materials (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24838995

Family Applications (1)

Country Status (11)

Cited By (7)

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Citations (5)

Family Cites Families (2)

• 1968
  • 1968-02-20 US US706775A patent/US3507684A/en not_active Expired - Lifetime
• 1969
  • 1969-01-29 GB GB1250411D patent/GB1250411A/en not_active Expired
  • 1969-02-04 IE IE145/69A patent/IE32948B1/xx unknown
  • 1969-02-14 NL NL6902404A patent/NL6902404A/xx unknown
  • 1969-02-18 LU LU58023D patent/LU58023A1/xx unknown
  • 1969-02-19 NO NO00686/69A patent/NO126315B/no unknown
  • 1969-02-19 DK DK92269AA patent/DK126307B/da unknown
  • 1969-02-19 BE BE728651D patent/BE728651A/xx unknown
  • 1969-02-19 DE DE19691908286 patent/DE1908286B2/de not_active Withdrawn
  • 1969-02-20 FR FR696904283A patent/FR2002274B1/fr not_active Expired
  • 1969-02-20 JP JP44012193A patent/JPS4947013B1/ja active Pending

Patent Citations (5)

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