Double-faced liner board

A recyclable double-faced liner bard, the board having a top layer, a medium corrugated layer, and a bottom layer, the top layer having a coating formed from an aqueous composition comprising (A) an emulsion of a curable butadience-styrene copolymer and (B) TiO.sub.2, the medium layer having a coating formed from an aqueous composition containing an emulsion of wax particles and a binder (preferably sodium alginate); and the bottom layer having a coating formed from an aqueous composition comprising about 10 to 85 percent by weight of a liquid curable styrene-butadiene copolymer (or a carboxylated copolymer) and wax.

The present invention relates to a recyclable double-faced liner board that 
has strength, resistance to penetration by water vapor, and resistance to 
penetration by water. 
BACKGROUND OF THE INVENTION 
It is desirable to provide a double-faced liner board that is waterproof 
and yet, can be easily made and recycled in contract to boards 
waterproofed by wax. 
Apparently articles (such as boxes) fabricated from double-faced liner 
boards, were coated on inside or outside surfaces to obtain waterproof 
properties. However, it was not feasible to recycle these liner board 
articles due to the wax. 
OBJECTS OF THE INVENTION 
It is an object of the present invention to provide a recyclable 
double-faced liner board, the board having a top layer, a medium 
corrugated layer, and a bottom layer, the top layer having a coating 
formed from an aqueous composition comprising (A) an emulsion of a curable 
butadience-styrene copolymer and (B) TiO.sub.2, the medium layer having a 
coating formed from an aqueous composition containing an emulsion of wax 
particles and a binder (preferably sodium alginate); and the bottom layer 
having a coating formed from an aqueous composition comprising about 10 to 
85 percent by weight of a liquid curable styrene-butadiene copolymer (or a 
carboxylated copolymer) and wax. 
It is an object of the present invention to provide a double-faced liner 
board having a top layer with a cured, waterproof coating formed from an 
aqueous composition containing a liquid, curable styrene-butadience 
copolymer and TiO.sub.2.

SUMMARY OF THE INVENTION 
The present invention provides a double-faced liner board comprising a 
double-faced liner board comprising a top layer, a medium corrugated layer 
and a bottom layer, the top layer having a coating from a coating 
composition, suitable for coating a liner board, comprising an emulsion in 
water of (A) a prepolymer of a styrene-butadiene copolymer, and (B) 
TiO.sub.2 ; the medium layer having a coating applied from an aqueous 
treating coating composition suitable for coating a middle corrugated 
layer of a double-faced liner board, the composition comprising 
(A) an emulsion of wax particles, and 
(B) a binder that is 
(1) an alkali metal alginate, or 
(2) a solvent soluble styrene/acrylic copolymer, or 
(3) a mixture of the styrene/acrylic copolymer with a water-soluble 
melamine/formaldehyde prepolymer; 
the bottom layer having a coating applied from an aqueous coating 
composition comprising (A) a latex of a styrene-butadiene copolymer or a 
latex of a carboxylated styrene-butadiene copolymer and (B) wax. 
The present invention also provides a double-faced liner board as set forth 
above in which the top layer coating is applied from a composition in 
which the following ingredients are present in approximate % by weight: 
______________________________________ 
Ingredient % by Weight 
______________________________________ 
Butadiene-styrene copolymer 
44 
emulsion (curable) 
TiO.sub.2 30 
Glycerin 12; 
______________________________________ 
the composition having a viscosity of about 9.3 to 10 (#3 Zahn) and a pH of 
about 9.8 to 10; 
the medium layer is applied from a composition, a composition containing 
wax emulsion and a binder that is a mixture of 15 to 40% by weight of the 
composition of the styrene/acrylic copolymer and about 3 to 6% by weight 
of the composition of the melamine/formaldehyde prepolymer; 
and the bottom layer is applied from an aqueous coating composition 
comprising the following ingredients in approximate percentages by weight: 
______________________________________ 
Ingredients % by Weight 
______________________________________ 
Styrene-butadiene copolymer 
70 
Sodium Alginate 20 
Carnauba Wax 5 
Polyethylene Wax 5 
______________________________________ 
the composition having a pH of about 8.5 to 9 and a viscosity of about 
12-13 (#3 Zahn). 
DETAILED DESCRIPTION OF THE INVENTION 
In the FIGURE, there is shown a double-faced liner board 1 having a top 
layer 3 with a waterproof top coating 5. Also shown is a medium corrugated 
layer 10 having a water resistant coating 15 preferably on one side 18 of 
the convoluted corrugated member 19. 
Also shown is a bottom coating 20 on the outside of a bottom layer 25. 
The top layer 3 and the bottom layer 20 are adhered to the middle layer 10 
by suitable adhesives. An acrylic starch adhesive, sold by Sonoco is a 
preferred adhesive or glue. 
The top layer coating is accomplisehd by a method of providing a water 
resistant, recyclable coating on a liner board, the method comprising 
applying to a surface of a liner board a thickness of about 0.1 to 5 mils 
of an aqueous coating composition consisting of an emulsion in water of 
(A) a curable prepolymer of a styrene-butadiene copolymer, and (B) 
TiO.sub.2. 
The top layer composition is easily applied to a substrate such as a liner 
board. The composition can be applied rapidly and the resultant coating 
formed merely by heating the composition to about 110.degree. F. to 
180.degree. F. or above to form the waterproof coating. 
The top layer composition can be used advantageously as a top coating of a 
double faced liner board, the composition being waterproof and being 
recyclable in contrast to wax coatings. The thickness of the coating is 
generally about 0.2 to 30 mils and preferably about 1 to 5 mils. 
The coatings are measured for waterproof qualities by standard ASTM tests 
and TAPP tests including the Cobb test. A lower Cobb value such as 10 to 
30 is generally preferred. 
Moisture resistant tests are descirbed in the Gotoh U.S. Pat. No. 4,117,199 
(Oji Paper Company, Ltd.). Suitable wax emulsion and meltects of coatings 
are also described. The patent is incorporated by reference. 
The amounts of the copolymer in the top layer coating composition is 
generally about 30 to 60% by wt., preferably about 40 to 50% by wt., and 
optimally, about 44 to 45% by wt. The TiO.sub.2 is generally about 20-400 
mesh and preferably 200 to 325 mesh in diameter. The amount of butadiene 
in the copolymer is generally about 25 to 40 percent by weight and 
preferably about 30 to 35 percent by weight. The optimum amount is 
generally about 32-33 percent by weight. 
The top layer coating pre-polymer can be cured or crosslinked with 
crosslinking agents such as acrylamides including N-methanol acrylamide. A 
suitable pre-polymer of a styrene-butadiene copolymer is sold by B.F. 
Goodrich to Specialty Chemical Division and distributed under the product 
name: WRL 706S1. 
The following examples illustrate the top layer coatings. 
EXAMPLE 1 
An aqueous composition was prepared by mixing the following ingredients in 
approximate percents by weight: 
______________________________________ 
Ingredients % by Weight 
______________________________________ 
Butadiene-styrene copolymer 
44 
emulsion (curable) 
TiO.sub.2 30 
Glycerin 12 
______________________________________ 
The viscosity of the composition was about 9.5 (No. 3 Zahn) and the pH was 
about 10.1. 
The composition was applied to a substrate to form, when heated, a 
waterproof coating. The coating was recyclable. 
EXAMPLE 2 
A composition was made as set forth in Example 1 except that 1 to 20% by 
weight of additional ingredients including calcium stearate, potassium 
phosphate, a wetting agent and a defoamer. 
Results similar to that of the composition and coating of Example 1 were 
obtained. 
The wax particles in the medium coating composition are generally about 0.1 
to 150 microns and preferably 1 to 100 microns in diameter. The amount of 
wax is generally about 40 to 98 percent by weight of the composition and 
preferably about 50 to 75 percent by weight, the optimum amount for most 
applications being about 65 to 75 percent by weight. A suitable wax 
particle emulsion is Aquabead 325-E.TM. wax (65 percent total paraffin 
solids). 
Suitable binders for the medium coating are an alkali metal alginate 
(preferably sodium alginate) a solvent soluble styrene/acrylic copolymer 
and a mixture of the styrene/acrylic copolymer and a water-soluble 
melamine/formaldehyde prepolymer. The binder is generally about 2 to 40 
percent by weight, preferably 10 to 35 percent by weight; and more 
preferably 22 to 32 percent by weight of the composition. A suitable 
acrylic/styrene copolymer is P-158.TM. copolymer. 
In the medium coating composition, a suitable melamine/formaldehyde 
prepolymer is Cymel 303.TM., there being cross-linking groups to cure the 
melamine/formaldehyde polymer. A preferred hexamethoxymethylmelamine 
material cross-linker is CYMEL.TM. 303 (Cyanamid). 
Generally, the viscosity of the medium coating composition at 
78.degree.-82.degree. F. is about 13.5 to 15.5 sec (#3 Zahn) and the pH is 
about 8.9 to 9.2. 
The water resistance and other properties were measured by standard ASTM or 
TAPP1 test methods including a Cobb test. The low Cobb values of 0.1 to 35 
obtained are generally under 30 and preferably under 15. 
The following illustrate aqueous medium coating compositions. 
EXAMPLE 3 
A formulation providing a waterproof coating was prepared from a 
composition as follows: 
______________________________________ 
Ingredient % by Weight 
______________________________________ 
Wax particle emulsion 
71.5 
Sodium Alginate 24 
______________________________________ 
The composition formed a coating on a liner board that was waterproof. 
EXAMPLE 
______________________________________ 
Ingredient % by Weight 
______________________________________ 
Wax particle emulsion 
68.4 
Styrene acrylic prepolymer 
26.5 
Melamine/formaldehyde prepolymer 
5.0 
______________________________________ 
The composition was applied to a substrate to form a waterproof coating. 
The bottom coating composition is easily applied to a substrate such as a 
liner board. The composition can be applied rapidly and the resultant 
coating formed merely by heating the composition to about 110.degree. F. 
to 180.degree. F. or above to form the waterproof coating. 
The composition can be used advantageously as a bottom coating of a bottom 
layer of a double-faced liner board, the composition being waterproof and 
being recyclable in contrast to wax coatings. 
The thickness of the coating is generally about 0.2 to 30 mils and 
preferably about 1 to 5 mils. 
The amounts of the copolymer in the bottom coating composition is generally 
about 30 to 85 percent by weight, preferably about 70 to 75 percent by 
weight, and optimally, about 68 to 72 percent by weight. The amount of 
butadiene in the copolymer is generally about 25 to 40 percent by weight 
and preferably about 30 to 35 percent by weight. The optimum amount is 
generally about 32-33 percent by weight. The pre-polymer or the 
carboxylated pre-polymer can be cured or crosslinked with, for instance, 
crosslinking agents such as acrylamides including N-methanol acrylamide. 
A suitable pre-polymer of a styrene-butadiene copolymer for the bottom 
composition is sold by Rhone-Poulene, Specialty Chemical Division under 
the product name: WRL 706S1. 
A suitable carboxylated styrene-butadiene latex is sold by Reichhold as 
Tylac.TM. Resin Emulsion 97757-02. 
In general, the carboxylated copolymer is made by reaction with an 
unsaturated carboxylic acid such as maleic acid or methacrylic acid. 
The alkali metal alginate is preferably sodium alginate although potassium 
and lithium can be used as the alkali metal. 
The polyethylene is a liquid (non-solid) low molecular polyethylene having 
a molecular weight of 2500 or lower--say 1000 or so. Chem Cor 260 can be 
used. 
The liquid carnauba wax helps give the resultant coating body and the wax 
is commercially available. A liquid emulsion of wax, including 
polyethylene wax, can be used in addition to the alginate or polyethylene 
as minor additives. 
The following illustrates the bottom layer coating compositions. 
EXAMPLE 5 
An aqueous coating composition was prepared by mixing the following 
ingredients in approximate percent by: 
______________________________________ 
Ingredient % by Weight 
______________________________________ 
Styrene-butadiene copolymer 
70 
(33% by weight butadiene 
emulsion -- curable) 
Sodium Alginate 20 
Carnauba Wax 5 
Polyethylene 5, 
______________________________________ 
the resulting composition had a pH of about 8.5 to 9 and a viscosity of 
about 12-13 (#3 Zahn). 
The composition was applied to a liner board substrate to form, when 
heated, a waterproof coating. The coating was recyclable. 
EXAMPLE 6 
A composition was made as in Example 5 except that a carboxylated 
styrene-butadiene (33% butadiene) copolymer was used instead of the 
styrene-butadiene copolymer. 
Substantially equivalent results were obtained. 
The Gotoh et al. U.S. Pat. No. 4,117,199 mentions a thermoplastic (uncured) 
styrene-butadiene copolymer to provide a thermoplastic polymer coating. 
The patent discloses, at its main thrust, a coating composition containing 
a styrene-methylmethacrylate copolymer latex and a wax emulsion to provide 
a low water vapor permeability, a low degree of defibering and a high 
degree of water resistance. Example 15, apparently to show a less 
desirable coating composition, discloses a mixture of a styrene (35% 
styrene) butadiene copolymer latex--100 parts by weight and 13 parts by 
weight of wax emulsion. The skilled person would be led away from an 
aqueous bottom layer composition containing 85% by weight of a 
styrene-butadiene copolymer and a 15 percent by weight of a wax emulsion 
(with sodium alginate), because Example 15 shows poor water vapor 
permeability and poor defibering compound compared to the superior main 
thrust butadiene-methyl methacrylate copolymer/wax composition.