CA1059269A - Flame resistant paperboard - Google Patents

Abstract

ABSTRACT

An aqueous solution of flame retardant and size material that can be used to treat a web of unsized cellulosic material such as paperboard or the like to impart fire resistant and water repellent properties thereto without markedly decreasing the strength of the treated material is described. The preferred composition comprises water, ammonium sulfate, ammonium phosphate and an alkyl-ketene dimer. Other combinations are described. The pH
of the solution should be between 3 and 8. The amount of the composition incorporated into the treated paper is described as are test results showing strength, water resistance and flame resistant characteristics of the resulting product. The manner of impregnation the cellu-losic material with the treating composition is also described.

Description

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This inven~ion relates to a fire retardant-water repellent treati~g co"position, to a flame and water resistant ccllulosic material prepared using such a compo-sition, and to the process for making that material. ~lore particularly, ~his invention relates to th2 treatment of a web of unsized paper with an aqueous solution of flame retardant salts and a sizing material to produce a flame resistant paper ~7ith qood sizing and strength.

B~C~GP~0~3D OF THE Ii~VELJTION

While the use of flame retardants to produce a flame resistant paper is well known, most flame retardants that can be applied to paper and maintain the sheet's strength are expensive. Many of these flame retardants will greatly reduce the paper's water resistance property.
Attempts to waterproof fibrous products previously impregnated with fire retardant salts by treating the sheet with a water repellent in aqueous suspension tend to leach the fire retardant from the fabric. If, on the other hand, the paper is first i~pregnated with a water repellent, this m.ay prevent sorption of the fire retardant salts by treatment with an aqueous bath containing the fire retardant sal.s. In addition, there is a tendency for the water repellert to be leached from the paper by treatment with the aqueous bath. Treating fibrous materials with a single solution of known flame retardants and sizing material, such as rosin size, has also failed to result in a product having satisfactory water resistant properties.

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~ tterlpts to ovcrcom~ th~se deficiencies and to produc~ a flame and wat~r resistant paper by treating an unsizcd paper ~lith flame rctardants and sizing materials have not prov~d satisfactory. U.S. patent ~o. 2,867,549 to Outterson disclo~es the p~oduction of a flameproof paper by impregnating partially sized paper with a rosin suspension containing water-soluble flameproofing salts having a maxi-m~ pH of about 7 and then drying the paper. The Outterson patent states that the use of his process to treat unsized paper prcduces a paper that is subject to afterslow, and therefore continues to smolder, and thus does not meet fire-proofing specifications.
U.S. patent No. 2,986,478 to Outterson discloses impregnating sized or unsized paper with an aqueous solution of water-soluble flameproofing salts containing finely divided particles of a rosin-petroleum wax mixture in stable emulsion and then drying the paper. While this process is said to improve the flame resistance and water resistance properties of the paper, it has been found that the use of a rosin-wax complex as a sizing agent results in a signifi-cant reduction in the sheet's dry strength.
Sun Chemical Corporation's product data sheet on the sizing agent sold under the trademark Sunsize 226-B
recommends that product as a water repellent "applied in conjunction with a ... flame retardant" and states that with "most flame retardants" it "showed good compatibility as evidenced by no precipitations or separations for at least 24 hours," but there is no disclosure of how such a co~?osi-tion is to bc used, or the rcsults achieved if used, or ~he conditions under which such a composition should be used.

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It is tilerefore a principal objcct of the prescnt invention to produce a flame and water resistant paper having good sheet strength.
It is a further object of the invention to provide an inexpensive process for making flame resistant paper with good sizing and sheet strength.
Another object of the invention is to provide a single inexpensive water-based composition that can be used to treat unsized fibrous material and produce a flame resistant, ~ater resistant material with good sheet strength.
It is another object of the invention to impart a substantial degree of fire and water resistance to a highly absorbent unsized paper by treating the paper with a single, inexpensive water-based composition.

SU~ ~ Y OF TH~ I~VE~TION

Broadly, the invention comprises i~pregnating an unsized paper with an aaueous solution of fla~e retardants and size material to produce a flameproof and water resist-ant paper without a significant loss in sheet strength.
The flame retardant used is selected from the group consist-ing of a~monium phosphate (dibasic), a mixture of am~.onium sulfate and am~onium phosphate, a mixture of ammonium sulfate and an inorganic nitrogen-containing aluminum phosphate, and a mixture of ammonium phosphate and ammonium brorllide. The sizing agent used is selected from the group consisting of an al~yl~etene dimer and a stearic anhydride.
The p}~ of the treating solution should be main-tained between about 3 and 8. Paper treated with the flæme retardant/sizing solution of my invention, but wherein the ~L~)5~f~
pH is above 8, has no flame resistance and/or poor sizing.
Where the pl~ is below about 3, the resulting product has satisfactory flame resistance and sizing, but there is a marked loss in sheet strength.

5 DETAILED DESC~IPTION OF THE INVENTION

According to the invention, a novel composition is provided which can be incorporated as a single ingredi-ent into unsized cellulosic material, such as paper or linerboard, to impart superior fire resistant and water repellent properties to the cellulosic material with~ut markedly decreasing the strength of the material. The composition has a high resistance to leaching out because of the sheet's high water resistance property. The preferred fire retardant-sizing composition of the present invention comprises an aqueous solution of ammonium sulfate, ammonium phosphate (dibasic), and an alkylketene dimer sizing agent.
Fire retardant salts that are suitable for prac-ticing the invention include ammonium phosphate (dibasic), a mixture of ammonium sulfate and ammonium phosphate, a mix-ture of ammonium sulfate and an inorganic nitrogen containingaluminum phosphate, and a mixture of ammonium phosphate and ammonium bromide. One such inorganic nitrogen containing aluminum phosphate is sold by Freeport Minerals Company under the trademar~ PA-l. I prefer to use a mixture of ammonium sulfate and ammonium phosphate. When only ammonium sulfate is used as the flame retardant, the treated paper is subject to afterglow and therefore does no~ meet flameproof specifications. The addition to ammoni~m sulfate of a phosphorous compound, such as ammonium phospilate or PA-l, reduces the afterglow~ A mixture of ammonium phos-phate and ammonium bromide is satisfactory but considerably more expensive than the mixture of ammonium sulfate and ammonium phosphate. The total amount of fire retardants used in the water-based treating composition is between about 10 and 30 weight percent.
Suitable sizing materials include an alkylketene dimer such as Hercules Incorporated's product bearing the trademark Aquapel 360C, and a stearic anhydride such as American Cyanamid Corporation's product bearing the trade-mar~ Cyanasize 400. The total amount of sizing material used in the water-based treating compositioA is bet~een about 0.30 and 0.6 weight percent based on the neat paper sheet.
~he amount of the fire retardant-sizing composi-tion of this invention that should be incorporated into the paper to provide a fire resistant and water repellent paper having good strength characteristics will vary from about 7 to 14 pounds per 1000 square feet of treated paper. The ~;
20 actual weight percent of the composition incorporated into ~ ~ .
the paper will depend, in part, on the type of paper being produced and the concentration of the treating solution used. A paper having a basis weight of 83.0 pounds per 1000 square feet and a salt-size pickup of 13.5 pounds per 25 1000 square feet has been found to have a slightly lower ~ -strength than a paper having a basis weight of 76.4 pounds per 1000 square feet and a salt-size pickup of 7 pounds per 1000 square feet. 8etween about 9 and 16 weight percen~, based on the basis weight of the unsized paper, of the fire .

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retardant, water rcpellcnt composition should be incorporated in the paper product. For a paper product having a very light basis wei~ht, for example tissue paper, the amount of the composition incorporated in the paper may exceed S 16 weight percent.
The pH of the aqueous treating composition is of importance in imparting the desired fire retardancy and water resistance to the paper. If the pH is too low, the resulting product will have low sheet strength. If the pH is too high, the product will have no flame resistance and/or poor sizing. I have found that the pH of the treat-ing composition should be maintaine~ between about 3 and 8.
The pH can be adjusted, for example, by the addition of sulfuric or hydrochloric acid and sodium hydxoxide.
The following compositions were prepared:

Pounds per 1000 lb. Batch Example 1 , Ammonium sulfate 130 ~ nonium phosphate 20 Aquapel* 5 Water 845 -- E mple 2 Ammonium sulfate 100 P~-l 50 Aquapel* 4 Water 846 Example 3 Ammonium sulfate 180 Aquapcl* 4 Watcr 816 Examplc 4 ~mmonium sulfate 130 Ammonium phos~hate 20 Cyan~ c 400 4 Watcr 846 *Trade Marks -e . ~
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{3 Pounds per 1000 lb. Batch Example 5 Ammonium sulfate 130 Ammonium phos~hate 20 Cyanasize 400 4 Water 846 Example 6 Ammonium sulfate 130 PA-l * 20 Cyanasize 400 4 Water 846 Example 7 Ammonium sulfate 129 : -Ammonium* phosphate 20 Aquapel 3 Water 848 Example 8 : :
Ammonium sulfate 258 Ammonium phosphate 37 ~
Aquapel* 5.8 ~ .
Water 699.2 :~

Example 9 Ammonium sulfate 129 Ammonium* phosphate 20 Aquapel 3 Water 848 Hand samples were made from prerefined primary liner-board stock containing 2 pounds of a wet strength agent per ton of stock using recirculating white water. The wet strength agent used was a product sold by Hercules Incorporated bearing the trademark Rymene 557. That product comprises the reaction product of polyamide and epichlorohydrin. Other wet strength agents could be used. Standard TAPPI procedure was used for sheetmaking, drying and conditioning. These unsized sheets were then impregnated with the aqueous solutions of flame retardant and size *Trade Marks material of L::ar~pl~s 1 thrc-ugh 3 by dip and wrinc3 mcthod a~ roo~ temF~r.ture ancl then dried on a felted drum dryer at 225~F. Ccntrol hands~eets t~ere internally sized with 4 pounds of rosin size per tOh, 2 pounds of Kymene 557 per ton, and adjusted tQ 5.5 pEI with alu~ to simulate regular linerboard stoc~.
The fl~e resistance, water resistance and stren~th charac.eristics of the treated handsheets are shown in Table 1. Cor~.parative data for the control hand~
sheets are also shown.

Table I

Contxol Ex. 1 Ex. 2 Ex. 3 Chemical Cost $/ton 2.26 23.38 41.90 18.9S

Linerboard basis wt.100.7 117.1 114.0 120.1 ~/3000 sa. ft.) Caliper, 0.001 in. 11.0 12.1 12.9 12.6 Cobb size, g.~sa.~. (2 min.) 49 58 58 67 Mullen, points (~ur~ting95 97 94 104 stren~th) Tear, grams 261 278 283 256 Flame resistance, T~PI
Char leng.h, lnchesBurn 0.3 0.3 0.5 Afterglotl, seconds Complete 0.6 0.7 16.3 ~n ex2~ination of the data fro~ Table I shows that the best combination to produce an economical flame resistant linerboard with good water resistance and strength is that shown in Exa~ples 1 and 2. The flar~e resistant paper of Exa~ples 1 and 2 had strength equal to or better than the rosin sized control sheets of the sa~e basis weight.
The use of ~oniu~ sulfate as the sole flar~e retardant (~a~.?le 3) produces an unsatisfactory after~Jlo~

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35~ 9 The use of ammonium phosphate as the sole flame retardant or the use of ammonium bromide results in exces-sive cost.
Additional hand samples, as described above, were impregnated with the aqueous solution of Examples 4 through 6 by the dip and wring method However, the pH of the treating composition was adjusted and the results ob-tained were as shown in Table II. Comparative data for control handsheets made as described above are also pre-sented.

Table II

Control Ex. 4 Ex. 5 Ex 6 Linerboard basis wt. 97.0 N.T.115.9 116.6 (~/3000 sq. ft.) Caliper, 0.001 in. 11.5 N.T. 12.6 12.5 pH ~adjusted with HCl) 4 8.3 6.3 6.0 Cobb size, g./sq.m. (2 min.) 41 lS6 61 53 Mullen, points (Bursting83 N.T. 94 92 strength) Tear, grams 267 N.T. 274 282 Flame resistance, T~PPI
- Char length, inchesBurn 0.3 0.3 0.2 Afterglow, seconds Complete 0.2 0.4 0.4 - The tests made on the sheets treated with the compositions of Examples 4 through 6 show that flame and water resistant paper may be made using stearic anhydride (Cyanasize 400) as the sizing material without a loss in sheet strength. However, the water resistance of Example 4, as indicated by Cobb size, is unsatisfactory. The pH of Example 4 was in excess of 8.

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~ .dditional tests werc run in which a continuous web of unsized linerboard was impregnated with the composi-tions of E~c~mples 7 throu~h 9, followed by conventional drying techniques. The treated linerboard was then tested for fl2~e resistanc~, water resistance and strength, with the results shown in Table III.

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~)5~ '3 Stren~th and sizing properties of treated impregnating Kraft sheets (Exs. 7, 8) were comparable to those of untreated, water-finish 69-pound linexboards.
This indicates that the treated impregnating Kraft sheet may be used for the base sheet for making flame resistant linerboard. Treated corrugating medium (Example 9) showed good flame resistance, good water resistance and good sheet strength.
The test results for Examples 7 and 8 show that a flame retardan~ salt and size pickup of about 7 pounds per thousand square feet results in slightly higher strength characteristics than achieved with a pickup of about 13 pounds per thousand square feet.
Additional hand sample tests were conducted in which unsized linerboard sheets made from linerboard pulp were impregnated with a solution having the following composition:

Pounds per 1000 lb. Batch Ammonium sulfate 90 Ammonium phosphate 14 Al~yl~etene dimer 3.48 Water 892.52 The alkylketene dimer used was a water solution (6 percent solids) of Hercules Incorporated's Aquapel size.
Fifty-eight pounds of this water solution were added to the batch (58 x .06 = 3.48 pounds). The p}i of the solution was adjusted with H2SO4 and NaOH to a different level for each of the series of tests shown in Table IV. The flame resistance, water resistance and strength characteristics of the treated specimens are shown in Table IV. Compara-tive data for the control specimen are also shown.

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A sheet with no flame resistance and poor sizing resulted when the p~ of the treating solution was 10.1 or above ~see Examples 19 to 22). The flame resistant sheet produced when the pH of the treating solution was below 3 S had very little strength (see Examples 10 and 11). For best results the pH of the treating solution should be maintained between about 3 and 8.
The terms and expressions which have been em-ployed here are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

Claims (18)

WHAT IS CLAIMED IS:

1. A fire retardant, water repellent composition adapted to be applied in aqueous form to cellulosic sheet material, said composition comprising a flame retardant selected from the group consisting of diammonium phosphate, a mixture of ammonium sulfate and di-ammonium phosphate, a mixture of ammonium sulfate and an in-organic nitrogen-containing aluminum phosphate, and a mixture of diammonium phosphate and ammonium bromide, a sizing agent selected from the group consisting of an alkylketene dimer and a stearic anhydride, and the balance water, said composition having a pH of between about 3 and 8.

2. The composition of claim 1 wherein the weight of said flame retardant is between about 10 and 30 percent of said composition and the weight of said sizing agent is between about 0.3 and 0.6 percent of said composition.

3. The composition of claim 1 wherein the flame retardant comprises a mixture of ammonium sulfate and diammonium phosphate.

4. The composition of claim 1 wherein the flame retardant comprises a mixture of ammonium sulfate and diammonium phosphate and wherein the sizing agent comprises an alkylketene dimer.

5. The composition of claim 4 comprising about 9 weight percent ammonium sulfate, about 1.4 weight percent di-ammonium phosphate, about 0.35 weight percent alkylketene dimer and the balance water.

6. A paper product in which is incorporated between about 9 and 16 weight percent, based on the basis weight of the paper, of the fire retardant, water repellent composition of claim 1.

7. The paper product of claim 6 wherein the said product is linerboard and the amount of fire retardant, water repellent incorporated into said paper is about 9 weight percent based on the basis weight of said linerboard.

8. A paper product in which is incorporated about 9 weight percent, based on the basis weight of the paper, of the fire retardant, water repellent composition of claim 4.

9. A process for the treatment of cellulosic sheet material such as paper to render the same substantially flame and water resistant which comprises forming a water-based composition comprising a flame retardant and a sizing agent, said flame retardant being selected from the group consisting of diammonium phosphate, a mixture of ammonium sulfate and diammonium phosphate, a mixture of ammonium sulfate and an inorganic nitrogen-containing aluminum phosphate, and a mixture of diammonium phosphate and ammonium bromide, said sizing agent being selected from the group con-sisting of an alkylketene dimer and a stearic anhydride, adjusting the pH of said water-based composition to between about 3 and 8, impregnating an unsized web of said cellulosic sheet material with said water-based composition in an amount suffi-cient to impart substantial flame and water resistance to said paper, and thereafter drying the impregnated sheet material, whereby the dried impregnated sheet comprises between about 9 and 16 weight percent, based on the basis weight of said sheet material, of said flame retardant and sizing agent.

10. The process of claim 9 wherein the weight of said flame retardant is between about 10 and 20 percent of said composition, the weight of said sizing agent is between about 0.3 and 0.6 percent of said composition, and the balance is water.

11. The process of claim 9 wherein the flame retardant comprises a mixture of ammonium sulfate and diammonium phosphate and the sizing agent comprises an alkylketene dimer.

12. The process of claim 12 wherein the flame retardant comprises about 9 weight percent ammonium sulfate, about 1.4 weight percent diammonium phosphate, about 0.35 weight percent alkylketene dimer and the balance water.

13. The process of claim 9 wherein the sizing agent is alkylketene dimer.

14. The process of claim 9 wherein the unsized web of cellulosic sheet material is impregnated by dipping the sheet material into the solution.

15. The process of claim 10 wherein the sizing agent is alkylketene dimer.

16. The composition of claim 1 wherein the sizing agent is alkylketene dimer.

17. The composition of claim 2 wherein the sizing agent is alkylketene dimer.

18. The paper product of claim 6 wherein the sizing agent is alkylketene dimer.