CA1089605A - Flame retarding compositions for cellulosic boards - Google Patents

Abstract

Abstract of the Invention Synergistically performing flame retarding composi-tions are provided for cellulosic boards, such as hardboards, particleboards and fiberboards. The synergistically perform-ing compositions consist of three components, namely, an aluminous material, a naturally occurring borate-containing mineral and a phosphate or sulfate salt. Incorporation of these compositions in the boards allows consistent production of flame-retarded products with a Class I or better fire rating.

Description

1 In recent times, more and more interest has focused on flame retardant materials for the construction of residen-tial, commercial and ind~strial buildings. Consequently, great em~hasis is being placed on compositions which are capable of imparting the desired flame retardancy to building materials, such as cellulosic boards, without, however,-dete-riorating the essential physical properties of the final produc~sO :~
~ithin the last few years, several flame retarding compositions have been suggested for cellulosic boards. Thus, in U.S. 4,008,214 (February 15, 1977), hard and particle-boards have been rendered flam~ retardant by incorporating in these boards a synergisticall~ acting composition containing alumina hydrate in combination with a melamine-formaldehyde phosphate, urea-formaldeh~de phosphate or dicyanamide-form-aldehyde phosphate.
In German Application (Offenlegungsschrift)

2,627,682 - Moore et al, published on Ja~uary 20, 1977, cel-lulosic products, such as hardboards, are rendered flame 20 retardant by incorporation in the boards a com~osition con- ~ ;
sisting of alumina hydrate and a boron source. As boron source B203, H3BO3 and ammonium borates are described. In this published application, reference is also made to com-position~ containing mixtures of alumina hydrate with mono~
25 ammonium phosphate or diammonium phosphate. These composi-tions have been found to be inferior in their flame-retarding e~ects for cellulosic boards~
In U.S. Patent 3,865,760 (February 11, 1975) -Pitts et al, rubber or plastic compositions are rendered ~, .

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l flame retardant by incorporation of an agent consisting of a naturally occurring boron-containing mineral, such as cole-manite, either alone or in combination with alumina hydrate.
In our co-pending U,S. application, Serial Number 780,725, filed March 24, 1977, now U.S. Patent No. 4,076,580 a synergistically acting ulexite-alumina hydrate flame re-tarding co~position is described, being capable of imparting Class I fire rating to cellulosic boards. By careful control of the loading of this composition, a flame-retarded product 10 is obtained which con~orms to Class I fire rating, while ~ -exhibiting suitable mechanical properties.
It has now been discovered that significantly improved flame retardancy can be imparted to cellulosic boards, while simultaneously retaining the important physical proper-ties of these boards, by using a three-com~onent flame-retar-ding agent consisting of a source of A1203 xH20, a naturally occurring boron-containing mineral, and an inorganic phosphate or sulfate containing cosynergist, to be defined in detail hereafter.
The instant flame-retarding com~osition consistent-ly provides Class I fire ratings or better, without genera-tion of undesirable a~terglow, by the unexpected interaction of the components.
Fla~e-retarded cellulosic boards are provided by 25 incorporating in the boards a flame-retarding agent consist-ing of (A) a source of A1203 xH20, (B) a naturally occurring boron-containing mineral and (C) an inorganic sulfate or phosphate-containing cosynergist; the source of A1203 xH20 being selected from the group of A1203~xH20, where x is in 30 the range of about 0.5-3.0 and bauxite, the boron-containing :, :

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~ ~96 1 mineral is ulexite, colemanite and mixtures thereof; whil~
the inorganic cosynergist is from the group of salts charac-terized by the general formulae MmHS04, Mm(HP04)n, Mm(H2P04)n, Mm(HP207)n, where M is Na, K, NH4, Mg and Al and m depends on the valency of M; Ca(H2P04)2, XmH4_mP207, or K; Na3P04, K3P04 and the polymeric phosphates of Na and K. In the cellulosic boards, the quantity of flame-retarding agent is kept within the range of about 20-60% by weight of the flame-retarded boards, preferably between about 35-50%
by weight of the total weight of the board. In the flame-retarding agent, the weight ratios of components A:B:C are kept within the range of about 10-90%:5-85%:5-40%.
This invention relates to the flame retarding of cellulosic boards. More particularly, it concerns novel, synergistically performing three-component flEme-retarding agents capable of imparting Class I or better fire rating ~ ~
to cellulosic ~oards. -For the purposes of the invention, the term "cellu-losic board" encom~asses boards, such as hardboards, parti-cleboards and ~iberboards, which are made of cellulosicmaterials of the group of wood fibers, sawdust, wood particles or chips, bagasse, cellulose ibers of all grades, The expressions ~'aluminous" material or a "source of A1203 xH20" refer to materials containing A1203 xH20, 25 where x îs in the range of about 0.5-3.0 and include bauxite -of whatever source. Thus, the aluminous materials usable ~ -for the purposes of the instant invention range from bauxite, containing at least 45% by weight A1203 (the weight being based on bauxite ignited for 1 hour at 1000C), to A12033H20, 30 c~mmonly referred to as "alumina hydrate", "hydrated alumina"
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1 or "aluminium hydroxide" including mixtures of bauxite and alumina hydrates. Composîtîons of typical bauxites are shown in Table I.

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', ' ' " ''' ' ', .. ' . . ;'; "' ': .: ' ,' ` ,.;' :' ', .'''. '' ~,, '."';, ~','.:' '.' ' ~, ~ ~9 6 ~ 5 1 The boron-containing, naturally occurring mineral employed by the instant invention as one of the components o~ the flame-retarding agent is a calcium borate and includes as the preferred minerals ulexite, having the generally accepted formula of Na.CaB509.8H20, sometimes also defined as Na20.2CaO.16H20; and colemanite, having the formula of Ca2B601l.5H20; or mixtures of these, a naturally occurring mixture being Gerstley borate~ Other naturally occurring calcium-boron containing minerals, although rarer in appear-ance, are also included, such as pandermite, meyerhofferiteand inyoite.
The third component of the three-component flame- -retarding agent, also referred to in the instant specfica-tion as "cosynergist", is a phosphate or sulfate-containing inorganic salt. Suitable cosynergists for the purposes of the invention are characterized by the general formulae:
MmHS4' Mm(HP4)n' ~ (H2P4)n~ where M is Na~ K9 NH4 Mg and Al and n depends on the valency of M; Ca(H2P04)2, ~H4 mP207 where X is Na, K, Mg and NH4 and m depends on the valency of X; Na3P04 and the polymeric phosphates of Na and K, such as Na or K-hexametaphosphates and also K3PO40 The expression "Class I fire rating", as used herein, refers to a flame spread defined in ASTM E 84-76a method for building materials as measured in a 25-foot (7.62 m) --tunnel. In the instant case, flame spread measurements werecarried out in a 2-foot (0.61 m) inclined tunnel substan~
tially equivalent to the tunnel described by Levy in the Journal o Cellular Plastics, pp. 168-173 (April 1967).
In that article, a correlation is presented between the results obtained in the 2-foot tunnel and the 25-foot tunnel.
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1 Although in the following description the flame-retarding agent of the instant invention is employed as a ~;
mixture of the three or more individual components, it is to be understood that it is not necessary to premix the components prior to incorporation in the cellulosic boards.
It is entirely possible to premix only two of the components of the ~lame-retarding agent and to add the remaining com-ponent to the board, or if desired, the components of the agent can be individually incorporated in the cellulosic 10 boards during the board manuacturing process. In any event, whether the agent is added to the board forming process in a premixed form or as individual components, care is to be taken to obtain substantially uniform distribution within the cellulosic board forming materials to obtain the desired 15 optimum fl~me-retarding effectO
The quantity of flame-retarding agent to be incor-porated in the cellulosic boards depends on the fl~me-retar-ding effect to be achieved. Thus, it has been discovered that in order to obtain flame spreads corresponding to Clas 9 20 I fire rating, the cellulosic board should contain from about 35% to about 50% by weight flame-retarding agent based on the weight of the flame-retarded board, regardless of the type o~ cosynergist and/or aluminous material utiliæed. Naturally, if one desires lower loadings, for example, in the range of 25 about 25-35%, with correspondingly increasing flammability, -such as de~ined for Class II fire-rated materials, the instant flame-retarding agent can be used in lower quantities, without, however, departing from the scope and spirit of the in~ention.
Higher quantitie~ than indica~ed above can also be , ~':

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~ 39ti~5 1 added to the cellulosic boards; however, the possible increase of flame retardancy of the boards can be detrimentally offset by a decrease in strength, undersirable appearance and poten-tial processing problems.
The instant flame-retarding composition as mentioned above is a mixture of components A, B and C. Component A, -~
which is an aluminous material, as defined hereinabo~e, is generally present in the mi~ture in an amount equivalent to about 10% to about 90% by weight of the mixture. Com~onent B, consisting of ulexite, colemanite and their mixtures, is usually employed in an ~mount corresponding to about 5% to about 85% of the total weight of the flame-retarding agent.
Component C, selected from the group of inorganic sulfates and phosphates, is present in the agent in an amount ranging 15 from about 5% to about 40% by weight of the mixture.
For optimum results in terms of imparting flame -retardancy to cellulosic boards, the weight ratios o~ A:B:C ~ ~
in the flame-retarding mixture are generally kept within the -. . -following limits: 40-75 : 20-60 : 5-30.
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In~orporation of the instant flame-retarding c~m~
position in the cellulosic boards, whether as a mixture or by sequential addition of the individual components, can ~
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proceed in sevPral ways depending on the type o~ board to be produced and also on the t~pe o board manufacturing method 25 selected. Two main types of manufacturing processes are -known to the celiulosic board producing trade and these can be designated as the "dry" process and the "wet" process.
Although there may be variations within each of these methods - as practiced by dlfferent plants, the principle of manufac- ;
30 ture for each of the~e main types remains essentially the '" .' .

- ; , , . ,; .,:, ~8~605 1 same regardless of the plant location. Both the "dry" and the "wet" processes have been extensively described in the art and the following U.S. patents provide some insight for these methods. Thus, U.S. 3,966,540 (Selander et al) provides a description of the "dry" process, while U.S. 3,873,662 (Cartlidge et al) concerns the production of particleboards by the "wet" method.
The instant synergistically acting flame-retarding -agent can be readily utilized in both of the wet and dry cellulosic board producing methods, provided the distribution of the agent within the boards is kept at a substantially uniform mannerO Unless a substantially uniform distribution is achieYed, locally there may occur too low or too high concentrations which can affect the board's physical and/or esthetlcal properties and can also lead to nonuniform flame retardancy of the board. In the "dry" board producing method, substantially uniform distribution of ~he flame retarding agent can be ~nsured, for example, by employing cellulosic materials having a moisture content between about 20-40% by weight.
The following exam~les demonstrate the synergistic 1ame-retarding effect obtained for cellulosic boards by use of the no~el, three-component s~stem of the in~entio~.
Example I
A series of flame-retarded hardboards was made from dry, unbleached wood fibers by incorporating in the boards the novel, three^c~mponent flame-retarding agent. All of the boards had an equal loading of 45% by weight flame-retarding ; ' agent and for the test only the type of the "C" component o~
the agent, e.-g., the inorganic sulfate or phosphate component, , . .

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l was varied. Within the agent, the weight ratios of the com-ponent were being kept constant in all of the mixtures at 45% 45% 10%o For each board, 260 grams of fluffed fiber was charged into a container of 19 liter (5 gallons) capacityO
The container was closed, then tumbled at an angle, while through an opening, an aqueous resin binder composition, containing 27 grams of phenolfo~naldehyde resin dispersed in 130 ml water, was added. Subsequently, 213 grams flame-10 retarding agent, composed of a mixture of A+B~C, was added, -and the admixture was vigorously mixedO The a~mixture was then transferred to a sheet mold of 2504 x 25~4 cm (10" x 10") size and compacted with a metal plateO The admixture7 now -in a mat form, was then further compacted in a platen press without employing heat, then the compacted mat was trans-ferred to a perforated aluminium plate on which it was pressed into a board. The board was prepared b~ using a platen temperature of about 215C (419F) with an initial force of about L~ tons (38Q psi) for 105 minutes, followed -~
~0 by a 4-minute pressure treatment at about the same tempera-ture using a pressure of 7.5 ~ons (140 psi), The finished boards were stored for 12-14 hours, then specimens of about 8 ~ 25 cm (3-I/4" x 10") were cut for fl~me retardancy test-ing. For comparison purposes, the following boards were also prepared by the same method: (a) control board with no flame retardant agent; (b) board with a 1:1 mixture o alumina hydrate ulexite; (c) board with alumina hydrate only; (d) board with ulexite only and (e) board with Ca(H2P04)2 only.
In boards (b)-(c), the loading of the additives was at the same level as in the boards prepared with the novel, three-:': .
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1 component agent. Specimens from boards (a)-(e) were also subjected to flame retardancy testing. The flame retardan-cies exhibi~ed by all specimens were tabulated and are shown in Table II.
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-~qJ~96~5 1 The results shown in Table II clearly indicate that the novel flame-retarding compositions impart improved flame retardancy to cellulosic boards signi~icantly beyond the additive results expected from the combination of the con-5 stituents. This denotes true synergism unexpectedly gener- -;
ated by the components of the instant flame~retarding agents.
Tests have also been conducted with ammonium sul- - ~ -fa~e [(NH4)2S04], A12(S04)3-18H2o, AlP04 and dibasic calcium ~-phosphate (CaHP04), which judging from the behavior of the rest o~ the salts in the class, should also have imparted a synergîs~ic ~lame-retarding effect to cellulosic hardboards.
Surprisingly, these salts were found to be ineffective in obtaining a Class I ~ire rating for cellulosic boards under -the manufacturing and testing conditions described in Example I. This further strengthens the uniqueness of the compositions disclosed and claimed.
Tests have also been performed for establishing the effective loading of the novel flame-retarding agent in cellulosic boards. These tests are described in Example II.
Exam~Ie II
A series of hardboards were prepared according to the method described in Example I. In this series, an alumina hydrate-ulexite-Ca(~2P04)2 composition was used as the flame-retarding agent at loadings varying between about 25% and 60% by weight based on the weight of the ~lame-re-tarded boards. The weight ratio of alumina hydrate-ulexite- -Ca(H2P~4)2 was establi hed at 45 :45 :10. From the boards specimens were taken for flame spread testing according to the method referred to abo~e and the results are shown in ;
30 Table III. ~ ~
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l TABLE III
Flammab;lity of hardboards at varying loadings of alumina hydrate-ulexite-Ca~H2PO4)2 flame retarding agent Loading in % by wt. Flame of flame-retarded spread board ~nches ~fterglow ~emarks 17-1/2 Yes 15-1/4 Yes 14-3/4 Yes 14 No 13 No 12-3/4 No Poor phys.
prop. ~;

It can be seen that for the particular com~osition em~loyed, loadings below about 40% by weight do not provide Class I
fire rating, while at loadings in the range of about 60% by weight of the flame-retarded board, the physical strength of the board did not meet requirements.
Example III
Tests were also conducted using colemanite as the naturally occ~rring Ca-borate mineral. The boards for this example were prepared in accordance with the method shown in Example I using a 35% by weight loading. For control purposes, boards were also made containing cole-manite only, alumina hydrate only and a 70:30 mixture of alumina hydrate with colemani~e. As cosynergist (NH4)2HP04 was selected~ The results of the flammability tests are shown in Table IV.
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~ 396~)5 1 TABLE''IV
Flammability of hardboard using colemanite in the flame-retarding composition .
r lame spread Composition ' ' '''in'ches' Afterg'low --Colemanite 17 Yes ' Alumina hydrate 16.5 No ~
Alumina hydrate-colemanite ' 70:30 mixture 15 Yes Alumina hydrate-colemanite- -' (NH4)~IPO4 68.2~:28.25:3.5 mixture 14 No - -Experiments were also conducted for the manufacture of flame-retarded hardboards by the wet method using the novel, three- ~
component flame-retarding agent. The boards produced in this -manner also exhibited the excellent flame retardancy shown above. ~
To establish the universal application of the novel ~ ' flame-retarding agent to boards other than hardboards, a number of experiments were also conducted with particle- a~d fiberboards. While there were mlnor variations in the flame spread result~, these were found to be insignificant and within the experimental error of the method em~loyed. This showed the adaptability of the novel flame-retarding co~o-sitions for cellulosic boards other than hardboards.
It is also to be understood that the term "cellu-losic board" i~cludes boards which have a core made of cel-lulosic materials and facing layers on one or both sides, ~ -'' which may be either of cellulosic materials or other materials ';
known in the art~ In case of such two- or three-layer com-30 posites, the quantity of flame retardant incorporated in the ' .. ., : . ........ . . . . . . ~
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1 core and in the facing layer may varyO In any event, however, to obtain the flame retardancy described hereinbe-fore, the total quantity of agent in the composite, regard-less o~ distribution, is kept ~ithin the ranges shown.
Although the in~ention has been described in great detail, it is not limited to the specific embodiments shown in the examples, only by the extent and scope of the appended : ~ .
claims.

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Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. Flame retardant composition for cellulosic boards which comprises (A) a source of A1203 ? xH20; (B) a naturally occurring calcium-borate mineral; and (C) an inorganic sulfate or phosphate-containing salt, wherein (A) is selected from the group of A1203 ? xH20, where x is in the range of about 0.5-3,0, bauxite and mixtures thereof;
(B) is selected from the group of ulexite, colemanite and mixtures thereof; and (C) is selected from the group of salts having the formulae MmHS04, Mm(HPO4)n, Mm(H2PO4)n, XmH4-mP207, where M is Na, K, NH4, Mg and Al and X is Na, K, Mg and NH4 and m and n depend on the valency of M, Ca(H2P04)2, K3P04, Na3P04 and the metaphosphates of Na and K; and wherein in the flame retardant composition, the percent weight ratios of A:B:C are kept within the range of about 10-90:5-85:5-40.

2. Flame retardant composition of claim 1, wherein the percent weight ratios of A:B:C are kept within the range of about 40-75:20-60:5-30.

3. Flame retardant composition of claim 1, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is Ca(H2PO4)2.

4. Flame retardant composition of claim 1, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is NaHS04.

5. Flame retardant composition of claim 1, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is Na2H2P207.

6. Flame retardant composition of claim 1, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is selected from the group consisting of NH4H2P04, (NH4)2HP04 and ammonium polyphosphate.

7. A Flame-retarded cellulosic board containing a flame retardant composition which comprises (A) a source of A1203?xH20; (B) a naturally occurring calcium-borate mineral and (C) an inorganic sulfate or phosphate-containing salt, wherein (A) is selected from the group of A1203?xH20, where x is in the range of about 0.5-3.0, bauxite and mixtures thereof; (B) is selected from the group of ulexite, colemanite and mixtures thereof; and (C) is selected from the group of salts having the formulae MmHS04, Mm(HP04)n, Mm(H2P04)n, XmH4-mP207, where M is Na, K, NH4, Mg and Al and X is Na, K, Mg or NH4 and m and n depend on the valency of M, Ca(H2P04)2, K3P04, Na3P04 and the metaphosphates of Na and K; and wherein in the flame retardant composition, the percent weight ratios of A:B:C are kept within the range of about 10-90:5-85:5-40;
and wherein the quantity of flame retardant composition in the board is kept within the range o about 25 to about 50%
by weight of the flame-retarded board.

8. Board according to claim 7, wherein the percent weight ratios o A:B:C are kept within the range of about 40-75:20-60:5-30 and the quantity of flame retardant composi-tion in the board is kept within the range of about 35 to about 50% by weight of the flame-retarded board.

9. Board according to claim 7 wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is Ca(H2P04)2.

10. Board according to claim 7, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is NaHSO4.

11. Board according to claim 7, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is Na2H2P207.

12. Board according to claim 7, wherein A is A1203?3H20 or bauxite, B is ulexite or colemanite and C is selected from the group consisting of NH4H2P04, (NH4)2HP04 and ammonium polyphosphates.