GB2032908A

GB2032908A - Smoke and Fire Retardants for Halogen-containing Plastic Compositions

Info

Publication number: GB2032908A
Application number: GB7931288A
Authority: GB
Original assignee: NL Industries Inc
Current assignee: NL Industries Inc
Priority date: 1978-09-11
Filing date: 1979-09-10
Publication date: 1980-05-14
Also published as: NL7906767A; IT7925501A0; DE2936511A1; IT1123550B; FR2435495A1

Abstract

A solid solution of zinc oxide, molybdenum oxide, and an oxide selected from magnesium oxide and calcium oxide and having a specific surface area of about 7 M<2>/g, when added to a halogen-containing plastic composition serves as a smoke and/or fire retardant agent.

Description

SPECIFICATION Smoke and Fire Retardants for Halogen-containing Plastic Compositions This invention relates to a solid solution containing zinc oxide, molybdenum oxide and magnesium oxide or calcium oxide and in particular to its use as a flame and smoke retardant material.

Plastic materials including plastic sheeting, synthetic fibers and the like are generally considered to be hazardous materials from the standpoint of flammability. In many cases, it is the practice to add various flame retardants to the plastic materials to reduce flammability during combustion. Recently, however, the propensity of plastics to create large volumes of smoke, when combusted, has come to be regarded as at least as hazardous, if not more so, than its flammability. Increasing concern with consumer safety and several tragic accidents have contributed to the recognition of smoke evolution as a significant hazard. In many instances of fire, the resulting fatalities have been due to smoke which has prevented safe evacuation of a structure due to lack of visibility, or to the toxic gases generated during combustion of the plastic.

Extensive studies have been made in the area of flame-retardant additives for halogen-containing plastic compositions, examples of which are antimony trioxide, antimony pentoxide, antimony-silica oxide and other organic and inorganic compositions of antimony. Zinc borate has also been used as a flame retardant, but generally not as a smoke suppressant and always at relatively high levels; for example from 3 to 8 parts per hundred parts resin are normally employed since less amounts do not exhibit effective flame retardancy.

One U.S. patent which deals with flame retardant additives is No. 3,723,1 39 which discloses the addition of antimony oxide in combination with sodium antimonate to polyvinyl chloride plastics to minimize flammability and to suppress smoke. In contrast, U.S. Patent No. 3,945,974 discloses halogen-containing plastic compositions which contain various zinc salts in amounts from 0.2 to 1 part calculated as zinc oxide per hundred parts of polymer resin, as useful smoke suppressants.

Unfortunately, when zinc salts are used at higher concentration than that specified above for retarding fire in addition to smoke. the zinc salts tend to degrade the plastic composition during processing under conventional high temperature techniques.

Another prior art fire and smoke retardant agent is disclosed in U.S. Patent No. 3,900,441 in which mixtures of various zinc and molybdenum compounds are employed. Additionally, U.S. Patents No. 3,845,001 and 3,903,028 disclose use of mixtures containing MoO3 and Cu2O and/or Fe203 as smoke retardants. Although these prior art agents are effective for retarding either fire or smoke in plastic materials, it has been unexpectedly discovered that the use of the solid solution composition of the instant invention produces unexpected flame and smoke resistant properties.

Figure 1 is a plot of specific surface area and oxygen index values, and Figure 2 is a plot of specific surface area and heat stability values.

A solid solution has been unexpectedly discovered containing zinc oxide, molybdenum oxide, and an oxide selected from the group consisting of magnesium oxide and calcium oxide. An unexpected flame and smoke resistant halogen-containing plastic composition has also been discovered, said composition containing from 0.1 to 10% of a solid solution of zinc oxide, molybdenum oxide, and an oxide selected from the group consisting of magnesium oxide or calcium oxide, the amount of molybdenum oxide, and magnesium oxide or calcium oxide present in said solution being from 0.01 to 10 parts for each part of zinc oxide. The solid solution should have a specific surface area of at least about 7 M2/g to obtain excellent flame and smoke resistance properties.

A true solution is a homogeneous mixture of two or more substances which has several characteristics, such as subdivision down to molecular formation, absence of settling, and no fixed proportions of the component substances. While the best known examples of solutions are cases where solids are dissolved in liquids, solutions of liquids in liquids and solids in solids are known. For example, published literature includes a tentative phase diagram for a ZnO/MgO system which shows that this system possesses two solid terminal phases, the periclase solid solution based on the MgO lattice (NaCI type cubic) and the zincite solid solution based on the ZnO Wurtzite type hexagonal lattice (i.e., E. M.Levin, et al, "Phase Diagram for Ceramists, 1969 Supplement", compiled at the NBS, 1 969, published by the America Chemical Society, p. 87, Figure 2312, System MgO--ZnO, tentative and J.

D. H. Donnay and H. M. Ondish, "Crystal Data," 3rd Ed., Vol. 2, Inorganic Compounds, published by the Joint Committee Power Defraction Standard, ZnO, H-1.5965, Data for MgO--ZnO Solid Solution).

In accordance with this invention, it has been found that ZnO/MgO and ZnO/CaO form solid solutions and that minor concentrations of magnesium and zinc molybdate are also produced. Further, it has been found that such solid solutions and compounds are effective flame and smoke retardants, as are ZnO/MgO solid solutions alone. See copending patent application 42523/77 (corresponding to U.S. Appln. Ser. No. 834486).

The solid solutions of zinc oxide, molybdenum oxide, and magnesium oxide or calcium oxide, according to this invention can be prepared by thoroughly mixing ground zinc oxide with ground molybdenum oxide, and magnesium oxide or calcium oxide in the desired proportions and calcining the mixture. It is desirable to calcine the oxide mixture at a temperature, and for a time, sufficient to produce a solid solution and preferably a solid solution which is effective as a smoke and flame retardant. Temperatures of from about 5500 to 9000C and preferably from about 6000C to 7500C for about 1 to about 8 hours, and preferably about 1 to about 6 hours, are typically suitable to form the solid solution.

The oxides can be admixed in the dry state or as a wet slurry mixture. Technical grade reagents may be used, as purity is not a critical factor. Alternatively, the magnesium oxide, calcium oxide, molybdenum oxide and zinc oxide may be added as hydroxides, carbonates or other radicals which decompose upon calcination to form the oxide compounds.

According to this invention, a wide range of oxide concentrations may be employed to prepare effective flame and smoke retardant additives providing the final composition contains (1) zinc oxide, (2) molybdenum oxide and (3) magnesium oxide or calcium oxide. Compositions exhibiting good properties are obtained for zinc oxide, magnesium oxide and molybdenum oxide systems when the solid solution contains about 10 to about 80% zinc oxide, about 10 to about 80% magnesium oxide and about 2 to about 80% molybdenum oxide. Optimum properties are obtained when the solid solution contains about 20 to about 60% zinc oxide, about 20 to about 60% magnesium oxide and about 2.5 to about 20% molybdenum oxide.In contrast, compositions exhibiting good properties which employ calcium oxide instead of magnesium oxide are obtained when the solid solution contains about 10 to about 80% zinc oxide, about 10 to about 60% calcium oxide and about 2 to about 40% molybdenum oxide with preferred concentrations for optimum results being about 20% to about 60% zinc oxide, about 20% to about 50% calcium oxide and about 2.5 to about 20% molybdenum oxide. All of the foregoing ranges are suitable for use with either molybdenum dioxide or molybdenum trioxide.

It has been surprisingly discovered that a plastic composition having exceptional flame and smoke resistance can be prepared by incorporating a solid solution of (1) zinc oxide, (2) molybdenum oxide, and (3) magnesium oxide or calcium oxide as a flame and smoke retardant in a halogencontaining plastic composition. In general, the plastic composition contains from about 0.1 to about 10 parts by weight of the solid solution. The solid solution itself contains zinc oxide and an amount of molybdenum oxide and magnesium oxide or calcium oxide effective to provide the zinc oxide with sufficient heat stability (i.e., the polymer does not discolor at temperatures up to about 200 to 21 00C) during processing, that is sheet and article formation, milling, and extruding of the plastic mass when using polyvinyl chloride and other halogen-containing polymer systems.Generally, from about 0.01 to 10 parts of molybdenum oxide and magnesium oxide or calcium oxide are used for each part of zinc oxide, the parts being expressed on a weight basis. Additionally, the solid solution may be used to partially replace conventionally used antimony trioxide to result in a mixed flame and smoke resistant agent for plastic compositions. Mixture of antimony trioxide and the inventive solid solution should be prepared by conventional procedures which enable from 0.1 to 10 parts of antimony trioxide to be present for each part of the solid solution in the mixture.

Most types of plastic composition can be satisfactorily treated with the flame and smoke retardant agents of this invention. Among those most commonly used are flexible, semi-rigid and rigid polyvinyl chloride, polyolefins, such as polyethylene and polypropylene, polystyrene, polyesters and acrylonitrile-butadiene-styrene, copolymers and the like. These plastic compositions typically contain a halogen. The expression "halogen-containing plastic composition" as used herein is intended to include both plastic compositions formed using a halogen-containing polymer such as polyvinyl chloride, and plastic compositions formed using a polymer which does not contain a halogen, such as a polyester, but to which a halogen containing compound is added.Suitable halogen-containing compounds which can be added in this manner are decabromodiphenyl oxide and Dechlorane 515, a chlorinated polyethylene of Hooker Chemicals Company containing about 65% chlorine and having a melting point more than about 3500C and a particle size of 5 to 15 microns. When such compounds are used, they are generally added in amounts of from about 10 to 35% preferably about 12 to 25% of the polymer composition.

Preparation of the halogen-containing composition can be effected by standard methods and standard equipment in the art. One such exemplary method involves placing the resin component on a two-roller, steam-heated differential mill maintained at a temperature of 1 630C. When the mass becomes molten, a blended mixture of the components to be added is added to the mill and the mixture blended for a few minutes until complete.

Precise lattice parameter measurements using x-ray diffraction have been made to verify the presence of solid solutions in the solid solution compositions of this invention. A Standard Norelco Diffractometer by Phillips Electronics was used for the purpose of obtaining the x-ray diffraction two theta spectra. The operating conditions were: 1) Two-theta spectrum range: 60--1450 2) KV/Ma: 45/35 3) Slit: 10 4) Chart Speed: 30"/hour 5) Goniometer Speed: 1/40/minute 6) Estimated precision of line measurements: +0.0050 7) Internal standard for correcting two-theta peak position: KCI powder crystals The following examples are given to illustrate the invention but are not deemed to be limiting thereof.All parts and percentages given are based upon weight unless otherwise indicated.

The following procedures were employed in the examples where applicable to determine smoke reduction, oxygen index and heat stability.

Smoke Reduction Smoke measurements were carried out in a National Bureau of Standards smoke density chamber. Sheets of milled stock, 3 inch (7.62 cm) square and 40 mils (1 mm) thick, were used as test samples. The time required in minutes to reach 90 percent maximum density (T90) and the maximum smoke corrected for deposition on chamber walls (Dmc) were measured in order to calculate the percent smoke reduction.

Oxygen Index Oxygen index values were determined in accordance with ASTM-D2863 method using 150 by 6.5 by 3 millimeter specimens.

Heat Stability The heat stability at 1 900C in PVC was obtained by milling the samples with the resin and other plastic additives. The specimen was cut from the formulated milled sheet and heated at 1 900C for specific time periods. Specimens were withdrawn at given time intervals and the color of the plastic composite was compared with that of the no-additive sample. A brown discoloration was considered a failure and the time (minutes) at failure was recorded and compared to a standard specimen containing no additives which failed at 45 minutes.

Example 1 Eleven grams of zinc oxide, 16.5 grams of magnesium oxide, and 22.5 grams of molybdenum dioxide were mixed thoroughly in a blender. All of the materials were added as powder. The mixture was placed in a ceramic tube and slowly tumbled throughout the calcination step. The mixture was heated to 7500C and maintained at that temperature for 5 hours. After the calcination was completed, the mixture was allowed to cool and the product was hammer milled through a 0.02 inch (0.5 mm) screen to break up the agglomerates which had formed.

The solid solution and products formed during calcination were added to a standard plasticized PVC formulation containing 1.5% antimony oxide. (In some cases the plasticized PVC did not contain antimony oxide). The amount of solid solution product added was 3.18 PHR (equal to 0.7% zinc oxide) and performance tests were conducted using this product to show its effectiveness. The percentages are expressed on a weight basis.

The oxygen index was 37.7, the smoke reduction was 41% and the heat stability was 1 5 minutes less than the no-additive control sample when 1.5% antimony oxide was added. With no addition of antimony oxide in the formulation, the oxygen index was 33.8; smoke reduction was 45%; and the heat stability was 1 5 minutes less than the standard of no-additive control sample.

In these evaluations, the plasticized PVC was prepared using the following formula: Ingredients Parts PVC resin 100.0 DOP [du(2-ethyl hexyl)phthalate] 23.5 Epoxidized soybean oil 1.5 Ba-Cd stabilizer 2.0 Stearic acid 0.5 Antimony trioxide 0 or 1.5 Additive as indicated in the examples Example 2 In this Example, 11 grams of zinc oxide, 16.5 grams of magnesium oxide and 22.5 grams of molybdenum trioxide were mixed together in powder form. The mixed solid was calcined in the same manner described in Example 1 at 7500C for 5 hours. After calcination, the calcined product was allowed to cool and then hammer milled through a 0.02 inch (0.5 mm) screen to break up the agglomerates which formed during the formation of the solid solution of the mixed oxides.

The solid solution and products formed during calcination were then added to Example 1 standard plasticized PVC formation containing 1.5% antimony oxide. The amount of solid solution added was 3.18% and the test results are shown in Table 1 along with those of Example 1.

Controls A-F In order to show the superiority of using a product formed for calcining zinc oxide, magnesium oxide and molybdenum oxides, several control tests were performed with the Example 1 PVC formulation. In the control run (control A) no additive was added to the standard PVC formulation, the heat stability and % smoke reduction were considered as standard for comparison. The oxygen index of the PVC material is poor, i.e., 28.7. Using molybdenum alone, either as is or calcined [control B (1.5 PHR) and C (2.1 PHR), respectively], very poor smoke reductions of 29% and 13%, respectively, were obtained. The same poor smoke reduction was also observed when the calcined magnesium oxide (2.1 PHR) was used alone (control F).

Additional control evaluations were performed [control D 0.7 PHR) and E (2.1 PHR)] in which zinc oxide, calcined or uncalcined, was used in the formulation. The results indicate heat stability was very poor, i.e., 20 minutes less than the standard PVC containing no additive.

Examples 3-10 In these examples, various (1) zinc oxide, (2) molybdenum oxide and (3) magnesium oxide or calcium oxide compositions were prepared and used to treat the Example 1 standard PVC formulations as follows: Example No. %ZnO %MgO %MoO3 %MoO2 %CaO 3 28 42 - 30 45 4 10 80 10 - - 5 33.3 33.3 33.3 - - 6 50 45 5 - - 7 13 80 7 ~ ~ 8 30 60 10 ~ ~ 9 45 - 10 - 45 10 33.3 - 33.3 - 33.3 The results were recorded in Table 1. The additive level was 2.1 PHR.

Table 1 Calcination Heat Stability Time Temp (Minutes less Oxygen % Smoke Example No. %ZnO %MgO %MoO2 %MoO3 %CaO (Hrs.) ( C) than standard) Index Reduction 1) ZnO/MgO/MoO2 22 33 45 - - 5 750 15 37.7 41 ZnO/MgO/MoO2 22 33 45 - - 5 750 15 33.8 45 ZnO/MgO/MoO3 22 33 - 45 - 5 750 15 36.7 45 Control A. No additive - - - - - - - 0 28.7 0 B. MoO3 alone* - - - 100 - - - 10(blue) 31.7 29 C. MoO3 alone - - - 100 - 5 750 0 33.5 13 D. ZnO alone 100 - - - - - - 20 35.5 42 E. ZnO alone 100 - - - - 5 750 20 33.0 21 F. MgO alone - 100 - - - 5 750 15 32.5 2 Example No.

3) ZnO/MgO/MoO2 28 42 30 - - 5 750 15 37.1 45 4) ZnO/MgO/MoO3 10 80 - 10 - 5 750 10 37.4 40 5) ZnO/MgO/MoO3 33.3 33.3 - 33.3 - 5 750 15 38.5 44 6) ZnO/MgO/MoO3 50 45 - 5 - 5 750 15 39.0 44 7) ZnO/MgO/MoO3 13 80 - 7 - 5 750 15 37.5 45 8) ZnO/MgO/MoO3 30 60 - 10 - 5 750 15 38.5 43 9) ZnO/CaO/MoO3 45 - - 10 45 5 675 13 36.2 42 10) ZnO/CaO/MoO3 33.3 - - 33.3 33.3 5 675 11 36.1 36 From the above description and by the examples presented, it has clearly been shown that a halogen-containing plastic composition containing a small percentage of a solid solution of zinc oxide, molybdenum oxide, and magnesium oxide or calcium oxide produces a highly desirable flame and smoke resistant plastic material.By using the solid solution agents of the instant invention as flame and smoke resistant agents, superior results are obtained over those which employ zinc oxide alone, mixtures of zinc oxide and molybdenum oxide and complex compositions of molybdenun oxide and zinc salts.

Table 2 lists the calcination parameters and properties for Examples 1115. The examples were comprised of wet slurry mixture zinc oxide, magnesium oxide, and molybdenum oxide in the weight percents of 38%, 57%, and 5% respectively. As may be seen from the data and the corresponding Figures 1 and 2, a specific surface area of at least about 7 M2/g leads a marked improvement of flame and smoke resistance properties. For this reason, such surface area should be employed in accordance with the invention.

The invention being thus described, it will be obvious that the same may be varied in many ways.

Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.

Table 2 Example Calcination Calcination Heat Stability Oxygen % Smoke Specific Surface No. Temp (OCI Time (Hrs) Min.Less Than Std. Index Reduction Area (Ml'g) 11 700 1 16 38.3 47 23.39 12 850 3 15 38.5 44 9.54 13 850 3 15 38.6 45 9.74 14 1000 1 9 37.0 38 5.29 15 1000 5 8 36.6 36 3.43

Claims

Claims

1. A flame and smoke resistant halogen-containing plastic composition containing from 0.1% to 10% of a solid solution of zinc oxide, molybdenum oxide, and magnesium oxide or calcium oxide, the amount of molybdenum oxide, magnesium oxide or calcium oxide present in the solid solution being from 0.01 to 10 parts for each part of zinc oxide, and the solid solution having a specific surface area of at least about 7 M2/g.

2. A composition as claimed in claim 1, wherein the solid solution contains about 10 to about 80% zinc oxide, and 10 to about 80% magnesium oxide and about 2 to about 80% molybdenum oxide.

3. A composition as claimed in claim 1, wherein the solid solution contains about 10 to about 8096 zinc oxide, and 10 to about 60% calcium oxide and about 2 to about 40% molybdenum oxide.

4. A method of preparing a flame and smoke resistant halogen containing plastic composition which comprises incorporating in said plastic composition from 0.1% to 10% of a solid solution of zinc oxide, molybdenum oxide, and an oxide selected from the group consisting of magnesium oxide and calcium oxide, the molybdenum oxide and magnesium oxide or calcium oxide present in the solid solution being from 0.01 to 10 parts for each part of zinc oxide, said solid solution having a specific surface area of at least about 7 M2/g.

5. The method of claim 4 wherein said solid solution contains zinc oxide, molybdenum oxide and magnesium oxide.

6. The method of claim 4 wherein said solid solution contains zinc oxide, molybdenum oxide and calcium oxide.

7. The method of claim 4, wherein said solid solution contains about 10 to about 80% zinc oxide, about 10 to about 80% magnesium oxide and about 2 to about 80% molybdenum oxide.

8. The method of claim 4 wherein said solid solution contains about 10 to about 80% zinc oxide, about 10 to about 60% calcium oxide and about 2 to about 40% molybdenum oxide.

10. A solid solution having a composition of from about 10 to about 80% zinc oxide, from about 10 to about 80% magnesium oxide, and from about 10 to about 80% molybdenum oxide and having a specific area of at least about 7 M2/g.

11. The solid solution of claim 10 containing about 20 to about 60% zinc oxide, about 20 to about 60% magnesium oxide and about 2.5 to about 20% molybdenum oxide.