Zinc borates

Flamtard ZIO Z15 - number is equivalent to the specific surface area 

MAJOR PRODUCT APPLICATIONS flame retarding compositions of polymers hsted below 

MAJOR POLYMER APPLICATIONS PA, PPO, PC, PVC, PE, EVA, EPDM, polychloroprene, polyesters, epoxy 

Zinc borate is an inorganic flame retardant which can be used by itself or in combination with aluminum hydroxide or magnesium hydroxide with which it forms synergistic mixtures of high performance flame retardants. It is frequently used as a surface coating on these two fillers. It reduces smoke emission and promotes char formation. 

in ultrafine grades with surface areas from 10 to 1 5 m g and thermally stable up to 29()°C, functions mainly in the condensed phase, promoting the formation of a char, which can be enhanced by the finer particle size. Grades are also suitable for use in translucent halogenated polyester resin systems, to improve fire performance while retaining clarity, and/or with a refractive index of 1,5 9 (similar to that of glass and many polyester resins). 

In a fire, zinc borate on its own forms a vitreous mass on the polymer surface providing a barrier between the flame and the source of support. In antimony- or halogen-based systems it helps formation of Sb-O-Cl groups, extinguishing the flame and suppressing fumes while promoting formation of polyaromatic structures. The Borax material has until now been used mainly for total (or more recently, partial (40-75%)) replacement of the more expensive antimony oxide in PVC, polyolefins, nylons, and elastomers. 

Borax has grades in its Firebrake range which retain their thermal stability up to 415 and 500°C and are therefore well suited to uses in technical plastics. 

Firebrake ZB 415 with Dechlorane Plus gives flame-retardant properties superior to those of antimony oxide alone. Grade ZB 500 makes it possible to suppress fumes from fluoropolymers, and gives good flame-retardant properties to poly(ether ketone)s and polyfether sulphone)s. Other key applications are talc-reinforced PP replacing PVC. ABS, and PA 66 in electrical/electronic applications, and EVC cable compounds. 

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Alumina trihydtate is also used as a secondary flame retardant and smoke suppressant for flexible poly(vinyl chloride) and polyolefin formulations in which antimony and a halogen ate used. The addition of minor amounts of either zinc borate or phosphoms results in the formation of glasses which insulate the unbumed polymer from the flame (21). 

Zinc Borate. Zinc borate is also effective in enhancing the flame-inhibiting powers of chlorine. Although zinc borate increases flame resistance, it is not as effective as antimony oxide, as is illustrated in Figure 3. However, zinc borate can be used in combination with antimony oxide to obtain equivalent and in some instances enhanced effects over what can be obtained using either of the two synergists alone (Table 9). 

Table 13. Fire Test Results of Laminates Containing Zinc Borate and Antimony Oxide ...

Sb202 Zinc borate Flame spread Oxygen index ... 

Zinc Borates. A series of hydrated 2inc borates have been developed for use as fire-retardant additives in coatings and polymers (59,153). Worldwide consumption of these 2inc salts is several thousand metric tons per year. A substantial portion of this total is used in vinyl plastics where 2inc borates ate added alone or in combination with other fire retardants such as antimony oxide or alurnina trihydrate. 

Zinc borate-forms a protective coating of a glass-like film, retards the burning process and protects the insulation... 

The role of antimony oxide is not entirely understood. On its own it is a rather weak fire retardant although it appears to function by all of the mechanisms listed above. It is, however, synergistic with phosphorus and halogen compounds and consequently widely used. Other oxides are sometimes used as alternatives or partial replacements for antimony oxide. These include titanium dioxide, zinc oxide and molybdenic oxide. Zinc borate has also been used. 

Antimony trioxide (SbaOj). It is produced from stibnite (antimony sulphide). Some typical properties are density 5.2-5.67 g/cm- pH of water suspension 2-6.5 particle size 0.2-3 p,m specific surface area 2-13 m-/g. Antimony trioxide has been the oxide universally employed as flame retardant, but recently antimony pentoxide (SbaOs) has also been used. Antimony oxides require the presence of a halogen compound to exert their fire-retardant effect. The flame-retarding action is produced in the vapour phase above the burning surface. The halogen and the antimony oxide in a vapour phase (above 315 C) react to form halides and oxyhalides which act as extinguishing moieties. Combination with zinc borate, zinc stannate and ammonium octamolybdate enhances the flame-retarding properties of antimony trioxide. 

Fillers. Fillers are not commonly added to CR adhesives. Calcium carbonate or clay can be primarily added to reduce cost in high-solids CR mastics. Maximum bond strength is obtained using fillers with low particle size (lower than 5 [jim) and intermediate oil absorption (30 g/100 g filler). In general, fillers reduce the specific adhesion and cohesion strength of adhesive films. Although polychloroprene is inherently flame retardant, aluminium trihydrate, zinc borate, antimony trioxide or... 

It is possible to determine components in complex EPs where matrix effects can be severe. For example, zinc (as zinc borate), chlorine (as dechlorane flame retardant), antimony (as oxide) and fibre-glass have been determined in nylon using just one standard. Many users have refined the universal precalibrated programmes for standardless XRF and made them more efficient for matrix correction by using variable correction coefficients. OilQuant offers possibilities for analysing polymers [243]. Software packages usually provide ... 

Zinc Borate as a Flame Retardant, Smoke Suppressant, and Afterglow Suppressant in Polymers... 

Zinc Borate (2Zn0-3B203-3.5H20) is a unique multifuntional fire retardant. It can function as a flame retardant, smoke suppressant, afterglow suppressant, as well as an anti-tracking agent in polymers. It has been used extnesively as a fire retardant in PVC, polyolefin, nylon, polyester, epoxy, acrylic, urethane, rubbers, etc. 

Zinc borates with different mole ratios of Zn0 B203 H20 can be readily prepared by reacting zinc oxide with boric acid (Fig. 1). Among all these zinc borates, the compound with a molecular formula of 2Zn0-3B203-3.5H20, is the most commonly used fire retardant. This article will review recent research results on the use of this particular form of zinc borate as a multifunctional fire retardant. 

The major advantages of using the zinc borate can be summarized as follows ... 

High Dehydration Temperature - In contrast to other forms of zinc borates, the water of hydration of the zinc borate is retained up to 290°C, thus allowing it to be used in polymers requiring high processing temperatures. The proposed molecular structure for the zinc borate is depicted in Fig. 

Completely Reacted Material - The zinc borate contains no free zinc oxide. Thus, it does not have serious detrimental effects on the thermal stability of PVC or chlorinated paraffin as free zinc oxide does. 

Low Tinting Strength - The zinc borate has a refractive index similar to most organic polymers, which results in the retention of considerable translucency. This provides for easy visual inspection of the finished products and allows the use of lower pigment loadings in formulations requiring deep shades. 

Improving Electrical Properties - The zinc borate has good antitracking and antiarcing properties. 

Low Toxicity - Unlike antimony oxide, the zinc borate is considered non-toxic. 

The performance of the zinc borate as a fire retardant is summarized in the following ... 

AS A FLAME RETARDANT. The zinc borate is an efficient synergist of organic halogen sources. In certain halogen-containing systems such as unsaturated polyester, epoxy (3), and rigid PVC, the zinc borate alone can outperform antimony oxide as shown by the Oxygen Index and UL-94 tests (Fig. 3, 4, and 5). 

In other halogen-containing systems, such as flexible PVC and polyolefins, it is preferable to use the zinc borate in conjunction with antimony oxide for maximum performance. In flexible PVC, for example, the zinc borate alone is not very effective in the Oxygen Index test (Fig. 6), but a combination of the zinc borate and antimony oxide (1 1 ratio) outperforms equal weight of antimony oxide at a total loading of more than 10 phr (4). In the presence of alumina trihydrate (ATH), the beneficial effect of using a combination of the zinc borate and antimony oxide is dramatically increased (Fig. 7). 

AS A SMOKE SUPPRESSANT. Antimony oxide performs well as a flame retardant in flexible PVC, however, as a gas phase flame retardant, its use can drastically increase the smoke production during PVC combustion as illustrated in Fig. 8. The zinc borate,... 

Fig. 3. Oxygen Index Test of Polylite 33-442 Containing Dibromoneopentyl Glycol, ZB - Zinc Borate, Sb - Antimony Oxide. (Reproduced with permission from Ref. 2. Copyright Plastics Compounding 1985).

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