WO2018099674A1

WO2018099674A1 - Nitrile rubber products and methods of forming nitrile rubber products

Info

Publication number: WO2018099674A1
Application number: PCT/EP2017/077951
Authority: WO
Inventors: Sivaynana Moorty NADESAN
Original assignee: Sibelco Nederland N.V.
Priority date: 2016-11-30
Filing date: 2017-11-01
Publication date: 2018-06-07
Also published as: CN110121524A; GB2557215A; EP3548552A1; MY174560A; GB201620319D0

Abstract

The present invention relates to nitrile rubber products and methods of forming nitrile rubber products.

Description

Title: Nitrile rubber products and methods of forming nitrile rubber products Description of Invention

The present invention relates to nitrile rubber products. In particular, the present invention relates to nitrile rubber products comprising a filler. The present invention also relates to a method of forming nitrile rubber products. The present invention also relates to nitrile rubber latex compositions.

Natural rubber is used in the formation of medical and consumer goods, for example in the formation of natural rubber gloves. Natural rubber includes polymeric long chain molecules of repeating units of isoprene.

Latex refers to a composition which is a stable dispersion of polymer microparticles in an aqueous medium. Natural rubber latex compositions found in nature are a milky fluid; they can be found in some plants (for example angiosperms; including Hevea brasiliensis, Parthenium argentatum and Taraxacum kok-saghyz).

In order to form medical and consumer goods from natural rubber latex compositions, the isoprene chains are crosslinked by vulcanisation, i.e. by the application of sulfur, peroxide or bisphenol, and heat. Vulcanisation increases the strength and elasticity of natural rubber.

Natural rubber is useful in forming medical and consumer products where a barrier for the skin is needed, for example in gloves. However, some people have a natural rubber allergy. Persons with a particularly serious natural rubber allergy can experience anaphylactic shock on contact with natural rubber. Nitrile rubber was developed as an alternative to natural rubber. Nitrile rubber is a synthetic rubber copolymer of acrylonitrile and butadiene. A nitrile rubber latex composition is a stable dispersion of polymer microparticles in an aqueous medium which can form nitrile rubber (in solid form). Examples of nitrile rubber are sold under the names Perbunan™, Nipol™, Krynac™ and Europrene™. Non-limiting examples of nitrile rubber latex compositions include: KNL830 as sold by Kumho™ Petrochemical; Synthomer 6328 and Synthomer 6330 as sold by Synthomer™; Nantex 672 as sold by Nantex Industry Co. Ltd.; LG-Lutex 105 and LG-Lutex 120 as sold by LG Chem™; BST 8503 S as sold by Bangkok Synthetics Co. Ltd; Polylac 580N as sold by Shin Foong Specialty and Applied Materials Co., Ltd.; and, Nipol™ LX 550 and Nipol™ LX 550L as sold by Zeon™ Chemicals L.P.

Some forms of nitrile rubber have the general formula:

where m and n are each an integer and are the same or different. This formula shows the two monomers which make up the copolymer; the order of the monomers in the copolymer can vary.

Nitrile butadiene rubber (NBR) is a type of nitrile rubber. In particular, NBR is a family of unsaturated copolymers of 2-propenenitrile and butadiene monomers (for example 1 ,2-butadiene and 1 ,3-butadiene). The physical and chemical properties of NBR vary depending on the relative amount of nitrile. Generally, NBR is resistant to oil, fuel and other chemicals. The higher the relative amount of nitrile within NBR, the higher the resistance to oil but the lower the flexibility of the NBR. NBR is used to make a variety of medical and consumer goods, for example fuel and oil handling hoses, seals, grommets, fuel tanks, protective gloves, moulded goods, footwear, adhesives, sealants, sponges, expanded foams and floor mats.

NBR can withstand temperatures from -40 to 108°C. Due to its resilience, NBR is often used to form disposable lab, cleaning, household, industrial and medical gloves. NBR is more resistant than natural rubber to oils and acids and has a superior strength. Gloves formed of NBR are more puncture- resistant than natural rubber gloves. Gloves formed of NBR are also preferred over natural rubber gloves because NBR is less likely to cause an allergic reaction. Whilst NBR has many beneficial properties in forming medical and consumer goods, for example gloves, it is formed of components derived from petrochemical components, namely, 2-propenenitrile and butadiene monomers. Petrochemical components are a finite resource, are relatively expensive and their production can contribute to global warming. 2- propenenitrile and butadiene monomer sources are also potential pollutants. Therefore, the present inventors considered the partial replacement of petrochemical components in NBR products. Whilst the present inventors found it desirable to reduce the petrochemical components in NBR products, they also sought to maintain the beneficial properties of the products.

The present inventors examined the preparation of nitrile rubber products including a filler. A filler is a component added to nitrile rubber which is generally inert. According to an aspect of the present invention, there is provided a nitrile rubber product comprising an aluminium silicate filler. Preferably, wherein the aluminium silicate filler has the formula:

xAI2O3.ySiO2.zH2O, where x, y and z are integers and can each be any one of 0, 1 , 2 or 3.

Further preferably, wherein the aluminium silicate filler comprises any one, two, three, four or five of: AI₂Si₂O₅(OH)₄; AI₂SiO₅; AI₂Si₂O₇; AI₆SiO ₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈. Advantageously, wherein the aluminium silicate filler is a kaolin filler.

Preferably, wherein the nitrile rubber is nitrile butadiene rubber (NBR).

Further preferably, wherein the aluminium silicate filler is milled aluminium silicate.

Advantageously, wherein the aluminium silicate filler has a maximum particle size of 10 m. Preferably, wherein the aluminium silicate filler has a maximum particle size of 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

Further preferably, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin.

Advantageously, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm. Preferably, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μηη, or less than 500 nm, or less than 100 nm. Further preferably, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 10 to 18 m²/g; optionally, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 14 to 16 m²/g.

Advantageously, wherein the BET surface area is measured by a

micromeritics™ TriStar II Plus.

Further preferably, wherein the maximum particle size is measured by a micromeritics™ SediGraph III Plus. Advantageously, wherein the aluminium silicate filler has a maximum particle size of from 50% to 90%, optionally 60%, below 2 μιτι measured by a micromeritics™ SediGraph III Plus.

Preferably, wherein the nitrile rubber product further comprises a biocide.

Further preferably, wherein the biocide is any one or more of:

a 1 ,2-benzisothiazol-3(2H)-one; optionally, Acticide™ B20, Nipacide™ BIT20 , Proxel™ GXL, Bioban™ ULTRA BIT20, Microcave™ BIT, Nuosept™ BIT Technical , Promex™ 20D and/or, Colipa™ P96;

a 2-methyl-4-isothiazolin-3-one.

Advantageously, wherein the nitrile rubber product is a fuel or oil handling hose, a seal, a grommet, a fuel tank, a glove, a moulded good, footwear, an adhesive, a sealant, a sponge, an expanded foam or a floor mat.

Preferably, wherein the nitrile rubber product is a glove. Further preferably, wherein the glove is an NBR glove.

Advantageously, wherein the NBR glove has a thickness of 0.05 mm (plus or minus 10%).

Preferably, wherein the NBR glove has a weight of 3.5 gm (plus or minus 10%). Further preferably, wherein at least 5% by weight of the nitrile rubber product is aluminium silicate filler.

Advantageously, wherein at least 10%, or 15%, or 20%, or 25%, or 30% or 35%, or 40% by weight of the nitrile rubber product is aluminium silicate filler.

According to another aspect of the present invention, there is provided a method of forming a nitrile rubber product, wherein the method comprises the steps of:

forming a nitrile rubber latex composition;

forming an aluminium silicate dispersion;

mixing the nitrile rubber latex composition and the aluminium silicate dispersion;

forming a nitrile rubber product covered former by placing a former in the mixed nitrile rubber latex composition and aluminium silicate dispersion.

Preferably, wherein the former is shaped corresponding to the shape of the product to be formed.

Further preferably, wherein the method further comprises one, two, three, four, five or six of the steps of: passing the covered former through a warm oven, optionally at from 85 to 95°C, for from 2 to 3 minutes;

leaching out excess additives by passing the covered former through one or more water baths, optionally at from 50 to 70°C;

vulcanising the nitrile with zinc oxide, sulfur, an accelerator and/or ΤΊΟ2, optionally at 120 to 140°C for 20 minutes (plus or minus 10%);

dipping the products in a slurry of starch and/or biocide;

stripping the products off the formers by mechanical or manual means; tumbling the products.

Advantageously, wherein the nitrile rubber latex composition comprises, consists of or consists essentially of: 2-propenenitrile, 1 ,2-butadiene and 1 ,3- butadiene; wherein if the nitrile rubber latex composition consists essentially of 2-propenenitrile, 1 ,2-butadiene and 1 ,3-butadiene the nitrile rubber latex composition comprises no more than 10% of other components.

Preferably, wherein the aluminium silicate dispersion comprises from 30 to 75% aluminium silicate by weight, from 30 to 60% aluminium silicate by weight, from 35 to 55% aluminium silicate by weight, from 60 to 75%

aluminium silicate by weight, from 40 to 50% aluminium silicate by weight, or 45% aluminium silicate by weight, the balance being water.

Further preferably, wherein the aluminium silicate dispersion consists of water and aluminium silicate, wherein the aluminium silicate has a maximum particle size of 10 μιτι, or 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

Advantageously, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin. Preferably, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm. Further preferably, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

Advantageously, wherein the aluminium silicate is a kaolin filler with a BET surface area of from 10 to 18 m²/g; optionally, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 14 to 16 m²/g. Preferably, wherein the BET surface area is measured by a micromeritics™ TriStar II Plus.

Advantageously, wherein the nitrile rubber is nitrile butadiene rubber (NBR) and the nitrile rubber latex composition is a nitrile butadiene rubber (NBR) latex composition; or, wherein the nitrile rubber latex composition is

carboxylated nitrile butadiene rubber (XNBR) latex composition.

Preferably, wherein the aluminium silicate dispersion has a pH of from 9 to 12. Further preferably, wherein the aluminium silicate has the formula:

Advantageously, wherein the aluminium silicate comprises any one, two, three, four or five of: AI₂Si₂O₅(OH)₄; AI₂SiO₅; AI₂Si₂O₇; AI₆SiOi₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈. Preferably, wherein the aluminium silicate is kaolin.

According to another aspect of the present invention, there is provided a nitrile rubber latex composition for dip-forming comprising:

a nitrile rubber latex; and,

an aluminium silicate.

Preferably, wherein the aluminium silicate is milled aluminium silicate.

Further preferably, wherein the aluminium silicate has a maximum particle size of 10 μιτι.

Advantageously, wherein the aluminium silicate has a maximum particle size of 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

Preferably, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin. Further preferably, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

Advantageously, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm. Preferably, wherein the aluminium silicate is a kaolin filler with a BET surface area of from 10 to 18 m²/g; optionally, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 14 to 16 m²/g. Further preferably, wherein the BET surface area is measured by a

micromeritics™ TriStar II Plus.

Preferably, wherein the maximum particle size is measured by a

micromeritics™ SediGraph III Plus.

Further preferably, wherein the aluminium silicate has a maximum particle size of from 50% to 90%, optionally 60%, below 2 μιτι measured by a

micromeritics™ SediGraph III Plus. Advantageously, wherein the nitrile rubber latex comprises, or consists of, one or more of: KNL830, Synthomer 6328, Synthomer 6330, Nantex 672, LG-Lutex 105, LG-Lutex 120, BST 8503 S, Polylac 580N, Nipol™ LX 550 or Nipol™ LX 550L. Preferably, wherein the aluminium silicate has the formula:

Further preferably, wherein the aluminium silicate comprises any one, two, three, four or five of: AI₂Si₂O₅(OH)₄; AI₂SiO₅; AI₂Si₂O₇; AI₆SiO ₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈.

Advantageously, wherein the aluminium silicate is kaolin. Preferably, wherein the nitrile rubber latex composition further comprises a dispersant. Further preferably, wherein the nitrile rubber latex composition comprises 20 to 30% by weight dispersant. Advantageously, wherein the dispersant is one or more of: SDBS (sodium dodecylbenzenesulfonate), sodium or ammonium salt of polyacrylic acid, sodium or ammonium salt of polymethacrylic acid, or a copolymer of acrylic acid with any one of: methacrylic acid, acrylamide or hydroxypropylacrylate. Preferably, wherein the nitrile rubber latex composition is an NBR latex composition.

Embodiments of the invention are described below with reference to the accompanying drawings, in which:

Figure 1 shows schematically a prior art method of forming NBR products, namely NBR gloves.

Figure 2 shows schematically a method of forming NBR products according to the present invention.

Manufacturing protocol for NBR products

NBR products, for example gloves, are commonly made by a dipping method (i.e. by dip-forming).

Figure 1 shows schematically a method of forming NBR products by dip- forming. Each numbered box shows a step in the method, as follows: 1 . Form an NBR latex composition. This composition is referred to as an NBR latex composition because it is a stable dispersion which can be used to form NBR products. In some non-limiting examples, NBR latex compositions comprise (in % by weight):

50-70% butadiene (total amount for 1 ,2-butadiene and 1 ,3- butadiene in equal molar amounts, plus or minus 1 , 2, 3, 4, 5, 10, 15, 20 or 25% (where the % refers to molar percentages)),

20-40% 2-propenenitrile,

5-10% of a carboxylic acid, for example methacrylic acid, the balance optionally being antioxidants and/or stabilisers. Non- limiting examples of antioxidants and/or stabilisers include sodium dodecylbenzenesulfonate (sometimes abbreviated as SDBS) and diphenyl oxide disulphonates (for example sodium dodecyl diphenyl ether disulfonate).

2. Mix the components of the NBR latex composition together with a stirrer (starting solids typically 45% solids (plus or minus 5%)).

Optionally, the NBR latex composition is stirred for 16-24 hours before use in dipping; stirring results in maturation of the composition, ultimately reducing the solids to working levels of from 10 to 20% solids. Optionally, the NBR latex composition is mixed with one or more stabilisers (for example KOH, ammonia and/or anionic surfactants) followed by a ZnO dispersion, a dispersant (for example, one or more of: SDBS (sodium dodecylbenzenesulfonate), sodium or ammonium salt of polyacrylic acid, sodium or ammonium salt of polymethacrylic acid, or a copolymer of acrylic acid with any one of: methacrylic acid, acrylamide or hydroxypropylacrylate), a sulfur dispersion, an

accelerator dispersion (for example, ZDEC (zinc

diethyldithiocarbamate) and/or ZDBC (zinc dibutyldithiocarbamate)), a ΤΊΟ2 dispersion and/or a colour dispersion.

3. Dip a coagulant covered former (from step 15 below) (for example a hand shaped former in the case of forming gloves) corresponding to the product to be formed into the mixture from step 2 at 25°C (plus or minus

10%). Optionally, the mixture from step 2 has working levels of from 10 to 20% solids. One example of a suitable coagulant is Ca(NO3)2- The former is typically composed of an inert ceramic material. The coagulant converts the liquid NBR latex composition into a wet-gel on the former.

4. Pass the wet-gel covered former through a warm oven, at from 85 to

95°C, for from 2 to 3 minutes. This step is sometimes referred to as gelling. In some examples, the film is made hard enough to form a beading on the cuff.

5. Leach out excess additives from previous steps by passing the NBR covered formers through one or more water baths at from 50 to 70°C.

6. Vulcanise the NBR with zinc oxide, sulfur and/or an accelerator; optionally, vulcanisation occurs at 120 to 140°C for 20 minutes (plus or minus 10%).

7. Optionally, pass the products through a water bath at from 40 to 60°C to cool down. Optionally, then pass the products through a chlorination bath at from 30 to 40°C (with chlorine at from 400 to 1 ,000 ppm);

optionally, followed by washing the products in a water bath at from 50 to 70°C; optionally, followed by placing the products in a drying oven at from 100 to 150°C for from 1 to 5 minutes.

8. Optionally, dip the products in a slurry of starch if the products are not powder-free. Optionally, dip the products in one or more biocides.

The biocides can be: a 1 ,2-benzisothiazol-3(2H)-one; optionally,

Acticide™ B20, Nipacide™ BIT20 , Proxel™ GXL, Bioban™ ULTRA

BIT20, Microcave™ BIT, Nuosept™ BIT Technical , Promex™ 20D and/or, Colipa™ P96; and/or, a 2-methyl-4-isothiazolin-3-one.

Alternatively, the one or more biocides can be included in the NBR latex composition formed at step 2.

9. Strip the products off the moulds by mechanical or manual means.

10. Optionally, tumble the products.

1 1 . Quality control by manual or automatic inspection or testing. 12. Take the finished product, for example gloves, out of the production line.

13. Cleanse the formers by washing in dilute nitric acid, 1 to 2% by mass in water, at 55°C (plus or minus 10%); followed by rinsing in water, following by washing in sodium hydroxide at 55°C (plus or minus

10%), followed by rinsing in water and optionally drying in an oven.

14. Coagulant dipping at from 55 to 65°C. One example coagulant is CaNO₃ at 10 to 20% by weight in water. Optionally, the coagulant can additionally include a wetting agent at 0.05 to 0.10% by weight in water and a mould release agent. Non-limiting examples of wetting agents include Teric 320™ as sold by Huntsman™ Corporation Australia Pty. Ltd., Triton X-100™ as sold by Dow™ Chemical and Igepal CO-630™ as sold by Solvay™ (Bangpoo) Specialty Chemicals Ltd. Non-limiting examples of mould release agents include a metal stearate (for example calcium stearate) at 1 to 2 % by weight.

15. Dry the coagulant covered former at from 55 to 65°C; return the coagulant covered former to step 3.

The general method above provides one non-limiting route to NBR products, for example gloves, formed of NBR. The method described with reference to Figure 1 can proceed continuously or can be stopped or paused by an operator at any particular step.

Figure 2, in contrast to Figure 1 , shows a method of forming products according to the present invention. The steps in Figure 2 are identical to the steps in Figure 1 save for the addition of step 16. In step 16, an aluminium silicate dispersion (for example, a kaolin dispersion) is added to the NBR latex composition before or during step 2, i.e. before or during stirring. Aluminium silicate dispersion

The term aluminium silicate refers to chemical compounds which are derived from aluminium oxide (AI₂O₃) and silicon dioxide (SiO₂) which may be anhydrous or hydrated, naturally occurring as minerals or synthetic. Their chemical formulae are expressed as xAI2O3.ySiO2.zH2O, where x, y and z are integers and can each be any one of 0, 1 , 2 or 3. This chemical formula includes the following compounds: · AI2S1O5 (AI2O3.S1O2), which occurs naturally as the minerals andalusite, kyanite and sillimanite (these three minerals each having different crystal structures).

• AI₂Si₂O₅(OH)₄ (AI₂O3-2SiO₂-2H₂O), which occurs naturally as the

mineral kaolinite and is also called aluminium silicate dehydrate.

· AI2S12O7 (AI2O3.2S1O2), called metakaolinite, formed from kaolin by

heating at 450°C (plus or minus 10%).

• AI₆SiO-i3 (3AI2O3.2S1O2), the mineral mullite, the only thermodynamically stable intermediate phase in the AI2O3-S1O2 system at atmospheric pressure. This also called '3:2 mullite' to distinguish it from 2AI2O3.S1O2, AI₄Si0₈ '2:1 mullite'.

. 2AI2O3.S1O2, AI₄SiO₈ '2:1 mullite'.

Kaolin dispersion One type of aluminium silicate is kaolinite. Kaolinite is a layered silicate material with the chemical composition AI₂Si2Os(OH) . Rocks that are rich in kaolinite are referred to as kaolin or china clay. Kaolinite is a common mineral and it is mined as kaolin around the world. In step 16 of Figure 2, a kaolin dispersion is added to the NBR latex

composition before or during stirring. This stirring step is sometimes referred to as compounding. Optionally, the kaolin dispersion is stabilised by one or more dispersants (for example, one or more of: SDBS (sodium dodecylbenzenesulfonate), sodium or ammonium salt of polyacrylic acid, sodium or ammonium salt of

polymethacrylic acid, or a copolymer of acrylic acid with any one of:

methacrylic acid, acrylamide or hydroxypropylacrylate) such that the kaolin dispersion is stable on storage and able to suspend even in low solids NBR (for example from 13 to 15% solids) in dip-tanks without sedimentation. The dispersant can be adsorbed on the interface of solid particles and the surrounding liquid; this creates repulsion between particles and prevents flocculation of the particles.

The kaolin is incorporated into the polymer matrix of the NBR products following the method of the present invention (for example as described with respect to Figure 2). The kaolin can be either hydrous or calcined kaolin. The kaolin dispersion added at step 16 comprises from 30 to 75% by weight kaolin, the balance being water. In some examples, the kaolin dispersion comprises from 30 to 60% by weight, or from 35 to 55% by weight, or from 60 to 75% by weight, or from 40 to 50% by weight, or 45% by weight kaolin, the balance being water.

The kaolin dispersion comprises fine kaolin formed by milling. In one non- limiting example, the fine kaolin is formed using a Buhler™ MicroMedia™ bead mill. In non-limiting examples, the fine kaolin has a maximum particle size of 10 μιτι, or 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι. Optionally, with each of these maximum particle sizes, at least 60% of the particles have a particle size below 2 μιτι with a median average of 1 .0 μηη (plus or minus 10%). The particle size measurements can be obtained on a micromeritics™ SediGraph III Plus. Alternatively or additionally, the milled kaolin can be passed through a filter with a suitably sized mesh to trap larger particles. In one embodiment, the fine kaolin has a maximum particle size wherein at least 60% of the kaolin particles have a particle size below 2 μιτι measured by a micromeritics™ SediGraph III Plus.

Optionally, the fine kaolin is substantially free of nano-kaolin; wherein, nano- kaolin has a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm. Optionally, the fine kaolin is substantially free of nano-kaolin in that the fine kaolin includes less than 5%, or less than 1 %, or less than 0.5%, or less than 0.1 % nano-kaolin by weight. Optionally, the fine kaolin has a BET surface area of from 10 to 18 m²/g; optionally, the fine kaolin has a BET surface area of from 14 to 16 m²/g. Optionally, the BET surface area is measured by a micromeritics™ TriStar II Plus. A BET surface area of greater than 20 m²/g in fine kaolin indicates the presence of nano-kaolin. Relatively pure nano-kaolin has a BET surface area of greater than 50 m²/g. The inclusion of substantial amounts (greater than 5% by weight, or greater than 1 % by weight, or greater than 0.5% by weight, or greater than 0.1 % by weight) of nano-kaolin results in a relatively thicker latex composition which is

Theologically unstable.

The present inventors tested the inclusion of a kaolin dispersion with different particle sizes. In one comparative example, the kaolin passed through a 45 μιτι sieve. Such less fine kaolin, when used in the kaolin dispersion at step 16 in Figure 2, did not suspend well in the NBR latex composition, causing sedimentation and disruption of movement of the glove moulds. In contrast, the present inventors did not see these problems when the kaolin particles in the kaolin dispersion had a maximum particle size of 10 μιτι. In one example, the kaolin dispersion was treated with one or more alkali metal hydroxides (sodium or potassium) and/or ammonium hydroxide providing an alkaline pH of from 9.0 to 12.0, in order for the kaolin dispersion to be compatible with alkaline NBR latex composition.

Milling to finer particle sizes (for example maximum particle sizes of 10 μιτι) also helped the kaolin attain higher brightness and whiteness which

complements the TiO₂ pigment sometimes used in NBR latex composition, and in some cases reduces the dosage of ΤΊΟ2 pigment required.

In some examples, to increase compatibility between the kaolin dispersion and the NBR latex composition, the kaolin dispersion is treated with a surfactant in order to reduce the surface tension of dispersion. Non-limiting examples of surfactants include non-ionic, anionic and amphoteric surfactants. An example of a non-ionic surfactant is Teric 320™ . Examples of anionic surfactants include Darvan WAQ™ and Rhodacal LDS-25/AP.

The inertness of kaolin made it insoluble to acid and alkali, especially chlorine water that is sometimes used in NBR product forming methods to improve the surface finish of NBR products (for example gloves). The inertness of kaolin helps reduce surface defects that could potentially arise due to dissolution of filler on glove surfaces, especially on NBR gloves having 0.05mm (plus or minus 10%) thickness and/or a weight of from 2.8 to 3.5 grams/piece. The kaolin dispersion used according to the present invention uses fine kaolin such that it attains a significant zeta potential, that is required for a good dispersion stability. Optionally incorporating a suitable biocide can increase the long term stability in terms of particle size distribution. The resultant surface area of kaolin due to fine milling, optionally

supplemented with a suitable dispersant, enables the intimate mixing of NBR latex composition (from 100 to 160 nm particle size) without causing undue agglomeration. Without wishing to be bound by theory, using a suitably fine kaolin filler provides NBR products with the same or improved properties as standard NBR products, whilst reducing the reliance on petrochemical components in the NBR products. The fine kaolin filler is substantially free of nano-kaolin. The inclusion of substantial amounts (greater than 5% by weight, or greater than 1 % by weight, or greater than 0.5% by weight, or greater than 0.1 % by weight) of nano-kaolin results in a relatively thicker latex composition which is Theologically unstable.

The kaolin dispersion, and resulting kaolin filler in the formed NBR products, according to the present invention, has the effect of reducing the amount of NBR latex composition needed to produce NBR products, for example gloves, without diminishing the effectiveness of the NBR products, for example gloves.

NBR Gloves

In one aspect of the present invention, the nitrile rubber product is an NBR glove.

Typically, natural rubber medical gloves are dipped with from 28 to 40% by weight solids (in the starting material) to make gloves of different sizes with minimum thicknesses of 0.08 mm. The minimum thickness of the gloves can be measured, for example, according to ASTM D 3578 (Standard Specification for Rubber Examination Gloves).

In contrast, most NBR gloves are made relatively thin, typically 0.05 mm (plus or minus 10%) thickness, with a typical weight of 3.5 gm/pc. Such relatively thin NBR gloves use a dilute starting NBR latex composition with total solids of from 14 to 16%, in the respective dip tank. With such low solids, the viscosity is too low (<100 centipoise [mPa.s]) to suspend relatively large kaolin particles without sedimentation in the dip tank.

The present inventors surprisingly found that milling the kaolin so that it is fine, i.e. has a maximum particle size of 10 μιτι, or 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι, provides a more efficient suspension with limited sedimentation in the dip tank. Optionally, with each of these maximum particle sizes, at least 60% of the particles have a particle size below 2 μιτι with a median average of 1 .0 μιτι (plus or minus 10%). The particle size measurements can be obtained on a micromeritics™ SediGraph III Plus.

Alternatively or additionally, the milled kaolin can be passed through a filter with a suitably sized mesh to trap larger particles. In one embodiment, the fine kaolin has a maximum particle size wherein at least 60% of the kaolin particles have a particle size below 2 μιτι measured by a micromeritics™ SediGraph III Plus.

Optionally, the fine kaolin is substantially free of nano-kaolin; wherein, nano- kaolin has a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm. Optionally, the fine kaolin is substantially free of nano-kaolin in that the fine kaolin includes less than 5%, or less than 1 %, or less than 0.5%, or less than 0.1 % nano-kaolin by weight. Optionally, the fine kaolin has a BET surface area of from 10 to 18 m²/g; optionally, the fine kaolin has a BET surface area of from 14 to 16 m²/g. Optionally, the BET surface area is measured by a micromeritics™ TriStar II Plus. A BET surface area of greater than 20 m²/g in fine kaolin indicates the presence of nano-kaolin. Relatively pure nano-kaolin has a BET surface area of greater than 50 m²/g.

Examples In certain non-limiting examples, the present inventors formed an NBR latex composition with the following composition (Table 1 ): Table 1

In this example, the NBR latex was KNL830 as sold by Kumho™

Petrochemical. In other examples, the NBR latex can be: Synthomer 6328 or Synthomer 6330 as sold by Synthomer™; Nantex 672 as sold by Nantex Industry Co. Ltd.; LG-Lutex 105 and LG-Lutex 120 as sold by LG Chem™; BST 8503 S as sold by Bangkok Synthetics Co. Ltd; Polylac 580N as sold by Shin Foong Specialty and Applied Materials Co., Ltd.; or, Nipol™ LX 550 and Nipol™ LX 550L as sold by Zeon™ Chemicals L.P.

The particle sizes of the kaolin particles in the kaolin dispersion were varied to test the suitability of the NBR latex composition in forming an NBR product, namely, gloves.

In examples according to the present invention, the kaolin particles in the kaolin dispersion having the components of Table 1 above (the variable being the particle sizes in the kaolin dispersion), as measured by a micromeritics™ SediGraph III Plus, had the size measurements of Table 2 below: Table 2 - Examples

In comparative examples, the kaolin particles in the kaolin dispersion having the components of Table 1 above (the variable being the particle sizes in the kaolin dispersion), as measured by a micromeritics™ SediGraph III Plus, had the size measurements of Table 3 below:

- Comparative Examples

When used in the kaolin dispersion at step 16 in Figure 2, samples 1 , 2, 3 and 4 of the Table 2 examples all suspended well in the NBR latex composition. In forming NBR gloves by the method described with reference to Figure 2, the NBR gloves passed the following tests: ASTM 6319 (Standard Specification for Nitrile Examination Gloves for Medical Application) and EN455 (the

European Standard for Medical Gloves). In particular, the gloves passed a water-tightness test, as specified in method EN455-Part 1 with AQL 1 .5 as well as ASTM D6319-10 with AQL 2.5.

When used in the kaolin dispersion at step 16 in Figure 2, comparative samples 1 , 2, 3 and 4 of the Table 3 comparative examples, the kaolin particles did not suspend well in the NBR latex composition, causing

sedimentation and disruption of movement of the glove moulds. NBR gloves formed using these NBR latex compositions were not well formed and did not pass the following tests: ASTM 6319 (Standard Specification for Nitrile

Examination Gloves for Medical Application) and EN455 (the European

Standard for Medical Gloves). In particular, the gloves did not pass a water- tightness test, as specified in method EN455-Part 1 with AQL 1 .5.

Furthermore, the gloves did not pass a water-tightness test, as specified in method ASTM D6319-10 with AQL 2.5.

In both the examples of Table 2 and the comparative examples of Table 3, the kaolin of the kaolin dispersions was substantially free of nano-kaolin, nano- kaolin having a particle size of less than 1 μιτι. The BET surface area of the dry kaolin used to make the kaolin dispersions in both the examples of Table 2 and the comparative examples of Table 3 (measured by a micromeritics™ TriStar II Plus) was from 14 to 16 m²/g. A BET surface area of greater than 20 m²/g indicates the presence of nano-kaolin. Relatively pure nano-kaolin has a BET surface area of greater than 50 m²/g. The present inventors discovered that the presence of a substantial amount of nano-kaolin (e.g. where the BET surface area of the dry kaolin used to make the kaolin dispersion is greater than 20 m²/g) results in a relatively thicker latex composition which is

Theologically unstable.

In some embodiments, from 5 to 10 parts by dry weight kaolin is used as a filler in nitrile gloves having a thickness of 0.05 mm (plus or minus 10%), with a typical weight of 3.5 gm (plus or minus 10%). The amount of kaolin can be increased if the glove thickness increases, for example 4 gm, 6 gm gloves. The median particle size of the kaolin, in the kaolin dispersion used with 4 gm and 6 gm gloves, is from 0.7 to 1 .0 μιτι.

While these specific examples relate to milled kaolin, the present inventors believe that similar results will be seen in substituting the kaolin in whole or in part with one or other milled aluminium silicate, where the aluminium silicate has the formula xAI₂O3.ySiO₂.zH₂O, where x, y and z are integers and can each be any one of 0, 1 , 2 or 3. Optionally, the milled aluminium silicate can be any one, two, three or more of: AI₂SiO₅ (AI₂O₃.SiO₂); AI₂Si₂O₅(OH)₄ (AI₂O3-2SiO2-2H₂O); AI₂Si₂O₇ (AI₂O₃.2SiO₂); AI₆SiO₁₃ (3AI₂O₃.2SiO₂); and/or, 2AI₂O₃.SiO₂, AI₄SiO₈.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Claims

1 . A nitrile rubber product comprising an aluminium silicate filler. 2. The nitrile rubber product of claim 1 , wherein the aluminium silicate filler has the formula:

xAI2O3.ySiO2.zH2O, where x, y and z are integers and can each be any one of 0, 1 ,

2 or 3.

3. The nitrile rubber product of any one of claims 1 or 2, wherein the aluminium silicate filler comprises any one, two, three, four or five of:

AI₂Si₂O₅(OH)₄; AI₂SiO₅; AI₂Si₂O₇; AI₆SiO ₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈.

4. The nitrile rubber product of any one of claims 1 , 2 or 3, wherein the aluminium silicate filler is a kaolin filler.

5. The nitrile rubber product of any one of claims 1 to 4, wherein the nitrile rubber is nitrile butadiene rubber (NBR).

6. The nitrile rubber product of one of claims 1 to 5, wherein the aluminium silicate filler is milled aluminium silicate.

7. The nitrile rubber product of any one of claims 1 to 6, wherein the aluminium silicate filler has a maximum particle size of 10 μιτι.

8. The nitrile rubber product of any one of claims 1 to 7, wherein the aluminium silicate filler has a maximum particle size of 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

9. The nitrile rubber product of claim 7 or claim 8, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin.

10. The nitrile rubber product of any one of claims 7 to 9, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

1 1 . The nitrile rubber product of claim 9 or claim 10, wherein the aluminium silicate filler is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

12. The nitrile rubber product of any one of claims 9 to 1 1 , wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 10 to

18 m²/g; optionally, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 14 to 16 m²/g.

13. The nitrile rubber product of claim 12, wherein the BET surface area is measured by a micromeritics™ TriStar II Plus.

14. The nitrile rubber product of any one of claims 6 to 13, wherein the maximum particle size is measured by a micromeritics™ SediGraph III Plus.

15. The nitrile rubber product of any one of claims 1 to 14, wherein the aluminium silicate filler has a maximum particle size of from 50% to 90%, optionally 60%, below 2 μιτι measured by a micromeritics™ SediGraph III Plus.

16. The nitrile rubber product of any one of claims 1 to 15, wherein the nitrile rubber product further comprises a biocide.

17. The nitrile rubber product of claim 16, wherein the biocide is any one or more of:

a 1 ,2-benzisothiazol-3(2H)-one; optionally, Acticide™ B20, Nipacide™ BIT20 , Proxel™ GXL, Bioban™ ULTRA BIT20, Microcave™ BIT,

Nuosept™ BIT Technical , Promex™ 20D and/or, Colipa™ P96;

a 2-methyl-4-isothiazolin-3-one.

18. The nitrile rubber product of any one of claims 1 to 17, wherein the nitrile rubber product is a fuel or oil handling hose, a seal, a grommet, a fuel tank, a glove, a moulded good, footwear, an adhesive, a sealant, a sponge, an expanded foam or a floor mat.

19. The nitrile rubber product of any one of claims 1 to 18, wherein the nitrile rubber product is a glove.

20. The nitrile rubber product of claim 19, wherein the glove is an NBR glove.

21 . The nitrile rubber product of claim 20, wherein the NBR glove has a thickness of 0.05 mm (plus or minus 10%).

22. The nitrile rubber glove of claim 20 or claim 21 , wherein the NBR glove has a weight of 3.5 gm (plus or minus 10%).

23. The nitrile rubber product of any one of claims 1 to 22, wherein at least 5% by weight of the nitrile rubber product is aluminium silicate filler.

24. The nitrile rubber product of any one of claims 1 to 23, wherein at least 10%, or 15%, or 20%, or 25%, or 30% or 35%, or 40% by weight of the nitrile rubber product is aluminium silicate filler.

25. A method of forming a nitrile rubber product, wherein the method comprises the steps of:

forming a nitrile rubber latex composition;

forming an aluminium silicate dispersion;

26. The method of claim 25, wherein the former is shaped corresponding to the shape of the product to be formed.

27. The method of claim 25 or 26, wherein the method further comprises one, two, three, four, five or six of the steps of:

passing the covered former through a warm oven, optionally at from 85 to 95°C, for from 2 to 3 minutes;

vulcanising the nitrile with zinc oxide, sulfur, an accelerator and/or TiO₂, optionally at 120 to 140°C for 20 minutes (plus or minus 10%);

dipping the products in a slurry of starch and/or biocide;

28. The method of any one of claims 25 to 27, wherein the nitrile rubber latex composition comprises, consists of or consists essentially of: 2- propenenitrile, 1 ,2-butadiene and 1 ,3-butadiene; wherein if the nitrile rubber latex composition consists essentially of 2-propenenitrile, 1 ,2-butadiene and 1 ,3-butadiene the nitrile rubber latex composition comprises no more than 10% of other components.

29. The method of any one of claims 25 to 28, wherein the aluminium silicate dispersion comprises from 30 to 75% aluminium silicate by weight, from 30 to 60% aluminium silicate by weight, from 35 to 55% aluminium silicate by weight, from 60 to 75% aluminium silicate by weight, from 40 to 50% aluminium silicate by weight, or 45% aluminium silicate by weight, the balance being water.

30. The method of any one of claims 25 to 29, wherein the aluminium silicate dispersion consists of water and aluminium silicate, wherein the aluminium silicate has a maximum particle size of 10 μιτι, or 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

31 . The method of claim 30, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin.

32. The method of claim 30 or claim 31 , wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

33. The method of claim 31 or claim 32, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

34. The method of any one of claims 31 to 33, wherein the aluminium silicate is a kaolin filler with a BET surface area of from 10 to 18 m²/g;

optionally, wherein the aluminium silicate is a kaolin filler with a BET surface area of from 14 to 16 m²/g.

35. The method of claim 34, wherein the BET surface area is measured by a micromeritics™ TriStar II Plus.

36. The method of any one of claims 25 to 35, wherein the nitrile rubber is nitrile butadiene rubber (NBR) and the nitrile rubber latex composition is a nitrile butadiene rubber (NBR) latex composition; or, wherein the nitrile rubber latex composition is carboxylated nitrile butadiene rubber (XNBR) latex composition.

37. The method of any one of claims 25 to 36, wherein the aluminium silicate dispersion has a pH of from 9 to 12.

38. The method of any one of claims 25 to 37, wherein the aluminium silicate has the formula:

39. The method of any one of claims 25 to 38, wherein the aluminium silicate comprises any one, two, three, four or five of: AI₂Si₂O5(OH)₄; AI2S1O5; AI₂Si₂O₇; AI₆SiO ₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈.

40. The method of any one of claims 25 to 39, wherein the aluminium silicate is kaolin.

41 . A nitrile rubber latex composition for dip-forming comprising:

a nitrile rubber latex; and,

an aluminium silicate.

42. The nitrile rubber latex composition of claim 41 , wherein the aluminium silicate is milled aluminium silicate.

43. The nitrile rubber latex composition of claim 41 or claim 42, wherein the aluminium silicate has a maximum particle size of 10 μιτι.

44. The nitrile rubber latex composition of any one of claims 41 to 43, wherein the aluminium silicate has a maximum particle size of 9 μιτι, or 8 μιτι, or 7 μιτι, or 6 μιτι, or 5 μιτι, or 4 μιτι, or 3 μιτι, or 2 μιτι.

45. The nitrile rubber latex composition of any one of claims 41 to 44, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin.

46. The nitrile rubber latex composition of any one of claims 44 or 45, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

47. The nitrile rubber latex composition of claim 45 or claim 46, wherein the aluminium silicate is a kaolin filler substantially free of nano-kaolin in that the kaolin filler includes less than 5% by weight, or less than 1 % by weight, or less than 0.5% by weight, or less than 0.1 % by weight nano-kaolin, the nano-kaolin having a particle size of less than 1 μιτι, or less than 500 nm, or less than 100 nm.

48. The nitrile rubber latex composition of any one of claims 45 to 47, wherein the aluminium silicate is a kaolin filler with a BET surface area of from 10 to 18 m²/g; optionally, wherein the aluminium silicate filler is a kaolin filler with a BET surface area of from 14 to 16 m²/g.

49. The nitrile rubber latex composition of claim 48, wherein the BET surface area is measured by a micromeritics™ TriStar II Plus.

50. The nitrile rubber latex composition of any one of claims 41 to 49, wherein the maximum particle size is measured by a micromeritics™

SediGraph III Plus.

51 . The nitrile rubber latex composition of any one of claims 41 to 50, wherein the aluminium silicate has a maximum particle size of from 50% to 90%, optionally 60%, below 2 μιτι measured by a micromeritics™ SediGraph III Plus.

52. The nitrile rubber latex composition of any one of claims 41 to 51 , wherein the nitrile rubber latex comprises, or consists of, one or more of: KNL830, Synthomer 6328, Synthomer 6330, Nantex 672, LG-Lutex 105, LG- Lutex 120, BST 8503 S, Polylac 580N, Nipol™ LX 550 or Nipol™ LX 550L.

53. The nitrile rubber latex composition of any one of claims 41 to 52, wherein the aluminium silicate has the formula:

54. The nitrile rubber latex composition of any one of claims 41 to 53, wherein the aluminium silicate comprises any one, two, three, four or five of: AI₂Si₂O₅(OH)₄; AI₂SiO₅; AI₂Si₂O₇; AI₆SiOi₃; and/or, 2AI₂O₃.SiO₂, AI₄SiO₈.

55. The nitrile rubber latex composition of any one of claims 41 to 54, wherein the aluminium silicate is kaolin.

56. The nitrile rubber latex composition of any one of claims 41 to 55, wherein the nitrile rubber latex composition further comprises a dispersant.

57. The nitrile rubber composition of claim 56, wherein the nitrile rubber latex composition comprises 20 to 30% by weight dispersant.

58. The nitrile rubber composition of claim 56 or claim 57, wherein the dispersant is one or more of: SDBS (sodium dodecylbenzenesulfonate), sodium or ammonium salt of polyacrylic acid, sodium or ammonium salt of polymethacrylic acid, or a copolymer of acrylic acid with any one of:

methacrylic acid, acrylamide or hydroxypropylacrylate.

59. The nitrile rubber latex composition of any one of claims 56 to 58, wherein the nitrile rubber latex composition is an NBR latex composition.

60. A method of forming a nitrile rubber product substantially as set out in figure 2.

61 . Any novel feature or combination of features disclosed herein.