additives for plastics handbook || other types of additivemiscellaneous additives

CHAPTER 18

Other Types of Additive: Miscellaneous Additives

18.1 Anti-bacterials and Biocides

Anti-microbial additives and fungicides are added to plastics to increase their resistance to micro-organisms such as bacteria, fungi, and algae, which can cause black pitting, pink staining or odour, impairment of properties, and reduction of product life. Polymers such as polysulphides and polyester-based polyurethanes are vulnerable, but the main culprits for microbial growth are additives such as plasticizers, starch fillers, lubricants, thickening agents, and oils. A main area is PVC, which is also used in many vulnerable applications.

Plasticized PVC film can be attacked by micro-organisms, especially fungi, which use the plasticizer or other ingredients as a carbon source, producing discolouration, bad odour, tackiness and eventual embrittlement over a period of time. Microbial attack can be prevented by incorporation of a fungistatic agent during processing. Biocides act by interfering with the metaboUsm of microorganisms by blocking one or more of the enzyme systems. To be effective, however, the additive should migrate to the surface, a process that is influenced both by its chemistry and compatibility. Also influential is the internal structure of the PVC film (ingredients), as well as the processing conditions.

Many chemicals have anti-microbial properties, such as quaternary ammonium salts, but few are suitable for use in plastics, requiring low cost, compatibility, thermal stability during processing, environmental stability, and safe and easy handling. Microbial agents must migrate to the surface of the plastic and prevent bacterial growth.

Additives for preservation of plastics will, however, undergo a significant shift in consumption patterns, away from arsenic-based products (which currently account for over 70% of the market). The market leader is OBPA (10,10'-oxybisphenox arsine), which, although seen as the most efficient and cost-effective preservative for plastics and accepted by the Environmental Protection Agency as able to be used safely, is regarded as dangerous by consumers.

However, the total US market is estimated to be worth only about US$30 million, and manufacturers are working more on adaptation of preservation additives used in other industries. It is estimated that the overall market will

220 Additives for Plastics Handbook

increase at a rate of about 6% year for the next five years, but the demand for non-arsenic based formulations will rise at 10-20% a year. N-(trichloromethyl-thio)phthalamide (Folpet) and isothiazolin will be the main additives preferred, but other active ingredients will also gain from the changeover.

Offering an effective alternative technology for biological control, the range of JMAC biocides from Johnson Matthey has recently received food contact approval from the US FDA and German BGA. These are potent broad-spectrum antimicrobials, based on controlled release of silver ions. They are non-hazardous, non-irritant, and non-sensitizing, even in concentrated form as supplied, and are gaining wide acceptance in the polymer emulsion industry. The latest approvals cover use in paper coatings with aqueous and fatty foods, and resinous coatings.

Good anti-mildew and algicide properties are claimed for a non-arsenic-based anti-microbial agent, Amical from Argus Chemical, which is also non-irritating. It is approved by the US EPA for plastics use. Low levels of dosage in plasticized PVC, polyurethane, rubber, and other products prevent embrittlement and premature decay.

Akcros' Intercide ABF-2711 is a special formulation of OBPA biocide - 2% solution in di-(heptyl. nonyl. undecyl) phthalate plasticizer - for PVC pool- and pond-liners, tarpaulins, and marine upholstery.

Ferro's Micro-Chek anti-microbial is an EPA-registered as an industrial anti-mildew agent for PVC, PIU and other polymers, particularly in stressful outdoor applications such as roof membranes.

A biocide developed by Akcros Chemical in its Intercide range is a solid product in granular form, readily dispersing in low-density polyethylene and other polyolefins during processing, to give anti-microbial, fungicidal properties on the surface of the processed product.

An important development in recent years has been the introduction of Microban, by the company of that name. Microban is an odourless, tasteless, and colourless ingredient that is incorporated into the structure of the polymer during compounding, using proprietary technology that introduces the additive into the empty spaces forming part of the structure. It acts by neutralizing the ability of organisms to function, grow or reproduce and is built directly into the structure of the gelcoat, so promising to last for the useful life of the product.

Following extensive testing and evaluation, the biocide additive has been approved for food contact by the US organization NSF International. The certification means that the additive meets the requirements of ANSI/NSF Standard 51 , covering safety of plastics materials and components developed for contact with food in the USA. The NSF mark can now be featured on products containing the ingredient and in promotional literature and will also encourage manufacturers of food equipment, who already hold NSF approval, to use the additive in their products.

DuPont has also introduced an anti-microbial product range based on inorganic additives which have lower active agents and are safe for use in applications such as medical packaging. Under the name MicroFree, it offers light-coloured powders that are unaffected by solvents and able to withstand high temperatures.

other Types of Additive: Miscellaneous Additives 221

A masterbatch has been introduced by compounder Hanna's UK subsidiary, Victor International Plastics. Under the name Neutrabac, the masterbatch can either inhibit or destroy bacteria on moulded products, depending on the addition rate. It has been formulated to work across a broad product range, but is particularly suited to polypropylene and polyethylene compounds.

It has minimal effect on colours and is unaffected by other additives, including HALS and anti-statics, while being heat stable under normal processing conditions, to 250°C. The company sees considerable scope for the masterbatch in cooking utensils, cosmetic packaging, baby care products, bathroom accessories, and other germ-critical environments. It conforms to European Pharmacopoeia and used industry-recognized standards so that 3% addition will inhibit bacterial growth and 5% will destroy a wide variety of bacteria.

A sheet from Royalite is based on an anti-microbial masterbatch, Actifresh -initially with high impact polystyrene and polypropylene sheet incorporating Actifresh - for applications in food processing, white goods and bathroom products, but to be extended as demand increases for formed sheet in applications where fungus or germ propagation is a problem.

A polyester gelcoat, based on Microban technology, has been introduced by Neste. The company sees it as particularly interesting for gelcoats on shower and bathroom equipment, sinks, tubs, vanity tops, food preparation equipment, and interior components for hospitals and boats.

18.1.1 Anti-allergy agent

A fibre containing a repellent for dust mites (one of the leading sources of human allergies) has been introduced by the French specialist Rhovyl. Where previously the method was to treat finished textile products with massive amounts of acaricide sprays or moist powders, the French company has approached the problem by introducing a mite repellent in the fibre itself, using some unique technology.

The new fibre, named RhovylAS+, incorporates an acaricide agent which is well known to allergy specialists, but the unique feature is that the agent is added prior to extrusion of the fibre. Products made with the fibre are claimed to retain their properties throughout their life, offering permanent effectiveness, proved by the Techniques Environnement Consultants (TEC) laboratory in Anglet, France.

The fibre also contains the antibacterial agent already used in Rhovyl'AS antibacterial fibre. It can be used alone or in combination with other synthetic or natural fibres, to adjust technical qualities to meet all uses.

18.2 Degradation Additives

The urge towards recycling has also created strong interest in additives which might render plastics degradable, but experience has shown that the practical use of such materials is less than was originally estimated (see Chapter 20).


18.3 Shrinkage Modifiers, Low-profile Additives

Using fillers as a partial replacement for a reactive resin which shrinks on curing can reduce the shrinkage of the completed system. Any inert filler will decrease shrinkage, but the most commonly used are silica, clay, calcium carbonate, alumina talc, powdered metals, and lithium aluminium silicate.

A new and revolutionary approach to obtaining low- and zero-shrink DMC and BMC mouldings is with the use of a combination of low-profile additive (LPA) and calcium carbonate. The degree of shrinkage that can be achieved gives low profile mouldings with gloss levels rarely obtained before. The materials can be easily dispersed, giving exceptionally even pigmentation with none of the colour variations experienced previously with LPAs because of phase separation. In these additives, the calcium carbonate particle is coated with the appropriate polymer, resulting in a more efficient low profile action. Low- and zero-shrink grades are available, in natural white or black, which can be blended to achieve a specific shrinkage control to match the resin system. The products are in the form of beads of 80 jim mean diameter and are free flowing and less dusty than other powders. During compounding they disperse easily.

Thermoplastic additives in RP help control shrinkage during cure, permitting good control of tolerances, dimensional accuracy, and surface finish to A classification.

18.4 Improved Barrier Properties

Additives that improve the barrier properties of compounds (to liquid, gas, and oil) are a key but specialized area of activity. Development has been stimulated by the growing understanding of nano-technology. Selar platelet technology was developed a few years ago by DuPont for use in packaging and automobile fuel tanks. Ube Industries reports that the addition of clay to the nylon source material caprolactam before polymerization can reduce the gas permeability of nylons. The company terms the resulting compound a nylon clay hybrid (NCH) and has applied the technology to types 6, 66, and 12, with emphasis on food packaging grades. The clay is a stratiform silicate, added in 1 nm thick platelets. It reduces oxygen permeation from 45 ml m~^ per 24 hours for a standard PA 6 to 15-22 and in PA 6/66 from 44 to 9-23 m~^ per 24 hours. There is a small reduction in tensile strength, but the process improves stiffness and heat resistance.

A high barrier nylon film has been developed by Bayer, also using nano-additives and Nanocor, USA, has developed an aluminosilicate with platelet-type particles in the nanometer (0.001 |im) size range has been shown to reduce permeability to gases by up to 45 times in polyolefin, PET, or EVOH films. Correctly added, the platelets overlap and present a difficult path to migration of molecules through the film.

other Types of Additive: Miscellaneous Additives 223

18.4.1 Gas barrier coating

A new generation of gas barrier coatings for PET bottles has made its debut in the USA, on single-serve juice bottles produced by Graham Packaging. It has been developed by PPG Industries, in its Bairocade range. Fully compatible with existing recycling technology, the coatings are an epoxy amine, applied by electrostatic spray and cured on infra-red ovens which create the gas barrier and produce a glossy finish that resists scuffing and improves the hazy look typical of PET containers.

Bairocade coatings comply with US Food and Drug Administration regulations and do not alter the identification code of PET for recycling. Coated bottles can be processed through existing recycling systems, as has been proved in three industrial scale trials and independent laboratory tests, confirming that conventional recycling technology separates the coating from the PET for disposal as non-hazardous waste, allowing the bottles to be recycled back to fibre, strapping, sheet or even single-layer food and beverage containers.

The coatings are being applied initially as clear coats, but the chemistry can provide a broad spectrum of colours (including amber, for the beer industry), that can be appUed to clear PET bottles without reducing the value of the recycled material.

18.4.2 Resorcinol additives

Resorcinol chemistry can aid in developing high barrier polymeric materials, according to Indspec Chemical Corp. Three relevant derivatives are resorcinol dioxyacetic acid (RDOA), bis-(hydroxyethyl)-ether of resorcinol (HER) and resorcinol diglycidyl ether (RDGE).

Six major breweries have successfully bottled beer in plastic containers: Miller, Heineken, Bass, Feldschlossen, Carlton United, and Carlsberg. The bottle for Miller Lite was developed by Continental PET Technologies, using five layers, with a PA (nylon MXD6) barrier layer less than 5 wt% of the container. In Australia, Carlton United introduced a monolayer bottle coated with PPG Industries' Bairocade coating.

Since the main component of these bottles is PET with a relatively low barrier, the expected shelf life is around three months but, with the development of improved oxygen permeability (P02) and carbon dioxide (PCO2), of the barrier materials, it should be possible to deliver bottles with a shelf life of 6-9 months. The industry is aiming at polymer combinations offering values of P02 < 0.5 BU andPco2 < 2-3 BU.

P02 values and tensile strength of polyamides and polyesteramides incorporating RDOA monomer suggest that there is a tremendous opportunity for development of high barrier packaging materials, considers Indspec. The lowest P02 values indicate that monolayer containers with high gas barrier properties can be made and used for preserving the taste of beer over an extended period of time, without further modifications.

MXD6 is a polyamide made from the reaction of MXDA and adipic acid, giving a P02 value of 0.6 BU. But a polyamide made from MXDA and RDOA shows a


value of 0.25 BU. The very low oxygen permeability obtained suggests that a multi-layer container using RDOA-based polyamides can extend shelf life of products such as beer for longer than MXD6.

Resorcinol chemistry is unique due to the meta-phenylene linkage of the resorcinol molecule. The asymmetrical nature of the derivatives offers improvements in products and processes and, for gas barrier polymers, such materials are expected to be more amorphous than crystalline, suggesting that packaging materials can be highly transparent. Meta-linkages are the reason for the exceptionally high gas barrier performance and the high flexibility of the linkages increases chain-to-chain close packing, and thus provides a compact backbone structure. Based on experimental results, polymers containing meta-phenylene linkages showed 30-40% reduction in oxygen permeability compared withp-phenylene groups.

As well as offering high barrier materials, RDGE-based thermoplastics could compete with EVOH in many applications and a thermoset coating based on RDGE gives a good opportunity to modify the low barrier monolayer PET container, providing an efficient and cost-effective container for beer.

18.43 Plasma technology

Plasma technology has been harnessed on a commercial scale by the French machinery company Sidel to produce PET bottles with barrier properties claimed to be unmatched. Up to 30 times the normal barrier to oxygen and seven times stronger barrier to carbon dioxide are claimed for the bottles. This makes them comparable with glass bottles and metal drink cans, and offers a new approach to packaging in PET one of the most difficult products: beer.

The process is called ACTIS (Amorphous Carbon Treatment on Internal Surface). It consists of coating the internal surface of a standard single-layer PET bottle with a layer of highly hydrogenated amorphous carbon, obtained from food gas in its plasma state. The coating creates a thin (about 0.1 jum thick) barrier inside the bottle. The food safety quality has been approved by the Dutch standards authority (which is also accredited to the European Union), and the coated bottle is 100% recyclable.

The plasma treatment is carried out downstream from the PET blow-moulding machine, and is of a design based on the company's own well-proven rotary high-output technology. The first model, ACTIS 20, has 20 stations and can treat 10 000 PET bottles up to 0.61 litre size an hour. According to Sidel calculations, the cost price of 33 and 50 cl size containers is, in fact, less than competitive packages.

18.4.4 Oxygen absorption in food packaging

The presence of oxygen in packaged foods has long been known to be a key problem of preservation and shelf-life, producing colour degradation, loss of nutrient, changes in flavour and odour, and microbial spoilage.

Other Types of Additive: Miscellaneous Additives 225

A more effective additive system, producing a clear packaging film incorporating a polymeric oxygen scavenging system that absorbs oxygen in modified atmosphere packages (MAP), has been introduced by Cryovac Sealed Air Corp. Named OS 1000, it is claimed to reduce the oxygen concentration inside the pack to less than 10% of that in conventionally packaged foods. The technology has been known for some time and, to minimize degradation, oxygen-scavenging (OS) films have been developed, containing pouches of iron powder or with special coatings.

The action of existing OS films has been 'triggered' by excessive heat or moisture, but this system has had its limitations. Polymer-based scavenging systems can oxidize prematurely if exposed to moisture or high humidity prior to the products being packaged.

The Cryovac system is believed to overcome this problem, with a film that is activated totally independent of moisture. An organic additive is used that does not oxidize until it is exposed to UV light. In addition, the film improves colour retention in processed meats and delays the growth of yeasts and moulds. It also slows the onset of aerobic microbial growth in fresh pasta.

Data produced by Cryovac shows that, when stored at 4°C, the oxygen level in fresh pasta increases from 0.35 to 4% after 15 days when packaged in conventional MAP, and then falls steadily to about 0.03%. But, in the OSIOOO film, it immediately falls rapidly to a constant level of about 0.05% (03/99).

18.5 Hard Coatings

By using chemical vapour deposition (CVD) technology at a relatively low temperature, Nissin Electric, Kyoto, Japan, claims it is able to apply diamond-like carbon coatings to materials such as plastics and rubber, improving their properties of friction, abrasion resistance and insulation.

Conventionally, this type of coating is applied by plasma at a temperature of about 200°C, which has limited its appUcation of surfaces such as metals and ceramics. The CVD technology, however, enhanced by a plasma source operated only intermittently (PECVD), can function at around 50-80°C. Combined with plasma washing in a specific atmospheric gas, it has been possible to coat thermoplastic materials with much lower softening points.

Surface properties (such as sliding friction, abrasion resistance and insulation) are claimed to be equal to, or better than, fluorine-treated surfaces and can be achieved at lower cost. In addition, the coated surfaces have good long-term reliability. Nissin also reports that it has developed a flexible diamond-like coating, which can be stretched up to 300%.

18.6 Thermal Insulation

Hollow nylon filaments that contain ceramics, to store heat, have been developed in Japan by Unitika. The company has been producing Microart


fabrics woven from hollow nylon incorporating a ceramic to give an effective thermal insulation, but its new advanced TM fibre contains the ceramic inside the hollow fibre itself. A special spinning technology and an advanced method of controlling the polymer have been developed. The company claims that the fabrics made from these fibres are bulky, light in weight and also water-repellent. It plans to start marketing them for outerwear, and is looking for sales of some 100 000 metres in the first year.

18.7 Fragrance

Additive masterbatches with fragrance have been developed by Clariant Masterbatches. Five flavours are available, initially for use with polyethylene, with let-down ratios of 2-10%. Formulations for other plastics are under development.

18.8 PVC Matting Agent

A novel matting agent for PVC, comprising very fine pearls of a cross-linked copolymer containing acrylic monomers, has been introduced by Elf Atochem's additives subsidiary Ceca. Under the name Acrylperl, it has a very fine powder structure (typically 20-30 }im) that promotes homogeneous distribution and outstanding dispersion in the polymer melt during processing.

It is effective at addition rates as low as 0.3 phr (of resin): normal use is at 0 . 3 -4 phr, depending on the degree of matt finish required. It is also stable at elevated temperatures and has no impact on the thermal stability of the PVC compound. There is no effect on mechanical properties, and the additive (which, unlike other matting agents, has no yellowing effect) is intrinsically UV resistant. In the finished product, it produces an even matt or frosted appearance as the particles on the surface diffuse light.

It can be used effectively in many rigid, flexible and PVC plastisol applications, and is reported to be in demand in the construction sector, for door panels, skirting boards, window ledges, electrical boxes, cable runs, pipe connections, furniture, cladding, and floor and wall coverings. It remains effective in thermoforming, as the bead-Uke structure is cross-linked and is not affected by heat. It also functions, at lower addition rates (of 0.1 phr) as an anti-blocking agent in calendered or blown films, the finely frosted finish imparted by the beads significantly reducing the tendency of films to stick together.

18.9 Anti-fogging

Anti-fogging - resisting the release of ingredients that can be deposited on nearby surfaces and cause fogging - is particularly demanded by the automotive industry for materials used inside a car. It especially affects PVC and


polyurethane formulations but, in most cases, is tackled by manufacturers at the polymer level. Fogging can also occur in packaging, and most additive suppliers have developed formulations and concentrates.

Typically, Ampacet Antifog PE MB is a new blown film concentrate in LDPE/ LLDPE carrier combination, with optimum anti-fog properties at typical let-down of 8%, acceptable for food contact in North America and Europe. An anti-fogging concentrate for food packaging film is Accurel 95CM209. Based on an LDPE microporous carrier containing 25% by weight of a special glycerol ester with high glycerol monooleate content, it is claimed to be very effective in preventing build-up of condensation inside food packages, which showing low tendency to plate-out. The recommended dosing level is 1.0%, and the system has good thermal stabiUty at processing temperatures, not impairing the clarity of the film.

18.10 Acoustic Insulation

Development and use of additives to improve sound insulation properties of plastics compounds (especially required by the automotive industry) has been a strong theme of recent development. In the past, insulation theory has taken it that the most significant factor is mass, and by increasing it, insulation can be improved. This has led to use of heavy loadings of heavy fillers, such as barytes, but it goes diametrically against the other requirement of the automotive industry, reduction in weight.

New technology has centred on diversion of some of the coherent molecular movement of acoustic pressure waves into random movement of heat, by molecular bonding within a material to increase internal friction (a small amount of water added to urethanes, for example, can disrupt internal bonding).

This approach has been shown that a 1.02 mm thick flexible silicone rubber sheet can have greater attenuation than six inches of concrete and it may be applied to a wide range of materials. Experimental evidence suggests that the impedance of a material is more important than its mass. Mixing of materials with differing impedance (low and high) together in a matrix has demonstrated improvement in attenuation. Particle types tested ranged from hollow glass microspheres to iron and lead, and matrices included different types of silicone rubber, urethane, and epoxy resin. The phase of reflections from localized reflecting nodes (particles) is a function of the relationship of characteristic acoustic impedance of the particle, relative to the matrix material. A higher impedance particle will produce an in-phase reflection; a lower impedance will produce an out-of-phase reflection.

Simultaneous in-phase and out-of-phase reflections within a particular locale greatly increase the possibility of phase cancellation, which is accomplished if both high- and low-impedance particle types are mixed together in a matrix material, or if two or more particle types with merely different acoustic impedance characteristics are combined. When two or more particle types are mixed into a matrix material base in the correct proportions, a synergistic effect


causes the compound to have more acoustical attenuation than the sum of the components.

Table 18.1 Acoustic properties of some commonly used materials

Material

Tungsten carbide Nickel, unmagnetized Iron, electrolytic Steel, mild Copper, annealed Brass(70%Cu, 30%Zn) Zinc, rolled Lead, annealed Glass, borosilicate Magnesium, annealed Marble, ground Acrylic Nylon 66 Polystyrene Rubber, polychloroprene Polyethylene Paraffin Cork flour Air, dry Hydrogen

Density (kgm-^)

13 800 8850 7900 7850 8930 8600 7100

11 400 2320 1740 2600 1180 1110

12 060 1330

900 900 250

1293 0.0899

Velocity of sound (ms"^)

6655 5480 5950 5960 4760 4700 4210 2160 5640 5770 3810 2680 2620 2350 1600 19 50 1300

500 331.45

1284

Impedance (ZinRayls)

9.18x10^ 4 .85x10^ 4 .70x10^ 4 .68x10^ 4 .25x10^ 4.04x10^ 2.99x10^ 2.46x10^ 1.31x10^ 1.00x10^ 9.91x10^ 3.16x10^^ 2.91x10^ 2.49x10^^ 2.13x10^ 1.76x10^^ 1.17x10^^ 1.25x10^ 4.29x10^ 1.15x10^

Source: Modern Plastics International

18.11 Surfactants^ Foam Control Additives

Surfactants are used, especially in water-based formulations, to improve wetting, dispersion, slip and mar properties and defoaming. The group includes ethoxylated products, acetylenic alcohols and diols and proprietary additives.

A new near-zero VOC nonionic wetting agent, said to be ideal for high-performance water-borne applications, is an acetylenic glycol-based material (Dynol 604, Air Products). It has the ability to reduce both equilibrium and dynamic surface tension to a degree not found in other surfactant chemistries, and its property mix allows use in difficult-to-wet substrates requiring good flow and levelling under various application conditions.

Foaming can often be a serious problem in production and processing of polymer dispersions and latices, and silicone-based control systems have been developed to counter this effect. A range of products is available, giving choice of an appropriate grade to achieve high antifoam efficiency and/or high compatibility with specific products.

Some foam control systems conform to the guidelines of the US Food and Drug Administration (FDA) and the German Health Office (BGA), for use in products, such as coated and printed packaging materials, which come into contact with foodstuffs.


Two developments have been reported (by Wacker Chemie) supplementing its range of foam-control systems: Silicone Antifoam Emulsions SE 84 and SE 85. Based on organically modified silicone fluids, they reduce or prevent flow defects in polymer films.

Air Products' Surfynol CT-324 is a pigment grind aid for high-solids coatings, providing pigment wetting and dispersion, dispersion/viscosity stability and low foam generation.

Surfynol DF-62 is liquid 100% active ether-modified silicone defoamer, giving knockdown defoaming and long-term anti-foaming.

Non-hydrolysable silicone surfactants (for Asian PU foam producers) are Dabco DC2583 and DCS 188, respectively reducing surface skin and producing open-cell foam at low mould temperatures, and producing fine even-cell structure and improved emulsification in flexible slabstock systems.

A nucleating agent for PS foam A 27608 (Polycom Huntsman) improves cell uniformity, for FDA compliance: a natural talc-filled nucleating agent A 2 7678 is recommended for fine cell PS foam, GP and high impact grades.

To minimize air entrapment in plastisol manufacture and application, promoting faster air release and quicker de-gassing under vacuum, methyl alkyl polysiloxane and silicone-free compounds of polyalkylane derivatives are used. Addition should not exceed 0.5 phr or 0.2-1.0% depending on plastisol formulation.

18.12 Mould Treatment Agents

Although not strictly additives, agents for cleaning and maintenance of moulds are important, and the following notes may therefore be helpful.

Pulisol-9 (WIZ chemicals) is an effective solvent for cleaning moulds, metals, and similar articles. A blend of high activity and penetration solvents, which is neutral and evaporates slowly, it is a transparent liquid which can remove traces of polyurethanes, polyesters, epoxy and phenolic resins, as well as release agents, waxes, rubbers, and fats. The flash point is 31°C. The cleaner is used undiluted and applied with a cloth or brush, left to act for a few minutes and then wiped with a clean, absorbent cloth. For used moulds, more than one application may be necessary; for new moulds, one application is sufficient. Protective gloves should be worn.

Wilax (also from WIZ chemicals) is a mould sealant and conditioner in paste form, for use with metal and glass fibre-reinforced resin moulds. It deals efficiently with porous or rough areas of the mould surface and gives moulded parts a glass finish, making release easier. A water-based emulsion of high molecular weight resins with small quantities of solvents, it is a non-flammable cream white paste. It can be applied after the mould has been cleaned, using a clean cloth and allowing drying for a few minutes before polishing with a soft cloth. An external release agent can then be applied. The whole operation should be repeated whenever the mould is polished or washed.

additives for plastics handbook || other types of additivemiscellaneous additives

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