GB2218422A - Fillers - Google Patents

Fillers Download PDF

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Publication number
GB2218422A
GB2218422A GB8811191A GB8811191A GB2218422A GB 2218422 A GB2218422 A GB 2218422A GB 8811191 A GB8811191 A GB 8811191A GB 8811191 A GB8811191 A GB 8811191A GB 2218422 A GB2218422 A GB 2218422A
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GB
United Kingdom
Prior art keywords
filler
particles
plastics
fire retardant
smoke suppressant
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB8811191A
Other versions
GB8811191D0 (en
Inventor
Stephen Clifford Brown
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Rio Tinto Alcan International Ltd
Original Assignee
Alcan International Ltd Canada
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcan International Ltd Canada filed Critical Alcan International Ltd Canada
Priority to GB8811191A priority Critical patent/GB2218422A/en
Publication of GB8811191D0 publication Critical patent/GB8811191D0/en
Publication of GB2218422A publication Critical patent/GB2218422A/en
Withdrawn legal-status Critical Current

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    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K9/00Use of pretreated ingredients
    • C08K9/04Ingredients treated with organic substances
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08KUse of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K9/00Use of pretreated ingredients
    • C08K9/02Ingredients treated with inorganic substances

Abstract

A filler for plastics materials which imparts electrical conductivity comprises particles of a fire retardant/smoke suppressant solid at least partially coated with at least one layer of an electrically conductive material. The preferred fire retardant/smoke suppressant is alumina trihydrate. The resulting filled plastics materials can be used in any situation where r.f. radiation shielding or an anti-static effect is desired, for example in the housing of electronic data processing equipment.

Description

FILLERS This invention relates to fire retardant/smoke suppressant fillers for plastics materials which impart electrical conductivity to the filled plastics material.
Plastics material formed of organic polymers have an enormous number of applications and commonly contain inorganic mineral fillers to modify their mechanical properties. Most plastics materials are good electrical insulators. In some situations it is desirable to modify the electrical properties of the plastics material. For example it may be desired to reduce the electrical resistance of a plastics article in order to render it anti-static, that is to allow accumulated static electric charge on its surface to be discharged through the article. It may also be desired to modify the electric resistance sufficiently to enable the plastics material to interact with radio frequency (r.f.) electromagnetic radiation so that the material can act as an r.f. radiation shield.Shielding is generally desired for r.f. radiation in the range 1OKHz to 20GHz.
The latter feature is becoming more and more important given the proliferation of electronic data processing equipment, including computers, and other electrical equipment in homes, offices and factories, which has led to a large increase in stray r.f. radiation of a wide range of frequencies. Such unwanted r.f. radiation can interfere with radio, and even cable, communications systems as well as with other sensitive electrical devices, sometimes with serious results. R.f. radiation shielding can be required both against the ingress of radiation from outside to a piece of equipment and against the egress of radiation to the outside from a piece of equipment.
Electrical equipment may be shielded by a metal casing in which it is enclosed, but much electrical equipment is nowadays mounted in plastics enclosures which, if electrically insulating, do not provide any significant shielding against r.f. radiation. Cables comprising a conducting core surrounded by a plastics sheath are likely to be affected in the same way.
It is generally possible to provide a shield against r.f. radiation by applying a metal sheath or conductive metal coating to the plastics article. A conductive coating may be applied by a number of methods such as the application of conductive paint, flame or arc spraying, electroless plating and vacuum metallising or cathode sputtering. All these processes require treatment of the plastics article after it is formed into shape, generally by moulding, and so are expensive in both labour and equipment. There are also dangers in surface treatment which involve high temperatures and chemical treatment, and/or the use of solvents, as these may attack the plastics material. Some of these methods are limited by geometrical considerations, for example a conductive paint may not penetrate recessed areas of the surface.Conductive finishes are also liable to degrade by flaking, chipping, peeling and corrosion.
Another approach is to provide a core of electrically conducting material within the plastics article, for example by forming a sandwich of metal foil between two plastics layers. Such a sandwich is expensive as it cannot be produced in a single operation.
It is possible to render plastics electrically conducting or semi-conducting by incorporating in the plastics material fillers which are electrical conductors. However known conducting fillers have serious disadvantages. For example, non-porous spherical glass particles coated with metal may be added to the material but a very high content of these particles is required, seriously affecting the mechanical properties of the plastics material and giving severe processing difficulties. Similar problems arise if large amounts of carbon black are added. Furthermore even relatively small amounts of carbon black colour the plastics material black which can be unacceptable.Conducting fillers with a high aspect ratio, such as metal fibres, metal-coated glass fibres, metal flakes and metal-coated flakes may be added but are likely to give a poor surface finish, rendering the plastics material unsuitable for many applications. Fibres and flakes also degrade when the material is shaped by injection moulding, so that the conductivity of the plastics material may be adversely affected.
There are also known certain inorganic materials which may be used as fillers and which impart to the plastics materials fire retardant properties and/or suppress the formation of smoke. These properties are important in many situations as most plastics are flammable when raised to a sufficient temperature. In particular, the plastics used in electrical cables or other electrical equipment may be heated to dangerously high temperatures in the event of a short-circuit or other electrical fault. Whether a given filler behaves as a fire retardant or as a smoke suppressant may depend on the particular plastics material into which the filler is incorporated. Some fillers can act as both a fire retardant and as a smoke suppressant. Accordingly the general term "fire retardant/smoke suppressant fillers will be used herein.Examples of such known fillers are alumina hydrates, magnesium hydroxide, zinc borates, magnesium carbonates, zinc stannate, zinc hydroxy stannate and antimony oxides. All these materials have a relatively low electrical conductivity and plastics materials containing them are good insulators.
The present invention seeks to provide inorganic filler materials for plastics materials which impart both fire-retardant/smoke suppressant properties and electrical conductivity to the filled plastics material.
According to one aspect of the present invention, a filler for plastics materials comprises particles of a fire retardant/smoke suppressant solid at least partially coated with at least one layer of an electrically conductive material, the filler being capable of imparting electrical conductivity to the plastics materials.
According to a second aspect of the present invention there is provided an electrically conductive plastics material having dispersed therein particles of a coated fire retardant/smoke suppressant filler of the present invention.
According to a third aspect of the present invention there is provided a shaped article when formed from a filled, electrically conductive plastics material of the present invention.
The nature of the electrically conductive material is not critical. The material can be a metal, such as copper, nickel, etc., a non-metal, such as tin oxide, zinc selenide, etc., or an organic polymer, such as a polyacetylene, a salt of 7,7,8,8-tetracyanoquinodimethane, etc.
The nature of the plastics material into which the coated filler is to be incorporated is not critical.
The plastics material can be thermoplastic, such as polypropylene, polystyrene, etc., or thermosetting, such as an acrylic, polyester or epoxy resin, etc. If the plastics material is transparent or even translucent, the filled plastics material can have application for covering, and thereby shielding, the face of instrument displays, e.g. for vehicles, aircraft, etc. The face cover can either be made wholly of the filled plastics material or can be made of, say, optical glass having thereon a thin layer of the filled plastics material.
Any conventional fire retardant/smoke suppressant filler can be used, if it can be incorporated into a plastics material in particulate form. Examples of such fillers are alumina trihydrate, magnesium hydroxide, magnesium carbonate, zinc borate, antimony oxide, zinc stannate, ferrocene, molybdenum compounds, etc., all of which can provide either fire-retardant and/or smoke suppressant properties when incorporated into at least one type of plastics materials. Combinations of two or more such fire retardant/smoke suppressant materials may be used.
The coated filler may improve the mechanical properties of the plastics material in known manner but this is not critical. The coated filler can be used with or without other conventional plastics additives, including processing aids such as plastics coupling agents applied to the surface of the coated filler particles. Known conductive additives such as metal fibres can also be added to assist the coated fillers of the present invention.
The particle size of the solid filler may generally be selected from the particle sizes in current use for plastics filler. However the smaller particle sizes within this range have the disadvantage that, because of the high surface area of the particles pe unit volume of the particles, a large amount of the coating material has to be applied to the particles in order to achieve the required electrical conductivity. The preferred median particle size is from 150 to 0.5 microns, more preferably from 80 to 10 microns The thickness of the coating on the filler particles does not appear to be critical once a certain minimum value is exceeded since anti-static properties and r.f.
radiation shielding both appears to rely on surface, rather than bulk, conduction of electricity. The electrical resistance of the conductive material and the extent to which the coating of the filler particles is complete, both on individual particles and on the bulk of the particles, are factors which affect the required thickness of coating to be achieved for a desired degree of r.f. radiation shielding or anti-static effect When a metal is used as the coating on the filler particles it can generally be present as a very thin layer. A metal which oxidises readily when in a finely divided form tends to become converted to its oxide when the coated filler particles are exposed to the atmosphere so that the coated particles become nonconducting. A metal which is resistant to oxidation is therefore preferred. Suitable metals are silver and nickel.Gold and the platinum metals may be used, but are likely to be expensive and therefore not commercially cost effective. Copper, which has a very high electrical conductivity, may be used but has the disadvantage that it is likely to oxidise on storage.
However a copper layer on the particles may be used if it is protected from oxidation by a thin further layer of conductive material such as a metal, e.g. nickel, applied on top of the copper layer. It has been found that when a metal is used as the conductive layer it can exhibit some degree of smoke-suppressing effect in its own right depending on the plastics material used.
It is generally desirable to obtain a uniform, complete coating of the conductive material over the whole surface of the particles but it has been found that an uneven and/or incomplete coating of the particle surfaces, as observed by EDS microscopy, still gives sufficient electrical conductivity for the filled plastics material to act as an effective r.f. radiation shield and/or anti-static body.
The conductive coating may be applied to the filler particles by any conventional method. For example a metal can be coated by treating the particles in a solution containing a dissolved salt of the metal and a reducing agent which reduces the salt to the metal itself. The metal is then deposited from the solution on to the particles. When the metal is silver, an aqueous solution containing silver nitrate and an organic reducing agent such as a sugar, in the presence of a metal ion chelating agent such as 2-amino-2methylpropan-l-ol may be used. When nickel is deposited an aqueous solution of a nickel salt and a more powerful reducing agent, such as sodium thio- sulphate may be used.The deposition may be carried out simply by stirring the solid particles in the solution at a sufficiently high temperature to effect the reduction and subsequently removing the particles by filtering or decanting, washing and drying. Stirring may be unnecessary if the solution is boiled during the reduction. When silver is deposited in this way the surfaces of the solid particles may first be treated with a sensitizer such as an acid solution of stannous chloride.
The fire-retardant/smoke suppressant electrically conducting fillers of the invention may be incorporated into plastic materials in the same way as known fillers and in conventional proportions, e.g. 5 to 80% by weight. Preferably for a fire retardant filler a filler content of from 20 to 70% by weight of the filled plastics material is used. For a smoke-retardant filler, a filler content of from only a few percent up to about 208 by weight is typically used. It is found that the fire-retardant properties of the filled polymer are not significantly affected by the presence of the conductive coating on the particles.
The particle size of the filler may be selected from the sizes used for conventional fillers. However a smaller particle size, which generally entails a higher surface area, implies that a greater proportion by weight of conductive material is required to produce a coating of the required thickness, increasing both the cost and the weight of a given volume of filler. Also, when the grains are very fine a higher proportion of filler in the plastics material may be required to make it electrically conducting. On the other hand, the surface finish and mechanical properties of the filled plastics material will deteriorate if the particles are too coarse. Using alumina trihydrate as the fire-retarding/ smoke suppressant filler, a particle size in the general range of 150 to 0.5 microns, more usually 80 to 1 microns, may be used.
Fillers and filled plastics materials according to embodiments of the invention will now be described by way of illustration in the following Examples.
ExampleThl-6 In separate experiments, particles of alumina trihydrate of the surface areas given in Table 1 were shaken in an aqueous solution containing 30 g/l of stannous chloride and 30 ml/l of concentrated hydrochloric acid to sensitize the surfaces of the alumina trihydrate particles. The particles were separated from the solution by filtration and the particles repeatedly washed with distilled water, washed with acetone and air dried at 1100C for 30 minutes.
The particles were then treated with a silver plating solution containing 50 ml of 2% w/v fructose solution and 50 ml of 2% w/v silver nitrate solution to which was added a 50% by weight solution of AMP (2-amino-2-methylpropan-l-ol) until the solution just cleared, followed by a few drops more of AMP. The quantity of solution used was sufficient to provide the quantity of silver nitrate given in Table 1. The solution containing the particles was heated at 800C for 45 minutes with stirring and the particles were then separated by filtration, washed repeatedly in distilled water, washed in acetone and dried at 110 C for one hour.
Table 1 Example Surfeçe area Silver ATH of ATH Nitrate (g) 1 0.05 0.2 1.5 2 3 1.3 10 3 3 1.3 5 4 3 15 10 5 1 0.2 2 6 0.2 0.2 2 The particles obtained in Examples 1 and 4 were blended into a polyester resin in an amount of 60% by weight (37% by volume) and the resin was formed into test bars and cured. The bars showed a degree of electrical conductivity that would be likely to provide useful protection against r.f. electromagnetic radiation or to permit dissipation of a static electric charge.
Examples 7-18 In separate experiments particles of alumina trihydrate of the surface areas given in Table 2 were shaken with aqueous solutions containing the amounts of nickel nitrate and sodium thiosulphate given in Table 2. In examples 7 and 8 the particles were first treated with stannous chloride and hydrochloric acid, in the other examples this step was omitted. The particles were treated with the boiling nickel nitrate/thiosulphate solution for 45 minutes and the particles were separated by filtration, washed first with distilled water and then with acetone, and dried at 1100C for one hour.
The particles from Examples 7-18 were used as fillers in a polyester resin in an amount of 36% by olu. The bars showed a degree of electrical conductivity that would be likely to provide useful protection against r.f. electromagnetic radiation or to permit dissipation of a static electric charge.
Example 19 A large scale test panel (2 metres x 2 metres x 1.25 cms) was constructed using an unsaturated polyester resin (Strand Glass Resin A) plus a 56.6% by weight addition of nickel coated ATH particles produced in accordance with Example 12. This product was found to render polymers electrically conductive when incorporated thereinto. The panel was submitted to the MIL-STD 285 Standard test method for shielding against electromagnetic interference. The test panel was compared to a control panel which was manufactured identically but without a nickel coating on its ATH particles. The coated ATH particles were found to impart an attenuation in r.f. electromagnetic interference greater than the control panel by the following amounts: 84 decibels at 100 KHz 62 decibels at 1 MHz 24 decibels at 10 MHz 24 decibels at 100 MHz This is a useful level of performance for protection against r.f. electromagnetic interference.
Table 2 Example Nickel Surface Nitrate Thiosulphonate (g) area of (g) (g) ATH (m/g) 7 30 40 3 1 8 10 10 25 1 9 50 70 5 1 10 25 35 5 1 11 15 20 5 1 12 25 40 10 1 13 25 45 15 1 14 100 140 5 3 15 100 140 10 3 16 50 70 5 3 17 20 28 5 3 18 30 50 5 3

Claims (11)

  1. CLAIMS 1. A filler for plastics materials comprising particles of a fire retardant/smoke suppressant solid at least part,at ' coated with at least one layer of an electrically conductive material, the filler being capable of imparting electrical conductivity to the plastics materials.
  2. 2. A filler as claimed in claim 1 wherein the electrically conducted material is copper, nickel, silver, gold or platinum.
  3. 3. A filler as claimed in claim 1 wherein the electrically conducted material is tin oxide or zinc selenide.
  4. 4. A filler as claimed in claim 1 wherein the electrically conducted material is a polyacetylene or a salt of 7,7,8,8-tetracyanoquinodimethane.
  5. 5. A filler as claimed in any one of the preceding claims wherein the fire retardant/smoke suppressant comprises alumina trihydrate.
  6. 6. A filler as claimed in any one of the preceding claims wherein the median particle size of the fire retardant/smoke suppressant is from 150 to 0.5 microns.
  7. 7. A filler as claimed in claim 6 wherein the median particle size of the fire retardant/smoke suppressant is from 80 to 10 microns.
  8. 8. An electrically conducted plastics material having dispersed therein particles of a coated fire retardant/ smoke suppressant filler as claimed in any one of the preceding claims.
  9. 9. A plastics material as claimed in claim 8 wherein the filler is present in an amount of from 5 to 80% by weight.
  10. 10. A plastics material as claimed in claim 9 wherein the filler is present in an amount of from 20 to 70% by weight.
  11. 11. A shaped article when formed from a filled, electrically conducted plastics material as claimed in any one of claims 8 to 10.
GB8811191A 1988-05-11 1988-05-11 Fillers Withdrawn GB2218422A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB8811191A GB2218422A (en) 1988-05-11 1988-05-11 Fillers

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Application Number Priority Date Filing Date Title
GB8811191A GB2218422A (en) 1988-05-11 1988-05-11 Fillers

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GB8811191D0 GB8811191D0 (en) 1988-06-15
GB2218422A true GB2218422A (en) 1989-11-15

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0503794A1 (en) * 1991-03-13 1992-09-16 Minnesota Mining And Manufacturing Company Radio frequency induction heatable compositions
WO1996031560A1 (en) * 1995-04-06 1996-10-10 Parker Hannifin Corporation Electrically conductive flame retardant materials and methods of manufacture
US6150447A (en) * 1995-06-22 2000-11-21 Itri Limited Fire retardant metal stannate coated inorganic fillers
US6372360B1 (en) 1996-05-01 2002-04-16 Itri Ltd. Fire retardant treatment
WO2005012435A1 (en) * 2003-07-31 2005-02-10 World Properties, Inc. Electrically conductive, flame retardant fillers, method of manufacture, and use thereof
WO2005019356A1 (en) * 2003-08-22 2005-03-03 Imperial Chemical Industries Plc Fire retardant coating compositions

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0107863A2 (en) * 1982-10-28 1984-05-09 Agency Of Industrial Science And Technology A shielding material of electromagnetic waves
EP0117700A1 (en) * 1983-02-21 1984-09-05 Kuraray Co., Ltd. Rigid resin composition having electromagnetic shielding properties

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0107863A2 (en) * 1982-10-28 1984-05-09 Agency Of Industrial Science And Technology A shielding material of electromagnetic waves
EP0117700A1 (en) * 1983-02-21 1984-09-05 Kuraray Co., Ltd. Rigid resin composition having electromagnetic shielding properties

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0503794A1 (en) * 1991-03-13 1992-09-16 Minnesota Mining And Manufacturing Company Radio frequency induction heatable compositions
US5529708A (en) * 1991-03-13 1996-06-25 Minnesota Mining And Manufacturing Co. Radio frequency induction heatable compositions
US5837088A (en) * 1991-03-13 1998-11-17 Minnesota Mining And Manufacturing Company Radio frequency induction heatable compositions
WO1996031560A1 (en) * 1995-04-06 1996-10-10 Parker Hannifin Corporation Electrically conductive flame retardant materials and methods of manufacture
US5674606A (en) * 1995-04-06 1997-10-07 Parker-Hannifin Corporation Electrically conductive flame retardant materials and methods of manufacture
US6150447A (en) * 1995-06-22 2000-11-21 Itri Limited Fire retardant metal stannate coated inorganic fillers
US6372360B1 (en) 1996-05-01 2002-04-16 Itri Ltd. Fire retardant treatment
WO2005012435A1 (en) * 2003-07-31 2005-02-10 World Properties, Inc. Electrically conductive, flame retardant fillers, method of manufacture, and use thereof
WO2005019356A1 (en) * 2003-08-22 2005-03-03 Imperial Chemical Industries Plc Fire retardant coating compositions
EP1512727A1 (en) * 2003-08-22 2005-03-09 Imperial Chemical Industries PLC Fire retardant coating compositions

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Publication number Publication date
GB8811191D0 (en) 1988-06-15

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