AU610240B2 - Ethylene propylene rubber mixtures and heat resistant conveyor belts produced using the same - Google Patents

Description

5845/2 5845/2 I i

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i ;-wI~ ~-c i as S F Ref: 72205 FORM COMMONWEALTH OF AUSTAL AL PATENTS ACT 19526 1 024 0 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class 4 4 o 4 o 9 4 4' Complete Specification Lodged: Accepted: Published: Priority: Related Art: Il"l As documnj,,. ont flt~ IiU s the "M1 dments made under ~Cti~ri' 49 and is correct fol L rintn61g, Name and Address of Applicant: Bando Chemical Industries, Ltd.

2-15, Meiwadori 3-chome Hyogo-ku Kobe

JAPAN

Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Complete Specification for the invention entitled: Ethylene Propylene Rubber Mixtures and Heat Resistant Conveyor Belts Produced Using the Same The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/3 Del-lared at Kobe this 1st day of December 1988 I Signature of Declarant(s) SFP3 To: The Comn:;ssioner of Patents 11/81 1

ABSTRACT

An ethylene propylene rubber mixture highly adhesive to zinc-plated metals and a heat resistant ethylene propylene rubber conveyor belt having load-carrying zinc-plated steel cords embedded therein are disclosed.

The heat resistant conveyor belt composed of an outer covering rubber layer and an inner covering rubber layer both of an ethylene propylene rubber and an adhesive rubber layer having load-carrying zinc-plated steel cords embedded therein parallel to each other at a distance there between in the londitudinal direction of the belt, the adhesive rubber layer being disposed between the covering rubber layers and bonded integrally to the covering rubber layers, the adhesive rubber comprising: an ethylene propylene rubber, an organic peroxide, a cross-linking aid, a cobalt salt of organic carboxylic acids, and sulfur.

kr~in n; Ethylene Propylene Rubber Mixtures and Heat Resistant Conveyor Belts Produced Using the Same I g r This invention relates to an ethylene propylene rubber 1 0 mixture and a heat resistant conveyor belt produced using the same. More particularly, the invention relates to an ethylene propylene rubber mixture improved in adhesion to zinc-plated metals such as zinc-plated steel cords, and further to a heat resistant conveyor belt which has load-carryi-ig zinc-plated steel cords embedded therein and bonded thereto by use of such a rubber mixture as an adhesive rubber.

A conveyor belt which is made of ethylene propylene rubber cross-linked with organic peroxides and contains duck in layers as load-carrying members enveloped therein finds wide applications where heat resistance of the bait is required on account of a high durability at high temperatures of the rubber.

However, as a request for a conveyor belt longer and higher in tensile strength is increasing, steel cords have very recently come to be preferred to duck In a steel cord reinforced belt, the steel cords are r 1 2 embedded usually as zinc-plated cords londitudinally along the length of the belt in vulcanized rubber. It is already known that a diene rubber can be directly bonded to zincplated steel cords by vulcanization or organic peroxide crosslinking of thz rubber containing cobalt salts of organic carboxylic acids both as a vulcanizing agent and an adhesive.

SHowever, ethylene propylene rubber, if it contains cobalt salts of organic carboxylic acids, can not be bonded directly to zinc-plated steel cords by organic peroxide cross-linking.

Therefore, in the production of zinc-plated steel cord reinforced conveyor belt, there has been utilized an adhesive rubber composed of a mixture of ethylene propylene diene rubber and styrene butadiene rubber containing therein sulfur and cobalt salts of organic carboxylic acids. More specifically, zinc-plated steel cords are placed between sheets of the adhesive rubber, and then sheets of covering rubber composed of ethylene propylene rubber containing organic peroxides therein are placed on both the outer sides of the adhesive rubber sheets, and the resultant sheets in layers are vulcanized under heating and pressures.

The thus obtained belts, however, is inferior in heat resistance and become stiff in a short period of time in use, and moreover, the adhesion between the adhesive rubber layer and covering rubber layer is insufficient. Accordingly the covering rubber layer and the adhesive rubber layer tend to I~ -3separate from each other, or cracks tend to be generated in the adhesive rubber layer during the use in a high temperature environment. Namely, the belt is very short in life and has no durability required in use at high temperatures.

A further zinc-plated steel cord reinforced conveyor belt has been also proposed, in which a mixture of ethylene propylene diene rubber and chlorinated ethylene propylene diene rubber is used as an adhesive rubber and ethylene propylene rubber Is used as a covering rubber. This conveyor belt is still found insufficient in heat resistance and durability.

It is, therefore, as object of the invention to provide a novel o :oo ethylene propylene rubber mixture which is highly adhesive to zinc-plated o° oO metals, for example, zinc-plated steel cords.

Oooo: It Is a further object of the invention to provide a heat resistant 0o 0 and a durable ethylene propylene rubber conveyor belt which has zinc-plated YS steel cords embedded therein utilizing such a rubber mixture as an adhesive 0 rubber.

0 According to a first embodiment of the present Invention there is o0 °0 provided an ethylene propylene rubber mixture adhesive to zinc-plated metals which comprises: an ethylene propylene rubber; an organic peroxide as a cross-linking agent in amounts of 0.01-0.02 moles per 100 g of the o:.0.0 ethylene propylene rubber; a polyhydrlc alcohol polyester of acrylic acid or methacrylic acid as a cross-linking aid in amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a cobalt salt of organic carboxylic acids in amounts of 0.2-0.5% by weight as metallic cobalt based on the rubber mixture; and either sulfur or an organic polysulfide or a mixture of these in amounts of 0.2-0.4% by weight based on the rubber So°0 0 mixture.

According to a second embodiment of the present invention there is provided a heat resistant conveyor belt composed of an ou.er covering rubber layer and an inner covering rubber layer both of an ethylene propylene rubber and an adhesive rubber layer between the covering rubber layers, the belt having load-carrying zinc-plated steel cords embedded therein parallel to each other at a distance therebetween in the longitudinal direction of the belt, the conveyor belt comprising: the zinc-plated steel cords enveloped In the adhesive rubber layer and bonded to the covering rubber layers integrally, the adhesive rubber comprising an ethylene propylene rubber, an organic peroxide as a cross-linking agent in c -'1 3A amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a polyhydric alcohol polyester of acrylic acid or methacrylic acid as a cross-linking aid in amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a cobalt salt of organic carboxylic acids in amounts of 0.2-0.5% by weight as metallic cobalt based on the rubber mixture; and either sulfur or an organic polysulfide or a mixture of these in amounts of 0.2-0.4% by weight based on the rubber mixture.

o0 i o f o a O S' 4 ppy oe-ne c u-b-be--a-Pobalt salt ef organic carbox ylic acids in amounts of about 0.2-0.5 by weight as m c cobalt based on the rubber mixture, either sulfur, an organic polysulfide mixture of these in amounts of about 0.2b- T y--e-i-ght basod on the ru-bbor mixture.

The ethylene propylene rubber used in the invention includes an ethylene propylene rubber (EPM) in the narrow sense, ethylene propylene diene rubber (EPDM) and a mixture of these. A mixture of EPM in amounts of about 10-90 by i S 10 weight and EPDM in amounts of about 90-10 by weight is I. particularly preferred in the invention. A portion of the ethylene propylene rubber may be displaced by other rubbers in amounts not adversely affecting the improved adhesion characteristics of the rubber mixture of the invention.

The rubber mixture of the invention contains as a vulcanizing agent an organic peroxide, which is exemplified by dicumylperoxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-di(t-butylperoxy)hexyne-3 and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, but is not limited to these. The organic peroxide is contained in the rubber mixture in amounts of 0.01- 0.02 moles pir 100 g of the ethylene propylene rubber used.

The cross-linking aid or auxiliary used in the invention includes'polyhydric alcohol polyesters of acrylic acid or methacrylic acid, suc c'asF ethylene glycol diacrylate,

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L i, ethylene glycol dimethacrylate, propylene glycol diacrylate, propylene flycol dimethacrylate, 1,4-butylene glycol diacrylate, 1,4-butylene glycol dimethacrylate, trimethylolpropane crimethacrylate. Triallylisocyanurate is also usable as a cross-linking aid. The cross-linking aid is contained in the rubber mixture in amounts of about 0.01-0.02 moles per 100 g of the ethylene propylene rubber used.

The rubber mixture of the invention further contains a cobalt salt of organic carboxylic acids as an adhesive, and o a sulfur or an organic polysulfide as an adhesion aid, the terms 0 0 0O0 the adhesive and the adhesion aid used herein being for con- 0 9 o°°0 venience only since the adhesion mechanism involved in the o o invention is not yet completely clear. The cobalt salt of 0 00 organic carboxylic acids preferably used in the invention includes naphthenic acid salts and aliphatic carboxylic salts. More specifically, therefore, cobalt naphthenate, cobalt octylate, cobalt stearate, cobalt palmitate, cobalt 0. neodecanoate or the like is preferred. A mixture of two or more of these may be used. The cobalt salt is contained in 20 the rubber mixture in amounts of about 0.2-0.5 by weight 00, as metallic cobalt based on the weight of the rubber mixture.

0 6 The sulfur used in the invention is not specifically limited, but includes, for example, powdered sulfur and insoluble sulfur. -he organic polysulfide used herein is such an organic compound as liberates sulfur when being heated, 6 and includes, for example, morpholine disulfide, alkylphenol disulfides, thiuram polysulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylenethiuram disulfide, dipentamethylenethiuram tetrasulfide and 2-(4-morpholino)benzothiazole. The sulfur or the organic polysulfide is contained in the rubber mixture in amounts of about 0.2-0.4 by weight, preferably of about 0.30-0.35 by weight, based on the weight of the rubber mixture.

0 00 1o 0 The rubber mixture of the invention may further contain o a conventional adhesive composed of a combination of a 0 0

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a methylene donor such as alkylphenols and a methylene acceptor 0 90 oo such as hexamethylenetetramine, together with, if needed, usual rubber chemicals such as antioxidants, reinforcements, Bg., inorganic or organic fibers, accelerator activators K ge.g., zinc oxide or stearic acid or zinc salt thereof, fillers, softners or processing aids.

The rubber mixture of the invention accieves a high adhesion to zinc-plated metals, for example, zinc-plated steel cords, by vulcanization, and further the resultant composite is of high heat resistance or durable at high temperatures.

Therefore, the rubber mixture is advantageous for use as an adhesive rubber in the production of a heat resistant ethylene propylene rubber conveyor belt which contains ethylene propylene covering rubber and has zinc-plated steel cords as 7 load-carrying members embedded therein to bond the cords to the ethylene propylene covering rubber. The cross-linking aid as hereinbefore described is particularly useful to improve the resistance to thermal aging or deterioration of the adhesion of ethylene propylene rubber to zinc-plated steel cords.

Ther-tire, as a further aspect of the invention, there is provided a heat resistant conveyor belt composed of (a) an outer and an inner covering rubber layer both of an ethylene propylene rubber and an adhesive rubber layer between the covering rubber layers, the belt having load-carrying zincplated steel cords embedded therein parallel to each other at a distance therebetween in the londitudinal direction of the belt, which comprises: the zinc-plated steel cords enveloped in the adhesive rubber layer and bonded to the covering rubber layers integrally, the adhesive rubber comprising an ethylene propylene rubber, an organic peroxide, a cross-linking aid, a cobalt salt of organic carboxylic acids, and either sulfur, an organic polysulfide or a mixture of these.

More specifically, the heat resistant conveyor belt of the invention composed of an outer and an inner covering rubber layer both of an ethylene propylene rubber and an adhesive rubber layer having load-carrying zinc-plated steel cords embedded therein parallel to each other at a distance therebetween in the londitudinal direction of the belt, the ~1 adhesive rubber layer being disposed between the covering rubber layers and bonded integrally to the covering rubber layers, the adhesive rubber comprising: an ethylene propylene rubber, an organic peroxide in amounts of about 0.01-0.02 moles per 100 g of the ethylene propylene rubber, a crosslinking aid in amounts of about 0.01-0.02 moses per 100 g of the ethylene propylene rubber, a cobalt salt of organic carboxylic acids in amounts of about 0.2-0.5 by weight as metallic cobalt based on tne rubber mixture, and either sulfur or an organic polysulfide or a mixture of these in amounts of about 0.2-0,4 by weight based on the rubber mi x ture.

In the production of the conveyor belt, the covering rubber and the adhesive rubber are used usually in the fore of sheet. The zinc-plated steel cords are placed between the adhesive rubber sheets parallel to each other at a distance therebetween In the londitudinal direction of the belt, and the covering rubber sheets are placed on either outer sides of the adhesive rubber sheets, and than the covering sheets and the adhesive sheets in layers are vulcanized under heating and pressures in accordance with conventional methods known in the art of ethylene propylene rubber.

The thus otained conveyor belt has zinc-plated steel cords embedded therein and directly bonded with a high adhesive force teo the ethylene propylene rubber, so that the 00 004 0 000~o 0 0 0 PC 00

PC

4 PC 9 belt is of high hleat resistance and durability.

The invention will now be more fully described wi th reference to examples, to Which, however, the invention is not l imi ted.

Examples 1-7 A rubber compound Was prepared composed of (in parts by weight): 100 parts of ethylene propylene rubber (EPtI by Japan Synthetic Rubber Co., Ltd.), 5 parts of zinc oxide, 2.7 parts of dicumylperoxide, 2 parts of ethylene glycol dimethacrylato, 40 parts of HAP carbon black, 5 parts of paraffin oil and 2 0 parts of an antioxidant.

0 The rubber compound was calendered to covering rubber sheets of 6.7 mm in thickness, While the rubber compounds an 015 shown in Table 1 Were calendered to adhesive rubber sheets,- of 2.7 mm in thickness, respectively, A plurality of zinc-plated steel cords of 4.6 mm in diame ter were placed parallel to each other at a distLance of 13 mm between tite adhesive rubber sheets, and then the cover- 20 ing rubber shieets were placed on ei ther outer sides of the adhesive rubber shieets, Then the thus layered sheets wero vulcanized under heating at 160*C for 40 minutes under a pressure of 25 kg/cm 2 to provide a conveyor belt.

At test specimen was prepared according to the JIS K 6319 method, and pulling strength or adhesion at an Initial 0 14 0 4 4,I zinc-plated steel cords enveloped in the adhesive rubber layer and bonded to the covering rubber layers integrally, the adhesive rubber comprising an ethylene propylene rubber, an organic peroxide as a cross-linking agent in /2 stage and after a forced thermal aging at heating 165°C for 225 minutes. The results are shown in Table 1.

Reference Examples 1-4 Without the use either or all of the cross-linking aids, cobalt salts and sulfur, and otherwise in the same manner as in the above examples, adhesive rubber sheets wore prepared.

Conveyor belts were produced using the above adhesive rubber sheets in the same manner as in the examples. The pulling strength of the cords at the initial stage and after the same thermal aging as above set forth are shown in Table 1.

Reference Examples 5 and 6 Using the adhesive rubber sheets composed of a mixture of ethylene propylene diene rubber and styrene butadiene rubber and a mixture of ethylene propylene diene rubber and chlorinated ethylene propylene diene rubber, respectively, as shown in Table 2, conveyor belts were produced in the same manner as in the examples. The pulling strength at the initial stage and after the t:ermal aging are shown in Table 2.

As will be apparent in Reference Example 1, the belt prepared by use of an adhesive rubber which contains neither cobalt salts nor sulfur has a very small pulling adhesion of zinc-plated steel cords. As is seen in Reference Example 2, 11 Table I Reference Examples Examples 1 2 1 2 3 4 Rubber Compounds (parts by weight) EP-11' 50 50 50 50 50 51 EP-33" 2 50 50 50 50 50 Zinc oxide 5 5 5 5 5 Stearic acid 1 1 1 1 1 1 Antioxidant 0.5 0.5 0.5 0.5 0.5 Dicumylperoxide 3.2 3.2 3.2 3.2 3.2 3.2 Cobalt neodecanoate 5 5 5 5 7

EGDMA

3 2.5 2.5 2.5 2.5 2.5 Sulfur 0.3 0.7 1.1 0.7 Carbon black 80 80 80 80 80 Processing oil 10 10 10 1, 10 Belt Properties, Initial stage Cord pulling strength (kg/5 cm) 180 320 480 550 480 555 Rubber adhesion on the cord 4 0 50 80 100 100 100 Belt Properties, After thermal aging" Cord pulling strength (kg/5 cm) -310 470 535 520 530 Rubber adhesion on the cord 4 -40 70 90 90

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-j i 0 a 0.0 000 0 0 0 0 0 0 0 0 a 0 0 0 00 0 0 0 0 4 000 000 000 000 00 Ila Table I (Continued) Reference Examples Examples 1 2 1 2 34 Notes: 1) EPMl by Japan Synthetic Rubber Co., Ltd.

2) F.PDI1 by Japan Synthetic Rubber Co., Ltd.

3) Ethylene glycol dimethacrylate 4) Percentage of the surface of cords covered withi rubber after Pulling out from the belt.

Heated at 165-C for 225 minutes 12 Table 1 (Continued) a- rs-ar 9 ~t

-I

Example 5 Reference Examples Examples 6 7 Rubber Compounds (parts by weight) EP-11 EP-33 Zinc oxide Stearic acid Antioxidant Dicumylperoxide Cobalt neodecanoate

EGDMA

Sulfur Carbon black 50 50 5 1 0.5 3.2 9 2.5 0.7 80 50 50 5 1 0.5 3.2 7 0,7 80 50 50 5 1 0.5 3.2 7 2.5 75 25 5

I

0.5 3.2 7 2.5 0.7 80 1 3.2 7 0.7 Processing oil 10 10 10 10 Belt Properties, Initial stage Cord pulling strength (kg/5 cm) 560 540 315 480 570 Rubber adhesion on the cord 100 100 50 100 100 Belt Properties, After thermal aging Cord pulling strength (kg/5 cm) 535 420 310 475 520 Rabber adhesion on the cord 90 60 40 90 -s AIL 1 In a steel cord reinforced belt, the steel cords are 13 Table 3 Reference Examples 6 S 10 o I 0 0 0 0 0 o 0o 0 0 0o 00 0 0 0 0 0 2 0 0 0 o 4 0 0 0 o o o *o o at a i Rubber Compounds (parts by weight) SBR 1500 2 Chlorinated EPDI'M Zinc oxide Accelerator Antioxidant Stearic acid Cobalt neodecanoate Sulfur Carbon black Processing oil 1 1 5 1.2 80 20 1 1.2 Belt Properties, Initial stage Cord pulling strength (kg/5 cm) 410 420 Rubber adhesion on the cord 4 70 Belt Properties, f, cer thermal Cord pulling strength (kg/5 cm) 350 300 Rubber adhesion on the cord 4 50 Notes: Gt 1) EPDMI by Japan Synthetic Rubber Co., Ltd.

2) Styrene hutadiene rubber by Japan Synthetic Rubber Co. Ltd.

3) Chlorinated EPDM by Japan Synthetic Rubber Co., Ltd.

4) Percentage of the surface of cords covered with rubber after pulling out from the belt.

Heated at 165*C for 225 minutes 110 Li tU V tI I11 I UUU a i iay GUi ai u LiU a u &i a j i 14 the use of cobalt salts in the adhesive rubber improves to a degree the pulling adhesion of the cords, but the adhesion is still insufficient, whereas the belt prepared without the use of cross-linking aids in Reference Example 3 is improved in pulling adhesion of the cords at the nitial stage, but still small after the thermal aging, thus is inferior in heat resistance. When an adhesive rubber containing a cross-linking aid but no sulfur therein is used, the resultant belt is much inferior in adhesion and heat resistance as seen in Reference .0 10 Example 4.

0 As is further shown in Table 2, the use of adhesive a o o 0o Srubbers composed either of a mixture of ethylene propylene o 0 0 0 diene rubber and styene butadiene rubber or a mixture of f o ethylene propylene diene rubber and chlorinated ethylene propylene diene rubber fails to provide a conveyor belt which o, has high adhesion to zinc-plated steel cords and is of highly 0o°o heat resistance.

The adhesion rate of the rubber to the surface of the cord is also small in the belts of Reference Examples, illustrating that the adhesion between the rubber and the cord is 00, insufficient and rather separable.

On the contrary, the pulling adhesion of zinc-plated steel cords in the conveyor belts according to the invention are very high even after the thermal aging. Further, the adhesion rate of the rubber to the surface of the cord is zinc-plated steel cords enveloped in the adhesive rubber layer and bonded to the covering rubber layers integrally, the adhesive rubber comprising an ethylene propylene rubber, an organic peroxide as a cross-linking agent in c~ I I ir;~,ic rc~sm~ L~~LL- i iii-~i- ~i-li- much larger, illustrating that the adhesive rubber of the invention is highly adhesive to zinc-plated steel cords even at high temperatures.

o o o o ,0 o ooo 0 00 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 00 0 00 0 0 0 0 00 °o oo 0000 o a 0000

Claims (6)

1. An ethylene propylene rubber mixture adhesive to zinc-plated metals which comprises: an ethylene propylene rubber; an organic peroxide as a cross-linking agent in amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a polyhydric alcohol polyester of acrylic acid or methacrylic acid as a cross-linking aid in amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a cobalt salt of organic carboxylic acids in amounts of 0.2-0.5% by weight as metallic cobalt based on the rubber mixture; and either sulfur or an organic polysulfide or a mixture of these in amounts of 0.2-0.4% by weight based on the rubber mixture.

2. The ethylene propylene rubber mixture as claimed in claim 1 wherein the ethylene propylene rubber is a mixture of ethylene propylene S rubber (EPM) in amounts of 10-90% by weight and ethylene propylene diene rubber (EPDM) in amounts of 90-10% by weight.

3. A heat resistant conveyor belt composed of an outer covering rubber layer and an inner covering rubber layer both of an ethylene :o propylene rubber and an adhesive rubber layer between the covering rubber layers, the belt having load-carrying zinc-plated steel cords embedded therein parallel to each other at a distance therebetween in the longitudinal direction of the belt, the conveyor belt comprising: the zinc-plated steel cords enveloped in the adhesive rubber layer and bonded to the covering rubber layers integrally, the adhesive rubber comprising an ethylene propylene rubber, an organic peroxide as a cross-linking agent In amounts of 0,01-0.02 moles per 100 g of the ethylene propylene rubber; a polyhydric alcohol polyester of acrylic acid or methacrylic acid as a cross-linking aid in amounts of 0.01-0.02 moles per 100 g of the ethylene propylene rubber; a cobalt salt of organic carboxylic acids in amounts of 0.2-0.5% by weight as metallic cobalt based on the rubber mixture; and either sulfur or an organic polysulfide or a mixture of these in amounts of 0.2-0.4% by weight based on the rubber mixture.

4, The conveyor belt as claimed in claim 3 wherein the ethylene propylene rubber is a mixture of ethylene propylene rubber (EPM) in amounts of 10-90% by weight and ethylene propylene diene rubber (EPDM) in amounts of 90-10% by weight. an organic compound as. liberates sultur when Deing neaLea, ri u 1. 17 An ethylene propylene ruober mixture adhesive to zinc-plated metals substantially as hereinbefore described with reference to any one of the Examples.

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6. A heat resistant conveyor belt substantially as hereinbefore described with reference to any one of the Examples. DATED this FOURTEENTH day of FEBRUARY 1991 Bando Chemical Industries, Ltd. oc q 0 i 0 Patent Attorneys for the Applicant SPRUSON FERGUSON AMV'