CA1046362A - Painted rubber parts - Google Patents

Abstract

ABSTRACT

Polyurethane paint is applied to a rubber surface by painting a rubber surface which is rubber derived from a composition comprising 30-100 parts by weight per hundred parts by weight of rubber (phr) of halogenated butyl rubber which has been cured using a metal oxide or halide and an alkyl phenol polysulphide accelerator with a paint selected from the group consist-ing of polyurethane ant acrylic paints. This process is simple and avoids disadvantages of prior art processes, e.g. U.V. irradiation and resin cures.

Description

104~362 This invention relates to a process of applyin~ paint, especially polyurethane paint, to vulcanized rubber parts.
There are at present two main processes for applying poly-urethane paint to vulcanized rubber parts. In one method the rubber surface is sensitised by a benzophenone spray on the rub-ber surface, the sprayed surface is then subjected to U.V. irradi-ation foilowed by primer application. Finally the polyurethane paint is applied. The disadvantage of this process is that it involves complicated and lengthy painting procedure and is ex-pensive due to the use of special chemicals and the various stepsinvolved.
In another process one has to use a resin cure for the rubber, activiated by the addition of halogenated rubbers. No primer is used and the polyurethane paint is simply applied onto the clean rubber part surface. The disadvantages of this process are that the resin cure is expensive, slow and steam cannot be used as the heat transfer agent. Also the resin cure is incom-patible with a sulphur cure which makes covulcanization of differ-ent parts more difficult. (e.g. the adhesion of sidewalls to a carcass.) We have now found a process of applying paint, e.g. poly-urethane paint, to a rubber surface which is simple and which avoids the disadvantages of the above-mentioned processes.
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According to this invention paint is applied to a rub-ber surface by a process which comprises applying a polyurethane or acrylic paint to a rubber surface which is rubber derived from a composition comprising 30-100 parts by weight pe,r hundred parts by weight of rubber (phr) of halogenated butyl rubber which has been cured either using a metal oxide or halide and an alkyl phenol polysulphide accelerator.

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-lo4G362 ^.. ~-The rubber composition comprising 30-100 phr of halogenatet butyl rubber, may be 100% halogenated butyl rubber e.g. chlorobutyl rubber, or blents of hslogenatet butyl rubber with other rubbers, e.g. natural rubber, styrene-butadiene rubbes, ethylene-propylene-diene terpolymer rubber (hereinafter abbreviated to EP W), polybutadiene rubber, acrylonitrile butatiene rubber, polychloroprene rubber, synthetic polyisoprene rubber or chlorosulphonatet polyethylene tHypalon~.
Butyl rubber comprises a copolymer of a major proportion, e.g. 85-99.9 wt.~, ' preferably 95-99.5 wt.Z of a C4-C8 isoolefin such as isobutene, with a minor psoportion, e.g. 0.1 to 15 ut.% preferably 0.5 to 5 wt.% of a C4-C14 multiolefin, -pr-f-r-bly a C4-C8 diolefin, 6uch as butadiene, dimethyl butadiene, piperylene l or isoprene. The preie~rel butyl r~bber is obt~incd by reacting 95-99.5 wt.~ of j isobutylene With 0.5 wt.% to 5 wt.% of isoprene.
`~ l In produclng halogenated butyl rubber unmod;f;ed, unvulcanized butyl rubbes ' - ~ ' ls halogonat-d, e.g. chlosinated os brominated, so a~ to contain at least 0.5 wt.Z
; and ps-ferably t least 1.0 wt.% of combinet halogen, but not more than one atom of chlorine or three atom~ of bromine contained in the polymes per molecule of , multiolefin present therein. ~alogenated butyl rubber usually has a vi~cosity i I` vorag- molecular welght of between 150,000 and 1,500,000 and a mole pes cent unsatusàtion of between 0.5 ant 152.
l 8tyrene~butadiene rubber ~abbseviated SBR) is usually made by the co-polymerisation ' `.. i, .
of bùt-diene with styrene, for example about 3 parts by weight of butadiene with 1 part ` by u~ight of tyrene, the monomers being suspended in finely divided emulsion fosm in las p psopostion of water in the presence of a detergent. Also SBR can be made by solution~polymesi-ation process. ;

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Ethylene-propylene-diene terpolymers are usually prepared by contacting a feed str-am containing ethylene, propylene and a polymerizable diolefin with a Ziegler catalyst in the presence of an inert saturatet C5 to C8 hytrocarbon diluen~, e.g.

an alkane or cycloalkane such as n-pentane, isopentane, n-hexane, isohexane or n-octane. The copolymerization i~ usually carriet out at a pressure of 1 to 5 atmaspheres. The third polymerization olefin is usually a C6 to C16 non-conjugated diolefin, e.g. 1,5-hexatiene, 1,5-octadiene or a 2-alkyl norbornadiene, preferably ethylitene norbornene or methylidene norbornene.
Examples of rubber compositions comprising 30-100 phr of halogenatet rubber are 75-85, e.g. 80, parts of chlorobutyl and 15-25, e.g. 20, parts of natural rubber;
30-40, e.g. 35, parts of chlorobutyl, 20-30, e.g. 25, parts of natural rubber, 20-30, e.g. 25, parts of styrene-butadiene rubber and 10-20, e.g. lS, parts of EPDM; and 40-60, e.g. 50, parts of chlorobutyl ant 40-60, e.g. 50, parts of EPDM, all part~ being parts by weight.
In order to obtain proper athesion of the paint to the halogenated butyl rubbor-containing composition it is essential that the rubber be cured using a mot81 oxite or halide with an alkyl phenol polysulphide accelerator.

The metal forming the oxide or halite is preferably a metal of Groups IIB, IIIB, IVB and VIII of the Periotic Table. Thus, these metal compounds may be an ox~de, chloride or bromide of zinc or tin, zinc oxide being particularly preferred.
The preferred quantity of metal oxide or halide which i8 uset is 3 to 20 parts by weight per 100 parts by weight of rubber.
Preferably an alkyl phenol t~s~lphide i~ uoet, and suitable alkyl phenol d~8ulphidos sre those having al~yl groups containing 1-5 carbon atoms. A
particularly preferred alkyl phenol disulphite i8 that known as Vultac 5.

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10463~2 Various fillers and extenders can be used, and these include various carbon blacks, e.g. SAF, HAF, SRF and EPC, clays, silicas, carbonates, oils, reslns and waxes. The carbon black is generally added in an amount of 30-150 parts by welght per hundred parts by weight of rubber.
Conventional curatives for halobutyl rubbers, including sulphur, sulphenamide derivatives, benzothia~yl disulphide (i.e. 2,2-dithiobis-benzothiazole) and tetramethyl thiuram disulphide, may also be present.
The curing usually takes place at a temperature of between 140C and 250C, preferab b 150C to 200C, and usually takes from 1 to 150 minutes, e.g. 20 to 60 minutes. The rubber may be press cured i.e. shaped and vulcanised by using a mould whlch 18 placed either in a conventional heated press, a transfer press or an in~ectlon moulding machine. -After curlng the rubber 18 then painted with the paint. Thls paint can be a polyurethane palnt, i.e. palnt contalnlng a polyurethane resln.
Such reslns result from the reaction of diisocyanates (e.g. toluene diiso-cyanate or 4,4 dlphenyl methane dlisocyanate) wlth polyols (e.g. glycerol, pentaerythritol, phenols, polyethers or polyester). They are usually p8ckaged a8 a single component or as a two component coating system. The other palnt whlch may be used is an acrylic palnt.
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Preferably the rubber is cleanet, e.g. with a hexane solvent, before painting.
It i8 found that by the process of this invention not only is there very good adhesion between the rubber and the paint coating but the trawbacks of the prior part proceas are eliminated, i.e. the procedure is simple, requiring no sensitizer or W treatment, steam cure is possible, compatibility with sulphur cures is obtainet and a rapit cure rate is available.
In the following Examples the rubbers which were uset have the following propertie~:

Chlorobutyl HT 10-68 - Viscosity molecular weight 400,000 to 480,000 Isobutylene content: 98.2 mole %
Isoprene content: 1.8 mole %

Vistalon 4608 - MooOney viscosity ML ~1+8) at ethylitene norbornene: 3-4 wt.%
ethylene 50-55 wt.%
remainder propylene .... ' "~' "
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~istalon 5600 ~ MooOney viscosity ML (1+8) at 126 C ~ 65-75 ethylidene norbornene: 6-7 wt.%
ethylene content: 60-70 wt.%
remainter propylene ~

SBR 1500 - A cold non pigmented styrene- ; -butadiene rubber containing 23.5 wt.% styrenOe - Viscosity ML (1~4~ at 100 C - 52.

Ex8~ple 1 ., The formulationa containing chlorobutyl were preparet and then press-cured.

After curing the ~uraces o the rubber were cleaned with a hexane solvent and .; *
then painted with a polyurethsne psint (Cuvertin Al paint.) ~ * Trade Nark ; ~ 6 The formulations were A (pt by wt) B (pt by wt) Chlorobutyl NT 10-68 100 100 HAF black 50 50 Napthenic oil 10 10 Stearic acid Zinc oxide 5 5 MBTS (benzothiazyl disulphîde) TMTDS (tetramethyl thiuram disulphide)2 0 0 Sulphur 0-5 Vultac 5 0 1.5 Adhesion was assessed following a standard paint athesion procedure (a) Tape test - tspe stripping of a 30 "X" cut. G.M. specification GM 4489 - PIV. Tape 3M Scotch N710 (or equivalent).
Stsndard tensile test pads (~heets of 2.0 mm thickness) were mouldet in the conventional manner except that the rubber surface was protected from contamination by mould release a8ents or dirt by means of a Mylar film.
After a one to two day contitioning period, the Mylar film was removet and the rubber was painted using an appropriate polyurethane based paint (one pack 0 ~aluminium pigmènted paint).
After a drying time of 2 to 4 days, the tape eest GM 4489 - PIY was carriet out ~b) Above test before ageing ant after ageing in an air oven (7 days at 60C) and water immersion ~7 daya at 50C).
~` The results were as follows ` Initial After Air AgeingAfter Water Ageing A fail fail fail B pass pass pass ~ ' ' ! * Trade Mark _ 7 _ "::
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Thus, the atvantage of using an alkyl phenol tisulphite accelerator (~ultac 5) i9 clearly shown Example 2 .
The formulations based on CHLOROBUTYL and natural rubber were prepared, press-curet ant then painted ant te~ted as in Example 1:
A ~pt by wt~ B (pt by wt) Natural Rubber 20 20 ~ :~
HAF Black 50 50 Napthenic Oil 10 , 10 :
Stearic Acit Zinc Oxide 5 5 ~ultac 5 O , 1 ~:
MBTS

Sulphur o . S o Reault~ of the Tests InitialAfter Air Ageing After Water Ageing A ~ fail fail ~ fail B pass pass pass ~`. Agsin the atvantage of using Vultac 5 ia clearly shown.

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Example 3 A typical radial tyre sidewall formulation based on a blend of EPDM (Vistalon 4608), CHLOROBUTYL HT 10-68, natural rub-ber and SBR 1500, (styrenebutadiene rubber) was prepared and test-ed as in Example 1.
The formulation was as follows:
Parts by weight Vistalon 4608 15 Natural Rubber 25 GPF Black 60 Napthenic Oil 30 Stearic Acid 2 ~ .
Zinc Oxide 3 Vultac 5 1. 5 MBTS 0.8 Sulphur 0.8 Results of the tests InitialAir Ageing Water Ageing Steam Cure pass pass pass Press Fure pass pass pass ~: :
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NB The above sidewall contains no chemical antiozonants which are normally incorporated in radial tyre sidewalls and are highly staining, and is therefore ideal for paint applica-tion. In this formulation protection against weathering and ozone attack is obtained via the incorporation of EPDM and chlorobutyl rubbers.

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Example 4 The following formulation was prepared, press-cured for 15 mins. at 165 C~
palnted and tested a~ before:

~istalon 5600 (EPDM~ 50 Paraffinic Oil 25 Zinc Oxide 5 Stearic Acid Sulphur 1.5 MBTS
Vultac 5 2 Result of tests Initial After Air Ageing After Water Ageing Paint adhe~ion pass pass pass ., '. . .

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE
IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process of applying paint to a rubber surface which comprises painting a rubber surface which is rubber derived from a composition comprising 30-100 parts by weight per hundred parts by weight of rubber (phr) of halogenated butyl rubber which has been cured using a metal oxide or halite and an alkyl phenol polysulphide accelerator with a paint selected from the group consisting of polyurethane and acrylic paints.

2. A process according to claim 1 wherein a blend of 75-85 parts by weight of chlorobutyl rubber ant 15-25 parts by weight of natural rubber are used.

3. A process according to either of claims 1 and 2 wherein the rubber derived from the halogenated butyl rubber containing composition is cured at a temperature of between 150°C and 200°C.

4. A process according to claim 1 wherein the rubber blend comprises 60-80 wt. % of EPDM and 20-40 wt. % of chlorobutyl rubber.

5. A process according to any one of claims 1, 2 and 4 wherein the metal oxide or halide is an oxide, chlorite or bromide of zinc or tin.