CA1037848A

CA1037848A - Composite structures

Info

Publication number: CA1037848A
Application number: CA207,331A
Authority: CA
Inventors: James F. Yardley; Reginald T. Wragg
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1973-08-29
Filing date: 1974-08-19
Publication date: 1978-09-05
Also published as: AU7273074A; IT1020186B; FR2257423A1; FR2257423B1; SE7410743L; NL7411447A; DE2441423A1

Abstract

A B S T R A C T
This invention relates to a composite structure and a method of making same. The composite structure comprises an unsaturated rubber selected from polychloroprene and copolymers of chloroprene with at least one copolymer-isable hydrocarbon and a polyester which is a reaction product of at least one aliphatic dihydric alcohol and at least one aromatic compound having two acidic groups attached to the aromatic nucleus one being a carbonyl-con-taining acidic group and the other being a carbonyl-con-taining acidic group or an acidic hydroxyl group, the rubber being bonded directly to the polyester without an adhesive interlayer. The method of making the composite structure comprises the steps of treating the surface of the rubber to be bonded to the polyester with a treatment agent selected from concentrated nitric acid, hypochlorous acid and hypochlo-rous acid generators, heating the polyester to melt at least to the surface to be bonded to the rubber and solidifying the molten polyester in contact with the treated rubber.

Description

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This invention relates to composite structures and in particular to composite structures of unsaturated rubbers and polyesters and to a method of making such structures.
It has been proposed to bond an epichlorhydrin rubber to a polyester by melting at least the surface of the polyester to be bonded to the rubber and solidifying the polyester in contact with the rubber (British Patent Serial No. 1387583).
We have now found that it is possible to bond certain polyesters to certain non-polar unsaturated rubbers by this method pro-vided that the rubber surface is subjected to a certain pre-treatment.
According to the present invention there is provided a composite structure of an unsaturated rubber selected from . polychloroprene and copolymers of chloroprene with at least one copolymerisable hydrocarbon and a polyester which is a reaction product of at least one aliphatic dihydric alcohol and at least one aromatic compound having two acidic groups attached to the aromatic nucleus one being a carbonyl-contain-ing acidic group and the other being a carbonyl-containing :
acidic group or an acidic hydroxyl group, the rubber being bonded directly to the polyester without ah adhesive inter-.~ layer.
According to the present invention also, a method : of making a composite structure of an unsaturated rubber selected from unsaturated hydrocarbon polymer rubbers, polychloroprene and copolymers of chloroprene with at least one copolymerizable hydrocarbon, and a polyester selected from reaction products of at least one aliphatic dihydric alcohol and at least one aromatic ompound having two acidic -.
, 30 groups attached to the aromatic nucleus, one being a carbonyl~

` containing acidic group and the other being a carbonyl-con-- taining acidic group or an acidic hydrozyl group and : .
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_z _ ;, , ~0371~8 elastoplastic linear block copolymers having at least one block of a reaction product defined in the rubber being bonded directly to the polyester without an adhesive interlayer, which comprises treating the surface of the rubber to be bonded to the polyester with a treatment agent selected from concentrated nitric acid, hypochlorous acid and hypochlorous acid generators, heating the polyester to melt at least the surface to be bonded to the rubber, and solidifying the molten polyester in contact with the treated rubber. -~ -10The treatment time should be sufficient to modify - -the rubber surface without undesirably degrading the bulk of the rubber, and any residual treatment agent reamining at the end of the treatment should be removed if its presence would undesirably affect the rubber or the polyester. The treatment agent is a modifying agent for the rubber surface and does not take the form of an adhesive composition or ;
cement between the rubber and the polester.
- The treatment agent may be applied by any convenient ; means, for example by dipping, spraying or brushing, and ,.
the treatment is suitably performed at room temperature (about 15-20 C). When the treatment agent is concentrated nitric acid this may be applied as a liquid or as a gel or paste with fine silica powder. Examples of treatment agents in the form of hypochlorous acid generators are acidified solutions of alkali metal hypochlorites, trichloroisocyanuric .l acid and alkali metal salts of mono- and di-chloroisocyanuric acid. The alkali metal is suitably sodium. The trichloro-isocyanuric acid may be employed as a solution in ethyl acetate and the alkali metal chloroisocyanurates may be , : .
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employed as aqueous solutions.
The rubber is usually in the vulcanized state in the composite structure. The rubber may be vulcanized in contact with the polyester, in which case the conditions of vulcanization may be sufficient to melt the polyester, or the rubber may be in the vulcanized state prior to contact with the polyester. The rubber may be peroxide-vulcanized but preferably it is vulcanized by a sulphur-based vulcanization system.
Although the treatment employed in this invention should improve the bond between the polyester and a rubber having any amount of unsaturation, it is preferred, in order to obtain a significant improvement for most practical purposes, that the rubber which is treated should have more than five carbon-carbon double bonds for every one hundred main-chain carbon atoms and more preferably in excess of fifteen carbon-carbon double bonds for every one hundred main-chain carbon atoms.
When the rubber is a hydrocarbon rubber it may suitably be a linear polymer of a cyclic hydrocarbon monoene, for example cyclopentene which polymerises to poly-1,5-- pentenamer, or a polymer of an aliphatic hydrocarbon diene. When the rubber is a copolymer of an aliphatic hydrocarbon diene, the comonomer(s) may be aliphatic and/or alkenyl-aromatic hydrocarbons. Examples of suitable aliphatic hlydrocarbon diene rubbers are -' natural rubber,i synthetic cis-polyisoprene, polybutadiene rubber, butadiene/styrene rubber and butadiene/alpha-.. :
.

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1~37~48 methylstyrene rubber. The rubbers referred to herein may be blended with each other and/or with one or more other rubbers, and are usually in compositions containing ingre- ;
dients normally used in rubber compositions, for instance fillers, processing aids, anti-ageing agents and vulcanizing - agents.
The polyester is normally thermoplastic before and -after being bonded to the rubber by the method of this invention. It is desirable that the polymer should not be heated too far above its softening point (i.e. the temperature ^
at which it become thermoplastically processible) which for elastoplastic linear block copolymers is in the region of 200 C because this may lead to loss of quality from thermal instability by, for example, pyrolysis or oxidative degrada-tion.
The polyester may be the reaction product of at least one aliphatic dihydric alcohol and at least one aroma-tic compound having two acidic groups attached to the aroma-tic nucleus, one being a carbonyl-containing acid group e.g.
' 20 a carboxylic acid group (COOH), a carboxylic ester group .;
(COOalkyl) or a carbonyl chloride group (COCl), the other being a carbonyl-containing acid group or an acidic hydro- ~
xyl group (OH). These reaction products are generally long ;
chain ester condensation polymers in which the carbonyl carbon atom of each ester group is in the polymer main chain and ; is attached directly to ah aromatic nucleus. The reaction 'r, product is preferably a poly(alkylene terephthalate), a ~-. . .
poly(alkylene isophthalate), and alkylene terephthalate/
isophthalate copolymer or a reaction product of an aliphatic diol and p-hydroxybenzoic acid. The alkylene groups, which are ; .
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, ,_ ,,, , ... ., . , . - ' ' ,, :, - !, , , ' .' ' ' ' .' ' . , ' . . ' ' , . : ' 1037~48 derived from the one or more dihydric alcohols, may have for instance from two to eight carbon atoms. Specific examples of suitable reaction products are poly(ethylene terephthalate), poly(butylene terephthalate), poly(1,4-dimethylenecyclohexane terephthalate) and 1,4-dimethylenecyclohexane terephthalate/
isophthalate copolymers. Poly(tetramethylene terephthalate) results in a particularly strong bond when employed in the present invention.
Alternatively, the polyester may be an elastoplastic linear block copolymer having at least one block of a reaction product defined in the immediately preceding paragraph. A
preferred block copolymer is one having (a) n (where n is a positive integer) substantially amorphous (in the unstretched state) blocks of a polyether e.g. polytetrahydrofuran or poly-~rimethylene glycol), an aliphatic acid polyester e.g. poly-(propylene adip~te ) or polycaprolactone, an olefin polymer e.g. ethylene/propylene copolymer, or two or more sub-blocks of - one or more of these species interlinked by means of, for example, a diisocyanate in the case of hydroxyl-terminated species, and (b) n + 1 blocks of the aforementioned reaction product which will generally be crystalline. The molecular weight of each of these blocks may suitably be in the range 1,000 to 10,000.
A particularly preferred block copolymer is one having n blocks of a polyether and n + 1 blocks of the aforementioned reaction product. The ratio of the number of carbon atoms ~
to the number of oxygen atoms in the repeating unit of ;
the polyether block should preferably be greater than

2.5:1 and the melting point of the polyether should -6- ~

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preferably be less than 55C. Preferably the average molecular weight of the polyether should lie wlthin the range 600 to 6,000. Preferred blocks of the aforementioned polyeeter reaotion product are crystalline block~ having a melting point greater than 170C and preferably from 30 to 60 per cent of the block copolymer is comprised of the polgesterreaction product. Other preferred feature~ of the polyester reaction product blocks are (i) from 50 to 90 per cent, especially from 65 to 85 per cent, of the ester units in each block are identical, (ii) a separate polymer ; of these identical units having a molecular weight of about 5,000 would have a melting point of about 174C, and (iii) a separatc polymer of a complete block having a molecular weight of about 5,000 would have a melting point of le~s than 200C.
I The bond between ad~acent polyether and polyester blocks is suitably an ester-linkage produeed by reaction of, for example, a hydroxyl-terminated polyether with a carbosyl-terminated polyester. The block copolymer may be prepared $rom a reaction mixture of (a) a polyether, allphatic ~ -acid polyester or olefin polymer, having two terminal hydroxyl groups, and (b) the reactants from which the polyester reaction product ie derived. For example, the block copoiymer may be made by melt copolymerisation of poly(tetramethylene ether) diol, 1,4-butane diol, dimethyl terephthalate and dimethyl isophthalate, or a~ternati~ely by melt copolymeri~ation of poly(tetramethylene ether) diol, 1,3-propane diol, 1,4-butane diol and dimethyl terephthPlate.
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'' , . '; ' ' ' ' ' . ~ ' ,' , , ' ~037848 Preferred block copolymers are those available under - the trade names Hytrel and Pelpren.
The polyester may be in a composition with ingredients normally present in polyester compositions, for example fillers, processing aids and anti-ageing agents.
In the method of this invention, the polyester may be melted by direct application of heat with or without an elevated pressure. Since the polyester is normally thermo-plastic before and after bonding, solidification normally occurs by mere cooling. Preferred methods of applying the polyester to the rubber are by injection-moulding or transfer-moulding, but other technia~ues such as compression-moulding, rotational-moulding, extrusion, powder-spraying or fluidised-bed coating may be employed if desired.
The invention is illustrated in the following Examples.
EXAMPLE I
' A rubber composition prepared from the following ;- formulation was w lcanized for 40 minutes at 150C. in a mould measuring 4.0 x 76.2 x 228.6 mm.
Formulation Parts bY weiaht Natural rubber (SMR 10) lOO
Carbon black (N330) 49.15 Mineral Oil 5.0 Zinc oxide 5 0 Stearic acid 1 2.0 Sulphur 2.5 N-cyclohexyl benzthiazole-2-sulphenamide 0.5 .

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1037~8 Formulation Parts bv wei~ht 4-isopropylamino-diphenylamine (Nonox ZA)* 0.15 Condensation product of acetone and di-phenylamine adsorbed on carbon black (Nonox BLB)* 1.70 The natural rubber had about 25 C=C per 100 main-chain carbon atoms.
One end of the slab of vulcanized rubber was immersed at a depth of 180 mm for five minutes in an acid hypochlorite 10 solution consisting of:-..
Water 1000 ml -Concentrated hydrochloric acid 5 ml Aqueous sodium hypochlorite solution containing 12 weight/volume per cent 15 of available chlorine 30 ml , . .~
The treated slab was allowed to dry and then placed in a plunger mould of the same dimensions. A sheet of a linear block copolymer containing 42% by weight polytetra-hydrofuran and 58% by weight poly(butylene terephthalate), ` 20 commercially available under the trade name Hytrel 4055, was compression moulded onto the 76.2 x 228.6 mm surface , of the slab at 250C until the plastic was molten, followed ;, by cooling under a slight pressure (about 40 kg/cm2). No i bond was produced between the block copolymer and the untreated rubber surface. The strength of the bond between the block copolymer and the hypochlorite-treated rubber surface was determined by a simple peel adhesion test at a jaw separation rate bf 500 mm per minute. A bond strength of 147 Newtons per 20 mm wide test-piece was obtained with failure of the rubber.
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EXAMPLE II
A rubber composition prepared from the formulation - given in Example I was vulcanized for 55 minutes at 135 C
in a mould measuring 2.5 x 76.2 x 228.6 mm. A slab measuring 2.5 x 76.2 x 30 mm was cut from the vulcanized composition and was immersed for 1 minute in an acid hypochlorite solution consisting of:-Water 1000 ml Concentrated hydrochloric acid 10 ml 10 Aqueous sodium hypochlorite solution 5 containing 12 weight/volume per cent ! of available chlorine 30 ml ~ -The treated slab was washed in water, allowed to dry ; and then placed in a mould measuring 7.0 x 76.Z x 30 mm.
Poly(tetramethylene terephthalate), commercially available as Dereton TAP10 , was injected into the mould from a Batenfeld 1/2 oz Type BSKM 15 HKF 4 injection-moulding machine 2 ~ -under a pressure of 700 kg/cm which was maintained for `~
12 seconds. The mould and injector nozzle were respectively '~
20 at 140 C and 265 C. After cooling for a total time of 40 seconds the composite was de-moulded. '' The strength of the bond between the rubber and the polydster was determined by peel adhesion at a jaw separation rate of 500 mm per minute. A bond strength of 25 216 Newtons per 30 mm wide test-piece was obtained with .
failure in the rubber phase.
' EXAMPLE III
Example II was repeated using a rubber composition prepared from the formulation given below which was ~.' .
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vulcanized for 40 minutes at 150 C.
Parts by weight Styrene/butadiene rubber (Intol 1502) 100 Carbon black (N330) 48.75 Mineral oil 5.0 Zinc oxide 3.0 Sulphur 1.75 Stearic acid 1.0 N-cyclohexyl benthiazole-2-sulphenamide 1.0 4-isopropylamino-diphenylamine (Nonox ZA) 0.15 *
BLE 25 1.25 1 -The rubber had about 19 C=C per 100 main-chain carbon ~ -atoms. ;
BLE is a high temperature reaction product of diphenyl- -~
amine and acetone.
A bond strength of 235 Newtons per 30 mm wide test-piece was obtained with failure in the rubber phase.
; EXAMPLE IV ~ -A rubber composition prepared from the formulation given below was vulcanized for 40 minutes at 150 C in a mould measuring 2.5 x 76.2 x 228.6 mm.
Parts by weight Oil-extended styrene/butadiene rubber (Intol 1712) 77.5 Styrene/butadiene rubber (Intol 1502) 22.5 ' Carbon black (N339) 59.0 Aromatic oil ~Dutrex RT) 5.0 j Zinc oxide 2.5 Stearic acid 1.0 ., ' ' .
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Parts bY wel~ht ~ineral oil 5.0 4-isopropylamino_diphenylamine (Nonox ZA) 2.0 BIE 25 2.0 40 mesh crumb natural rubber 5.0 B ~-nitrOso-diphenylamine (Vulcatard A)~ 0.4 2-Morpholinothio-benzthiazole (Santocure ~OR) 1~0 Sulphur 1075 The rubbers hsd about 19 C=C per 100 main-chain carbon atom3.
A slab measuring 2.5 x 76.2 x 30 mm was cut from the vulcanized composition and was treated with the acid -~
hypochlorite solution as described in Example II. The treated slab was washed with water, allowed to dry and then ~ -placed in a mould measuring 7.0 x 76.2 x 30 mm. A block ~- ~
copolymer containing 35.5% by weight polytetrahydrofuran --and 64.5% by weight poly(butylene terephthalate), ~ -commercially available under the trade ~ 4 Hytrel 5555, was lnjected into the mould at a pressure of 210 k~ cm2 which was maintained for 12 seconds. The mould and injector nozzle were at 100C and 260C respectively. After cooling for a total time of 40 seconds, the composite was de-moulded.
; The peel adhesion strength of the bond between the rubber and the block copolymer measured at a jaw separation rate of 500 mm per minute was 324 Newtons per 30 mm wide test-piece with fallure of the rubber.
EXAMP~E V
Example IV was repeated except that the block copolymer .

' i was a copolymer of polytetrahydrofuran and poly(ethylene terephthalate), commercially available under the Trade Mark Pelpren P7os~ and the injector nozzle temperature was 250C.
m e peel adhesion bond strength was 274 Newtons per 5 30 mm wide test-piece with failure of the rubber. -EXAMPLE VI
A hypochlorite-treated vulcanized rubber composition was prepared as described in Example III. m e treated slab was washed with water, allowed to dry and placed in a mould -~ -- 10 measuring 7.0 x 76.2 x 30 mm. A glass-reinforced poly(tetra-methylene terephthalate) containing 20 weight per cent glass reinforcement and commercially available under the trade mark -' Dereton T&A50 was injected into the mould at a pressure of 500 kg/cm2 which was maintained for 12 seconds. m e mould and injector nozzle temperatures were respectively at 100C.
and 260C. After cooling for a total time of 24 seconds the composite was de-moulded.
Failure occurred in the rubber upon testing of the bond strength.
~MPLE VII
A vulcanized rubber composltion was prepared as described in Example II. A slab measuring 2.5 x 76.2 x 30 mm was cut from the vulcanized composition and was immersed in a saturated aqueous solution of sodium dichloroisocyanurate, available under the trade mark Fi-clor 60S, for 15 minutes.
The treated slab was washed with water, allowed to dry and placed in a mould m~asuring 7.0 x 76.2 x 30 mm. Poly(tetra-methylene terephthalate), commercially available under the Trade Mark Tenite ' 13.

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6PR0, was injected into the mould under a pressure of 700 kg/cm2 which was maintained for 12 seconds. The mould and injector nozzle temperatures were 100C and 260C respectively.
After cooling for a total time of 24 seconds the composite was de-moulded.
Upon testing the bond strength, failure occurred in the rubber.
EXAMPLE VIII
Example VII was repeated except that the vulcanized rubber slab was treated by painting the slab surface with a saturated ethyl acetate solution of trichloroisocyanuric acid, available under the trade mark Fi-clor 91, and leaving - it to dry at room temperature.
Failure occurred in the rubber upon testing the bond strength.
The same result was obtained when the treatment agent was applied by immersion in the Fi-clor 91 solution for 5 minutes followed by washing with water and drying. ;
EXAMPLE IX
Example VII was repeated except that the vulcanized rubber slab was treated by immersion in commercially available concentrated nitric acid for 30 seconds before .
washing with water and drying.
Failure occurred in the rubber on testing the bond - -strength.
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Claims

1. A method of making a composite structure of (i) an unsaturated rubber selected from unsaturated hydrocarbon polymer rubbers, polychloroprene and copolymers of chloroprene with at least one copolymerizable hydrocarbon, and (ii) a polyester selected from (A) reaction products of at least one aliphatic dihydric alcohol and at least one aromatic compound having two acidic groups attached to the aromatic nucleus, one being a carbonyl-containing acidic group and the other being a carbonyl-containing acidic group or an acidic hydroxyl group and (B) elastoplastic linear block copolymers having at least one block of a reaction product defined in (A) the rubber being bonded directly to the polyester without an adhesive interlayer, which comprises (a) treating the surface of the rubber to be bonded to the polyester with a treatment agent selected from concentrated nitric acid, hypochlorous acid and hypochlorous acid generators, (b) heating the polyester to melt at least the surface to be bonded to the rubber, and (c) solidifying the molten polyester in contact with the treated rubber.

2. A method according to claim 1 in which the treatment is performed at room temperature.

3. A method according to claim 1 in which the hypochlorous acid generator is selected from acidified alkali metal hypochlorites, trichloroisocyanuric acid, alkali metal salts of monochloroisocyanuric acid and alkali metal salts of dichloroisocyanuric acid.

4. A method according to any of claims 1, 2 or 3 in which the rubber is in the vulcanized state prior to contact with the polyester.

5. A method according to claim 1, 2 or 3 in which the polyester is applied to the rubber by injection-moulding or transfer-moulding.

6. A method according to claim 1, 2 or 3 in which the rubber before being bonded to the polyester has more than five carbon-carbon double bonds for every one hundred main-chain carbon atoms.

7. A method according to claim 6 in which the rubber before being bonded to the polyester has more than fifteen carbon-carbon double bonds for every one hundred main-chain carbon atoms.

8. A method according to claim 1, 2 or 3 in which the rubber is an unsaturated hydrocarbon polymer rubber selected from linear polymers of cyclic hydrocarbon monoenes and polymers of aliphatic hydrocarbon dienes.

9. A method according to claim 1, 2 or 3 in which the rubber is selected from natural rubber, synthetic cis-polyisoprene, polybutadiene rubber, poly-1,5-pentenamer, polychloroprene, butadiene/styrene rubber and butadiene/alpha methylstyrene rubber.

10. A method according to claim 1 in which the polyester is selected from poly(alkylene terephthalate), poly(alkylene isophthalate), alkylene terephthalate/isophthalate copolymer, reaction products of an aliphatic diol and parahydroxybenzoic acid and elastoplastic linear block copolymers having at least one block of a polymer selected from these.

11. A method according to claim 10 in which the alkylene groups have from two to eight carbon atoms.

12. A method according to claim 1, 2 or 3 in which the polyester is selected from poly(ethylene terephthalate), poly(butylene terephthalate), poly(1,4-dimethylenecyclohexane terephthalate), 1,4-dimethylenecyclohexane terephthalate/isophthalate copolymers and elastoplastic linear block copolymers having at least one block of a polymer selected from these.

13. A method according to claim 1 in which the polyester is an elastoplastic linear block copolymer having:
a) n substantially amorphous (in the unstretched state) blocks selected from polyether, aliphatic acid polyester, olefin polymer and at least two interlinked sub-blocks of at least one of these polymers, and b) n + 1 crystalline blocks of the reaction product (A), where n is a positive integer.

14. A method according to claim 13 in which the substantially amorphous blocks are of a polyether in which the ratio of the number of carbon atoms to the number of oxygen atoms in the repeating unit of the polyether is greater than 2.5:1.

15. A method according to claim 14 in which the polyether is polytetrahydrofuran.

16. A method according to claim 1, 2 or 3 in which the polyester is an elastoplastic linear block copolymer, from 30 to 60 per cent of which is comprised of at least one block of the reaction product (A).

17. A composite structure when made by a method in accordance with claim 1, 2 or 3.

18. A composite structure of:-(i) an unsaturated rubber selected from polychloroprene and copolymers of chloroprene with at least one copolymerisable hydrocarbon and (ii) a polyester which is a reaction product of at least one aliphatic dihydric alcohol and at least one aromatic compound having two acidic groups attached to the aromatic nucleus one being a carbonyl-containing acidic group and the other being a carbonyl-containing acidic group or an acidic hydroxyl group, the rubber being bonded directly to the polyester without an adhesive interlayer.

19. A composite structure of:-(i) an unsaturated rubber selected from unsaturated hydrocarbon polymer rubbers, polychloroprene and copolymers of chloroprene with at least one copolymerizable hydrocarbon, and (ii) a polyester which is an elastoplastic linear block copolymer having at least one block of a reaction product of at least one aliphatic dihydric alcohol and at least one aromatic compound having two acidic groups attached to the aromatic nucleus, one being a carbonyl-containing acidic group and the other being a carbonyl-containing acidic group or an acidic hydroxyl group, the rubber being bonded directly to the polyester without an adhesive interlayer.

20. A composite structure according to claim 18 or 19 in which the rubber is in the vulcanized state.

21. A composite structure according to claim 18 or 19 in which the polyester is thermoplastic.