GB2205575A - Insulating adhesive tapes suitable for use with pipes placed in the soil - Google Patents

Description

COATING OR ADHESIVE TAPES, AND A PROCESS FOR THEIR PREPARATION AND USE

2205575 The invention relates to coatinm or adhesive tapes, for coating certain articles, particularly pipes placed in the soil that are exposed to shearing stress, electric polarization and higher temperatures. Moreover, the invention relates to a process for the preparation of said coating or adhesive tapes, as well as to a process for the insulation of certain articles placed in the soil by using the coating or adhesive tape of the invention.

The use of anti-corrosive coatings may be considered to be as old as the us-e of steel pipes them selves. Previously various dyes, tars, paraffin, bitumen or the like have been used for the anti-cerrosive urotec tion of steel Dipes.

On spreading of the Dlastics, an over,,Thel,-,,--r.,-, ma-jority of tulnee formerly used coatings were replaced by insulating systems formed from polymer-s. The reason CD thereof was that the pipelines were built larger and larger dimensions, mainly with larger liameters thus, the traditional coatings could not s-ntisfy the insulating demands in31reased both -,ual-;---:;7--,jelly an quant-Ltatively.

In the case of pipelines of large diameters placed in the soil, a shearing stress acts jn the coat- ing after re-filliner and on compactlion of\-he soil.

0 0 A 3921-2275-SI 2 Under this effect, the adhesive layer may be shorn, thereby causing the damage of the insulation.

It often happens that a warm medium is trans- ported in the pipeline and thus, the protective coating also becomes warm. At higher temperatures, reaching 0 even 100 C, the softening of the protective coatings leads to a decrease in the adhesion to the metal and in the adhesion of the layer against shearing whereby the accessibility of the metal by the aggressive medium is promoted.

For the prevention or diminution of the corro- sion damages, a combined protective system was intro duced. This means that the metal, e.g. the pipe coated with the insulating material is usually subjected to a cathodic polarization to an extent requi-red to abolish the corrosion current. It can experimentally be shown that the coating separates from metal 4-n the envi CD ronment of 'U-e defect site of t--- lamagei insulation under -the effect c--.' the ca-uhodic polariza-__fon and th.is separation increases in the course of ti:-.e.

The tape-like insulating materials consist CD of a carrying foil and an adhesive layer applied there to. The carrying foils are commonly thermoplastic poly mers, most frequently polyethylene (PE) or polyvinyl chloride (PVC) polymers The adhesive layers are mainly synthetic rubber-based or bitumen-based preparationP.

There are known insulating processes, wherein the adhesive layer is applied to the carrying layer directly on the spot of the insulation.

In Hungarian patent specification No. 168 381 a process and equipment are described, wherein the warm bitumen-based adhesive layer is smeared onto the foil on the spot of the pipe-laying and rolled helical ly up the pipe previously treated with a solut-lon contain ing bitumen. This method is more advantageous as compared to the insulating processes using warm bitumen, however, it has several drawbacks. On the spot of the insulation, e.g. in the course of building long-distance transmis sion lines, the heating of bitumen is difficult under field work conditions. On pipes having large diameters and transDorting warm media, the bitumen softens and rapidly deteriorates under the pressure of the soil.

Hungarian patent specificatLon No. 171 611' relates tc the Drecaration of a combi-ed self-adhesive coati ng m at erial. 'i3c- ordinc- 11 o this s-ce-, if:)n C a solu-1ion of modiffied bitumen is applied a PVC foil optionally con-uaining bitumen, then scivent is evaporated and a second layer ensuring self-adhesion C, ivapplied to the first layer and the solvent is again evaporated.

As a drawback of said process it can be men- tioned that specific solvent-removing and separate solvent-eradicating or recovering systems are required for accomplishing the process whereby the process be- comes more expensive. Another disadvantage of this C) process is that he adhesive layer is weakened by 4 the bitumen content of the coating material.

In Hungarian patent specification No. 174 391 the preparation of a plastic foil-based anti-corro- sive system is described. According to this process, an adhesion-strengthening layer is smeared up from a solution to a polymeric carrier then, after evapor ation of the solvent, it is combined by doubling with the previously prepared rubber- und/or polymer-based adhesive layer. This process is more preferable as compared to the former ones, however, it has several drawbacks. On the insulation of warm pipelines of large diameters, the adhesive layer softens similarly to the bitumen insulations but to a lower extent; the adhesion against smearing of the adhesive layer is decreased thus, the coating becomes folded by -the compac -4on of the soil and its durability decreases.

in Bri-1kish Datent s-2eci-1'-icaticn No 3'74 317, a protective composition is --escribed which is 'Cased on an improved coal tar of high elasticity. Inf-s composi tion has a good adhesion and provides an advantageous.

corrosion res 41 stance. The com:)osition may be applied to a stiffening material which may be a textile or a polymeric foil. The drawbacks of this protective composition are similar to those of the bitumen-based materials in the case of which the rheological proper ties of the adhesive layer are weak either under effect or in the absence of heat.

British patent specification No. 1 402 418 relates to adhesives which are useful for sticking rubber to a metal. The binding of the rubber to the metal is provided by vulcanization at a temperature of at least 150 0 C, in the presence of at least one halogenated elastomer in the adhesive. The composition of said patent specification can not be used for insula tion purposes e.g. because the rubber does not adhere to the metal without a heat-treatment. Neither a composi tion, nor a process which may be considered as an insulat ing material or a process for the preparation thereof are reported in this specification.

A well-known process consists in that a bitumen- and/or coal tar-based adhesive layer is smeared onto a carrying foil and an separating material, e.g. silicone-treated paper is used tz avo-- tline sticking.

7his latter material should be rer.DveA- be--'2re use and the removal is difficult, -La'--ourso.-.e and e---z-oens4-,.e.

The aim of invention is t2 the disadvan- tages of the prior art method and t,- _;e_vel--p an adhesive layer or rather a tape-like pipe-insu'-atin,=. system which can be used in case of large pipe diameters, under warm operation condition of the pipelines, and in case of polarization caused by electric current as well, which system is endowed additionally with all of the properties characterizing the known tape- -like self-adhesive insulating systems. \ W In the course of our investi.-at4--,ns we have 6 recognized that the polarization dama-e can be diminished and the adhesion against shear can be increased by adding appropriate polymers or other substances to the adhesive layer and/or to the priming solution.

The use -of e.g. atactic polypropylene, ethylene/propy lene copolymers and/or terpolymers or polyisobutylene is preferred.

The invention is also based on the recognition that some vulcanizing components may be mixed in appro priate amounts to the rubber-based adhesion-promoting materials, whereby a broader scope of use may be achieved; e.m. the adhesion against shear and the binding to C) the metal are preferably altered in the course of e.,-,.

a warm operation.

According to the invention an ad"e-sion-strenghten- in.c.; layer is applied optionally to a poly77eric foil preferably to a PVC, polyethylene or other thermoplastic foill in a manner known Der se, then _--sive layer of the invention optionally ccmprisin- at least. one 2-- of the cc.mponents required for vulcanizaticn and/or the materials increasing the adhesion against shear icidal and decreasing the polarization; as well as fung and bactericidal substances is applied to it in a thickness of 0.05 to 1.5 mm. When the adhesive layer of the invention contains a vulcanizing agent, the CD other components required for the vulcaniz-tion should be mixed to the priming solution. N 0 Thus, the invention relates io coating or 7 adhesive tapes for coating articles particularly pipes placed in the soil that are exposed to shearing stress, electric polarization and higher temperatures. These coating or adhesive tapes comprise an adhesive mixture containing to 60 % by mass of synt I hetic and/or natural rubbers, preferably an isoprene/isobutylene copolymer as well as styrene/butadiene copolymer or a mixture thereof; 2 to 20 % by mass of an adhesion improving material, preferably hydrocarbon resin, and optionally vulcanization-inducing materials, sulfur, metal oxides such as zinc oxide, magnesium oxide, lead oxide and silicon dioxide and/or secondary or tertiary amines; t'O % by mass of substances modifying insulating o :=I 0 characteristics such as atactic polypropylene, ethylene/propylene copolymers and/or -,eri ly-_ mers, bitumen or a mixture -there--."; and 30 to 70 % by mass of filling materials and auxiliarf-es 0 such as carbon black and/or limestone fluor, chalk, talc, kaolin, factice and the like as well as fungicidal and bactericidal agents applied to a polyvinyl chloride (PVC), polyethylene (PE) or other thermoplastic carrying foil optionally with the insertion of an adhesion-strenghtenin (adhesion -transmitter) layer. N A further object of the invention is a process for the preparation of the coating or adhesive -,apes 8 of the invention which comprises preparing an adhesive mixture containing to bO 7a by mass of synthetic and/or natural rubbers, preferably an isoprene/isobutylene copolymer as well as styrene/butadiene copolymer or a mixture thereof; 2 to 20 % by mass of an adhesion improving material, 0 preferably hydrocarbon resin, and optionally vulcanization-inducing materials, sulfur, metal oxides such as zinc oxide, magnesium oxide, lead oxide and silicon dioxide and/or secondary or tertiary amines; 3 to 30 'o by mass of substances modifying insulating 0 characteristics such as atactic polypropylene, ethylene/propylene copolymers and/or terpoly- mers, bitumen or a mixture thereof; and 39 to 70 by mass of filling materials and auxiliaries such as carbcn black and/or 1-4..-.estone -aic, I'laclin, factice and the like c h al'..-, t 2-' as well as fungicidal and bactericidal agents _:er,_z_y an irterral 7-Ler a-d a,-plying it refer3hly Iry:,alaariliering or a carzT-Lr,- foil, Imfembly to a pc1-,YrvL-,r_'I cl-L-oi-i--4e, polylere cr 3try-er -J%eizrmplasriz foill cpticnaLy by =.g an Finally, the object of the invention is a processs for the insulation of articles, particularly pipes placed in the soil and exposed to shearing stress, 0 electric polarization and higher tempera-Dure, which comprises treating the surface to be protected with C) 9 a priming solution of known composition optionally contain ing at most 10 % by mass of a vulcanization accelerating agent such as dithiocarbamate, preferably piperidine pentamethylenedithiocarbamate or zinc diethyldithio 5- carbamate and/or a thiuram, preferably tetramethylthiuram disulfide and/or a thiazole, preferably 2-mercapto benzothiazole, then coating it preferably helically with the coating tape of the invention.

As a carrying foil, a soft PVC, polyethylene or other foil prepared from a thermoplastic material and/or textiles prepared from polymers (e.g. polyamide, polyester and the like) may preferably be used.

Some essential properties of the carrying foils preferably used in the invention are illustrated below.

Characteristics Polyethylene Sof-. _PVC f cil foi I sign "A" si i " B " Thickness (mm) 0.2 0.25 Elongation at rupture 315 176 Tensile strength (N/mm 2 17.5 18.6 Dielectric strength (KV/mm) 27 22 Volume resistance (ohm.mm) 2.10 2 3.10 12 0 Cold-bending (pike of 5 mm below -25 below -29 C The adhesive layer of the inveniion is based on rubber-type materials. The adhesive layer contains to 60 % by mass of synthetic and/or natural rubbers, preferably an isoprene/isobutylene copolymer as well as a styrene/butadiene copolymer or a mixture thereof; 2 to 20 % by mass of an adhesion-increasing material and optionally vulcanization-inducing materials; 3 to % by mass of substances improving the insulating properties, e.g. materials diminishing the harmful effect to the polarization such as atactic polypropylene and bitumen; 30 to 70 % by mass of filling materials and auxiliaries such as carbon black, talc, kaolin, limestone flour, chalk or factice. At the expense of the filling material the composition may also contain a fungicidal or bactericidal agent in an amount of 0 to I % by mass.

T Lhe scope and properties of the materials preferred for preparing the adheqive layer of the inven- re illustrated as follows.

ion a.

Suitable rubbers are those having a Mooney viscosity Of 4T 1+8 20 to 75 at 100 OC; further on, preferably an isoprene/isoblitylene copolymer with an unsaturation of 0.6 to 5 %; as well as a styrene/butadiene copolymer containing 60 to 80 % butadiene and having 0 er a Mooney viscosity of MI 1+4 30 to 90 at 100 OC, pref ably of.46 to 48 such as Buna SB 152H.

Useful adhesion-increasing materials are hydro 0 0.1 carbon resins with a softening point of aO to 140 C, acid value lower than 50 m- of KOH/a- and a molecular CD C) mass of I-ICO to 1500. Suitable vulcanization-inducing substances are sulfur and secondary as well as tertiary amines, such as triethanolamine; metal oxides such as zinc oxide, magnesium oxide, lead oxide and silicon dioxide may also be used.

Useful substances modifying the insulating properties and diminishing the polarization damages are those decreasing the porosity of the mixture and thereby the permeability thereof against Plectrolytes.

Atactic polypropylenes having a molecular mass of 5000 a) to 100000, a softening point of 110 to 160 0 C, a density of 0.8 to 0.95 g/mIl and an elongation rupture higher' than 3 % and bitumens with an average molecular mass lower than 6000 and a softening point of 50 to 120 0 C may preferably be used for this purpose.

Preferable fillers and auxiliary materials are: carbcn black with an ash conten7 of a-- most 0.1 /o 2 1 by mass and by mass, moisture content at most.5 io carbon content off at leasIt 95 -7, by mass; as well as limestone flour, talc, kaolin, chalk, fa---tioe and the like; and bactericidal as well-as fungicidal agents such as Mistox LPL.

As vulcanization-accelera-ting agents dithio- carbamates, preferably piperidine pentamezhylenedithio carbamate, zinc diethyldithiocarbamate; thiurams, such as tetramethylthiuram disulfide and thiaz--l--s such as 2-mercaptobenzothiazole may suitable be uleed.

12 The process of the invention is illustrated in detail by the following non-limiting Examples.

Example 1

Composition of the adhesive mixture containing no vulcanization-inducing ingredients:

parts by mass Butyl rubber (BK 1675) 90.00 Styrene/butadiene copolymer (Buna SB 152H) 10.00 Carbon black (PGM 33) 135-00 Factice RPM 70/30 15-00 Hydrocarbon resin (Escorez 1102/B) 11.25 Atac-1-1 01 -B) 14 -ic polypropylene (Tipplen AIP.50 Stearin 1.00 Total: 276-75 The mixture -4s homogenized in an internal CD mixer in a known mnanner, rcilled -Io a shee7 with a -thickness of 0.25 mm and doubled on-to a ?7 foill o--:' sign "B" ore 2", viously coated with the adhesion-transmi-,-er.

ExamiDle 2 a) The composition of the mixture and the process are as described in Exam-le 1 except tha7 the mixture also contains 2.0 parts by mass of sulfur and 4.0 parts by mass of zinc oxide as vulcaniZation or cross-linking agents.

0 13 b) To a priming solution of known composition, 3 % by mass (as calculated for the dry substance content thereof) of tetramethylthiuram disulfide (Hermat TMT) as vulcanization-accelerating agent are mixed.

Example 3

Compositon of the adhesive mixture parts by mass Butyl rubber (BK 1675) 100.00 Carbon black (PGM 33) 136.00 Hydrocarbon resin (Escorez 1102/B) 15-00 Factice RPM 70/30 11-50 Atactic polypropylene (Tipplen APP-B) 40.00 Stearin 1.00 Mistox LPL 0.50 0 4.

The mixture is prepared as de-scribeed in -Example I and then pressed onto a PVC fo-41 of sign "B".

ExamDle 4 Composition of the adhesive mixture parts by mass Butyl rubber (BK 1675) 100.00 Carbon black (PGM 33) 136.00 Hydrocarbon resin (Escorez 1102/B) 15-00 Factice RPM 70/30 11.00 Bitumen (sign "K-3" with a softening point of 85-90 oc) 28.00 14 Stearin 1.00 Total: 29,1.00 The mixture is homogenized in an internal mixer, t.hen rolled to a sheet with a thickness of 0.20 mm and pressed onto a PVC foil of sign "B".

Example 5 a) Composition of the adhesive mixture also contain- ing vulcanization-inducing ingredients parts by mass Butyl rubber (BK 1675) 90.00 Native rubber (RSS 1) 10.00 Carbon black (PGM 33) 135.00 Hydrocarbon resin (Mafkirez 101) 15.00 Factice RPM 70/30 11.50 Bitumen (sign "K-Y' with a softeninc. Doin-! m 0.10 90 OC) 1-13.00 Atact -ic -coDypropylene (Tipplen APP-B) 23 Sulfur 2.25 Zinc oxide 4.50 Stearin 1.00 Total: 302.90 Lhe adhesive mixture is prepared as describbed in Example 1 and applied onto a PVC foil.

b) To a primer of known composition, 3 % by mass (as calculated for the dry substance content thereof) of piperidine pentamethylene-dithiocarbamate as vulcaniza tion-accelerating agent are mixed.

Example 6

Example for the use The product described in Example 1 was sticked onto the one side of a steel plate of 5 x 5 cm in such a way that the plate had previously been cleaned up to the pure metal, coated with a priming solution of known composition (by brush-coating) and the product of Example 1 of the same dimension was immediately levelled onto the plate. After having left to stand for 7 days, the free metal parts were insulated and in the middle Example 1 of the side insulated with the product of the insulation was bored through up -o -the metal by using a drill with a diameter of 6 mm. T--- pla-t;es were placei into an electrolyte (an aqueous solution contain :C inz I % of sodium carbonate and 1 % of scd-Jum chloride) and polarized cathodically by using 1.3 V for 7 days.

The extent of the damage amounted to 237 mm 2 during the experimental period.

For comparison, a measurement was carried out wi-,h the composition of Example I without atactic polypropylene, i.e. the substan-ce diminishing the harmful material, i.e.

effect of the polarization. (A filling N talc was used instead of polypropylene). This composi-ion resulted in a damage of 612 =_2- The prcducc of Example 4 16 - 2 resulted in a damage of 312 mm On carrying out +be measurement with an other known insulating system, a damage of 1820 mm 2 was ob tained.

Example 7

Example for the use An insulating foil was prepared according to Example 2 a) and sticked to a clean-to-metal steel plate of 250 x 40 mm by using the priming solution of Example 2 b) in such a way that the foil was longer by 5 to 6 cm than the metal plate. The product was put into an oven at 50 0 C for 48 hours and the adhesion against shear of the insulating system was investigated at 70 OC as follows.

The test sample was placed with --he -netal side onto a metal plate fitted w4.-,h rezulated heatin,-, anll fixed in such a way that the free end the foil hung down from the heating plate.!'-e Lree end of the C) - W 23 foill was squeezed in between two sheets. 1Previously, an elastic bowden had been fixed to the plate; and a ballast of 3.2 kg had been placed to the free end of the bowden. The bowden was led through an easily moving screw fixed to the heated plate in such a way that the ballast hung down freely.

During the experiment, the extent of the shear- ing (i.e. the slipping on the metal plate) was measured 17 as a function of the time.

The data of these measurements are shown on the curve 1 of Figure 1.

For comparison, the product of Example 3 was used with a priming solution of known composition. Re sults of the measurement are illustrated on curve 2 of Figure 1.

Under the same experimental conditions, curve 3 of Figure 1 was obtained by using an other known insulat ing system.

Example 8

Example for the use An experimental method was developed for studying the effect of simultaneous and cooperating factors, i.e. an aggressive electrolyte, pressure and cathodic -IurJ - operation.

polarization on the insulated systems -W The method of the measurement and evaluation were described in the Czechoslovakian journal Plyn 62 (8), 230 (1982).

The specimen according to the above description was coated with the priming solution of Example 5 b) and coated with the product of Example 5 a) before carry ing out the measurement.

After an experimental period lasting for 21 days, a current of 4 to 5 uA penetrated through the M insulating system according to Example 5.\ For comparison, an other known insulating system was also investigated. This measurement resulted in a value higher by an order of magnitude, i.e. 35 1 to 40 /uA.

1 1 19

Claims (1)

1. Claims

   1. A coating or adhesive tape comprising a carrier material and an adhesive mixture containing 20 to 60% by weight of at least one synthetic and/or natural rubber; 2 to 20% by weight of at least one adhesion-improving 5- material; 3 to 30% by weight of at least one substance modifying the electrically insulating properties: and 30 to 70% by weight of at least one filler and/or auxiliary material 2. A coating or adhesive tape as claimed in claim 1 in which the rubber component is an isoprene/isobutylene copolymer or a styrene/butadiene copolymer or a mixture of both.

   3. A coating or adhesive tape as claimed in claim 1 or 2 in which the adhesion-improving material is a hydrocarbon resin.

   4. A coating or adhesive tape as claimed in claim 3 in which the hydrocarbon resin has a softening point of 80 to 2400C, an acid value less than 50 mg of KOH per gram and a molecular weight of 800-1500.

   5. A coating or adhesive tape as claimed in any one preceding claim which further comprises a vulcanisation-inducing substance.

   6. A coating or adhesive tape as claimed in claim 5 in which the vulcanization-inducing substance is sulphur, a secondary or tertiary amine, or a metal oxide.

   I.

   7. A coating or adhesive tape as claimed in any one preceding claim in which the substance modifying the electrically insulating characteristics is an atactic polypropylene; a copolymer of, or terpolymer comprising, ethylene and propylene; or a polyisobutylene.

   8. A coating or adhesive tape as claimed in claim 7 in which the atactic polypropylene has a molecular weight of 5000 to 100000, a softening point between 110 and 1600C, a density of 0.8 to 0.95g/ml, and elongation at break geater than 3%.

   9. A coating or adhesive tape as claimed in any one preceding claim in which the substance modifying the electrically insulating characteristics is a bitumen.

   10. A coating or adhesive tape as claimed in claim 9 in which the bitumen has an average molecular weight of less than 6000 and a softening point between 50 0 and 12011C.

   21 11. A coating or adhesive tape as claimed in any one preceding claim in which the filler material is chosen from one or more of carbon black, limestone flour, talc.

   kaolin. chalk and factice.

   12. A coating or adhesive tape as claimed in any one preceding claim in which the said auxiliary material is a bactericide and/or a fungicide.

   13. A coating or adhesive tape as claimed in any one preceding claim in which the carrier material is a synthetic polymeric fabric or foil.

   14. A coating or adhesive tape as claimed in claim 13 in which the synthetic polymer material of the carrier is a polyvinylchloride or a polyethylene.

   15. A coating or adhesive tape as claimed in any one preceding claim in which the adhesive mixture is present as a layer from 1 to 5mm thick.

   16. A coating or adhesive tape as claimed in any one preceding claim in which the adhesive mixture is present as a layer and an adhesion-strengthening or adhesion-transmitting layer is present between the adhesive mixture and the carrier material.

   22 17. A coating or adhesive tape as claimed in claim I and substantially as herein described with reference to any example.

   18. A process for the preparation of a coating or adhesive tape as claimed in any one preceding claim in which a layer of the adhesive mixture is calendered or extruded upon the carrier material.

   19.A process as claimed in claim 18 in which an adhesion-strengthening or adhesion-transmitting layer is applied to the carrier material prior to the extrusion or calendering thereon of the adhesive mixture.

   20. A process for improving the electrically insulated characteristics of articles in which a surface of the article is treated with a priming solution and thereafter coated with a coating or adhesive tape as claimed in any one of claims 1 to 17.

   21. A process as claimed in claim 20 in which the article is a pipe for installation underground and is helically wound with the tape.

   22. A process as claimed in claim 20 or 21 in which the priming solution contains a vulcanization-accelerating agent.

   23 23. A process as claimed in claim 22 in which the vulcanisaton-accelerating agent is a dithiocarbamate, a thiuram or a thiazole.

   Published 1985 z T_e 2_ C, 72 WC1F, 4TF cOPI.Es mkv be cl.^aine- frcn Tlrie Patent Office, 5-cS Bra,:-. 5-. Kn-, E--15 I= S. 1 - C-. KE, -Z CO- 1 87.

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