DK158154B - Process for producing coverings, especially for use when renovating and repairing car tyres - Google Patents

Abstract

In a process for producing coatings adhering to the surface while being removable, a treatment liquid is produced from PUR elastomers enabling a thermoplastic treatment by admixing a solvent. Said treatment liquid, fluid or viscous depending on the mixture ratio, is applied to the surface and forms after evaporation of the solvent a coating adhering solidly to the surface while being completely removable if required. Even in the case of a thin wall, said coating has an excellent tear resistance while being elastic and flexible. Its surface is absolutely tight and it provides a reliable protection against the mechanical effects and the like. It is preferably used for the reconditioning and the repair of tyres of motor vehicles, the necessary rubber envelope being replaced by the coating. Said coating may also be used as a protection against oxidation and adverse mechanical influences for the rough lower surface of the prefabricated rubber tread for the reconditioning of tyres of motor vehicles.

Description

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DK 158154 B

The invention relates to a method of making coatings which can be adhered to surfaces, but which can be removed from them, especially for use in the renovation and repair of automobile tires.

5 In many areas of the art, there is a need for coatings to be affixed to surfaces that can be pulled off, but which can be pulled off as needed, primarily having fabric adhesion and high flexibility, tightness and tear strength and elasticity. . Rubber covers are admittedly elastic, flexible and dense, but their tear strength leaves some to be desired and their adhesiveness is limited.

It is therefore the object of the present invention to provide a method by which 15 simple coatings can be made which are securely adhered to the surface of articles of as many different materials as possible, but which may also be removed from the surfaces as required.

The method according to the invention consists in the characterizing part of claim 1.

20 From the Plastic Handbook, vol. VII, Polyurethane, 1966, p. 294, it is known that thermoplastic polyurethanes are soluble in solvents such as dimethylformamide, dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, pyridine and tetrahydrofuran. However, a further 25 instructions are lacking on how to further process the thermoplastic polyurethanes dissolved in this way.

By Ullmann's Encyclopedia of Technical Chemistry, 4th edition, vol. 11, 1946, p. 316, it is stated in the chapter "Fasern, einzelne synthetische organicische" under middle heading 30 "3.2.3. The spinning process" as known in the art that high viscous elastomer solutions (about 20-25% in dimethylformamide, vis. - 2 -

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quality approx. 50-150 PAs) can be spun vertically through multi-hole nozzles in heated spinning shafts to which additional hot air is fed. Only the suitability of such high viscosity elastomer solutions for spinning is mentioned herein by which polyurethane elastomer wires are spun from high viscous elastomer solutions.

Finally, thermoplastic processable polyurethane elastomers are particularly suitable for injection molding or worm pressing for extrusion, usually by heating to a temperature which depends on their exact composition, for example in the range of 180-240 ° C. . In commerce they usually go as granules. When cooled after processing, they cure very quickly. The formation of thin coatings by, for example, spraying 15 on the surface of articles is difficult, because the elastomer particles are already strongly cooled before they reach the surface of the articles. Measures to counteract premature cooling of the elastomer particles are costly.

In the method of the invention for the preparation of coatings, polyurethane elastomers intended for thermoplastic processing are used to prepare a treatment liquid. This is prepared by simply mixing a thermoplastic processable polyurethane polymer with one of the three solvents specified in the above-mentioned mixing ratio so that no special thermal setting is needed.

A treatment liquid thus prepared can be applied in extremely fine distribution on practically any surface 30 to form an absolutely closed surface coating.

After the rapid evaporation of the solvent, it is found that the coating thus formed adheres securely to the surface, but that it can nevertheless be pulled off as a whole or, if required, under certain conditions - 3 -

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circumstances should be desirable, in single pieces. The thickness of the coating is practically arbitrary and depends solely on how much treatment liquid is applied per surface unit of the surface. It is possible to make 5 quite thin foil-like coatings as well as several millimeters thick coatings.

The most prominent features of a coating made by the method according to the invention are high adhesiveness on virtually any surface, great flexibility so that even surfaces on, for example, flexible articles can be coated, and high tear strength, elasticity and density.

Since the treatment liquid is readily prepared by simple mixing of the thermoplastic processable polyurethane elastomer with one of the three specified solvents and is likewise easily processable, and since finally a coating thus formed has the aforementioned properties, there are innumerable uses are possible. either the coating must be used to protect a surface or to change a surface condition or to achieve a better association with an object.

The treatment liquid can also be applied at room temperature by means of a spatula or a brush. It can also be sprayed using a spray gun on the particular surface.

As solvent, first and foremost N, N-dimethylformamide (C CH H ^NO) is considered. This solvent produces in the mixture a solution of the polyurethane elastomer, which is usually obtained as a granulate, to form a homogeneous treatment liquid.

Instead, N-methylpyrrolidone can also be used as a solvent. Certainly, in that case, a tempera- ture is required.

DK 158154B

- 4 - trip of at least 50 ° C. A similar temperature requires tetrahydrofuran as the solvent. In particular, due to its simple processability, Ν, Ν-dimethylformamide is preferred as a solvent.

Depending on how thin or viscous the treatment liquid is, 10-30% by weight of polyurethane elastomer granulate is admixed into the solvent.

As thermoplastic processable elastomers, the following types of Desmopan types from Bayer are considered in principle (R):

Shore Proximity A / D Desmopan - 150 97/52 - 385 85/33 - 455 97/57 - 460 97/59 - 588 89/33 - 786 87/34 - 790 92/42 -DD-1478 98/60 - DD-1573 80 -DD-1581 98/72 -PU-1769 93/40 (T?)

The "soft" Desmopan types W 385, 588, 786 and DD-1573 are best suited to form the treatment liquid by the process of the invention.

Immediately after application of the treatment liquid, a cut-off piece of textile fabric can be applied to the still fresh coating. Thus, the fabric section is firmly anchored to the coating and in practice forms a reinforcement which can be used when the coating is formed on a very rough surface and yet must be able to be pulled off in one piece.

2o The tear resistance of the coating is further enhanced significantly by the introduction or application of a fabric fabric.

A particularly advantageous embodiment of the method according to the invention is characterized by the features set out in claim 2.

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- 5 - cut.

5 DE-PS 1779113 discloses a similar approach to tire renovation, where the pre-made rubber tread, after being placed on the prepared carcass in the area of the side exit points of the binder rubber layer by mechanical action, must be connected firmly and tightly to the carcass. Among a number of different mechanical connecting means is also a measure according to which the rubber tread is to be connected to the carcass by spraying or applying a self-curing heat-resistant layer over the area of the adhesive rubber's exit sites, which 15 layers after the vulcanization of the adhesive rubber coating must be removed. However, no suitable material is proposed for the manufacture and use of the self-curing heat-resistant layer.

The claim of claim 2 solves precisely the problem in the field of revulcanization.

In particular, for this application of the method of the invention, it is important that the coating adheres securely to the surface of the carcass and tread, that is, on a rubber surface. It has been found that the coating also has the necessary heat resistance for the necessary pressure and heat treatment of the blank in the overpressure chamber. The tear strength and also the high tensile strength are necessary so that the coating is not damaged and thereby permeable. The above-mentioned properties in connection with a high adhesive capacity 30 ensure that the abrasion strip edges are not loosened when the binder duct disease shortly before the vulcanization becomes almost liquid and therefore loses its adhesive capacity. The coating itself is closed, ie close to dirt and moisture. Wood - 6 -

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at the end of the vulcanization, it can be removed without a trace without difficulty in one piece. However, it can also be left to protect the shoulders of the tire.

It is essential that the coating engages over the side exit sites of the adhesive rubber layer. Whether the cover is unpainted to the tread or carcass side depends on the circumstances. Normally, one simply needs a narrow annular strip covering the likewise annular side exit sites of the binder rubber layer on both sides thereof.

In order to achieve uniformity in the layer structure of the blank, a further feature of the invention is essential, namely that the coating until the final evaporation of the solvent shrinks a little and thus promotes an even better consistency among the parts which it covers.

Equally advantageous, the invention can be used in the context of a method of repairing holes and other damage to automobile tires. For this purpose, in particular for the repair of earth-moving tires, a method is known by means of a sleeve which at least ends the tire repair site airtight, to cover and enclose the repair site as protection against oxidation and dirt or moisture and possibly for removing air and gas inclusions from the space between the casing 25 and the tire by the use of vacuum and / or overpressure, and during vulcanization of the raw rubber introduced on or into the tire by heat application. This known method is further developed according to the invention by the design of the method according to the invention as set forth in claim 3. Thus, no more is required to place a sheath part with associated circumferential sealing by means of an adhesive material, but the sheath is formed by means of the coating, which itself adheres to the repair site and can still be pulled off after - 7 -

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the execution of the repair. However, the coating can also remain in the repair area as an additional protection.

Regardless of whether a casing is formed for circumferential refurbishment or for repair, any air enclosures can be sucked away with a hollow needle with the tip of the cover pierced, after which the insertion site is again sealed.

In all embodiments of the method according to the invention it is possible to proceed as set out in claim 10 4.

Also, in another context of the revolving renovation of automobile tires within the framework of a method of the aforementioned kind, the invention is of particular importance. According to the invention, it is possible that a rough surface formed on a rubber tread, segments or bricks in the mold or after compression is closed air-tight with a coating of treatment liquid. After the coating has been pulled off, the rubber tread is reprocessable without further processing, whether the further processing takes place shortly after the manufacture of the rubber tread or after prolonged storage. The coating provides protection against mechanical or chemical damage to the rough surface, and it can be made adherent to the rough surface of the rubber tread by simply applying the treating liquid 25. This raw method of preserving the raw surface of a rubber tread far exceeds all conventional methods for the same purpose by its simplicity.

The invention will be explained in more detail by the following examples.

30 To renovate the tread of a worn-out automobile tire is made using the cold renovation method - where the use of a full sleeve or part sleeve - 8 -

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is appropriate or necessary - a treatment fluid by means of which a coating can be formed on the tire blank which replaces the full sleeve or the sub-sleeve. In addition, the repair must be carried out on the carcass, to which a coating is also needed instead of a casing section.

First, a liter of treatment fluid is prepared in which (R) 25% by weight of Desmopan 385 from the firm of Bayer is intensively mixed for as long as 75% by weight of Ν, Ν-dimethylformamide 10 (C, H7N0) as solvent that the polyurethane elastomer (R) granules of Desmopane 385 is completely dissolved and regularly distributed in the solvent.

The treatment liquid thus produced is viscous and can be applied to surfaces by means of a brush, a putty or also by means of a spray gun using cartridges.

(R)

It should further be added that Desmopan 385 is by itself intended for processing into injection molding or extrusion in a temperature range of 180-220 ° C.

20 The carcass on the tire that needs to be renovated all the way around is usually processed in a running machine, blown clean with air and applied to a commercially available solution such as gasoline. On the thus prepared carcass a approx. 1 millimeter thick binder rubber layer of a binder rubber blend in the male part. A tread similar to the carcass diameter, which in the present case is 210 millimeters wide, is also wiped with a commercial solvent, and the same applies to the binder carbide layer on the carcass. It is easy to push the tread on the carcass by the action of the solvent which produces a sliding effect, at least before the solvent or solvent is drawn into the binder car layer and dried.

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By means of a spatula, the treatment fluid is now applied annularly to both carcass sides in the area of the side exit sites of the binder rubber layer, and this is done in such a way that the exit sites are covered and closed.

5 The application of the treatment fluid extends to the can of the tread shoulder outwards and - from the point of exit of the adhesive rubber layer - approximately as far radially inwards. However, in each case the width required depends on the present claims, and it is difficult to determine in general.

On the applied treatment liquid is applied a roughly as wide nylon tissue strip, which is pressed, after which the surface facing the carcass is wetted completely with treatment liquid.

15 The drying of the treatment liquid or the evaporation of the solvent creates a firmly and securely adhering coating to the rubber surface of the carcass structure with a completely dense and closed surface. During the drying of the treatment liquid, a shrinkage of the coating is observed, thereby exerting pressure on the coated parts.

Due to the high strength values and absolute insensitivity of the coating, a thickness of 0.2-0.4 mm is already enough.

After complete drying of the treatment fluid, the tire is heated in a pressure chamber to a temperature of 95 ° C at a pressure of 5-6 bar.

After removing the finished tire from the pressure chamber, the coating on both sides of the tire can be easily torn off. However, it can also remain on the carcass, especially as the coating is colorless and transparent and thus barely visible. A nylon fabric strip is used because the tire carries a two-sided side decoration and because the treatment fluid, therefore, for absolute density penetrates deep

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- ίο - bumps on the carcass flank and anchor the cover in this place accordingly. In order to be able to easily and completely remove the coating from the carcass in each case, in these circumstances, a nylon-5 fabric strip is used so that carcasses with a relatively smooth surface can fall away.

The carcass repair site is otherwise vulcanized in one workflow with the binder rubber layer on the carcass. Following the usual preparation of the repair site and the placement and attachment of a binder rubber cone, the repair site - in the same way as before the side exit points on the binder juk layer - is coated with treatment liquid, so that an adhesive covering around the repair site is formed here as well. The ease of operation of using such a coating is particularly marked in repair, because here, especially in the case of large bricks, the placement of a circular vacuum-tight casing section to be sealed is often quite difficult.

Claims (4)

A process for the manufacture of coatings which are adhesive to surfaces but which are easy to pull off, especially for use in the renovation and repair of automobile tires, characterized in that a treatment liquid of 10-30% by weight thermoplastic processing is formed polyurethane elastomer and 70-90% by weight of solvent consisting of a) Ν, Ν-dimethylformamide (C ^H ^NO) or b) N-methylpyrrolidone or c) tetrahydrofuran by mixing and applying a dense coating. surface the treatment liquid using a spatula or brush or spray it using a spray gun and the solvent is evaporated. A method according to claim 1, characterized in that, for renovating the tread on a worn-out pneumatic or solid rubber tire on the tire's prepared carcass, a binder rubber layer is applied and on this a prefabricated rubber tread, removing gaseous inclusions between the applied layers and heating the thus prepared blank for vulcanizing the binder duct layer in an overpressure chamber, forming a coating according to claims 1, 25 prior to heating in the overpressure space in the area of the side outlet locations of the binder duct layer, and removing the cover completely or partially after the heat treatment as required. Method according to claim 1, characterized in that at least in the area of the tire repair site, which is filled with raw rubber, for repairing automobile tires, as an airtight envelope for covering the repair site for protection against oxidation and dirt, a coating is formed. according to claim 1, which after completion DK 158154 B of the heat treatment for vulcanization of the raw rubber as required is fully or partially deducted. Process according to claims 1-3, characterized in that the fresh coat formed is reinforced by the application and printing of a piece of textile fabric.