This invention is about a multi-layer hose with an internal layer resistant to high temperatures and oil and an outer layer resistant to low temperatures. The invention relates more specifically to a multi-layer hose that will meet the heat resistance requirements in fluid lines, especially in charge-air lines of motor vehicles.

Prior ArtRubber hoses used in the charge-air lines of motor vehicles are expected to be resistant to the high temperature air conveyed, which is also generally contaminated by aggressive chemicals like engine oil. Rubber blends used in the layers of these hoses are mainly based on ethylene acrylic acid elastomer (AEM) (trade name Vamac®), which is known to be resistant to high temperatures and oil. AEM elastomer is a copolymer of ethylene, methyl acrylate with a cure site monomer containing carboxylic acid groups.

Although different grades of AEM elastomer can be derived by controlling the monomer selection- ratio and distribution of molecular weight during the production, available grades are divided into two groups, elastomers in dipolymer form which are cured using a peroxide-based vulcanization system, and elastomers in terpolymer form which are cured using a diamine-based vulcanization system.

Crosslinking bond energy of a diamine-cured AEM terpolymer is much higher than that of a peroxide-cured AEM dipolymer. As a result, it is possible to achieve a higher heat resistance with AEM terpolymer blends and that's why in charge air lines they are preferred over AEM dipolymer blends. Rubber blends made of amine-cured AEM terpolymer are used in the inner and outer layers of charge air hoses. As the required permanent deformation and heat resistance values can only be met by AEM terpolymer - amine vulcanization system.

For a charge air hose to function properly, individual hose layers should be bonded to each other and act as a whole. In other words, the interlayer adhesion value measuring the level of bonding strength between the layers of the hose has to be high.

Inner layer of a charge air hose should meet high heat-resistance and oil- resistance requirements. However, for the outer layer oil resistance is not necessary and heat resistance requirement is considerably low. Therefore, instead of using an AEM based blend on the outer layer, utilizing a peroxide- cured rubber blend based on EP(D)M elastomer ensures a more cost-effective hose structure. The major concern hindering this point is the adherence of polar AEM inner layer to apolar EPDM outer layer. European patent numbered EP1546595 B1 discloses a multilayer hose with an AEM based inner layer, an EPDM based outer layer and a bonding layer interposed between the inner and outer layers, which is based on a peroxide cured blend of AEM dipolymer and EP(D)M elastomer. As described in the patent, the rubber blend used in the intermediate layer comprises peroxide- curable AEM dipolymer, and as specified before, this cannot ensure desired dynamic specifications and permanent deformation values.

In order to overcome the disadvantages of AEM dipolymer, patent application no. WO2011012374 discloses a multilayer hose with an outer layer comprising EP(D)M elastomer and an inner layer comprising terpolymer AEM elastomer wherein the intermediate bonding layer is based on EP(D)M elastomer which is only curable by peroxide vulcanization system. However, there are two important contradictions in the given solution. Firstly, it is not possible for a hose with an intermediate layer comprising only EP(D)M rubber to compensate the effect of heat transferred from the inner section of the hose. Temperature of the fluid conveyed through a charge air line reaches 180 ^° C in continuous state with a 200 ^° C peak. As the inner layer of the hose is constantly in contact with the fluid, the operating temperature that the intermediate layer exposed is 160 ^° C or higher depending on the wall thickness of the inner layer. However, EP(D)M elastomer is not able to endure an operating temperature above 160 ^° C. The second crucial issue is the fact that the desired interlayer adhesion cannot be attained with such a hose construction as the polarities of EPDM and AEM do not match.

In order to overcome the above stated problems, the present invention discloses a multi-layer hose with improved dynamic properties, interlayer adhesion and high heat and oil resistance, wherein the hose has an inner layer of AEM elastomer, an outer layer of EP(D)M elastomer and a bonding intermediate layer made of a blend of AEM terpolymer and EPDM and/or EPM elastomers.

Detailed Description of the InventionThis invention presents a multilayer hose having at least;

^■ an inner layer (10) comprising amine-curable AEM terpolymer,

■ an intermediate bonding layer (12) comprising a blend of AEM terpolymer and ethylene propylene diene terpolymer (EPDM) and/or ethylene propylene copolymer (EPM) and

^■ an outer layer (16) comprising peroxide-curable EPDM and/or EPM

The intermediate layer (12) comprising the blend of AEM terpolymer and EPDM and/or EPM adheres to both the inner and outer layers (10, 16) during vulcanization and bonds them together. According to the invention, the blend used in the intermediate layer (12) comprises EPDM and/or EPM elastomer as well as AEM elastomer in terpolymer form; and it is vulcanized by a (amine + peroxide) vulcanization system. It is not possible to cure the intermediate layer blend only with peroxide system. Intermediate layer (12) of the invention comprises the following for each 100 weight units of EPDM and / or EPM;

^■ 40-95 units of AEM in terpolymer form

^■ 50-200 units of filling material

^■ 5-50 units of plasticizer

" 0.5-10 units of organic peroxide vulcanization agent

^■ 0.5-8 units of amine based vulcanization agent

In the preferred application of the invention, the blend of the intermediate layer (12) comprises the following for each 100 units of EPDM and/or EPM;

^■ 75-95 units of AEM in terpolymer form

■ 130-160 units of filling material

^■ 25-35 units of plasticizer

^■ 4-7 units of organic peroxide vulcanization agent

^■ 2.5-5 units of amine based vulcanization agent

Ethylene acrylic elastomer used in the blend is in terpolymer form and it can be cross-linked with amine vulcanization agent. Dipolymer-based ethylene acrylic elastomers can be cross-linked with peroxide vulcanization agents, but not amine vulcanization agents. Crosslinking bond energy generated by AEM elastomers in terpolymer form is higher than the AEM elastomers in dipolymer form. Therefore, higher heat resistance is attained with blends comprising AEM elastomers in terpolymer form. Increase in the crosslinking bond energy affects the heat resistance and aging qualities of elastomers drastically. So, AEM elastomers in terpolymer form comprising higher crosslinking bond energy show better thermal and dynamic properties compared to the AEM elastomers in dipolymer form with lowcrosslinking bond energy. Furthermore, higher crosslinking bond energy show lower permanent deformation values at higher temperatures.

Filling material used in the blend is preferably carbon black; however, it can also be furnace black, lamp black or thermal black. Plasticizer may be mineral-based and/or ether-/ester-based or preferably a blend of both.

Organic peroxide vulcanization agent to be used in the blend can be diacyl, peroxiester, peroxiketal and dialcyl-type peroxide. Preferred peroxide type is dicumyl peroxide. Amine-based vulcanization agents used in the rubber blend can be hexamethylene diamine (HMD) and/or hexamethylene diamine carbamate (HMDC), while the vulcanization agents to be used as accelerator may be DOTG (di-o-tolyl guanidine) and / or DBU (1.8-Diazabicyclo-(5.4.0)-undec-7- ene) and/or DPG (diphenyl guanidine). DOTG is not used in the rubber blend due to carcinogenic and toxic effects.

According to the invention, EPDM or EPM used in both intermediate layer (12) and outer layer (16) can be maleicized. These ethylene propylene-based elastomers may be used together or separately in various ratios.

In another application of the invention, amine-curable polyacrylic elastomer (ACM) may be used in the inner layer (10) and/or in the intermediate layer (12) instead of ethylene acrylic acid (AEM) terpolymer elastomer. Alternatively, ACM can be used by blending with AEM terpolymer.

Different elastomer groups are subjected to cross-linking process with different vulcanization agents in the intermediate layer (12) rubber blend of the present invention. Cross-linking depends on the type, amount, activity and reaction time of the vulcanization agents. In order to obtain the desired cross-link density, vulcanization kinetics should be adjusted according to the elastomer groups.

The acrylic-based elastomer used in the intermediate layer (12) rubber blend of the disclosed invention is polar, and ethylene propylene-based elastomer is apolar. In the rubber blends, in which elastomers with different polarities and viscosities are used, ensuring blend homogenization by exceeding the material surface tensions of the components constituting the rubber blend is essential for the end product to show desired mechanical, chemical and dynamic characteristics. Therefore, in order to ensure the desired characteristics of the intermediate layer (12) rubber blend, a special blending technique has been employed.

Details of the production technique are as follows:

Step 1 : Acrylic-based elastomer, filling material and oil are simultaneously fed to the internal mixer and mixed. Mixing stops as the maximum temperature of the blend reaches 120°C, which provides the 1 st blend composition.

Step 2: Firstly, filling material and oil, then 0-60 seconds later- ethylene propylene-based elastomer are fed into the internal mixer and mixed. Mixing stops as the maximum temperature of the blend reaches 120°C, which provides the 2 ^nd blend composition. Step 3: 1 st and 2nd blend compositions are mixed together, and intermediate layer (12) blend composition within the scope of the invention is obtained.

According to the present invention, the hose may also contain one or more reinforcing layers (14) between inner and outer layers (10, 16). Reinforcing layer (14) may be in the form of braid, spiral, wound or any other type known in the art, produced from yarns made of preferably aramide as well as polyester, rayon, cotton, nylon or similar materials. Anti -static agents, filling materials, pigments, vulcanizer and other rubber additives known in the state of the art can be used in the blends of the inner, intermediate and outer layers (10, 12, 16).

The hose of the present invention may comprise additional layers as long as it includes the disclosed inner, intermediate and outer layers (10, 12, 16).

The hose of the present invention can be produced by conventional manufacturing methods like coextrusion or calendering.

In order to improve the adhesion between the layers, bonding promoters can be added to the blends of the inner, intermediate and outer layers (10, 12, 16), or an adhesive solution can be applied between the layers.

In the preferred application of the hose, the wall thickness of the inner layer (10) is between 1.2 and 1.5 mm, whereas the wall thickness of the intermediate bonding layer (12) is between 1.5 and 1.8 mm and outer layer (16) is between 1.9 and 2.2 mm. However, depending on the application, these thicknesses may be 0.5 to 2.0 mm for inner layer, 0.5 to 2.0 mm for intermediate layer and 1.0 to 3.0 mm for the outer layer.

The multi-layer hose of the invention is preferably produced through the following stages: a) extrusion of the inner layer (10)

b) coextrusion of the intermediate layer (12) on the former (10) c) coextrusion of the outer layer (16)

d) Vulcanizasation of the hose with high-pressure steam

Knitting a reinforcement layer (14) between stage b and c is also possible.

The production stages may also include a step where the adhesive solution is applied.