DE102012108247B4 - Method for producing a tread of a pneumatic vehicle tire - Google Patents

Abstract

bestimmt wird, wobei
d_A die Gesamtdicke der Laufstreifencap (3),
WM_A der Anteil an migrationsfähigem Weichmacher in einer theoretischen Ausgangsmischung für die Laufstreifencap (3),
doben die Dicke der äußeren Capschicht (5),
WM_oben der gewählte Anteil an migrationsfähigem Weichmacher in der äußeren Capschicht (5) und
dinnen die Dicke der inneren Capschicht (4)
sind,
und wobei sich die theoretische Ausgangsmischung lediglich im Anteil an migrationsfähigem Weichmacher von den Kautschukmischungen für die innere und
die äußere Capschicht (4, 5) unterscheidet.

Method for producing a tread (1) of a pneumatic vehicle tire with a tread base (2) and a tread cap (3) made of layers of different rubber mixtures, wherein the tread cap (3) contains migratory plasticizer and in the vulcanized state a certain Shore hardness A value having,
characterized,
in that the tread cap (3) is composed of an inner cap layer (4) and a thinner outer cap layer (5) which covers the outside and whose rubber compounds contain different amounts of migratory plasticizer in other congruences, wherein in the rubber mixture the inner cap layer (4) the proportion of migratory plasticizer is greater than in the rubber composition of the outer cap layer (5),
wherein the proportion of migratory plasticizer in the inner cap layer (4) is selected such that migration of part of this plasticizer from the inner cap layer (4) into the outer cap layer (5) during vulcanization, and to a smaller one Part after vulcanization during storage of the finished tire, a compensation of the plasticizer components in the inner and outer cap layer (4, 5) takes place, so that the resulting tread cap (3) has the determined Shore hardness A value,
wherein the proportion of migratory plasticizer (WM _inside ) in the rubber composition of the inner cap layer (4) according to the formula $${\text{WM}}_{\text{Inside}}=\frac{{\text{d}}_{\text{A}}\times {\text{WM}}_{\text{A}}-{\text{d}}_{\text{above}}\times {\text{WM}}_{\text{above}}}{{\text{d}}_{\text{Inside}}}$$

is determined, where
d _{A is} the total thickness of the tread cap (3),
WM _{A is} the proportion of migratory plasticizer in a theoretical starting mixture for the tread cap (3),
doben the thickness of the outer cap layer (5),
WM _above the selected proportion of migratory plasticizer in the outer cap layer (5) and
the thickness of the inner cap layer (4)
are,
and wherein the theoretical starting mixture only in the proportion of migratory plasticizer from the rubber mixtures for the inner and
the outer cap layer (4, 5) differs.

Description

The invention relates to a method for producing a tread of a pneumatic vehicle tire with a tread base and a tread cap of several layers of different rubber mixtures, wherein the tread cap contains migratory plasticizer and has a certain Shore hardness A value in the vulcanized state.

In the production of rubber compounds for treads of pneumatic vehicle tires, depending on the application, different amounts of plasticizer are used. Tires intended to be particularly well suited for use in winter driving conditions use relatively high levels of plasticizer in the tread compounds to ensure good snow and ice grip on winter road conditions. It is known and customary to use low-aromatics, mineral oils or resins - ie plasticizers that are capable of migration. Additionally, one or more liquid polymers may be included as plasticizers in the tread. Especially at higher levels of plasticizer, during the vulcanization of the tire, the attachment or adhesion of emanating from the tread compound plasticizers on the inside of the Reifenheizform can be problematic. Through oxidation processes, incrustations form on the mold surfaces over time, which are very difficult and expensive to remove and which increase the mold release forces of the vulcanized tires.

From the DE 10 2008 018 241 A1 is a pneumatic vehicle tire, in particular for commercial vehicles, known with a profiled tread, which has at least three superimposed layers whose rubber compositions differ from each other with respect to their content of butadiene rubber. The amount of processing oil in the layers is ≤ 5 phr. The WO 2012/004038 A1 discloses a special rubber compound, in particular for pneumatic vehicle tires, for example also for the tread base of a tread. The base blend contains from 5 phr to 10 phr of process oil, with the low level of plasticizer intended to limit the migration of plasticizer.

The invention has for its object to produce the tread cap such that in the vulcanization of the tire, these deposits or dirt on the Reifenheizform no longer occur or only to a negligible extent.

bestimmt wird, wobei

• d_A die Gesamtdicke der Laufstreifencap,
• WM_A der Anteil an migrationsfähigem Weichmacher in einer theoretischen Ausgangsmischung für die Laufstreifencap,
• doben die Dicke der äußeren Capschicht,
• WM_oben der gewählte Anteil an migrationsfähigem Weichmacher in der äußeren Capschicht und
• dinnen die Dicke der inneren Capschicht

sind,
und wobei sich die theoretische Ausgangsmischung lediglich im Anteil an migrationsfähigem Weichmacher von den Kautschukmischungen für die innere und die äußere Capschicht unterscheidet.The object is achieved according to the invention by
that the tread cap is composed of an inner cap layer and a thinner outer cap layer which covers the outside and whose rubber compounds contain different amounts of migratory plasticizer in other conformation, the proportion of migratory plasticizer in the rubber mixture of the inner cap layer being greater than in the rubber mixture of outer cap layer,
wherein the proportion of migratory plasticizer in the inner cap layer is selected such that migration of a portion of this plasticizer from the inner cap layer into the outer cap layer during vulcanization, and to a lesser extent after vulcanization upon storage of the finished tire in that compensation of the softener components takes place in the inner and outer cap layers, so that the resulting tread cap has the determined Shore hardness A value,
wherein the proportion of migratory plasticizer in the rubber composition of the inner cap layer according to the formula $${\text{WM}}_{\text{Inside}}=\frac{{\text{d}}_{\text{A}}\times {\text{WM}}_{\text{A}}-{\text{d}}_{\text{above}}\times {\text{WM}}_{\text{above}}}{{\text{d}}_{\text{Inside}}}$$

is determined, where

• d _{A is} the total thickness of the tread cap,
• WM _{A is} the amount of migratory plasticizer in a theoretical starting mixture for the tread cap,
• doben the thickness of the outer cap layer,
• WM _above the selected proportion of migratory plasticizer in the outer cap layer and
• the thickness of the inner cap layer

are,
and wherein the theoretical starting mixture differs from the rubber mixtures for the inner and the outer cap layer only in the proportion of migratory plasticizer.

The outer cap layer therefore consists of a rubber mixture which, in the vulcanized state, would in principle be harder than the inner cap layer due to the low proportion of plasticizers and would lead to an undesirably hard tire surface. However, this does not occur, since even during the vulcanization of the tire migration-capable plasticizer from the rubber mixture of the inner cap layer migrates into the outer cap layer and leads to a softening of the same. The majority of plasticizer migration takes place in the Reifenheizform during vulcanization, a small part also after the storage of the tire. The ready-to-use tire has a uniform tread of desired hardness due to the migration of the plasticizer that is capable of migration. Since the cap layer coming into contact with the inside of the vulcanization mold contains very little or no plasticizer, the deposits and soiling by plasticizers on the inside of the mold are small or negligible and have no consequences on the demolding forces.

The rubber mixtures of the inner and the outer cap layer may contain, as migration-capable plasticizer, at least one low-aromatics mineral oil and / or at least one resin. These plasticizers may be the common types of plasticizer used in tread blends.

An optimal migration behavior can be achieved by a certain choice of the thicknesses of the cap layers. It is particularly advantageous if the inner cap layer has a thickness between 5.5 mm and 7.5 mm at least in its central region and the outer cap layer has a thickness of 0.5 mm to 4 mm, in particular 1.5 mm to 2 mm. 5 mm.

The invention will now be described in more detail with reference to the drawing. It shows 1 schematically a cross section through the tread of a pneumatic vehicle tire.

The Shore A hardnesses of vulcanized rubber mixtures specified in the description are determined in accordance with DIN 53505 (at 23 ° C.).

1 shows schematically a cross section through the tread portion of a car tire, which is constructed in a conventional radial design. The left half of the 1 shows the tread area before the vulcanization of the tire, therefore, when the tire is raw, the right half of the 1 after vulcanization and a certain storage time, wherein in the right half circumferential grooves of a tread profiling are indicated. The tread 1 in the finished tire consists of a radially inner rubber layer, the tread base 2 , which usually has a thickness of 1 mm to 2 mm, and a tread cap 3 , In the unvulcanized state, the cap 3 made of two cap layers consisting of different rubber compounds, an inner cap layer 4 and an outer cap layer 5 which the inner cap layer 4 completely covered, built up. The thickness of the inner cap layer 4 is between 5.0 mm and 7.5 mm, the thickness of the outer cap layer 5 between 0.5 mm and 4 mm, in particular between 1.5 mm and 2.5 mm. The thickness of the inner cap layer 4 is in the middle area of the tread 1 determined. The production of the raw tread from the cap layers 4 and 5 and the base 2 can be done in a conventional manner by coextrusion in an aggregate with appropriate extruders.

Depending on the intended use of the tire, the tread cap has a certain shore hardness A, which is attributable to the proportion of plasticizer in the starting mixture, with higher proportions of plasticizer, in particular in winter tire treads. Winter tires usually have the tread cap 3 a Shore hardness A ≤ 65, in particular between 50 and 60, and therefore contains a corresponding amount of plasticizer. Plasticizers which can be added are migration-capable plasticizers, such as low-aromatics, mineral oil and / or resin and optionally liquid polymer, for example liquid butadiene rubber or liquid styrene-butadiene rubber, to the starting mixture. The amount of migratory resin / oil in the tread cap 3 is usually between 8 phr and 65 phr.
The more plasticizer the rubber compound for the tread cap 3 The more sticky it is, and the more likely it is during the vulcanization of the tire in the vulcanization mold, that the inside of the vulcanization mold is wetted by softeners to be expelled from the tread surface. As a result, deposits or encrustations form on the inside of the mold, which are difficult and expensive to remove. After repeated use of the tire mold, it may happen that a tire inserted in the tire mold "sticks" to the deposits and the vulcanized tire can only be released from the mold by applying high demolding forces. These effects are enhanced by any amount of liquid polymer in the tread cap, as leaking liquid polymer under the action of atmospheric oxygen during opening and closing the mold and crosslinked by the prevailing high temperatures in the vulcanization mold on the inside of the tire mold.

The invention shows a possibility of largely preventing the deposition of migratory plasticizer on the inside of the mold and at the same time to achieve that the Shore A hardness of the finished vulcanized tread cap has the originally intended value. This is the outer cap layer 5 made of a rubber mixture containing no or a smaller proportion of migratory plasticizer than the rubber composition of the inner cap layer 4 , wherein the rubber mixtures are otherwise identical. The vote of the rubber mixtures with respect to the proportions of migrationsfähigem plasticizer is preferably such that a vulcanizate of the rubber composition for the outer cap layer 5 At least four Shore A points would be harder than a Vulkanisat from the rubber mixture for the inner cap layer 4 , The difference in hardness in this regard may in particular be up to twenty points of hardness.

The proportion of migratory plasticizer in the inner cap layer 4 is adjusted so that by the migration or migration of this plasticizer from the inner cap layer 4 in the outer cap layer 5 During vulcanization, and to a lesser extent after vulcanization during storage of the finished tire, a balance of the plasticizer components in the inner and outer cap layer 4 . 5 takes place so that the tread cap 5 the finished tire has a uniform hardness, namely the originally intended or desired hardness.

Table 1 contains examples of rubber blends for the inner cap layer 4 and the outer cap layer 5 , The mixtures have matching polymer systems and also agree in their other constituents, with the exception of the proportions of migratory plasticizer. The mixtures may also contain liquid polymer. The usual ingredients, such as the vulcanization system and the polymer system, are not specified, they may be the known for tread compounds substances with the usual proportions. The proportions given are phr (parts by weight, based on 100 parts by weight of polymer in the respective mixture). Table 1 Cap layer 4 Cap layer 5 Polymer (s) 100 100 Plasticizer (eg low in aromatics, mineral oil) 26.7 0.0 N 121 (soot) 10 10 silica 85 85 Thickness of the layer 6 mm 2 mm Hardness Shore A of the vulcanized mixture 55 68

Based on an associated theoretical starting mix for the entire, uniform tread cap 3 is calculated, which proportion of migratory plasticizer in the inner cap layer 4 should be included, so that after migration of a part of this plasticizer from the inner cap layer 4 in the outer cap layer 5 throughout, uniformly formed tread cap 3 the level of plasticizer is substantially equal to that in the theoretical starting mixture and the resulting uniform tread cap 3 the desired, predetermined Shore Hardness A has.

The "starting mixture" would have, for example, the following proportions (polymer system and other constituents correspond to those in the rubber mixtures of the inner and the outer Capschicht 4 . 5 ): Polymer (s) 100 phr Plasticizer (eg low in aromatics, mineral oil) 20 phr N 121 (soot) 10 phr silica 85 phr Thickness of the tread cap 8 mm

d_A

Dicke der Laufstreifencap 3 aus der Ausgangsmischung (= Summe aus d_oben und d_innen)

WM_A

Anteil an migrationsfähigem Weichmacher in der Ausgangsmischung

d_oben

Dicke der äußeren Capschicht 5

WM_oben

Anteil an migrationsfähigem Weichmacher in der äußeren Capschicht 5, wird gewählt, ist in jedem Fall kleiner als WM_innen

d_innen

Dicke der inneren Capschicht 4

The hardness Shore A of the vulcanized starting mixture would be 58, for example. The proportion of migratory plasticizer (WM _inside ) in the rubber mixture of the inner cap layer 4 is calculated according to the following formula: $${\text{WM}}_{\text{Inside}}=\frac{{\text{d}}_{\text{A}}\times {\text{WM}}_{\text{A}}-{\text{d}}_{\text{above}}\times {\text{WM}}_{\text{above}}}{{\text{d}}_{\text{Inside}}}$$

d _A

Thickness of the tread cap 3 from the starting mixture (= sum of d _above and d _inside )

WM _A

Proportion of migratory plasticizer in the starting mixture

d _above

Thickness of the outer cap layer 5

WM _above

Proportion of migratory plasticizer in the outer cap layer 5 , is chosen, is in any case smaller than WM _in

_inside

Thickness of the inner cap layer 4

From the data in Table 1 and those of the starting mixture, the proportion of 26.7 phr of migratory plasticizer given in the example of Table 1 for the rubber mixture of the inner cap layer is calculated 4 ,

The invention is therefore based on the idea that a higher proportion of migratory plasticizer in the inner cap layer 4 a low or nonexistent level of this plasticizer in the outer, thinner cap layer 5 in vulcanizing the tire by migration of plasticizer into the outer cap layer 5 is compensated. Much of the "plasticizer hike" already takes place during vulcanization in the tire mold, a small part of the migration during the subsequent storage of the tire over several weeks.

LIST OF REFERENCE NUMBERS

1

tread

2

Tread rubber base

3

tread cap

4

inner cap layer

5

outer cap layer

Claims (4)

Method for producing a tread (1) of a pneumatic vehicle tire with a tread base (2) and a tread cap (3) made of layers of different rubber mixtures, wherein the tread cap (3) contains migratory plasticizer and in the vulcanized state a certain Shore hardness A value characterized in that the tread cap (3) of an inner cap layer (4) and this outside covering, thinner outer cap layer (5) is composed, the rubber mixtures contain different proportions of migrationsfähigem plasticizer in another match, wherein in the rubber mixture of inner cap layer (4) the proportion of migratory plasticizer is greater than in the rubber composition of the outer cap layer (5), wherein the proportion of migratory plasticizer in the inner cap layer (4) is selected such that by the migration or migration of a part of this Plasticizer a the inner cap layer (4) into the outer cap layer (5) during vulcanization, and to a lesser extent after the vulcanization during storage of the finished tire, a compensation of the softener components in inner and outer cap layer (4, 5) takes place resulting tread cap (3) has the determined Shore hardness A value, wherein the proportion of migratory plasticizer (WM _inside ) in the rubber composition of the inner cap layer (4) according to the formula $${\text{WM}}_{\text{Inside}}=\frac{{\text{d}}_{\text{A}}\times {\text{WM}}_{\text{A}}-{\text{d}}_{\text{above}}\times {\text{WM}}_{\text{above}}}{{\text{d}}_{\text{Inside}}}$$

where _{A is} the total thickness of the tread cap (3), WM _{A is} the amount of migratory plasticizer in a theoretical starting mixture for the tread cap (3), the thickness of the outer cap layer (5), WM _{top is} the selected level of migratory plasticizer in the outer cap layer (5) and inside are the thickness of the inner cap layer (4), and wherein the theoretical starting mixture differs from the rubber mixtures for the inner and outer cap layers (4, 5) only in the proportion of migratory plasticizer. Method according to Claim 1 , characterized in that the rubber mixtures of the inner and the outer cap layer (4, 5) contain as migratory plasticizer at least one aromaticsarmes mineral oil and / or at least one resin. Method according to Claim 1 or 2 , characterized in that the inner cap layer (4) has a thickness between 5.5 mm and 7.5 mm at least in its central region. Method according to Claim 1 or 2 , characterized in that the outer cap layer (5) has a thickness of 0.5 mm to 4 mm, in particular from 1.5 mm to 2.5 mm.

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