DE2750836C2 - Rubber mixture for direct bonding to metallic reinforcements - Google Patents

Description

The invention relates to a rubber mixture for direct bonding to metallic reinforcements (as Inserts of rubber bodies), in particular unplated steel cables, bare spring band steels and the like, based on natural and / or synthetic rubbers, the fillers, processing aids, vulcanizing agents and contain resorcinol and hexamethylenetetramine as formaldehyde donors as adhesive components.

Rubber mixtures of different structures for adhesion to metallic reinforcements, such as. B. Steel cables, in particular brass-plated steel cables, are known per se. They usually contain as Adhesive components Cobalt compounds or resorcinol, a formaldehyde-releasing compound and highly active Silicic acid using the usual mixing components such as carbon blacks, processing aids and vulcanizing agents. In a technical report from Degussa, liability of Rubber compounds for metals, A-15-6710, 19G7, page 5 six adhesive compounds for cord fabric with Steel inserts indicated, of which the mixtures No. 5 and 6 to 100 parts of rubber in addition to usual

ι ο Additions 2.5 parts of resorcinol, 1.5 parts of hexa and 4.0 parts contain insoluble sulfur. Depending on the type of use of adhesive mixtures in the various Rubber objects, such as B. Pneumatic vehicle tires, conveyor belts This or that type of mixture is used to achieve maximum adhesive strengths and the like. It is now known that these adhesive mixtures designed for plated, in particular brass-plated metal surfaces In terms of binding, zones also have to be covered where there is no longer any brass plating is located. In the manufacture of pneumatic vehicle tires with brass-plated steel cables z. B. the rubberized Wire layers cut into appropriate processing parts. To cover the resulting bare Rope cut edges will be the same blends

_> 5 used specifically for brass-plated metal surfaces were developed. When retreading tires z. B. are often used when renewing a belt Steel cable layers exposed by the roughening process, sometimes even completely roughened. Here, too, it becomes brighter

jo Stahl about adhesive mixtures for brass-plated wire surfaces bound to adjacent tire structural components during vulcanization. Cut edges of plated Steel ropes, partially or completely bare roughened wire layers put in the various rubber counterparts

i) there has always been a particularly difficult problem of detention This can be seen from the fact that this bond - bare steel / rubber - is causal There is a connection with the solution defects emanating from these points. It becomes clear that about conventional adhesive mixtures do not provide adequate bonding to unplated metal surfaces can be achieved, and that the bond to bare steel in the manufacture of rubber-metal composite bodies represents a problem that has not yet been sufficiently resolved. Since the highest demands are placed on tires with steel cable inserts There is a legitimate interest in having rubber-to-metal adhesion, but cutting edges always represent areas of weakness in the bond on rubber compounds that adhere specifically to bare steel. In addition, there is a further interest in such mixtures for all articles in which unplated steel with rubber must be connected or where costly metal coatings or labor-intensive processes of the Metal pretreatment for adhesion can be dispensed with, such. B. for rubber-metal components.

There is often the opinion that the adhesive mixtures developed for brass-plated or galvanized metal coatings also bind sufficiently to bare steel.

bo Such mixtures that are based mainly on are composed of resorcinol, formaldehyde donors and highly active silica in combination with sulfur, however, do not show sufficient bond strength to bare steel.

b5 The comparisons available from the specialist literature of adhesion values between rubber compounds and brass-plated or bare steel cables make it clear that the adhesive strength of bare rope

Rubber, depending on the type of compound, is only around 20 to 50% of the values of brass-coated ropes It can be said that adhesion values with regard to bare steel can simulate a bond which is in Reality does not exist at all, because practically only the mechanical anchoring of the reinforcement opposite the vulcanizate is measured. When looking at the ropes detached from the adhesion test specimens it is shown that even with adhesion values of up to approx. 300 N / 20 mm embedment length, the adhesion zone is more or is less bare; so there is no real bond between metal and rubber. From the presented Reasons it follows that only mixtures can be used for adhesion to bare steel, which in the The structure of the adhesion components are specially designed for this reinforcement.

The invention is essentially based on the object of proposing a rubber mixture which allows. Rubber with metallic reinforcements, namely bare reinforcements, such as Steel ropes or smooth unplated metal parts, safe to connect, in such a way that such a bond from a pretreatment of the reinforcement, such as B. general cleaning, degreasing or mechanical roughening, can refrain.

According to the invention, this object corresponds to the proportion of hexamethylenetetramine about that of resorcinol or else it is above Proportion of resorcinol, specifically for the resorcinol / Hexamethylenentc tramin molar ratios of about 1: 0.75 to about 1: 2. The proportion of hexamethylenetetramine is expediently above that of the Resorcinol, specifically for the resorcinol / hexamethylenetetramine molar ratios of about 1: 1 to about 1: 2. the end the reasons listed below can also be the proportion of hexamethylenetetramine about that of the Resorcinol, for a resorcinol / hexamethylene tetramine molar ratio of about 1: 0.75.

Known adhesion promoters, such as resorcinol and hexamethylenetetramine, are thus used to solve this problem. With regard to the adhesion components, there is no difference between mixtures for bonding to bare steel and those for bonding to brass-plated steel, with the exception that only hexamethylenetetramine can be used as a formaldehyde donor for bare steel. Other formaldehyde releasers that are equally suitable for brass-plated surfaces, such as B. Hexamethyloimelamine ether, tri- and hexamethylolmelamine, paraformaldehyde, polyoxymethylene and the like are ineffective with respect to unplated steel and can therefore be excluded. Pre-condensed resins made from resorcinol and formaldehyde, which can be used for adhesion to brass-plated steel surfaces, also remain ineffective with regard to bare surfaces. Compared to conventionally constructed adhesive mixtures for brass-plated steel, provided they have resorcinol and hexamethylenetetramine as the basis, ^r I further shown that, surprisingly, than are required for the binding over bare steel fundamentally different molar ratios of resorcinol and hexamethylenetetramine for brass-plated steel. This shift in the molar ratios between resorcinol and hexamethylenetetramine makes it possible for rubber compounds to bond to bare steel in the first place. In addition, it has also been shown that for bare steel, higher dosages of resorcinol and hexamethylenetetramine for each of the molar ratios described below strengthen the adhesion. At doses of around 7.5 parts of resorcinol, based on rubber, excellent bonding strengths are even obtained without sulfur being present

The rubber mixtures according to the invention are therefore based on the known adhesion promoters resorcinol and Hexamethylenetetramine. Compared to mixtures of the same basis for brass-plated metal surfaces however, the crucial difference is in one

ίο molar ratio deviating from the conventional system between resorcinol and hexamethylenetetramine. It has been shown that the best bond between bare steel and rubber can only be achieved with mixtures that have a molar ratio at which the

ι ϊ The proportion of hexamethylenetetramine is higher than that of resorcinol. This is only the case from a molar ratio of 1: 1. With a molar ratio of resorcinol to hexamethylenetetramine of 1: 0.75, the proportion of both adhesion promoters is roughly the same, ie the proportion of formaldehyde donor is just below that of resorcinol. This ratio does not represent the optimum of the adhesion, because here binding is only obtained with increasing dosages of adhesion promoters.
Mixtures for adhesion to brass-plated steel, insofar as they are based on resorcinol and hexamethylenetetramine, contain, based on 100 parts of rubber, usually 2.5 parts of resorcinol and 1.5 parts of hexamethylenetetramine. The dosage of 2.5 parts of resorcinol in such

ίο Adhesive mixtures represents an empirical value and is practiced in most cases. The proportion based on this empirical value of 2.5 parts of resorcinol of 1.5 parts of hexamethylenetetramine corresponds to a molar ratio of resorcinol to hexamethylenetetramine

J-) of 1: 0.5. This relationship is provided for explanation from the following calculation method:

The molecular weights of the reactants resorcinol and hexamethylenetetramine are for resorcinol 110 and for the formaldehyde dispenser 140. With one

j »molar ratio between resorcinol and hexamethylenetetramine from 1: 0.5 to 110 or 11 g of resorcinol reacted with 70 or 7 g of hexamethylenetetramine. When 11 g of resorcinol with 7 g of hexamethylenetetramine react, not applicable, to the empirical value of 2.5

4-> parts related to resorcinol, 1.6 parts of hexamethylenetetramine. This dosage ratio between resorcinol and hexamethylene cetramine, which is a molar ratio of 1: 0.5, is easily modified to 2.5: 1.5, usually practiced. The one from this Molar ratio resulting quantitative ratios, based on 100 parts of rubber:

2.5 resorcinol: 1.6 hexamethylenetetramine

5.0 resorcinol: 3.2 hexamethylenetetramine

7.5 resorcinol: 4.8 hexamethylenetetramine

10.0 resorcinol; 6.4 hexamethylenetetramine

With a molar ratio of resorcinol to hexamethylenetetramine of 1: 0.5, the proportion of

bo formaldehyde donors far below hexamethylenetetramine that of resorcinol. As has been shown again and again, the reactant becomes at this dosage ratio excellent bonding strength to brass-plated metal surfaces, but not too

b5 unplated steel. The for a liability to bare steel suitable molar ratios and the corresponding quantitative ratios for each molar ratio are listed below:

Molar ratio
Resorcinol - hexamethylenetetramine - 1: 0.75

Quantity ratio

2.5 resorcinol: 2.4 hexamethylenetetramine

5.0 resorcinol: 4.8 hexamethylenetetramine

7.5 resorcinol: 7.2 hexamethylenetetramine

10.0 resorcinol: 9.6 hexamethylenetetramine

At this molar ratio, the proportion of hexamethylenetetramine is just below that of resorcinol.

Molar ratio
Resorcinol - hexamethylenetetramine - 1: 1

Quantity ratio

2.5 resorcinol: 3.2 hexamethylenetetramine 5.0 resorcinol: 6.4 hexamethylenetetramine 7.5 resorcinol: 9.6 hexamethylenetetramine 10.0 resorcinol: 12.8 hexamethylenetetramine

From a molar ratio of 1: 1, the proportion of hexamethylenetetramine is higher than that of resorcinol and increases with increasing molar ratio.

Molar ratio
Resorcinol - hexamethylenetetramine - 1: 1.25

Quantity ratio

2.5 resorcinol: 4.0 hexamethylenetetramine 5.0 resorcinol: 8.0 hexamethylenetetramine 7.5 resorcinol: 12.0 hexamethylenetetramine

Resorcinol - hexamethylenetetramine molar ratio - 1

1.5

Quantity ratio

2.5 resorcinol:
5.0 resorcinol:
7.5 resorcinol:

4.8 hexamethylenetetramine

9.6 hexamethylenetetramine

14.5 hexamethylenetetramine

Resorcinol - hexamethylenetetramine molar ratio - 1: 2

Quantity ratio

6.4 hexamethylenetetramine 12.8 hexamethylenetetramine

2.5 resorcinol
5.0 resorcinol

The higher quantitative ratios of the molar ratios from 1: 1.25 are to illustrate the invention The procedure is not listed here, as they are not very suitable for a practical application.

According to the procedure outlined above, adhesion to the reinforcement "bare steel", be it steel ropes or smooth, polished steel surfaces, such as B. spring band steel, summarized by the following Measures to be achieved:

as far as this is due to resorcinol and various formaldehyde donors based.

2. It was also shown that for liability on unplated steel is the molar ratio of

-, resorcinol to hexamethylenetetramine plays a crucial role. So it becomes an optimal Steel adhesion achieved with a ratio of the adhesion components of 1: 1, a dosage ratio in which the proportion of hexamethylene

ID tramin is well above that of resorcinol. With the Molar ratios at which the proportion of formaldehyde donor continuously increases is also used ensures good adhesion. The molar ratio 1: 0.75 does not represent the optimum adhesion, because here only a bond with higher dosages of adhesion promoters is achieved, but what this molar ratio, especially at the higher dosages or in conjunction with higher ones Sulfur additives, do not exclude from protection

2Ii can. To the conventional system for brass binding, as far as this is based on resorcinol and hexamethylenetetramine, there is a difference in the fact that, as a rule, only the molar ratio of resorcinol - hexamethylenetetramine to the brass bond of 1: 0.5 is used, since molar ratios increase with the proportion of hexamethylenetetramine deteriorate the adhesion to brass.

3. It can also be said that the jo proportions of a molar ratio of Meaning are. Except for the 1: 1 molar ratio, where all quantitative ratios have the same adhesion rating ■ received, the steel adhesion usually increases with increasing dosage of adhesion promoter

j5 at the other molar ratios. This too Behavior is in contrast to the conventional brass adhesive system, as far as it is based on resorcinol and Hexamethylenetetramine based. Here the binding values drop with high dosages of adhesion promoters usually off.

4. The adhesive system for bare steel also differs significantly from all of them Brass binding processes, insofar as these are based on resorcinol and various formaldehyde donors, thereby that adhesion can also be achieved with "sulfur-free" adhesive mixtures. So revealed z. B. rubber mixtures with 7.5 and 10 parts of resorcinol, based on 100 parts of rubber, and the corresponding proportions of hexamethylenetetramine (molar ratio 1: 1) with bare steel excellent bond strengths without the use of sulfur or a sulfur-releasing compound was present in the mixture. Such recipes are not found in practice or in the specialist literature known for bonding to brass-plated, galvanized and unplated steel.

1. About rubber compounds, in addition to the usual compound components and vulcanizing agents Contain resorcinol and the formaldehyde donor hexamethylenetetramine. Other formaldehyde releasers remain to bind to bare steel just as ineffective as pre-condensed resorcinol-formaldehyde resins. In the confinement There is a difference to hexamethylenetetramine as a formaldehyde donor conventional systems for brass bonding, as another and surprising feature of the Adhesion of rubber compounds to bare steel

bo it has been found that a Relationship between the proportions of resorcinol and hexamethylenetetramine (also resin former called) and the sulfur of the rubber mixture. The same bond strengths are then obtained

b5 compared to bare steel, e.g. B. with the molar ratio: 1 ₁ according to the guideline: high dosages of adhesion promoters require small amounts of sulfur or function sulfur-free (point 4). Low

7 8

Dosages of resin formers, on the other hand, require a not inconsiderable part of the bond strength Sulfur gifts. In one of the following the mechanical anchoring of the ropes compared to the It is shown which sulfur dosing vulcanizate is covered. To demonstrate liability

at the molar ratio of 1: 1 for the resorcinol proportions of rubber mixtures according to the invention on blank

2.5-10, based on rubber, no bond or core steel and about the effect of mechanical

result in a secure liability. Anchoring was therefore excluded from this representation in the

can be smoother, more polished for each resorcinol dosage between the attempts listed below

examined proportions of 2.5; 5.0; 7.0 and 10.0, which is used by the spring steel strip for assessing adhesion

required amount of sulfur can be read off. Adhesion of the vulcanized compounds to spring tape

this relationship between the adhesion promoter combina- io steel and the assessment of the bond strength was like

tion from resorcinol and hexamethylenetetramine on the one hand is determined as follows:

and sulfur, on the other hand, is not known. On a 6 mm thick plate of the to be assessed

Overall, adhesive mixes differ from raw mixes, spring band steels were placed on top

Tests for bare steel in principle of such and the underside of these test specimens were covered with foil

for brass metal surfaces, insofar as they are covered on the i 5 After heating these test specimens, the

Based on resorcinol and hexamethylenetetramine steel sheets using pliers from the vulcanizate

are constructed even if they separated out the same combination The adhesion and rubber covering

Contained by adhesion promoters. was assessed objectively

The rubber mixtures according to the invention “- ·. .

naturally also include those from these mixtures

gen produced gasoline-free solutions, which in the form of the model recipe reproduced in Example 1 No. 1

of spray and brush solutions are used for an adhesive mixture for bare steel is also used in

can. the following embodiments with the

As is known, smooth and polished listed molar ratios can be changed accordingly. It is difficult to bind metal surfaces to rubber because 25 th doses of resorcinol and hexamethylene tetra-

Compared to steel ropes, the mechanical min and different amounts of sulfur continue here

Anchoring of the surface opposite the vulcanizate used is absent When the adhesion of steel cables to rubber is

Recipe no.

12 3 4 5 6

Natural rubber, RSS3! 00

Zinc oxide 8

Carbon black N33O 40

Active silica 15

Resorcinol 7.5 - -

Sulfur 3

Accelerator 0.8 Formaldehyde dispenser Hexamethylenetetramine 9.6 - - - 9.6 9.6 Hexamethylolmelamine - 7.5 - -

ether

Paraformaldehyde 3 - Curable phenolic resin 9.6 Resorcinol formaldehyde resins Precondensed 7.5 -

kesorcin-formaldehyde-

resin

Resorcinol formaldehyde 7.5 Resin with modified Degree of condensation Vulcanization time:

W at 150 "C

Adhesion to spring steel strip + -____ Rubber cover + _____ Assessment: liability

+ very good

- no Assessment: Gi coverage

+ νοΠ covered

-blank

In the example formulation No. 1, resorcinol and hexamethylenetetramine were used in a molar ratio of 1: 1 used accordingly. A formaldehyde dispenser was added to mix # 2 according to the usual procedure dosed in the same amount as resorcinol. In Mixture No. 3, a practical dosage chosen. Example 1 makes it clear that adhesion to bare steel only is to be produced via the adhesion promoter combination of resorcinol and hexamethylenetetramine. Other formaldehyde donors and pre-condensed resorcinol-formaldehyde resins remain ineffective.

Further examples are explained using the attached diagrams:

Example! 2

The adhesion assessments shown in Examples 2 and 3 are to be understood as the mean from several test series and essentially show the binding capacity of the reinforcements as a function of the molar ratios. For “bare steel”, in addition to spring band steel, steel ropes 7 3 / 0.15 from various manufacturers were also investigated. ^{The 1} : 1 molar ratio also represents an optimum adhesion for bare steel ropes.

The representation according to Example 2 shows that for brass-plated steel cables an optimum adhesion in the molar ratio Resorcinol - hexamethylenetetramine of 1: 0.5 exists, as there is a bond in all proportions is achieved. With an increase in the dosage ratios, there is a decrease in the brass-plated steel Liability connected. In addition, it becomes clear that with increasing molar ratios of resorcinol and hexamethylenetetramine - with corresponding transitions - the adhesion worsens and liability In comparison to example 3 it can be seen that the optimal adhesion area for brass-plated surfaces and for bare steel is determined by different molar ratios.

Example 3

The representation according to Example 3 shows that for bare steel there is optimum adhesion at a molar ratio of 1. · 1 2.5 resorcinol - 6.5 sulfur - total = 9.0 5.0 resorcinol - 2.0 sulfur - total = 7.0 7.5 resorcinol - 0.0 sulfur - total = 7.5 According to this illustration, the following general dosage rule can be drawn up for the sulfur dosage to be used for all amounts between Z3 and 7.5 parts resorcinol, based on rubber:

For all resorcinol doses between 2J5 and 7.5 since all dose ratios were given practically the same adhesion assessment. Furthermore, it can be seen that the steel bond, in contrast to the brass bond, is mostly improved with increasing dosage ratio. It is also clear that mixtures for adhesion to brass-plated surfaces, insofar as these contain resorcinol and hexamethylenetetramine and the adhesion components correspond to the most common molar ratio of 1: 0.5, cannot cover areas with bare steel in terms of bonding, since brass and unplated steel are used for adhesion require different molar ratios.

Example 4

This representation shows that bare steel with a molar ratio of 1: 1 and above even without its presence of sulfur adheres to rubber compounds if the resorcinol content is 7.5-10.0 parts on rubber related, amounts to.

This representation can also be seen that even with a sulfur-free adhesion of bare steel Rubber the molar ratio of 1: 1 is optimal in terms of bonding.

Example 5

In example 5 it is shown that for comparable Adhesion strengths the rule of thumb is that low adhesion promoter dosages high amounts of sulfur, In contrast, high dosages of adhesion promoter require low or no amounts of sulfur.

This relationship "high resin - low sulfur, low resin - high sulfur" can tend but not in principle with regard to the representations shown by heating time, vulcanization temperature and by mixing ingredients, such as. B. Processing aids experience minor deviations.

The amounts of sulfur assigned to the resorcinol components for secure adhesion are for the molar ratio 1: 1:

30th

40

50 mean 8.0

The amount of sulfur must be chosen so that the sum of these amounts to 8 to be on the safe side

For example, 3.5 parts of resorcinol requires 4.5 parts of sulfur, sum = 8. A sum greater than 8 further reinforces the security of the bond.

Example 6

Example 6 shows that when the relationship "low resin - high sulfur, high resin - low sulfur" is used, the value of 1: 0.5, which is practically ineffective with conventional sulfur content, is also used for the

For Z3 resorcinol - 9.0 sulfur - total = 11.5

5.0 resorcinol - 5.0 sulfur - total = 10.0

7.5 resorcinol - 3.5 sulfur - total = 11

10.0 resorcinol - 2.0 sulfur - total = 12

As a rule of thumb for all doses between 2 and 10 parts resorcinol, it is good that the sum of resorcinol and steel adhesion can be used for a secure bond.

With this molar ratio, the following amounts of sulfur are required for excellent bond strengths:

Means

Sulfur, on must be.

Obtain rubber , at least 11

example

Very good

Adhesion area - measured q ter steel

ν e r m. S tah IseiL

7x3 / O. 1 5

Good

liability

No or not reichendeHaftun

Molver - holds η is

I: O.

1 :

1: 1

: 1.2 5

·. 1.5

: 2

Amounts ver ratio resorc in: hexamethylenetetramine

2.5 5.0

1.6 3.2

10.0 6.4

2.5 2.4

5.0 7 ί, .θ

2.5 50 7.5
3 2 6.4 9.6

10 0 12 5

2.5 4 0

100
O 16.0

5
4. 8

5.0 7.5
9.6 14 L

2.5

4th

5.0
8th

Volcano, 3O'l5db

liability

UEUBLtfcLl

Adhesive area - bare steel

Spring band steel

Very good

Good

Liability

No or insufficient liability

Molar ratio

:

1: O. 7 I: 1

1: 1.2 5

I: 2

Quantity ratio

HahnIs Resorcinol: Hexamethy-lentetramine

2.5 5.0 7 5 10.0

1.6 3.2 4.8

2.5 5.0 7.5 2.4 4 8 7 2 2.5 5.0 75 lO.O.
3.2 6.4 9 6 12.8

2.5
U O

5 0
8.0

75 10.0
12.0 160

2.5
4.8

5.0
9 ß

7 5 14.4

2.5 6.4

5ü 12.8

Vulcanization 307150'C

Very good

Good

liability

None resp. not suffice de liability

Molverh eldni s

Quantity ratio

Ratio of resorcinol: Hexamethy -len t e tr α m in

VuI sewer 30 '/ 15O ⁰ C

Example / ♦ Bare steel

- Loan w e f e t f r e ι e h a t m ices

Spring band steel

1 :

2.5

I.

5.0 3

7.5 4

10.0 6.4

2.5 3

7.5
9.6

0

Irishman

2.5

1.8

5.0 9.6

75

10.0 I9fl

Natural rubber formulation RSS

Zinc oxide active silica e

lOO

40

15th Q β

accelerator

Schwe fe I

Resorcinol vunauei

Hexamethylenetetramine variable

vari a be

liability Ex el 5 Fashion 5
6th 0
L.
0 Bl ι 7 5
96
30th α π k he Sta Hi I: I Spring strap ahl animal - sulfur Men q e η b e ζ i 5.0
6 4
2.0 very good I ι e Liability ζ e ρ t u r m i tt I e eh u η q Good r - sulfur : Liability liability None or η icht
sufficient e
liability Molver oil tn is Quantity ratio
Resorc in
Hexame thy len -
tetramine
Sulfur Vulcanization
307 I 50 ° C 2
3
3 5
2
0 10 0
I 2.θ
3 0 7 5 10 0
9.6 2 8
0 0 mi I 2 5
3.2
6 5 Bezιe hun g

By S pie I 6 1-0. Ha 5 7th
4th
3 Blan I. k he St a St. Bez fei : 0 5 heather band steel H aft u ηq 5 0
3.2
3.0 M e η qe relation 5 0
3 2
5 0 Molver holds ? zep t u I: C ). 5 η is Mode Ir « ftve rm 5
8th
0 ittl er - Schwe Haf tv he mi tt f Very good I. r Good liability None or not
sufficient
liability Molar ratio 2.!
1.6
3. 0 Quantity ratio
Resorcinol
Hexamethylene
tetramine
sulfur 7 5 10 0
4 8 6.4
35 2.0 vulcanization
307 150 ° C ! 00
6 4
3 0 25th
1.6
9.0 I er - Schw ef el i ehun g:

Claims (7)

Patent claims: 1. Rubber mixture for direct bonding to metallic strength supports, consisting of mixtures Made of natural and / or synthetic rubbers, fillers. Processing aids, vulcanizing agents and as adhesive components resorcinol and hexamethylenetetramine as formaldehyde donors, characterized in that the proportion of hexamethylenetetramine is about that of the Resorcinol corresponds to or is above the proportion of resorcinol, namely for the molar ratios Resorcinol: hexamethylenetetramine from 1: 0.75 to 1: 2. 2. Rubber mixture according to claim 1, characterized in that the proportion of hexamethylenetetramine is above that of resorcinol for the molar ratios of resorcinol: hexamethylenetetramine from 1: 1 to 1: 2. 3. Rubber mixture according to claim 1, characterized in that with the usual sulfur content for the molar ratios from 1: 0.75 to 1: 2, the resorcinol content of the rubber mixture is above 2.5 Parts based on 100 parts of rubber. 4. Rubber mixture according to claim 1, characterized in that it does not contain sulfur has a resorcinol content of 7.5 and more at a molar ratio of the adhesive components from 1: 1. 5. Rubber mixture according to claim 1, characterized in that at a molar ratio of 1: 1 their resorcinol and sulfur content results in at least the sum of 7 parts. 6. Rubber mixture for direct bonding to metallic reinforcements, consisting of mixtures Made from natural and / or synthetic rubbers, fillers, processing aids, vulcanizing agents and as adhesive components resorcinol and hexamethylenetetramine as formaldehyde donors, characterized in that at a molar ratio of resorcinol: hexamethylenetetramine of 1: 0.5 you Resorcinol and sulfur content add up to at least 10 parts based on rubber. 7. Rubber mixture according to claim 6, characterized in that with the usual sulfur content for a molar ratio of 1: 0.5, the resorcinol content of the rubber mixture is 7.5 to 10 parts, per 100 Parts related to rubber, lies.