Hot vulcanization bonding of rubber to metal
Influence of rubber type
Degree of unsaturation:
Rubber with a high degree of unsaturation and high polarity bonds easily
Adhesion Index:
NBR > CR > SBR > NR > BR > IIR > EPDM
Non-diolefin elastomer:
Sulfur-free and accelerator-free vulcanization (e.g. peroxide vulcanization) containing high specific surface area fillers are easy to bond;
Contains plasticizers, softening oils, waxes, etc., which are detrimental to bonding.
Elastomer mixtures: elastomer mixtures are not mutually soluble, but an elastomer in a continuous phase or dispersed phase distributed in another elastomer, resulting in a mixture of elastomers in one of the easier to vulcanize, the results of the bonding shadow has a great impact.
For example: NBR + NR hybrid elastomers are harder to bond than NBR.
Influence of vulcanization system
Vulcanizing agent:
Generally, rubber with higher sulfur content is easier to bond.
Bonding of elastomers with different vulcanization systems:
Conventional vulcanization systems are better than semi-cured systems;
Semi-cure system is better than effective cure system (low sulfur high promotion cure system);
Sulfur vulcanization is better than other vulcanization systems, such as peroxide vulcanization system, bisphenol A vulcanization system, amine vulcanization system, etc..
(Silently inserted: consider good vulcanization system oh!)
Promoter:
MBT (2-thiol benzothiazole): easy bonding
ZDMC (zinc dimethyl dithiocarbamate), TMTD (tetramethyl thiuram disulfide): difficult to bond, especially when in the effective vulcanization system, semi-effective vulcanization system.
Anti-coking agent:
Difficult to bond in large quantity, <0.15% easy to bond
Filler:
The type and amount of filler is the key factor.
Carbon black is generally 40-80 parts easier to bond; carbon black main filler rubber containing 3-5 parts of silica is easier to bond.
Elastomers that do not use carbon black but use clay and silica have the same trend as carbon black.
Plasticizer type and content of the shadow
Plasticizers:
Plasticizers need to be used with caution, the content should not exceed 20phr.
Oil, plasticizers are not conducive to bonding; especially ester plasticizers, ester plasticizers should be less than 10phr.
(1) Wax, oil: migrate to the surface of the elastomer causing bonding difficulties. Including: low molecular weight polyolefins, aromatic oils, fatty acid esters.
(2) Plasticizers: phthalates, adverse to bonding; but high surface area fillers such as silica can neutralize the negative effects of phthalates.
Anti (odor) oxygen agent:
Anti-ozone agent, anti-oxidant in large quantities is unfavorable to bonding; p-phenylenediamine-type anti-(odor) oxygen agent is unfavorable to bonding.
Effect of scorching period:
Long charring period is good for bonding
Influence of Menni viscosity:
Low Mooney viscosity is good for bonding
Influence of hardness of vulcanized rubber:
Between A45 and A85 Shore, easy to bond.
Substrate surface treatment ¦ Method
①Degreasing, mechanical treatment and cleaning
②Degreasing and chemical treatment
③Degreasing, mechanical treatment, cleaning and chemical treatment.
Substrate surface treatment ¦ Degreasing method
▓Lye degreasing
▓ Solvent degreasing
-Impregnation
-Washing
-Steam
▓Ultrasonic degreasing
Lye degreasing ¦
① Main components and characteristics of commonly used lye:
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②Typical steel degreasing lye formula:
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Temperature：80～100℃、Time：20～40 minutes
Solvent degreasing ¦
Commonly used solvents:
120 # gasoline, butanone, ethyl acetate, toluene, xylene
Perchloroethylene, 1,1,1-trichloroethane, acetone, etc.
The workpiece is heavily contaminated and needs to be cleaned twice; even steam degreasing is used.
Steam degreasing ¦
Solvent
1,1,1-trichloroethane, trichloroethylene, perchloroethylene
Metal parts must not intrude into the solvent and must not be above the condensation zone and not in contact with each other.
The temperature of the metal parts reaches the boiling point of the solvent and degreasing is finished.
The PH value of the solvent is kept between 7.0 and 7.5.
The solvent should be renewed when the oil content reaches 25%.
Mechanical treatment ¦
Shot blasting or sand blasting materials: steel balls, diamond sand, quartz sand, adamantine, etc.,.
Parts need to be cleaned after sand blasting or shot blasting.
Substrate surface treatment ¦ Phosphating
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Common adhesive method: hard glue method, adhesive method, brass plating method and direct adhesive method.
I. Rigid adhesive method
This method is the first in the metal surface paste or coated with a hard adhesive layer, and then paste the soft adhesive to be bonded, and finally vulcanized by hot pressing to form a whole. Hard glue in the raw rubber content should not be too high, sulfur dosage is generally 30 ~ 40 parts, can be added to improve the adhesive force of iron oxide, dosage of about 20 parts, the bonding temperature can be doubled, more than 20 parts, the performance decline. In order to prevent the free sulfur in the hard glue to the soft glue layer diffusion, you can add a sulfur-free or low-sulfur semi-hard transition layer between the hard glue and soft glue.
Hard glue and metal bonding before the hard glue material with a slurry (solvent with gasoline, the proportion of 1:1.5), the slurry coated in the metal surface to be adhered to, with the solvent evaporation is complete, the hard film to the surface of the metal, in the hard glue and soft glue adhesive before the hard glue surface coated with slurry, and then adhesive soft glue.
Since the coefficient of thermal expansion of rigid adhesive is larger than that of steel and iron, the rigid adhesive is easy to delaminate with the metal core when the temperature changes.
Precautions:
① The glue content of the hard glue should not be too high.
② The dosage of sulfur is large (30~40 parts).
③ Appropriately increase the content of iron oxide (about 20 parts).
④ The vulcanization speed of the adhered rubber material should not be too fast, and the vulcanization speed of hard rubber and soft rubber should be equal.
⑤ Add sulfur-free or low-sulfur intermediate layer between hard and soft rubber.
⑥ The metal surface should be sandblasted and cleaned with gasoline.
⑦ The metal surface should be coated with hard adhesive paste or in the form of adhesive paste to the metal surface.
⑧ Use low temperature or gradually increase the temperature for a long time vulcanization.
Characteristics:
① High bonding strength, good corrosion resistance.
② process is simple, suitable for bonding of large metal components such as various rubber rollers, large chemical container lining.
③ poor heat resistance, working temperature of more than 70 ℃, the bond strength drops sharply.
④ poor dynamic fatigue resistance.
Second, adhesive method
After surface treatment of metal surfaces, the fresh surface coated with a layer of adhesive, and then paste the rubber vulcanization. The method is simple and practical, does not need to use processing equipment, wide applicability, is currently the most widely used method between rubber and metal. The adhesive effect of rubber and metal depends largely on the results of metal surface treatment and the nature and performance of the adhesive. For different metal materials, it is very important to select the appropriate adhesive. The disadvantages of the adhesive method are toxic solvents, pollution of the environment, damage to human health, poor storage stability
Third, brass plating method
Brass or surface plated brass metal materials, in the rubber material reasonable formula composition, can not use the adhesive can realize good adhesion with a variety of rubber. The advantages of this method is high adhesive strength, good heat resistance, absorption of shock vibration, etc., fatigue resistance, good aging resistance, is one of the common methods for manufacturing small-size metal parts. However, the storage period of brass plated parts can not be too long, the copper plating medium is toxic and pollutes the environment, and the bonding effect is affected by the quality of plating and plating parameters.
1、The structure of brass layer
The copper content of the surface layer of the plating layer is low, the more in the copper content, gradually close to the average copper content. Brass surface contains more than ten kinds of elements, but the main four kinds of copper, zinc, oxygen, iron, and copper / zinc ratio varies with the depth of the plating layer, the plating of the most surface of the zinc content is more, and in the form of ZnO exists, the structure of the bonding to play a stabilizing role, can regulate the reaction rate of the rubber and brass, and affects the chemical composition of the interfacial transition layer and interfacial vulcanization film growth rate and thickness. So. Brass plating should have a suitable Cu/Zn ratio. too much ZnO, due to its own structure of brittle, easy to constitute a weak interface layer in the interfacial transition layer, causing bonding damage.
2、Rubber and brass reaction
There exists a chemical reaction between rubber, sulfur yellow, brass and ZnO.
3、Rubber and brass interface layer structure
Surface layer of CuxS layer due to the filling of rubber molecular chain, can not be crystallized, so the CuxS-Sy-Rub interface modulus difference is small, the amount of CuxS should be appropriate, not too much, easy to be brittle and destroyed.
Direct bonding method
1、Mesyl white system
Resorcinol (3 parts), formaldehyde donor (accelerator H 1.6 parts), silica (15 parts) composition. Suitable for tires, hoses, tapes and other rubber-metal bonding. The method has some effect, but the effect is not very high.
2, organic cobalt salt system
Good adhesive effect, but poor heat resistance.
Rubber in the amount of S I 3, accelerator to NOBS is the best, followed by DM, CZ. carbon black to the mixable slot black, furnace black is better, followed by FEF, silica, SRF, the amount of 5 appropriate, the amount of cobalt salts to be appropriate.
Cobalt stearate RC-S95 2.0~4.0 parts
Cobalt naphthenate RC-N10 2.0~4.0 parts
Cobalt neodecanoate RC-D20 1.5~2.5 parts
Cobalt boronylide RC-B23 1.0~2.0 parts
Boronylated cobalt RC-B16 1.8~2.2 parts
3、Methyl white/organic cobalt salt system
The amount of cobalt salt is 30%~50% of the amount of cobalt salt system alone.
4、Mesityl white/organic cobalt salt/persulfuration stabilizer HTS
The dosage of HTS is 1.5 parts.
5、Methoxymethylene white/organic cobalt salt/HTS/coupling agent Si-69
Most suitable for bonding of steel and rubber
6、Organic cobalt salt/white carbon black
Replace part of carbon black with silica to improve the bonding effect after aging.
7、Bonding with peroxide
Dikuyu peroxide is used as a vulcanizing agent with silica, ZnO and SA are not used, and it is suitable for bonding of steel and rubber.
8、Triazine bonding
SW 2 parts, S 3 parts
Steel wire and rubber bonding problems (tire as an example)
Bead steel wire and steel cord are both tire skeleton materials, Figure 1 is a schematic diagram of bead steel wire and steel cord in a tire. For the skeleton material, and rubber adhesion is a more important technical indicators, the tire factory are more attention, the author from the steel wire production aspects of improving the steel wire and rubber adhesion method.
1 The problem
Steel wire or steel cord facing customers are tire factories, is used as a skeleton material to the tire. Its and rubber adhesion directly affect the quality of the tire, so the tire factory are very important to the adhesion of this indicator. Production of steel cord or bead steel wire enterprises, are spending a lot of manpower and material resources to constantly research and improve this index.
2 steel wire and rubber adhesion mechanism
Rubber vulcanization can be very good and copper bonding, adhesive layer of the bonding force over the rubber itself, this phenomenon is mainly attributed to the surface of the cord copper-plated steel wire, in the production of cord steel wire plating as a steel wire pulling lubricant. When copper-plated cord wire is used in tires, a sulfide is formed at the interface between the rubber and the steel cord that facilitates bonding (Figure 2).
As can be seen from the bonding mechanism between copper-plated steel wire and rubber, the adhesion depends mainly on the quality of the copper plating. For the improvement of copper plating quality, the adhesion is mainly improved through the improvement of glossy steel wire quality and copper plating treatment. The author through several ways to improve the adhesive force of the test, for your reference.
2.1 Improvement of polished steel wire quality
For the study of product quality in the dry drawing process, the main problem is the scratching of the steel wire surface, as shown in Figure 3.
Through the test analysis, caused by similar bad surface of the steel wire is mainly steel wire lubrication effect is not good, in order to improve the lubrication effect of the steel wire in the drawing process, an enterprise mainly using pressure mold, the pressure die is a group type. Through the use of the production process, the same specifications of the drawing speed in about 20% increase in speed, the quality of the steel wire surface has also improved. The use of pressure lubrication technology for drawing, steel wire surface lubrication film level quality than with the traditional method of drawing increased by 50% to 80%, after drawing the steel wire surface quality failure rate is also significantly reduced (Figure 4).
After improving the surface quality of the steel wire, after copper plating and rubber adhesion test, the test results are also significantly improved (Figure 5).
2.2 Surface treatment of steel wire before copper plating
The steel wire must be cleaned and cleaned by acid treatment before copper plating, so the effect of acid washing before copper plating is different, which directly affects the adhesion between copper plated steel wire and rubber. Strengthen the strength of copper plating before pickling, to ensure that the steel wire surface has a good surface quality, to improve the adhesion has a very good effect. Tests have shown that the use of hydrochloric acid cleaning and electrolytic pickling of steel wire before plating than a single use of electrolytic pickling of bead steel wire production, the adhesion and adhesion rate are significantly improved.
Electrolytic pickling electrode plate connection method also has a great impact on the quality of pickling. Nowadays, most of the manufacturers use the connection method of electrode plate is -, +, -, +, which has a good improvement on the effect of pickling, but the author through the test, in the case of the same concentration of pickling and current, by adjusting the connection method of electrode plate, especially the last 3 plates, the adhesion also has a different degree of improvement. Figure 6 shows the comparison of the adhesive force and the overlay rate before and after the adjustment of the electrode plates.
2.3 Copper plating process
Most of the skeleton materials used in tires are copper-plated steel wires, and the difference in copper plating content also has an effect on the adhesive force. Whether it is electroplating or chemical plating, although the principle is different, the purpose is to deposit copper onto the surface of the steel base. Electroplating compared to chemical plating, copper plating effect is better, high density, and the steel base bonding is more solid. Steel cord production in order to pull the tank, are used in electroplating copper plating, bead wire in order to reduce costs, most of the chemical copper plating. For different copper content, through the vulcanization mechanism mentioned above, the steel wire and rubber adhesion or have an impact. The author of the bead steel wire with different copper content using the same kind of rubber to do adhesion test, the test results have a big difference. Therefore, whenever the steel wire and some kind of rubber adhesion is bad, you can adjust the copper content to test, in order to quickly meet customer requirements. Figure 7 is the bead steel wire with different copper content and an adhesive material adhesion comparison.
It is obvious from Fig. 7 that low copper content is good for adhesion, and the plating on the surface of bead steel wire is an alloy of copper and tin, which indicates that for bead steel wire, the improvement of adhesion should also take into account the influence of the plating composition.
2.4 Copper-plated post-treatment
For copper-plated steel wire, after copper plating for different copper plating process using different post-plating treatment. Cord plating steel wire treatment is mainly to deal with zinc oxide after diffusion, because the zinc oxide content is more, not only affect the effect of wet pulling, but also has a certain effect on the adhesive force. Most customers require low zinc oxide content, one is conducive to wet pulling, and the other is helpful to the adhesion of the cord. But there are individual customers need high zinc oxide content, this is the metal products industry some open secrets.
For bead steel, in order to prevent the steel wire from rusting, it is necessary to apply some rust inhibitor on the surface of the steel wire. Rust inhibitor is used in the solution of Gumarone indene resin, and add a certain amount of other chemicals, now using the rust inhibitor on the adhesive force to improve some help. The author through some tests, in the same formula of rust inhibitor solution, different adhesion amount of rust inhibitor, steel wire and rubber adhesion has an impact. This requires in the actual production process, for different manufacturers of rubber to make some coating adhesion amount of adjustment.
