Adhesion of rubber to metal
Methods include: hard glue method, adhesive method, brass plating method and direct bonding method.
1. Hard glue method
This method is to first affix or coat a hard adhesive layer on the metal surface, then apply the soft adhesive to be bonded, and finally hot-press and vulcanize to form a whole. The raw rubber content in hard rubber should not be too high. The dosage of sulfur is generally 30 to 40 parts. Iron oxide can be added to improve the bonding strength. When the dosage is about 20 parts, the bonding temperature can be doubled. If it exceeds 20 parts, the performance will decrease. In order to prevent the free sulfur in the hard rubber from diffusing to the soft rubber layer, a sulfur-free or low-sulfur semi-hard transition layer can be added between the hard rubber and the soft rubber.
Before bonding hard glue to metal, first use hard glue to prepare glue (use gasoline as solvent, ratio 1:1.5), apply the glue on the surface of the metal to be bonded, and after the solvent has evaporated, apply The hard film is attached to the metal surface. Before the hard glue and the soft glue are bonded, glue is applied to the surface of the hard glue, and then the soft glue is glued.
Since the thermal expansion coefficient of hard glue is larger than that of steel and iron, hard glue can easily delaminate from the metal core when the temperature changes.
Notes:
① The glue content of 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 adhesive material should not be too fast, and the vulcanization speeds of hard glue and soft glue should be equal.
⑤ Add a sulfur-free or low-sulfur intermediate rubber layer between the hard rubber and the soft rubber.
⑥ The metal surface needs to be sandblasted and cleaned with gasoline.
⑦ Apply hard glue to the metal surface, or apply it to the metal surface in the form of glue.
⑧ Use low temperature or gradually increase the temperature for long-term vulcanization.
Features:
① High bonding strength and good corrosion resistance.
② The process is simple and suitable for bonding large metal components such as various rubber rollers and large chemical container linings.
③ It has poor heat resistance. When the working temperature exceeds 70℃, the bonding strength drops sharply.
④ Poor dynamic fatigue resistance.
Recipe example:
① Rubber roller hard rubber:
NR 100, Fe2O3 20, Zinc Barium White 20, CaCO3 32, MgCO3 11, Clay 60, Gumalon 2, Asphalt 12, Slaked Lime 5.6, Sulfur 33.6.
② Solid tire hard rubber:
NR 100, reclaimed rubber 33.3, ZnO 5, Fe2O344.4, clay 46.4, hydrated lime 15, stearic acid 1.4, accelerator M 1.7, accelerator D 1.3, sulfur 37.5.
2. Adhesive method
After the metal surface is surface treated, a layer of adhesive is applied to the fresh surface, and then rubber is applied for vulcanization. This method is simple and practical, does not require the use of processing equipment, and has wide applicability. It is currently the most widely used method between rubber and metal. The bonding effect between rubber and metal depends to a large extent on the results of metal surface treatment and the properties and performance of the adhesive. For different metal materials, it is very important to choose the appropriate adhesive. The disadvantages of the adhesive method are that the solvent is toxic, pollutes the environment, damages human health, and has poor storage stability
1. Isocyanate adhesive
Mainly used for bonding between NR, CR, NBR and other rubbers and various metal materials such as steel, stainless steel, aluminum and zinc. It has high bonding strength, simple operation process, oil resistance, solvent resistance, aging resistance, acid resistance and corrosion resistance, but its heat resistance is not as good as brass plating method.
Commonly used polyisocyanate adhesives:
① Lek sodium (JQ-1 adhesive): triphenylmethane triisocyanate, easily soluble in dichloromethane, dichloroethane or chlorobenzene as an adhesive. It is generally a 20% dichloroethane solution of triphenylmethane triisocyanate, which is less toxic than diisocyanate, oil-resistant, and fatigue-resistant.
Note when using:
a. The coating should be thin, <10µm, and the maximum should not exceed 30µm.
b. Dilute the adhesive with pure dichloroethane at a ratio of 1:1 or 1:3 before use.
c. The operating environment humidity is <60%~70%.
d. Generally apply 1 to 2 times. After application, it needs to be dried. Then apply a layer of protective adhesive or stick a thin layer (0.5mm) of film with a hardness of about 60 degrees as a transition layer. It is not suitable to use direct steam. vulcanization.
e. Leka sodium is easy to agglomerate, so the injection process and rapid vulcanization method should be used; if molding is used to produce��
The surface properties of the coating include the mechanical properties, crystallization properties, chemical reactivity, surface morphology, etc. of the material surface, among which surface chemical reactions have the greatest impact. The surface layer has a high copper content and has a good bonding effect with rubber, but it is highly sensitive to temperature and the copper content cannot be too high.
(3) Influence of rubber formula
Raw rubber: The polarity and degree of unsaturation have a great influence. Rubber with high polarity has a good bonding effect on brass. The bonding effect between NBR, CR and brass. IIR has poor bonding effect with brass.
Vulcanization system: Sulfur is the main vulcanizing agent. There is no sulfur in the rubber, and there is basically no adhesion between rubber and brass. Since sulfur needs to react with brass and cross-link rubber, the amount of sulfur in the rubber compound cannot be less than 2 to 3 parts, 4 to 5 parts is most suitable, but not too much, as it is easy to bloom and affect the bonding effect. The use of insoluble sulfur is beneficial to bonding, but the amount must be controlled. Accelerators affect the vulcanization reaction speed and scorch time. Slow-acting accelerators such as sulfonamide accelerators (CZ, DZ, NOBS, etc.) are beneficial to adhesion. Thiazole accelerators (M, DM) can also be used in the dosage range. 0.7~1.5 parts. It is not suitable to use thiuram and dithiocarbamate accelerators, but they can be used in IIR. Adding an anti-scorch agent facilitates adhesion. Stearic acid is not good for adhesion due to its lubricity, so it can be used sparingly or not at all.
Reinforced filling system: The hardness of rubber is in the range of 50 to 70 degrees and has a good bonding effect with brass. Adding reinforcing fillers such as carbon black can improve the bonding effect, but the amount should not be too large, 50 parts is appropriate.
Anti-aging agent: generally has little effect, but affects the thermal stability of the transition layer. MB is detrimental to bonding, while BLE is beneficial to bonding, especially the bonding of NBR, CR, NR and brass. The bonding effect is better than that of the methylene white system.
Plasticizer: Use an appropriate amount of plasticizer that is not easy to bleed out, which is beneficial to adhesion. Do not use too much. It is best not to use wax.
Adhesive system: The use of cobalt salts in the rubber can promote the reaction between brass and sulfur to form more CuxS. Therefore, it is beneficial to the bonding of brass with medium and low copper content and rubber. Among cobalt salts, borated cobalt salts have the highest activity. The amount of cobalt salt should not be too much. If it is too much, it will easily accelerate the aging of the rubber, and the performance of the interface layer will decline quickly after aging. The optimal dosage of cobalt salt is 0.3% of the rubber hydrocarbon.
The metamethyl white system is beneficial to the bonding of brass with high brass content to rubber.
(4) Environmental impact
Humidity is the main factor affecting bonding. Different rubber formulations have obvious differences in sensitivity to humidity.
The higher the humidity, the worse the bonding effect, and the faster it decreases as the temperature increases. The moisture content in the rubber is high, and the bonding effect between rubber and brass is poor.
4. Direct bonding method
1. Methylorine system
Composed of resorcinol (3 parts), formaldehyde donor (accelerator H 1.6 parts), and silica (15 parts). Suitable for tire, hose, tape and other rubber-to-metal bonding. This method has a certain effect, but the effect is not very high.
Typical formula: NR 100, FEF 40, silica 15, ZnO 3, SA 2, high aromatic oil 6, antioxidant A 1, sulfenamide accelerator 1, S 2.5, resorcinol 2.5, accelerator Agent H 1.6
Metaxylorine component is not easy to disperse in the rubber compound, and is prone to blooming and scorching. Currently, it is mostly modified; use modified metthylene white system, such as RE/RH, RE/A, RS/RH, RS/A, RA (or RL), silica can be added or not.
Radial tire carcass rubber formula: NR 100, ZnO 10, (SA 2), pine tar 6, HAF 45, accelerator DZ 1.2, 4010NA 2, S 3, binder A 3, binder RE 3 .
If resorcinol polysulfide (2.5 parts) is added, the bonding effect will be better.
2. Organic cobalt salt system
The bonding effect is good, but the heat resistance is poor.
The amount of S in the rubber compound is 3 parts. The best accelerator is NOBS, followed by DM and CZ. Mixable tank black and furnace black are the best carbon blacks, followed by FEF, white carbon black, and SRF. The appropriate dosage is 5 parts, and the dosage of cobalt salt must be appropriate.
3. Meta-methyl white/organic cobalt salt system
The dosage of cobalt salt is 30%~50% of the dosage when using cobalt salt system alone.
4. Meta-methyl white/organic cobalt salt/oversulfide stabilizer HTS
The dosage of HTS is 1.5 servings.
5. Meta-methyl white/organic cobalt salt/HTS/coupling agent Si-69
Ideal for bonding steel and rubber
6. Organic cobalt salt/silica black
Replace part of the carbon black with white carbon black to improve the bonding effect after aging.
7. Peroxide bonding
Dicumyl peroxide is used as vulcanizing agent, mixed with white carbon black, without ZnO and SA, steel-rubber bonding
8. Triazine bonding
