Plastics can be divided into two categories: thermoplastics and thermosetting plastics. Under normal circumstances, thermosetting plastics are easier to bond than thermoplastics. However, their surface energy is lower than that of hydrophilic materials such as glass, ceramics, and metals, and their surfaces often adhere to release agents or release plasticizers, so they are not easily wetted by adhesives, which affects the bonding strength. Therefore, plastics generally need to be surface treated. Due to the large variety of plastics and the great differences in various properties, the surface treatment methods are also very different. The following introduces several common plastic surface treatment methods.

[Method 1]

This method is mainly suitable for polyethylene, polypropylene, polyisobutylene, polyvinyl chloride, and perchloroethylene.

The degreasing solvents for the above plastics are acetone and butanone.

After degreasing, oxidizing flame treatment is carried out: first use emery cloth to roughen it, place it on the oxidizing flame and burn it for 3-5s, three times in a row. Then use 30% sodium hydroxide solution, soak at 65-70°C for 3-5min, rinse with cold water, and then activate with the following solution, soak at 65-70°C for 5-10min:

Chromic acid 10 Concentrated sulfuric acid 20 Water 40
After washing with water, oxidize in the following solution at 70-75°C for 5-7min:
Potassium dichromate 10 Concentrated sulfuric acid 50 Water 340
Then wash in hot water at 70-75°C for 5-7min, rinse with distilled water and dry at 65-70°C.

[Method 2]

This method is applicable to the same objects as above.

Treat in the following solution at 20°C for 90min:

Sodium dichromate 5 Sulfuric acid (d=1.84 ) 100 Water 8
After washing with cold water, dry at room temperature.

[Method 3]

This method is applicable to the same objects as above.

Expose in any of the following gases activated by corona discharge:

(1) Dry air, 15 min;

(2) Nitric oxide, 10 min;

(3) Wet air, 5 min;

(4) Nitrogen, 5 min.

Bonding should be performed within 15 min after treatment.

[Method 4]

This method is applicable to polystyrene and its modified varieties, such as ABS and AS.

Degrease after sandblasting or sandpaper polishing.

Degreasing solvent: acetone, anhydrous ethanol.

After degreasing, immerse in chromic acid solution at 60°C for 20 min.

[Method 5]

This method is applicable to nylon.

Degreasing solvent: acetone, anhydrous ethanol, ethyl acetate, butanone. Apply a layer of 10% nylon-phenol solution on the surface, keep it at 60-70°C for 10-15 min, then wipe it with solvent (or apply a layer of resorcinol-formaldehyde primer on the surface), and bond it immediately.

[Method 6]

This method is applicable to polyester film.

Degreasing solvent: acetone, anhydrous ethanol.
After degreasing, immerse in 80°C sodium hydroxide solution for 5 minutes, and then immerse in stannous chloride solution for 5 seconds.

[Method 7]

This method is applicable to polyoxymethylene and other acetal polymers.

Degreasing solvent: acetone, butanone.
Dry at 120°C for 1 hour, and then immerse in the following solution at 120°C for 5 minutes:
p-Toluenesulfonic acid 1　　Dioxane　 10　Perchloroethylene　 200
After washing with cold water and hot water, dry with hot air.

[Method 8]

This method is applicable to polytetrafluoroethylene and other fluorocarbon polymers.

Degreasing solvent: trichloroethylene, benzene, toluene, acetone, butanone, cyclohexanone.
After degreasing, immerse in the following solution at room temperature for 30 minutes:
Sodium hydroxide 10 Diethylene melamine 8
Then dry at room temperature.

[Method 9]

This method is a radiation-induced grafting method. The applicable objects are the same as above.

Use high-energy rays such as cobalt-60 rays or ultraviolet light below 2000Å, in the presence of styrene monomer, to slightly degrade the surface of fluoroplastics, generate active centers at the chain ends, and form a layer of transparent graft copolymers.
After treatment with this method, the color remains unchanged and the electrical properties do not decrease.

[Method 10]

This method is a fluorinated hydrocarbon-titanium polymer method. The applicable objects are the same as above.

Immerse in a solution containing tetrabutyl titanate, perfluorooctyl ester and water to form a thin film layer of alkyl-titanium-oxygen and perfluoro branched polymer on the surface.

[Method 11]

This method is applicable to the same objects as above.

Dissolve 128g of refined naphthalene in 1000ml of tetrahydrofuran (or ethylene glycol methyl ether, ethylene glycol dimethyl ether, dioxane), slowly add 23g of metallic sodium within 2h under stirring, and strictly control the temperature at 3-5°C. After adding, continue stirring until the solution turns blue-black. Under nitrogen protection, put polytetrafluoroethylene in for treatment for 5min, then take it out, rinse it with cold water, then wash it with distilled water, and dry it with warm air.

This method is safe and reliable, with high bonding strength, and is currently the most used method in fluoroplastic surface treatment.

[Method 12]

This method is applicable to the same objects as above.

After degreasing the fluoroplastic, apply a layer of epoxy resin glue on the surface, heat it at 370°C for 10min, and then heat it at 400°C for 5min to melt the glue layer into the surface of the fluoroplastic, and then glue it.

Rubber surface treatment method

Generally, the surface of rubber materials is relatively smooth, and it needs to be mechanically or chemically treated to increase its roughness in order to achieve higher mechanical strength.

Rubber can be divided into two categories: natural rubber and synthetic rubber. Synthetic rubber can be divided into chloroprene rubber, chlorosulfonated polyethylene rubber, styrene-butadiene rubber, butyl rubber, ethylene-propylene rubber, nitrile rubber, polysulfide rubber, polyurethane rubber, silicone rubber and fluororubber. Among them, silicone rubber and fluororubber have saturated molecular structures, high chemical inertness, low surface energy, and are difficult to bond. At present, the method of applying a layer of silane treatment agent is usually adopted.

[Method 1]

This method is the grinding method.

For natural rubber, gently grind with a brush, blow off fine particles, and then wipe with toluene or acetone.

For synthetic rubber, first clean the surface with methanol, then grind with fine sandpaper, then clean with methanol and dry.

[Method 2]

This method is the sulfuric acid method.

For natural rubber, soak in concentrated sulfuric acid for 10-15 minutes. After the hard surface is formed, wash with distilled water (or soak in 5-10% ammonia water for 5 minutes and then wash), and dry at room temperature. Then bend the rubber to produce fine cracks on the surface, increase the surface area and improve the bonding strength.

For synthetic rubber, first wipe it with methanol, then soak it in concentrated sulfuric acid for 10-15 minutes, and then wash it with distilled water. Then soak it in 28% ammonia solution at room temperature for 5-10 minutes, and then wash it with distilled water. And bend it repeatedly to produce fine cracks on the surface.

[Method 3]

This method is suitable for silicone rubber.

Degrease the surface after roughening it appropriately with a wood file. Then treat it in a 1% toluene solution of tetrachlorosilane for 10 minutes and dry it. Alternatively, after roughening and degreasing, brush it with 5-10% dichloroethane solution of tert-butyl titanate and dry it in the air. Alternatively, after roughening and degreasing, apply a layer of the following solution: Vinyl triethoxysilane 100 Dibenzoyl peroxide 5 Boric acid 0.5

[Method 4]

This method is suitable for fluororubber.

After the surface is properly roughened by a wood file, immerse it in the following solution at room temperature for several minutes:

Sodium acetylene (or lithium acetylene) 　6　　Ammonium hydroxide　 1000
Take it out, wash it with water, and dry it. Alternatively, apply a layer of propylene triethoxysilane and dry it for 30 minutes.

Other material surface treatment methods

I. Glass surface treatment method

1. Solvent washing method First wash with acetone, then degrease with trichloroethylene vapor, then use a sandblaster to lightly spray some micropowder, absorb the micropowder under vacuum, and finally blow it dry with clean air.

2. Degreasing and solvent treatment method First degrease, then immerse it in a solution made of 1 part chromic acid and 4 parts distilled water at room temperature for 15-20 minutes, then wash it with distilled water, and dry it at 82-93°C for 20-30 minutes.

3. Ultrasonic washing method First treat it in an ultrasonic washing tank, then wash it with distilled water and dry it at room temperature.
4. Detergent treatment method: First, gently wipe with emery leather and neutral detergent, then rinse with distilled water and dry at room temperature.

2. Ceramic surface treatment method

1. Grinding method: Gently grind with fine sandpaper, and then blow away the fine powder with dry air.
2. Acid treatment method: First, immerse in a treatment solution made of 3.5 parts of sodium dichromate and 200 parts of concentrated sulfuric acid (or 1 part of chromic acid and 4 parts of water) at room temperature for 10-15 minutes, then rinse with water and dry at 65°C.

3. Concrete surface treatment method

The main method is pickling, which has the following two types:
(1) First use a hard brush with high-efficiency detergent to remove surface dirt and rinse with cold water; then sandblast or polish to remove the 1-2mm thick surface layer and blow away fine powder with clean air; then apply a solution made of 15 parts hydrochloric acid and 85 parts water to the surface (the dosage is about 1.13L/m2), leave it at room temperature for 20 minutes; finally use a pump to pump high-pressure cold water to rinse until neutral and dry.
(2) First use a hard brush with detergent to scrub the surface, rinse with pressurized cold water; then apply a solution made of 1 part hydrochloric acid and 2 parts water at room temperature, leave it for 15 minutes, then rinse with cold water, and then neutralize it with ammonia water made of 3 parts ammonia and 97 parts water to neutralize it; finally rinse it with pressurized cold water and dry it at room temperature.

4. Wood surface treatment method

Appropriate planing, appropriate roughening with wood sandpaper, and control the moisture content to less than 6-12%. For cork, a layer of primer can be applied to increase the bonding strength.