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Silica gel, vulcanization, mixing and common problems
time : 2018-03-02 11:27 Browsing volume : 44

Common vulcanizing agent for silica gel

Vulcanizing agent

Abbreviation

Amount, portion

Vulcanization temperature

Use

Benzoyl peroxide

Vulcanizing agent BP

4~6

0.5 ~ 2

110~135

General, mold pressure, steam continuous vulcanization, bonding

2, 4- two chloro benzoyl chloride

Vulcanizing agent DCBP

4~6

0.5 ~ 2

100~120

General type, hot air vulcanization, steam continuous vulcanization, mould pressing

Tert butyl phthalate

Vulcanizing agent TBPB

0.5 ~ 1.5

135~155

General-purpose, sponge and high temperature vulcanization

Peroxide di Ding Ji

Vulcanizing agent DTBP

0.5 ~ 1

160~180

Vinyl, molding, thick products, carbon black adhesives

Two isopropyl peroxide

Vulcanizing agent DCP

0.5 ~ 1

150~160

Special vinyl, molding, thick products, carbon black rubber, steam vulcanization, bonding

2 5-, two methyl, 5- Di tert butyl peroxide hexane

Vulcanizing agent DBPMH (double 2, 5)

0.5 ~ 1

160~170

Vinyl, molding, thick products, carbon black adhesives

(2) the amount of BP paste of vinyl silicone vulcanizing agent (containing 50% of the vulcanizing agent in the paste, BP). (1) the dosage of BP paste for methyl silicone vulcanization (containing 50% of the vulcanizing agent in the paste, BP).



硅胶硫化剂

Silicone vulcanizing agent




Dosage and performance of silica gel reinforcing agent

Category

Name

A quantity (weight, 100 meter rubber)

Properties of vulcanizate

Tensile strength, MPa (kgf/cm2)

Elongation%

Reinforcing filler

fumed silica

precipitated silica

Deal with Bai Tanhei

Acetylene black

30~60

40~70

40~80

40~60

3.9 ~ 8.8 (40~90)

2.9 ~ 5.9 (30~60)

6.9 ~ 13.7 (70~140)

3.9 ~ 8.8 (40~60)

200~600

200~400

400~800

200~350

Weak reinforcing filler

Diatomite

Titanium white powder

Quartz flour

Calcium carbonate

Zinc oxide

Ferric oxide

50~200

50~300

50~150

2.9 ~ 3.9 (30~60)

1.5 ~ 3.4 (15~35)

-

2.9 ~ 3.9 (30~40)

1.5 ~ 3.4 (15~35)

1.5 ~ 3.4 (15~35)

75~200

300~400

-

100~300

100~300

100~300

Silica gel coloring agent

Name

Color

Name

Color

Iron oxide (Fe2O3)

Chrome green (Cr2O3)

Titanium dioxide (titanium dioxide)

red

green

white

Cadmium yellow (cadmium oxide two)

carbon black

Ultramarine

yellow

black

blue



硅胶着色剂

Silica gel coloring agent



Basic formula and physical and mechanical properties of vinyl silica gel and fluoro silica gel

Formula and properties

Vinyl silica gel

Fluorosilicone rubber

General type

General type

High resistance tearing

General type

Vinyl silicone rubber (110-2)

Fluorosilicone rubber

precipitated silica

2 gas phase white carbon black

4 gas phase white carbon black

The treatment of No. 2 gas phase silica by eight Oracle base ring four siloxane

Two phenyl silyl diol

Hexamethylcyclotrisiloxane silicon silazane and eight methyl siloxane ring four blends

Hydroxyl-fluoro silicone oil

Ferric oxide

Organic peroxide

One hundred

-

40~60

-

-

-

-

-

-

3~5

0.5 ~ 1

One hundred

-

-

45 - 60

-

-

3~6

-

-

3~5

0.5 ~ 1

One hundred

-

-

-

40~50

-

-

8~10

-

-

0.5 ~ 1

One hundred

-

-

-

-

45~60

-

-

-

3~5

0.5 ~ 1

Three

One hundred

-

40~45

-

-

-

-

2~3

3~5

0.5 ~ 1

Physical mechanical properties before aging

Tensile strength, MPa

Elongation%

Hardness (Shao Er)

Tear Taiwan, kN/m

Brittleness temperature, centigrade

3.9 ~ 5.9

150~250

45~65

-

-65

5.9 ~ 7.8

203~350

45~65

-

-65

7.8 ~ 9.8

400~600

40~55

30~50

-65

6.9 ~ 8.8

300~500

45~60

-

-65

5.9 ~ 7.8

150~250

40~60

-

-60

After 200 c 27h aging

Tensile strength, MPa

Elongation%

Hardness (Shao Er)

-

-

-

-

-

-

5.9 ~ 7.8

300~500

45~60

-

-

-

3.9 ~ 5.9

100~200

45~65

After 250 C 72h aging

Tensile strength, MPa

Elongation%

Hardness (Shao Er)

2.9 ~ 4.9

150~250

45~65

3.9 ~ 5.9

150~300

45~65

-

-

-

4.9 ~ 6.9

200~400

50~60

-

-

-

Compression permanent deformation (compression rate 30%)

150 c * 24h,%

200 c * 24h,%

-

10~20

-

20~30

30~50

-

-

40~60

20~30

-

Electrical properties

Breakdown voltage, MV/m

Volume resistance Omega cm

18~20

1014~1015

20~25

1015~1016

20~25

1015~1016

20~25

1015~1016

12~15

1012~1015

Oil resistance

No. 2 aero kerosene volume expansion rate at 150 C 24h%,%

-

-

-

-

15~20

1. mixer mixing

The speed ratio of the double roll opening roller is 1.2 ~ 1.4:. After the fast roll is in, the higher speed ratio leads to the faster mixing and the low speed ratio can make the film smooth. The roller must be provided with cooling water, mixing temperature is below 40 DEG C, in order to prevent the volatilization of coke burning or vulcanizing agent. When mixing, the roll distance is smaller (1 ~ 5mm) and then gradually magnified. Feeding and operation order: Rubber (package roll), reinforcing filler, structure control agent, heat-resistant additive, colorant, thin 5 times, cutting, heat treatment oven, back mixing, curing agent, thin, overnight, parked remiling, a piece of. The rubber can also be heated without heat treatment. After adding heat resistant auxiliaries, the vulcanizing agent will be added, then the thin film will pass through the night, then it will be reused for several days. The mixing time is 20~40 minutes (the size of the opening mixer is 250mm x 620mm).

If a single precipitated silica or a weakly reinforcing filler (titanium dioxide, Zinc Oxide, etc.) is used alone, the structure control agent can not be added to the adhesive. Should be added slowly filling, to prevent floating spheroids formed in the accumulation of filler and rubber glue on the top of lead to uneven dispersion. If you want to add a large number of fillers, it is best to add two or three times, and make a knife in the meantime, to ensure good dispersion. It is found that the rubber has a tendency of granulation, and the roll distance can be tightened so as to improve the mixing. The particles falling on the receiving plate should be cleaned and collected by brush, and return to the roller of the rubber mixing machine immediately, otherwise, the rubber will contain rubber sticks, which will lead to poor appearance of the products. The incremental packing should be added after the reinforcing filler is added, and a wider roll distance should be used.

Loading capacity (mixed rubber): 1~2 kg for phi / 320mm refining machine and 3 to 5kg for phi 620mm refining machine.

The silica gel packages the slow roll (front roller) when it is added to the refiner. When mixing, it can quickly wrap the fast roll (Hou Gun). It must be operated on two sides when the rubber is made. Because silicone rubber compound is relatively soft, it can be operated by ordinary knife when mixing. When it is thin, it cannot be pulled down like ordinary rubber, and scraped down with steel, nylon or abrasion resistant plastic scraper. Active baffles should be used to facilitate the cleaning and prevention of leakage of lubricating oil into the glue. Gas phase white carbon black is easy to fly and is harmful to the human body. Corresponding measures should be taken to protect the white carbon black. If the powder peroxide is used directly in mixing, it is necessary to take explosion-proof measures, and the best use of paste peroxide.

As in the rubber mixed with impurities, lumps, can mix through the glue filter filter, filter, generally use 80~140 mesh.



开炼机混炼

Mill Mixing




2. mixer mixing

The use of this method can improve production efficiency and improve labor conditions. The test shows that the property of the closed type compound is similar to that of the open compound. The mixing time of the 2L mixer in the test room is 6~16 minutes, and there is no special difficulty in mixing. When the loading coefficient of a 160mm is 0.74, the mixing can also be carried out normally. The discharging temperature is related to the type of reinforcing filler. When using weak reinforcing filler and precipitated silica, the temperature of rubber discharge is below 50 C; when the fumed silica is used, the glue temperature is about 70 C.

3. glue parked and returning

Silicone rubber mixing after the end, after a period of time should be parked (generally not less than 24 hours is appropriate), make different agents (especially the structure control agent) can play a role and were fully. After the suspension, the rubber material becomes hard and the plasticity is reduced. It must be returned before use. Back refining adopts the opening machine, at the beginning, the roll distance is larger (3 ~ 5mm), at this time the glue is hard, the surface is wrinkled, and the front roll (slow roll) is wrapped. With the lengthening of the return time, the rubber is gradually softened, and the roll distance is gradually reduced (0.25 to 0.5mm), and the glue is quickly wrapped in the back roll (fast roll). "When the glue is fully soft, the surface is smooth and smooth, then the sheet can be cut out. There are wrinkles on the surface of the film and the adhesive roll is caused by the stickiness of the adhesive. The return temperature is generally controlled at room temperature. If the gum is stored for more than a month (for a month or more), when the adhesive is soft and the surface is wrinkled, 5~10 parts of fumed silica can be added to improve the technological properties of the rubber and ensure the quality of the vulcanizate.

4. pressure

Generally, the silica gel is relatively soft, so its effect is better and easy to operate. Silica gel can be used to press out a variety of different shapes and sizes, and its processing equipment and tools are basically similar to ordinary rubber.

The extruder usually uses a single screw screw of 30mm or 65mm, and the ratio of length to diameter is 10 ~ 12:1. To keep the low temperature as much as possible, not more than 40 degrees centigrade, so the cylinder and screw must be cooled with cooling water. For high quality products, 80~140 mesh filters can be installed near the head of the machine to remove impurities from the rubber and improve the quality of the extrusion. Silicone rubber expands when it comes out of the mouth. The expansion rate depends on the flow performance of the rubber, the thickness of the billet and the pressure when the rubber enters the mouth. However, increasing or decreasing the extraction speed will change the elongation of the non vulcanized extruded products and make the size change slightly. According to the experience, the rubber tube expands about 3% compared with its mouth shape, and the soft material has a larger expansion rate and a smaller hardness. When pressing other shaped products, the holes of the mouthpiece are seldom the same as the cross section of the extruded products, which is due to the different frictional forces acting on the different points of the flowing rubber. Therefore, for a certain type, it must be repeated repeated tests in order to get the desired shape of the product.

The pressure out of the coated wire requires the use of the T type head on the extruder. The mouth type and the extruder barrel are mounted at the right angle on the T type head. The core line can be coated with a silica gel sheath through a hollow mouth tube (core type). Reinforced hose can also use the T die for continuous production, first with the general method of pressure tube, and pre vulcanized, then woven reinforced steel wire or nylon on the outside, which is then coated a layer of outer layer in the outside through the T die, finally to vulcanization, in the molding process, if the hose filled with compressed air. The inner rubber can prevent collapse.

Silica gel is soft and easy to deform, so it is usually necessary to vulcanization immediately. The most commonly used method is the continuous vulcanization of hot air; the industry of wire and cable is usually vulcanized continuously with high pressure steam. If it is pressed out, it can not be continuously vulcanized to prevent deformation. After pressing out, the disc, round drum or conveyor belt should be immediately taken and separated from each other with talcum powder. If it is found that the rubber is too soft and is not suitable for the exit, the glue can be mixed into 3~5 parts of the gas phase white carbon black.

Generally used to press out the adhesive formula, the dosage of its vulcanizing agent should be more appropriately increased than the molded products. The extrusion speed of silica gel is lower than that of other rubber, and higher screw speed should be used when the same pressing speed is required to be reached with other rubber.



硅胶硫化



5. calendering

The vertical three roll calender is generally used for the calender of silica gel. For producing film, the middle roll is fixed, the middle roller speed is faster than the upper roller, the speed ratio is 1.1 ~ 1.4:1, the speed of the lower roller and the middle roller are higher than that of the middle roll, when the calender is running, the upper roller temperature is 50 degrees, the middle roller should be kept at room temperature, and the lower roller is cooled by cooling water. The calendering speed should not be too fast, usually 60 ~ 300cm/min. First, adjust the roller spacing (middle and lower roller) at low speed (30 ~ 60cm/min) to ensure a certain calendering thickness, and then increase to normal speed (150 ~ 300cm/min) for continuous operation. The cloth (usually with polyester film) in the middle and lower end through, should maintain a small amount of rubber product in the middle and lower rollers, so that the whole cloth and rubber tightly. After rolling the film roll tightly, and sent to the curing oven or autoclave in. The core shaft of the coiling roll should be hollow metal pipe with the thickness of the film not more than 12cm, otherwise it can not be fully vulcanized.

In general, the roll can be used in the middle and upper rolls, and the temperature of the roll is at normal temperature. There is a way to make the vulcanized film or thin film directly on the rear end machine. At this time the roll temperature is: the upper roll is 60~90 C, the middle roll is 50~80 C, and the lower roll is 110~120 C. The rubber is removed by the upper and middle rolls, and the required specifications are obtained and preheated, and then the middle roll is transferred to the lower roll for a section of vulcanization.

When the three roll calender for silicone adhesive and rubberized fabric, will replace the cloth (polyester film) through between the middle and lower rollers. The three roll calender is only suitable for one side compound glue. If you have to compound the glue on two sides, the four roll calender should be used in the case of long term production.

The rubber used for calendering must be properly controlled for its reversion level. It is better not to fully refine on the rubber mixing machine, so as to get enough recharging during the rolling process, so that the glue can be prevented from rolling during the calender process. The adhesive formula has a certain influence on the calendering, and the rubber calendering process with reinforcing filler is better.

6. gummy

Refers to the use of silicone glue glue dipping method or scraping the uniform distribution on the fabric, to improve the film product strength and flexibility, make the fabric moisture to produce high temperature electrical insulating materials etc..

1. slurry preparation

The silicone rubber compound for rubber mortar is mostly vulcanized agent BP (peroxide benzoyl two), which is because the vulcanizing agent BP is not volatile at room temperature and has good adhesion with fabric. The dosage is a little more than the general model. If gas phase white carbon black is used for reinforcing filler, the dosage should not exceed 40, and the amount of structural control agent should be increased properly. Solvents should be volatile, such as toluene, xylene, etc.

The mixing rubber is fully reprocessed and then sliced down, then cut into small pieces, soaked in solvent for the night, and stirred by a mixer or mixer. The glue with a concentration of 15 to 25% (solid content) is prepared. The slurry should be kept in the environment below 40 degrees C.

2. fabric pretreatment

The underlying fabric used for silica gel coating, a section of glass cloth, nylon, and polyester. The glass cloth is used more because of its good heat resistance, high strength and low hygroscopicity.

The glass fiber is coated with paraffin lubricants (0.2 to 0.5% of the weight of the fabric) during the drawing process. It is not easy to volatilize at the vulcanization temperature, which affects the combination of the fabric and the fabric. It must be removed before coating. The lubricants are often removed by heating in industry. The heating method is also divided into low temperature treatment and high temperature treatment. The former is the glass cloth at a temperature of 200~300 DEG C, continuous heating for 20~30 minutes, or by constant hot roller heated to 275~325 DEG C, the lubricant thermal decomposition and volatile escape; the latter is to glass cloth at a temperature of 500 DEG C baking for 2~4 hours, or 2 ~ 6m/min speed through the oven heat to 600 C, the removal of lubricant. The strength loss of low temperature treated glass cloth is small (down 15 to 25%), but lubricants are difficult to remove (content is reduced to 0.2 ~ 0.5%). The strength loss of high temperature treatment is large (down 30 to 70%), but the lubricant content can be removed to below 0.2%. In order to reduce the loss of strength, low temperature treatment is generally used.

The thermal deformation of nylon is large, which affects the combination of rubber and fabric. For this reason, heat setting is necessary before coating, and the fabric will be treated for a short time under certain draft. The treatment temperature is 170~175 degrees centigrade.

Polyester and nylon, like the heat, also need to be treated with a temperature of 215~220. The difference is that polyester is also treated by surface chemical treatment, that is, 25% NaOH aqueous solution is soaked for 6 hours at room temperature, so that its surface is easy to bond with rubber.

3. gummy

After the fabric is pretreated, the surface adhesive is also treated, and then the adhesive can be coated. The adhesive is a solution consisting of alkoxy silane, borate, vulcanizing agent and solvent (ethyl acetate or ethanol). The commonly used adhesives for different fabrics are listed in table 9-21.

Table 9-21 commonly used adhesives for fabric

Fabric name

Adhesive composition

Glass cloth

Nylon polyester, etc.

Ethylene triethoxy silane 3, alcohol 50, water 50

(1) vinyl triethoxy silane 5, acryl triethoxy silane 15, butyl borate 2, vulcanizing agent DCP 4, ethyl acetate 100

(2) vinyl triethoxy silane 20, butyl borate 1~2, vulcanizing agent DCP 3 (or vulcanizing agent BP 5), ethyl acetate 10

Common quality problems and solutions for pressure vulcanization of flat plate

Quality problems

Cause

Terms of settlement

Cracking of the surface of the product (occurring at the joint of the die)

Vulcanization


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