Effect of fumed silica on silica gel

Knowledge of preparation: silicone materials commonly used in silicone rubber

■ 107 glue

■ Rubber

   Methyl silicone rubber

   Methyl vinyl silicone rubber

   Methyl phenyl vinyl silicone rubber

■ Methyl silicone oil

■ The hydroxyl silicone oil

(mineral oil, white oil)

Room temperature vulcanized silicone rubberRTV

Classification by curing system

■ Acid curing

■ Take off the oxime curing

■ Take off alcohol curing

According to the application of classification

■ Structural adhesive

■ Weather resistance adhesive

■ Special purpose

■ Stone, sanitary ware, aquatic animals, the mirror, refractory

■ General filling

It is critical to control the moisture content of raw materials by air moisture

RTV Grade

■ High-end products

100％organosilicon

25％Displacement capacity

Semi-structured large plate glass for assembly

■ Mid-range products

Better comprehensive performance

20％Displacement capacity

■ Economic product

Solvent dilution

15％Displacement capacity

RTV production process

Main composition and feeding sequence of RTV

How to evaluate the sealant?
By feeling
Is it smooth?
Very few particles or more particles?
Stick or not?
Yellowing over time?
Cracking?
Pollution?

Sealant standards

■ Chinese standard 《Silicone sealant for building》  GB/T 14683-93

■ Chinese standard 《Architectural structural silicone sealant》  GB 16776-93

■ China standard 《Interior decoration decoration materials in the limit of harmful substances》 GB 18583-2001

■ Building materials standard 《Anti mildew sealants for building》 Manuscript

■ International standard《Building and construction-Sealants-Classification and requirements》ISO 11600

■ Other national standards

RTV Key business indicators

Business indicators
-- apparent
-- flowing
-- extrusion rate
-- skin time
-- hardness

Internal control index
-- mobility

Apparent

■ The view is very important to the customer

Class A            No surface defects, No blocks and particles

second level    A small amount of surface defects, small blocks and particles

Three              Apparent surface defects, blocks and particles

Four                Severe surface defects, large blocks and particles

Used for testing the thixotropy of uncured sealant flow or flow.
Condition: 232C, 505%RH
Result: mm

Skin time

From the glue from the plastic bucket out of contact with air, through the surface with thin material touch adhesive, sealant crust formation time observation.
Condition: 232C, 505%RH
Results: minutes

Hardness

Test on the cured elastomer.
Condition: in 232C, 505%RH cured after 72 hours
Sample: 3 2mm film
Data: Shore hardness (Shore A)

Extrusion rate
At a certain temperature and pressure and instrument conditions, determination of weight per unit time of sealant extrusion, for constant uncured sealant extrudability.
Condition: 3MPa pressure, 23C and corresponding test equipment.
Sample: rubber products
Data: g / min

Mechanical property
The mechanical performance test after curing sealant: (condition: in 232C, 505%RH cured after 72 hours)
Tensile strength
100% tensile modulus
Elongation at break

Addition of fumed silica in RTV
White carbon black in RTV?
Why not silicone in some color glue systems?
Other system sealant system with no silicone?
PU, acrylic acid, butyl rubber, polysulfide, epoxy, MS adhesive

The thixotropy of fumed silica in RTV

RTV Problems associated with silicon gas

■ Particles

- reason (white carbon black reunion water (107), for other reasons, skinning) 
- glue st13 neutral transparent st13 noise sensitivity acid
- may cause: powder together, has high moisture and other structural problem

■ Rheology: flow, low thixotropy, slow recovery

-- Not enough specific surface area, reunion, surface groups

■ Strength is not enough

-- Specific surface area, reunion, surface groups and other reasons

■ Shortening product life

-- Moisture content is exorbitant, consumption of crosslinking agent

High temperature vulcanization silicone rubber

■ Raw rubber

-- dimethyl silicone rubber
-- methyl vinyl silicone rubber
-- methyl phenyl vinyl silicone rubbe

■ Application field:

-- Universal type, high strength, high temperature resistant, low temperature, low compression permanent deformation, oil resistant, solvent resistance, flame retardant, conductive, thermal shrinkage, etc

The composition of high temperature vulcanized silicone rubber
Main ingredients: raw rubber
Coordinate syste

■ reinforcing agent
■ structure control agent 
■ tearing resistance agent
■ crosslinking agent
■ and molding (out) 
■ peroxide (double 24, double 25)
■ catalyst 
■ paint

The evaluation formula:
Raw rubber: 100
Silica: 40
Processing AIDS: 1-6
Pairs of 2, 4, 0.5

The processing technology of the high temperature vulcanization silicone rubber

■ Mixing process

■ Vulcanization process

A sulfide (time, temperature, pressure, vulcanizing agent)

10－20min，165－170C，10MPa

After secondary sulfide (oven curing/sulfide), remove the vulcanizing agent

4－20hr， 200－250C

The properties of high temperature vulcanization silicone rubber associated with white carbon black
■ transparency and yellowing
■ strength
■ structured
■ heat resistance
■ processing not to form a smooth dough

Xin 'an gas silicon application in the high temperature glue problem

■ Poor stability between batches (stability)

■ Plasticity is high or low (stability)

■ Transparency is bad (look)

■ Yellowing secondary sulfide (look)

■ Poor workability (structure)

■ Heat resistance is bad (structure)

■ Low hardness of high hardness rubber (cost?)

Transparency

Poor appearance and possible causes

■ Poor transparency:

The particle size is larger than the actual thickness (the deviation of the table, the dispersion is not good)

Mixing and curing after rapid white (surface hydrophilic groups more?)

■ Yellow:

Iron ions on the high side
Degradation of hydroxyl groups on the high side, prompting raw rubber chain is brok

Gas silica reinforcing effect of silicone rubber

■ Active reinforcing agent: white carbon black

■ Half active or inactive reinforcing agent: diatomite, quartz powder

■ Strength comes from and crosslinking between polymer chain and polymer and the interaction between white carbon black

■ But the white carbon black reinforcing effect more apparent (5-10 times)

Gas silica reinforcing effect of silicone rubber

Reinforcing effect of silicon on silicon rubber

Poor heat resistance

To improve the heat resistance of the solution: active white carbon black or white carbon black modified processing

■ Processability problem

structured
Because white carbon black surface groups and main chain, hydroxyl-terminated and their interaction, after storing the formation of strong interaction, serious word hard to processing
Solution: join the structure control agent, or in addition to hydroxyl grou

■ Processing not clouds

The chloride ion?

The pros and cons of white carbon black in high temperature vulcanization silicone rubber

■ For hydroxyl of the white carbon black reinforcing a significant contribution
■ And hydroxyl for structured and heat resistance has important influence 
■ In addition to hydrophobic treatment agent is added in the high temperature adhesive and heat resistant additives, advanced study differences in xinan white carbon black and white carbon black is also a important topic

Good prospects for development of liquid silicone rubber

■ Usually in the form of two components

A component vinyl raw rubber, fillers and additives 
Part B organic silicon polymer crosslinke

■ Compared with the glue

No by-product 
Good storage temperature
Fast processing (injection forming a few seconds to a few minutes, the high temperature heating to remove volatile

Silicon is an essential raw material in LSR
■ High - purity
■ High transparency
■ High reinforcement

Requirements for liquid silicone rubber

Resolvent

■ And RTV in both the reinforcement and thickening of the different, LSR to strengthen not thickening

■ Hydroxyl elimination

In China, the high specific surface area of silicon and silicon gas

■ Selectivity:

Structural modification products such as R8200