Production technology of rubber pad printing head
1.Formula of the rubber pad printing head
(1) silicone rubber, various types of room temperature vulcanized silicone rubber
(2) silicone oil - used to improve the rubber pad printing head hardness and processing performance of the structure control agent
(3) months acid tin - promoter
(4) ethyl silicate - crosslinking agent
2.The content of silicone oil
The content of silicone oil more little direct impact on the hardness of rubber pad printing head, but the proportion of silicone oil and silicone rubber has a permissible range, in this range, the physical properties of the rubber pad printing head better.The smaller the range, the smaller the compatibility of silicone oil and silicone rubber;The greater the extent, the greater the compatibility.The range can be determined through the experiment, that is to say, the proportion is not arbitrary, more than the proportion, make the rubber head cannot be used.
3.The content of curing agent
Vulcanizing agent content of general control within 5% mass ratio, low silicon rubber crosslinking inadequate, would contain raw rubber vulcanizates composition, expression is sticky;Curing agent content is too large, makes the rubber head become brittle, tear strength is low.To improve the silicone head tear strength can add right amount of reinforcing agent in rubber formulations such as not black and white carbon black, etc.
4.The technological process
(1) preparation of adhesive solution
According to the formula of each component in the proportion,
To calculate the first to make rubber head size,
And then calculated roughly the quality of the components,
And respectively in a fixed containers.
(2) stir
Blending adhesive solution under the mixer fully mixing, mixing, forming stable liquid, colour and lustre is consistent.
(3) the vacuum
Put mixed liquid in vacuum pump, vacuum processing.There will be water vapor produced in the process of silicone rubber vulcanization, and because of its high viscosity of silicone rubber mixture, stirring easily when mixed with air, so as to prevent gas mixed with elastic body, vacuum processing beforehand is necessary.
(4) to produce rubber head model
Substrates of different shape and size to design the corresponding plastic head.The design of rubber head should consider exhaust function and the expected deformation processing.Design good glue head model are then passed on to the machining department made aluminum alloy, and then with unsaturated polyester resin casting out button.Button is used to cast an essential tool for finished product rubber head.Before casting, on the inner wall of the cavities evenly coated mold release agent, mold release.
(5) curing conditions
Room temperature 25 ℃
Gel time 2 h
Cure time 8 h
The nature of the rubber pad printing head
1.hardness
Hardness characterization of rubber head compression deformation resistance.In printing, a soft rubber head can obtain larger deformation, suitable for large curvature of substrates and printing;And a hard rubber head deformation is small, when printing dot enlargement also small, apply to the face print or order printed matter printing.Adjust the hardness of rubber head, in addition to adjust the content of silicone oil, the key is to choose the softener.
2.Tear strength
Rubber torn from defects or micro cracks usually occur, then to rupture.Tear strength is often associated with crosslink density, under the proper crosslinking density, the tear strength is the largest.But the content of crosslinking agent is too much, often tear strength decreased.
3.Resistance to fatigue damage
Rubber pad printing head under the effect of dynamic compression by repeatedly, changes in the structure and the properties of the phenomenon, referred to as the "fatigue".With the continuation of fatigue, silicone rubber is flabby, surface crack, fissure, and gradually extended to collapse, it's called "fatigue".
Fatigue process of silicone rubber contains cracks generated and crack extension two stages.In general, can use rubber and or combination of sulfide method to improve the fatigue resistance of silicone rubber.
4.Resistance to organic solvents
Rubber pad printing head often contact printing ink and solvent, solvent resistance how will directly affect the service life.
How the interaction between rubber and solvent can be said with solvent solubility of silicone rubber.The more similar chemical structure, the stronger the solvent dissolving force of silicon rubber.Experiments show that in addition to the benzene and dimethyl benzene can cause certain harm to silicone rubber, other solvents will not have impact on silicone rubber.
The size of the silicone rubber solubility in organic solvent solubility parameters available, the closer the solubility parameter, the stronger the dissolving capacity;Solubility parameter difference, the greater the ability to dissolve the weaker.Table 1 shows the silicone rubber and several kinds of solvent solubility parameters.
Silicone rubber and several kinds of solvent solubility parameters in table 1
Chemical name solubility parameters
Silicone rubber was 7.3
Toluene 8.97
Xylene 8.83 ~ 9.03
Ethyl acetate is 9.10
9.22
Butanone 9.56
Acetone 9.74
Ethanol is 12.97
From table 1 can be seen, the solubility parameters of silicone rubber with toluene, xylene, benzene is relatively close, with ethyl ketone, acetone, ethanol, etc.
35% for mixed solvent such as benzene, toluene, acetone, butanone, 10% and 40%, 15%, have a great effect to silicone rubber, silicone rubber in among them, the quality change.Therefore, we should avoid glue head and frequent contact with the mixed solvent.
5.Spray frost
Rubber pad printing head in storage after a certain period of time, there will be a bloom phenomenon, namely the compound of the promoter, age resister and packing from rubber internal migration to the surface and the phenomenon of precipitation.Bloom in addition to affect the appearance quality of the head, also do harm to use effect.Rubber head spray frost, mainly due to silicone oil or excessive promoting agent, the control method is in accordance with the formula, not blindly increase the content of silicone oil to reduce hardness and so on.Optional increase or decrease the dosage of the curing agent can also lead to insufficient sulfur and sulfide.