The impact of various factors on the polyurethane soft foam materials-Iota

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News > Dynamic industry > The impact of various factors on the polyurethane soft foam materials

The impact of various factors on the polyurethane soft foam materials

1, polyether
Polyether as the main material, the reaction of urethane isocyanates, the reaction is the skeleton of the foamed article. Under the same functionality, the molecular weight increases, the tensile strength of the foam, the elongation and resilience increase, decrease reactivity similar polyethers; at equivalent value (molecular weight / functionalities) the same circumstances, a functional increasing degree, the reaction is relatively rapid, the degree of crosslinking to form polyurethanes improved foam hardness increase as the elongation decreased. Average Off functionality polyols should be 2.5 or more, if the average clearance can be too low, the foam is poor in recovery properties after compression.
If more than the amount of polyether, equivalent to other materials (TDI, water, catalysts, etc.) to reduce, could easily lead to cracking or fallen bubble foam products.
If polyether with less rigid foam products, elasticity, feel good.
3, toluene diisocyanate
Generally soft foam mixture TDI80 / 20,2,4 and 2,6 isomer with. Available cooling Prepared T100 that pure 2,4TDI.
TDI amount = (8.68 + m water × 9.67) × TDI index. TDI index is generally 110-120.
Isocyanate index is increased in a certain range, the foam hardness is increased, but after a certain point no longer significantly increased hardness, and tear strength, tensile strength and elongation decreased, the foam-forming macropores, obturator rise, back rate dropped bombs, sticky surface for a long time, long time aging, causing burning core.
Isocyanate index is low, it will cause the foam crack, poor resilience, strength, poor compression set is large, the surface of a wet feeling.
2, foaming
Generally in the manufacture of polyurethane block when the bubble density is greater than 21, use only water (chemical blowing agent) do foaming agent, only use methylene chloride density formula or super-soft formula (MC) and other low-boiling compounds (physical hair foaming agent) as an auxiliary blowing agent.
Auxiliary blowing agent and the foam density will decrease in hardness, due to its gasification will absorb some of the heat curing reaction slows down, an additional amount of catalyst. Due to absorption of heat, avoiding the risk of burning the core. uc;!, JX bN
Foaming ability available foaming index (100 parts of the polyether by the number of equivalents of water, or water) to reflect: m --- foaming agent
Foaming index IF = m (water) + m (F-11) / 10 + m (MC.) / 9 (100 points polyether)
Water as a blowing agent reacts with isocyanate urea bond and release a lot of CO2 and heat, is a chain reaction.
More water, foam density reduction, increased hardness, while cell pillars smaller, weaker, reducing the carrying capacity, easy bubble collapse, crack bubble. Increased consumption of TDI, release heat more easily heartburn. If more than 5.0 parts water, you must add a physical blowing agent to absorb some of the heat to avoid burning core phenomenon.
Less water, a corresponding reduction in the amount of catalyst, but the density increases "" F '
4, catalyst
Amine: A33 with its general effect is to promote the reaction of isocyanate and water, adjusting the density of the foam, bubble opening ratio, are primarily promote the blowing reaction.
Amine and more: foam products appear split, there are holes in the foam or blister
Amine less: bubble contraction, closed-cell, foam products emit thick bottom.
Tin: general use stannous octoate T-9; T-19 is very high catalytic activity gel catalyst, mainly to promote gel reaction, i.e., the late reaction.
Tin: gelled quickly, increasing the viscosity, elasticity is poor, poor ventilation, causing the obturator phenomenon. If you get the proper amount of slack to improve their well-cut foam, further increasing the amount of foam gradually become closer, so that contraction, obturator.
Tin less: less gel, foaming process causing splitting. Or top edge cracking, and off billet, flash phenomenon.
Reducing amine or tin can be increased to increase the strength of the polymer membrane wall bubble in a high incidence of the gas, thereby reducing a hollow or cracking.
Polyurethane foam having a desirable whether open or closed cell structure, depending on the foam formation during the reaction rate and the gas gel] expansion rate is balanced. This balance can be achieved by adjusting the kind and amount of the formulation of tertiary amine catalysts and foam stabilizers and other additives are.
5, foam stabilizer (silicone oil)
Foam stabilizer is a surfactant, can make good polyurea dispersed in the foaming system, acts as a "physical crosslinking point", and can significantly increase the viscosity of the foam mixture in the early, to avoid cracking foam. Which on the one hand has the emulsion, so that to enhance the miscibility of the components between the foam material, is added after the other silicone surfactants can reduce the surface tension of liquid r, the desired increase in free energy of the gas dispersion reduced, and the dispersion air in the raw material in the mixing process more nucleation, the generation of fine bubbles help to adjust the foam pore size, the control cell structure, improve the foam stability; prevent cell foam collapse, burst, so that the foam wall having elastic, foam control pore size and uniformity. Its stable foam foaming at the beginning, in the mid-fired prevent bubbles and bubbles in the foam so late bubble hole. The more general foaming agent, POP greater the amount of silicone oil consumption.
The amount and more: so late foam wall elasticity increases, not broken, small cell. Causing the obturator.
With less: the bubble burst, after falling from the hair bulb, the larger the aperture, easy and bubble.
6, the influence of temperature
With the rise of polyurethane foam reaction temperature of the material is accelerated in sensitive formulations will cause burning of the core and the risk of fire. Usually the temperature control polyol and isocyanate component unchanged. Foam density decreases when the material temperature increased. The same formula, the same material temperature high summer temperatures, the reaction speed, resulting in foam density, hardness decreased, increased elongation, increased mechanical strength. Summer may be appropriate to increase the TDI index fell to correct hardness.
7, the effect of air humidity
Humidity increases, due to the foam portion of the isocyanate groups reacted with the moisture in the air, resulting in decrease in hardness, it may be appropriate to increase the amount of TDI foaming. Too large will cause the curing temperature is too high causing heartburn.
8, the impact of the atmospheric pressure
The same formula, foaming at high altitudes, low density foam products.
Note:
1, in the foam forming process, the gel with the foaming reaction and the reaction occurs, but each
There is competition between the reaction, the reaction rate is generally greater than the foaming gel reaction rate.
--- Urethane formation reaction of the gel reaction, (reaction with -OH)
--- Means a water blowing reaction participated reaction of urea and bubbles
2, a nucleating agent --- causing substance bubble formation, such as the system of fine solid particles, liquid
Foam stabilizers or originally dissolved in the material of fine bubbles and the like; include air or nitrogen is dissolved in the polyol and the isocyanate, carbon dioxide, foam stabilizers, fillers such as carbon black. However, to produce more gas bubbles in the material; and the more stable the more fine-generated cell.
The number and size of bubbles in the foam cell foam formed in the system depends on the additional role of a nucleating agent; more nucleating agents, bubbles, small cell.
When the temperature rises, reducing the solubility of the gas in the liquid, and thus there will be more bubbles start to form or to grow up earlier. Long cream time, help the growth of large bubbles.
Increasing the amount of catalyst, the cream time can be shortened, due to the competition reaction the reaction and gel pores obtained foam bubble formation.
3, if the foam having the desired open or closed cell structure, the foam-forming process depending on the rate of expansion of the gel and the gas velocity is balanced. This balance can be adjusted by the kinds and amounts of tertiary amine catalysts in formulations and foam stabilizer additives to achieve.

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