The influence of various raw materials of polyurethane on the soft foam-Iota

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Service > The influence of various raw materials of polyurethane on the soft foam

The influence of various raw materials of polyurethane on the soft foam

1, polyether
Polyether as the main raw material, reacts with the isocyanate urethane, foam skeleton reaction products. In the case of the same functionality, the molecular weight increases, the tensile strength of the foam, improved elongation and resiliency, polyether similar reactivity decreases; when the value in (molecular weight / functionalities) of the same case, a functional increase the degree, the reaction is relatively rapid, cross-linked to form polyurethanes improve foam hardness increase as elongation decreased. Off functionality polyols average should be 2.5 or more, if the average clearance can too low, the foam after compression response is poor.
If more than the amount of polyether, equivalent to other materials (TDI, water, catalysts, etc.) decrease, could easily lead to cracking or collapse bubble foam products.
If polyether with less rigid foam products, elasticity, feel good.
2, the blowing agent
Generally in the manufacture of polyurethane block when the bubble density is greater than 21, use only water (chemical blowing agent) foaming agent, only use methylene chloride in a low density formula or super-soft formula (MC) and other low-boiling compounds (Physical Development foaming agent) as an auxiliary blowing agent.
Auxiliary blowing agent causes the foam density and hardness decreased, due to its vaporization heat will absorb some of the curing reaction slows down, the need to increase the amount of catalyst. Due to the absorption of heat, to avoid the risk of burning the core. uc;!, JX bN
Available foaming foaming ability index (100 parts of the polyether the water or the water equivalent number) 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 and an isocyanate-reactive form a urea bond and release a lot of CO2 and heat, is a chain-reaction.
More water, foam density reduction, increased hardness, while the cell pillars smaller, weaker, reducing the carrying capacity, easy to collapse the bubble, crack bubble. Increase the amount of consumption of TDI, release heat more easily heartburn. If the water is more than 5.0 parts, 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 '
3, toluene diisocyanate
Usually soft foam mixture TDI80 / 20,2,4 and 2,6 isomer with. Available cooling Preparation T100 ie pure 2,4TDI.
TDI amount = (8.68 + m water × 9.67) × TDI index. TDI index is generally 110-120.
Isocyanate index within a certain range is increased, the foam hardness increases, but reaches a certain point no longer significantly increased hardness, and tear strength, tensile strength and elongation decreased foam formation of large holes, closed cell rises back rate dropped bombs, sticky surface for a long time, long curing time, causing heartburn core.
Isocyanate index is low, it will cause the foam crack, resilience poor, poor strength, compression set larger surface wet feeling.
4, catalyst
Amine: general use A33 whose role is to promote the reaction of isocyanate and water, adjusting the foam density, the bubble opening rate, mainly to promote the blowing reaction.
Amine and more: foam products appear split, foam or blister holes
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 gelation reaction, i.e., the late reaction.
TIN: gelled quickly, increasing the viscosity, elasticity is poor, poor ventilation, resulting in a closed-cell phenomenon. If an appropriate increase in their amount of good openings available loose foam, further increasing the amount of the foam gradually become closer, so that contraction, obturator.
Tin less: insufficient gel, foam process resulting in splitting. Or top edge cracking, and de-blank, feathering.
Reduce or increase the tin amine polymer bubble film can increase wall strength occurs when a large number of gas, thereby reducing hollow or cracking.
Whether polyurethane foam having open or closed cell structure desired, depending on the foam formed during gelation reaction rate and gas] 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 polyurea good dispersion in the foaming system, plays the role of "physical crosslinking point", and can significantly increase the viscosity of the foam mixture early, to avoid cracking bubble. On the one hand it has emulsification, enhanced miscibility of the components so that the foam material between the other hand, after the silicone surfactant was added to reduce the surface tension of the liquid r, the desired increase in free energy of the gas dispersion reduce the dispersion the air in the raw material in the mixing process easier nucleation of fine bubbles generated help adjust foam pore size, the control cell structure, improve the foam stability; prevent cell foam collapse, burst, with the foam wall flexibility, control the pore size and uniformity of foam. Its stable foam in the early foaming, in the mid-fired prevent foam and bubble in the late foaming make cell communication. The more general foaming agent, POP greater the amount of silicone oil consumption.
More than the amount: so late foam wall elasticity increase, not broken, small cell. Causing the obturator.
With less: the bubble burst, after the collapse from the hair bulb, the larger the aperture, easy and bubble.
6, the effect of temperature
Polyurethane foam reaction temperature rises with materials accelerated in sensitive formulations will cause wick and fire hazard. General 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, causing the 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, the bubble of the isocyanate moiety reacted with moisture in the air, resulting in decrease in hardness, it may be appropriate to increase the amount of foaming TDI. It can cause excessive ripening temperature is too high causing heartburn.
8, the impact of atmospheric pressure
The same formula, foaming at high altitudes, low density foam products.
Note:
1, the foam forming process, foamed gel reaction in the same reaction occurred, but all
There is competition between the reaction, the reaction rate is generally higher than the foaming gel reaction speed.
--- Urethane formation reaction of the gel reaction, (reaction with -OH)
--- Foaming reaction refers to participate in the water reacts urea and bubbles
2, nucleating agents --- bubble formation caused by substance, such as the system of fine solid particles, liquid
Foam stabilizer or have been dissolved in the material of fine air bubbles; including dissolved air or nitrogen in the polyol and isocyanate, and carbon dioxide, foam stabilizers, fillers such as carbon black. But to produce more gas bubbles in the material; the finer and more stable generation of cell.
The number and size of bubbles in the foam cell formation depends on the foaming system role plus nucleating agent; more nucleating agents, bubbles, small cell.
When the temperature rises, the gas solubility decreases in the liquid, and thus there will be more bubble formation or to the previous starting to grow up. Long cream time, favor the growth of large bubbles.
Increase the amount of catalyst, the cream time can be shortened, due to the competitive reaction gel reaction and bubble formation pore foam available.
3, if the foam having open or closed cell structure desired, depending on the formation of gel foam and gas expansion velocity speed is balanced. This balance can be adjusted by the kind and amount of tertiary amine catalyst formulations and foam stabilizer additives to achieve.

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