1 Introduction
Polyurethane soft foam series products mainly include block, continuous, sponge, high resilience foam (HR), self-skin foam, slow resilience foam, microcellular foam and semi-rigid energy-absorbing foam. This type of foam still accounts for about 50% of the total polyurethane product. A large variety with an expanding application, it has been involved in various fields of the national economy: household appliances, automobiles, home improvement, furniture, trains, ships, aerospace and many other fields. Since the advent of PU soft foam in the 1950s, especially after entering the 21st century, there has been a leap in technology, variety and product output. Highlights are: Environmentally friendly PU soft foam, namely green polyurethane product; low VOC value PU soft foam; low atomization PU soft foam; full water PU soft foam; full MDI series soft foam; flame retardant, low smoke, full MDI series Foam; new types of additives such as reactive high molecular weight catalysts, stabilizers, flame retardants and antioxidants; polyols with low unsaturation and low monoalcohol content; ultra-low density PU soft foam with excellent physical properties; low resonance frequency , low transfer PU soft foam; polycarbonate diol, polyε-caprolactone polyol, polybutadiene diol, polytetrahydrofuran and other special polyols; liquid CO2 foaming technology, negative pressure foaming technology, etc. . In short, the emergence of new varieties and new technologies has promoted the further development of PU soft foam.
2 Foaming principle
In order to synthesize the ideal PU soft foam that meets the requirements, it is necessary to understand the chemical reaction principle of the foam system in order to select the appropriate main and auxiliary raw materials and manufacturing processes. The development of the polyurethane industry to this day is no longer in the imitation stage, but according to the performance requirements of the final product, it can be achieved through the structure of raw materials and synthetic techniques. Polyurethane foam participates in chemical changes during the synthesis process, and the factors affecting the structural properties of the foam are complex, which not only involves the chemical reaction between isocyanate, polyether (ester) alcohol and water, but also involves the colloid chemistry of foaming. The chemical reactions include chain extension, foaming and cross-linking. It also affects the structure, functionality and molecular weight of the substances participating in the reaction. The general reaction of the synthesis of polyurethane foam can be expressed by the following formula:
9b0722b7780190d3928a2b8aa99b1224.jpg
However, the actual situation is more complicated, and the important responses are summarized as follows:
01 Chain extension
Multifunctional isocyanates and polyether (ester) alcohols, especially difunctional compounds, the chain extension is carried out as follows:
07b0ec2de026c48dd018efaa5ccde5c1.jpg
In the foaming system, the amount of isocyanate is generally greater than that of the active hydrogen-containing compound, that is, the reaction index is greater than 1, usually 1.05, so the end of the chain-extended final product in the foaming process should be an isocyanate group.
5ed385eebd04757bda026fcfb4da4961.jpg
The chain extension reaction is the main reaction of PU foam, and it is the key to physical properties: mechanical strength, growth rate, elasticity, etc.
02 Foaming reaction
Foaming is very important in the preparation of soft foams, especially when synthesizing low-density products. There are two general foaming effects: the use of reaction heat to vaporize low-boiling hydrocarbon compounds, such as HCFC-141b, HFC-134a, HFC-365mfc, cyclopentane, etc., to achieve foaming purposes, and the other is to use water and isocyanate. The chemical reaction produces a large amount of CO2 gas foaming:
04d3b707849aaf9b1ee6f1b8d19c1ce7.jpg
In the absence of a catalyst, the reaction rate of water with isocyanates is slow. The reaction rate of amines and isocyanates is quite fast. For this reason, when water is used as a foaming agent, it brings a large number of rigid segments and urea compounds with high polarity, which affect the feel, resilience and heat resistance of foam products. To produce a foam with excellent physical properties and low density, it is necessary to increase the molecular weight of the polyether (ester) alcohol and the softness of the main chain.
03 Gel action
Gel reaction is also called cross-linking and curing reaction. In the foaming process, gelation is very important. Too early or too late gelation will cause the quality of foam products to decline or become waste products. The most ideal state is that the chain extension, foaming reaction and gel reaction reach equilibrium, otherwise the foam density will be too high or the foam will collapse.
There are three gelling actions during the foaming process:
1) Gels of multifunctional compounds
Generally, compounds with more than three functionalities can react to form compounds of body structure. We use polyether polyols with more than three functionalities in the production of polyurethane flexible foams. Recently, polyisocyanates with fn ≥ 2.5 are also used in the development of all MDI systems to improve the load-bearing capacity of low-density foams. These are the basis for the formation of three-phase cross-linked structures:
42a37c3572152ae1f6c386b7bd177bf8.jpg
It is worth noting that the molecular weight between the cross-linking points directly reflects the cross-linking density of the foam. That is to say, the crosslinking density is large, the hardness of the product is high, and the mechanical strength is good, but the softness of the foam is poor, and the resilience and elongation are low. The molecular weight (Mc) between the cross-linking points of the soft foam is 2000-2500, and the semi-rigid foam is between 700-2500.
2) Formation of urea
When water is used as a foaming agent, corresponding urea bond compounds are generated. The more water, the more urea bonds. They will further react with excess isocyanate at high temperature to form biuret bond compounds with a three-phase structure:
896b42df0d91543a61d1e68f91c1d829.jpg
3) Formation of allophanate Another type of cross-linking reaction is that the hydrogen on the main chain of urethane further reacts with excess isocyanate at high temperature to form an allophanate bond with a three-phase structure:
4a6fdae7620ef5333bd14c6973a26a37.jpg
The formation of biuret compounds and allophanate compounds is not ideal for foaming systems because these two compounds have poor thermal stability and decompose at high temperatures. Therefore, it is very important for people to control the temperature and isocyanate index in production.
3 Chemical calculations
Polyurethane synthetic material is a polymer synthetic material that can synthesize polymer products from raw materials in one step, that is to say, the physical properties of the products can be directly adjusted artificially by changing the specifications and composition ratios of raw materials. Therefore, how to correctly apply the principle of polymer synthesis and establish a simple calculation formula is very important to improve the quality of polyurethane products
01 Equivalent value
The so-called equivalent value (E) refers to the molecular weight (Mn) corresponding to the unit functionality (f) in a compound molecule;
2a931ca68a4ace0f036e02a38adee698.jpg
For example, the number average molecular weight of polyether triol is 3000, then its equivalent value:
e3295f1d515f5af4631209f7b49e1328.jpg
The commonly used cross-linking agent MOCA, namely 4,4′-methylene bis(2 chloroamine), has a relative molecular mass of 267. Although there are 4 active hydrogens in the molecule, only 2 hydrogens participate in the isocyanate reaction. atom, so its functionality f=2
0618093a7188b53e5015fb4233cccdc9.jpg
In the product specification of polyether or polyester polyol, each company only provides hydroxyl value (OH) data, so it is more practical to directly calculate the equivalent value with hydroxyl value:
8a7763766e4db49fece768a325b29a61.jpg
It is worth reminding that the actual measurement of product functionality is very time-consuming, and there are many side reactions. Often, the actual functionality of triol polyether (ester) is not equal to 3, but is between 2.7 and 2.8. Therefore, it is recommended to use (2 ) formula, that is, the hydroxyl value is calculated as well!
02 Requirement of isocyanate
All active hydrogen compounds can react with isocyanate. According to the principle of equivalent reaction, it is a common practice in PU synthesis to accurately calculate the amount of isocyanate consumed by each component in the formula:
a63972fdc4f16025842815cb1d008cfe.jpg
In the formula: Ws—amount of isocyanate
Wp—polyether or polyester dosage
Ep—polyether or polyester equivalent
Es—Isocyanate equivalent
The molar ratio of I2—NCO/-OH, that is, the reaction index
ρS—purity of isocyanate
As we all know, when synthesizing a prepolymer or semi-prepolymer with a certain NCO value, the amount of isocyanate required is related to the actual amount of polyether and the NCO content required by the final prepolymer. After summarizing:
83456fb6214840b23296d5ff084c4ab8.jpg
In the formula: D——the mass fraction of NCO group in the prepolymer
42—— Equivalent value of NCO
In today’s all-MDI system foams, high molecular weight polyether-modified MDI is generally used to synthesize semi-prepolymers, and its NCO% is between 25 and 29%, so formula (4) is very useful.
A formula for calculating molecular weight between cross-linking points related to cross-link density is also recommended, which is very useful in formulating formulations. Whether it is an elastomer or a high-resilience foam, its elasticity is directly related to the amount of cross-linking agent:
b9fd1ca1ee9bebc558731d065ac3254b.jpg
In the formula: Mnc——number-average molecular weight between cross-linking points
Eg——Equivalent value of cross-linking agent
Wg——Amount of cross-linking agent
WV – the amount of prepolymer
D——NCO content
4 raw materials
Polyurethane raw materials are divided into three categories: polyol compounds, polyisocyanate compounds and additives. Among them, polyols and polyisocyanates are the main raw materials of polyurethane, and auxiliary agents are compounds that supplement the special properties of polyurethane products.
All compounds with hydroxyl groups in the structure of organic compounds belong to organic polyol compounds. Among them, the two most commonly used polyurethane foams are polyether polyols and polyester polyols.
polyol compound
Polyether polyol
It is an oligomeric compound with an average molecular weight of 1000~7000, which is based on the raw materials of petrochemical industry: propylene oxide and ethylene oxide, and two and three functional hydrogen-containing compounds are used as initiators, and are catalyzed and polymerized by KOH. .
Generally, the molecular weight of ordinary soft foam polyether polyol is in the range of 1500~3000, and the hydroxyl value is between 56~110mgKOH/g. The molecular weight of high resilience polyether polyol is between 4500 and 8000, and the hydroxyl value is between 21 and 36 mgKOH/g.
It is worth mentioning that several large varieties of polyether polyols newly developed in recent years are very beneficial to improve the physical properties of polyurethane flexible foam and reduce the density.
l Polymer-grafted polyether polyol (POP), which can improve the load-carrying capacity of PU soft foam, reduce the density, increase the opening degree, and prevent shrinkage. The dosage is also increasing day by day.
l Polyurea polyether polyol (PHD): The polyether function is similar to polymer polyether polyol, which can improve the hardness, bearing capacity, and promote the opening of foam products. The flame resistance is increased, and the MDI series foam is self-extinguishing and widely used in Europe. l Combustion-grade polymer polyether polyol: It is a nitrogen-containing aromatic hydrocarbon polymer grafted polyether polyol, which can not only improve the load-bearing, open-cell, hardness and other characteristics of foam products, but also make PU seat cushions synthesized from it. It has high flame retardancy: the oxygen index is as high as 28% or more, the low smoke emission ≤60%, and the low flame spread speed. It is an excellent material for automobiles, trains and furniture to make seat cushions.
l Low unsaturation polyether polyol: Since it uses double cyanide metal complex (DMC) as a catalyst, the content of unsaturated double bonds in the synthesized polyether is less than 0.010mol/mg, that is to say, it contains monool The low compound, that is, the high purity, leads to better resilience and compression set properties of HR foam synthesized based on it, as well as good tear strength and indentation factor. The recently developed low resonance frequency, 6Hz low transmission rate car seat cushion foam is very good.
l Hydrogenated polybutadiene glycol, this polyol has been recently used in PU foam products abroad to greatly improve the physical properties of the foam, especially the weather resistance, moisture and heat resistance compression set and other problems for many years, so that the car seat cushion etc. are used in tropical regions of Africa.
l Polyether polyols with high ethylene oxide content, generally high-activity polyether polyols, in order to improve the reactivity of polyethers, add 15~20% EO to the end during synthesis. The above polyethers are EO content up to 80%, PO content On the contrary, it is lower than 40%. It is the key to the development of all MDI series PU soft foams, which should be paid attention to by people in the industry.
l Polyether polyols with catalytic activity: mainly introduce tertiary amine groups with catalytic properties or metal ions into the polyether structure. The purpose is to reduce the amount of catalyst in the foaming system, reduce the VOC value and low atomization of foam products.
l Amino-terminated polyether polyol: This polyether has the largest catalytic activity, short reaction time, fast demoulding, and greatly improved product strength (especially early strength), mold release, temperature resistance, and solvent resistance. , the construction temperature is reduced, the scope is widened, and it is a promising new variety.
polyester polyol
Early polyester polyols all refer to adipic acid-based polyester polyols, and the largest market is microcellular foam, which is used in shoe soles. In recent years, new varieties have appeared one after another, expanding the application of polyester polyols in PUF.
l Aromatic dicarboxylic acid-modified adipic acid-based polyester polyol: mainly synthesizing polyester polyol by partially replacing adipic acid with phthalic acid or terephthalic acid, which can improve the early strength of the product and improve the moisture resistance and hardness, while reducing costs.
l Polycarbonate polyol: This type of product can greatly improve the hydrolysis resistance, weather resistance, temperature resistance and hardness of foam products, and is a promising variety.
l Poly ε-caprolactone polyol: The PU foam synthesized from it has excellent temperature resistance, hydrolysis resistance and abrasion resistance, and some high-performance products must be made of it.
l Aromatic polyester polyol: It was developed by comprehensive utilization of waste polyester products in the early stage, and it is mostly used in PU rigid foam. Now it is extended to PU soft foam, which is also worthy of attention.
Others Any compound with active hydrogen can be applied to PUF. According to market changes and environmental protection requirements, it is imperative to make full use of rural products and synthesize biodegradable PU soft foam.
l Castor oil-based polyols: These products have been used in PUF earlier, and most of them are made from unmodified pure castor oil to make semi-rigid foams. I suggest using transesterification technology, and various high molecular weight alcohols are introduced into castor oil to synthesize various specifications.
Derivatives, can be made into various soft and hard PUF.
l Vegetable oil series polyols: Recently affected by oil prices, such products have developed rapidly. At present, most of the products that have been industrialized are soybean oil and palm oil series products, and cottonseed oil or animal oil can also be used to develop series products, which can be comprehensively utilized, reduce costs, and are biodegradable and environmentally friendly.
polyisocyanate
Two types of isocyanates, TDI and MDI, are commonly used in the production of flexible polyurethane foam, and the derived TDI/MDI hybrids are also widely used in HR series. Due to environmental protection requirements, the automotive industry has very low requirements for the VOC value of foam products. Therefore, pure MDI, crude MDI and MDI modified products have been widely used in PU soft foam as the main PU soft products.
polyol compound
Liquefied MDI
Pure 4,4′-MDI is solid at room temperature. The so-called liquefied MDI refers to MDI that has been modified in various ways and is liquid at room temperature. The functionality of liquefied MDI can be used to understand which group-modified MDI it belongs to.
l urethane-modified MDI with a functionality of 2.0;
l Carbodiimide-modified MDI with a functionality of 2.0;
l MDI modified with diazetacyclobutanone imine, the functionality is 2.2;
l MDI modified with urethane and diazetidinimine with a functionality of 2.1.
The vast majority of these products are used in molded products such as HR, RIM, self-skinning foams, and micro-foams such as shoe soles.
MDI-50
It is a blend of 4,4′-MDI and 2,4′-MDI. Since the melting point of 2,4′-MDI is lower than room temperature, about 15°C, MDI-50 is a liquid stored at room temperature and is easy to use. Pay attention to the steric hindrance effect of 2,4′-MDI, which is less reactive than the 4,4′ body and can be adjusted by a catalyst.
Coarse MDI or PAPI
Its functionality is between 2.5 and 2.8, and it is generally used in rigid foams. In recent years, due to price factors, it has also been used in the soft foam market, but it should be noted that due to its high functionality, it is necessary to reduce the amount of cross-linking in formula design. Joint agent, or increase the internal plasticizer.
Auxiliary
catalyst
The catalyst has a great effect on the polyurethane foam, and with it, the rapid production at room temperature can be achieved. There are two main categories of catalysts: tertiary amines and metal catalysts, such as triethylenediamine, pentamethyldiethylenetriamine, methylimidazole, A-1, etc., all belong to tertiary amine catalysts, while stannous octoate, diethylene diamine, etc. Dibutyltin laurate, potassium acetate, potassium octoate, organic bismuth, etc. are metal catalysts. At present, various delayed-type, trimerization-type, complex-type and low-VOC value-type catalysts have been developed, which are also based on the above types of catalysts.
For example, the Dabco series of gas products company, the basic raw material is triethylenediamine:
l Dabco33LV contains 33% triethylenediamine/67% dipropylene glycol
l Dabco R8020 Triethylenediamine contains 20%/DMEA80%
l Dabco S25 triethylenediamine contains 25%/butanediol 75%
l Dabco8154 triethylenediamine/acid delayed catalyst
l Dabco EG Triethylenediamine contains 33%/ Ethylene Glycol 67%
l Dabco TMR series trimerization
l Dabco 8264 Compound Bubbles, Balanced Catalysts
l Dabco XDM low odor catalyst
Under the condition of multiple catalysts, we must first understand the characteristics of various catalysts and their working principles to obtain the balance of the polyurethane system, that is, the balance between the foaming speed and the gelation speed; the balance between the gelation speed and the foaming rate, and the foaming Speed and material fluidity balance, etc.
Metal catalysts are all gel-type catalysts. Conventional tin-type catalysts have a strong gel effect, but their disadvantages are that they are not resistant to hydrolysis and have poor thermal aging resistance. The recent emergence of organic bismuth catalysts should attract attention. It not only has the function of tin catalyst, but also has good hydrolysis resistance and heat aging resistance, which is very suitable for compounding materials.
foam stabilizer
It plays the role of emulsifying the foam material, stabilizing the foam and adjusting the cell, and increases the mutual solubility of each component, which is helpful for the formation of bubbles, controls the size and uniformity of the cell, and promotes the balance of the foam tension. The walls are elastic to retain the cells and prevent collapse. Although the amount of foam stabilizer is small, it has a significant impact on the cell structure, physical properties and manufacturing process of PU flexible foam.
At present, hydrolysis-resistant silicone/polyoxyalkylene ether block oligomers are used in China. Due to the application of different foam systems, the ratio of hydrophobic segment/hydrophilic segment is different, and the change of the chain link at the end of the block structure is different. , to produce silicon stabilizers for various foam products. Therefore, when choosing a foam stabilizer, you must understand its function and function, don’t forget it, don’t use it indiscriminately, and cause adverse consequences. For example, soft foam silicone oil cannot be applied to high-resilience foam, otherwise it will cause foam shrinkage, and high-resilience silicone oil cannot be applied to block soft foam, otherwise it will cause foam collapse.
Due to the needs of environmental protection, the automobile and furniture industries require products with low atomization and low VOC value. Various companies have successively developed low atomization and low VOC value foam stabilizers, such as Dabco DC6070 launched by Gas Products Company, which is a low atomization silicone oil for TDI system. ; Dabco DC2525 is a low fogging silicone oil for MDI systems.
foaming agent
The foaming agent for PU soft foam is mainly water, supplemented by other physical foaming agents. In the production of block foam, considering the large amount of water in low-density products, often exceeding 4.5 parts per 100 parts will cause the internal temperature of the foam to rise, exceeding 170~180 ° C, resulting in spontaneous combustion of the foam, and a low-boiling hydrocarbon foaming agent must be used. One assists in reducing the density, and the other removes a large amount of reaction heat. In the early days, the combination of water/F11 was used. Due to environmental protection issues, F11 was banned. At present, most of the transitional water/dichloromethane series products and water/HCFC-141b series are used. Because dichloromethane series products also pollute the atmosphere, it is a transitional nature, while HFC series products: HFC-245fa, -356mfc, etc. or cyclopentane series products are all environmentally friendly, but the former is expensive and the latter is flammable, so In order to meet the needs of reducing the degree of temperature, people have introduced new processes, negative pressure foaming technology, forced cooling technology and liquid CO2 technology to solve the problem, the purpose is to reduce the amount of water or reduce the internal temperature of the foam.
I recommend the liquid CO2 technology for the production of block bubbles, which is more suitable for small and medium-sized enterprises. In LCO2 technology, 4 parts of LCO2 are equivalent to 13 parts of MC. The relationship between the water consumption and liquid CO2 used to produce foams of different densities Foam density, kg/m3 water, parts by mass LCO2, parts by mass equivalent MC, parts by mass
13.34.86.520.0
15.24.55.015.3
16.04.54.012.3
17.33.94.313.1
27.72.52.06.2
flame retardant
Flame retardant and fire prevention are people’s concern all the time. my country’s newly released “Requirements and Standards for Combustion Performance of Flame Retardant Products and Components in Public Places” GB20286-2006 has new requirements for flame retardancy. For flame retardant grade 1 foam Plastic requirements: a), peak heat release rate ≤ 250KW/m2; b), average burning time ≤ 30s, average burning height ≤ 250mm; c), smoke density grade (SDR) ≤ 75; d), smoke toxicity grade Not less than 2A2 level.
That is to say: three factors should be considered: flame retardant, low smoke, and low smoke toxicity. In order to put forward higher requirements for the selection of flame retardants, according to the above standards, I believe that it is best to choose varieties that can form a thick carbon layer and release non-toxic or low-toxic smoke. At present, it is more suitable to use phosphate ester-based high molecular weight flame retardants, or halogen-free aromatic hydrocarbons with high temperature resistance heterocyclic varieties, etc. In recent years, foreign countries have developed expanded graphite flame retardant PU flexible foam, or nitrogen heterocyclic flame retardant The drug is correct.
other
Other additives mainly include: pore openers, cross-linking agents, antioxidants, anti-fogging agents, etc. When selecting, the influence of additives on the performance of PU products should be considered, as well as its toxicity, migration, compatibility, etc. question.
5 products
In order to further understand the relationship between the formula and performance of PU soft foam, several representative examples are introduced for reference:
1. Typical formula and properties of block polyether PU soft foam
Polyether triol 100pbw TDI80/20 46.0pbw Organotin catalyst 0.4pbw Tertiary amine catalyst 0.2pbw Silicon foam stabilizer 1.0pbw Water 3.6pbw Co-foaming agent 0~12pbw Properties: Foam density, kg/m3 22.4 Tensile strength, kpa 96.3 Elongation, % 220 Tear strength, N/m 385 Compression set, 50% 6 90% 6 Cavitation load, kg (38cm×35.6cm×10cm) Deformation 25% 13.6 65% 25.6 Falling ball rebound, % 38 In recent years, in order to meet the needs of the market, some enterprises often produce low-density (10kg/m3) foam. When producing ultra-low-density flexible foam, it is not simply to increase the foaming agent and auxiliary foaming agent. What can be done must also be matched with a relatively high-stability silicon surfactant and a catalyst.
Production of low-density ultra-low-density flexible foam reference formula: name medium-density low-density ultra-low density
Continuous box continuous box box polyether polyol 100100100100100 Water 3.03.04.55.56.6 A-33 catalyst 0.20.20.20.250.18 Silicon surfactant B-81101.01.21.11.93.8 Stannous octoate 0.250.280.350.360.40 Agent 7.57.512.515.034.0 TDI80/2041.444.056.073.0103.0 Density, kg/m3 23.023.016.514.08.0
Cylindrical foam formula: EO/PO type polyether polyol (OH:56) 100pbw Water 6.43pbw MC foaming agent 52.5pbw Silicon surfactant L-628 6.50pbw Catalyst A230 0.44pbw Stannous octoate D19 0.85pbw TDI80/20 index 0.99 Dosage 139pbw Foam density, kg/m3 7.5
2. Liquid CO2 co-foaming agent to make low-density foam
Polyether triol (Mn3000) 100 100 Water 4.9 5.2 Liquid CO2 2.5 3.3 Silicone surfactant L631 1.5 1.75 B8404 Amine catalyst A133 0.28 0.30 Stannous octoate 0.14 0.17 Flame retardant DE60F 0 114 TDI 80/20 Foam density , kg/m3 16 16
The typical formula is as follows: Polyether triol (Mn3000) 100pbw Water 4.0pbw LCO2 4.0~5.5pbw Catalyst A33 0.25pbw Silicon surfactant SC155 1.35pbw Stannous octoate D19 0.20pbw TDI80/20 index 110 Foam density, kg/ m3 14.0~16.5
3. Full MDI low density polyurethane soft foam
Soft PU molded foam is widely used in the production of car seat cushions. Density reduction without affecting physical properties is the goal of development.
Formula: High activity polyether (OH: 26~30mgKOH/g) 80pbw Polymer polyol (OH: 23~27mgKOH/g) 20pbw Crosslinking agent 0~3pbw Water 4.0pbw Amine catalyst A-33 2.8pbw Surface activity of silicone oil Agent B8716 1.0pbw MDI index 90pbw Performance: Foam center density 34.5kg/m3 Hardness ILD25% 15.0kg/314cm2 Tear strength 0.8kg/cm Tensile strength 1.34kg/cm2 Elongation 120% Rebound rate 62% Permanent compression set (Dry) 5.0% (Wet) 13.5%
4. Low density, full MDI environment-friendly vehicle seat cushion
The homologue of pure MDI: M50—that is, the product of 4,4′MDI 50% 2,4′MDI 50%, can be foamed at room temperature, improve fluidity, reduce product density, and reduce vehicle weight, which is very promising. The product:
Formulation: High active polyether polyol (OH: 28mgKOH/g) 95pbw 310 Auxiliary* 5pbw Dabco 33LV 0.3pbw Dabco 8154 0.7pbw Silicon surfactant B4113 0.6pbw A-1 0.1pbw Water 3.5pbw Cyanate index M50 50pbw 8
Physical properties: Drawing time (s) 62 Rise time (s) 98 Free foam density, kg/m3 32.7 Compression load deflection, kpa: 40% 1.5 Elongation, % 180 Tear strength, N/m 220
Note: *310 Auxiliary: I sell it, it is a special chain extender.
5. High resilience, comfortable riding PU foam
Recently, the market demanded that the physical properties of foam seat cushions remain unchanged, but people would not be fatigued and motion sickness high-quality seat cushions after long-term driving. After research, the internal organs of the human body, especially the stomach, have a frequency of around 6Hz. If resonance occurs, it will cause nausea and vomiting.
Generally, the vibration transmittance of high-resilience foam at 6Hz is 1.1~1.3, that is to say, when the vehicle is running, it does not weaken but increases, and some formula products can reduce the vibration to 0.8~0.9. A product formulation is now recommended, and its 6Hz vibration transmission is at the level of 0.5~0.55.
Formulation: High activity polyether polyol (Mn6000) 100pbw Silicon surfactant SRX-274C 1.0pbw Tertiary amine catalyst, Minico L-1020 0.4pbw Tertiary amine catalyst, Minico TMDA 0.15pbw Water 3.6pbw Isocyanate prepolymer (NCO%= 29.7%) INDEX 100
Physical properties: Overall density, kg/m3 48.0 25%ILD, kg/314cm2 19.9 Rebound, % 74 50% compression
Shrinkage Strength, (Dry) 1.9 (Wet) 2.5 6Hz Vibration Transmittance 0.55
6. Slow rebound or viscoelastic foam
The so-called slow-rebound PU foam refers to the foam that is not restored to its original shape immediately after the foam is deformed by external force, but is slowly restored without residual surface deformation. It has excellent cushioning, sound insulation, sealing and other properties. It can be used in noise control of automobile engines, carpet backing, children’s toys and medical pillows.
Example formula: High activity polyether (OH34) 40~60pbw Polymer polyether (OH28) 60~40 pbw Cross-adhesive ZY-108* 80~100 pbw L-580 1.5 pbw Catalyst 1.8~2.5 pbw Water 1.6~2.2 pbw Isocyanate index** 1.05 pbw Note: *ZY-108, a compound of multifunctional low molecular weight polyether** PM-200, a blend of liquefied MDI-100, both are Wanhua products Properties: Foam density, kg/ m3 150~165 Hardness, Shore A 18~15 Tear strength, kN/m 0.87~0.76 Elongation, % 90~130 Rebound rate, % 9~7 Recovery time, seconds 7~10
7. Polyether type self-skinned microcellular foam resistant to flex fatigue million times
The foam can be applied to PU soles and steering wheels
实例： DaltocelF-435 31.64 pbw Arcol34-28 10.0 pbw DaltocelF-481 44.72 pbw Arcol2580 3.0 pbw 乙二醇6.0 pbw 催化剂Dabco EG 1.8 pbw A-1 0.3 pbw Dabco1027 0.3 pbw 硅表面活性剂DC-193 0.3 pbw L1 412T 1.5 pbw Water 0.44 pbw Modified MDI Suprasec2433 71 pbw
Physical properties: Foam density: about 0.5g∕cm3 β-belt deflection, KCS 35～50, very good
8. Flame retardant, low smoke, high resilience foam
With the rapid development of the national economy, various departments have higher and higher requirements for the flame retardancy of foam products, especially aviation, cars, high-speed passenger cars, and household sofas, etc. Nontoxic.
In view of the above situation, the author and colleagues have developed a flame retardant grade (oxygen index 28~30%), which has a very low smoke density (the international value is 74, and this product is only about 50), and the foam rebound remains unchanged. Produces white smoke.
Example formula: YB-3081 flame retardant polyether 50 pbw High activity polyether (OH34) 50 pbw Silicone surfactant B 8681 0.8~1.0 pbw Water 2.4~2.6 pbw DEOA 1.5~3 pbw Catalyst A-1 etc. 0.6~1.1 pbw isocyanate index 1.05
Physical properties: Foam density, kg/m3 ≥50 Compressive strength, kPa 5.5 Tensile strength, kPa 124 Rebound rate, % ≥60 Compression deformation, 75% ≤8 Oxygen index, OI% ≥ 28 Smoke density ≤50
9. Water is the foaming agent, all environmentally friendly self-skin foam
HCFC-141b foaming agent has been completely banned in foreign countries. CP foaming agent is flammable. HFC-245fa and HFC-365mfc foaming agent are expensive and unacceptable. Leather foam. In the past, PU workers at home and abroad only paid attention to the modification of polyether and isocyanate, so the surface layer of the foam was unclear and the density was high.
A set of formulas are now recommended, which are characterized by:
l The basic polyether polyol remains unchanged, and the conventional Mn5000 or 6000 is used. ·
l The isocyanate remains unchanged, C-MDI, PAPI or modified MDI can be used.
l Use special additive SH-140 to solve the problem. ·
Basic formula:
l High activity polyether triol Mn5000 65pbw
l SH-140* 35pbw
l Chain extender: 1,4-butanediol 5pbw
l Cross-linking agent: glycerol 1.7pbw
l Opening agent: K-6530 0.2~0.5pbw
l Catalyst A-2 1.2~1.3pbw
l Color paste appropriate amount l Water 0.5pbw
l MR-200 45pbw
Note: *SH-140 is our product.
Physical properties: the overall density of the foam is 340~350kg/m3
Products: smooth surface, clear crust, low density.
Post time: Aug-12-2022