Talking about the production technology and formula of several special polyurethane foams
Times: 2020-07-16 | Hit：1086
Abstract: This article introduces the basic characteristics, physical properties and applications of polyurethane hydrophilic foam, non-yellowing foam and microcellular foam, and describes their common raw materials, processes, formulas, and basic ideas for formula design.
Keywords: polyurethane, hydrophilic foam, non-yellowing foam, microcellular foam, formulation design
About the author: Jiang Shuhui, born in Suzhou, Anhui Province in 1953, senior engineer, has been engaged in the production and research and development of polyurethane materials for 38 years. He has worked in the production, technology and research and development of polyurethane materials in Dow Chemical, Japan, and Inoue China Technology Center of Japan. After that, he worked for many years in the development of polyurethane technology in Suzhou Yitong Polyurethane Company and Zhejiang Huafeng Group Shanghai New Materials Research Institute.
Polyurethane flexible foam refers to a porous or reticulated foam (sponge) material with certain elasticity and relatively soft. Its outstanding properties are softness, good resilience, sound absorption, ventilation, heat preservation, cushioning, energy absorption, etc., and according to different There are also various characteristics of the application field.
Polyurethane flexible foam has been industrially produced since Bayer’s polyester flexible foam (sponge) in 1952. After more than 60 years of development, it has been widely used in all aspects of people’s daily life and many industrial fields. At present, domestic flexible foam The actual output is estimated at more than 3 million tons. The main types of products include shockproof materials, sound insulation materials, filter materials, warmth-keeping materials, packaging materials, decoration materials, clothing materials, etc. In terms of the type of production, the flexible polyurethane foam mainly includes: block foam (ordinary sponge), high resilience molded foam, self-skin foam, slow resilience foam, etc. What I want to introduce below is a kind of special polyurethane soft sponge, specific products such as water-friendly (absorbent) foam, non-yellowing foam and microporous sheet sponge; these are also soft polyurethane foam, but are different from the above-mentioned ordinary polyurethane soft Compared with high-quality foam, each has special properties and applications, and is also an indispensable product for people's daily life and industrial production. This article introduces the basic raw materials, production processes and formulas of these foams.
First, the production formula and process of hydrophilic polyurethane flexible foam
1. Its basic characteristics: It has a great affinity for water, rapid water absorption and large water absorption, high softness (good hand feeling), good elasticity; microscopic cells are delicate and have a mesh open structure, and its excellent biological Affinity and blood compatibility broaden its wide application in cosmetics and medical fields.
2. Current application scope:
The characteristics of hydrophilic polyurethane foam also determine that it will have good applications in certain fields.
(1) Nursing and sanitary supplies such as mattresses for bedridden patients, accessories for sanitary napkins,
(2) Medical accessories, surgical accessories (absorption of blood is similar to the effect of cotton wool),
(3) Accessories for wound dressing, such as medical anti-inflammatory products such as band-aids, etc.
(4) Daily cleaning block, bath block, etc.,
(5) Cosmetic care products, such as powder puffs, etc.,
(6) Absorption treatment materials in special fields.
Polyurethane soft water-philic (absorbent) foam is mainly because its molecular chain itself has a structure containing ethylene oxide and other similar segments and is hydrophilic; polyester polyols and polyether polyols only need to contain these or similar hydrophilic segments to a certain extent It can make water-absorbent foam products.
In terms of materials, there are polyether type and polyester type, but suitable production methods and raw materials are selected according to the application and specific requirements of the product.
3. Basic raw materials: the most commonly used mainly include the following,
(1) The polyol part is mainly polyether polyol, that is, polyether polyol with high EO content. Generally, the content is required to reach more than 50%. Both random and block copolymerization are possible. There are more random in actual production. The functionality is generally 2-3, the molecular weight is generally 1000-8000 can be used, the most commonly used is 2000-6000.
(2) Polyethylene glycol (PEG), molecular weight 1000-6000, most commonly used 1000-4000
(3) Polyester polyol, adipic acid series, polyol with high ethylene oxide structure, functionality 2-2.3, molecular weight 1000-2000
(4) Small molecular polyols (chain extenders or crosslinkers), commonly used are ethylene glycol, diethylene glycol, triethylene glycol, glycerol, TMP, etc.
(5) Isocyanate: the raw material of isocyanate here includes two types
TDI-100, TDI-80, HDI, IPDI, HMDI
(6), other additives
Surface active agent: Silicone oil series: L-580, Y10366, B8715, B-8123, etc.,
Foaming agent: mainly water,
Catalyst: Organotin, commonly used such as T-9, T-12, T-120, organic amines, such as A-33, pentamethyldiethylenetriamine, diazabicyclo(2,2,2)octane Alkane etc.,
Hydrophilic resins: such as polyacrylates, hydroxycellulose, etc.
6. Basic production methods
At present, there are two main process methods that have been industrialized or are being developed, one is the one-step method (the same as the production method of ordinary PU foam), and the other is the two-step method, the prepolymer method.
Here is a brief introduction to the basic process of the polyether two-step method (Dow Chemical already has a variety of such prepolymer brands in the international market, and the NCO% content ranges from 3% to 13%)
Typical two-step method:
(1) Prepolymer synthesis basic formula
Polyether polyol 0-100
Small molecule polyol 0-10
Catalyst 0.2-0.6
TDI 20-50 (HDI, IPDI, HMDI, etc. can be used for non-yellowing)
NCO% 3-14%
(2) Key points of prepolymer synthesis
(A) The polyol part must be dehydrated in a vacuum at a high temperature of 120°C in advance to less than 0.05%,
(B) Low-activity isocyanate needs to be catalyzed to promote the reaction process,
(C) Generally, the reaction temperature cannot be lower than 80℃,
(D) The viscosity is best controlled below 8000 mpa.s/25℃,
(E) The activity of different aliphatic isocyanates is different, and the process conditions need to be adjusted.
(F) The foam made of HMDI prepolymer is harder, and the water absorption performance will be reduced, and the structure is highly open.
(2) Foam foaming formula
Prepolymer 100
Water 10 or more (adjust as required)
Silicone oil L580 0.5-2.0
Polyether or polyol 0-30
Other additives 2-7
(3) Key points of manual foaming process
The stirring speed is 3000-5000 rpm, the stirring time is 4-8 seconds, and the temperature is controlled at 25-70°C.
(4) Foaming requirements for pouring machine
The metering gear pump requires high precision, the stirring speed is not less than 5000 rpm (the thickness of the production sheet is generally 2-5mm, the width is 500mm), the production line requires a drying tunnel of generally 15-30 meters, and the release paper can be used repeatedly .
The foam has an open-cell structure with a pore size of about 120-250 microns, and the usual density range is generally 100-200 (kg/m3).
7. Basic physical properties of polyether hydrophilic foam
(1) Water absorption performance
*The physical meaning of the MVTR test index: the water permeability per unit time area of the foam sheet (water vapor transmission capacity). Now the standard indexes in Europe and the United States are inconsistent, and the method is different. Conversion is not possible, only samples can be taken The same test method can be used for comparison, but the only water absorption speed index method is basically the same.
(2) Mechanical properties
An obvious defect of polyether-type water-absorbing foam is that its strength decreases greatly after absorbing water.
For PEG, the molecular weight is usually increased and the water absorption is enhanced. It is advisable to select a molecular weight of 1000-4000, otherwise the viscosity is too large.
7. Foaming process of one-step polyester hydrophilic foam
() If it is produced by manual intermittent tank foaming, it is basically the same as the ordinary polyester foam foaming method. It should be noted that the surfactant silicone oil must be special for polyester foam, and the catalyst is organic tin and organic amine. The morpholine-based composite type catalyst is usually more suitable.
Related physics and water absorption properties of polyester hydrophilic foam
* The hydrophilic foam samples tested above are processed. The processing method is to immerse the foam in lye at a certain temperature and time.
Second, the production formula and foaming process of non-yellowing sponge soft foam
1. At present, the bulk of polyurethane flexible foams (sponges) are easy to yellow, so now what everyone calls yellowing resistant foam usually refers to the addition of antioxidants, heat stabilizers and light stabilizers during foam production. This can temporarily alleviate the yellowing speed of the foam; it is easy to yellow because the benzene ring on the isocyanate can be gradually oxidized into a quinone structure and become yellow. In addition, the foam macromolecular chain contains carbonyl groups, amino groups, and azo groups. Chromophoric groups such as, alkenyl, etc., when light enters, will selectively absorb and emit light of a certain wavelength, resulting in a certain degree of soft foam yellowing.
2. Effective solutions to solve yellowing
The most effective way is to use non-yellowing aliphatic isocyanates for foaming. Aliphatic isocyanates, such as IPDI, HDI, and HMDI, etc. The urethane bonds formed by these isocyanates are relatively stable, even if they are decomposed into Aliphatic amines also have no benzene ring conjugated structure and will not form auxochrome groups, and the aliphatic amine itself is not easy to be oxidized, and is not easy to cause yellowing; therefore, the use of aliphatic isocyanates can significantly reduce the yellowing of foam.
3. Technical difficulties of aliphatic isocyanate foaming
In fact, many people have tried this aspect of foaming production for many years, but most people have encountered some technical problems more or less, that is, aliphatic isocyanates are generally low in activity, and the foaming process is more difficult to control. The range or latitude is very narrow, and it is difficult to make flexible foam that meets the requirements. The problems that often occur in the foaming process are: collapsed foam or partial collapsed foam, coarse foam, powdered surface or closed cells, more serious block Bubble shrinkage.
What needs to be explained here is that the foam sponge made of aliphatic isocyanate does not never turn yellow at all, but will oxidize and turn yellow very slowly under long-term light, water and heat conditions. The yellowing rate of this type of foam is very low, and it seems to people that it does not yellow.
4. Main raw materials and additives
(1) Polyol:
Polyether polyol Polyether 210, 220, 560s, etc.
Highly active polyether polyol, molecular weight 4500-6000, such as 330N, 4701, etc.
Small molecule polyols ethylene glycol, propylene glycol, butylene glycol, DEG, DPG,
(2) The commonly used isocyanates are HDI, IPDI, HMDI,
(3) Catalysts, there are mainly two types of catalysts. One is organic amines, which are foaming and gel types. The main ones that can be used are: triethylenediamine, pentamethyldiethylenetriamine, pentamethyl Dipropylene triamine, triethylamine, diazabicyclo(2,2,2)octane, dimethylcyclohexylamine, 2,4,6-tris(dimethylaminomethyl)phenol, etc.; metals The main catalysts are: stannous octoate, organic bismuth, organic zirconium, organic titanium, and organic cobalt.
(4) Surfactant, mainly including high activity and medium activity, such as L-580, B-8123, B-8002, L-6900, DC-4900, DC-5169, B-8681, Y-10366 .
(5) Foaming agent, water and its physical foaming agent
5. Basic formula
Highly active polyether polyol 90-100
Polyether 560s 0-10
Small molecule polyol 0-10
IPDI 25-45
Water 1.5-2.5
Silicone oil B 8123 1.0-2.0
The above amine catalyst 0.2-1.5
Metal salt catalyst 0.5-1.75
Opening aid 0.5-3.0 (pore opening agent for high resilience such as KF-28)
6. Foaming process
Different people or regions may have different foaming process methods. The main reason is that the formula, catalyst selection and dosage are different. The plan or method is not unique. The method here is only for reference.
Highly active polyether and other additives are mixed uniformly at room temperature in advance, then poured into IPDI and stirred for 6-15 seconds evenly, then poured into the pre-heated foaming box, it is best to use an oven not lower than 30 ℃ for heat preservation and foaming, 20 -30 minutes later, push the block out and aging at room temperature for 24 hours before cutting. The cells are uniform and delicate, with high strength, good elasticity, no powdering, and generally do not shrink. You need to press lightly when shrinking slightly. Need special reminder not to use grafted polyether polyol.
7. The difference in reactivity between different aliphatic isocyanates and hydroxyl groups
This is a technical difficulty in the production of aliphatic isocyanate foam. The key to the technology is the selection and adjustment of formula and catalyst. There are still some technical know-hows.
8. Anti-yellowing performance of foam
According to the ASTM-D-1148 yellowing resistance test method, the test conditions are: 50℃, 300 watts of Xenon light illumination results:
From the test results in the above table, it can be seen that the yellowing resistance of aliphatic isocyanate foam is relatively excellent.
Third, talk about the foaming production formula and technology of microporous flexible foam materials
1. Application of microporous soft foam
What needs to be explained here is that microcellular foam does not refer to microporous PU elastomers (such as shoe soles, insoles, high-speed rail gaskets, tires, car springs and other foams), but a soft, high-density polyurethane foam sheet. It is a special soft polyurethane foam. The typical cell structure is shown in Figure-1.
This flexible polyurethane foam sheet has been widely used in communications, computers, household appliances, digital products, other electronic products, shoe materials, medical equipment, hardware, etc. as sealing, shock absorption, and cushioning materials.
2. Outstanding features
High sealing, high energy absorption (high cushioning), high dimensional stability.
Excellent resistance to compression deformation, water resistance, high temperature resistance, aging resistance, environmental protection and pollution-free.
3. Density and specifications
The density of this kind of soft foam is generally between 240-480kg/m3, and the pore size of the foam is generally 100-250 microns. Different application fields or different products have different density, thickness and hardness, and the opening and closing of microcellular foam. Pore degree, etc., the performance is also different; for example, the sealing, waterproof, and dustproof effect of the foam with high closed cell rate is more prominent; the high micropore open rate has good elasticity, and the compression deformation is small; the thickness generally ranges from 0.1-6mm. Total selection, there will be many specific detailed specifications.
4. Similar typical products at home and abroad
There are Rogers’ PORON brand, Japan’s Inoue poron, South Korea’s SK and GMC’s similar products.
The physical properties of several typical microporous flexible foam sheets (taking poron as an example)
6. Material and formula composition
(1) The basic composition of the hydroxyl component: Polyester polyol 16-30
Polyether polyol 0-50
Polymer polyether polyol 20-40
Small molecule polyol 1.5-16
Surface active agent (silicone oil) 0.1-1.0
Color paste 0.5-3.0 (mainly carbon black paste)
Antioxidant 0.2-0.4
Solid powder 0-20 (silica, aluminum hydroxide,)
Flame retardant appropriate amount (on request)
Organometallic catalyst
Organic amine catalyst 0-0.5
(For different specifications
Keywords: polyurethane, hydrophilic foam, non-yellowing foam, microcellular foam, formulation design
About the author: Jiang Shuhui, born in Suzhou, Anhui Province in 1953, senior engineer, has been engaged in the production and research and development of polyurethane materials for 38 years. He has worked in the production, technology and research and development of polyurethane materials in Dow Chemical, Japan, and Inoue China Technology Center of Japan. After that, he worked for many years in the development of polyurethane technology in Suzhou Yitong Polyurethane Company and Zhejiang Huafeng Group Shanghai New Materials Research Institute.
Polyurethane flexible foam refers to a porous or reticulated foam (sponge) material with certain elasticity and relatively soft. Its outstanding properties are softness, good resilience, sound absorption, ventilation, heat preservation, cushioning, energy absorption, etc., and according to different There are also various characteristics of the application field.
Polyurethane flexible foam has been industrially produced since Bayer’s polyester flexible foam (sponge) in 1952. After more than 60 years of development, it has been widely used in all aspects of people’s daily life and many industrial fields. At present, domestic flexible foam The actual output is estimated at more than 3 million tons. The main types of products include shockproof materials, sound insulation materials, filter materials, warmth-keeping materials, packaging materials, decoration materials, clothing materials, etc. In terms of the type of production, the flexible polyurethane foam mainly includes: block foam (ordinary sponge), high resilience molded foam, self-skin foam, slow resilience foam, etc. What I want to introduce below is a kind of special polyurethane soft sponge, specific products such as water-friendly (absorbent) foam, non-yellowing foam and microporous sheet sponge; these are also soft polyurethane foam, but are different from the above-mentioned ordinary polyurethane soft Compared with high-quality foam, each has special properties and applications, and is also an indispensable product for people's daily life and industrial production. This article introduces the basic raw materials, production processes and formulas of these foams.
First, the production formula and process of hydrophilic polyurethane flexible foam
1. Its basic characteristics: It has a great affinity for water, rapid water absorption and large water absorption, high softness (good hand feeling), good elasticity; microscopic cells are delicate and have a mesh open structure, and its excellent biological Affinity and blood compatibility broaden its wide application in cosmetics and medical fields.
2. Current application scope:
The characteristics of hydrophilic polyurethane foam also determine that it will have good applications in certain fields.
(1) Nursing and sanitary supplies such as mattresses for bedridden patients, accessories for sanitary napkins,
(2) Medical accessories, surgical accessories (absorption of blood is similar to the effect of cotton wool),
(3) Accessories for wound dressing, such as medical anti-inflammatory products such as band-aids, etc.
(4) Daily cleaning block, bath block, etc.,
(5) Cosmetic care products, such as powder puffs, etc.,
(6) Absorption treatment materials in special fields.
Polyurethane soft water-philic (absorbent) foam is mainly because its molecular chain itself has a structure containing ethylene oxide and other similar segments and is hydrophilic; polyester polyols and polyether polyols only need to contain these or similar hydrophilic segments to a certain extent It can make water-absorbent foam products.
In terms of materials, there are polyether type and polyester type, but suitable production methods and raw materials are selected according to the application and specific requirements of the product.
3. Basic raw materials: the most commonly used mainly include the following,
(1) The polyol part is mainly polyether polyol, that is, polyether polyol with high EO content. Generally, the content is required to reach more than 50%. Both random and block copolymerization are possible. There are more random in actual production. The functionality is generally 2-3, the molecular weight is generally 1000-8000 can be used, the most commonly used is 2000-6000.
(2) Polyethylene glycol (PEG), molecular weight 1000-6000, most commonly used 1000-4000
(3) Polyester polyol, adipic acid series, polyol with high ethylene oxide structure, functionality 2-2.3, molecular weight 1000-2000
(4) Small molecular polyols (chain extenders or crosslinkers), commonly used are ethylene glycol, diethylene glycol, triethylene glycol, glycerol, TMP, etc.
(5) Isocyanate: the raw material of isocyanate here includes two types
TDI-100, TDI-80, HDI, IPDI, HMDI
(6), other additives
Surface active agent: Silicone oil series: L-580, Y10366, B8715, B-8123, etc.,
Foaming agent: mainly water,
Catalyst: Organotin, commonly used such as T-9, T-12, T-120, organic amines, such as A-33, pentamethyldiethylenetriamine, diazabicyclo(2,2,2)octane Alkane etc.,
Hydrophilic resins: such as polyacrylates, hydroxycellulose, etc.
6. Basic production methods
At present, there are two main process methods that have been industrialized or are being developed, one is the one-step method (the same as the production method of ordinary PU foam), and the other is the two-step method, the prepolymer method.
Here is a brief introduction to the basic process of the polyether two-step method (Dow Chemical already has a variety of such prepolymer brands in the international market, and the NCO% content ranges from 3% to 13%)
Typical two-step method:
(1) Prepolymer synthesis basic formula
Polyether polyol 0-100
Small molecule polyol 0-10
Catalyst 0.2-0.6
TDI 20-50 (HDI, IPDI, HMDI, etc. can be used for non-yellowing)
NCO% 3-14%
(2) Key points of prepolymer synthesis
(A) The polyol part must be dehydrated in a vacuum at a high temperature of 120°C in advance to less than 0.05%,
(B) Low-activity isocyanate needs to be catalyzed to promote the reaction process,
(C) Generally, the reaction temperature cannot be lower than 80℃,
(D) The viscosity is best controlled below 8000 mpa.s/25℃,
(E) The activity of different aliphatic isocyanates is different, and the process conditions need to be adjusted.
(F) The foam made of HMDI prepolymer is harder, and the water absorption performance will be reduced, and the structure is highly open.
(2) Foam foaming formula
Prepolymer 100
Water 10 or more (adjust as required)
Silicone oil L580 0.5-2.0
Polyether or polyol 0-30
Other additives 2-7
(3) Key points of manual foaming process
The stirring speed is 3000-5000 rpm, the stirring time is 4-8 seconds, and the temperature is controlled at 25-70°C.
(4) Foaming requirements for pouring machine
The metering gear pump requires high precision, the stirring speed is not less than 5000 rpm (the thickness of the production sheet is generally 2-5mm, the width is 500mm), the production line requires a drying tunnel of generally 15-30 meters, and the release paper can be used repeatedly .
The foam has an open-cell structure with a pore size of about 120-250 microns, and the usual density range is generally 100-200 (kg/m3).
7. Basic physical properties of polyether hydrophilic foam
(1) Water absorption performance
*The physical meaning of the MVTR test index: the water permeability per unit time area of the foam sheet (water vapor transmission capacity). Now the standard indexes in Europe and the United States are inconsistent, and the method is different. Conversion is not possible, only samples can be taken The same test method can be used for comparison, but the only water absorption speed index method is basically the same.
(2) Mechanical properties
An obvious defect of polyether-type water-absorbing foam is that its strength decreases greatly after absorbing water.
For PEG, the molecular weight is usually increased and the water absorption is enhanced. It is advisable to select a molecular weight of 1000-4000, otherwise the viscosity is too large.
7. Foaming process of one-step polyester hydrophilic foam
() If it is produced by manual intermittent tank foaming, it is basically the same as the ordinary polyester foam foaming method. It should be noted that the surfactant silicone oil must be special for polyester foam, and the catalyst is organic tin and organic amine. The morpholine-based composite type catalyst is usually more suitable.
Related physics and water absorption properties of polyester hydrophilic foam
* The hydrophilic foam samples tested above are processed. The processing method is to immerse the foam in lye at a certain temperature and time.
Second, the production formula and foaming process of non-yellowing sponge soft foam
1. At present, the bulk of polyurethane flexible foams (sponges) are easy to yellow, so now what everyone calls yellowing resistant foam usually refers to the addition of antioxidants, heat stabilizers and light stabilizers during foam production. This can temporarily alleviate the yellowing speed of the foam; it is easy to yellow because the benzene ring on the isocyanate can be gradually oxidized into a quinone structure and become yellow. In addition, the foam macromolecular chain contains carbonyl groups, amino groups, and azo groups. Chromophoric groups such as, alkenyl, etc., when light enters, will selectively absorb and emit light of a certain wavelength, resulting in a certain degree of soft foam yellowing.
2. Effective solutions to solve yellowing
The most effective way is to use non-yellowing aliphatic isocyanates for foaming. Aliphatic isocyanates, such as IPDI, HDI, and HMDI, etc. The urethane bonds formed by these isocyanates are relatively stable, even if they are decomposed into Aliphatic amines also have no benzene ring conjugated structure and will not form auxochrome groups, and the aliphatic amine itself is not easy to be oxidized, and is not easy to cause yellowing; therefore, the use of aliphatic isocyanates can significantly reduce the yellowing of foam.
3. Technical difficulties of aliphatic isocyanate foaming
In fact, many people have tried this aspect of foaming production for many years, but most people have encountered some technical problems more or less, that is, aliphatic isocyanates are generally low in activity, and the foaming process is more difficult to control. The range or latitude is very narrow, and it is difficult to make flexible foam that meets the requirements. The problems that often occur in the foaming process are: collapsed foam or partial collapsed foam, coarse foam, powdered surface or closed cells, more serious block Bubble shrinkage.
What needs to be explained here is that the foam sponge made of aliphatic isocyanate does not never turn yellow at all, but will oxidize and turn yellow very slowly under long-term light, water and heat conditions. The yellowing rate of this type of foam is very low, and it seems to people that it does not yellow.
4. Main raw materials and additives
(1) Polyol:
Polyether polyol Polyether 210, 220, 560s, etc.
Highly active polyether polyol, molecular weight 4500-6000, such as 330N, 4701, etc.
Small molecule polyols ethylene glycol, propylene glycol, butylene glycol, DEG, DPG,
(2) The commonly used isocyanates are HDI, IPDI, HMDI,
(3) Catalysts, there are mainly two types of catalysts. One is organic amines, which are foaming and gel types. The main ones that can be used are: triethylenediamine, pentamethyldiethylenetriamine, pentamethyl Dipropylene triamine, triethylamine, diazabicyclo(2,2,2)octane, dimethylcyclohexylamine, 2,4,6-tris(dimethylaminomethyl)phenol, etc.; metals The main catalysts are: stannous octoate, organic bismuth, organic zirconium, organic titanium, and organic cobalt.
(4) Surfactant, mainly including high activity and medium activity, such as L-580, B-8123, B-8002, L-6900, DC-4900, DC-5169, B-8681, Y-10366 .
(5) Foaming agent, water and its physical foaming agent
5. Basic formula
Highly active polyether polyol 90-100
Polyether 560s 0-10
Small molecule polyol 0-10
IPDI 25-45
Water 1.5-2.5
Silicone oil B 8123 1.0-2.0
The above amine catalyst 0.2-1.5
Metal salt catalyst 0.5-1.75
Opening aid 0.5-3.0 (pore opening agent for high resilience such as KF-28)
6. Foaming process
Different people or regions may have different foaming process methods. The main reason is that the formula, catalyst selection and dosage are different. The plan or method is not unique. The method here is only for reference.
Highly active polyether and other additives are mixed uniformly at room temperature in advance, then poured into IPDI and stirred for 6-15 seconds evenly, then poured into the pre-heated foaming box, it is best to use an oven not lower than 30 ℃ for heat preservation and foaming, 20 -30 minutes later, push the block out and aging at room temperature for 24 hours before cutting. The cells are uniform and delicate, with high strength, good elasticity, no powdering, and generally do not shrink. You need to press lightly when shrinking slightly. Need special reminder not to use grafted polyether polyol.
7. The difference in reactivity between different aliphatic isocyanates and hydroxyl groups
This is a technical difficulty in the production of aliphatic isocyanate foam. The key to the technology is the selection and adjustment of formula and catalyst. There are still some technical know-hows.
8. Anti-yellowing performance of foam
According to the ASTM-D-1148 yellowing resistance test method, the test conditions are: 50℃, 300 watts of Xenon light illumination results:
From the test results in the above table, it can be seen that the yellowing resistance of aliphatic isocyanate foam is relatively excellent.
Third, talk about the foaming production formula and technology of microporous flexible foam materials
1. Application of microporous soft foam
What needs to be explained here is that microcellular foam does not refer to microporous PU elastomers (such as shoe soles, insoles, high-speed rail gaskets, tires, car springs and other foams), but a soft, high-density polyurethane foam sheet. It is a special soft polyurethane foam. The typical cell structure is shown in Figure-1.
This flexible polyurethane foam sheet has been widely used in communications, computers, household appliances, digital products, other electronic products, shoe materials, medical equipment, hardware, etc. as sealing, shock absorption, and cushioning materials.
2. Outstanding features
High sealing, high energy absorption (high cushioning), high dimensional stability.
Excellent resistance to compression deformation, water resistance, high temperature resistance, aging resistance, environmental protection and pollution-free.
3. Density and specifications
The density of this kind of soft foam is generally between 240-480kg/m3, and the pore size of the foam is generally 100-250 microns. Different application fields or different products have different density, thickness and hardness, and the opening and closing of microcellular foam. Pore degree, etc., the performance is also different; for example, the sealing, waterproof, and dustproof effect of the foam with high closed cell rate is more prominent; the high micropore open rate has good elasticity, and the compression deformation is small; the thickness generally ranges from 0.1-6mm. Total selection, there will be many specific detailed specifications.
4. Similar typical products at home and abroad
There are Rogers’ PORON brand, Japan’s Inoue poron, South Korea’s SK and GMC’s similar products.
The physical properties of several typical microporous flexible foam sheets (taking poron as an example)
6. Material and formula composition
(1) The basic composition of the hydroxyl component: Polyester polyol 16-30
Polyether polyol 0-50
Polymer polyether polyol 20-40
Small molecule polyol 1.5-16
Surface active agent (silicone oil) 0.1-1.0
Color paste 0.5-3.0 (mainly carbon black paste)
Antioxidant 0.2-0.4
Solid powder 0-20 (silica, aluminum hydroxide,)
Flame retardant appropriate amount (on request)
Organometallic catalyst
Organic amine catalyst 0-0.5
(For different specifications
Liu Bin