Examples of the hottest polyurethane sealant ingre

2022-08-23
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Examples of polyurethane sealant formula components (I)

1 Polyurethane prepolymer

one component moisture curing polyurethane sealant is composed of NCO based prepolymer, filler and additive, and its composition ratio is roughly as follows:

prepolymer thixotropic agent 0-5

filler and pigment catalyst 0-0.5

plasticizer 5-25 stabilizer 0-0.5

solvent 0-10 other 0-5

two component polyurethane sealant is composed of main agent and curing agent. Among them, the main agent is generally NCO terminated prepolymer, and the curing agent is generally composed of active hydrogen compounds such as polyether polyols, fillers, thixotropic agents and other additives. The composition ratio is roughly:

polyether polyols 15-20 plasticizers 0-15

fillers 55-65 catalysts 0..5

thixotropic agents 0-3 other 0-5

prepolymers in one-component adhesives and polyether in two-component adhesives and curing agents, It is the base polymer of sealant. Basic polymers account for about 35% - 65% of the sealant, and their cured properties have a great impact on the performance of the whole sealant

compared with the other two types of elastic sealant silicone and polysulfide, a special advantage of polyurethane adhesive is that the raw material composition and structure of polyurethane resin can vary widely, because the degree of freedom of polyurethane molecular design is large. This section will introduce the main component of polyurethane sealant - polyurethane prepolymer of 175 steel pipe scaffold fasteners, and the relationship between its composition and structure and the performance of sealant

2. NCO terminated polyurethane prepolymer

prepolymer is an important component of Pu sealant formula. The basic polymer used in most Pu sealant is pure NCO terminated polyether PU prepolymer. During its preparation, suitable prepolymers are usually prepared by selecting the molecular weight of Polyether Polyols (generally diols or triols), the proportion of diols and triols mixed, and the types of diisocyanates (TDI and MDI). When designing the preparation formula of prepolymer, it is generally considered to control the NCO/Oh molar ratio of raw materials within the range of 1.5-2.5, and the mass percentage of free NCO of the prepared prepolymer is between 1% and 4%

according to the report of ITO et al. Of sunsta Technology Research Co., Ltd., prepolymer A is prepared by using polyoxypropylene ethylene oxide triol with molecular weight between (the amount of EO chain link is less than 20%) and excess MDI, and prepolymer B is prepared by reacting PPG with excess TDI. A. B mix with the mass ratio of 95:5--70:30 (preferably in the range of 90:10--80:20) to obtain the mixed prepolymer as the basic polymer of one component PU sealant

as another example, 3000g of propylene oxide ethylene oxide triol with molecular weight of 7000 (the amount of EO is 15%) reacts with 370g of MDI at about 80 ℃ after vacuum dehydration, and 1 g of 1% toluene solution of catalyst dbdtl is added. The reaction is continued for 4 hours and then cooled. The content of free NCO in this prepolymer is 2.2%, and the viscosity at 20 ℃ is 4.5pa · s

Another prepolymer with viscosity of 15pa · s and free NCO content of 2.0% was prepared from 3000g PPG with molecular weight of 3000 and 298g TDI

450g of the mixture of the above two prepolymers, 300g of DOP, 550G of dry carbon black and 80g of toluene are kneaded in vacuum, then 0.5g of curing catalyst dbdtl is added, mixed and sealed. The adhesive has the required curing speed (20 ℃ and 65%rh, non stick time of about 45 minutes, time of drying and fixing of about 10min), hardness (according to jisk6301), tensile strength of about 6Mpa, elongation of 550%-600%, and good storage stability. The sealant is suitable for painted parts on the surface, and primer is not required

in this example, if the proportion of prepolymer a in the mixed prepolymer is less than 70%, the curing speed is low, and the strength of the cured product decreases (for example, when the first prepolymer accounts for about 67%, and the second prepolymer accounts for about 33%, the overall tensile strength of the sealant is about 4MPa, and the hardness is about 45). When prepolymer A is used completely, the curing speed of sealant is too fast

3. Closed prepolymer system

for one component polyurethane sealant, how to shorten the curing time without foaming due to C02 diffusion and ensure storage stability has always been the focus of research, because compared with adhesives, especially solvent based adhesives, the curing of sealant is shortened slowly. For the two-component solvent-free adhesive and sealing colloid system, it can be solved by adding catalyst to the hydroxyl component. The single component wet curing adhesive, if equipped with more catalysts, can improve the curing speed, but may cause the storage stability to decline. Therefore, in order to suppress the accuracy of the experimental results, it is difficult to ensure the cross-linking reaction between the free NCO group and the urethane bond (i.e. the formation reaction of urea formate) and other side reactions of the free NCO, improve the storage stability of the prepolymer, and can quickly cure without foaming. The sealing method can be used to partially or completely seal the NCO group at the end of the prepolymer, or the sealed diamine (i.e. two-component single package) can be mixed in the one-component glue. When the sealant is used, Under the action of moisture in the air and catalyst in the glue, the blocked group dissociates and carries out cross-linking and curing reaction

(1) the sealing agent used by the sealing prepolymer in the sealing of one component PU sealant is generally compounds containing active methyl groups, such as dimethyl malonate, diethyl malonate, acetylacetone, ethyl acetoacetate, etc

the following describes a closed Pu sealant formula

the formula of the closed prepolymer is:

high activity polyether 350 phr stannous octanoate

MDL 40 diethyl malonate

with the above closed prepolymer, Prepare one-component sealant according to the following formula:

partially sealed prepolymer 33.3 partially hydrogenated terphenyl

furnace carbon black 9.9 toluene

thermal carbon black 34.3 1, 2, 4-trimethylpiperazine

the one-component polyurethane sealant of this formula has no foaming in high temperature and high humidity environment, fast curing (about 50min non stick time at 20t and 65% RH), and high strength

(2) one component system composed of prepolymer and latent curing agent in order to avoid direct reaction of water with free NCO groups in prepolymer, some people have studied some types of latent curing systems. These latent curing agents are blocked polyamines (such as ketimine, aldehyde imine, ketene) or compounds that can produce polyamines after hydrolysis (such as oxazolidine)

the above compounds are hydrolyzed with moisture at room temperature to obtain primary or secondary amines, which can react rapidly with free NCO in PU prepolymer to form polyurethane urea and cure. Because the reaction rate between amine and NCO is much faster than that of water, in fact, water does not directly participate in the curing reaction of NCO group, so bubbles will not be generated

because keto imine is extremely sensitive to water, the primary amine produced after hydrolysis has high activity and can react with NCO quickly. Therefore, if keto imine is used as a latent curing system, the prepolymer should preferably also be blocked, and the blocking agent is phenol with low dissociation activity at room temperature, substituted phenols, caprolactam, etc. This is because the primary amine has high activity and can promote the deblocking of the blocked prepolymer and react with it

the following is a formula example of one component PU sealant composed of closed prepolymer and latent curing agent (closed polyamine)

formula for preparing blocked PU prepolymer (mass fraction):

polyether triol (mw6200) 4310 3-hydroxymethylphenol 248

toluene diisocyanate 384 dibutyltin dilaurate 2

toluene 500

formula for preparing blocked crosslinker (mass fraction):

polyoxypropylene diamine (mw400) 3246 methyl trimethoxysilane 104

methyl isobutyl ketone 454 2,2,4-trimethyl hexamethylene 188

p-methylbenzenesulfonic acid 4.3 methyl diisocyanate these facilities have also passed the ISO 13485 medical device quality management certification, ester

sealant formula (mass fraction) :

the above closed prepolymer 100 methyltriethoxysilane 3.5

surface treatment calcium carbonate 42.5 methanol 0.88

thixotropic agent 15.7 operating oil 3.9

pigment 7.5 Trimethylphenol phosphate 15.9

aminopropyl triethoxysilane 1.0 closed crosslinker 8.5

relatively speaking, the enamine system and nianzolidine system are latent curing agents that are less sensitive to moisture and temperature, which are more promising than ketone (aldehyde) imines in practice. If the enamine system is used, the aromatic PU prepolymer still needs to be blocked because of its high activity; NCO of aliphatic or alicyclic prepolymers does not need to be closed

as a latent curing crosslinker of sealant or adhesive system, the influence of released sealant (such as ketone) on the properties of cured products should be considered when using

a kind of Ji'nan assay ring expanding experimental machine is mainly used in steel pipe enterprises and steel pipe welding after welding and the performance and strength test of the whole pipe. The properties of the wet cured Pu sealant used in the "enamine system" are as follows:

100% modulus 0.2MPa curing rate (20 ℃) 3mm/d

elongation 450% sag no

recovery rate after 100% elongation 80% storage stability 6 months

hardness (Shore A) 15

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