The design of adhesive is to obtain the final use performance as the purpose. The formulation design of polyurethane adhesive should consider the construction (operability), curing conditions bonding strength, heat resistance, chemical resistance, durability other performance requirements of the adhesive.
Polyurethane molecular design - structure properties polyurethane, because of the variety composition of its varieties, can be used to synthesize various kinds of high-performance polymers, for example, the appearance of its bulk materials (i.e. solvent free), it can be obtained soft to rigid elastomer, foam material, polyurethane its physical properties ( its cured products). Basically, the properties of the last elastomer, some of its physical chemical properties, such as adhesive strength, mechanical properties, durability, low temperature resistance drug resistance, mainly depend on the chemical structure of the cured polyurethane. Therefore, molecular design is the first step in the formulation design of polyurethane adhesive, That is to know the relationship between the variety of polyurethane raw materials the chemical structure properties the influence of chemical structure composition on properties.
The preparation of PU adhesive is designed the perspective of raw materials. Three kinds of raw materials are commonly used in the formulation of polyurethane adhesive: NCO raw materials (i.e. diisocyanate its modifier, polyisocyanate), one is oh type raw materials (i.e., oligomer polyol chain extender containing hydroxyl group, in a broad sense, it is a compound containing active hydrogen, so it also includes polyamine, water, etc.), There are two methods to design the formula of polyurethane adhesive the perspective of raw materials.
(1) The simplest preparation method of polyurethane adhesive directly prepared the above raw materials is that 0h raw materials NCO raw materials ( additives) are simply mixed directly used. This method is often used in the formulation design of polyurethane adhesives, because most of the oligomer polyols have low content (usually polyether Mr < 6000, polyester Mr < 3000), Therefore, the prepared adhesive composition has low viscosity low initial adhesion. Sometimes, even if catalyst is added, the curing speed is still slow, the strength of the cured product is low, so the practical value is great. Moreover, the steam pressure of the unmodified TDI is high, the smell is big, the volatilization toxicity is high. However, MDI is solid at room temperature, which is inconvenient to use, Only a few commercial polyisocyanates, such as papledesmodur rdesmodur rfcoronate L, can be used as isocyanate raw materials. However, there are several cases in which polyurethane adhesives can be prepared by the above methods, such as
1) The two-component polyurethane adhesive composed of organic solution of high molecular weight polyester (mr5000-50000) polyisocyanate solution (such as coronate L) can be used for laminating films with good performance, because the main component of high molecular weight polyester has high initial adhesion force high cohesive strength
(2) The composition composed of polyether ( polyester) water, polyisocyanate, catalyst, etc. has a certain practical value as foaming polyurethane adhesive, adhesive, bonding manufacturing of thermal insulation materials.
(2) As mentioned above, most oligomer polyols have low molecular weight, high volatile toxicity of TDI, MDI is solid at room temperature, the general properties of directly prepared adhesive are poor. Therefore, in order to improve the initial viscosity of the adhesive shorten the time required to produce a certain adhesive strength, polyether polyester polyol is usually reacted with TDI MDI monomer, The NCO Oh terminated carbamate prepolymer is prepared used as NCO component Oh component.
The PU adhesive is designed according to the requirements of the use form, which is divided into single component two-component.
A. One component polyurethane adhesive
The advantage of one component polyurethane adhesive is that it can be used directly without the trouble of mixing before using two-component adhesive. There are two main types of one component polyurethane adhesive.
(1) Wet curing polyurethane adhesive with NCO terminated polyurethane prepolymer as the main body is synthesized cured by using trace moisture in the air micro adsorbed water on the surface of the substrate. It can also react with the active hydrogen groups on the surface of the substrate to form a strong chemical bond. This type of polyurethane adhesive is generally solvent-free, its viscosity cannot be too high for the convenience of sizing, One component wet curing polyurethane adhesive is mostly polyether type, that is, the main raw material containing monooh is polyether polyol. The appropriate content of free NCO in this kind of adhesive should be determined according to the viscosity (affecting operability), coating method, thickness type of adhesive, the storage stability of the adhesive should be considered
(2) One component solvent based polyurethane adhesive based on thermoplastic polyurethane elastomer, the main component is high molecular weight Oh terminated baseline polyurethane, the hydroxyl number is very small. When the solvent begins to volatilize, the viscosity of the adhesive increases rapidly, resulting in the initial adhesion force. When the solvent is basically completely volatilized, sufficient adhesion force is generated. After being placed at room temperature, most of the polyurethane elastomers crystallize in the chain segment, This kind of one component polyurethane adhesive generally uses crystalline polyester as the main raw material of polyurethane. One component polyurethane adhesive also has polyurethane hot melt adhesive, one component waterborne polyurethane adhesive so on.
B. Two component polyurethane adhesive
The two-component polyurethane adhesive is composed of the main agent containing hydroxyl end group curing agent containing NCO group. Compared with single component, the two-component polyurethane adhesive has better performance higher bonding strength. The two-component distribution ratio of the same two-component polyurethane adhesive can allow a certain range, which can adjust the properties of the cured product,
PU adhesive is designed according to performance requirements. If there are special performance requirements for polyurethane adhesive, formula design should be carried out according to the relationship between polyurethane structure performance. Different substrates, different application fields application environment often have some special requirements for polyurethane adhesive. For example, polyurethane adhesive used in industrial production line requires rapid curing, The polyurethane adhesive for composite flexible packaging film is required to be acid resistant hydrolysis resistant, the adhesive for cooking flexible packaging also requires a certain degree of high temperature adhesion, etc.
A. High temperature resistance polyurethane adhesive is generally insufficient in high temperature resistance. If it is to be used in special temperature resistant occasions, the polyurethane adhesive can be designed in advance. There are several ways to improve the heat resistance of polyurethane adhesive, such as
1) Polyether, polyester isocyanate containing benzene ring were used as raw materials
(2) Increase the content of isocyanate chain extender (they form hard segment)
(3) Increase the amount of curing agent
(4) High temperature resistant polyisocyanate (if containing
Isocyanurate ring), isocyanurate is produced during curing
(5) It is an effective way to improve the compatibility of polymer by blending epoxy resin polysulfonamide with polyurethane, using PN technology.
B. Hydrolysis resistance: the hydrolysis resistance of polyester polyurethane adhesive is poor. Hydrolysis stabilizer (such as carbodiimide? Epoxy compound, etc.) can be added to improve the hydrolysis resistance of polyester. In order to improve the hydrolysis resistance of polyester, long-chain dicarboxylic acid diols (such as sebacic acid, 1,6-hexanediol, etc.) can be used, Branched diols such as neopentyl glycol can also improve the hydrolysis resistance of polyester? Polyether has better hydrolysis resistance. Sometimes it can be used with polyester to prepare polyurethane adhesive. Adding a small amount of silicone coupling agent in the adhesive formula can also improve the hydrolysis resistance of the adhesive layer.
C. One of the main methods to improve the curing speed is to make the polyurethane adhesive have a certain initial adhesion, that is, it is no longer easy to separate after bonding. Therefore, increasing the molecular weight of the main agent using raw materials that can produce crystalline polyurethane are effective methods to improve the initial adhesion curing speed, Sometimes adding a small amount of triethanolamine as a catalytic crosslinking agent can also help to improve the initial viscosity? Adding catalyst is also the main way to accelerate the curing
1、 Two component polyurethane adhesive
100 parts of TDI modified tree ester (dissolved in ethyl acetate) of component a toluene diisocyanate (TDI)
10-50 parts of modification of hydroxyl compound of component B curing agent TDI
This method is suitable for the adhesion between metals. A kind of
100 parts of component A 10 parts of component B
This method is suitable for bonding between general materials. A kind of
Component A: 100 parts; component B: 5-10 parts
This method is suitable for the bonding between paper, leather wood. A kind of
2、 One component polyurethane adhesive
Formula: 38 parts of castor oil
Toluene diisocyanate 11.75 phr, styrene 49.75 phr, dibenzoyl peroxide 0.5 phr
When the temperature is above 20-80 ℃, the mixture is uniform. A kind of
This product is suitable for packaging of electrical materials.