CN112852373B - Moisture-curing type polyurethane hot melt adhesive - Google Patents
Moisture-curing type polyurethane hot melt adhesive Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
- C09J175/00—Adhesives based on polyureas or polyurethanes; Adhesives based on derivatives of such polymers
- C09J175/04—Polyurethanes
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/30—Low-molecular-weight compounds
- C08G18/32—Polyhydroxy compounds; Polyamines; Hydroxyamines
- C08G18/3225—Polyamines
- C08G18/3253—Polyamines being in latent form
- C08G18/3256—Reaction products of polyamines with aldehydes or ketones
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- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
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Abstract
The invention discloses a moisture-curing polyurethane hot melt adhesive which comprises the following raw materials in parts by weight: 20-30 parts of thermoplastic resin, 15-25 parts of polyester polyol, 25-35 parts of polyether polyol, 3-8 parts of trifunctional micromolecule polyol, 15-25 parts of polyisocyanate, 0.01-1 part of catalyst, 3-5 parts of latent curing agent, 0.4-5 parts of silane coupling agent and 0.1-2 parts of defoaming agent. The latent curing agent is aldimine and/or ketimine, and preferably, the latent curing agent also comprises disilazane and/or cyclodisilazane. The latent curing agent is applied to the moisture curing type polyurethane hot melt adhesive, and the problem of bubbles in the thick adhesive layer and large-area bonding and curing process of the polyurethane hot melt adhesive is successfully solved. Secondly, the latent curing agent used in the invention can also reduce the viscosity of the colloid, so that the colloid has better shear strength.
Description
Technical Field
The invention belongs to the technical field of polyurethane sealants, and particularly discloses a deep-curable moisture-curable polyurethane hot melt adhesive.
Background
The moisture curing type polyurethane hot melt adhesive is prepared by synthesizing an isocyanate group-terminated prepolymer from polyester or polyether polyol and diisocyanate and adding additives such as thermoplastic resin which does not react with isocyanate groups, tackifying resin, an antioxidant, an accelerator, a catalyst and the like. In the using process, the isocyanate end group in the glue layer reacts with ultraviolet light or moisture in the air to generate chemical crosslinking and solidification, so that the bonding effect is achieved. Therefore, the moisture-curable polyurethane hot melt adhesive has the characteristics of high initial viscosity, high positioning speed and the like of the hot melt adhesive, has the characteristics of heat resistance, water resistance, chemical resistance, creep resistance and the like, and is widely applied to the industries such as the automobile industry, the shoe industry, the textile industry, the wood industry, the electronic industry, white household appliances, book binding and the like.
In the curing process of the conventional moisture-curing polyurethane hot melt adhesive, isocyanate groups and moisture in the air are subjected to chemical reaction to release CO2Gas productionIf the generated gas cannot be timely dissipated into the air, bubbles are generated inside the adhesive layer, and the bonding strength and the appearance are affected. Meanwhile, the permeation of moisture in the air to the colloid is a slow diffusion process from outside to inside, the surface layer is high in skinning speed, and a gas escape channel is blocked, so that the bubbling phenomenon is frequent in the practical application of sealing and bonding of a thick glue layer. Therefore, the traditional moisture-curing type polyurethane hot melt adhesive cannot be thickly coated in the construction process, and the cured coating film is easy to have the phenomena of incompact and bubbling, so that the application of the moisture-curing type polyurethane hot melt adhesive is greatly limited.
In order to solve the problem of bubbling of moisture-curable polyurethane hot melt adhesives, patent document 200780042808.4 discloses a moisture-curable hot melt adhesive composition comprising a polyaldimine which is a tertiary aliphatic, tertiary alicyclic aldehyde, or a polyamine which is prepared by polymerizing an aromatic aldehyde with an aliphatic primary amino group. The polyaldimines are storage-stable under conditions in which moisture is excluded, and the aldimine groups can be hydrolyzed via intermediates to give amino groups and aldehydes of corresponding structure upon moisture ingress. In the presence of isocyanate groups, the hydrolyzable aldimine groups react with isocyanate groups to form urea groups. Although the polyaldimine disclosed by the technical scheme can solve the bubbling problem in the curing process of the hot melt adhesive, the added polyaldimine is a polymer with a relatively large molecular weight, the viscosity of a hot melt adhesive system can be increased, the dispensing temperature can be increased, and the polyaldimine is fundamentally not beneficial to field operation especially in the construction field requiring thick coating of an adhesive.
In addition, patent document 2017106441889.5 discloses a modified single-component polyurethane waterproof coating, which is prepared by preparing a single-component polyurethane waterproof coating in a conventional manner, adding polyethyleneimine hydrogel and a coupling agent into the single-component polyurethane waterproof coating, and stirring and mixing to obtain the modified single-component polyurethane waterproof coating. The addition of the polyethyleneimine hydrogel can effectively avoid foaming in the curing process, and the principle is as follows: the polyethyleneimine hydrogel can perform chemical reaction with carbon dioxide generated in the curing process of the single-component polyurethane waterproof coating to form ammonium carbamate, and a three-dimensional network structure is spontaneously formed due to interaction between charges, so that the binding force between the interiors of the systems is improved, and bubbles and pinholes are effectively avoided after the single-component polyurethane waterproof coating is cured into a film. Also, polyethyleneimine hydrogels are polymers that increase the viscosity of polyurethane systems, are also useful in thin-coat coatings, and are clearly unsuitable in thick-coat hot melt adhesives. In addition, the addition of a gel component to the adhesive also undoubtedly reduces the adhesive properties of the adhesive.
In order to solve the bubbling problem in the application of the polyurethane hot melt adhesive, the invention provides the moisture curing type polyurethane hot melt adhesive capable of being deeply cured.
Disclosure of Invention
The invention mainly aims to provide a moisture-curing type polyurethane hot melt adhesive capable of realizing deep curing and a preparation method thereof. Introducing a latent curing agent into a moisture curing type polyurethane hot melt adhesive system, wherein the latent curing agent can generate hydrolysis reaction with moisture in the air to generate amino or silanol groups, and further generates chain extension and crosslinking reaction with isocyanate group terminated prepolymer in the system to realize curing. Particularly, silanol groups introduced by disilazane added into the latent curing agent can also obviously improve the storage stability, mechanical properties and wet-heat-resistant aging performance of the polyurethane hot melt adhesive. Compared with the isocyanate group terminated prepolymer directly reacting with water vapor, the CO is obviously reduced after the latent curing agent is added2Gas is released, and the bubbling phenomenon when the thick glue layer is applied is avoided.
The purpose of the invention is realized by the following technical scheme:
in a first aspect, the invention provides a moisture-curable polyurethane hot melt adhesive, which is characterized in that raw materials for preparing the hot melt adhesive contain a latent curing agent, wherein the latent curing agent contains aldimine and/or ketimine.
Wherein the aldimine is prepared by dehydrating and condensing one or two of benzaldehyde, furfural, octanal, 2-dimethylbutyraldehyde and at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, m-xylylenediamine and isophoronediamine.
Preferably, the aldimine is obtained by dehydration condensation of one of benzaldehyde and furfural and at least one of m-xylylenediamine and isophoronediamine.
In the most preferred embodiment of the present invention, the aldimine is formed by dehydration condensation of furfural and isophoronediamine.
The ketimine is prepared by dehydrating and condensing one or two of cyclohexanone and methyl isobutyl ketone and at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, m-xylylenediamine and isophorone diamine.
Preferably, the ketimine is formed by dehydrating and condensing cyclohexanone and at least one of m-xylylenediamine and isophorone diamine.
In the most preferred embodiment of the present invention, the ketimine is formed by dehydration condensation of cyclohexanone and isophoronediamine.
Furthermore, the latent curing agent also comprises disilazane as shown in formula I and/or cyclodisilazane as shown in formula II,
wherein R is1、R2、R3、R1’、R2’、R3' independently selected from H, C1-4Alkyl radical, C1-4An alkoxy group; preferably, the compound of formula I is of symmetrical structure, provided that R1And R1’、R2And R2’、R3And R3' same and independently selected from H, methyl, ethyl, R1、R2、R3、R1’、R2’、R3' not both are H.
In a preferred embodiment of the invention, the compound of formula I is hexamethyldisilazane of the formula
R4、R5、R6、R4’、R5’、R6' independently selected from H, C1-4Alkyl radical, C1-4Alkoxy, phenyl, R7、R8、R7’、R8' independently selected from C1-2An alkyl group; preferably, the compound of formula II is of a symmetrical structure, R4And R4’、R5And R5’、R6And R6' same, and independently selected from H, methyl, phenyl, provided that R4、R5、R6、R4’、R5’、R6' not both are H.
In a most preferred embodiment of the invention, the cyclodisilazane is N, N' -bis (diphenylsilyl) tetramethylcyclodisilazane of the formula
In a preferred embodiment of the invention, the moisture-curable polyurethane hot melt adhesive comprises the following raw materials in parts by weight: 20-30 parts of thermoplastic resin, 15-25 parts of polyester polyol, 25-35 parts of polyether polyol, 3-8 parts of trifunctional micromolecule polyol, 15-25 parts of polyisocyanate, 0.01-1 part of catalyst, 3-5 parts of latent curing agent, 0.4-5 parts of silane coupling agent and 0.1-2 parts of defoaming agent.
Preferably, the latent curing agent is aldimine and/or ketimine, and is compounded with hexamethyldisilazane and/or N, N '-bis (diphenyl silyl) tetramethyl cyclodisilazane according to the mass ratio of 1-4:1, and more preferably, the latent curing agent is aldimine and/or ketimine, and is compounded with hexamethyldisilazane and/or N, N' -bis (diphenyl silyl) tetramethyl cyclodisilazane according to the mass ratio of 2-3: 1;
the aldimine is formed by dehydrating and condensing furfural and isophorone diamine, and the ketimine is formed by dehydrating and condensing cyclohexanone and isophorone diamine.
In a preferred embodiment of the invention, the moisture-curing type polyurethane hot melt adhesive further comprises 0.5-2 parts of a small molecule reactive diluent, wherein the small molecule reactive diluent is one or a combination of more than two of vinylidene fluoride, chlorotrifluoroethylene and 1, 2-difluorodichloroethylene.
In the invention, the thermoplastic resin comprises one or a mixture of more than two of thermoplastic polyurethane, thermoplastic polyester resin, thermoplastic acrylic resin and thermoplastic EVA resin.
The polyester polyol comprises one or more than two of 1, 6-adipic acid, sebacic acid and 1, 4-butanediol, diethylene glycol, methyl propylene glycol, neopentyl glycol, 1, 5-pentanediol and 1, 6-hexanediol, and the molecular weight of the polyester polyol is 8000-8000.
The polyether polyol comprises one or a mixture of more than two of PPG (polypropylene glycol) 400, PPG600, PPG1000, PPG2000, PPG4000, PPG6000, PTMG (polytetramethylene glycol) 1000 and PTMG 2000.
The trifunctional small molecular polyol comprises one or a mixture of more than two of trimethylolethane, trimethylolpropane and glycerol.
The isocyanate comprises one or a mixture of more than two of TDI (toluene diisocyanate), HDI (hexamethylene diisocyanate), MDI (isocyanate), HMDI (dicyclohexylmethane-4, 4' -diisocyanate) and XDI (xylylene diisocyanate).
The catalyst comprises one or a mixture of more than two of dibutyltin dilaurate, stannous octoate, triethylene diamine, 2- (2-dimethylamino-ethoxy) ethanol and N- (dimethylamino propyl) diisopropanolamine.
The silane coupling agent comprises one or a mixture of more than two of A1160, KH560, KH580 and Y9669;
the defoaming agent comprises one or a mixture of more than two of BYK 066N, BYK 1790, BYK A535, BYK-067, BYK-051, BYK-077, BYK-352 and BYK-359.
In a second aspect, the invention provides a preparation method of a moisture-curable polyurethane hot melt adhesive, which comprises the following steps:
(1) stirring and dehydrating thermoplastic resin, polyester polyol, polyether polyol and trifunctional micromolecular polyol at 100-130 ℃ for 2-4h under the vacuum condition at 200 r/min;
(2) cooling the dehydrated mixture obtained in the step (1) to 70-80 ℃, adding polyisocyanate and a catalyst, and stirring and reacting for 1-2h under the nitrogen atmosphere to obtain a prepolymer A;
(3) and (3) adding a latent curing agent, a silane coupling agent and a defoaming agent into the prepolymer A, and stirring and defoaming for 15-30min under a vacuum state to obtain the moisture-cured polyurethane hot melt adhesive.
Preferably, the step (3) further comprises adding a small molecule reactive diluent.
According to the invention, aldimine and/or ketimine are introduced into the moisture curing type polyurethane hot melt adhesive system, and are subjected to hydrolysis reaction with water vapor in the air to generate amino groups, so that chain extension and crosslinking reaction of prepolymer molecules are completed, the probability of direct reaction of isocyanate terminated prepolymer and water vapor is reduced, and CO is reduced2And the generation of gas avoids the bubble phenomenon in the curing process. Furthermore, disilazane is introduced into the moisture curing type polyurethane hot melt adhesive system, is easy to hydrolyze, can preferentially perform hydrolysis reaction with water vapor in the air, plays the same role as aldimine and ketimine, and solves the bubbling problem of the moisture curing type polyurethane hot melt adhesive in the application scene of a thick adhesive layer. Secondly, the inventor unexpectedly discovers that silanol groups generated by hydrolysis of silazane can be crosslinked with isocyanate-terminated prepolymer, so that the storage stability, the mechanical property and the wet-heat-aging resistance of the polyurethane hot melt adhesive can be obviously improved.
And compared with the addition of a high-molecular-weight compound containing an imine structure, the low-molecular-weight aldimine and/or ketimine can reduce the viscosity of the system, so that the dispensing temperature is reduced, the glue discharging fluency is improved, and the construction is facilitated.
Drawings
FIG. 1 is a schematic representation of the surface of the hot melt adhesive after curing in comparative example to example 1.
FIG. 2 is a schematic cross-sectional view of a hot melt adhesive of comparative example and example 1 after curing.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Preparation example 1 preparation of aldimine
Dehydrating and condensing benzaldehyde and 1, 2-propane diamine
Heating the flask in a water bath at 80 ℃, adding a benzaldehyde alcohol solution into the flask, slowly dropwise adding a1, 2-propylene diamine alcohol solution into the flask, wherein the molar ratio of benzaldehyde to 1, 2-propylene diamine is 2:1, stirring while dropwise adding, and continuously stirring for 5min after crystals are separated out. After cooling to room temperature, the crystals were filtered with suction on a buchner funnel, washed with ethanol, dried with suction and pressure and dried under an infrared lamp to give the target compound aldimine 1.
Dehydration condensation of furfural and isophoronediamine
Heating the flask in a water bath at 80 ℃, adding a furfural ethanol solution into the flask, slowly dropwise adding an isophorone diamine ethanol solution into the flask, wherein the molar ratio of furfural to isophorone diamine is 2:1, stirring while dropwise adding, and continuously stirring for 5min after crystals are separated out. After cooling to room temperature, suction filtration was carried out on a Buchner funnel, the crystals were washed with ethanol, suction filtered and pressed to dryness, and the crystals were dried under an infrared lamp to give the target compound aldimine 2.
Dehydration condensation of octavaleraldehyde and m-xylylenediamine
Heating the flask in a water bath at 80 ℃, adding an ethanol solution of octavaleraldehyde into the flask, slowly dropwise adding an ethanol solution of m-xylylenediamine into the flask, wherein the molar ratio of octavaleraldehyde to m-xylylenediamine is 2:1, stirring while dropwise adding, and continuously stirring for 5min after crystals are separated out. After cooling to room temperature, the crystals were filtered with suction on a buchner funnel, washed with ethanol, dried with suction and pressed, and dried under an infrared lamp to give the target compound aldimine 3.
Preparation example 2 preparation of ketimine
Dehydration condensation of methyl isobutyl ketone and m-xylylenediamine
Heating the flask in a water bath at 100 ℃, adding a methyl isobutyl ketone solution into the flask, slowly dropwise adding an m-xylylenediamine ethanol solution into the flask, wherein the molar ratio of the methyl isobutyl ketone to the m-xylylenediamine is 2:1, stirring while dropwise adding, and continuously stirring for 5min after crystals are separated out. After cooling to room temperature, the crystals were filtered with suction on a buchner funnel, washed with ethanol, dried under suction and pressure, and dried under an infrared lamp to give the target compound ketimine 1.
Dehydration condensation of Cyclohexanone with Isophoronediamine
Heating the flask in a water bath at 100 ℃, adding a cyclohexanone alcohol solution into the flask, slowly dropwise adding an isophorone diamine alcohol solution into the flask, wherein the molar ratio of cyclohexanone to isophorone diamine is 2:1, stirring while dropwise adding, and continuously stirring for 5min after crystals are separated out. After cooling to room temperature, the crystals were filtered with suction on a buchner funnel, washed with ethanol, dried under suction and pressure, and dried under an infrared lamp to give the target compound ketimine 2.
Comparative examples moisture-curing polyurethane hot melt adhesives commonly used in the market
S1: stirring and dehydrating 30 parts of thermoplastic polymethacrylic resin, 25 parts of 2000 molecular weight hexanediol adipate glycol, 35 parts of 2000 molecular weight PPG and 0.5 part of carbon black at 130 ℃ and under the vacuum condition of-0.1 MPa for 2h at 200 r/min;
s2: cooling the dehydrated mixture to 80 ℃, adding 15 parts of MDI (diphenylmethane diisocyanate) and 0.5 part of dibutyltin dilaurate, and stirring to react for 2 hours in a nitrogen atmosphere to obtain a prepolymer A;
s3: adding 1 part of KH580 and 0.2 part of BYK A535 into the prepolymer A, uniformly stirring under a vacuum state of-0.1 MPa, and defoaming to obtain the polyurethane hot melt adhesive CT-0.
Example 1
S1: stirring and dehydrating 30 parts of thermoplastic polymethacrylic resin, 25 parts of 2000 molecular weight hexanediol adipate diol, 35 parts of 2000 molecular weight PPG and 3 parts of trimethylolethane at 130 ℃ and under the vacuum condition of-0.1 MPa for 2h at the speed of 200 r/min;
s2: cooling the dehydrated mixture to 80 ℃, adding 15 parts of MDI (diphenylmethane diisocyanate) and 0.5 part of dibutyltin dilaurate, and stirring to react for 2 hours in a nitrogen atmosphere to obtain a prepolymer A;
s3: adding 1 part of KH580, 0.2 part of BYK A535 and 3 parts of aldimine 1 obtained in the preparation example into the prepolymer A, uniformly stirring under a vacuum state of-0.1 MPa, and defoaming to obtain the polyurethane hot melt adhesive CT-1.
Example 2
The preparation method is the same as example 1, except that 3 parts of aldimine 2 obtained in the preparation example is added in step S3 to prepare the polyurethane hot melt adhesive CT-2.
Example 3
The preparation method is the same as example 1, except that 3 parts of aldimine 3 obtained in the preparation example is added in step S3 to prepare the polyurethane hot melt adhesive CT-3.
Example 4
The preparation method is the same as example 1, except that 3 parts of ketimine 1 obtained in the preparation example is added in step S3 to prepare polyurethane hot melt adhesive CT-4.
Example 5
The preparation method is the same as example 1, except that 3 parts of ketimine 2 obtained in the preparation example is added in step S3 to prepare polyurethane hot melt adhesive CT-5.
Example 6
The preparation process is the same as example 1, except that 3 parts of ketimine 2 obtained in preparation example and 1 part of hexamethyldisilazane are added in step S3 to prepare polyurethane hot melt adhesive CT-6.
Example 7
The preparation process is identical to example 1, except that 3 parts of ketimine 2 from the preparation and 1 part of N, N' -bis (diphenylsilyl) tetramethylcyclodisilazane are added in step S3 to prepare polyurethane hotmelt CT-7.
Example 8
The preparation method is the same as example 6, except that 0.5 part of a small-molecule reactive diluent, namely vinylidene fluoride, is further added in step S3 on the basis of example 6 to prepare the polyurethane hot melt adhesive CT-8.
Examples of effects
Test objects: examples 1-8, comparative example polyurethane hotmelt adhesives were prepared.
1. And (3) appearance testing: the hot melt adhesive was stored at room temperature and 60% RH for 2 weeks and observed for apparent changes.
2. And (4) testing the storage stability: the product prepared in the embodiment is hermetically placed by a packaging can, is placed in an electric heating air blowing drying oven, is stored at the set temperature of 50 ℃, is detected whether the hot melt adhesive has the skinning and layering phenomenon every 7 days (1 week), and records the time when the skinning and layering phenomenon occurs in the last detection.
3. And (3) viscosity testing: the melt viscosity of the hot melt adhesive was measured at 120 ℃ on a Brookfield viscometer using a 27# spindle at 20 rpm/min.
4. Melting and dispensing at 110 ℃, preparing a shear sample, controlling the thickness of a glue layer to be 0.25mm, standing and curing for 3 days (the temperature is 25 ℃, and the humidity is 60% RH), testing the shear strength of the sample, carrying out three groups of tests in parallel, and taking an intermediate value.
5. And (3) testing the bubbling rate: embodiment Using high definition digital CameraThe surface of the prepared product is photographed, and the relative diameter H of the bubbles in the vertical direction is measuredrThe bubble size is characterized by the average diameter H of the bubbles, H being defined as
Wherein n is H in cross sectionrThe number of the bubbles larger than 0.5mm is more than or equal to 10 in each calculation. By HfRoughly calculating the total planar area S occupied by the bubbles with the average diameter of more than 0.5mm, wherein the bubbling rate (%) is S and the area S of the polyurethane hot melt adhesive to be tested0The ratio of (a) to (b).
6. And (3) testing high temperature and high humidity resistance: after the sample is cured for 7d under the condition of 85 ℃/85% RH, the sample is placed into an oven at 120 ℃ for 24h, and then the tensile shear strength of the sample is tested in a high-low temperature tensile machine at 120 ℃.
7. And (3) testing the cold and hot shock aging resistance: tensile shear strength was tested at 40 ℃/30min, 80 ℃/30min, 168 Cycle.
TABLE 1 basic Performance test results for polyurethane hotmelt adhesives
The hot melt adhesive prepared by the comparative example is common moisture curing type polyurethane hot melt adhesive in the market, and the polyurethane prepolymer directly reacts with water vapor to generate CO in the curing process2The hot melt adhesive prepared by the comparative example has obvious bubbles and pinholes, and the bubbling rate is 2.01 percent. In the embodiments 1-5, aldimine or ketimine is added on the basis of the prior art, and the compound with an imine structure and water vapor in the air undergo hydrolysis reaction, so that the reaction probability of the polyurethane prepolymer and the water vapor is reduced, and CO is reduced2The gas release amount is smooth and compact, no pinhole is formed, and the bubbling rate is between 1.26 and 1.53 percent. The aldimine and the ketimine can really solve the problem that the polyurethane hot melt adhesive is curedThe problem of bubbling in the process. Examples 6-8 are based on the prior art and have added disilazane, which also preferentially reacts with water vapor in the air, so that no pinholes are formed on the hot melt surface and the bubbling rate is further reduced to a minimum of 0.67%. The left side and the right side in fig. 1 and fig. 2 are schematic diagrams of the cured surfaces of the hot melt adhesives prepared in the comparative example and the example 1 respectively, and it can be clearly seen that compared with the conventional moisture-curable polyurethane hot melt adhesives on the market, the hot melt adhesive prepared in the example 1 of the present invention forms fewer bubbles, does not have raised radian on the surface, and has a small thickness of the cured adhesive layer and denser adhesive body.
It can be seen from the data of the storage stability of the hot melt adhesive that, compared with the conventional products in the market, after the aldimine or the ketimine is added as the latent curing agent, the storage stability is obviously improved, optimally increased from 2 weeks to 5 weeks, because the ketimine and water are subjected to hydrolysis reaction to directly generate amino groups, isocyanate groups in the polyurethane prepolymer are not consumed, more urea bonds with strong polarity and high bond energy are formed, the storage stability is increased, and the shear strength is synchronously enhanced. When ketimine and silazane are added as the latent curing agent, the storage stability is improved again because silanol groups generated by the hydrolysis of silazane can be crosslinked with the isocyanate end-capping prepolymer, so that the shear strength and stability of the hot melt adhesive are improved.
In addition, compared with the comparative hot melt adhesive, the viscosity of the prepared hot melt adhesive is reduced by adding aldimine or ketimine, and particularly, the viscosity is reduced from 4650mPa.s to 4100mPa.s after adding the small molecular reactive diluent. Because the aldimine and the ketimine used by the invention, including silazane, are low molecular weight substances, the aldimine and the ketimine have a diluting function on a curing system, the viscosity of the system is reduced, the glue is smoothly discharged, and the construction is facilitated.
TABLE 2 ageing resistance test results of polyurethane hot melt adhesive
As can be seen from the data of the results of the high temperature, high humidity and aging resistance of the hot melt adhesive in the table above, the less decrease of the shear strength of PC indicates the better high temperature, high humidity resistance. Compared with the comparative example, the high temperature and high humidity resistance of the hot melt adhesive prepared in the examples 1 to 8 is obviously improved. In examples 1 to 5, the effects of examples 2 and 5 are better because the content of cycloalkyl in the molecular structure of aldimine obtained by condensing furfural and isophorone diamine and the content of cycloalkyl in ketimine obtained by condensing cyclohexanone and isophorone diamine are higher, so that the strength of a curing system obtained by hydrolyzing the imine structure and participating in curing of a polyurethane prepolymer is better, and the high temperature and high humidity resistance is stronger.
Compared with the cold and hot impact aging resistance data of the hot melt adhesive, the imine compound with more cycloalkyl structures is added into the hot melt adhesive curing system, so that the cold and hot impact resistance of the hot melt adhesive can be effectively improved, and the shear strength of the hot melt adhesive is improved. Because the polyurethane hot melt adhesive has a microphase separation structure of a soft section and a hard section to a certain degree after being cured at room temperature, when a temperature impact aging test is carried out in a temperature range of-40 ℃ to 80 ℃, the motion capability of a molecular chain section is enhanced at a high temperature of 80 ℃, thereby being beneficial to further microphase separation, improving the colloid strength and further improving the shear strength. In addition, trace NCO end-capping prepolymer still remains in the sample piece after complete room temperature curing, the molecular motion capability is enhanced at the high temperature of 80 ℃, and due to the existence of the latent curing agent, after contacting trace water vapor at the high temperature, the sample piece is decomposed to generate a substance containing active hydrogen, and the substance continues to react with the residual NCO end-capping prepolymer to generate chain extension reaction, so that the molecular weight is improved, and the strength is increased. Or the NCO end-capping prepolymer and the urethane bond react slowly to generate allophanate, and crosslinking is generated, so that the strong shearing degree is increased.
In addition, the inventor can find that when the latent curing agent with the imine structure and the silazane are added into the hot melt adhesive system at the same time, the high-temperature high-humidity aging resistance and the cold-thermal shock aging resistance of the prepared hot melt adhesive are improved, because silanol groups generated after the silazane is hydrolyzed can participate in the curing of the polyurethane prepolymer, so that silicon atoms are uniformly dispersed in the curing system, and the shear strength and the weather resistance of the hot melt adhesive are improved.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (11)
1. A moisture-curing type polyurethane hot melt adhesive is characterized in that raw materials for preparing the hot melt adhesive contain a latent curing agent, the latent curing agent contains ketimine and disilazane shown as a formula I and/or cyclodisilazane shown as a formula II, the mass ratio of the ketimine to the disilazane shown as the formula I and/or the cyclodisilazane shown as the formula II is 1-4:1,
（Ⅰ）
（Ⅱ）
wherein R is1、R2、R3、R1’、R2’、R3' independently selected from H, C1-4Alkyl radical, C1-4An alkoxy group; r4、R5、R6、R4’、R5’、R6' independently selected from H, C1-4Alkyl radical, C1-4Alkoxy, phenyl, R7、R8、R7’、R8' independently selected from C1-2An alkyl group;
the ketimine is prepared by dehydrating and condensing one or two of cyclohexanone and methyl isobutyl ketone and at least one of ethylenediamine, propylenediamine, butylenediamine, pentylenediamine, hexylenediamine, m-xylylenediamine and isophorone diamine.
2. The moisture-curable polyurethane hot melt adhesive according to claim 1, wherein the ketimine is formed by dehydrating and condensing cyclohexanone and at least one of m-xylylenediamine and isophorone diamine.
3. The moisture-curable polyurethane hot melt adhesive according to claim 2, wherein the ketimine is formed by dehydrating and condensing cyclohexanone and isophorone diamine.
4. The moisture-curable polyurethane hot melt adhesive according to claim 1, wherein the compound of formula I has a symmetrical structure, R1And R1’、R2And R2’、R3And R3' same, and independently selected from H, methyl, ethyl, provided that R1、R2、R3、R1’、R2’、R3' not simultaneously H;
the compound of formula II is of a symmetrical structure, R4And R4’、R5And R5’、R6And R6' same, and independently selected from H, methyl, phenyl, provided that R4、R5、R6、R4’、R5’、R6' not both are H.
5. The moisture-curable polyurethane hot melt adhesive according to claim 4, wherein the compound of formula I is hexamethyldisilazane having the structural formula
；
The compound of the formula II is N, N' -bis (diphenyl silyl) tetramethylcyclodisilazane with the structural formula
。
6. The moisture-curing polyurethane hot melt adhesive according to claim 1, which is characterized by comprising the following raw materials in parts by weight: 20-30 parts of thermoplastic resin, 15-25 parts of polyester polyol, 25-35 parts of polyether polyol, 3-8 parts of trifunctional micromolecule polyol, 15-25 parts of polyisocyanate, 0.01-1 part of catalyst, 3-5 parts of latent curing agent, 0.4-5 parts of silane coupling agent and 0.1-2 parts of defoaming agent.
7. The moisture-curable polyurethane hot melt adhesive according to claim 6,
the ketimine is formed by dehydrating and condensing cyclohexanone and isophorone diamine.
8. The moisture-curable polyurethane hot melt adhesive according to claim 7, wherein the latent curing agent is a mixture of ketimine and hexamethyldisilazane and/or N, N' -bis (diphenylsilyl) tetramethylcyclodisilazane in a mass ratio of 2-3: 1.
9. The moisture-curing polyurethane hot melt adhesive according to claim 1, further comprising 0.5-2 parts of a small molecule reactive diluent, wherein the small molecule reactive diluent is one or a combination of more than two of vinylidene fluoride, chlorotrifluoroethylene and 1, 2-difluorodichloroethylene.
10. A method for preparing the moisture-curable polyurethane hot melt adhesive according to any one of claims 1 to 8, comprising the steps of:
(1) thermoplastic resin, polyester polyol, polyether polyol and trifunctional micromolecular polyol are stirred and dehydrated for 2-4h under the vacuum condition of 100-130 ℃ and-0.01- (-0.1) MPa;
(2) cooling the dehydrated mixture obtained in the step (1) to 70-80 ℃, adding polyisocyanate and a catalyst, and stirring and reacting for 1-2h under the nitrogen atmosphere to obtain a prepolymer A;
(3) and (3) adding a latent curing agent, a silane coupling agent and a defoaming agent into the prepolymer A, and stirring and defoaming for 15-30min under a vacuum state to obtain the moisture-cured polyurethane hot melt adhesive.
11. The method of claim 10, wherein the step (3) further comprises adding a small molecule reactive diluent.
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| CN103923565A (en) * | 2014-03-26 | 2014-07-16 | 浙江鲁班建筑防水有限公司 | Uncured polyurethane waterproofing coating and preparation method thereof |
| CN110835497A (en) * | 2018-08-17 | 2020-02-25 | 襄阳九阳防水材料有限公司 | Single-component polyurethane waterproof coating |
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| CN104087230A (en) * | 2014-06-18 | 2014-10-08 | 广州新展化工新材料有限公司 | Silane-modified polyurethane sealing material and preparation method thereof |
| EP3336114A1 (en) * | 2016-12-15 | 2018-06-20 | Sika Technology Ag | Two-component polyurethane sealant for application at low temperature |
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| CN110835497A (en) * | 2018-08-17 | 2020-02-25 | 襄阳九阳防水材料有限公司 | Single-component polyurethane waterproof coating |
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