JPS6341954B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to urethane-based adhesives, and more specifically, to materials that contain moisture, materials that are hydrophilic and contain active hydrogen groups that can react with isocyanate groups, and in particular have excellent adhesion to raw wood and wood with high moisture content. The present invention relates to the urethane adhesive shown in FIG. Logs and other timber resources are decreasing year by year due to over-harvesting not only in Japan but also overseas.In order to utilize them effectively, improve product yields, and improve productivity, we are developing excellent logs and lumber with high moisture content. At present, applications for new adhesives are awaited. Conventionally, adhesives for wood have mainly been thermosetting types such as urea-formalin type, melamine type, and phenol type, hot melt types such as EVA and polyamide resin, and urethane prepolymer type. Thermosetting types have excellent adhesive strength, water resistance, and heat resistance, but formalin remains even after bonding, causing problems such as odor and environmental pollution.
The drawback was that the adhesion to logs and wood with high moisture content was very weak. In addition, hot-melt products have problems with the limitations of heat-melting equipment, heat resistance, etc., and also have very weak adhesion to logs and wood with high water content. Urethane prepolymer-based products do not stain wood, and form primary chemical bonds with wood that has alcoholic hydroxyl groups, and have extremely excellent adhesive strength and heat resistance, but they generally do not stain wood with high moisture content. On the other hand, there are problems such as foaming due to reaction with water on the wet surface, poor adhesion to adhesive parts, and long curing time, and improvements are desired. These disadvantages related to foamability, penetrability, and reactivity are disadvantages of urethane adhesives for all materials, not just wood, and in this sense, it is desired to develop urethane adhesives that solve these problems. . From this point of view, the inventors of the present invention have conducted intensive research to provide a urethane adhesive that does not have the above-mentioned drawbacks and has excellent adhesion to water-containing materials.
This has led to the present invention. The urethane prepolymer containing a terminal isocyanate group obtained from the reaction of a polyoxyalkylene polyol containing a hydrophilic ethylene oxide chain in its molecule with an organic isocyanate contains a hydrophilic component in its main chain. It is already known that it is used as an adhesive for materials containing active hydrogen that can react with isocyanate groups, especially raw wood and wood with high moisture content, and is well known to be used as an adhesive for these materials. A prepolymer containing a terminal isocyanate group made from a polyoxyalkylene polyol containing ethylene oxide and an organic isocyanate is too hydrophilic, and the adhesive layer foams due to the carbon dioxide gas generated by the reaction between the isocyanate group and water, resulting in a homogeneous and sufficient adhesion. is difficult to obtain. On the other hand, urethane prepolymers containing terminal isocyanate groups made from hydrophobic polyoxypropylene polyols and organic isocyanates have very poor compatibility and diffusion with water, and are not suitable for materials containing large amounts of moisture, logs and wood with high moisture content, etc. It is also known that the adhesion is quite poor. Based on these known facts, the present inventors have investigated in detail the structure including the higher-order structure of the prepolymer containing terminal isocyanate groups as an adhesive, and the resulting physicochemical properties, reactivity, and structure of the reaction product. After extensive research, we have finally provided the urethane adhesive of the present invention. That is, the present invention is a polyoxyalkylene polyol () having a molecular weight of 1000 to 8000 and having 2 to 3 hydroxyl groups, which is obtained by randomly adding and polymerizing an alkylene oxide containing 50 to 90% ethylene oxide to an active hydrogen group, and hydroxyl group 2 obtained by addition polymerization of propylene oxide to active hydrogen group
Polyoxypropylene polyol () with a molecular weight of 200 to 800 having ~3 polyols () and, if necessary, a monomolecular glycol () having an ether group in the molecule
(A) Average molecular weight ( _OH ) 1000~
5000, ethylene oxide addition% ( _OH %) 60
80, a mixed polyol with a mixing ratio of number average acoustic group number ( _OH ) 2.2 to 2.5, and 2 isocyanate groups.
(B) Isocyanate group content (NCO%) 2~
20, Ethylene oxide addition% ( _U %) 35~
70, relates to a urethane adhesive comprising a urethane prepolymer containing terminal isocyanate groups having a number average functional group number ( _U ) of 2.02 to 2.35. (A) Number average molecular weight _O of mixed polyol structure factor
_H , ethylene oxide addition % _OH , and _OH are determined as follows. However, the molecular weight of each polyol (), (), () is M〓, M〓, M〓,
The number of functional groups is f〓, f〓, f〓, the ethylene oxide addition rate is EO〓, the mixing weight (g) is W〓, W〓, W〓
and the subscript , . (However, the amount of initiator is ignored in the amount of EO added.) (B) Isocyanate group content NCO% of the urethane prepolymer structure factor containing terminal isocyanate groups,
The ethylene oxide content _U % and the number average number of functional groups _U are determined as follows. However, the number average molecular weight of the mixed polyol is _OH , the ethylene oxide content% is _OH %, the number average number of functional groups is _OH ,
Let W _OH be the weight ratio of the reaction, M _NCO be the molecular weight of the organic isocyanate, and f _NCO be the number average number of functional groups. The present invention will be explained in more detail. It reacts with organic isocyanate and is contained in the molecule of the urethane polymer containing terminal isocyanate groups, giving the adhesive appropriate hydrophilicity and giving the adhesive layer after curing adhesive strength, flexibility, water resistance, heat resistance, and flexibility. The polyoxyalkylene polyol to be provided must be a mixed polyol of two or more components with a large difference in molecular weight from the viewpoint of molecular chain arrangement, chain length, and balance between flexibility and adhesive strength, which affect hydrophilicity. The following can be said about each component of this mixed polyol. In other words, a polyol () selected as the ethylene oxide-containing polyol component has a high molecular weight that gives the adhesive compatibility with wet surfaces, the ability to penetrate into wood, etc., and gives the adhesive layer flexibility and water-retaining properties after curing. In the case of block addition polymerization, the resulting urethane adhesive thickens or solidifies in the winter, resulting in poor product storage stability and a significant decrease in workability for areas that require uniform application. Furthermore, since the adhesive strength varies greatly depending on the water content, it must be a random addition polymer. If the amount of ethylene oxide is less than 50%, the hydrophilicity of the obtained urethane adhesive will be insufficient, it will not be compatible with wet surfaces or penetrate into the material, and it will remain in the adhesive layer and material during and after curing. The adsorption interface between the adhesive layer and the material is weakened due to the lack of ethylene oxide, which adsorbs moisture into the molecular chains and adjusts curing and adhesive properties. On the other hand, if the amount of ethylene oxide is greater than 90%, the freezing point and viscosity of the polyol () itself will become very high, causing problems in industrial production such as solidification in winter, and even if industrial production is possible, Urethane adhesives using this as a component of mixed polyols have a high freezing point and high viscosity, causing problems in terms of quality control as they precipitate as white crystals in winter. Polyol ()
Regarding the number of hydroxyl groups, if it is less than 2, the adhesive strength of the obtained urethane adhesive will be low, and if it is larger than 3, it will have excellent strength, but will have poor storage stability and will tend to thicken, and will have a long pot life. This causes problems in workability. Regarding the molecular weight of polyol (),
If the molecular weight is less than 1000, the hydrophilic chains are cut due to urethane bonds, resulting in a decrease in conformability to wet surfaces and infiltration into materials. molecular weight
If it is larger than 8,000, the viscosity of the polyol () becomes high, causing problems in industrial production, and the resulting urethane adhesive has poor workability, and furthermore, it causes problems in water resistance. Next, the polyol () was selected as a low molecular weight polyol component that imparts a certain degree of hydrophobicity to the adhesive and imparts hardness, water resistance, heat resistance, adhesive strength, etc. to the adhesive layer after curing. If the number of hydroxyl groups is less than 2, the adhesive strength of the obtained urethane adhesive will be low, and if it is greater than 3, the viscosity of the obtained urethane adhesive will be high, causing problems in workability. Regarding the molecular weight of the polyol (), if it is less than 200, the yield will be poor and industrial production will be difficult.
Hydrophobicity becomes too strong due to the propylene oxide chain, and the resulting urethane adhesive has poor adhesion to wet surfaces due to its ability to penetrate into materials. In addition, if it is larger than 800, the polyol () itself is highly hydrophobic, and the molecular weight is too large to give hardness to the adhesive layer after curing, and the resulting urethane adhesive does not conform to the wet surface. , poor penetration into the material, low heat resistance, and low adhesive strength. Polyol () is added as necessary to maintain the structural factors of the mixed polyol component, ie, average molecular weight, ethylene oxide addition rate, and number of functional groups, within specified ranges. The following can be said about the structural factors of mixed polyols. If _{the OH} of the mixed polyol is less than 2.2,
The pot life and curing time of the obtained urethane adhesive are long, so the workability is poor, and the branching concentration of the cured adhesive layer is low.For processing, etc., it is heated to a high temperature of around 200℃ during or after curing. If a step is included, a problem arises in the heat resistance of the adhesive layer in that step. On the other hand, if _OH is greater than 2.5, the resulting urethane adhesive has a strong viscous surface and a short pot life when bonding materials with high water content such as wood, and may gel during the process or cause damage to the wood. The adhesive layer tends to increase in viscosity before it is sufficiently penetrated, making it difficult to obtain sufficient adhesion, and the cured adhesive layer lacks flexibility and becomes brittle with little elongation. Since _OH is affected by _OH , it must be considered in relation to _OH , but if _OH is less than 1000, the urethane group concentration of the urethane adhesive obtained is high, and if _OH % is within the specified range. Also, the hydrophilicity is reduced and the adhesion to wet surfaces is poor. On the other hand, if _OH is greater than 5000, the hydrophilicity becomes too strong and the reaction with water becomes easy, resulting in foaming, resulting in a decrease in the strength of the adhesive layer, and furthermore, the water resistance of the adhesive layer after curing is poor. Speaking of _OH %,
When it is less than 60%, the resulting urethane adhesive has poor hydrophilicity, takes a very long curing time, and has poor compatibility with wet surfaces such as wood, and its adhesive properties vary greatly depending on the water content. On the other hand, if it exceeds 80%, foaming occurs due to reaction with moisture during curing, reducing the strength of the adhesive layer. The characteristics that the urethane prepolymer containing terminal isocyanate groups obtained by reacting such a mixed polyol with an organic isocyanate having two or more isocyanate groups will be described below. That is, when the NCO% is greater than 20%, even if the mixed polyol satisfies the above conditions, the resulting urethane prepolymer containing terminal isocyanate groups tends to foam when adhering materials with high moisture content, and is prone to excessive foaming. The concentration of urea bonds generated by the reaction between isocyanate groups and water increases, causing the adhesive layer to lose its flexibility, and its water resistance deteriorates in proportion to the increase in the urea bond concentration. Furthermore, when toluene diisocyanate is used as the organic isocyanate, the amount of free toluene diisocyanate is large, which is unfavorable in terms of the working environment, and when 4,4'-diphenylmethane diisocyanate is used, unreacted 4,4'-diphenyl diisocyanate is present in the winter. Crystals of enylmethane diisocyanate precipitate, causing storage stability problems. On the other hand, if NCO% is less than 2%, even if the mixed polyol satisfies the above conditions, the viscosity of the urethane prepolymer containing terminal isocyanate groups will be high, and the wettability of the material will be poor, so the water content of the material and other conditions may be affected. This difference causes variations in adhesive properties, and the prepolymer itself has poor storage stability. If _{the U} % of the urethane prepolymer is less than 35%, the urethane polymer will have poor hydrophilicity and will have poor wettability and penetration into water-containing materials, resulting in poor adhesion. Conversely, if it is greater than 70%,
Because urethane polymer has a high viscosity and a high freezing point, crystallization is inevitable in winter, and foaming tends to occur when adhering to materials with high moisture content.
This causes a decrease in the strength of the adhesive layer. If the number average functional group number _U of the urethane polymer is less than 2.02, the adhesion and workability are good, but there are problems with the heat resistance, chemical resistance, and stain resistance of the adhesive layer. On the other hand, if f _U is greater than 2.35, the pot life will be short and the resulting adhesive layer will be brittle without elongation, and will have poor impact resistance due to lack of stickiness. The urethane adhesive of the present invention is obtained from the polyol () described in claim 1, a mixed polyol that satisfies characteristic (A) obtained by mixing polyol () and, if necessary, polyol (), and an organic isocyanate. In addition to those consisting of a urethane prepolymer containing terminal isocyanate groups that satisfies property (B), polyol (), polyol (), and polyol () described in claim 2 may be used singly or as a mixture thereof. A mixture of two or more terminal isocyanate group-containing prepolymers obtained from a polyol and an organic isocyanate so as to contain polyol () and polyol () as essential components has characteristics (A) [polyol in the mixed prepolymer]. It also includes those that satisfy the conditions for components] and property (B), and includes those that are blended with commonly used inert solvents, if necessary. Polyol () used in the present invention has a molecular weight of 1000 and has 2 to 3 hydroxyl groups obtained by random addition polymerization of an alkylene oxide containing 50 to 90% ethylene oxide to an active hydrogen group.
~8000 polyoxyalkylene polyol is
Compounds with active hydrogen groups, such as ethylene glycol, propylene glycol, 1,4- and 1,3-butylene glycol, 1,6-hexane glycol, neopentyl glycol, bisphenol A, hydroquinone, glycerin, trimethylolpropane, 1 , 2,6-hexanetriol, triethanolamine, diethanolamine, monoethanolamine, triisopropanolamine, diisopropanolamine, monoisopropanolamine, etc. and/or triols such as ethylene oxide, propylene oxide, butylene oxide, styrene oxide, etc. It refers to a copolymer having 2 to 3 hydroxyl groups obtained by mixing two or more alkylene oxide components and subjecting them to random addition polymerization. As described above, the mixing ratio of ethylene oxide and alkylene oxide other than ethylene oxide is in the range of 50/50 to 90/10 (weight ratio), and the resulting molecular weight is in the range of 1,000 to 8,000. In addition, polyoxypropylene polyol with a molecular weight of 200 to 800 and having 2 to 3 hydroxyl groups obtained by addition polymerizing propylene oxide to the active hydrogen group shown as polyol () is a polyoxypropylene polyol with an active hydrogen group mentioned in the above polyol (). Refers to addition polymerization of propylene oxide to alcohol, etc. Ether group-containing monomolecular glycol shown as polyol () is a hydrophilic glycol having an ether group and two hydroxyl groups in the molecule, such as diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and ditetramethylene glycol. Refers to good low molecular weight monomolecular diols. As the organic isocyanate having two or more isocyanate groups, aliphatic, alicyclic, aromatic polyisocyanates and polymeric polyisocyanates are used alone or in combination. For example, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, m- or p-xylene diisocyanate, m- or p-phenylene diisocyanate, tetramethylene diisocyanate, hexamethylene Examples include diisocyanates such as diisocyanate, lysine diisocyanate, 1,4-cyclohexylene diisocyanate, 4,4'-cyclohexylmethane diisocyanate, and isophorone diisocyanate, and polymeric polyisocyanates such as polymethylene polyphenyl isocyanate and crude tolylene diisocyanate. In addition, in order to prevent deterioration of the working environment due to free isocyanate molecules, organic isocyanates with low vapor pressure are preferred, such as 4,4'-
Diphenylmethane diisocyanate, polymers thereof, lysine diisocyanate, 4,4'-cyclohexylmethane diisocyanate, and the like are suitable. The urethane adhesive of the present invention is obtained by reacting the polyol () and polyol () shown above, and if necessary, the polyol () and an organic isocyanate. This reaction is accomplished by heating at 70 to 90°C for 3 to 8 hours in the presence of a conventional urethanization catalyst, such as a tertiary amine or an organometallic compound, if necessary. In addition, examples of organic solvents (inert solvents) without active hydrogen groups that may be added to the obtained urethane adhesive as needed include methyl ethyl ketone, acetone, ethyl acetate, toluene, xylene, dioxane, etc. is preferably 5 to 40%. In addition, the adhesive of the present invention contains a urethanization catalyst such as a tertiary amine, an organometallic compound, hydrochloric acid, acetic acid,
The curing speed can be adjusted by adding acidic substances such as benzoyl chloride. Further, colorants such as pigments and dyes, fillers such as talc, calcium carbonate, clay, and finely powdered silica, and surfactants such as silicone and paraffin may be added. The urethane adhesive according to the present invention has excellent operability, curing speed, pot life, compatibility with materials, and the adhesive strength, flexibility, water resistance, and heat resistance of the produced adhesive layer. , and have a good balance between water-containing materials, materials that are hydrophilic and contain active hydrogen groups (e.g., hydroxyl groups, amino groups, amide groups, thiol groups, etc.) that can react with isocyanate groups, and wood (e.g., wet raw materials). wood, veneer that contains a large amount of moisture, plywood, verteckle board, etc.),
Suitable for bonding paper, cellulose (e.g. paper waste, pulp, sludge emitted during pulp production, etc.), inorganic materials (e.g. asbestos, concrete, plaster, silicon oxide compounds, etc.), cloth, fiber, etc., especially wood, especially , exhibits excellent adhesion to logs and wood with high moisture content. The present invention will be explained in more detail with reference to Examples below, in which parts and percentages are by weight. Example <1> Method for producing urethane prepolymer. Molecular weight of random addition polymerization of 80% ethylene oxide and 20% propylene oxide
Mix 691 parts of diol 4000 (abbreviated as (EO/PO=80/20) _R -4000) and 37 parts of a triol with a molecular weight of 400 (abbreviated as GP=400) obtained by addition polymerization of propylene oxide using glycerin as an initiator. , mixed polyol ( _OH = 2740, _OH = 76%, _OH =
2.35). This mixed polyol was added dropwise over 10 to 15 minutes to a 1-volume four-necked flask in which 272 parts of 4,4'-diphenylmethane diisocyanate (abbreviated as MDI) was dissolved, and then stirred at 85°C for 4 hours to react. urethane prepolymer containing terminal isocyanate groups (NCO = 6.5%, _U = 55%, _U
= 2.13) was obtained. This urethane prepolymer was liquid at room temperature and had a viscosity of 11,000 Cp/25°C.
15% methyl ethyl ketone (MEK) was added to this urethane prepolymer to obtain a prepolymer solution with a viscosity of 1200 cp/25°C. <2> Adhesion test method (2-1) Compression shear adhesive strength Two lauan veneers (water content 35%) and lauan (water content 65%) were coated with the above prepolymer at 250 g/m ² and then stretched. After applying a pressure of 5 kg/cm ² at room temperature for 1 hour, the pressure was released and the mixture was left at room temperature. Three days after depressurization, the compressive shear adhesive strength was measured according to ASTM D-905-49. (2-2) Boiling test A sample prepared in the same manner as in (2-1) was boiled for 3 hours and its condition was observed. Regarding the results, ◎ indicates that the bonded area has not changed at all, 〇 indicates that the bonded area has changed slightly but there is no practical problem, △ indicates that the bonded area has slightly peeled off, and × indicates that the bonded area has peeled off slightly. It shows. (2-3) Tensile shear adhesive strength 250 for plywood, cardboard, PVC foam, slate board, etc.
After applying g/m ² , the lamination was left at 25±1° C. for 3 days, and then measured according to JISK-6851. Urethane adhesives of the present invention and those other than the present invention were produced in a similar manner, and the results of determining the adhesive properties were evaluated in the first
Shown in Table and Table 2.

【table】

【table】

[Table] In the table, the composition of each polyol is as follows. (EO/PO=80/20) _R −6000 EO/PO=80/
20 random addition polymerized diol, molecular weight 6000 (EO/PO=80/20) _R −4000 EO/PO=80/20
Random addition polymerized diol, molecular weight 4000 (EO/PO=80/20) _B −4000 EO/PO=80/
20EO terminal block addition polymerized diol, molecular weight 4000 PEG-4000 polyoxyethylene glycol,
Diol, molecular weight 4000, GP-3000 polyoxypropylene triol,
Molecular weight 3000 (EO/PO=50/50) _R −2600 EO/PO=50/50
Random addition polymerization, triols, molecular weight
2600 PEG-100 Polyoxyethylene diol, molecular weight 1000 PEG-2000 Polyoxyethylene diol, molecular weight 2000 PP-2000 Polyoxypropylene diol, molecular weight 2000 GP-400 Polyoxypropylene triol, molecular weight 400 PP-400 Polyoxypropylene diol, molecular weight 400 DEG Diethylene glycol MDI Diphenylmethane diisocyanate TDI 2.4/2.6.=8/20 Toluene diisocyanate The test results are ◎Excellent, ○Good, △Acceptable, ×Not acceptable.
〓 indicates material failure. Further, the term "foaming" in the operability section of Table 1 indicates that the resin foams due to moisture in the material to be bonded. (), (), () in the raw materials in Table 2 are polyol (),
It means (), (). As is clear from the above table, the urethane prepolymer adhesive of the present invention exhibits excellent adhesive properties and operability.

Claims (1)

[Scope of Claims] 1. A polyoxyalkylene polyol having a molecular weight of 1000 to 8000 and having 2 to 3 hydroxyl groups obtained by randomly adding and polymerizing an alkylene oxide containing 50 to 90% ethylene oxide to an active hydrogen group ( ), and a polyoxypropylene polyol () having a molecular weight of 200 to 800 and having 2 to 3 hydroxyl groups obtained by addition polymerizing propylene oxide to an active hydrogen group, and, if necessary, a monomolecular glycol having an ether group in the molecule ( ) mixed with
(A) A mixed polyol with a mixing ratio of average molecular weight ( _OH ) 1000 to 5000, ethylene oxide addition % ( _OH %) 60 to 80, number average functional group number ( _OH ) 2.2 to 2.5, and two or more isocyanate groups. (B) A terminal isocyanate obtained by reaction with an organic isocyanate and having an isocyanate group content (NCO%) of 2 to 20, an ethylene oxide addition percentage ( _U %) of 35 to 70, and a number average functional group number ( _U ) of 2.02 to 2.35. A urethane adhesive consisting of a group-containing urethane prepolymer. 2 Polyoxyalkylene polyol () with a molecular weight of 1000 to 8000 and having 2 to 3 hydroxyl groups obtained by randomly adding and polymerizing alkylene oxide containing 50 to 90% ethylene oxide to active hydrogen groups, Molecular weight with 2 to 3 hydroxyl groups obtained by addition polymerization of propylene oxide
200 to 800 polyoxypropylene polyol () and a monomolecular glycol () having an ether group in the molecule, or a mixed polyol in which polyols (), (), () are optionally mixed, and an organic isocyanate. A mixture of two or more types of prepolymers containing terminal isocyanate groups containing polyol () and polyol () as essential components has the property (A) [average molecular weight ( _OH ) of 1000 ~5000, ethylene oxide addition % ( _OH %) 60~80, number average functional group number ( _OH )
2.2 to 2.5], and as a prepolymer, properties (B) [Isocyanate group content (NCO%) 2 to 20, ethylene oxide addition % ( _U %) 35 to 70, number average number of functional groups ( _U ) 2.02 to 2.35] A urethane adhesive made of a urethane prepolymer containing isocyanate groups that satisfies the following requirements.