JPH0116278B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new and useful water-based adhesive, and more particularly, it has excellent adhesion and heat creep properties even after long-term storage, and has other properties such as initial adhesion. This invention relates to an aqueous adhesive mainly consisting of a cationic aqueous polyurethane and a polyvinyl acetate emulsion, which has a specific mixing ratio and has an ionizable cationic nitrogen atom content of 0.4% by weight or more, and has excellent adhesion performance. It is something. Although polyvinyl acetate emulsions have been widely used as adhesives for adherends such as wood, paper, cloth, polyvinyl chloride, or aluminum, their adhesive performance is still insufficient. For example, for hydrophobic adherends such as polyvinyl chloride or water-repellent paper, emulsions such as ethylene-vinyl acetate copolymer or acrylic ester-vinyl acetate copolymer are used. However, in the case of such polyvinyl acetate emulsions, the adhesion performance such as adhesion and heat-resistant creep properties is not necessarily satisfactory, and furthermore, peeling such as blistering is often observed during use, which needs to be solved. There is a problem that cannot be solved. In order to solve such adhesive performance, for example, JP-A-53-134833 discloses that a water-based polymer such as an ethylene-vinyl acetate copolymer emulsion and a hydroxyl group on the side chain or terminal of a urethane resin are used.
Examples include water-based adhesives mainly consisting of a mixture with a water-soluble or water-dispersible polyurethane resin into which a hydrophilic group such as an amino group or a carboxyl group has been introduced. Among these, urethane resins with only hydroxyl or amino groups introduced into the side chains or terminals have poor water solubility and require a large amount of emulsifier to make them water-dispersible; On the other hand, adhesives that use anionic water-soluble or water-dispersible urethane resins with carboxyl groups introduced into the side chains and salted with ammonia etc. If abnormal phenomena such as separation, viscosity change, or gelation occur during storage after preparation, or even in the absence of such abnormal phenomena, significant heat creep may occur when using adhesives that have been used for a long period of time. In any case, there is still room for improvement, as a significant decline was observed. For this reason, such adhesives should be prepared immediately before use.
It was necessary to use a so-called two-component type, or to use it within a relatively short period of time after preparation. However, the inventors of the present invention have conducted intensive research to obtain a water-based adhesive that is free from these various drawbacks, and have found that the content of ionizable nitrogen atoms is 0.4% by weight or more based on the solid content. Based on a mixture of cationic water-based polyurethane and polyvinyl acetate emulsion in a specific ratio, the PH
Water-based adhesives with a value of 7 or less have excellent adhesion properties such as adhesion, heat-resistant creep, and initial adhesion, and
It was discovered that the adhesive performance does not deteriorate even after long-term storage, and the present invention was completed. That is, the present invention consists of a cationic aqueous polyurethane having an ionizable nitrogen atom content of 0.4% by weight or more and a polyvinyl acetate emulsion as main components in a ratio of 2 to 50:98 to 50 (solid content weight ratio).
The present invention provides an aqueous adhesive characterized in that it contains the following proportions and has a pH of 7 or less. The cationic water-based polyurethane (hereinafter abbreviated as cationic water-based polyurethane) having a content of ionizable nitrogen atoms of 0.4% by weight or more, which is the first component of the water-based adhesive in the present invention, refers to the main chain of the polyurethane. , a water-soluble product obtained by introducing 0.4% by weight or more of ionizable nitrogen atoms into the side chain or terminal, based on the solid content, and cationizing some or all of these nitrogen atoms with an acid or an alkylating agent. Or it refers to water-dispersible water-based polyurethane,
The ionizable nitrogen atom is preferably a tertiary or quaternary nitrogen atom. When producing a cationic water-based polyurethane, if the content of cationic nitrogen atoms is too low, a large amount of emulsifier is required to obtain a stable cationic water-based polyurethane, and it is difficult to obtain a stable cationic water-based polyurethane. Water-based adhesives containing cationic water-based polyurethane inevitably suffer from heat-resistant creep or poor adhesion. In order to improve such heat-resistant creep and adhesion, it is absolutely necessary to increase the content of ionizable nitrogen atoms to 0.4% or more. Next, typical examples of the production method of the cationic water-based polyurethane used in the present invention will be given, but the production method is not limited to these. (1) After adding an alkylating agent to a solvent solution of polyurethane consisting of a polyol, polyisocyanate, and a tertiary nitrogen-containing chain extender to quaternize it,
(2) A method for obtaining aqueous polyurethane by mixing this with water. (3) A method for obtaining an aqueous polyurethane by mixing a urethane polymer consisting of a polyol, a polyisocyanate and a tertiary nitrogen-containing chain extender with an acid aqueous solution, (4) A polyol, in part A method in which a urethane prepolymer consisting of a blocked polyisocyanate and a tertiary nitrogen-containing chain extender is reacted with an alkylating agent to quaternize it, and then mixed with an aqueous diamine solution to obtain an aqueous polyurethane. (5) Polyol (6) A method for obtaining an aqueous polyurethane by mixing a polyurethane consisting of a polyisocyanate, a tertiary nitrogen-containing chain extender, and a tertiary nitrogen-containing monool with an acid aqueous solution; This method involves reacting with a polyamine, then introducing a quaternary nitrogen atom using epihalohydrin and trialkylamine, and mixing with water to obtain an aqueous polyurethane. Further, a solvent that dissolves in polyurethane, such as acetone, ethyl acetate, methyl ethyl ketone, or toluene, may be included as long as the aqueous properties of the cationized polyurethane are not impaired. As shown in the above-mentioned production method example, when obtaining a cationic water-based polyurethane, first, a compound containing an ionizable nitrogen atom and also a reactive hydrogen atom is used as a component of the polyurethane. Representative examples of such compounds include the following. (a) N-alkyldialkoxylated amines: for example N-methyldiethanolamine, N-ethyldiethanolamine, N-propyldiethanolamine, N-isopropyldiethanolamine, N-butyldiethanolamine, N-isobutyldiethanolamine, N-oleyldiethanolamine, N-stearyl Diethanolamine, ethoxylated amine of coconut oil, N-
Allyldiethanolamine, N-methyldiisopropanolamine, N-ethyldiisopropanolamine, N-butyldiisopropanolamine or N-cyclohexyldiisopropanolamine (b) N,N-diethoxyaniline, N,N-diethoxy-α-amino Pyridine, N,N'-diethoxypiperazine, dimethyl-bis-ethoxy-hydrazine, N,N'-bis-(β-hydroxyethyl)-N,N'-diethyl-hexahydro-P-phenylenediamine or N- β-hydroxyethylpiperazine (c) Polyalkoxylated amines such as propoxylated methyldiethanolamine (d) N-methyl-N,N-bis-γ-aminopropylamine, N-(γ-aminopropyl)-N,
N'-dimethylethylenediamine, N-(γ-aminopropyl)-N-methylethanolamine,
N,N'-bis-(γ-aminopropyl)-piperazine, N,N'-bis-ethoxypropylenediamine, 2,6-diaminopyridine, diethanolamine acetamide, diethanolamine propionamide, N,N-bis-ethoxy Phenyl-thiosemicarbazide, N,N-
Bis-ethoxymethyl semicarbazide or P.P'-bis-aminomethyl dibenzylamine (e) Tertiary nitrogen-containing monools, such as dimethylethanolamine, diethylethanolamine, dimethylisopropanolamine or diethylisopropanolamine. On the other hand, any aromatic, aliphatic, or cycloaliphatic diisocyanate can be used as the polyisocyanate, and the following are typical among them. 1,5-Naphthylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyldimethylmethane diisocyanate, di- and tetra-
alkyl diphenylmethane diisocyanate,
4,4'-dibenzyl diisocyanate, 1,3-
Each isomer of phenylene diisocyanate, 1,4-phenylene diisocyanate, toluylene diisocyanate (and optionally a mixture of the isomers); 1-methyl-2,4-diisocyanatocyclohexane, 1,6-diisocyanate isocyanate-2,
2,4-trimethylhexane, cyclohexane-
1,4-diisocyanate, dicyclohexylmethane diisocyanate, 1-isocyanatomethyl-3-isocyanate-1,5,5-trimethylcyclohexane; chlorinated and brominated diisocyanates; phosphorus-containing diisocyanates;
4,4'-diisocyanate-phenyl-perfluoroethane; tetramethoxybutane-1,4-diisocyanate, butane-1,4-diisocyanate, hexane-1,6-diisocyanate, ethylene-diisocyanate; P-xylylene diisocyanate, m - xylylene diisocyanates and the hydrogenated products of each of the above aromatic diisocyanates, and furthermore, containing excess amounts of these diisocyanates and water, diamines, glycols, polyalcohols or aminoalcohols, or tertiary nitrogen atoms. , and a reaction product with a compound that also has a reactive hydrogen atom. Further, as the polyamine, a compound having amino groups at both ends and a -NH- group in the main chain can be used. Typical examples include polyamines such as diethylenetriamine, dipropylenetriamine, or tetraethylenediamine. It is an alkylene polyamine. Furthermore, as a polyol, a relatively high molecular weight compound having a reactive hydrogen atom at the end, e.g.
Examples thereof include polyethers, polyesters, polyester amides, polyacetals, polythioethers, polyamides, and polybutadiene glycols having a molecular weight of 200 to 20,000. Furthermore, as the tertiary nitrogen-containing polyol, a compound containing a tertiary nitrogen atom and also a reactive hydrogen atom may be reacted in combination with a relatively high molecular weight polyol, or for example, ester reaction, etherification, etc. It may also be obtained by incorporating it into a polymer polyol by applying an elementary reaction such as reaction or amidation reaction. As the chain extender, relatively low molecular weight compounds having reactive hydrogen atoms can be used, such as glycols, aliphatic, cycloaliphatic and aromatic diamines, amino alcohols, water or Examples include compounds that contain a tertiary nitrogen atom and also have a reactive hydrogen atom. Examples of alkylating agents used for cationizing polyurethane include the following. Methyl chloride, methyl bromide, methyl iodide, ethyl bromide, propyl bromide, butyl bromide, dimethyl sulfate, diethyl sulfate chloromethyl ether, methyl-1,2-dichloroethyl ether, ethyl chloromethyl ether, Benzyl chloride, benzyl bromide, ethylene chlorohydrin, epichlorohydrin, ethylene oxide,
Propylene oxide, styrene oxide, ethyl benzyl sulfonate, chloroacetic acid, glycol
Examples include monobromoacetic acid esters, glycerin monochloroacetate, promoethyl ester of acetic acid, 1,4-dibromobutane, and P-xylylene dichloride. Similarly, as the acid used to cationize polyurethane, ordinary acids can be used, but representative ones include hydrochloric acid, sulfuric acid, sulfurous acid, hydrobromic acid, hydrofluoric acid, and phosphorous acid. Inorganic acids such as hypophosphorous acid, fluoroboric acid, amidosulfonic acid, phosphoric acid and its derivatives; and organic carboxylic acids such as tartaric acid, oxalic acid, lactic acid, formic acid, acetic acid and acrylic acid. . On the other hand, the polyvinyl acetate emulsion which is the second component of the adhesive of the present invention is a vinyl acetate polymer emulsion; or a combination of vinyl acetate monomer and one or more other monomers. It is a polymer in which vinyl acetate monomer accounts for 50% of the weight composition.
% or more; it is also possible to use mixtures of these emulsions. Typical examples of the other monomers mentioned above include esters of acrylic acid or methacrylic acid such as methyl, ethyl, butyl, 2-ethylhexyl or glycidyl, and α such as ethylene, propylene or isobutylene. -Olefins, diesters of itaconic acid or maleic acid, vinyl propionate,
Examples include acrylamide, acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and crotonic acid. In addition, it is of course possible to use other types of monomers that cannot be directly copolymerized with vinyl acetate via monomers that can be copolymerized with the vinyl acetate monomer. be. The polyvinyl acetate emulsion used in the present invention is produced by combining vinyl acetate monomer or vinyl acetate monomer and other monomers in the presence of one or more surfactants or protective colloids. can be obtained by emulsion polymerization using a conventional method.
The above-mentioned surfactant or protective colloid used in this case is preferably nonionic or cationic, and on the contrary, strongly anionic is preferable since it impairs the stability of the aqueous adhesive of the present invention. do not have. The composition ratio of the cationic water-based polyurethane and the polyvinyl acetate emulsion, which are the main components of the water-based adhesive of the present invention, is a solid content weight ratio of 2-50:98-50. If the composition ratio of the cationic water-based polyurethane is less than 2, the desired adhesion performance such as adhesion or heat-resistant creep cannot be obtained;
The larger the adhesive becomes, the more difficult it becomes to adjust the viscosity of the adhesive, and the initial adhesiveness tends to gradually deteriorate, which is also economically disadvantageous. The pH of the aqueous adhesive of the present invention needs to be acidic at 7 or less, and more preferably PH2 to 6. An alkaline pH higher than 7 is disadvantageous because the adhesive may gel after preparation, change in viscosity, or deteriorate adhesive performance due to heat-resistant creep. Other compounding agents conventionally used in polyvinyl acetate emulsion adhesives can be added to the aqueous adhesive of the present invention thus obtained, if necessary. Typical examples of such compounding agents include solvents such as toluene, xylene, chlorobenzene, trichlorethylene, butyl acetate, or butyl cellosolve; polyvinyl alcohol, cellulose derivatives such as hydroxyethyl cellulose, casein, polyvinylpyrrolidone, and polyalkylene ethers. , water-soluble polymeric substances such as esters or ether derivatives of polyalkylene ethers, polyamides, polyacrylic acids, polyacrylamides or polyamines;
Examples include plasticizers such as DBP or DOP; tackifiers such as terpene resins; inorganic fillers and pigments. The water-based adhesive of the present invention is suitable for cellulosic materials such as paper, fibers, and wood; inorganic materials such as concrete and silica boards; plastic materials such as vinyl chloride and polystyrene; metal materials such as aluminum;
It can be used as an adhesive for many other materials. Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. In the following, all references to "%" mean "% by weight" unless otherwise specified. Reference Example 1 200 g of poly-1,6-hexane adipate with a hydroxyl value of 56.3 and an acid value of 0.5, 12 g of 1,6-hexanediol, 12 g of methyldiethanolamine, and 105 g of 2,4-toluylene diisocyanate were mixed into 165
12 g of methyl sulfuric acid was added to the prepolymer solution obtained by reacting it in 1 g of toluene, and the mixture was stirred at 40°C for 2 hours. Then, 165 g of acetone was added to make a homogeneous solution, and 340 g of water was added with vigorous stirring to dissolve the milk. It became a cloudy liquid. Next, the solvent was removed under reduced pressure to obtain a cationic aqueous polyurethane. This is a milky white viscous liquid with a non-volatile content of 50.2
%, PH=4.8, and viscosity 9200 cps. The content of ionizable nitrogen atoms was 0.4% in the solid content of the polyurethane. Hereinafter, this cationic aqueous polyurethane emulsion will be abbreviated as "A-1". Reference Example 2 Adding acetone to the prepolymer obtained in Reference Example 1
After adding 165 g, this was added dropwise to a mixture of 340 g of water and 6 g of acetic acid to form a milky white liquid, and then the solvent was removed under reduced pressure to obtain a cationic aqueous polyurethane. This substance is a milky, viscous liquid;
The nonvolatile content was 49.9%, the pH was 5.0, and the viscosity was 12,000 cps.
Further, the content of ionizable nitrogen atoms was 0.4% in the solid content of the polyurethane. Hereinafter, this cationic aqueous polyurethane emulsion will be abbreviated as "A-2". Reference example 3 50 g of methylamine propylene oxide adduct with hydroxyl value 225.0, hydroxyl value 56.5 and acid value 0.4
200g of poly-1,4-butane adipate, 1,
6.0 g of glacial acetic acid was added to a prepolymer solution obtained by reacting 4.5 g of 4-butanediol and 84 g of hexamethylene diisocyanate in 340 g of methyl ethyl ketone, and after uniform stirring, this was mixed into a mixture of 11.0 g of piperazine and 360 g of water. A milky white liquid was obtained. Next, the solvent was removed under reduced pressure to obtain a cationic aqueous polyurethane. This is a milky white viscous liquid with a non-volatile content of 48.3
%, PH=6.0, and viscosity 6000 cps. Further, the content of ionizable nitrogen atoms was 0.4% in the solid content of the polyurethane. Hereinafter, this polyurethane emulsion will be abbreviated as "A-3". Reference example 4 Poly-1,6 with hydroxyl value 112.1 and acid value 0.3
- 200 g of hexane maleate, 12 g of triethanolamine and 2,4/2,6 = 80/20 (weight ratio)
6.0 g of glacial acetic acid was added to a polyurethane solution obtained by reacting 35 g of toluylene diisocyanate in 247 g of acetone, and the mixture was stirred and mixed uniformly. After that, 380 g of water was added to form an aqueous dispersion, and then the solvent was removed under reduced pressure. After removal, a cationic water-based polyurethane was obtained. This is a milky white viscous liquid, non-volatile content 40.1%, PH = 6.2, viscosity 1600cps
It was hot. Further, the content of ionizable nitrogen atoms is 0.55% in the solid content of the polyurethane. Hereinafter, this polyurethane emulsion will be referred to as "A-4".
It is abbreviated as Comparative production example 1 Poly-1,6 with hydroxyl value 56.3 and acid value 0.5
-Hexane adipate 200g, 1,6-hexanediol 12g, methyl diethanolamine 1.2
g and 2,4-toluylene diisocyanate
73.5g was reacted in 143g of toluene to obtain a prepolymer solution, 1.2g of dimethyl sulfuric acid was charged, and the mixture was stirred at 40°C for 2 hours. Then, 143g of acetone was added to make a homogeneous solution.
When 317 g of water was added with vigorous stirring, the mixture became gel-like and could not be dispersed in water. Comparative production example 2 Poly-1,6 with hydroxyl value 56.3 and acid value 0.5
-200g of hexane adipate, 12g of 1,6-hexanediol, 13.4g of dimethylolpropionic acid
and 2,4-toluylene diisocyanate 105
165 g of acetone was added to the prepolymer solution obtained by reacting 165 g of toluene with 165 g of acetone to make a homogeneous solution.
g, piperazine (23 g) and water (360 g) to form a milky white liquid, and then the solvent was removed under reduced pressure to obtain an anionic water-based polyurethane. This product was a milky white liquid with a nonvolatile content of 49.7%, a pH of 8.1, and a viscosity of 300 cps. below,
This anionic aqueous polyurethane emulsion was
It is abbreviated as ``1''. Examples 1 to 5 and Comparative Examples 1 to 4 Water-based polyurethane and "Evadik EP-11"
[Ethylene-vinyl acetate copolymer emulsion manufactured by Dainippon Ink and Chemicals Co., Ltd.; solid content = 53%, 25°C
viscosity = 6000 cps, PH = 4.2] in the proportions listed in Table 1 (units are parts by weight),
Further, 3 parts by weight of toluene was added to 100 parts by weight of the solid content of the mixture to prepare an adhesive. At this time, only the adhesive of Comparative Example 3 was used at pH=7.5.
Except for adjusting to (slightly alkaline), PH=
Adjusted to 4.2 (acidic). This adhesive was applied to JAS Class 1 lauan plywood at a rate of 110 g/m ² , a polyvinyl chloride sheet, usually called a doubling sheet, was applied, and the adhesive was pressed at a pressure of 1 kg/cm ² for 15 hours, and then depressurized. After curing for one week, the samples were subjected to the next test. Normal Adhesion Test A 180° peel test was conducted on a test piece with a width of 25 mm at a speed of 200 mm/min. Heat resistance creep test A polyvinyl chloride sheet with a width of 25 mm x 200 mm was peeled 50 mm in the vertical direction, and the test piece was placed horizontally and the peeled polyvinyl chloride sheet was placed vertically in an atmosphere of 60℃. After placing it in a dryer and leaving it for 10 minutes, a load of 500 g was applied to the tip of the polyvinyl chloride sheet, and the length of the sheet was measured after 15 minutes. In this case, the shorter the peeled length, the better the heat-resistant creep property. Adhesion test Two polyvinyl chloride sheets were placed from a 25 mm wide test piece.
Good adhesion is achieved when peeling is performed at a rate of 90° at a speed of mm/sec, and there is no specular peeling between the polyvinyl chloride sheet and the adhesive layer. In this adhesion test, the test piece was tested immediately at 23°C and when it was left at -5°C for 20 hours. For the adhesive that had been left at a temperature of 23° C. for 3 weeks after preparation, test pieces were prepared in the same manner as above, and the same normal adhesive strength, heat resistance creep and adhesion tests were repeated. The above results are shown in Table 1.

【table】

[Table] Examples 6 to 7 and Comparative Example 5 Water-based polyurethane and commercially available paper adhesive polyvinyl acetate emulsion (solid content 45%, viscosity 1300 cps,
PH4.2; polyvinyl alcohol, toluene, DBP
(containing)) in the proportions shown in Table 2 to prepare an adhesive. The pH was adjusted to 4.2. Then apply this adhesive to K-liner paper at 50 g/m ²
While applying the adhesive, immediately attach the other K-liner paper to which no adhesive has been applied, and after a predetermined period of time, peel it off at 180°. Find the time for 25% and 100%. It can be said that the shorter the time, the better the initial adhesion. Note that the test was conducted at both temperatures of 23°C and 5°C. The results are summarized in Table 2.

[Table] It can be seen that the product of the present invention has a shorter paper tearing time and superior initial adhesion than the conventional product (Comparative Example 5). Examples 8 to 9 and Comparative Example 6 Commercially available polyvinyl acetate emulsion (solid content) used for water-based polyurethane and adhesive for decorative plywood
42%, viscosity 25000 cps at 25°C, PH 4.2; containing polyvinyl alcohol, DBP and titanium oxide) were mixed in the proportions shown in Table 3 to prepare an adhesive. Decorative plywood is manufactured using the obtained adhesive, and tests are conducted on the surface condition of the decorative plywood and in accordance with JAS special plywood standards - printed plywood class 2. The drying oven at the manufacturing site is 15m long, and the laminator is 25mmφ.
5 rolls (2 heated to 100℃, others at room temperature), the base plate is 3mm thick lauan plywood, the decorative paper is 23g/ ^m2 tissue paper, and the amount of coating before gluing is 65mm.
g/m ² , the line speed was 45 m, and the drying oven temperatures were compared at three points: 80°C, 120°C, and 150°C, respectively. The results are summarized in Table 3.

【table】

[Table] It can be seen that the product of the present invention is much better than the conventional product (Comparative Example 6).

Claims (1)

[Claims] 1. A cationic aqueous polyurethane containing 0.4% by weight or more of ionizable nitrogen atoms and a polyvinyl acetate emulsion as main components, 2.
50:98-50 (solid content weight ratio), and has a pH of 7 or less.