JP2008239848A - Adhesive agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive agent excellent in viscosity stability, initial adhesiveness, water-resistant adhesive property and further safety. <P>SOLUTION: The adhesive agent is an aqueous adhesive prepared by dissolving (A) a polyvinyl alcohol based polymer having ≥90 mol% of vinyl alcohol unit and 300-4,000 of degree of polymerization and (B) a polyacrylic acid based copolymer containing 5-40 mol% of a monomer unit originating from ethylenic unsaturated monomer containing an acetal group prepared by the copolymerization of acrylic acid with the ethylenic unsaturated monomer containing an acetal group, in an aqueous solvent (C), wherein the content of the component (A) to the component (C) is 5-25 wt.%, and the weight ratio of the component (A) and the component (B), that is, (A):(B) is 99:1-50:50. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an adhesive. More specifically, it is mainly composed of a specific vinyl alcohol polymer and a copolymer of a specific acrylic acid and an acetal group-containing ethylenically unsaturated monomer, and is excellent in viscosity stability, initial adhesion, and water-resistant adhesion. Furthermore, the present invention relates to a water-based adhesive that is excellent in terms of safety.

Conventionally, as adhesives, particularly as paper adhesives, natural pastes such as starch, casein, gelatin, guar gum, gum arabic and sodium alginate, processed natural pastes such as CMC, oxidized starch and methylcellulose, acrylic emulsions, Mainly composed of polyvinyl acetate emulsion, ethylene-vinyl acetate copolymer emulsion, synthetic resin emulsion such as SBR latex, various rubber latex, and vinyl alcohol polymer (hereinafter abbreviated as “PVA”). Such adhesives are widely used alone or in combination.
However, natural glues and processed pastes have problems such as insufficient adhesive strength, lack of viscosity stability of the adhesive solution, and spoilage. In addition, it is not possible to obtain products with consistent quality over a long period of time. There is. On the other hand, emulsions and latexes are excellent in adhesive strength but often have problems such as lack of mechanical stability and severe surface skinning.

On the other hand, PVA-based adhesives are inexpensive and have excellent adhesiveness, and are widely used for paperboard bonding, cardboard bonding, paper tube bonding, paper and wallpaper, etc. Has been used as an award. However, in recent years, PVA-based adhesives have been increasingly used for high-speed coating of adhesives with the aim of reducing costs and improving productivity, and require stronger adhesive strength and durability (water resistance, etc.). It has come to be.
As an improvement measure for these requirements, for example, an adhesive composed of PVA and boric acid has been widely used for the purpose of improving high-speed adhesion, initial adhesion, and water resistance, but there is a concern about the impact on the environment. The use of boric acid is in a limited situation and there is a strong need for an alternative. Similarly, many attempts have been made to improve the initial adhesiveness and water resistance by using a compound (for example, urea-formalin resin) that becomes a cross-linking agent for PVA. In many cases, there is a problem in the safety of the compound used as the selenium, and there are many problems in the viscosity stability of the composition.

  For example, in Japanese Patent Laid-Open No. 04-239085 (Patent Document 1), an adhesive containing a specific metal salt is proposed. However, although high-speed coating property and initial adhesive force are improved, there is a problem in solution stability. However, it was not fully satisfactory industrially. Further, JP-A-11-021530 (Patent Document 2) proposes an adhesive comprising modified polyvinyl alcohol (A), starch (B) and saccharide (C) containing 1 to 20 mol% of ethylene units. However, although the adhesive strength, water-resistant adhesive strength, and storage stability are improved, it may be insufficient in terms of high-speed coating property, heat resistance, and creep resistance. Japanese Patent Application Laid-Open No. 2001-164219 (Patent Document 3) contains 1.8 to 3.5 mol% of 1,2-glycol bond in the molecule and has a caking degree of 90 mol% or more. Adhesives comprising a polymer (a) and an inorganic filler (b) as essential components have been proposed. Although the viscosity stability, high-speed coating property and initial adhesive force have been remarkably improved, In some cases, the durability is not sufficient.

Prior art documents relating to the present invention include the following.
Japanese Patent Laid-Open No. 04-239085 JP-A-11-021530 JP 2001-164219 A

  The present invention was devised to eliminate the above-mentioned drawbacks of the prior art, and is an aqueous adhesive that is excellent in viscosity stability, initial adhesion, water-resistant adhesion, and also in terms of safety. The purpose is to provide.

  As a result of intensive studies to solve the above problems, the inventors of the present invention have a vinyl alcohol unit (A) having a vinyl alcohol unit of 90 mol% or more and a polymerization degree of 300 to 4000, and acrylic acid. A polyacrylic acid copolymer (B) obtained by copolymerization with an acetal group-containing ethylenically unsaturated monomer and containing 5 to 40 mol% of units derived from the acetal group-containing ethylenically unsaturated monomer Is an aqueous adhesive dissolved in the aqueous medium (C), wherein the component (A) is 5 to 25% by weight with respect to (C), and the weight ratio (A) of the components (A) and (B): An adhesive having (B) of 99: 1 to 50:50 was found, and the present invention was completed.

  The adhesive of the present invention satisfies all of viscosity stability, high-speed coating property, initial adhesiveness, and water-resistant adhesiveness at the same time. Therefore, since the viscosity stability (storage stability) of the adhesive solution is good, in addition to excellent workability, high-speed coating property is good, and adhesive force is expressed from the very initial stage after bonding. The bonding speed can be increased as compared with the adhesive, and since the water resistance is high, the durability around water or in high humidity is excellent. Moreover, since the adhesive of the present invention does not contain harmful components, it is excellent in safety.

  PVA (A) used in the present invention is not particularly limited as long as it has 90 mol% or more of vinyl alcohol units, has a polymerization degree of 300 to 4000, and is water-soluble.

The vinyl alcohol unit in the PVA used in the present invention needs to be 90 mol% or more, preferably 90 to 99.9 mol%, more preferably 92 to 99.6 mol%, and 93 More preferably, ˜99.5 mol%. When the vinyl alcohol unit is less than 90 mol%, the initial adhesive strength is not sufficiently developed, and the level of water-resistant adhesive strength is insufficient.
The “vinyl alcohol unit in PVA” as used herein is the mol% of the vinyl alcohol group in the monomer unit in PVA, and is a portion excluding unsaponified vinyl acetate units and modified group units other than vinyl acetate. Point to.

  The PVA used in the present invention is required to have a degree of polymerization of 300 to 4000, more preferably 500 to 3500, and particularly preferably 1000 to 3000. If PVA with a polymerization degree of less than 300 is used, the adhesive strength and water resistance of the resulting adhesive will decrease, and if the polymerization degree exceeds 4000, industrial production will be difficult and the viscosity of the adhesive will increase. There is a risk that problems such as a decrease in high-speed coating property and initial adhesive strength may occur.

  As PVA, usually a vinyl ester monomer represented by vinyl acetate is usually polymerized by various methods (bulk polymerization, solution polymerization using methanol as a solvent, emulsion polymerization, suspension polymerization, etc.) PVA obtained by saponification by means of is used. In addition to vinyl acetate, vinyl formate, vinyl propionate, vinyl versatate, vinyl pivalate and the like can be used as the vinyl ester monomer.

  In addition, the PVA used in the present invention can be copolymerized in the coexistence of a monomer copolymerizable with a vinyl ester monomer within a range not impairing the effects of the present invention. For example, olefins such as ethylene, propylene, 1-butene, isobutene, acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, t-butyl acrylate Acrylic acid esters such as 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, Methacrylic acid esters such as t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, methyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether , Vinyl ethers such as i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether and stearyl vinyl ether, nitriles such as acrylonitrile and methacrylonitrile, vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride and vinylidene fluoride , Allyl compounds such as allyl acetate, allyl chloride, fumaric acid, maleic acid, itaconic acid, maleic anhydride, phthalic anhydride, trimetic anhydride or itaconic anhydride and other carboxyl group-containing compounds and esters thereof, ethylenesulfonic acid, Sulfonic acid group-containing compounds such as allyl sulfonic acid, methallyl sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, diacetone acrylamide, diacetone acrylate, diacetone methacrylate Seton group-containing compounds, vinylsilane compounds such as vinyltrimethoxysilane, isopropenyl acetate, 3-acrylamidopropyltrimethylammonium chloride, 3-methacrylamidopropyltrimethyl ammonium chloride.

  Further, terminal thiol group-modified PVA obtained by polymerizing a vinyl ester monomer such as vinyl acetate in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid and saponifying it can also be used.

  In addition, the PVA used in the present invention can be modified PVA obtained by modifying the PVA by a post-reaction by a conventionally known method within a range that maintains water solubility and does not impair the effects of the present invention. Examples of PVA modified by post-reaction include acetal-modified PVA modified with an aldehyde such as butyraldehyde, acetoacetyl-modified PVA modified with diketene, and the like.

  In the present invention, when ethylene-modified PVA and / or acetoacetyl-modified PVA is used as PVA (A), viscosity stability, initial adhesiveness, and water-resistant adhesiveness are particularly good, which is preferable.

  When ethylene-modified PVA obtained by copolymerizing ethylene is used as PVA (A), the ethylene-derived unit is preferably 2 to 8 mol%, more preferably 2 to 7.5 mol%. When the modification amount is less than 2 mol%, the water-resistant adhesive strength may not be remarkably improved, and when it exceeds 8 mol%, the viscosity stability may decrease.

  When an acetoacetyl-modified PVA having an acetoacetyl group introduced is used as PVA (A), generally the acetoacetyl modification amount is preferably 2 to 8 mol%, more preferably 2 to 7.5 mol%. preferable. When the modification amount is less than 2 mol%, the water-resistant adhesive strength may not be remarkably improved, and when it exceeds 8 mol%, the viscosity stability may decrease.

  The polyacrylic acid copolymer (hereinafter sometimes abbreviated as PAA copolymer) (B) used in the present invention is obtained by copolymerization of acrylic acid and an acetal group-containing ethylenically unsaturated monomer. can get. The PAA copolymer needs to contain 5 to 40 mol% of a unit derived from the acetal group-containing ethylenically unsaturated monomer (sometimes abbreviated as acetal modification amount), preferably 5 to 5 mol%. 35 mol%, more preferably 5 to 30 mol%. When the amount of acetal modification is less than 5 mol%, the effect of using an acetal group-containing ethylenically unsaturated monomer may not be sufficiently exhibited. When the amount of acetal modification exceeds 40 mol%, The compatibility between the coalesced and PVA (A) is lowered, and the water-resistant adhesiveness, which is the object of the present invention, may not be sufficiently developed.

The amount of acetal modification of the PAA copolymer (B) can be determined from proton NMR. As an example of a PAA copolymer obtained using N-2,2-dimethoxyethyl (meth) acrylamide as the acetal group-containing ethylenically unsaturated monomer, the method for obtaining the acetal modification amount will be described. A PAA copolymer is dissolved in D ₂ O, and proton NMR is measured at room temperature using 500 MHz proton NMR (JEOL GX-500). As a result of the measurement, the peak α (2.0 to 2.4 ppm) derived from the main chain methine of acrylic acid and the peak β (4.1 to 4.5 ppm derived from methine of —CH— (OCH ₃ ) ₂ are obtained. ), The acetal modification amount is calculated using the following formula.
Acetal modification amount (mol%) = {number of protons of β / (number of protons of α + number of protons of β)} × 100

  The molecular weight of the PAA copolymer (B) used in the present invention is preferably 1,000 to 1,000,000. When the molecular weight exceeds 1,000,000, the water solubility of the PAA copolymer may decrease.

  In the present invention, the acetal-containing ethylenically unsaturated monomer used for the production of the PAA copolymer (B) can be used as long as it is an ethylenically unsaturated monomer containing an acetal group. However, it is preferable to use an ethylenically unsaturated monomer represented by the formula (1).

（式中、Ｒ１は水素原子または−ＣＯＯＭであり、ここでＭは水素原子、アルカリ金属またはアンモニウム基を意味し、Ｒ２は水素原子、メチル基または−ＣＨ_２−ＣＯＯＭであり、ここでＭは前記定義のとおりであり、Ｒ３およびＲ４は同一または異なりそれぞれ炭素数１〜４の飽和アルキル基であり、Ｘは−ＣＯ−、−ＣＯ−Ｏ−または−ＣＯ−ＮＲ５であり、ここでＲ５は水素原子または炭素数１〜４の飽和アルキル基を意味し、ｎは１〜８の整数である。）

(Wherein R1 represents a hydrogen atom or —COOM, wherein M represents a hydrogen atom, an alkali metal or an ammonium group; R2 represents a hydrogen atom, a methyl group or —CH ₂ —COOM, where M represents As defined above, R 3 and R 4 are the same or different and each is a saturated alkyl group having 1 to 4 carbon atoms, X is —CO—, —CO—O— or —CO—NR 5, wherein R 5 is A hydrogen atom or a C1-C4 saturated alkyl group is meant, and n is an integer of 1-8.)

Specific examples of the acetal-containing ethylenically unsaturated monomer include N-2,2-dimethoxyethyl acrylamide, N-2,2-diethoxyethyl acrylamide, N-2,2-diisopropoxyethyl acrylamide, N- 2,2-dibutoxyethyl acrylamide, N-2,2-di-t-butoxyethyl acrylamide, N-2,2-dimethoxyethyl methacrylamide, N-2,2-diethoxyethyl methacrylamide, N-2, 2-diisopropoxyethyl methacrylamide, N-2,2-dibutoxyethyl methacrylamide, N-2,2-di-t-butoxyethyl methacrylamide, N-3,3-dimethoxypropyl acrylamide, N-3, 3-diethoxypropylacrylamide, N-3,3-diisopropoxypropylacrylic N-3,3-dibutoxypropyl acrylamide, N-3,3-di-t-butoxypropyl acrylamide, N-3,3-dimethoxypropyl methacrylamide, N-3,3-diethoxypropyl methacrylamide, N-3,3-diisopropoxypropyl methacrylamide, N-3,3-dibutoxypropyl methacrylamide, N-3,3-di-t-butoxypropyl methacrylamide, N-4,4-dimethoxybutyl acrylamide, N-4,4-diethoxybutylacrylamide, N-4,4-diisopropoxybutylacrylamide, N-4,4-dibutoxybutylacrylamide, N-4,4-di-t-butoxybutylacrylamide, N- 4,4-dimethoxybutylmethacrylamide, N-4,4-diethoxybutylmeta Rilamide, N-4,4-diisopropoxybutyl methacrylamide, N-4,4-dibutoxybutyl methacrylamide, N-4,4-di-t-butoxybutyl methacrylamide, N-methyl-N-2, 2-dimethoxyethyl acrylamide, N-methyl-N-2,2-diethoxyethyl acrylamide, N-methyl-N-2,2-diisopropoxyethyl acrylamide, N-methyl-N-2,2-dibutoxyethyl Acrylamide, N-methyl-N-2,2-di-t-butoxyethyl acrylamide, N-methyl-N-2,2-dimethoxyethyl methacrylamide, N-methyl-N-2,2-diethoxyethyl methacrylamide N-methyl-N-2,2-diisopropoxyethyl methacrylamide, N-methyl-N-2,2-dibutoxy Ciethyl methacrylamide, N-methyl-N-2,2-di-t-butoxyethyl methacrylamide, 4-{(2,2-dimethoxyethyl) amino} -4-oxo-2-butenoic acid, 4- { (2,2-diethoxyethyl) amino} -4-oxo-2-butenoic acid, 4-{(2,2-diisopropoxyethyl) amino} -4-oxo-2-butenoic acid, 4-{( 2,2-dibutoxyethyl) amino} -4-oxo-2-butenoic acid, 5,5-dimethoxy-3-oxo-pentene, 5,5-diethoxy-3-oxo-pentene, 5,5-diiso Propoxy-3-oxo-pentene, 5,5-dibutoxy-3-oxo-pentene, 4-{(2,2-dimethoxyethyl) amino} -4-oxo-3-methylene-butanoic acid, 4-{(2 , 2-Diethoxyethyl) a No} -4-oxo-3-methylene-butanoic acid, 4-{(2,2-diisopropoxyethyl) amino} -4-oxo-3-methylene-butanoic acid, 4-{(2,2-di Butoxyethyl) amino} -4-oxo-3-methylene-butanoic acid, 2,2-dimethoxyethyl acrylate, 2,2-diethoxyethyl acrylate, 2,2-diisopropoxyethyl acrylate, 2,2-dibutoxy Although ethyl acrylate etc. are mentioned, it is not limited to these.
In the above formula (1), R1 is preferably a hydrogen atom, R2 is preferably a hydrogen atom or a methyl group, R3 and R4 are preferably both methyl groups, and X is —CO—N ( H)-or -CO-N (CH3)-is preferred. Further, n is preferably 1 or 2, and more preferably 1.
Further, in the above formula (1), R 1 is a hydrogen atom, R 2 is a hydrogen atom or a methyl group, R 3 and R 4 are both methyl groups, and X is —CO—N (H) — or —CO It is more preferably —N (CH 3) — and n is 1.

  As a polymerization method used for copolymerizing acrylic acid and an acetal group-containing ethylenically unsaturated monomer, any of batch polymerization method, semi-batch polymerization method, continuous polymerization method and semi-continuous polymerization method can be used. It may be adopted. As the polymerization method, any known method such as a bulk polymerization method or a solution polymerization method can be used. Among these, the solution polymerization method is preferably employed. As the initiator used for copolymerization, conventionally known azo initiators, peroxide initiators, redox initiators and the like are appropriately selected according to the polymerization method. As the azo initiator, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4- Dimethyl valeronitrile) and the like. Peroxide compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate; t-butyl Perester compounds such as peroxyneodecanate, α-cumylperoxyneodecanate, t-butylperoxydecanate; acetylcyclohexylsulfonyl peroxide; 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, etc. Is mentioned. Further, the initiator may be combined with potassium persulfate, ammonium persulfate, hydrogen peroxide, or the like. Examples of the redox initiator include a combination of the above-described peroxide and a reducing agent such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, or longalite.

  The weight ratio (A) :( B) of PVA (A) and PAA polymer (B) needs to be in the range of 99: 1 to 50:50. The weight ratio of the component (A) and the component (B) is preferably 95: 5 to 60:40, and more preferably 90:10 to 65:35. When the component (B) is less than (A) :( B) = 99: 1, the water-resistant adhesiveness is not sufficiently exhibited, and the component (B) is larger than (A) :( B) = 50: 50. In some cases, the viscosity stability deteriorates and the initial adhesiveness decreases.

  The adhesive of the present invention is an aqueous adhesive in which the PVA (A) and PAA polymer (B) are dissolved in an aqueous medium (C). Here, the aqueous medium (C) means water or a mixed medium of water and an organic solvent. In the case of a mixed medium of water and an organic solvent, examples of the organic solvent include methanol, ethanol, isopropanol, and the like. The water-soluble organic solvent is preferable. In general, water or a mixed medium containing 20% by weight or less of a water-soluble organic solvent is preferably used.

  The adhesive of the present invention requires that the PVA (A) is in a ratio of 5 to 25% by weight, preferably 6 to 20% by weight, more preferably 7 to 7%, based on the aqueous medium (C). 18% by weight. When the PVA (A) with respect to the aqueous medium (C) is less than 5% by weight, there is a problem that the initial adhesive strength is lowered, and when it is more than 25% by weight, there is a problem in high speed coating property and viscosity stability. May occur.

  A filler (D) can be added to the adhesive of the present invention. As fillers, inorganic fillers such as kaolinite, halloysite, pyroferrite or sericite clay, heavy, light or surface treated calcium carbonate, aluminum hydroxide, aluminum oxide, gypsum, talc, titanium oxide, etc. And organic fillers such as additives, starches, oxidized starches, wheat flours, and wood flours. Of these, various clays and various starches can be suitably used. These fillers (D) are present in a dissolved or dispersed form in the aqueous medium (C), and the filler (D) is usually 300 parts by weight or less, preferably 250 parts by weight with respect to 100 parts by weight of PVA (A). Or less, more preferably 200 parts by weight or less. In general, an adhesive to which a filler is added tends to develop an initial adhesive force because the total solid concentration increases, and the adhesive layer tends to become hard because the adhesive layer tends to become hard. There are advantages. However, when the amount of the filler (D) is more than 300% by weight relative to 100 parts by weight of the PVA (A), the fluidity of the adhesive is deteriorated, the filler is settled, and further the adhesive strength is reduced. May be undesirable.

  An additive may be added to the adhesive of the present invention as long as the effects of the present invention are not impaired. Examples of these additives include metal salts of phosphate compounds such as sodium polyphosphate and hexametaphosphate, inorganic dispersants such as water glass, polyacrylic acid and its salts, sodium alginate, α-olefin-maleic anhydride Nonionic surfactants such as anionic polymer compounds such as copolymers and their metal salts, ethylene oxide adducts of higher alcohols, copolymers of ethylene oxide and propylene oxide, carboxymethylcellulose, methylcellulose, sodium alginate, polyethylene oxide And various antifoaming agents, antiseptics, antifungal agents, coloring pigments, deodorants, and fragrances. In addition, synthetic resin emulsions such as acrylic emulsion, polyvinyl acetate emulsion, ethylene-vinyl acetate copolymer emulsion, SBR latex, and various rubber latexes can be used in combination.

  In the adhesive of the present invention, the process of forming a film formed by evaporation and drying of the aqueous medium (C) is an important factor for performance. Even in the case of a film formed under mild drying conditions at about room temperature, sufficient water resistance is exhibited. However, when the film is subjected to heat treatment, the water resistance is drastically improved. Also, the film exhibits extremely excellent water resistance by making the pH of the adhesive acidic. Furthermore, even when the pH of the adhesive is adjusted using ammonia or the like, and the treatment is performed such that ammonia evaporates and the pH is lowered during drying, the film exhibits excellent water resistance.

  As a method for preparing the adhesive of the present invention, first, a mixture of other additives such as PVA (A) and filler (D) is added in water with stirring, or various additives, The slurry (D) and the PVA (A) are added to water while sequentially stirring to prepare a slurry liquid. The adhesive can be prepared either batchwise or continuously. The adhesive can be heated and dissolved by any heating method such as a jet cooker or a preparation tank, in which steam is blown directly into the slurry, or an indirect heating method using a jacket. Can be prepared.

  The viscosity of the adhesive of the present invention can be arbitrarily selected depending on the application, but when high-speed coating property is intended, the viscosity at the bonding temperature is often B-type viscosity of 100 to 8000 mPa · S. .

  Since the adhesive of the present invention is excellent in viscosity stability, initial adhesiveness, water-resistant adhesiveness, and also in terms of safety, it has been known that it has been used for conventional applications using PVA adhesives. It can be suitably used as an agent. These applications include, but are not limited to, paperboard adhesion, cardboard adhesion, paper tube adhesion, paper adhesives such as paper and wallpaper.

  Although the reason why the adhesive of the present invention exhibits excellent performance has not been fully elucidated, the compatibility between PVA (A) and PAA copolymer (B) is remarkably high. As the crosslinking reaction between the aldehyde unit generated from the acetal unit of the copolymer and the hydroxyl group of PVA proceeds, and esterification of the hydroxyl group of PVA and the carboxyl group of the PAA copolymer proceeds, (A) It is assumed that this is because an extremely strong bridge structure is formed between the component and the component (B).

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited at all by these Examples. In the following Examples and Comparative Examples, “parts” and “%” mean weight basis unless otherwise specified.

In Examples and Comparative Examples, adhesives prepared using various PVA and PAA copolymers were evaluated according to the following methods.
[Viscosity stability]
The viscosity when the adhesive solution is allowed to stand at 5 ° C. for 3 days is measured with a B-type viscometer, and the ratio to the initial viscosity (viscosity when the adhesive is cooled to 5 ° C. in an ice water bath from 20 ° C.). Was determined as a thickening ratio (5 ° C, viscosity after standing for 3 days / initial viscosity), and viscosity stability was determined according to the following criteria.
○: Less than 3.0 times △; 3.0 times or more but does not lead to gelation (having fluidity)
×: Gelled by 3 days [High speed coating property]
The adhesive solution was supplied to a spreader roll, applied at 30 ° C. at a speed of 100 m / min for 30 minutes, and the situation was observed.
○: Can be applied without problems.
Δ: Decrease in jumping of the adhesive solution (spattering from the roll) was slightly observed, and streaks were generated on the roll surface.
X: Jumping is severe, roll surface is disturbed, eventually gums up, and coating cannot be continued.
[Initial adhesion]
The initial adhesion strength was measured under the following conditions using an initial adhesion tester manufactured by Nippon Tobacco Inc.
Conditions: Kraft paper / craft paper adhesion Application speed 0.5 m / sec Shear speed 300 mm / sec Open time 1 sec Crimping time 2 sec Curing time 20 sec Adhesive area 1 mm x 25 mm x 8 locations (2 cm ^{2 in} total)
Temperature and humidity 20 ℃, 65% RH
[Waterproof adhesive strength]
An adhesive was applied to one side of the kraft paper (coating amount 50 g / m ² ) and bonded together, and then lightly pressed with a rubber hand roller and dried for one day at 20 ° C. and 65% RH. Then, the state at the time of being immersed in 20 degreeC water for 3 days was observed (5-step evaluation).
5; 100% kraft paper destroyed (material breakage)
4; Material breakage of 80% or more 3; Material breakage of 50% or more 2; Material breakage is recognized but 50% or less 1; Natural peeling (no material breakage)

[Production of PAA copolymer]
Production of PAA1 A 2 L reaction vessel equipped with a stirrer and a reflux condenser was charged with 90 g of acrylic acid, 10 g of N-2,2-dimethoxyethylmethacrylamide and 400 g of methanol, and the contents were heated to 65 ° C. Next, after bubbling with nitrogen for 30 minutes and sufficiently degassing, 1.0 g of 2,2′-azobisisobutyronitrile (AIBN) was added as an initiator. Three hours after the addition of the initiator, an additional 0.5 g of the initiator was further added and driven for 1 hour. Thereafter, 500 g of methanol was added and cooled to stop the polymerization. When this methanol solution was dried under reduced pressure at 60 ° C., 90 g of a white solid PAA copolymer (PAA1) was obtained. When PAA1 was dissolved in D ₂ O and ¹ H-NMR was measured, peaks suggesting the presence of polyacrylic acid were confirmed in the vicinity of σ1.5 ppm and σ2.1 ppm, and dimethyl was observed in the vicinity of σ3.0 to 3.3 ppm. A peak indicating the presence of the methoxy group (—OCH ₃ ) of the acetal was observed. Moreover, the modification amount of the acetal calculated from this NMR spectrum was 5.5 mol%. The weight average molecular weight (Mw) of PAA1 is GPC [apparatus: 150C-2 (manufactured by Waters), column: GMPWXL (manufactured by Tosoh), mobile phase: 0.2M phosphoric acid Buffer, sample: PEO / PEG] As a result of measurement using M, the Mw was 420,000.

Production of PAA2-4 Various types of PAA copolymers by the same method as PAA1, except that the types and amounts of acrylic acid and acetal-containing ethylenically unsaturated monomers and the polymerization conditions were changed to those shown in Table 1. (PAA2-4) were produced.

PAA5
As an unmodified PAA polymer, Aldrich Chemical Company, Inc. Polyacrylic acid made (Mw = 2000) was used.

[Production of PVA]
Production of PVA1 70.0 kg of vinyl acetate and 30.0 kg of methanol were charged into a 250 L reaction vessel equipped with a stirrer, a nitrogen inlet and an initiator addition port, heated to 60 ° C., and then nitrogen bubbling was performed for 30 minutes. Replaced with nitrogen. Next, 10 g of AIBN was added as an initiator to initiate polymerization. During the polymerization, the temperature was maintained at 60 ° C., and after 4 hours, when the polymerization rate reached 30%, the polymerization was stopped by cooling. After the reaction vessel was opened, it was bubbled with nitrogen gas. Next, unreacted vinyl acetate monomer was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate. 46.5 g (in polyvinyl acetate) was added to 333 g of polyvinyl acetate methanol solution (100 g of polyvinyl acetate in the solution) adjusted to a concentration of 30% by adding methanol to the obtained polyvinyl acetate solution. Saponification was carried out by adding an alkaline solution (10% methanol solution of NaOH) in a molar ratio of 0.10 to the vinyl acetate unit. About 1 minute after the addition of alkali, the gelled system was pulverized with a pulverizer, allowed to stand at 60 ° C. for 1 hour to allow saponification to proceed, and then 1000 g of methanol was added to the white solid obtained by filtration. And washed for 3 hours. After the above washing operation was repeated three times, the PVA obtained by centrifugal drainage was left to dry in a dryer at 70 ° C. for 2 days to obtain PVA (PVA1). PVA1 was PVA having a polymerization degree of 1740 and containing 98.5 mol% of vinyl alcohol units.

Manufacture of PVA2-10 PVA (PVA2-10) containing a polymerization degree and a vinyl alcohol unit shown in Table 2 was manufactured by changing the polymerization conditions and / or saponification conditions employed in the manufacture of PVA1.

Manufacture of PVA11 A 250 L pressure reactor equipped with a stirrer, nitrogen inlet, ethylene inlet, initiator inlet and delay solution inlet was charged with 106.1 kg of vinyl acetate and 43.9 kg of methanol and heated to 60 ° C. After heating, the system was purged with nitrogen by nitrogen bubbling for 30 minutes. Next, ethylene was introduced and charged so that the pressure in the reaction tank was 1.4 kg / cm ² . A 2,8'-azobis (4-methoxy-2,4-dimethylvaleronitrile) (AMV) solution as an initiator was dissolved in methanol to prepare a 2.8 g / L solution, and nitrogen gas was bubbled into the nitrogen. Replaced. After adjusting the polymerization tank internal temperature to 60 ° C., 53 ml of the initiator solution was injected to initiate polymerization. During the polymerization, ethylene was introduced to maintain the reaction vessel pressure at 5.9 Kg / cm ² , the polymerization temperature at 60 ° C., and polymerization was carried out by continuously adding AMV at 168 ml / hr using the above initiator solution. did. After 4 hours, the polymerization rate was stopped when the polymerization rate reached 20%. After the reaction vessel was opened to remove ethylene, nitrogen gas was bubbled to completely remove ethylene. Next, unreacted vinyl acetate monomer was removed under reduced pressure to obtain a methanol solution of polyvinyl acetate. 46.5 g (in polyvinyl acetate) was added to 333 g of polyvinyl acetate methanol solution (100 g of polyvinyl acetate in the solution) adjusted to a concentration of 30% by adding methanol to the obtained polyvinyl acetate solution. Saponification was carried out by adding an alkaline solution (10% methanol solution of NaOH) in a molar ratio of 0.10 to the vinyl acetate unit. About 1 minute after the addition of alkali, the gelled system was pulverized with a pulverizer, allowed to stand at 60 ° C. for 1 hour to allow saponification to proceed, and then 1000 g of methanol was added to the white solid obtained by filtration. And washed for 3 hours. After repeating the above washing operation three times, the PVA obtained by centrifugal drainage was left to dry in a dryer at 70 ° C. for 2 days to obtain ethylene-modified PVA (PVA11).
The degree of polymerization of PVA11 was 1500, the content of vinyl alcohol units was 95.5 mol%, and the ethylene modification amount was 3.0 mol%.

Preparation of PVA12 A PVA powder containing 0.3% sodium acetate (polymerization degree 1200, saponification degree 99.4%, average particle size 100 mesh) was prepared, and 100 g of this was charged into a kneader, and 60 g of acetic acid was added thereto. The mixture was swollen and heated at 60 ° C. with stirring at a rotation speed of 20 rpm. After that, a mixed solution of 25 g of diketene and 2 g of acetic acid was added dropwise over 4 hours and reacted for 30 minutes. After completion of the reaction, the reaction mixture was washed with 500 g of methanol, dried at 70 ° C. for 6 hours, and then mixed with acetonitrile containing 0.05% sodium acetate and 0.1% acetic acid (alkali metal acetate / acetic acid weight ratio 0.5). Acetyl-modified PVA (PVA12) was obtained.
The degree of polymerization of PVA12 was 1200, the content of vinyl alcohol units was 93.4 mol%, and the amount of acetoacetyl modification was 6.0 mol%.

Example 1
PVA1 and PAA1 were mixed at a weight ratio of 80:20, and the mixture was poured into stirring room temperature water and heated to 95 ° C. from the outside for dissolution to obtain an adhesive having a PVA1 concentration of 13%. Using this adhesive, the viscosity stability, high-speed coating property, initial adhesiveness, and water-resistant adhesive strength were evaluated according to the methods described above. The results are shown in Table 3.

Examples 2-11, Comparative Examples 1-5
An adhesive was prepared and evaluated in the same manner as in Example 1 except that PVA and PAA shown in Table 3 were used instead of PVA1 and PAA1 in Example 1. The results are shown in Table 3.

Examples 12-13, Comparative Examples 6-7
An adhesive was prepared and evaluated in the same manner as in Example 1 except that the ratio of PVA1 and PAA1 in Example 1 was changed as shown in Table 3. The results are shown in Table 3.

Examples 14-15, Comparative Examples 8-9
An adhesive was prepared and evaluated in the same manner as in Example 1 except that the aqueous solution concentration of PVA1 in Example 1 was changed as shown in Table 3. The results are shown in Table 3.

Examples 16-20
PVA1 and PAA1 are mixed at a weight ratio of 80:20, and the filler shown in Table 4 is mixed with powder, and it is poured into agitated room temperature water and heated to 95 ° C from outside to dissolve. Thus, an adhesive having a PVA1 concentration of 10% was obtained. Using this adhesive, the viscosity stability, high-speed coating property, initial adhesiveness, and water-resistant adhesive strength were evaluated according to the methods described above. The results are shown in Table 4.

  As can be seen from the results of Tables 3 and 4, the adhesive of the present invention expresses viscosity stability, high-speed coating property, initial adhesiveness, and water-resistant adhesive strength at a high level in a well-balanced manner. It is industrially useful compared to agents and technologies.

  Since the adhesive of the present invention is excellent in viscosity stability, initial adhesiveness, water-resistant adhesiveness, and also in terms of safety, it has been known that it has been used for conventional applications using PVA adhesives. It can be suitably used as an agent. In particular, it can be suitably used for adhesion of paperboard, adhesion of corrugated cardboard, adhesion of paper tubes, adhesives for paper such as bags and wallpaper, adhesives for films (PVA film, triacetate film, etc.).

Claims (5)

  Obtained by copolymerization of a polyvinyl alcohol polymer (A) having a vinyl alcohol unit of 90 mol% or more and a polymerization degree of 300 to 4000, and acrylic acid and an acetal group-containing ethylenically unsaturated monomer, A polyacrylic acid copolymer (B) containing 5 to 40 mol% of a unit derived from the acetal group-containing ethylenically unsaturated monomer is an aqueous adhesive in which the aqueous medium (C) is dissolved, The adhesive whose (A) component is 5-25 weight% with respect to C), and the weight ratio (A) :( B) of (A) component and (B) component is 99: 1-50: 50. The adhesive according to claim 1, wherein the acetal group-containing ethylenically unsaturated monomer is a monomer represented by the formula (1).

(Wherein R1 represents a hydrogen atom or —COOM, wherein M represents a hydrogen atom, an alkali metal or an ammonium group; R2 represents a hydrogen atom, a methyl group or —CH ₂ —COOM, where M represents As defined above, R 3 and R 4 are the same or different and each is a saturated alkyl group having 1 to 4 carbon atoms, X is —CO—, —CO—O— or —CO—NR 5, wherein R 5 is A hydrogen atom or a C1-C4 saturated alkyl group is meant, and n is an integer of 1-8.)   Furthermore, the adhesive agent of Claim 1 or 2 containing a filler (D).   The adhesive according to any one of claims 1 to 3, wherein the polyvinyl alcohol polymer (A) is an ethylene-modified polyvinyl alcohol polymer containing 2 to 8 mol% of an ethylene-derived unit.   The adhesive according to any one of claims 1 to 4, wherein the polyvinyl alcohol polymer (A) is an acetoacetyl-modified polyvinyl alcohol polymer.