Aqueous emulsion and method for producing the same

Abstract

This aqueous emulsion comprises a dispersoid (A), a dispersant (B), and inorganic fine particles (C), wherein: a polymer (A1), which contains 95-99.95 mass% of an unsaturated monomer unit having no carboxyl group and 0.05-5 mass% of an unsaturated monomer unit having a carboxyl group, is contained as the dispersoid (A); an ethylene-vinyl alcohol copolymer (B1) having an ethylene unit content of 1-12 mol% (exclusive of 12) is contained as the dispersant (B); the content of the dispersant (B) is 2-20 parts by mass with respect to 100 parts by mass of the dispersoid (A); and the content of the inorganic fine particles (C) is 0.2-15 parts by mass with respect to 100 parts by mass of the dispersoid (A). Consequently, an aqueous emulsion having excellent adhesiveness when used as an adhesive is provided.

Description

[Technical Field]

[0001] The present invention relates to an aqueous emulsion comprising a dispersed phase, a dispersant, and inorganic fine particles. The present invention also relates to a method for producing the aqueous emulsion. [Background technology]

[0002] Traditionally, in adhesives used for applications such as woodworking, papermaking, and textile processing, when high adhesive strength and water resistance were required, thermosetting resins such as melamine resin and urea resin, or vinyl acetate resin emulsions copolymerized with crosslinkable monomers such as N-methylolacrylamide, have been used. However, all of these resins emit formaldehyde. While formaldehyde is known to be harmful, the revision of the Building Standards Act has prohibited or restricted the use of materials that emit formaldehyde above a certain standard. As a result, there is a growing tendency to avoid the use of formaldehyde-emitting adhesives and materials manufactured using them more than ever before.

[0003] To address this, methods have been investigated that use acetoacetylated PVA, obtained by introducing acetoacetyl groups into polyvinyl alcohol (hereinafter abbreviated as PVA), as a protective colloid, and that improve water resistance and adhesive strength by emulsifying copolymerizing an acetoacetyl group-containing monomer with vinyl acetate, thereby crosslinking the acetoacetyl groups (Patent Document 1). However, polymers obtained by this method have the problem of thickening and solidifying during storage due to self-crosslinking reactions between acetoacetyl groups. Although improvements using additives and other methods have been investigated, an effective method has not yet been found.

[0004] Furthermore, a method has been investigated using polymer fine particles in which at least one monomer unit selected from ethylenically unsaturated monomer units and diene-based unsaturated monomer units is the main component as the dispersed phase, and a small amount of unsaturated monomer units having silyl groups is also contained (Patent Document 2). In this case, the resulting polymer shows excellent water-resistant adhesion. However, it has been found that there are problems in terms of polymerization stability, such as the unsaturated monomers having silyl groups destabilizing polymerization and causing aggregates to form. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2000-282004 [Patent Document 2] Japanese Patent Publication No. 2007-23148 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide an aqueous emulsion that exhibits excellent adhesive properties when used as an adhesive. Furthermore, the present invention aims to provide a method for producing an aqueous emulsion with excellent polymerization stability. [Means for solving the problem]

[0007] As a result of diligent research, the inventors have found that an aqueous emulsion containing a polymer (A1) comprising unsaturated monomer units without carboxyl groups and unsaturated monomer units having carboxyl groups as a dispersed phase (A), an ethylene-vinyl alcohol copolymer (B1) containing ethylene units as a dispersant (B), and further containing inorganic fine particles (C) can solve the above problems, and have completed the present invention.

[0008] In other words, the above problem is solved by providing an aqueous emulsion comprising a dispersed phase (A), a dispersant (B), and inorganic fine particles (C); wherein the dispersed phase (A) comprises a polymer (A1) containing 95 to 99.95% by mass of unsaturated monomer units without carboxyl groups and 0.05 to 5% by mass of unsaturated monomer units having carboxyl groups, and the dispersant (B) comprises an ethylene-vinyl alcohol copolymer (B1) having an ethylene unit content of 1 mol% or more and less than 12 mol%, the content of the dispersant (B) is 2 to 20 parts by mass per 100 parts by mass of the dispersed phase (A), and the content of inorganic fine particles (C) is 0.2 to 15 parts by mass per 100 parts by mass of the dispersed phase (A).

[0009] In this case, it is preferable that the viscosity-average degree of polymerization of the ethylene-vinyl alcohol copolymer (B1) is 200 to 5000 and the degree of saponification is 80 to 99.7 mol%.

[0010] Furthermore, it is preferable that the average particle size of the inorganic fine particles (C) is 10 to 500 nm. It is also preferable that the inorganic fine particles (C) are silica, zirconia, or alumina. It is also preferable that the dispersed phase (A) contains an additional 0.1 to 5 parts by mass of a trivalent or tetravalent metal salt (D) in terms of metal element per 100 parts by mass.

[0011] The above problem can also be solved by providing a method for producing the aqueous emulsion, which involves emulsion polymerization of an unsaturated monomer without a carboxyl group and an unsaturated monomer having a carboxyl group in the presence of a dispersant (B), followed by the addition of inorganic fine particles (C). [Effects of the Invention]

[0012] The aqueous emulsion of the present invention exhibits excellent adhesive properties when used as an adhesive. Furthermore, the manufacturing method of the present invention has excellent polymerization stability, making it possible to obtain an aqueous emulsion with few aggregates. [Modes for carrying out the invention]

[0013] Hereinafter, the present invention will be described in detail. The aqueous emulsion of the present invention contains a polymer (A1) containing an unsaturated monomer unit having no carboxyl group and an unsaturated monomer unit having a carboxyl group as a dispersoid (A), an ethylene-vinyl alcohol copolymer (B1) containing an ethylene unit as a dispersant (B), and further contains inorganic fine particles (C).

[0014] (Dispersoid (A)) The aqueous emulsion of the present invention contains, as a dispersoid (A), a polymer (A1) containing 95 to 99.95% by mass of an unsaturated monomer unit having no carboxyl group and 0.05 to 5% by mass of an unsaturated monomer unit having a carboxyl group.

[0015] Here, the unsaturated monomer having no carboxyl group refers to a monomer composed of a compound having one or more carbon-carbon unsaturated bonds in the molecule and having no carboxyl group. Since this compound has a carbon-carbon double bond in the molecule, it is addition-polymerizable. The compound is not particularly limited, and examples thereof include vinyl esters, (meth)acrylate esters, dienes, olefins, (meth)acrylamides, (meth)acrylonitriles, aromatic vinyl compounds, heterocyclic vinyl compounds, vinyl ethers, allyl compounds, polyfunctional acrylates, and the like. Among these, at least one unsaturated monomer selected from the group consisting of vinyl esters and dienes is preferable, and vinyl esters are more preferable. These may be used alone or in combination of two or more.

[0016] The vinyl ester is not particularly limited, but examples include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, vinyl cinnamate, vinyl crotate, vinyl decanoate, vinyl hexanoate, vinyl octanoate, vinyl isononanoate, vinyl trimethylacetate, 4-tert-butylbenzoate, vinyl 2-ethylhexanoate, vinyl caproate, vinyl caprylate, vinyl laurate, vinyl palmitate, vinyl stearate, vinyl oleate, vinyl benzoate, etc., and vinyl acetate is particularly preferred from an industrial standpoint. These may be used individually or in combination of two or more.

[0017] If the content of unsaturated monomer units without carboxyl groups in polymer (A1) exceeds 99.95% by mass, the heat-resistant and water-resistant adhesion will decrease when an aqueous emulsion is used as an adhesive. The content is preferably 99.9% by mass or less, and more preferably 99.5% by mass or less. On the other hand, if the content is less than 95% by mass, aggregates will form during emulsion polymerization, making the polymerization unstable. The content is preferably 98% by mass or more.

[0018] On the other hand, an unsaturated monomer having a carboxyl group is a monomer consisting of a compound having one or more carbon-carbon unsaturated bonds in its molecule and a carboxyl group. This compound is capable of addition polymerization due to having a carbon-carbon double bond in its molecule. The carboxyl group may be present in the form of its anhydride. The compound is not particularly limited as long as it does not impair the effects of the present invention, but examples include carboxylic acids such as (meth)acrylic acid, crotonic acid, isocrotonic acid, citraconic acid, itaconic acid, maleic acid, maleic anhydride, and fumaric acid. Note that (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0019] If the content of unsaturated monomer units having carboxyl groups in polymer (A1) is less than 0.05% by mass, the heat-resistant and water-resistant adhesion will decrease when an aqueous emulsion is used as an adhesive. The content is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. On the other hand, if the content exceeds 5% by mass, aggregates will form during emulsion polymerization, making the polymerization unstable. The content is preferably 2% by mass or less.

[0020] (Dispersant (B)) The aqueous emulsion of the present invention contains an ethylene-vinyl alcohol copolymer (B1) as a dispersant (B), having an ethylene unit content of 1 mol% or more and less than 12 mol%. The copolymer (B1) is a copolymer having ethylene units and vinyl alcohol units. The copolymer (B1) can be obtained, for example, by saponifying a copolymer of ethylene and a vinyl ester using an alkaline catalyst or the like. Vinyl acetate is a typical example of a vinyl ester, but other fatty acid vinyl esters (such as vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, and vinyl versatate) can also be used.

[0021] The ethylene unit content in the copolymer (B1) of the present invention is 1 mol% or more and less than 12 mol%. If the ethylene unit content is less than 1 mol%, the surfactant activity will be insufficient, which may reduce polymerization stability, and the water-resistant adhesion will be reduced when used as an adhesive. The ethylene unit content is preferably 2 mol% or more, and more preferably 3 mol% or more. On the other hand, if the ethylene unit content is 12 mol% or more, a large amount of aggregates will be generated in the resulting aqueous emulsion, making filtration difficult. The ethylene unit content is preferably less than 10 mol%, and more preferably less than 9 mol%. 1 This can be determined by known methods such as 1H-NMR measurement.

[0022] The degree of saponification of the vinyl ester component of copolymer (B1) is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 92 mol% or more, and particularly preferably 97 mol% or more. Furthermore, the degree of saponification is preferably 99.7 mol% or less, and more preferably 99 mol% or less. By setting the degree of saponification within the above range, copolymer (B1) with excellent water resistance is obtained. 1 This can be determined by known methods such as 1H-NMR measurement. Furthermore, any ethylene-vinyl alcohol copolymer with an average saponification degree within the above range may be used in combination with ethylene-vinyl alcohol copolymers having different saponification degrees.

[0023] The viscosity-average degree of polymerization (hereinafter sometimes simply referred to as the degree of polymerization) of copolymer (B1) is acceptable as long as it is within the range of the degree of polymerization of copolymers commonly used as dispersants for emulsion polymerization. A degree of polymerization of 200 or higher is preferable because it provides sufficient stability during emulsion polymerization, and a degree of polymerization of 5000 or lower is preferable because it prevents the solution viscosity from becoming too high during emulsion polymerization, making stirring and heat removal easier. The degree of polymerization was determined by the method described in JIS K 6726 (1994). Specifically, when the degree of saponification was less than 99.5 mol%, the viscosity-average degree of polymerization (P) was determined by formula using the intrinsic viscosity [η] (liters / g) measured in water at 30°C for copolymers that had been saponified to a degree of saponification of 99.5 mol% or higher. P = ([η] × 10 4 (8.29) (1 / 0.62)

[0024] The content of dispersant (B) is 2 to 20 parts by mass per 100 parts by mass of dispersed phase (A). If the content of dispersant (B) is less than 2 parts by mass, sufficient stability during emulsion polymerization cannot be obtained. It is preferable that the content of dispersant (B) is 4 parts by mass or more. On the other hand, if the content of dispersant (B) exceeds 20 parts by mass, the water-resistant adhesion decreases when the aqueous emulsion is used as an adhesive. It is preferable that the content of dispersant (B) is 11 parts by mass or less.

[0025] The copolymer (B1) may contain monomer units other than vinyl alcohol units, vinyl ester units, and ethylene units, as long as the effects of the present invention are not impaired. The content of other monomer units is preferably 6 mol% or less, more preferably 3 mol% or less, and even more preferably 1 mol% or less. The copolymer (B1) may be used alone or in combination of two or more types.

[0026] (Inorganic fine particles (C)) The inorganic fine particles (C) content in the aqueous emulsion of the present invention is 0.2 to 15 parts by mass per 100 parts by mass of dispersed phase (A). If the content is less than 0.2 parts by mass, the heat-resistant adhesion decreases when the aqueous emulsion is used as an adhesive. The content is preferably 0.5 parts by mass or more, and more preferably 0.8 parts by mass or more. On the other hand, if the content exceeds 15 parts by mass, a large amount of aggregates are generated in the resulting aqueous emulsion, making application difficult. Furthermore, the aggregates act as defects in the adhesive layer, reducing adhesion. The content is preferably 12 parts by mass or less, and more preferably 10 parts by mass or less.

[0027] The type of inorganic fine particles (C) is not particularly limited, but silica, zirconia, or alumina are preferably used. Silica is more preferably used due to its availability. Among these, colloidal silica is more preferably used.

[0028] The average particle size of the inorganic fine particles (C) is preferably 10 to 500 nm. If the average particle size of the inorganic fine particles (C) is less than 10 nm, the emulsion may thicken. The average particle size is more preferably 12 nm or more. On the other hand, if the average particle size of the inorganic fine particles (C) exceeds 500 nm, it may not disperse well in the emulsion and aggregates may form. The average particle size is more preferably 400 nm or less. The inorganic fine particles (C) are used in sol form during emulsion polymerization. Here, the average particle size is the arithmetic mean of the particle sizes observed with a transmission electron microscope.

[0029] (Salts of trivalent or tetravalent metals (D)) The aqueous emulsion of the present invention preferably further contains a salt (D) of a trivalent or tetravalent metal. This allows the copolymer (B1) to coordinate with the ions of the metal to form a chelate structure, and also allows the copolymer (B1) to crosslink via the metal ions, thereby improving the water resistance of the aqueous emulsion. It is preferable to further contain 0.1 to 5 parts by mass of salt (D) in terms of metal elements per 100 parts by mass of dispersed phase (A). If the salt (D) content is less than 0.1 parts by mass, when the aqueous emulsion is used as an adhesive, the heat-resistant adhesion and water-resistant adhesion may decrease. The salt (D) content is preferably 0.5 parts by mass or more, and more preferably 1 part by mass or more. On the other hand, if the salt (D) content exceeds 5 parts by mass, the water-resistant adhesion of the resulting aqueous emulsion may decrease. The metal salt (D) content is preferably 4 parts by mass or less, and more preferably 3.5 parts by mass or less.

[0030] The type of salt (D) is not particularly limited. Suitable trivalent or tetravalent metal ions in salt (D) include aluminum ions, titanium ions, and zirconium ions. Among these, aluminum ions are the more preferred metal ions.

[0031] Examples of anionic species in salt (D) include inorganic acids such as nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, and carbonic acid; and organic acids such as acetic acid and lactic acid. Among these, inorganic acids are preferred, and nitric acid is more preferred. Double salts containing ammonium, sodium, potassium, etc., can also be given as salt (D).

[0032] The salt (D) is preferably aluminum nitrate, titanium lactate, or zirconium ammonium carbonate. Among these, aluminum nitrate is more preferable from the viewpoint of obtaining better heat resistance and water resistance when an aqueous emulsion is used as an adhesive.

[0033] The aqueous emulsion of the present invention may contain other components besides the polymer (A1) as the dispersed phase (A), the copolymer (B1) as the dispersant (B), the inorganic fine particles (C), and the salt (D), as long as they do not impair the effects of the present invention. Examples of such other components include defoamers, pH adjusters, solvents, pigments, dyes, preservatives, thickeners, crosslinking agents, and plasticizers. The content of such other components in the aqueous emulsion is usually 10% by mass or less.

[0034] The solid content concentration of the aqueous emulsion of the present invention can be set appropriately depending on the application, but is preferably 35 to 60% by mass. If the solid content concentration is less than 35% by mass, the viscosity of the aqueous emulsion is too low, which may cause particles to settle easily. A solid content concentration of 40% by mass or more is more preferable. On the other hand, if the solid content concentration exceeds 60% by mass, aggregation may occur during emulsion polymerization. A solid content concentration of 58% by mass or less is more preferable. The solid content concentration of the aqueous emulsion referred to here is the value obtained by [weight of dry sample (g) / weight of aqueous emulsion (g)] × 100.

[0035] (Method for producing aqueous emulsion) The method for producing the aqueous emulsion of the present invention is not particularly limited, but a preferred method is to emulsion polymerize an unsaturated monomer without a carboxyl group and an unsaturated monomer having a carboxyl group in the presence of a dispersant (B), and then add inorganic fine particles (C).

[0036] In the emulsion polymerization described above, a water-soluble single initiator or a water-soluble redox initiator commonly used in emulsion polymerization can be used as the polymerization initiator. These initiators may be used individually or in combination of two or more. Among these, redox initiators are preferred. Examples of water-soluble single initiators include azo initiators, hydrogen peroxide, and peroxides such as persulfates (potassium, sodium, or ammonium salts). As a redox initiator, a combination of an oxidizing agent and a reducing agent can be used. Peroxides are preferred as the oxidizing agent. Examples of reducing agents include metal ions and reducing compounds.

[0037] Furthermore, during emulsion polymerization, commonly used surfactants, polymerization initiators, reducing agents, buffers, polymerization degree regulators, etc., may be used as appropriate, provided that the effects of the present invention are not impaired.

[0038] The dispersion medium in the emulsion polymerization described above is an aqueous medium mainly composed of water. The aqueous medium mainly composed of water may contain a water-soluble organic solvent (alcohols, ketones, etc.) that is soluble in water in any proportion. Here, "aqueous medium mainly composed of water" refers to a dispersion medium containing 50% by mass or more of water. From the viewpoint of cost and environmental impact, the dispersion medium is preferably an aqueous medium containing 90% by mass or more of water, and more preferably water.

[0039] In the above method for producing the aqueous emulsion, it is preferable to add the dispersant to the dispersion medium before starting emulsion polymerization, heat and dissolve it, then cool and purge with nitrogen. The heating temperature is preferably 80 to 100°C. The emulsion polymerization temperature is not particularly limited, but is usually 20 to 100°C, preferably 40 to 90°C, and more preferably 50 to 90°C.

[0040] The aqueous emulsion of the present invention can be used for adhesive applications such as woodworking and paper processing, as well as for paints, textile processing, etc., with adhesive applications being particularly preferred. In other words, an adhesive made from the aqueous emulsion of the present invention is a preferred embodiment. The aqueous emulsion obtained by the above method may be used as is, or other components as described above (defoaming agents, pH adjusters, solvents, pigments, dyes, preservatives, thickeners, crosslinking agents, plasticizers, etc.) may be added as needed.

[0041] The aqueous emulsion of the present invention exhibits excellent adhesive properties when used as an adhesive. Furthermore, the aqueous emulsion of the present invention is highly safe as it does not emit formaldehyde. Moreover, the manufacturing method of the present invention has excellent polymerization stability, making it possible to obtain an aqueous emulsion with few aggregates. [Examples]

[0042] The present invention will be described in more detail below with reference to examples. In the following examples and comparative examples, unless otherwise specified, "parts" and "%" refer to parts by mass and mass%, respectively.

[0043] The solid content concentration, emulsion polymerization stability, and adhesive performance (water-resistant adhesion, heat-resistant adhesion) of the aqueous emulsion were evaluated using the methods described below.

[0044] (1) Solid content concentration 2-3 g of the aqueous emulsion obtained in the examples and comparative examples were accurately weighed to four decimal places using a precision balance, and then left to stand in a 100°C drying oven for more than 3 hours to remove moisture and obtain dried samples. The weight of the dried samples was accurately weighed to four decimal places using a precision balance, and the solid content concentration was calculated from the weight ratio of the dried sample to the aqueous emulsion according to the following formula. Solid content concentration (%) = [Weight of dry sample (g) / Weight of aqueous emulsion (g)] × 100

[0045] (2) Emulsion polymerization stability 500 g of the aqueous emulsions obtained in the examples and comparative examples were filtered through a 60-mesh wire mesh, and the filtration residue was weighed. The ratio of the filtration residue to the mass of the aqueous emulsion was evaluated according to the following evaluation criteria. A smaller filtration residue indicates fewer aggregates and more stable emulsion polymerization. A: The filtration residue was 1.0% by mass or less. B: The filtration residue was greater than 1.0% by mass and less than or equal to 2.0% by mass. C: The filtration residue exceeded 2.0% by mass. D: A large amount of filtration residue was present, making filtration difficult.

[0046] (3) Water resistant adhesion Cold water resistance and adhesion were evaluated in accordance with EN204. The resulting aqueous emulsion was applied to European beech wood (straight grain) at a rate of 200g / m². 2 A test specimen was obtained by coating the wood with the aqueous emulsion and then bonding it to the beech wood that had not been coated with the aqueous emulsion. This test specimen was measured at 20°C for a load of 0.7 N / mm². 2It was compressed for 2 hours under the load. Then, it was immersed in water at 20°C for 4 days, the test piece was taken out while still wet, and the adhesive strength (unit: N / mm 2 ) was measured.

[0047] (4) Heat-resistant adhesiveness The heat-resistant adhesiveness was evaluated in accordance with WATT’91. The obtained aqueous emulsion was applied to European beech wood (plain-sawn) at 200 g / m 2 and laminated with the above beech wood without the application of the aqueous emulsion to obtain a test piece. This test piece was compressed for 2 hours under a load of 0.7 N / mm 2 at 20°C. Then, it was left standing in a dryer at 80°C for 1 hour, the test piece was taken out while still hot, and the adhesive strength (unit: N / mm 2 ) was measured.

[0048] Example 1 (Production of PVA-1) A polymerization vessel (continuous polymerization tank) equipped with a reflux condenser, a raw material supply line, a thermometer, a nitrogen inlet, a stirring blade, and a reaction liquid extraction line was used. Vinyl acetate (726 L / h), methanol (145 L / h), and a 1% methanol solution of 2,2’-azobis(4-methoxy-2,4-dimethylvaleronitrile) (AMV) (2.4 L / h) were continuously supplied to the continuous polymerization tank using a metering pump. The ethylene pressure in the tank was adjusted to 0.39 MPa. The polymerization liquid was continuously taken out from the polymerization tank so that the liquid level in the polymerization tank became constant. The polymerization rate at the outlet of the polymerization tank was adjusted to 28%. The residence time of the polymerization tank was 5 hours. The temperature at the outlet of the polymerization tank was 60°C. The polymerization liquid was recovered from the polymerization tank, and unreacted vinyl acetate monomer was removed by introducing methanol vapor into the recovered liquid to obtain a methanol solution (concentration 30%) of an ethylene-vinyl acetate copolymer.

[0049] The above ethylene-vinyl acetate copolymer (EVAc) / methanol solution (30% by mass) was fed as the saponification raw material solution at 4700 L / h, and a sodium hydroxide / methanol solution (4% by mass) was fed as the saponification catalyst solution at 198 L / h. The fed saponification raw material solution and saponification catalyst solution were mixed, and the resulting mixture was placed on a belt and held at 40°C for 18 minutes to allow the saponification reaction to proceed. Subsequently, it was crushed and dried to obtain ethylene-vinyl alcohol copolymer (PVA-1) to be used as a dispersant (B). The ethylene unit content, degree of polymerization, and degree of saponification of PVA-1 are shown in Table 1.

[0050] (Manufacturing of water-based emulsion Em-1) A 1-liter glass polymerization vessel equipped with a reflux condenser, dropping funnel, thermometer, and nitrogen inlet was charged with 275 g of deionized water and heated to 85°C. 21.0 g of PVA-1 (corresponding to 7.5 parts by mass per 100 parts by mass of dispersed phase (A)) was added as dispersant (B) and stirred for 45 minutes until dissolved. 0.3 g of sodium acetate was then added as a pH buffer and mixed until dissolved. Next, the aqueous solution containing PVA-1 was cooled, purged with nitrogen, and heated to 60°C while stirring at 200 rpm. Subsequently, 2.4 g of a 20% by mass aqueous solution of tartaric acid as a reducing agent and 3.2 g of 5% by mass hydrogen peroxide solution as a polymerization initiator were added. Then, 27 g of vinyl acetate (VAc) and 0.3 g of acrylic acid (AA) (corresponding to 1 part by mass of acrylic acid per 100 parts by mass of total vinyl acetate) were added as dispersed phase (A) and polymerization was started.

[0051] After 30 minutes from the start of polymerization, it was confirmed that the initial polymerization (residual vinyl acetate content less than 1%) had been completed. Then, 1 g of a 10% by mass aqueous solution of tartaric acid and 3.2 g of 5% by mass hydrogen peroxide solution were added. Following this, a mixture of 250 g of vinyl acetate and 2.5 g of acrylic acid was continuously added over 2 hours, maintaining the polymerization temperature at 80°C to complete the polymerization and obtain a polyvinyl acetate emulsion with a solid content of 50% by mass. To the obtained emulsion, WR Grace's colloidal silica "LUDOX" was added as inorganic fine particles (C). TMAqueous emulsion (Em-1) was obtained by mixing 1.75 parts by mass of TMA with 100 parts by mass of dispersed phase (A) and 2.6 parts by mass of aluminum nitrate nonahydrate as salt (D). The solid content concentration of this aqueous emulsion (Em-1) was 49.6% by mass. Here, "LUDOX TM "TMA" is colloidal silica in which silica is dispersed colloidally in water, with an average particle size of 34.5 nm and a solid content concentration of 35.1 mass%.

[0052] (Evaluation of Em-1) The polymerization stability, water-resistant adhesion, and heat-resistant adhesion of the obtained aqueous emulsion (Em-1) were evaluated according to the method described above. The results are shown in Table 2.

[0053] Examples 2 and 3 Colloidal silica "LUDOX" used as inorganic fine particles (C) TM Aqueous emulsions (Em-2 and Em-3) were obtained in the same manner as in Example 1, except that the amount of TMA added was 5.0 parts by mass or 12.0 parts by mass per 100 parts by mass of dispersed phase (A). The evaluation results of the aqueous emulsions are shown in Table 2.

[0054] Example 4 The type of colloidal silica used as inorganic fine particles (C) is "LUDOX" colloidal silica manufactured by WR Grace. TM The aqueous emulsion (Em-4) was obtained in the same manner as in Example 1, except that the "HSA" was changed, the amount added was 1.5 parts by mass per 100 parts by mass of dispersed phase (A), and salt (D) was not added. The evaluation results of the aqueous emulsion are shown in Table 2. Here, "LUDOX TM HSA is colloidal silica in which silica is dispersed colloidally in water. Its average particle size is 24.0 nm, and its solid content concentration is 29.8% by mass.

[0055] Example 5 (Manufacturing of PVA-2) Ethylene-vinyl alcohol copolymer (PVA-2) was produced in the same manner as in Example 1, except that the polymerization conditions, such as the feed amounts of ethylene, vinyl acetate, and methanol, the amount of initiator added, and the polymerization rate, as well as the feed amounts and concentrations of the EVAc solution and saponification catalyst solution during saponification, were changed as shown in Table 1. The ethylene unit content, degree of polymerization, and degree of saponification of PVA-2 are shown in Table 1.

[0056] (Manufacturing and evaluation of aqueous emulsion Em-5) An aqueous emulsion (Em-5) was obtained in the same manner as in Example 1, except that the amount of acrylic acid used was 0.5 parts by mass per 100 parts by mass of vinyl acetate, PVA-2 was used as the copolymer (B1) at 10 parts by mass per 100 parts by mass of dispersed phase (A), and aluminum nitrate nonahydrate was used as the salt (D) at 1.2 parts by mass per 100 parts by mass of dispersed phase (A). The evaluation results of the aqueous emulsion are shown in Table 2.

[0057] Example 6 (Manufacturing of PVA-3) Ethylene-vinyl alcohol copolymer (PVA-3) was produced in the same manner as in Example 1, except that the polymerization conditions, such as the feed amounts of ethylene, vinyl acetate, and methanol, the amount of initiator added, and the polymerization rate, as well as the feed amounts and concentration conditions of the EVAc solution and saponification catalyst solution during saponification, were changed as shown in Table 1. The ethylene unit content, degree of polymerization, and degree of saponification of PVA-3 are shown in Table 1.

[0058] (Manufacturing and evaluation of aqueous emulsion Em-6) Instead of acrylic acid, methacrylic acid (MAA) is used at a ratio of 0.5 parts per 100 parts by mass of vinyl acetate, PVA-3 is used as the copolymer (B1) at a ratio of 7.5 parts by mass per 100 parts by mass of dispersed phase (A), and colloidal silica "LUDOX" is used as the inorganic fine particles (C). TM An aqueous emulsion (Em-6) was obtained in the same manner as in Example 1, except that 1.2 parts of "HSA" were used per 100 parts by mass of dispersed phase (A), and 1.2 parts of aluminum nitrate nonahydrate were used as salt (D) per 100 parts by mass of dispersed phase (A). The evaluation results of the aqueous emulsion are shown in Table 2.

[0059] Example 7 The amount of acrylic acid used is 2 parts per 100 parts vinyl acetate, PVA-3 is used as the copolymer (B1) at 7.5 parts by mass per 100 parts by mass of dispersed phase (A), and colloidal silica "LUDOX" is used as the inorganic fine particles (C). TM An aqueous emulsion (Em-7) with a solid content of 48% by mass was obtained in the same manner as in Example 1, except that 0.7 parts by mass of "TMA" was used per 100 parts by mass of dispersed phase (A), and 3.2 parts by mass of aluminum nitrate nonahydrate was used as salt (D) per 100 parts by mass of dispersed phase (A). The evaluation results of the aqueous emulsion are shown in Table 2.

[0060] Example 8 An aqueous emulsion (Em-8) was obtained in the same manner as in Example 7, except that 1.8 parts by mass of titanium lactate (relative to 100 parts by mass of dispersant (A)) was added as salt (D). The results of various evaluations of the aqueous emulsion are shown in Table 2.

[0061] Example 9 An aqueous emulsion (Em-9) with a solid content of 48% by mass was obtained in the same manner as in Example 1, except that 1.0 part by mass of methacrylic acid (MAA) was used instead of acrylic acid (per 100 parts by mass of vinyl acetate units), 7.5 parts by mass of PVA-3 as copolymer (B) per 100 parts by mass of dispersed phase, and 3.0 parts by mass of zirconium ammonium carbonate as salt (D). The evaluation results of the aqueous emulsion are shown in Table 2.

[0062] Comparative Example 1 (Manufacturing of PVA-4) Ethylene-vinyl alcohol copolymer (PVA-4) was produced in the same manner as in Example 1, except that the polymerization conditions, such as the feed amounts of ethylene, vinyl acetate, and methanol, the amount of initiator added, and the polymerization rate, as well as the feed amounts and concentrations of the EVAc solution and saponification catalyst solution during saponification, were changed as shown in Table 1. The ethylene unit content, degree of polymerization, and degree of saponification of PVA-4 are shown in Table 1.

[0063] (Manufacturing and evaluation of aqueous emulsion Em-10) An aqueous emulsion (Em-10) was obtained in the same manner as in Example 1, except that PVA-4 was used as the copolymer (B1) in an amount of 7.5 parts by mass per 100 parts by mass of the dispersant (A). The evaluation results of the aqueous emulsion are shown in Table 2. In particular, the value in the water-resistant adhesion test was 1.3 N / mm². 2 It was low and not sufficient.

[0064] Comparative Example 2 An aqueous emulsion (Em-11) was obtained in the same manner as in Comparative Example 1, except that inorganic fine particles (C) were not added. The evaluation results of the aqueous emulsion are shown in Table 2. In particular, the values ​​for heat resistance and water resistance were 1.7 N / mm². 2 , 1.1 N / mm 2 Both were low, and the adhesion was insufficient.

[0065] Comparative Example 3 (Manufacturing of PVA-5) Ethylene-vinyl alcohol copolymer (PVA-5) was produced in the same manner as in Example 1, except that the polymerization conditions, such as the feed amounts of ethylene, vinyl acetate, and methanol, the amount of initiator added, and the polymerization rate, as well as the feed amounts and concentration conditions of the EVAc solution and saponification catalyst solution during saponification, were changed as shown in Table 1. The ethylene unit content, degree of polymerization, and degree of saponification of PVA-5 are shown in Table 1.

[0066] (Manufacturing and evaluation of aqueous emulsion Em-12) An aqueous emulsion (Em-12) was obtained in the same manner as in Example 1, except that 10 parts by mass of PVA-5 was used as the copolymer per 100 parts by mass of vinyl acetate units. When the polymerization stability of the obtained aqueous emulsion was evaluated, a large amount of filtration residue was found, making filtration difficult, and therefore the adhesiveness could not be evaluated. The evaluation results of the aqueous emulsion are shown in Table 2.

[0067] Comparative Example 4 An aqueous emulsion (Em-13) with a solid content of 48% was obtained in the same manner as in Example 1, except that the amount of acrylic acid used was 0.5 parts by mass per 100 parts by mass of vinyl acetate units, PVA-3 was used as copolymer (B1) in an amount of 7.5 parts by mass per 100 parts by mass of dispersant (A), aluminum nitrate nonahydrate was used as salt (D) in an amount of 1.2 parts by mass per 100 parts by mass of dispersant (A), and inorganic fine particles (C) were not added. The evaluation results of the aqueous emulsion are shown in Table 2. In particular, the value for heat resistance adhesion was 1.9 N / mm 2 The bond was weak and lacked sufficient heat resistance.

[0068] Comparative Example 5 An aqueous emulsion (Em-14) with a solid content of 48% was obtained in the same manner as in Example 1, except that acrylic acid was not used, 7.5 parts by mass of PVA-2 was used as the copolymer (B1) per 100 parts by mass of the dispersed phase (A), and neither inorganic fine particles (C) nor salt (D) were added. The valence results of the aqueous emulsion are shown in Table 2. In particular, the values ​​for heat-resistant adhesion and water-resistant adhesion were 1.5 N / mm², respectively. 2 , 1.0 N / mm 2 Both were low, and the adhesion was insufficient.

[0069] Comparative Example 6 Polymerization was attempted in the same manner as in Example 1, except that 10 parts by mass of acrylic acid was used per 100 parts by mass of vinyl acetate units, 7.5 parts by mass of PVA-2 was used as the copolymer (B1) per 100 parts by mass of dispersed phase (A), and neither inorganic fine particles (C) nor salt (D) were added. However, a large amount of aggregates were generated and emulsion polymerization could not be achieved.

[0070] Comparative Example 7 Polymerization was attempted in the same manner as in Example 1, except that 6 parts by mass of acrylic acid were used per 100 parts by mass of vinyl acetate units, and neither inorganic fine particles (C) nor salt (D) were added. However, a large amount of aggregates were generated, and emulsion polymerization could not be achieved.

[0071] Comparative Example 8 The amount of acrylic acid used is 0.03 parts by mass per 100 parts by mass of vinyl acetate, and colloidal silica "LUDOX" is used as inorganic fine particles (C). TM An aqueous emulsion (Em-17) was obtained in the same manner as in Example 1, except that the amount of TMA added was 2.0 parts by mass per 100 parts by mass of dispersed phase (A). The evaluation results of the aqueous emulsion are shown in Table 2. In particular, the values ​​for heat resistance and water resistance were 1.7 N / mm². 2 , 0.6 N / mm 2 Both were low, and the adhesion was insufficient.

[0072] [Table 1]

[0073] [Table 2]

Claims

1. An aqueous emulsion comprising a dispersed phase (A), a dispersant (B), and inorganic fine particles (C); The dispersed phase (A) contains a polymer (A1) comprising 95 to 99.95% by mass of vinyl acetate units and 0.05 to 5% by mass of (meth)acrylic acid units. The product contains an ethylene-vinyl alcohol copolymer (B1) as a dispersant (B), having an ethylene unit content of 1 mol% or more and less than 12 mol%, The content of the dispersant (B) is 2 to 20 parts by mass per 100 parts by mass of the dispersed phase (A). The inorganic fine particles (C) are colloidal silica with an average particle size of 10 to 500 nm. An aqueous emulsion having an inorganic fine particle (C) content of 0.2 to 10 parts by mass per 100 parts by mass of dispersed phase (A).

2. The aqueous emulsion according to claim 1, wherein the viscosity-average degree of polymerization of the ethylene-vinyl alcohol copolymer (B1) is 200 to 5000 and the degree of saponification is 80 to 99.7 mol%.

3. The aqueous emulsion according to claim 1 or 2, further comprising 0.1 to 5 parts by mass of a trivalent or tetravalent metal salt (D) in terms of metal element, per 100 parts by mass of dispersed phase (A).

4. A method for producing an aqueous emulsion according to any one of claims 1 to 3; A method for producing an aqueous emulsion, comprising emulsion polymerization of vinyl acetate and (meth)acrylic acid in the presence of a dispersant (B), followed by the addition of inorganic fine particles (C).

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