WO2020213550A1 - Coating liquid for paper and coated paper using same - Google Patents

Abstract

This coating liquid for paper contains an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of carboxylic acid, wherein: the content of an ethylene unit in the ethylene-vinyl alcohol copolymer (A) is 1-20 mol% (exclusive of 20); the degree of crystallinity Cw(30ºC) in water at 30ºC and the degree of crystallinity Cw(70ºC) in water at 70ºC, as measured by pulsed NMR, satisfy the formula (I); and the alkali metal salt (B) of carboxylic acid is contained in an amount of 0.001-1 part by mass, in terms of the mass of alkali metal, with respect to 100 parts by mass of the ethylene-vinyl alcohol copolymer (A). Consequently, provided is a coating liquid for paper having excellent water resistance and excellent barrier properties.

Description

Coating liquid for paper and coated paper using it

The present invention relates to a coating liquid for paper containing an ethylene-vinyl alcohol copolymer. It also relates to coated paper and release paper using the same. It should be noted that this application claims the priority of Japanese Patent Application No. 2019-077137 filed on April 15, 2019, and the whole thereof is cited as a part of this application by reference.

Polyvinyl alcohol (hereinafter, may be abbreviated as "PVA") is known as a water-soluble synthetic polymer, and is a raw material for vinylon, which is a synthetic fiber, a paper processing agent, a fiber processing agent, an adhesive, and an emulsion. It is widely used as a stabilizer for polymerization and suspension polymerization, an inorganic binder, a film, and the like. In particular, it is known that by applying PVA to paper, it is possible to enhance paper strength, make it water resistant, make it oil resistant, and impart gas barrier properties, and it is widely used. PVA is also used as an inorganic binder and a dispersion stabilizer, and as an auxiliary agent for imparting functionality to paper.

Of the coated papers, especially release papers, PVA is used as a sealing layer (barrier layer) for the purpose of reducing voids between pulp fibers constituting the paper and improving the surface yield of the silicone coated on the paper surface. Is commonly used. Among them, partially saponified PVA is known to have excellent barrier properties.

However, since partially saponified PVA is inferior in water resistance, there is a problem that PVA is eluted and blocked by humidification in an adhesive processing process or the like. Further, there is a problem that the water-dispersed varnish cannot be used in the post-processing process.

In response to the above problem, Patent Document 1 describes that both barrier properties and water resistance can be achieved by using a mixture of an ethylene-vinyl alcohol copolymer and carboxymethyl cellulose.

However, since the ethylene-vinyl alcohol copolymer contains a hydrophobic ethylene unit, it is less soluble in water than unmodified PVA, and remains undissolved when preparing an aqueous solution (hereinafter, "insoluble matter"). It may be abbreviated as.). On the other hand, if the degree of saponification is lowered in order to suppress the formation of insoluble matter, the particles may aggregate with each other during dissolution to form a powder. When an aqueous solution containing an insoluble matter or a step powder is used as a coating liquid for paper, the barrier property may be reduced because they become minute defects on the coated surface.

Japanese Unexamined Patent Publication No. 11-21788

The present invention has been made to solve the above problems, and an object of the present invention is to provide a coating liquid for paper containing an ethylene-vinyl alcohol copolymer. An object of the present invention is to provide a coated paper and a release paper having excellent water resistance and barrier properties by using the coating liquid for paper.

The above problem is a coating liquid for paper containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of a carboxylic acid; the ethylene unit of the ethylene-vinyl alcohol copolymer (A). The content is 1 mol% or more and less than 20 mol%, and the crystallinity Cw (30 ° C) in water at 30 ° C and the crystallinity Cw (70 ° C) in water at 70 ° C determined by pulse NMR are expressed by the following formulas (70 ° C). It satisfies I) and contains 0.001 to 1 part by mass of the alkali metal salt (B) of the carboxylic acid with respect to 100 parts by mass of the ethylene-vinyl alcohol copolymer (A) in terms of mass of alkali metal. It is solved by providing a coating liquid for paper.

At this time, the viscosity average degree of polymerization of the ethylene-vinyl alcohol copolymer (A) is preferably 900 to 2400. It is also preferable that the degree of saponification of the ethylene-vinyl alcohol copolymer (A) is 90 to 98.5 mol%.

The above problem is also solved by providing a coated paper in which the coating liquid is applied to the surface of the paper. At this time, a preferred embodiment of the coated paper is a release paper base paper. Further, a release paper in which a release layer is formed on a sealing layer formed by applying the coating liquid to paper is also a suitable embodiment. At this time, it is preferable that the release layer contains a silicone resin.

The coated paper coated with the coating liquid of the present invention has excellent barrier properties and water resistance. Therefore, it is preferably used for release paper. Further, the coating liquid for paper of the present invention has excellent water resistance and is also excellent in blocking resistance, and a water-dispersible varnish can be used in the post-processing step.

The coating liquid for paper of the present invention is a coating liquid containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of a carboxylic acid; the ethylene-vinyl alcohol copolymer (A). The ethylene unit content of ethylene is 1 mol% or more and less than 20 mol%, and the crystallinity in water at 30 ° C. Cw (30 ° C.) and the crystallinity in water at 70 ° C. Cw (70 ° C.) determined by pulse NMR. Satisfies the following formula (I), and 0.001 to 1 part by mass of the alkali metal salt (B) of the carboxylic acid in terms of mass of the alkali metal with respect to 100 parts by mass of the ethylene-vinyl alcohol copolymer (A). It is characterized by including.

[Ethylene-vinyl alcohol copolymer (A)]
The ethylene-vinyl alcohol copolymer (A) contained in the paper coating liquid of the present invention has an ethylene unit content of 1 mol% or more and less than 20 mol%, and is subjected to pulse NMR (nuclear magnetic resonance absorption method). A major feature is that the required crystallinity in water Cw (30 ° C.) at 30 ° C. and crystallinity Cw (70 ° C.) in water at 70 ° C. satisfy the above formula (I). This point will be described below.

(Crystallinity in water)
First, the meaning of measuring a polymer sample by pulse NMR will be described. The pulse NMR apparatus has a static magnetic field generated by an electromagnet in the apparatus. In a static magnetic field, the direction of nuclear spins of hydrogen nuclei is oriented in the same direction as the static magnetic field. When a pulsed magnetic field is applied here, the nuclear spins of the hydrogen nuclei are excited by 90 ° from the direction of the static magnetic field. After that, the process until the direction of the excited nuclear spins macroscopically returns to the original static magnetic field direction is called T ₂ relaxation or lateral relaxation, and the time required for this process is called relaxation time (Tau). In the case of single-component relaxation, the magnetization intensity (y) at time (t) is determined by the following equation using the relaxation intensity (A), relaxation time (Tau) and constant (y ₀ , W) in the excited state. It is indicated by (II). W is a Weibull coefficient, and when W = 1, the equation (II) becomes an Exp type, and when W = 2, it becomes a Gauss type. In the case of a general polymer sample, 1 ≦ W ≦ 2.

In the case of T ₂ relaxation, the hydrogen nucleus decays while exchanging energy with other hydrogen nuclei. Therefore, when the molecular motion of the sample is high, the interaction with the protons adjacent to each other is small, so that the energy decay of the entire system is unlikely to occur and the relaxation time becomes long. On the other hand, when the molecular motility is low, the relaxation time becomes short. Therefore, in the case of a crystalline polymer material, the relaxation time is short in the crystalline portion and long in the amorphous portion. In an actual crystalline polymer, a crystalline portion and an amorphous portion are present, and in the transition curve, the sum of the relaxation component derived from the crystalline portion having a short relaxation time and the relaxation component derived from the amorphous portion having a long relaxation time is observed. If the relaxation intensity derived from the crystalline portion is A ₁ , the relaxation intensity derived from the amorphous portion is A ₂ , the relaxation time derived from the crystalline portion is Tau ₁ , and the relaxation time derived from the amorphous portion is Tau ₂ , then time (t). The magnetization intensity (y) of the entire sample in the above is expressed by the following equation (III) using a constant (y ₀ ). Note that y ₀ is a component derived from thermal noise derived from the measuring device, is a parameter that does not depend on time t, and does not affect the values of relaxation intensity (A ₁ ) and (A ₂ ). Crystallinity (Cw) is not affected by y ₀ . Since the crystal component often exhibits Gauss-type relaxation, it was fixed at W = 2 in the first term representing the crystal component of the formula (III). A ₁ / (A ₁ + A ₂ ) derived from this equation is the crystallinity obtained by pulse NMR. In the present specification, a pulse sequence called a Solid-echo method is used for the measurement using pulse NMR.

As described above, the ratio of the crystalline component and the amorphous component in the polymer sample can be obtained from the transition curve measured by pulse NMR. The ethylene-vinyl alcohol copolymer is a hydrophilic polymer having a large number of hydroxyl groups, and swells in water to reduce the crystallinity, but the degree of swelling is greatly affected by the water temperature. The higher the water temperature, the higher the degree of swelling, and as a result, the degree of crystallinity decreases. In the present invention, attention was paid to the crystallinity Cw (30 ° C.) (%) in water at 30 ° C. and the crystallinity Cw (70 ° C.) (%) in water at 70 ° C., which are obtained by pulse NMR. Here, the ethylene-vinyl alcohol copolymer (A) is a water-soluble polymer, but in order to dissolve the once crystallized ethylene-vinyl alcohol copolymer (A) in water, high temperature conditions and a stirring operation are performed. is necessary. Therefore, the sample does not dissolve and only swells when it is allowed to stand in water at 30 ° C. or 70 ° C., and exists in a solid state. Therefore, in the pulse NMR measurement, the measurement is performed in the solid state.

The ethylene-vinyl alcohol copolymer (A) of the present invention satisfies the following formula (I). Here, the crystallinity in water (Cw) is not determined by the absolute value of the relaxation time, but the relaxation intensity (A ₁ ) and (A ₂ ), which are the ratios of the system divided into two components having different relaxation times. ) Is a parameter determined by. Since the relaxation intensities (A ₁ ) and (A ₂ ) are not affected by the change in the resonance frequency, the value of the crystallinity (Cw) in water is not affected by the resonance frequency.

In the above formula (I), [(100-Cw (30 ° C.)) / 100] represents the ratio of the amorphous portion at 30 ° C., and takes a value of 0 to 1. Further, [Cw (30 ° C.)-Cw (70 ° C.)] is an index of the difference in crystallinity in water between 30 ° C. and 70 ° C., that is, the amount of increase in amorphous portion with an increase in water temperature, and a value of 0 to 100 Take. Therefore, the formula (I) obtained by multiplying these is an index of the easy solubility of the ethylene-vinyl alcohol copolymer (A), and the value of the formula (I) has a large absolute value [Cw (30 ° C.)-. Cw (70 ° C)] has a greater effect. Generally, an ethylene-vinyl alcohol copolymer having an ethylene unit content of 1 mol% or more and less than 20 mol% is soluble in water because the ethylene unit content is low. Such a water-soluble ethylene-vinyl alcohol copolymer usually has a large value of [(100-Cw (30 ° C.)) / 100] and a value of [Cw (30 ° C.)-Cw (70 ° C.)]. As a result, the value of the formula (I) becomes small, and the value of [(100-Cw (30 ° C.)) / 100] is small, and [Cw (30 ° C.)-Cw (70 ° C.)] Since the value of is large, the value of the formula (I) may be large as a result. That is, when the value of the formula (I) is less than 4, it is easy to dissolve at a low temperature, but it is easy to form a splicing powder, and since the splicing powder once formed is difficult to dissolve in water, it takes a long time to dissolve completely. Become. The lower limit of the formula (I) is preferably 5 or more, and more preferably 6 or more. On the other hand, when the value of the formula (I) exceeds 22, the solubility in water decreases and the dissolution time until total dissolution becomes long. The upper limit of the formula (I) is preferably 21 or less, and more preferably 20 or less. When the above formula (I) satisfies a specific range, an ethylene-vinyl alcohol copolymer (A) having a high dissolution rate and less likely to form a powder during dissolution can be obtained.

In the measurement, the sample of ethylene-vinyl alcohol copolymer (A) was allowed to stand in H ₂ Od ₂ at each temperature (30 ° C., 70 ° C.) for 40 minutes, and then the temperature was the same as that at the time of standing. Pulse NMR measurement is performed at the temperature of. The range of 0 to 0.8 ms of the obtained transition curve is fitted by the above equation (III) using the error least squares method.

The ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) produces less insoluble matter and aggregates derived from the splicing powder when dissolved in water. Therefore, for example, an emulsion polymerization stabilizer. By emulsion polymerization of an ethylenically unsaturated monomer using an ethylene-vinyl alcohol copolymer (A), it is possible to obtain an aqueous emulsion having less agglomerates and excellent water adhesion and film forming properties. it can.

The ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) is a special method for producing an ethylene-vinyl alcohol copolymer, which comprises a polymerization step, a saponification step, a pulverization step, a liquid removal step and a drying step. Can be obtained by This manufacturing method will be described in detail later. In the present invention, by adopting such a special production method, an ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) and having excellent solubility in water can be obtained for the first time. It was. Hereinafter, the ethylene-vinyl alcohol copolymer (A) will be described in more detail.

(Vinyl ester)
The ethylene-vinyl alcohol copolymer (A) can be obtained by including a step of saponifying the ethylene-vinyl ester copolymer obtained by copolymerizing ethylene and vinyl ester. Examples of the vinyl ester used include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, vinyl pivalate, vinyl versatic acid and the like. Of these, vinyl acetate is preferable.

(Ethylene unit content)
The content of ethylene units in the ethylene-vinyl alcohol copolymer (A) is 1 mol% or more and less than 20 mol%. When the content of ethylene units is less than 1 mol%, the water-resistant adhesiveness of the obtained aqueous emulsion is lowered. The ethylene unit content is preferably 1.5 mol% or more, and more preferably 2 mol% or more. On the other hand, when the content of ethylene units is 20 mol% or more, the ethylene-vinyl alcohol copolymer (A) becomes insoluble in water, making it difficult to prepare an aqueous solution. The content of ethylene units is preferably 15 mol% or less, more preferably 10 mol% or less, and further preferably 8.5 mol% or less.

The content of ethylene units can be determined from, for example, ¹ H-NMR of an ethylene-vinyl ester copolymer which is a precursor of an ethylene-vinyl alcohol copolymer (A) or a revinegared product. The ethylene-vinyl ester copolymer of the sample was reprecipitated and purified three times or more using a mixed solution of n-hexane and acetone, and then dried under reduced pressure at 80 ° C. for 3 days to have an ethylene-vinyl ester copolymer for analysis. Make a coalescence. The ethylene-vinyl ester copolymer for analysis is dissolved in DMSO-d ₆ and measured at ¹ H-NMR (500 MHz) at 80 ° C. The ethylene unit content was determined using the peak derived from the main chain methine of vinyl ester (4.7 to 5.2 ppm) and the peak derived from ethylene and the main chain methylene of vinyl ester (0.8 to 1.6 ppm). Can be calculated.

(Saponification degree)
The degree of saponification of the ethylene-vinyl alcohol copolymer (A) is not particularly limited, but is preferably 80 to 99.99 mol%. If the degree of saponification is less than 80 mol%, the solubility of the ethylene-vinyl alcohol copolymer (A) in the obtained aqueous solution becomes insufficient. The saponification degree is more preferably 82 mol% or more, further preferably 85 mol% or more, and particularly preferably 90% or more. On the other hand, when the saponification degree exceeds 99.99 mol%, it tends to be difficult to stably produce the ethylene-vinyl alcohol copolymer (A). The saponification degree is more preferably 99.5 mol% or less, further preferably 99 mol% or less, and particularly preferably 98.5 mol% or less. The saponification degree of the ethylene-vinyl alcohol copolymer (A) can be measured according to JIS K6726 (1994).

(Viscosity average degree of polymerization)
The viscosity average degree of polymerization of the ethylene-vinyl alcohol copolymer (A) is not particularly limited, but is preferably 200 to 5000. When the viscosity average degree of polymerization is less than 200, the storage stability of the obtained aqueous emulsion is lowered. The viscosity average degree of polymerization is more preferably 250 or more, further preferably 300 or more, even more preferably 400 or more, and particularly preferably 900 or more. On the other hand, when the viscosity average degree of polymerization exceeds 5000, the viscosity of the ethylene-vinyl alcohol copolymer aqueous solution becomes too high, and it tends to be difficult to handle. The viscosity average degree of polymerization is more preferably 4500 or less, further preferably 4000 or less, still more preferably 3500 or less, and particularly preferably 2400 or less. The viscosity average degree of polymerization P can be measured according to JIS K6726 (1994). That is, the ethylene-vinyl alcohol copolymer (A) was re-saponified to a saponification degree of 99.5 mol% or more, purified, and then measured in water at 30 ° C. from the ultimate viscosity [η] (L / g). Can be obtained by.
P = ([η] x 10000 / 8.29) ^{(1 / 0.62)}

(Other monomer units)
The ethylene-vinyl alcohol copolymer (A) may contain a monomer unit other than the vinyl alcohol unit, the ethylene unit and the vinyl ester unit as long as the effect of the present invention is not impaired. Examples of such monomers include α-olefins such as propylene, n-butene, and isobutylene; acrylic acid and salts thereof; acrylic acid esters; methacrylate and salts thereof; methacrylic acid esters; acrylamide; N-methylacrylamide, N. -Acrylamide derivatives such as ethyl acrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamide propanesulfonic acid and its salts, acrylamide propyl dimethylamine and its salts or quaternary salts thereof, N-methylol acrylamide and its derivatives; methacrylamide Acrylamide derivatives such as N-methylmethacrylate, N-ethylmethacrylate, methacrylamidepropanesulfonic acid and its salts, methacrylamidepropyldimethylamine and its salts or quaternary salts thereof, N-methylolmethacrylamide and its derivatives; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; nitriles such as acrylamide and methacrylnitrile; chloride. Vinyl halides such as vinyl and vinyl fluoride; vinylidene halides such as vinylidene chloride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; unsaturated dicarboxylic acids such as maleic acid, itaconic acid and fumaric acid and salts thereof. Alternatively, an ester thereof; a vinylsilyl compound such as vinyltrimethoxysilane; isopropenyl acetate and the like can be mentioned. The content of these monomers varies depending on the purpose and use of use, but is preferably 10 mol% or less, more preferably less than 5 mol%, still more preferably less than 1 mol%. It is particularly preferably less than 0.5 mol%.

[Method for producing ethylene-vinyl alcohol copolymer (A)]
A preferred method for producing the ethylene-vinyl alcohol copolymer (A) is a polymerization step of copolymerizing ethylene and a vinyl ester to obtain an ethylene-vinyl ester copolymer; saponifying the ethylene-vinyl ester copolymer. A saponification step of obtaining a solid block containing an ethylene-vinyl alcohol copolymer and a solvent; a pulverization step of crushing the solid block to obtain wet particles; mechanically removing a part of the solvent from the wet particles. A method for producing an ethylene-vinyl alcohol copolymer, which comprises a deflating step of obtaining deflated particles; and a drying step of removing the rest of the solvent from the deflated particles by heating to obtain dry particles. hand;
The deflated particles contain 40 to 65% by mass of the solvent, and the content of the deflated particles passing through a sieve having an opening of 5.6 mm is 80% by mass or more, and the opening is 1 This is a production method in which the content of particles passing through a 0.0 mm sieve is less than 2% by mass.

It is important that the deflated particles obtained by pulverizing the solid block after the saponification step and then deflating the solid block as in the above production method contain a specific ratio of solvent and have a specific particle size distribution. Therefore, when preparing an aqueous solution of the ethylene-vinyl alcohol copolymer (A), the powder does not form a powder and the dissolution rate increases. Hereinafter, each step of the manufacturing method will be described in detail.

(Polymerization process)
Examples of the method for copolymerizing ethylene and vinyl ester include known methods such as a massive polymerization method, a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Of these, a bulk polymerization method or a solution polymerization method in which polymerization is carried out in a solvent-free environment or in an organic solvent such as alcohol can be usually adopted, but the solution polymerization method is preferable. Examples of the alcohol include lower alcohols such as methanol and ethanol, and methanol is particularly preferable. In the polymerization operation, any of the batch method, the semi-batch method and the continuous method can be adopted. Examples of the polymerization reactor include a batch reactor, a tubular reactor, and a continuous tank reactor. The initiators used in the copolymerization include 2,2'-azobis (isobutyronitrile), 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile), and 2,2'-azobis. Examples thereof include azo-based initiators such as (2,4-dimethyl-valeronitrile), benzoyl peroxide, n-propylperoxydicarbonate, and known initiators such as peroxide-based initiators.

The polymerization temperature is not particularly limited, and is preferably about 0 to 180 ° C, more preferably room temperature to 160 ° C, and even more preferably 30 to 150 ° C. When polymerizing below the boiling point of the solvent used for polymerization, either vacuum boiling polymerization or normal pressure non-boiling polymerization can be selected. Further, when polymerizing above the boiling point of the solvent used at the time of polymerization, either pressure non-boiling polymerization or pressure boiling polymerization can be selected.

The ethylene pressure in the polymerization reactor at the time of polymerization is preferably 0.01 to 0.9 MPa, more preferably 0.05 to 0.7 MPa, still more preferably 0.1 to 0.65 MPa. The polymerization rate at the outlet of the polymerization reactor is not particularly limited, but is preferably 10 to 90%, more preferably 15 to 85%.

In the polymerization step, a chain transfer agent may coexist for the purpose of adjusting the viscosity average degree of polymerization of the obtained ethylene-vinyl ester copolymer. Examples of the chain transfer agent include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone and cyclohexanone; mercaptans such as 2-hydroxyethanethiol; thiocarboxylic acids such as thioacetic acid; trichloroethylene and perchloro. Examples thereof include halogenated hydrocarbons such as ethylene. Of these, aldehydes and ketones are preferably used. The amount of the chain transfer agent added is determined according to the chain transfer constant of the chain transfer agent to be added and the viscosity average degree of polymerization of the target ethylene-vinyl ester copolymer, but is usually 100 parts by mass of the vinyl ester used. It is 0.1 to 10 parts by mass with respect to.

(Saponification process)
The ethylene-vinyl ester copolymer obtained in the polymerization step is saponified in an organic solvent by an alcohol decomposition or hydrolysis reaction in the presence of a catalyst. Examples of the catalyst used in the saponification step include basic catalysts such as sodium hydroxide, potassium hydroxide and sodium methoxydo; or acidic catalysts such as sulfuric acid, hydrochloric acid and p-toluenesulfonic acid. The organic solvent used in the saponification step is not particularly limited, and examples thereof include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene. These can be used alone or in combination of two or more. Above all, it is convenient and preferable to carry out the saponification reaction in the presence of sodium hydroxide, which is a basic catalyst, using methanol or a mixed solution of methanol and methyl acetate as a solvent. The amount of the saponification catalyst used is preferably 0.001 to 0.5 in terms of molar ratio to the vinyl ester monomer unit in the ethylene-vinyl ester copolymer. The molar ratio is more preferably 0.002 or more. On the other hand, the molar ratio is more preferably 0.4 or less, and further preferably 0.3 or less.

The preferred embodiment of the saponification step is as follows. First, a saponification catalyst such as sodium hydroxide is added to the ethylene-vinyl ester copolymer solution obtained in the polymerization step and mixed. The solvent at this time is preferably methanol. Although it is a uniform liquid at the beginning of mixing, when the saponification reaction proceeds and the vinyl ester units in the polymer are saponified and converted to vinyl alcohol units, the solubility in the solvent decreases and the polymer precipitates in the solution. To do. At this time, the solution contains methyl acetate produced by alcoholesis with methanol. As the saponification reaction progresses, the amount of polymer precipitated gradually increases to form a slurry, which then loses its fluidity. Therefore, in order for the saponification reaction to proceed uniformly, it is important to mix sufficiently until the fluidity is lost.

The method of mixing the ethylene-vinyl ester copolymer solution and the saponification catalyst is not particularly limited, and various methods such as a static mixer, a kneader, and a stirring blade can be adopted, but using a static mixer continuously and uniformly mixes. It is preferable to be able to do it. In this case, a saponification catalyst is added to the ethylene-vinyl ester copolymer solution after the polymerization step in a pipe connected to the polymerization tank, and then the mixture is passed through a static mixer to obtain a paste. The temperature of the reaction solution in the static mixer is usually 20 to 80 ° C.

The method for advancing the saponification reaction of the ethylene-vinyl ester copolymer in the paste that has passed through the static mixer is not particularly limited, but the paste is placed on a moving belt and the belt is kept at a constant temperature. A method in which the saponification reaction proceeds while moving in a dripping tank is preferable. The paste on the belt loses its fluidity and becomes a solid state, and the saponification reaction proceeds in the solid state. By this method, the saponification reaction can be continuously carried out in a solid state, and a solid block containing an ethylene-vinyl alcohol copolymer and a solvent can be obtained. The saponification temperature is preferably 20 to 60 ° C. If the saponification temperature is too low, the reaction rate will decrease. The saponification temperature is more preferably 25 ° C. or higher, and even more preferably 30 ° C. or higher. On the other hand, if the saponification temperature is too high, a large amount of solvent evaporates, the content of the solvent in the obtained solid block becomes low, and the solubility of the obtained ethylene-vinyl alcohol copolymer deteriorates. The saponification temperature is more preferably 55 ° C. or lower, and even more preferably 50 ° C. or lower. The saponification time is preferably 5 minutes or more and 2 hours or less. The saponification time is more preferably 8 minutes or more, and even more preferably 10 minutes or more. The saponification time is more preferably 1 hour or less, and further preferably 45 minutes or less.

(Crushing process)
Wet particles containing a solvent can be obtained by pulverizing the solid block obtained in the saponification step. The crusher used at this time is not particularly limited as long as it can adjust the rotation speed of the crusher and the like to obtain a particle size distribution described later, and a known crusher or crusher can be used. Due to the mechanical properties of the ethylene-vinyl alcohol copolymer obtained through the saponification step, a cutting type crusher such as a cutter mill, a guillotine type cutting machine, a reciprocating cutter type, a uniaxial, biaxial or triaxial shear crusher is preferable. The Rockwell hardness (HRC) of the crushing blade that comes into contact with the solid block during crushing is preferably 40 to 70. The hardness is more preferably 45 or more. On the other hand, the hardness is more preferably 65 or less. The rotation speed of the crushing blade is preferably 200 to 550 rpm. The rotation speed is more preferably 225 rpm or more, and further preferably 250 rpm or more. On the other hand, the rotation speed is more preferably 500 rpm or less, and further preferably 450 rpm or less.

Conventionally, for crushing a solid block obtained in a saponification step, a crusher equipped with a crushing blade having a Rockwell hardness of less than 40 and operated at a rotation speed of more than 550 rpm has been generally used. Since the Rockwell hardness of the crushing blade used is low, the crushing blade is easily worn, and uneven crushing is likely to occur due to cutting with the worn crushing blade. Further, when the solid block is crushed at a high rotation speed, the solid block vibrates greatly up and down at the crusher inlet due to the impact of the crushing, resulting in uneven breakage during crushing. Due to such circumstances, it has been difficult to stably obtain particles having a specific particle size distribution, which will be described later. On the other hand, when the Rockwell hardness of the crushing blade exceeds 70, the toughness is lowered while the hardness is high, so that minute chipping of the crushing blade occurs during crushing, which tends to cause uneven crushing. .. Further, when the rotation speed of the crusher is less than 200 rpm, the crushing efficiency tends to decrease.

(Washing process)
After the pulverization step, if necessary, the wet particles may be washed by adding a washing step for the purpose of removing impurities such as sodium acetate. Examples of the cleaning liquid include lower alcohols such as methanol and ethanol, lower fatty acid esters such as methyl acetate, and mixtures thereof. The conditions of the washing step are not particularly limited, but it is preferable to wash at a temperature of 20 ° C. to the boiling point of the washing liquid for about 30 minutes to 10 hours.

(Liquid removal process)
After the pulverization step, and in some cases, after the washing step, the deflated particles are obtained by mechanically deflating a part of the solvent from the wet particles. The liquid remover used at this time is preferably a centrifugal liquid remover. The centrifugal deliquescent machine is preferably one capable of continuous centrifugal deliquescent. Examples include a liquid machine. Conventionally, a squeeze deflating machine has been used to deflate pulverized particles. However, in order to bring the solvent content of the obtained deflated particles into the above-mentioned specific range, it is necessary to increase the pressing strength, and as a result, the deflated particles are deformed or broken, and the particle size distribution is out of the range described later. It was. That is, it has been difficult to simultaneously achieve the particle size distribution of the deflated particles and the solvent liquid content, which will be described later, by the conventional method. In the liquid removal step, by using the above-mentioned centrifugal liquid removal machine, liquid removal particles having a particle size distribution and a solvent content described later can be easily obtained.

It is important that the deflated particles thus obtained contain a solvent of 40 to 65% by mass. When the content of the solvent is less than 40% by mass, the particles that are overdried will be mixed, and the ethylene-vinyl alcohol copolymer that is difficult to dissolve after the drying step will be mixed, which satisfies the above formula (I). The ethylene-vinyl alcohol copolymer (A) to be used cannot be obtained. The content of the solvent is preferably 42% by mass or more, and more preferably 45% by mass or more. On the other hand, when the content of the solvent exceeds 65% by mass, a difference in thermal history occurs between the surface and the inside of the particles, and the ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) cannot be obtained. , The energy required for drying increases. The content of the solvent is preferably 62% by mass or less, and more preferably 59% by mass or less. The solvent content is the average value of the deflated particles. The content of the solvent in the deflated particles is preferably 3% by mass or more lower than the content of the solvent in the wet particles, more preferably 5% by mass or more, and further preferably 10% by mass or more.

Further, the content of the particles passing through the sieve having a mesh size of 5.6 mm is 80% by mass or more, and the content rate of the particles passing through the sieve having a mesh size of 1.0 mm is less than 2% by mass. It is important that That is, it is important that it does not contain many coarse particles and also does not contain many fine particles. In the present invention, the mesh opening of the sieve conforms to the nominal opening of JIS Z8801-1 (2006).

The content of the particles passing through the sieve having a mesh size of 5.6 mm in the liquid removal particles is 80% by mass or more. When the deflated particles contain a large amount of coarse particles, high temperature or long-term drying is required in order to sufficiently dry to the center of the particles, and the energy required for drying increases. Moreover, by drying at high temperature or for a long time, crystallization of smaller particles progresses too much, and ethylene-vinyl alcohol copolymer particles that are difficult to dissolve after the drying step are mixed. In addition, the presence of coarse particles causes uneven heat transfer in the dryer. Due to the above circumstances, the ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) cannot be obtained. The content of the particles passing through the sieve having a mesh size of 5.6 mm is preferably 82% by mass or more, and more preferably 85% by mass or more. On the other hand, considering the production efficiency, the content of the particles passing through the sieve having a mesh size of 5.6 mm is preferably 99% by mass or less, and more preferably 98% by mass or less.

The content of the deflated particles passing through the sieve having a mesh size of 1.0 mm is less than 2% by mass. When the deliquescent particles contain a large amount of fine particles, the fine particles are subsequently dried to allow the fine particles to crystallize too much, and a large amount of ethylene-vinyl alcohol copolymer particles that are difficult to dissolve after the drying step are mixed. It ends up. In addition, the fine particles stay at the bottom of the dryer and receive excessive heat to increase the crystallinity, and ethylene-vinyl alcohol copolymer particles having reduced solubility are mixed. Due to these circumstances, the ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) cannot be obtained. The content of the particles passing through the sieve having a mesh size of 1.0 mm is preferably 1.9% by mass or less, and more preferably 1.8% by mass or less. On the other hand, considering the production efficiency, the content of the particles passing through the sieve having a mesh size of 1.0 mm is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more.

(Drying process)
An ethylene-vinyl alcohol copolymer can be obtained by subjecting the deflated particles to a drying step after the deflating step. Specifically, hot air drying using a cylindrical dryer is preferable, and the temperature of the particles at the time of drying is preferably 80 to 120 ° C. If the temperature is too low, the production efficiency will decrease. The temperature is more preferably 90 ° C. or higher. On the other hand, if the temperature is too high, particles that crystallize too much are generated, and the solubility is deteriorated. The temperature is more preferably 110 ° C. or lower. The drying time is preferably 2 to 10 hours, more preferably 3 to 8 hours. By setting the drying conditions within the above range, an ethylene-vinyl alcohol copolymer satisfying the formula (I) can be easily produced.

(Additional crushing process)
After the drying step, it is preferable to provide an additional pulverization step in order to further reduce the particle size. As a result, the particles can be made into particles having a high dissolution rate in water. As the crusher used in the additional crushing step, the same crusher used in the crushing step can be used.

The particles of the ethylene-vinyl alcohol copolymer (A) obtained in the additional pulverization step preferably have a content of particles passing through a sieve having a mesh size of 2.5 mm or more of 80% by mass or more. When the number of particles passing through the sieve having a mesh size of 2.5 mm is less than 80% by mass, the dissolution rate becomes low when the particles of the ethylene-vinyl alcohol copolymer (A) are dissolved in water to prepare an aqueous solution. It requires heating at high temperature for a long time. The content of the particles passing through the sieve having a mesh size of 2.5 mm is more preferably 83% by mass or more, and further preferably 85% by mass or more. Further, the particles of the ethylene-vinyl alcohol copolymer (A) preferably have a content of 80% by mass or more of the particles passing through a sieve having a mesh size of 1.0 mm. As a result, the dissolution rate in water is further improved. The content of the particles passing through the sieve having a mesh size of 1.0 mm is more preferably 83% by mass or more, and further preferably 85% by mass or more.

On the other hand, the particles of the ethylene-vinyl alcohol copolymer (A) obtained in the additional pulverization step preferably have a content of particles passing through a sieve having a mesh size of 0.15 mm of 20% by mass or less. When the content of the particles passing through the sieve having a mesh size of 0.15 mm exceeds 20% by mass, splicing tends to easily occur in the aqueous solution containing the ethylene-vinyl alcohol copolymer (A). The content of the particles passing through the sieve having a mesh size of 0.15 mm is more preferably 17% by mass or less, and further preferably 15% by mass or less.

[Metal salt of carboxylic acid (B)]
The coating liquid of the present invention is characterized by containing an alkali metal salt (B) of a carboxylic acid. The content ratio of the alkali metal salt (B) of the carboxylic acid to 100 parts by mass of the ethylene-vinyl alcohol polymer (A) is 0.001 to 1 part by mass in terms of mass of the alkali metal, and 0.01 to 0.9. By mass is preferable, and 0.02 to 0.8 parts by mass is more preferable. If the content exceeds 1 part by mass, the barrier property and water resistance of the coated paper are lowered. Although the reason for this has not been clarified, the excessive presence of the alkali metal salt (B) of the carboxylic acid reduces the water solubility of the ethylene-vinyl alcohol copolymer (A), resulting in an increase in insoluble matter and formation. It is presumed that this is because the splicing powder is poorly dissolved. On the other hand, it is difficult to make the content less than 0.001 part by mass due to the manufacturing method of the ethylene-vinyl alcohol copolymer (A), and excessive cleaning work or the like is required to achieve the content, which increases the manufacturing cost. Invite.

In the present invention, the content of the alkali metal salt (B) of the carboxylic acid (in terms of the mass of the alkali metal) is determined by ashing the coating liquid dried on a platinum crucible and then analyzing the obtained ash by ICP emission analysis. It can be obtained from the amount of alkali metal ions obtained by measurement.

In the present invention, the alkali metal salt (B) of the carboxylic acid is not particularly limited. For example, sodium acetate, potassium acetate, sodium propionate, potassium propionate, sodium glycerate, potassium glycerate, sodium malate, potassium malate, sodium citrate, potassium citrate, sodium lactate, potassium lactate, sodium tartrate, tartrate. Potassium, sodium salicylate, potassium salicylate, sodium malate, potassium malonate, sodium succinate, potassium succinate, sodium maleate, potassium maleate, sodium phthalate, potassium phthalate, sodium oxalate, potassium oxalate, glutaric acid Sodium, potassium glutarate, sodium avietate, potassium avietate, sodium sorbate, potassium sorbate, sodium 2,4,6-octatriene-1-carboxylate, 2,4,6-octatorien-1-carboxylic acid Potassium, Sodium Eleostearate, Potassium Eleostearate, Sodium 2,4,6,8-Decatetraene-1-carboxylate, Potassium 2,4,6,8-Decatetraene-1-carboxylate, Sodium retinoate, Examples include potassium retinoate.

In the present invention, the method of incorporating the alkali metal salt (B) of a specific amount of carboxylic acid in the coating liquid is not particularly limited. For example, 1) a method of dissolving both an ethylene-vinyl alcohol copolymer and an alkali metal salt of a carboxylic acid in water, and 2) an alkali metal as a saponification catalyst when the ethylene-vinyl ester copolymer is saponified in a solvent. A method of dissolving an ethylene-vinyl alcohol copolymer containing an alkali metal salt of a carboxylic acid in water, which is obtained by using an alkaline substance, and 3) a raw material vinyl ester monomer such as vinyl acetate used in the polymerization step. A method of dissolving an ethylene-vinyl alcohol copolymer containing an alkali metal salt of a carboxylic acid in water, which is obtained by neutralizing the carboxylic acid added for the purpose of suppressing alcohol decomposition in a saponification step. 4) When a carboxylic acid having a conjugated double bond is used as a prohibitive agent added to terminate radical polymerization, an alkali metal salt of the carboxylic acid obtained by neutralizing the carboxylic acid in the saponification step is blended. Examples thereof include a method of dissolving the ethylene-vinyl alcohol copolymer in water.

The method for producing the coating liquid for paper of the present invention is not particularly limited. The paper coating liquid of the present invention can be obtained by dissolving the particles of the ethylene-vinyl alcohol copolymer (A) satisfying the formula (I) in water. A suitable production method includes a method in which particles of an ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) and containing an alkali metal salt (B) of a carboxylic acid are dissolved in water. Further, as another suitable production method, a method of dissolving the particles of the ethylene-vinyl alcohol copolymer (A) satisfying the above formula (I) and the alkali metal salt (B) of the carboxylic acid in water can be mentioned. Be done.

<Manufacturing of coated paper>
The paper coating liquid of the present invention contains, if necessary, a water resistant agent such as glioxal, urea resin, melamine resin, polyvalent metal salt, water-soluble polyamide resin; a plasticizer such as glycols and glycerin; ammonia, caustic soda. , Sodium carbonate, phosphoric acid and other pH adjusters; defoaming agents; mold release agents; surfactants; colorants such as pigments and other various additives may be added. Further, the coating liquid for paper of the present invention contains various modified PVAs such as unmodified PVA, carboxyl-modified PVA, sulfonic acid group-modified PVA, acrylamide-modified PVA, cationic-group-modified PVA, and long-chain alkyl-group-modified PVA; casein. , Raw starch (wheat, corn, rice, horse bells, sweet potato, tapioca, sago palm), raw starch decomposition products (dextrin, etc.), starch derivatives (oxidized starch, etherified starch, esterified starch, cationized starch, etc.) ), Seaweed polysaccharides (soda alginate, carrageenan, agar (agarose, agaropectin), starch, etc.), water-soluble cellulose derivatives (carboxyalkyl cellulose, alkyl cellulose, hydroxyalkyl cellulose, etc.) and other water-soluble polymers; styrene- Synthetic resin emulsions such as butadiene copolymer latex, polyacrylic acid ester emulsion, vinyl acetate-ethylene copolymer emulsion, vinyl acetate-acrylic acid ester copolymer emulsion, etc. are used in combination as long as the effects of the present invention are not impaired. May be good.

The concentration of the ethylene-vinyl alcohol copolymer (A) in the coating liquid in the present invention depends on the coating amount (increase in the dry mass of the paper generated by the coating), the apparatus used for the coating, the operating conditions, and the like. Although it is arbitrarily selected depending on the situation, 1.0 to 10% by mass is preferable, and 2.0 to 9.0% by mass is more preferable. The coating amount can be arbitrarily selected according to the properties of the paper to be coated, but is preferably about 0.3 to 3.0 g / m ² per side of the normal paper. The viscosity of the coating liquid is preferably about 0.001 to 1 Pa · s at 40 ° C.

As a method of applying the coating liquid of the present invention, which is an aqueous solution or an aqueous dispersion, to paper, one side of the paper or one side of the paper using a known method such as a size press, a gate roll coater, a simsizer, a bar coater or the like is used. A method of coating on both sides is usually used, and a method of impregnating paper with a coating liquid may be used. Further, the coated paper can be dried by a known method, for example, hot air, infrared rays, a heating cylinder or a method in which these are combined, and the dried coated paper is subjected to humidity control and calendar treatment. The barrier property can be further improved. As the calendar processing conditions, it is preferable that the roll temperature is room temperature to 100 ° C. and the roll linear pressure is 20 to 300 kg / cm.

The coating paper using the coating liquid of the present invention is not particularly limited, but a release paper is preferable. The release paper has a sealing layer (barrier layer) formed by applying the paper coating liquid on the base material (paper). That is, a release paper in which a release layer is formed on a sealing layer formed by applying the coating liquid of the present invention to paper is a preferred embodiment. The paper used is not particularly limited, and examples thereof include paperboards such as Manila balls, white balls, and liners; printing papers such as general high-quality paper, medium-quality paper, and gravure paper. In addition, the release paper further has a release layer formed on the sealing layer. The release layer is not particularly limited, but a silicone resin is preferable. The silicone resin is not particularly limited, and known silicone resins can be used. Examples of such silicone resins include solvent-based silicones, solvent-free silicones, and emulsion-type silicones.

In addition to the above, the release layer of the release paper of the present invention includes pigments, fluorescent whitening agents, dyed substances for fluorescent whitening agents, defoaming agents, mold release agents, and colorants that can be generally used for papermaking. Various commonly used chemicals such as water retention agents can be appropriately blended.

The coating liquid for the release layer can be applied with general coated paper application equipment, for example, blade coater, air knife coater, transfer roll coater, gate roll size press, 2-roll size press, rod metering. The coating liquid can be applied to the base paper in one layer or multiple layers by an on-machine coater or an off-machine coater provided with a coating device such as a size press coater or a curtain coater. Above all, it is preferable to use a gate roll size press, a 2-roll size press, and a rod metering size press coater from the viewpoint of being suitable for an on-machine coater. Further, as a drying method in the dryer part, for example, various heating and drying methods such as a hot rotating drum, hot air heating, gas heater heating, and infrared heater heating can be appropriately adopted. The coating amount of the release layer is preferably 0.3 to 1.8 g / m ^{2 in} terms of dry mass, and more preferably 0.5 to 1.5 g / m ² .

The method for producing the release paper of the present invention is not particularly limited. It can be produced by applying the coating liquid of the present invention to paper to form a sealing layer, and then applying the coating liquid for a release layer on the sealing layer.

Examples of the water-dispersible varnish used in the post-processing step include conjugated diene latex such as styrene-butadiene copolymer latex, methyl methacrylate-butadiene copolymer latex, and styrene-methyl methacrylate-butadiene copolymer latex; acrylic. Acrylic latex such as polymer latex or copolymer latex of acid ester and / or methacrylic acid ester; vinyl latex such as ethylene-vinyl acetate polymer latex, etc., and one or more of these. Can be appropriately selected and used.

The coated paper coated with the coating liquid for paper of the present invention has a transmittance of 20000 seconds measured using a Wangken type slippery air permeability tester according to JIS P 8117 (2009). The above is preferable, the one for 23000 seconds or more is more preferable, and the one for 25,000 seconds or more is further preferable. As a result, the voids between the pulp fibers constituting the paper can be reduced and the barrier property can be improved. Then, the release paper base paper having the sealing layer formed by applying the coating liquid of the present invention to the paper base material can have an excellent barrier property against an organic solvent or the like. As a result, the surface yield of the silicone resin can be improved when the release layer is applied on the sealing layer.

Further, as the coating liquid for paper of the present invention, the water absorption degree measured by the Cobb method when the contact time between the coated paper and water is 60 seconds according to JIS P 8140 (1998). , 70 g / m ² or less is preferable, 50 g / m ² or less is more preferable, and 45 g / m ² or less is further preferable. As a result, the water resistance of the sealing layer in the release paper is improved, and a water-dispersible varnish can be used in the post-processing step.

The present invention includes various combinations of the above configurations within the technical scope of the present invention as long as the effects of the present invention are exhibited.

The coated paper coated with the coating liquid of the present invention has excellent water resistance and barrier properties. Therefore, the coated paper is suitably used for, for example, a release paper. Further, the coating liquid for paper of the present invention is excellent in blocking resistance due to the improvement of water resistance, and a water-dispersible varnish can be used in the post-processing step.

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

[Ethylene unit content of ethylene-vinyl alcohol copolymer (A)]
It was determined from ¹ H-NMR of an ethylene-vinyl ester copolymer which is a precursor of an ethylene-vinyl alcohol copolymer or a revinegarized product. That is, the obtained ethylene-vinyl ester copolymer was redisposited and purified using a mixed solution of n-hexane and acetone three times or more, and then dried under reduced pressure at 80 ° C. for three days for analysis. An ethylene-vinyl ester copolymer was prepared. Ethylene for analysis - the vinyl ester copolymer dissolved in _{DMSO-d 6,} and ¹ H-NMR (500MHz) determined at 80 ° C.. The content of ethylene units is determined by using the peak derived from the main chain methine of vinyl ester (4.7 to 5.2 ppm) and the peak derived from ethylene and the main chain methylene of vinyl ester (0.8 to 1.6 ppm). Calculated.

[Viscosity average degree of polymerization of ethylene-vinyl alcohol copolymer (A)]
The viscosity average degree of polymerization of the ethylene-vinyl alcohol copolymer (A) was determined by the method described in JIS K6726 (1994).

[Saponification degree of ethylene-vinyl alcohol copolymer (A)]
The saponification degree of the ethylene-vinyl alcohol copolymer (A) was determined by the method described in JIS K6726 (1994).

[Measurement of alkali metal salt content of carboxylic acid of ethylene-vinyl alcohol copolymer (A)]
The alkali metal salt content of the carboxylic acid of the ethylene-vinyl alcohol copolymer (A) (in terms of the mass of the alkali metal) is determined by the ICP emission of Jarrel Ash after the ethylene-vinyl alcohol copolymer (A) is incinerated. It was determined by measuring the amount of alkali metal in the obtained ash using an analyzer "IRIS AP".

[Crystallinity of ethylene-vinyl alcohol copolymer (A) in water]
A sample of ethylene-vinyl alcohol copolymer (A) was allowed to stand in H ₂ Od ₂ at each temperature (30 ° C., 70 ° C.) for 40 minutes, and then at the same temperature as the standing temperature. Pulse NMR measurement was performed. The range of 0 to 0.8 ms of the obtained transition curve was fitted by the following equation (III) using the error least squares method.

[Powderability]
150 ml of distilled water was placed in a 300 ml separable flask, and the temperature was raised until the internal temperature reached 70 ° C. After the temperature was raised, 6 g of an ethylene-vinyl alcohol copolymer was added under stirring at 150 rpm. The state of the ethylene-vinyl alcohol copolymer particles immediately after the addition was visually observed and evaluated as follows.
A: It does not become a powder.
B: The powder was sprinkled, but the powder was eliminated by stirring for 5 minutes.
C: The powder was sprinkled, and the sprinkled powder was not eliminated even after stirring for 5 minutes.

[Solubility]
288 g of distilled water was placed in a 500 ml separable flask, and the temperature was raised until the internal temperature reached 85 ° C. After the temperature was raised, 12 g of an ethylene-vinyl alcohol copolymer was added under stirring at 150 rpm. An aqueous ethylene-vinyl alcohol copolymer was collected 30 minutes after the addition. The collected aqueous solution was referred to as No. The filter paper was filtered through a filter paper of 5A, and the filtrate was dried at 125 ° C. for 3 hours to determine the mass A (g) of the ethylene-vinyl alcohol copolymer dissolved in the aqueous solution. Further, 12 g of ethylene-vinyl alcohol copolymer particles of the sample were dried at 125 ° C. for 3 hours to determine the non-volatile content B (g). Then, solubility (mass%) = A / B × 100 was calculated. The calculated solubility was evaluated according to the following criteria.
A: 60% by mass or more B: 50% by mass or more and less than 60% by mass C: less than 50% by mass

[Measurement of alkali metal salt content of carboxylic acid in coating liquid]
The alkali metal salt content of the carboxylic acid in the coating liquid (in terms of the mass of the alkali metal) is determined by the ICP luminescence analyzer "IRIS AP" manufactured by Jarrel Ash after ashing the coating liquid dried in a platinum crucible. It was determined by measuring the amount of alkali metal in the obtained ash content using.

[Water absorption of coated paper]
As an index of water resistance of coated paper, a water absorption tester (trade name: Garecob size tester, manufactured by Kumagai Riki Kogyo Co., Ltd.) is used by the Cobb method according to JIS P 8140 (1998). The water absorption was measured.

[Measurement of air permeability of coated paper]
The air permeability of the sample was measured using a Wangken-type slipperiness air permeability tester according to JIS P8117.
[Evaluation of toluene barrier property of coated paper]

Toluene colored red was applied on the coated surface of the sample (5 x 5 cm), and after drying, the degree of strike-through to the back surface (occurrence of small red spots or coloring of the entire coated surface) was determined according to the following criteria. ..
A: No spots were generated on the back surface.
B: Spots were generated, but the colored area was 20% or less of the toluene-coated surface.
C: The colored area was more than 20% and less than 80% of the coated surface.
D: The colored area was 80% or more of the coated surface.

[Manufacturing Example 1]
(Polymerization process)
A continuous polymerization tank equipped with a reflux condenser, a raw material supply line, a reaction liquid take-out line, a thermometer, a nitrogen inlet, an ethylene inlet and a stirring blade was used. A 1% methanol solution of vinyl acetate 671 L / hr, methanol 147 L / hr, and 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) 2.6 L / hr in a continuous polymerization tank using a metering pump. Supplied continuously. The ethylene pressure in the tank was adjusted to 0.23 MPa. The polymerization liquid was continuously taken out from the continuous polymerization tank so that the liquid level in the polymerization tank became constant. The polymerization rate at the outlet of the continuous polymerization tank was adjusted to 30%. The residence time of the continuous polymerization tank was 5 hours. The temperature at the outlet of the continuous polymerization tank was 60 ° C. The polymerization solution was recovered from the continuous polymerization tank, and the unreacted vinyl acetate monomer was removed by introducing methanol vapor into the recovered solution, and the methanol solution (concentration: 32% by mass) of the ethylene-vinyl ester copolymer (PVAc) was removed. ) Was obtained.

(Saponification process)
A methanol solution of sodium hydroxide (concentration: 4% by mass) as a saponification catalyst is added to a methanol solution (concentration: 32% by mass) of the ethylene-vinyl ester copolymer obtained in the polymerization step, and the ethylene-vinyl ester copolymer weight is added. It was added so that the molar ratio of sodium hydroxide to the vinyl acetate unit in the coalescence was 0.01. The ethylene-vinyl ester copolymer solution and the saponification catalyst solution were mixed with a static mixer to obtain a mixture. The paste of the obtained mixture was placed on a belt and held at 40 ° C. for 18 minutes to allow the saponification reaction to proceed. As a result, a solid block containing an ethylene-vinyl alcohol copolymer and a solvent was obtained. The polymerization conditions and saponification conditions are summarized in Table 1.

(Crushing process)
The solid block obtained in the saponification step was pulverized with a uniaxial shear crusher to obtain wet particles. The crusher was equipped with a crushing blade having a Rockwell hardness of 45, and the rotation speed of the crushing blade was 250 rpm.

(Liquid removal process)
By deflating the wet particles obtained in the pulverization step with a screw discharge type centrifugal deflated machine, the proportion of particles that have passed through a sieve having a mesh size of 5.6 mm is 94% by mass, and the mesh size is 1.0 mm. Liquid particles having a content of 1.6% by mass and a content of a solvent of 58% by mass were obtained. Table 2 summarizes the crushing conditions and the liquid removal conditions.

(Drying process)
The deliquescent particles of 600 kg / hr (solid content) obtained in the deliquescent step were continuously supplied to a dryer whose temperature inside the dryer was controlled so that the particle temperature was 100 ° C. The average residence time of the particles in the dryer was 4 hours.

(Additional crushing process)
The dried particles obtained in the drying step were additionally pulverized with a hammer mill and passed through a filter having a mesh size of 1.4 mm to obtain an ethylene-vinyl alcohol copolymer 1. The content of ethylene units in the copolymer 1 was 2 mol%, the viscosity average degree of polymerization was 1700, and the saponification degree was 93.0 mol%. The content of the alkali metal salt (sodium acetate) of the carboxylic acid was 0.33 parts by mass in terms of mass of alkali metal (sodium equivalent) with respect to 100 parts by mass of the copolymer 1. The Cw (30 ° C.) of the copolymer 1 was 9.7%, the Cw (70 ° C.) was 2.1%, and the value of the formula (I) was 6.9. Further, in the entire copolymer 1, the ratio of passing through the filter having a mesh size of 2.5 mm was 99% by mass, and the ratio of passing through the filter having a mesh size of 1.0 mm was 94% by mass. The percentage that passed through the 15 mm filter was 5% by mass. Table 3 shows the results of evaluating the powdering property and solubility of the copolymer 1 according to the above method.

[Manufacturing Examples 2 to 11]
Ethylene-vinyl alcohol copolymers (copolymers 2 to 11) by the same method as in Example 1 except that the polymerization conditions, saponification conditions, pulverization conditions, and liquid removal conditions were changed as shown in Tables 1 and 2. Manufactured. The content of the obtained copolymer in ethylene units, the degree of polymerization, the degree of saponification, the content of the alkali metal salt of carboxylic acid, the particle size, the degree of crystallinity in water at 30 ° C. and 70 ° C., and the value of the formula (I) are set. Table 3 summarizes the results of evaluation according to the above-mentioned method and the results of evaluation of the powdering property and solubility of the obtained copolymer according to the above-mentioned method.

[Example 1]
(Making coated paper)
Copolymer 1 was added to ion-exchanged water heated to 85 ° C. and stirred for 45 minutes to obtain a solution having a solid content concentration of 7% by mass. The alkali metal salt (B) of the carboxylic acid in this solution was 0.33 parts by mass with respect to 100 parts by mass of the copolymer 1. Using this as a coating liquid, a test sim sizer (manufactured by Kumagai Riki Kogyo Co., Ltd.) was applied to PPC (plane paper copier) paper having a basis weight of 70 g / m ² and an air permeability of 20 sec at a speed of 300 m / min. .. The coated paper was dried in a hot air dryer at 100 ° C. for 5 minutes. The coating amount of the obtained coated paper was adjusted to 0.5 g / m ² in terms of solid content. The obtained coated paper was humidity-controlled at 20 ° C. and 65% RH for 72 hours, and then the physical properties of the coated paper were evaluated. The results are shown in Table 4.

[Examples 2 to 7, Comparative Examples 1 to 3, 5]
A coated paper was prepared in the same manner as in Example 1 except that the copolymers 2 to 11 shown in Table 4 were used instead of the copolymer 1 of Example 1. Table 4 shows the results of evaluating the physical properties of the coated paper.

[Comparative Example 4]
1 part by mass of sodium acetate was mixed with 100 parts by mass of the copolymer 3, and the obtained powder was added to ion-exchanged water heated to 85 ° C. and stirred for 45 minutes to have a solid content concentration of 7. A mass% solution was obtained. The alkali metal salt (B) of the carboxylic acid in this solution was 1.8 parts by mass with respect to 100 parts of the copolymer 1. Using this as a coating liquid, a test sim sizer (manufactured by Kumagai Riki Kogyo Co., Ltd.) was applied to PPC (plane paper copier) paper having a basis weight of 70 g / m ² and an air permeability of 20 sec at a speed of 300 m / min. .. The coated paper was dried in a hot air dryer at 100 ° C. for 5 minutes. The coating amount of the obtained coated paper was adjusted to 0.5 g / m ² in terms of solid content. The obtained coated paper was humidity-controlled at 20 ° C. and 65% RH for 72 hours, and then the physical properties of the coated paper were evaluated. The results are shown in Table 4.

As shown in Table 4, the coated papers obtained by applying the coating liquids obtained in Examples 1 to 7 have a long air permeability value and are excellent in barrier properties. And, in fact, it is also excellent in toluene barrier property. Therefore, the coated paper on which the sealing layer is formed by using the coating liquid of the present invention has a high surface yield of the silicone resin and is peeled off when the release layer is applied on the sealing layer. It was found that it has sufficient performance to produce paper.

Claims (7)

1. A coating liquid for paper containing an ethylene-vinyl alcohol copolymer (A) and an alkali metal salt (B) of a carboxylic acid;
   The ethylene unit content of the ethylene-vinyl alcohol copolymer (A) is 1 mol% or more and less than 20 mol%.
   The crystallinity in water Cw (30 ° C.) at 30 ° C. and the crystallinity Cw (70 ° C.) in water at 70 ° C. determined by pulse NMR satisfy the following formula (I), and the ethylene-vinyl alcohol copolymer (A) A coating liquid for paper containing 0.001 to 1 part by mass of the alkali metal salt (B) of the carboxylic acid with respect to 100 parts by mass of the alkali metal.
   

   
2. The paper coating liquid according to claim 1, wherein the ethylene-vinyl alcohol copolymer (A) has a saponification degree of 90 to 98.5 mol%.
3. The paper coating liquid according to claim 1 or 2, wherein the ethylene-vinyl alcohol copolymer (A) has a viscosity average degree of polymerization of 900 to 2400.
4. A coated paper in which the coating liquid according to any one of claims 1 to 3 is applied to the surface of the paper.
5. The coated paper according to claim 4, which is a base paper for release paper.
6. A release paper in which a release layer is formed on a sealing layer formed by applying the coating liquid according to claims 1 to 3 to paper.
7. The release paper according to claim 6, wherein the release layer contains a silicone resin.