JP7535655B2 - Water dispersion and film of chlorinated vinyl polymer - Google Patents

Description

The present invention relates to an aqueous dispersion of a chlorinated vinyl polymer and a film having a layer coated with the aqueous dispersion.

To maintain the quality of food and medicines, the films used to package them must adequately block and seal out gases in the atmosphere, such as oxygen, nitrogen, carbon dioxide, and water vapor. In this regard, among various resins, films having layers formed from chlorinated vinyl copolymer aqueous dispersions, particularly vinylidene chloride copolymer aqueous dispersion resins, have excellent barrier properties against water vapor and oxygen, making them highly suitable for food and medicine packaging applications.

In recent years, packaging films are required to have higher gas barrier properties for the following reasons.
1) Maintaining the quality and efficacy of medicines and food ingredients for a longer period of time;
2) Thinner packaging to meet the demand for improved extrusion of contents in packaging products due to the aging population;
3) Thinner film to improve productivity.
As aqueous dispersions of vinylidene chloride copolymers that constitute films having barrier properties, those described in Patent Documents 1 to 5 are known.

International Publication No. WO 2013/125699 Special Publication No. 2001-526315 Japanese Patent Application Publication No. 05-202107 JP 2018-127523 A Japanese Unexamined Patent Publication No. 60-192768

The chlorinated vinyl copolymers described in Patent Documents 1 to 5 have a problem in that they turn yellow over time while stored in the form of a film, that is, their appearance gradually deteriorates.
In particular, the chlorinated vinyl copolymers described in Patent Documents 4 and 5 have higher barrier properties than those described in Patent Documents 1 to 3, but have room for further improvement in terms of yellowing. This is because the comonomers that increase the barrier properties also have the property of increasing yellowing, and there is a trade-off between barrier properties and yellowing resistance.

Therefore, the object of the present invention is to provide an aqueous dispersion of a chlorinated vinyl polymer that can suppress yellowing while maintaining high water vapor barrier properties in the coated film.

As a result of extensive research into solving the problems described above, the inventors discovered that by creating an aqueous dispersion of a chlorinated vinyl polymer designed to undergo a certain level of discoloration when an aqueous potassium iodide solution is dropped onto it, films coated with the dispersion exhibit excellent resistance to yellowing while retaining high water vapor barrier properties, and thus completed the present invention.

That is, the present invention is as follows.
[1] An aqueous dispersion of a vinylidene chloride polymer , the aqueous dispersion of the vinylidene chloride polymer comprising an oxygen-based bleaching agent, characterized in that, when a color difference of a mixture obtained by adding 75 g of pure water and 10 mL of 1 mol/L hydrochloric acid to 35 g of the aqueous dispersion of the vinylidene chloride polymer and stirring at 300 rpm at 20° C. for 5 minutes to 35 g of the aqueous dispersion of the vinylidene chloride polymer and stirring at 300 rpm at 20° C. for 5 minutes is measured with respect to a reference color, the ΔE*ab value is 15 or more and 1,000 or less.
[2 ] The aqueous dispersion of vinylidene chloride polymer according to [1] , wherein the mass ratio of structural units derived from vinylidene chloride is 70 mass% or more when the total mass of the vinylidene chloride polymer is 100 mass%.
[ 3 ] The aqueous dispersion of the vinylidene chloride polymer according to [1] or [2] , which has a solid content of 10% by mass or more as determined using a microwave solid content meter under an environment of 20° C. and 50% RH.
[ 4 ] The aqueous dispersion of vinylidene chloride polymer according to any one of [1] to [3], comprising structural units derived from vinylidene chloride and structural units derived from a copolymerization monomer having a reactivity ratio r1 to vinylidene chloride of less than 0.7, wherein the mass ratio of the structural units derived from the copolymerization monomer having the reactivity ratio r1 of less than 0.7 is 1 mass% or more when the total mass of the structural units derived from the vinylidene chloride, the structural units derived from the copolymerization monomer having the reactivity ratio r1 of less than 0.7, and the structural units derived from the copolymerization monomer having the reactivity ratio r1 of 0.7 or more is taken as 100 mass%.
[ 5 ] The aqueous dispersion of vinylidene chloride polymer according to [ 4 ], wherein the copolymerizable monomer having a reactivity ratio r1 of less than 0.7 is at least one selected from the group consisting of a monomer having a nitrile group, a monomer having a carboxyl group, and methyl methacrylate .
[ 6 ] The aqueous dispersion of vinylidene chloride polymer according to [ 5 ], wherein the monomer having a nitrile group is methacrylonitrile.
[ 7 ] The aqueous dispersion of vinylidene chloride polymer according to [5] or [6], wherein a mass ratio of the structural units derived from the monomer having a nitrile group is 1 mass% or more, when a total mass of the structural units derived from the vinylidene chloride, the structural units derived from the copolymerization monomer having the reactivity ratio r1 of less than 0.7 , and the structural units derived from the copolymerization monomer having the reactivity ratio r1 of 0.7 or more is taken as 100 mass%.
[ 8 ] The aqueous dispersion of vinylidene chloride polymer according to any one of [ 5 ] to [ 7 ], wherein the monomer having a carboxyl group is acrylic acid, itaconic acid, maleic acid or methacrylic acid.
[ 9 ] The aqueous dispersion of vinylidene chloride polymer according to any one of [4] to [8], wherein a mass proportion of the structural units derived from a copolymerization monomer having a reactivity ratio r1 of less than 0.7 is 5 mass% or more and 20 mass% or less, when a total mass of the structural units derived from the vinylidene chloride- derived structural units, the structural units derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7, and the structural units derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more is taken as 100 mass%.
[ 10 ] A film having a layer coated with an aqueous dispersion of the vinylidene chloride polymer according to any one of [1] to [ 9 ].

The aqueous dispersion of the chlorinated polymer of the present invention has the effect of providing a coated film with excellent resistance to yellowing while maintaining high water vapor barrier properties.

The following describes in detail the form for implementing the present invention (hereinafter simply referred to as the "present embodiment"). The following present embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented with appropriate modifications within the scope of its gist.

[Water Dispersion of Chlorinated Vinyl Polymer]
The aqueous dispersion of a chlorinated vinyl polymer according to the present embodiment (hereinafter, also simply referred to as "aqueous dispersion") is characterized in that, when the color of a mixture obtained by adding 75 g of pure water and 10 mL of 1 mol/L hydrochloric acid to 35 g of the aqueous dispersion of a chlorinated vinyl polymer and stirring at 20° C. for 5 minutes at 300 rpm is used as a reference color, ΔE*ab is 1.0 or more when the color difference of a mixture obtained by adding 65 g of pure water, 10 mL of 1 mol/L hydrochloric acid, and 10 mL of a 10 w/V % aqueous potassium iodide solution to 35 g of the aqueous dispersion of a chlorinated vinyl polymer and stirring at 20° C. for 5 minutes at 300 rpm is measured.

In the aqueous dispersion of the chlorinated vinyl polymer of this embodiment, the ΔE*ab is 1.0 or more, preferably 6.0 or more, and particularly preferably 15 or more. It is also preferably 1000 or less, more preferably 500 or less, and even more preferably 200 or less. When the ΔE*ab is in the above range, the film after coating can be well suppressed from yellowing while maintaining high water vapor barrier properties. In particular, when the ΔE*ab is 1000 or less, the risk of the initiator remaining in the film after coating migrating to the outside (for example, food or medicine when the film is used for food packaging or medicine packaging) can be suppressed.
As a method for controlling ΔE*ab within the above range, for example, an oxidizing agent described below is added to the aqueous dispersion, preferably after the polymerization of the chlorinated vinyl polymer is completed. The higher the content of the oxidizing agent in the aqueous dispersion, the larger the value of ΔE*ab becomes.

<Method of measuring ΔE*ab>
Specifically, the above ΔE*ab can be measured as follows.
Sample Preparation
All reagents used in the measurement are kept at 20°C. 100mL of aqueous dispersion obtained by diluting 35g of aqueous dispersion with 65g of pure water is placed in a 250mL PP reagent bottle. 10mL of 10w/V% potassium iodide aqueous solution and 10mL of 1mol/L hydrochloric acid are dropped into the bottle, the lid is closed, and the bottle is stirred at 300rpm for 5 minutes using a 25mm x φ8mm stirrer. The obtained aqueous dispersion is used as a sample for measuring ΔE*ab.
As the reference color, the measurement result of a sample which has been subjected to the same procedure but with 10 mL of pure water added instead of the aqueous potassium iodide solution is used.
(Discoloration measurement)
Discoloration is measured using a Konica Minolta color difference meter CM-5. 10 mL of the above sample is measured into a 30 mm diameter petri dish of the CM-5 option, and petri dish measurement, which is one of the measurement methods of CM-5, is performed under the following measurement conditions. The measurement is performed three times, and the average value is taken as ΔE*ab for each sample.
Measurement conditions:
Color system: L*a*b*
Index: YI ASTM E313-96
Field of view: 10°
Main light source: D65
Secondary light source: None. After the potassium iodide aqueous solution is added, the potassium iodide may be oxidized by oxygen in the air to produce iodine. Therefore, after the specified 5 minutes of stirring, measure the color change as soon as possible, but no later than within 5 minutes.

(Chlorinated vinyl polymer)
The chlorinated vinyl polymer contains at least a structural unit derived from a chlorinated vinyl monomer, and may further contain a structural unit derived from a monomer copolymerizable with the chlorinated vinyl monomer.
In this specification, the monomer copolymerizable with the chlorinated vinyl monomer may be referred to as a "copolymerization monomer". Examples of the copolymerization monomer include a copolymerization monomer having a reactivity ratio r1 to vinylidene chloride of less than 0.7 (sometimes referred to as a "copolymerization monomer having a reactivity ratio r1 of less than 0.7"), a copolymerization monomer having a reactivity ratio r1 to vinylidene chloride of 0.7 or more (sometimes referred to as a "copolymerization monomer having a reactivity ratio r1 of 0.7 or more"), and the like. Preferably, the structural unit is derived from a copolymerization monomer having a reactivity ratio r1 to vinylidene chloride of less than 0.7.

The chlorinated vinyl monomer is a general term for monomers containing chlorine, and is preferably vinyl chloride or vinylidene chloride, and particularly preferably vinylidene chloride (hereinafter also referred to as VDC).
The chlorinated vinyl monomers may be used alone or in combination of two or more kinds.

Examples of monomers copolymerizable with chlorinated vinyl monomers include maleic anhydride, itaconic acid, methyl acrylate (hereinafter also referred to as MA), methyl methacrylate (hereinafter also referred to as MMA), ethyl acrylate, ethyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, acrylonitrile (hereinafter also referred to as AN), and methacrylonitrile (hereinafter also referred to as MAN). Examples of the monomer that can be copolymerized with the chlorinated vinyl monomer include, but are not limited to, (meth)acrylic monomers such as acrylic acid (hereinafter also referred to as AA), methacrylic acid (hereinafter also referred to as MAA), acrylamide, and N-methylolacrylamide; 2-acrylamido-2-methylpropanesulfonic acid (AMPS) or a salt thereof (such as a sodium salt); 2-sulfoethylmethacrylic acid (2-SEM) or a salt thereof (such as a sodium salt); a phosphate ester of methacrylate-terminated polypropylene glycol or a salt thereof (such as a sodium salt); and the like.
The monomers copolymerizable with the chlorinated vinyl monomer may be used alone or in combination of two or more kinds.

The mass ratio of the structural unit derived from the chlorinated vinyl monomer is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 85% by mass or more, and even more preferably 87% by mass or more, when the total mass of the chlorinated vinyl polymer is 100% by mass. The mass ratio is preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 93% by mass or less, and even more preferably 92% by mass or less.
By setting the mass proportion of the structural unit derived from the chlorinated vinyl monomer within the above range, it becomes possible for a film having a layer formed from the aqueous dispersion of the chlorinated vinyl polymer (copolymer) of this embodiment to exhibit barrier properties that adequately preserve the quality of the encapsulated contents.

The mass ratio of the structural unit derived from the monomer copolymerizable with the chlorinated vinyl monomer is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 13% by mass or less, when the total mass of the chlorinated vinyl polymer is taken as 100% by mass. The mass ratio is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, and even more preferably 8% by mass or more.
When the mass proportion of the structural unit derived from a monomer copolymerizable with the chlorinated vinyl monomer is within the above range, the aqueous dispersion of the chlorinated vinyl polymer tends to have a good balance between barrier properties and film-forming properties.

As mentioned above, the chlorinated vinyl polymer may optionally contain structural units derived from comonomers having a reactivity ratio r1 to vinylidene chloride of less than 0.7.
The mass ratio of the structural unit derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7 is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less, when the total mass of the structural unit derived from the chlorinated vinyl monomer, the structural unit derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7, and the structural unit derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more is taken as 100% by mass. The mass ratio is preferably 1% by mass or more, more preferably 5% by mass or more, and particularly preferably 7% by mass or more.

In addition, the proportion of the total mass of the structural units derived from the chlorinated vinyl monomer and the structural units derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7 in the total mass of the chlorinated vinyl polymer (100% by mass) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 100% by mass.

As mentioned above, the chlorinated vinyl polymer may optionally contain structural units derived from a comonomer having a reactivity ratio r1 to vinylidene chloride of 0.7 or more.
The mass proportion of the structural units derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more to vinylidene chloride is preferably 5 mass% or less, and more preferably 3 mass% or less, when the total mass of the structural units derived from the chlorinated vinyl monomer, the structural units derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7, and the structural units derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more is taken as 100 mass%.

When the mass ratio of each of the structural units of the chlorinated vinyl polymer is within the above range, a film having a layer formed from the aqueous dispersion of the chlorinated vinyl polymer of this embodiment can exhibit barrier properties that adequately preserve the quality of the encapsulated contents.

The reactivity ratio r1 to vinylidene chloride is a general monomer reactivity ratio r1 calculated by r1 = k11/k12, where k11 is the rate constant of the reaction in which the radical of M1 reacts with M1 and k12 is the rate constant of the reaction in which the radical of M1 reacts with M2, where vinylidene chloride is monomer 1 (M1) and the comonomer is monomer 2 (M2). The reactivity ratio r1 may be any value listed in Polymer Handbook Fourth Edition (ISBN: 0-471-48171-8). However, if multiple values are listed, the lowest value shall be used.

As an example, the reactivity ratio r1 of some monomers to vinylidene chloride is shown.
Butyl acrylate: 0.84
Ethyl acrylate: 0.58
Methyl acrylate: 0.7
Acrylic acid: 0.29
Acrylonitrile: 0.28
Methyl methacrylate: 0.02
Methacrylic acid: 0.15
Methacrylonitrile: 0.036
Vinyl chloride: 1.8

As the copolymerization monomer having a reactivity ratio r1 to vinylidene chloride of less than 0.7, known monomers can be used, and preferred are methyl methacrylate, monomers having a nitrile group, and monomers having a carboxyl group.
The copolymerizable monomer having a reactivity ratio r1 of less than 0.7 may be used alone or in combination of two or more kinds, and more preferably contains a monomer having a nitrile group.

The monomer having a nitrile group is preferably acrylonitrile or methacrylonitrile, and particularly preferably methacrylonitrile.
The mass ratio of the structural unit derived from the monomer having a nitrile group is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more, when the total mass of the structural unit derived from the chlorinated vinyl monomer, the structural unit derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7, and the structural unit derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more is taken as 100 mass%. Moreover, the mass ratio is preferably 15 mass% or less, more preferably 13 mass% or less, and even more preferably 10 mass% or less. When the mass ratio of the structural unit derived from the monomer having a nitrile group is within the above range, the film produced from the aqueous dispersion of the chlorinated vinyl polymer tends to exhibit high water vapor barrier properties.

The monomer having a carboxyl group is preferably acrylic acid, itaconic acid, maleic acid, or methacrylic acid, and more preferably acrylic acid or methacrylic acid.

Known monomers having a reactivity ratio r1 to vinylidene chloride of 0.7 or more can be used, and preferred are vinyl chloride, methyl acrylate, and butyl acrylate.

By copolymerizing these monomers, the film made from the aqueous dispersion of the above chlorinated vinyl polymer has high water vapor barrier properties.

The monomer composition of the chlorinated vinyl polymer can be evaluated by dissolving a sample collected by the method described below in tetrahydrofuran-d8 and performing NMR measurement.

1) When a water dispersion of a chlorinated vinyl polymer is available, the following method is used.
Freeze-dry 10 mL of the aqueous dispersion of the chlorinated vinyl polymer, and collect 0.5 g of the freeze-dried product. Dissolve the collected freeze-dried product in 10 mL of tetrahydrofuran with a purity of 99.9% by mass or more, and add 40 mL of acetone dropwise to the solution. Filter the resulting precipitate, and collect the remaining insoluble matter.
The collected insoluble matter is used as a measurement sample.
2) When an aqueous dispersion of a chlorinated vinyl polymer is not available and only a film coated with the aqueous dispersion is available, the following method is used.
The chlorinated vinyl polymer is separated from the film coated with the chlorinated vinyl polymer, 0.5 g of the chlorinated vinyl polymer is collected and completely dissolved in 10 mL of tetrahydrofuran with a purity of 99.9% by mass or more. If the polymer does not dissolve at room temperature, it is heated to 60° C. or less to dissolve it completely. 40 mL of acetone is dropped into the solution, and the resulting precipitate is filtered, and the remaining insoluble matter is collected by filtration. The collected insoluble matter is used as the measurement sample.
In the above steps 1) and 2), if the freeze-dried product is difficult to dissolve in tetrahydrofuran, the mixture may be heated and stirred within a range in which the tetrahydrofuran does not boil.

As a method for separating the chlorinated vinyl polymer from the film coated with the chlorinated vinyl polymer, the following methods (A) to (C) are used if possible. If (A) is possible, use (A); if (A) is difficult and (B) is possible, use (B); if (A) and (B) are difficult and (C) is possible, use (C). If any of (A) to (C) is difficult and there is another means for separation, that may be used. In this case, it is preferable to wash and dry the separated product so that the content of impurities other than the chlorinated vinyl polymer in the separated product is as small as possible. The mass ratio of the above impurities is preferably 0.5 mass% or less in the measurement sample. The drying treatment conditions are a temperature of 60° C. or less and a treatment time of 10 hours or less. Here, the impurities refer to components that are not contained in the aqueous dispersion of the chlorinated vinyl polymer before coating, such as mixed primers and solvents, and do not include additives such as emulsifiers that are added to the aqueous dispersion from the beginning. The amount of emulsifier in the separated product can be measured by the following procedure. i) The mass of the dried separated product is W1. ii) Wash the separated product with a large amount of pure water, at least 50 times its mass. At this time, care is taken not to let the polymer flow out together with the separated product. iii) Dry the washed separated product and call its mass W2. iv) Calculate the mass of the emulsifier by subtracting W1 from W2.
(A) Physically peel it off with tweezers or scrape it off.
(B) The chlorinated vinyl polymer is not dissolved, but the primer is dissolved in a solvent, which is chemically separated from the chlorinated vinyl polymer by using a solvent, preferably acetone, which dissolves the primer.
(C) The chlorinated vinyl polymer is dissolved using a solvent in which the chlorinated vinyl polymer dissolves but the substrate film does not dissolve, and the chlorinated vinyl polymer is separated by drying.
When separation is performed using a solvent by the method (B) or (C), the separated product is dried in a drying oven or the like to the extent that the chlorinated vinyl polymer does not decompose, and the measurement is performed after confirming that the weight of the solvent in the separated product is 0.5 mass % or less. The drying conditions are a temperature of 50° C. or less, a drying time of 10 hours or less, and, if necessary, under reduced pressure.

The NMR measurement conditions are as follows.
Equipment: JEOL RESONANCE ECS400 (1H), Bruker Biospin Avance600 (13C)
Observed nuclei: 1H (399.78MHz), 13C (150.91MHz)
Pulse program: Single pulse (1H), zgig30 (13C)
Accumulation count: 256 times (1H), 10,000 times (13C)
Lock solvent: THF-d8
Chemical shift reference: THF (1H: 180 ppm, 13C: 67.38 ppm)
Using the obtained NMR spectrum, monomers are assigned, and the composition in the polymer is identified by integrating the peaks.

For example, in the case of a polymer containing structural units derived from vinylidene chloride, methacrylonitrile, methyl methacrylate, and acrylic acid, the content of structural units derived from vinylidene chloride is determined by integrating from 80 to 90 ppm in the ¹³ C-NMR spectrum, the content of structural units derived from methacrylonitrile is determined by integrating from 110 to 130 ppm, the content of structural units derived from methyl methacrylate is determined by integrating from 170 to 180 ppm, and the content of structural units derived from acrylic acid is determined by integrating from 180 to 200 ppm, and the composition ratio of each monomer in the whole is calculated.

In the calculation of the above composition ratio, the peak of the COOCH ₃ group (a in the formula below) is integrated to determine the amount of methyl methacrylate. Methyl acrylate is another monomer that has a COOCH ₃ group and is often copolymerized with vinylidene chloride. To distinguish between the two, the presence or absence of a peak of ^a methyl group (b in the formula below) bonded to the carbon of the main chain to which the COOCH ₃ group is bonded is judged in the 1 H NMR spectrum. This methyl group is not split because the carbon of the main chain to which it is bonded is not bonded to hydrogen, and the peak position is about 2 ppm. If a monomer having a methyl group other than methyl methacrylate, such as methacrylonitrile, is included, it can be judged from the number of methyl group peaks around 2 ppm.

Acrylonitrile and methacrylonitrile can also be distinguished by the presence or absence of a peak for the methyl group (b in the above formula).

If necessary, the insoluble matter may be subjected to additional measurements such as two-dimensional NMR and infrared spectroscopy to identify the monomers. It is also possible to polymerize a copolymer with a known composition and measure it in the same manner to compare the results.

The aqueous dispersion of the chlorinated vinyl polymer of the present embodiment preferably contains any oxidizing agent, more preferably an oxidizing agent that is publicly used as a bleaching agent, and even more preferably an oxidizing agent that is publicly used as an oxygen-based bleaching agent.
These oxidizing agents may be used alone or in combination of two or more kinds.

Although there are no particular limitations on oxygen-based bleaching agents, preferred are ozone, persulfates (sodium persulfate, potassium persulfate, ammonium persulfate, etc.), percarbonates (sodium percarbonate, potassium percarbonate, ammonium percarbonate, etc.), peracetic acid, and peroxides (hydrogen peroxide, etc.), with hydrogen peroxide being particularly preferred.

Other bleaching agents include chlorine bleaching agents, and are not particularly limited, but are preferably hypochlorous acid and hypochlorites (sodium hypochlorite, calcium hypochlorite, potassium hypochlorite, etc.). When using chlorine bleaching agents, there is a possibility of harmful chlorine being generated, so it is preferable to make the aqueous dispersion basic, and it is particularly preferable to make it basic and have buffering capacity.

Bleaching agents that are generally used are preferred because they have a strong effect of suppressing yellowing. Chlorine-based bleaching agents generate chlorine gas that is harmful to the human body under acidic conditions, which limits the pH of the aqueous dispersion. On the other hand, oxygen-based bleaching agents are more preferred because they can be designed to any pH, especially a low pH at which the dehydrochlorination reaction that causes yellowing is likely to occur. Among oxygen-based bleaching agents, hydrogen peroxide is the most preferred because it decomposes into oxygen and water and does not generate impurities that can cause odors.

The content of the oxidizing agent is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.05% by mass or more, when the total mass of the chlorinated vinyl polymer is 100% by mass. As the amount of the oxidizing agent increases, the discoloration resistance of the film improves. In addition, it is preferably 5% by mass or less, and more preferably 1% by mass or less. By setting it within this range, it is possible to prevent the oxidizing agent from migrating from the film having a layer formed from the aqueous dispersion of this embodiment to the contents.

By adding the oxidizing agent, the oxidizing agent oxidizes the double bonds generated by the decomposition of the chlorinated vinyl polymer, which causes yellowing, and suppresses coloring. Surprisingly, the decomposition of the double bonds by the oxidizing agent added to the aqueous dispersion of the chlorinated vinyl polymer is very slow, and yellowing is suppressed for a long period of time even after processing into a film, which is convenient for practical use.
In addition, the chlorinated vinyl polymer decomposes preferentially from the part of the main chain skeleton that is easily decomposed. For example, the part that is easily decomposed is a structural unit derived from a chlorinated vinyl monomer adjacent to a structural unit derived from a comonomer that enhances barrier properties. When an oxidizing agent is added, such a structural unit that is likely to cause coloring is oxidized preferentially, and since this is an irreversible reaction, the structural unit will not decompose thereafter. Therefore, even after the oxidizing agent is consumed, the chlorinated vinyl polymer of this embodiment is suppressed from yellowing.
Moreover, the chlorinated vinyl polymer in which yellowing has been suppressed by adding the above-mentioned oxidizing agent surprisingly has the same barrier properties as a chlorinated vinyl polymer in which no oxidizing agent has been added, which is extremely advantageous for food packaging and pharmaceutical packaging applications in which high barrier properties are required.
Another advantage of suppressing yellowing by adding an oxidizing agent is that it is sufficient to simply add an oxidizing agent to an existing aqueous dispersion of a chlorinated vinyl polymer. In Patent Document 4, the monomer composition is optimized to suppress yellowing, but in the chlorinated vinyl polymer of the present embodiment, yellowing can be improved by adding an oxidizing agent without changing the design of the aqueous dispersion of the chlorinated vinyl polymer. This property is convenient in the development of an aqueous dispersion of a chlorinated vinyl polymer, which usually requires a test of long-term storage stability.

If the aqueous dispersion of chlorinated vinyl polymer contains an oxidizing agent, potassium iodide is oxidized by the oxidizing agent to produce iodine in the above-mentioned ΔE*ab measurement. Since iodine is brown, discoloration of the aqueous dispersion is observed. If the aqueous dispersion contains enough oxidizing agent to suppress yellowing of the film after coating, ΔE*ab will be 1.0 or more.

The amount of the oxidizing agent contained in the aqueous dispersion of the chlorinated vinyl polymer can be measured by the following oxidation-reduction titration.
<Quantitative determination of oxidizing agent: redox titration>
All reagents used in the measurement are kept at 20°C. 100 mL of aqueous dispersion obtained by diluting 35 g of aqueous dispersion with 65 g of pure water is placed in a 250 mL PP reagent bottle. 10 mL of 10 w/V% potassium iodide aqueous solution and 10 mL of 1 mol/L hydrochloric acid are dropped into the bottle, the lid is closed, and the bottle is stirred for 5 minutes at 300 rpm with a 25 mm x φ8 mm stirrer. 0.1 mol/L sodium thiosulfate solution is dropped into the resulting aqueous dispersion once every 30 seconds, and the end point is when the brown color disappears. The amount of sodium thiosulfate solution required to reach the end point is recorded. Measurements are performed several times, and the amount of sodium thiosulfate solution per drop is adjusted so that the drop is completed in 10 to 15 drops. After adjustment, measurements are performed three or more times, and the average value is taken as the result after confirming that the standard deviation is within 20% of the titration value.

The amount of sodium thiosulfate solution dropped per 1% of solid content of the aqueous dispersion is proportional to the amount of oxidizing agent per 1% of solid content, and can be used as an index of the amount of oxidizing agent.
The amount of sodium thiosulfate solution to be dropped per 1% solid content is calculated by dividing the amount of sodium thiosulfate aqueous solution required for titration by the solid content. For example, if the amount of sodium thiosulfate solution to be dropped for an aqueous dispersion with a solid content of 10% is 10 mL, the amount of sodium thiosulfate solution to be dropped per 1% solid content is 1 mL.
The amount of sodium thiosulfate solution dropped per 1% solid content is preferably 0.001 mL or more, more preferably 0.01 mL or more, and even more preferably 0.1 mL or more. Within this range, a sufficient amount of oxidizing agent to suppress discoloration remains even after film formation.

One method for identifying the type of oxidizing agent contained in an aqueous dispersion is to separate the aqueous phase by centrifugation and then analyze the aqueous phase by high performance liquid chromatography.

The oxidizing agent may be added to the aqueous dispersion at any time, but is preferably added after the completion of polymerization of the chlorinated vinyl polymer, and particularly preferably immediately before coating. By shortening the time from addition of the oxidizing agent to coating as much as possible, it is possible to prevent the oxidizing agent from being deactivated in the aqueous solution, and to improve the effect of preventing yellowing after formation into a film.
Although it is possible to add an oxidizing agent during the polymerization of chlorinated vinyl polymer, the oxidizing agent is reduced by the added reducing agent or decomposed by heating, and thus the maximum effect is not obtained. As described in Patent Documents 1 to 5, it is common to add peroxides or persulfates as initiators in polymerization. However, the oxidizing agent is prone to decomposition during polymerization, and the oxidizing agent added as an initiator is completely consumed, so that the aqueous dispersions described in Patent Documents 1 to 5 do not become colored when an aqueous potassium iodide solution is dropped as described above.

A stabilizer for the oxidizing agent may be added to the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment.
Examples of stabilizers for the oxidizing agent include silicates, petrochemical chelating agents such as EDTA and DTPA, synthetic chelating agents such as condensed phosphates, phytic acid and phytates. In the aqueous dispersion of this embodiment, it is important that the oxidizing agent remains even after the film is applied. If the oxidizing agent is inactivated in the aqueous dispersion, the yellowing suppression effect is reduced, but by adding these stabilizers, the oxidizing agent is stabilized in the aqueous dispersion, and the yellowing suppression effect after the film is applied is improved. In addition, it is possible to reduce the variation in the discoloration speed after the film is applied due to the variation in the storage period, which is convenient in practical use.

Furthermore, the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment may contain, as necessary, various additives that are commonly used, such as, for example, a defoamer, a rheology modifier, a thickener, a dispersant, a stabilizer such as a surfactant, a wetting agent, a plasticizer, a colorant, silicone oil, a light stabilizer, an ultraviolet absorber, a silane coupling agent, an inorganic filler, a color pigment, and an extender pigment.
The solvent of the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment may be water alone, or may contain water and other solvents (e.g., alcohols, acetone, etc.). When other solvents are contained, the amount of the other solvents is preferably 10 parts by mass or less per 100 parts by mass of water.

The pH of the aqueous dispersion of the chlorinated vinyl polymer of this embodiment may be adjusted using a base.
The lower the pH, the lower the yellowing of the film after coating, which is preferable. This is because, when the aqueous dispersion contains an oxidizing agent, the higher the pH, the easier the oxidizing agent is to decompose and is more likely to be consumed before coating, and also because, the higher the pH, the easier the structural unit derived from the chlorinated vinyl monomer is to decompose and generate a double bond.
The pH of the aqueous dispersion is preferably 4.0 or less, particularly preferably 3.0 or less, and further preferably 2.5 or less. However, when a chlorine bleach is used, toxic chlorine gas is generated under acidic conditions, so the preferred pH range is 6.0 or more.
As described above, the higher the pH, the easier it is for the structural units derived from chlorinated vinyl monomers to decompose and form double bonds, so the higher the pH, the easier it is for the ink to turn yellow, regardless of whether an oxidizing agent is added or not. However, since a high pH has the effect of improving the aggregation stability of the aqueous dispersion and also has the effect of suppressing corrosion of metals used in coating machines by acids, it is preferable to adjust the pH to a high level depending on the application.
Any base can be used for adjusting the pH, and examples of the base include ammonia, hydroxides such as sodium hydroxide and potassium hydroxide, and phosphates such as tetrasodium pyrophosphate and trisodium phosphate. Phosphates are preferred, as they also have the effect of suppressing the decomposition of the oxidizing agent.

The solid content of the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment is preferably 10% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more, and is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 63% by mass or less.
The higher the solid content, the greater the coating amount per coating, and the higher the barrier properties per coating. If the solid content is less than 10% by mass, it is difficult to perform stable coating due to insufficient concentration. In addition, by increasing the coating amount per coating, the number of coatings required to obtain the target film thickness is reduced. This shortens the time the film is exposed to heat during drying, and discoloration of the halogenated vinyl copolymer is suppressed. Furthermore, decomposition of the oxidizing agent due to heat is also suppressed, so that the effect of suppressing discoloration of the film due to the oxidizing agent is easily effective.
The solid content in the aqueous dispersion of the present embodiment refers to the ratio of the total mass of all solid components contained in the aqueous dispersion, and may be only the chlorinated vinyl polymer, or may contain other resin components and the above-mentioned additives. Examples of other resin components include the seed latex described below and a polymer that coats the chlorinated vinyl polymer particles.
When the solid content contains a mass proportion of components other than the chlorinated vinyl polymer, the mass proportion of the components other than the chlorinated vinyl polymer is preferably 7 mass % or less, taking the water dispersion as 100 mass %.

The solid content can be measured by the following method.
<Measurement of solid content>
2.5 g of the aqueous dispersion is weighed into a solid content meter SMART SYSTEM 5 manufactured by CEM, and measurement is performed under an environment of 20° C. and 50% RH. The results of three measurements are averaged, and the solid content is calculated by the formula (dry mass/mass of aqueous dispersion)×100.

(Method for producing aqueous dispersion)
The aqueous dispersion of the chlorinated vinyl polymer of this embodiment can be produced by emulsion polymerization of the monomer mixture. Although not particularly limited, the emulsion polymerization is usually carried out at a temperature of 30 to 70°C. The polymerization temperature is preferably within the range of 40 to 60°C. By setting the polymerization temperature at 70°C or less, decomposition of the raw materials during polymerization can be suppressed, which is preferable. By setting the polymerization temperature at 30°C or more, the polymerization rate can be increased, improving the efficiency of the polymerization.

When carrying out emulsion polymerization of the above-mentioned chlorinated vinyl monomer, an aqueous dispersion synthesized by raw material monomers having different monomer compositions synthesized in the same or different polymerization machines may be added as a seed latex as a raw material.Preferably, it is an aqueous dispersion obtained by emulsion polymerization of an acrylic monomer or a methacrylic monomer, more preferably, it is an aqueous dispersion of a homopolymer or copolymer of methyl methacrylate or a copolymer of glycidyl methacrylate, and even more preferably, it is an aqueous dispersion of a homomethyl methacrylate polymer.
The addition of seed latex is expected to increase the polymerization rate as well as improve the film-forming life of the product.
The amount of the seed latex added is preferably 10 parts by mass or less based on 100 parts by mass of the chlorinated vinyl polymer.
The seed latex is preferably added before the start of polymerization of the chlorinated vinyl monomer, but the seed latex may be added continuously in parallel with the continuous addition of the monomer.

After the emulsion polymerization of the aqueous dispersion of the chlorinated vinyl polymer is completed, additional polymerization may be carried out by adding raw material monomers having a different monomer composition to the aqueous dispersion in the same or another polymerization machine. This allows the polymer formed by polymerizing the newly added monomers to form a structure that coats the chlorinated vinyl polymer particles, and is expected to improve the film-forming life and the mechanical properties of the film.
The amount of the polymer formed by the additional polymerization is preferably 10 parts by mass or less based on 100 parts by mass of the chlorinated vinyl polymer.

Examples of surfactants that can be used in the emulsion polymerization of the above-mentioned aqueous dispersion of chlorinated vinyl polymer include anionic surfactants such as alkyl sulfate ester salts, alkyl benzene sulfonate salts, alkyl sulfosuccinate salts, alkyl diphenyl ether disulfonate salts, and alkyl sulfonate salts.

Examples of polymerization initiators include persulfates such as sodium persulfate and potassium persulfate, and peroxides such as hydrogen peroxide, t-butyl hydroperoxide, and cumene hydroperoxide. Preferred is t-butyl hydroperoxide.

It is preferable to add a polymerization activator such as sodium hydrogen sulfite or sodium D-araboascorbate, which accelerates the radical decomposition of the initiator. These polymerization activators are preferably added to promote the decomposition of the polymerization initiator. However, on the other hand, in order to promote the decomposition of the oxidizing agent, the smaller the amount added, within the range necessary for radical decomposition of the polymerization initiator, the better.

These polymerization additives are not particularly limited and may be, for example, types that have traditionally been preferably used in this technical field.

The chlorinated vinyl polymer particles contained in the aqueous dispersion of the chlorinated vinyl polymer of this embodiment are not particularly limited, but it is preferable that the average particle size is 10 to 1000 nm. By setting the average particle size in this range, the storage stability of the aqueous dispersion is good and the coatability is improved.

The aqueous dispersion of the chlorinated vinyl polymer of the present embodiment preferably contains a crystal nucleating agent. The crystal nucleating agent is an additive that promotes the crystallization of a film formed from the aqueous dispersion, and any known crystal nucleating agent that promotes the crystallization of a resin can be used.
Examples of such crystal nucleating agents include metal phosphates, metal benzoates, metal pimelates, metal rosins, benzylidene sorbitol, quinacridone, cyanine blue, metal oxalates, metal stearates, ionomers, high melting point PET, carbon black, metal oxides, metal sulfates, kaolin, clay, high melting point polyamides, crystalline resins having a composition different from that of the chlorinated vinyl polymer of the present embodiment described above, silica, titanium oxide, wax, highly crystalline chlorinated vinyl polymer particles different from that of the chlorinated vinyl polymer of the present embodiment described above, and the like. It is also possible to use one or more of these in combination.
Preferred are silica, titanium oxide, wax, and highly crystalline chlorinated vinyl polymer particles, and particularly preferred are wax and highly crystalline chlorinated vinyl polymer particles.
The content of the crystal nucleating agent is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, even more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, based on 100 parts by mass of the chlorinated vinyl polymer. The content of the crystal nucleating agent is preferably 0.05 parts by mass or more.
When multiple crystal nucleating agents are added, the total amount is used.

The term "wax" is understood herein to refer to any natural or synthetic wax, including, but not limited to, hazel wax, urushi wax, sugar cane wax, palm wax, candelilla wax, jojoba oil, beeswax, spermaceti wax, ivory wax, wool wax, FT wax, paraffin wax, microwax, carnauba wax, beeswax, china wax, ozokerite, polyolefin wax and montan wax, and esters thereof.

The highly crystalline chlorinated vinyl polymer particles are chlorinated vinyl polymer particles whose addition increases the crystallization rate of the chlorinated vinyl polymer after film formation, and have a maximum melting peak temperature of 190°C or less as measured by DSC of preferably 160°C or more, and particularly preferably 170°C or more.
Here, the maximum melting peak temperature is measured according to the melting peak measurement method described below, and the maximum peak temperature at 180° C. or less is used.
Furthermore, the highly crystalline chlorinated vinyl polymer particles are preferably vinylidene chloride copolymer particles, and particularly preferably vinylidene chloride copolymer particles in which 91% by mass or more of vinylidene chloride is copolymerized when the vinylidene chloride copolymer is taken as 100% by mass.
<Measuring method of melting peak>
(i) When an aqueous dispersion of a chlorinated vinyl polymer is available, the following method is used.
A water dispersion of chlorinated vinyl polymer is applied to an aluminum plate with a Mayer bar so that the dry coating amount is 10 g/ ^m2 , and then dried for 1 minute in an oven maintained at 100°C. The dried film is peeled off with tweezers within 5 minutes to obtain a single film of chlorinated vinyl polymer. 5 mg of the single film is taken and used for measurement.

(ii) When an aqueous dispersion of a chlorinated vinyl polymer is not available and only a film coated with the aqueous dispersion is available, the following method is used.
The chlorinated vinyl polymer is separated from the film on which it is applied, and 5 mg of the polymer is sampled for measurement.
As a method for separating the chlorinated vinyl polymer from the film coated with the chlorinated vinyl polymer, the following methods (A) to (C) are used if possible. If (A) is possible, use (A); if (A) is difficult and (B) is possible, use (B); if (A) and (B) are difficult and (C) is possible, use (C). If any of (A) to (C) is difficult and there is another means for separation, that may be used. In this case, it is preferable to wash and dry the separated product so that the content of impurities other than the chlorinated vinyl polymer in the separated product is as small as possible. The mass ratio of the above impurities is preferably 0.5 mass% or less in the measurement sample. The drying treatment conditions are a temperature of 60°C or less and a treatment time of 10 hours or less. Here, the impurities refer to components that are not contained in the aqueous dispersion of the chlorinated vinyl polymer before coating, such as mixed primers and solvents, and do not include additives such as emulsifiers that are added to the aqueous dispersion from the beginning. The amount of emulsifier in the separated product can be measured by the following procedure. i) The mass of the dried separated product is W1. ii) Wash the separated product with a large amount of pure water that is at least 50 times its mass. Be careful not to let the polymer flow out together with the washed separated product. iii) Dry the washed separated product and call its mass W2. iv) Calculate the mass of the emulsifier by subtracting W1 from W2.
(A) Physically peel it off with tweezers or scrape it off.
(B) The chlorinated vinyl polymer is not dissolved, but the primer is dissolved in a solvent, which is chemically separated from the chlorinated vinyl polymer by using a solvent, preferably acetone, which dissolves the primer.
(C) The chlorinated vinyl polymer is dissolved using a solvent in which the chlorinated vinyl polymer dissolves but the substrate film does not dissolve, and the chlorinated vinyl polymer is separated by drying.
When separation is performed using a solvent by the method (B) or (C), the separated product is dried in a drying oven or the like to the extent that the chlorinated vinyl polymer does not decompose, and the measurement is performed after confirming that the weight of the solvent in the separated product is 0.5 mass % or less. The drying conditions are a temperature of 50° C. or less, a drying time of 10 hours or less, and, if necessary, under reduced pressure.

The sample collected using the above method is heated to 170°C at 10°C/min in a nitrogen atmosphere using a TAintsruments Q-2000 differential scanning calorimeter, and cooled to -40°C at 10°C/min. It is then heated to 190°C at 10°C/min, and measurement data is obtained up to 190°C. Of the measurement data obtained up to 190°C, data above 180°C is not used because vinylidene chloride begins to decompose at temperatures above 180°C. The maximum melting peak temperature is determined using the measured values from -40°C to 180°C during the second heating.

In this measurement, an aluminum Tzero Pan and Tzero hermetic lid (manufactured by TAinstruments) are used as the sample pan, and an empty pan is used as the reference. In other words, the maximum melting peak temperature is calculated based on the value obtained by subtracting the empty pan measurement result from the sample measurement result.

The addition of these crystal nucleating agents promotes the progression of crystallization after film formation, providing the coating with high water vapor barrier properties.

The aqueous dispersion of the chlorinated vinyl polymer of this embodiment can be used as a coating material for films used in blister packages, food packaging, etc.

[film]
The film of the present embodiment has a layer to which the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment is applied. The layer contains at least the chlorinated vinyl polymer, and may be a layer consisting of the chlorinated vinyl polymer alone.

The film of this embodiment preferably has a layer in which the aqueous dispersion of the chlorinated vinyl polymer of this embodiment is applied onto a film substrate. There are no particular limitations on the film substrate, but representative examples include films made of polyvinyl chloride, polyester, polyamide, and polypropylene. Most commonly, a film made of polyvinyl chloride is used. The thickness of the film substrate varies depending on the material used, but may usually be 8 to 300 μm.

The film of the present embodiment may optionally further include at least one layer of a chlorinated vinyl polymer having chemical or physical properties different from those of the chlorinated vinyl polymer of the present embodiment. For example, a film in which an aqueous dispersion of a chlorinated vinyl polymer having a different composition is applied on a layer of the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment for the purpose of preventing blocking or improving the slipping property of the film can be mentioned.
Another example is a film in which layers of the chlorinated vinyl polymer of the present embodiment and layers of a chlorinated vinyl copolymer copolymerized with a highly plastic comonomer, such as methyl acrylate or butyl acrylate, are alternately laminated. A film having this structure is expected to have high impact resistance.
In the case of a film having layers of a plurality of kinds of chlorinated vinyl polymers, the thickness of the chlorinated vinyl polymer layer is the sum of the thicknesses of all the layers.

The outermost surface of the film of this embodiment is preferably composed of a layer other than the layer to which the chlorinated vinyl polymer of this embodiment is applied. With such a layer configuration, when the film of this embodiment contains an oxidizing agent, it is possible to prevent the oxidizing agent from dissolving and coming into contact with the contents.

The coating weight of the layer coated with the aqueous dispersion of the chlorinated vinyl polymer after drying is not particularly limited, but is preferably 1 g/m ² , more preferably 10 g/m ² or more, and even more preferably 40 g/m ² or more. By increasing the coating weight after drying, the barrier property of the entire film can be improved.
However, the thicker the layer of the chlorinated vinyl polymer, the greater the discoloration of the film as a whole appears, even if the discoloration of the chlorinated vinyl polymer per unit volume is small. Therefore, the chlorinated vinyl polymer of the present embodiment, which suppresses discoloration of the chlorinated vinyl polymer, is more effective as the thickness increases.

Optionally, the film of this embodiment may include a layer of a functionally adjusted copolymer mainly composed of a monomer other than chlorinated vinyl having high polymerization activity, in addition to the layer coated with the aqueous dispersion of the chlorinated vinyl polymer. For example, such a layer may be formed by forming a primer on the film substrate using an aqueous resin emulsion or an acrylic dispersion, and then providing a layer coated with the aqueous dispersion of the chlorinated vinyl polymer of this embodiment.

The aqueous dispersion of the chlorinated vinyl polymer of this embodiment is preferably applied to a film substrate as exemplified above and used as a blister package. The resulting blister package exhibits excellent barrier properties (e.g., oxygen barrier properties, water vapor barrier properties).

Furthermore, in addition to being applied to blister packages, the film of this embodiment can also be used directly as a coating agent to form a clear film.

As a method for applying the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment to the above-mentioned film substrate, a known method such as air spray, airless, roll coater, curtain flow coating, roll coating, dip coating, spin coating, etc., can be used for the surface of the substrate. After application to the film substrate, the coating is usually dried by keeping it at room temperature or under heating for a predetermined time.

For a film having a layer coated with an aqueous dispersion of the chlorinated vinyl polymer of this embodiment, the water vapor barrier property and the change in yellowing of the film due to storage, ΔYI, can be evaluated using the following parameters (1) and (2).

(1) Water Vapor Barrier Property The water vapor barrier property of a film having a layer coated with the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment can be evaluated using a water vapor transmission rate measuring device PERMATRAN 3/33 manufactured by MOCON under conditions of 38°C and 100% RH (unit: g/ ^m2 ·day@38°C, 100% RH).
However, the water vapor permeability is defined as the average value of the measured values between 48 hours and 60 hours after the start of the measurement.
The measurement is carried out four times and the average value is used.
Although not particularly limited, a film having a layer coated with the aqueous dispersion of the chlorinated vinyl polymer of the present embodiment can be used in applications requiring high barrier properties (e.g., water vapor barrier properties), and the preferred numerical range of the water vapor permeability is 0.6 g/ ^m2 ·day or less, more preferably 0.5 g/ ^m2 ·day or less, and even more preferably 0.4 g/ ^m2 ·day or less.

(2) Measurement of film yellowing (preparation of coated film for yellowing measurement)
A primer, Emulder 381A manufactured by BASF, is applied to a stretched polyvinyl chloride film (thickness 250 μm) that has been subjected to a corona discharge treatment, using a Mayer rod to give a coating mass of 2 g/ ^m2 after drying, and then dried in a hot air circulation dryer at 85° C. for 15 seconds. An aqueous dispersion of a chlorinated vinyl polymer is applied to this film using a Mayer rod to give a coating mass of 10 g/ ^m2 after one drying, and then dried in a hot air circulation dryer at 85° C. for 15 seconds, and recoated until the coating mass after drying reaches 60 g/ ^m2 .
(Yellowing degree measurement)
The obtained coated film is cut into a 5 cm square, and three sheets are stacked to prepare a measurement sample. The yellowing degree (YI value) is measured under the following measurement conditions using a Konica Minolta color difference meter CM-5. The value measured is the yellowing degree before storage. The measurement sample is then placed in an oven at 40°C and stored for 30 days, after which the yellowing degree is measured again under the following measurement conditions. The value measured is the yellowing degree after storage. Each measurement is carried out three times, and the average value is the yellowing degree. The value obtained by subtracting the yellowing degree before storage from the yellowing degree after storage is the change in yellowing degree due to storage, ΔYI.
Measurement conditions:
Color system: L*a*b*
Index: YI ASTM E313-96
Field of view: 10°
Main light source: D65
Secondary light source: None

The change in color tone at 40°C for 30 days is equivalent to about one year of storage at room temperature (20°C). The above ΔYI is preferably 1.4 or less, more preferably 0.5 or less, and even more preferably 0 or less. A value of 0 or less means that yellowing is completely suppressed.

The present invention will now be described more specifically with reference to examples.
In the examples , reference examples and comparative examples, "parts" and "%" respectively indicate "parts by mass" and "% by mass".

<Polymerization Example of Water Dispersion>
[Example 1]
In a glass-lined pressure reactor, 57 parts of pure water, 0.03 parts of D-araboascorbate sodium, and 0.2 parts of sodium alkylsulfonate were charged relative to a total mass of 100 parts of monomers, and the mixture was degassed while stirring, then pressurized with nitrogen to atmospheric pressure, and the temperature of the contents was kept at 45°C. In another container, a raw material monomer mixture with a mass composition ratio of VDC/MAN = 91/9 was prepared. 20 parts of the raw material monomer mixture was added in one go to the pressure reactor, and polymerization was carried out until the internal pressure dropped. Subsequently, the remaining monomer mixture of 80 parts was continuously quantified and pressurized.
In parallel, an initiator prepared by dissolving 0.014 parts of t-butyl hydroperoxide in 3.5 parts of pure water, a reducing agent prepared by dissolving 0.015 parts of sodium D-araboascorbate in 3.5 parts of pure water, and an emulsifier prepared by dissolving 1.6 parts of sodium alkyldiphenyletherdisulfonate in 2.5 parts of pure water were continuously and quantitatively injected. During this time, the contents were kept at 45° C. while being stirred, and the reaction was allowed to proceed until the internal pressure had sufficiently dropped.
The polymerization yield was 99.9%. Since the polymerization yield was nearly 100%, the composition of the copolymer was nearly equal to the raw material charge ratio. The unreacted monomers were removed from the aqueous dispersion thus obtained by steam stripping.
In this polymerization, 80 parts of the monomer mixture was continuously injected, and the time required for the entire amount to be injected was 40 hours.
Hydrogen peroxide was added to the obtained aqueous dispersion so that the mass ratio of hydrogen peroxide was 0.1 part per 100 parts of the solid content of the aqueous dispersion. Then, the aqueous dispersion was adjusted to pH 2.5 and the solid content to 60% using a saturated aqueous solution of tetrasodium pyrophosphate at 20° C. and pure water.

[Comparative Example 1]
An aqueous dispersion of a vinylidene chloride copolymer was prepared in the same manner as in Example 1 of Patent Document 4.
In a glass-lined pressure reactor, 57 parts of pure water, 0.03 parts of D-sodium araboascorbate, and 0.2 parts of sodium alkylsulfonate were charged relative to a total mass of 100 parts of monomers, and the mixture was degassed while stirring, and the temperature of the contents was maintained at 45°C. In another container, a raw material monomer mixture having a mass composition ratio of VDC/MMA/AN=90.1/9.4/0.5 was prepared. 20 parts of the raw material monomer mixture was added to the pressure reactor in one go, and polymerization was carried out until the internal pressure dropped. Subsequently, the remaining monomer mixture of 80 parts was continuously quantified and pressurized.
In parallel, an initiator prepared by dissolving 0.014 parts of t-butyl hydroperoxide in 3.5 parts of pure water, a reducing agent prepared by dissolving 0.015 parts of sodium D-araboascorbate in 3.5 parts of pure water, and an emulsifier prepared by dissolving 1.6 parts of sodium alkyldiphenyletherdisulfonate in 2.5 parts of pure water were continuously and quantitatively injected. During this time, the contents were kept at 45° C. while being stirred, and the reaction was allowed to proceed until the internal pressure had sufficiently dropped.
The polymerization yield was 99.9%. Since the polymerization yield was nearly 100%, the composition of the copolymer was nearly equal to the raw material charge ratio. After removing unreacted monomers from the aqueous dispersion thus obtained by steam stripping, the solid content was adjusted to 50-60%.
In this polymerization, 80 parts of the monomer mixture was continuously injected, and the time required for the entire amount to be injected was 21 hours.

[Comparative Example 2]
An aqueous dispersion was prepared in the same manner as in Example 1, except that hydrogen peroxide was not added.

[Comparative Example 3]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the mass composition ratio of the raw material monomer mixture was VDC/MA=91/9 and hydrogen peroxide was not added.

[Comparative Example 4]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the mass composition ratio of the raw material monomer mixture was VDC/AN=91/9 and hydrogen peroxide was not added.

[Comparative Example 5]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the mass composition ratio of the raw material monomer mixture was VDC/MMA=91/9 and hydrogen peroxide was not added.

[Comparative Example 6]
An aqueous dispersion was prepared in the same manner as in Example 1, except that sodium hydrogen sulfite, which is known as a reducing bleaching agent, was added in an amount of 0.1 part per 100 parts of the solid content of the aqueous dispersion, instead of hydrogen peroxide.

[Comparative Example 7]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the pH was adjusted to 8.0 and hydrogen peroxide was not added.

[Comparative Example 8]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the pH was adjusted to 4.0 and hydrogen peroxide was not added.

[Comparative Example 9]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the pH was adjusted to 1.6 and no hydrogen peroxide was added.

[Comparative Example 10]
An aqueous dispersion was prepared in the same manner as in Comparative Example 2, except that the solid content was adjusted to 1%.
When the obtained aqueous dispersion was applied to measure the water vapor transmission rate, the film had cracks and it was not possible to obtain a uniform coating.

[Example 2]
An aqueous dispersion was prepared in the same manner as in Example 1, except that the mass ratio of hydrogen peroxide was changed to 1.0 part instead of 0.1 part.

[ Reference Example 3]
A water dispersion was prepared in the same manner as in Example 2, except that the mass ratio of hydrogen peroxide was changed to 0.01 part instead of 0.1 part.

[Example 4]
An aqueous dispersion was prepared in the same manner as in Example 2, except that sodium persulfate was added in place of hydrogen peroxide so that the total amount was 1.0 part.

[Example 5]
An aqueous dispersion was prepared in the same manner as in Example 2, except that sodium percarbonate was added in place of hydrogen peroxide so that the total amount was 1.0 part.

[Example 6]
An aqueous dispersion was prepared in the same manner as in Example 2, except that peracetic acid was added in place of hydrogen peroxide so that the total amount was 1.0 part.

[ Reference Example 7]
An aqueous dispersion was prepared in the same manner as in Example 2, except that sodium hypochlorite was added in place of hydrogen peroxide so that the total amount was 1.0 part, and the pH was adjusted to 8.0.

[Example 8]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the pH was adjusted to 4.0.

[Example 9]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the pH was adjusted to 1.6.

[Example 10]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the mass composition ratio of the raw material monomer mixture was VDC/AN=91/9.

[Example 11]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the mass composition ratio of the raw material monomer mixture was VDC/MMA=91/9.

[Example 12]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the mass composition ratio of the raw material monomer mixture was VDC/MA=91/9.

[Example 13]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the mass composition ratio of the raw material monomer mixture was VDC/MAN=90/10.

[Example 14]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the mass composition ratio of the raw material monomer mixture was VDC/MAN=89/11.

[Example 15]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the raw material monomer mixture had a mass composition ratio of VDC/MAN = 89/11, and an aqueous dispersion of a vinylidene chloride copolymer synthesized in the same manner as in Comparative Example 1 using raw material monomers having a mass composition ratio of VDC/AN = 98/2 was added as a crystal nucleating agent in an amount of 2.0 parts by dry mass.
The maximum melting peak of the vinylidene chloride copolymer added as a crystal nucleating agent was measured by the following measurement method and was found to be 179° C. It was confirmed that the addition of the crystal nucleating agent improved the crystallization rate compared to the aqueous dispersion before the addition.
(Measurement of maximum melting peak)
The aqueous dispersion of vinylidene chloride copolymer was applied to an aluminum plate with a Mayer bar so that the dry coating amount was 10 g/ ^m2 , and then dried for 1 minute in an oven maintained at 100°C. The dried product was collected with tweezers within 5 minutes to obtain a dried product of vinylidene chloride copolymer. 5 mg of the dried product was collected and used for the measurement.
The sample was heated to 170°C at 10°C/min under a nitrogen atmosphere using a TAintsruments Q-2000 differential scanning calorimeter, and cooled to -40°C at 10°C/min. Next, the sample was heated to 190°C at 10°C/min, and measurement data was obtained up to 190°C. Of the measurement data obtained up to 190°C, data above 180°C was not used because vinylidene chloride begins to decompose at 180°C or higher, and the maximum melting peak temperature was obtained using the measured values from -40°C to 180°C during the second heating.
The aluminum Tzero Pan and Tzero hermetic lid (manufactured by TA instruments) were used as the sample pan, and an empty pan was used as the reference. That is, the maximum melting peak temperature was calculated based on the value obtained by subtracting the measurement result of the empty pan from the measurement result of the sample.

[Example 16]
An aqueous dispersion was prepared in the same manner as in Example 2, except that 0.1 parts of sodium phytate was added in addition to hydrogen peroxide.

[Example 17]
An aqueous dispersion was prepared in the same manner as in Example 2, except that 0.1 part of sodium silicate was added in addition to hydrogen peroxide.

[Example 18]
An aqueous dispersion was prepared in the same manner as in Example 2, except that 0.1 parts of disodium ethylenediaminetetraacetate (EDTA-2Na) was added in addition to hydrogen peroxide.

[ Reference Example 19]
A water dispersion was prepared in the same manner as in Example 2, except that the mass ratio of hydrogen peroxide was changed to 0.001 part instead of 0.1 part.

[Example 20]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the pH was adjusted with 2.5% ammonia water.

[Example 21]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the pH was adjusted with a 1 mol/L aqueous sodium hydroxide solution.

[Example 22]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the solid content was adjusted to 10%.

[Example 23]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the solid content was adjusted to 40%.

[Example 24]
An aqueous dispersion was prepared in the same manner as in Example 2, except that the solid content was adjusted to 50%.

The obtained aqueous dispersion of vinylidene chloride copolymer was subjected to the following measurements, the results of which are shown in Table 1.
The measurements were carried out within one day after the preparation of the aqueous dispersion, and the aqueous dispersion was stored at 5° C. until the measurements were carried out.

<Measurement of ΔE*ab>
(1) Sample preparation All reagents used in this measurement were kept at 20°C. 35 g of the aqueous dispersion was diluted with 65 g of pure water to obtain 100 mL of aqueous dispersion, which was placed in a 250 mL PP reagent bottle. 10 mL of 10 w/V% potassium iodide aqueous solution and 10 mL of 1 mol/L hydrochloric acid were dropped into the bottle, the lid was closed, and the bottle was stirred at 300 rpm for 5 minutes using a 25 mm x φ8 mm stirrer. The obtained aqueous dispersion was used as a sample.
As the reference color, the measurement result of a sample in which 10 mL of pure water was added instead of the potassium iodide aqueous solution and the same operation was carried out was used.
(2) Discoloration Measurement Discoloration measurement was performed using a color difference meter CM-5 manufactured by Konica Minolta. 10 mL of the above sample was measured and placed in a 30 mmφ petri dish of the CM-5 option, and a petri dish measurement, which is one of the measurement methods of CM-5, was performed under the following measurement conditions. The measurement was performed three times, and the average value was taken as ΔE*ab for each sample.
Measurement conditions:
Color system: L*a*b*
Index: YI ASTM E313-96
Field of view: 10°
Main light source: D65
Secondary light source: None. After the potassium iodide aqueous solution was added, the potassium iodide could be oxidized by oxygen in the air to produce iodine. Therefore, after the specified 5 minutes of stirring, the color change was measured as soon as possible, but no later than within 5 minutes.

<Quantitative determination of oxidizing agent: redox titration>
For the Examples and Reference Examples , oxidation-reduction titration was carried out as follows to quantify the oxidizing agent. For the Comparative Examples, no oxidizing agent was added, and the amount of t-butyl hydroperoxide used as an initiator was also considered to be zero after polymerization, so the following measurements were not carried out and the results were recorded as zero.
All the reagents used in this measurement were kept at 20°C. 35 g of the aqueous dispersion was diluted with 65 g of pure water to obtain 100 mL of aqueous dispersion, which was taken in a 250 mL PP reagent bottle. 10 mL of 10 w/V% potassium iodide aqueous solution and 10 mL of 1 mol/L hydrochloric acid were dropped therein, the lid was closed, and the mixture was stirred at 300 rpm for 5 minutes using a 25 mm x φ8 mm stirrer. 0.1 mol/L sodium thiosulfate solution was dropped into the obtained aqueous dispersion once every 30 seconds, and the point at which the brown color disappeared was taken as the end point. The amount of sodium thiosulfate solution required to reach the end point was recorded. Measurements were performed several times, and the amount of sodium thiosulfate per drop was adjusted so that the drop was completed in 10 to 15 times. After adjustment, measurements were performed three or more times, and the average value was taken as the result after confirming that the standard deviation was within 20% of the titration value.
As a result of the above measurements, it was found that the aqueous dispersions obtained in the Examples and Reference Examples contained a sufficient amount of oxidizing agent to remain even after film formation.

<Measurement of solid content>
2.5 g of the aqueous dispersion was weighed out into a solid content meter SMART SYSTEM 5 manufactured by CEM, and measurement was performed under an environment of 20° C. and 50% RH. The results of three measurements were averaged, and the solid content was calculated according to the formula (dry mass/mass of aqueous dispersion)×100.

<Measurement of water vapor permeability (moisture permeability)>
(Preparation of coating film for measuring moisture permeability)
On a stretched polyvinyl chloride film (thickness 250 μm) subjected to corona discharge treatment, BASF Emulder 381A was applied as a primer using a Mayer rod so that the coating mass after drying was 2 g/m ² , and a drying treatment was performed in a hot air circulation dryer at 85 ° C. for 15 seconds. On this film, the aqueous dispersion of the vinylidene chloride copolymer obtained in each of the Examples , Reference Examples , and Comparative Examples was applied using a Mayer rod so that the coating mass after one drying was 10 g/m ² , and a drying treatment was performed in a hot air circulation dryer at 85 ° C. for 15 seconds, and the coating mass after drying was 40 g/m ^2. The obtained coated film was stored in a 40 ° C. oven for 24 hours, and then conditioned in a constant temperature and humidity chamber at 20 ° C. and humidity of 55% for 2 hours.

(Measurement of water vapor permeability (moisture permeability))
The water vapor transmission rate of the resulting coated film was measured under conditions of 38° C. and 100% RH using a water vapor transmission rate measuring device PERMATRAN 3/33 manufactured by MOCON (unit: g/m ² ·day@38° C., 100% RH).
The water vapor permeability was determined as the average value of the measurements taken between 48 hours and 60 hours after the start of the measurements.
The measurement was carried out four times, and the average value was used.

<Measurement of film yellowing>
(Preparation of coated film for measuring yellowing degree)
On a stretched polyvinyl chloride film (thickness 250 μm) that had been subjected to a corona discharge treatment, BASF Emulder 381A was applied as a primer using a Mayer rod so that the coating mass after drying would be 2 g/ ^m2 , and a drying treatment was carried out in a hot air circulation dryer at 85° C. for 15 seconds. Onto this film, the aqueous dispersion of the vinylidene chloride copolymer obtained in each of the Examples , Reference Examples, and Comparative Examples was applied using a Mayer rod so that the coating mass after one drying would be 10 g/ ^m2 , and a drying treatment was carried out in a hot air circulation dryer at 85° C. for 15 seconds, and recoated until the coating mass after drying reached 60 g/ ^m2 .
(Yellowing degree measurement)
The obtained coated film was cut into a 5 cm square, and three sheets were stacked to prepare a measurement sample. The yellowing degree (YI value) was measured under the following measurement conditions using a color difference meter CM-5 manufactured by Konica Minolta. The value at this time was taken as the yellowing degree before storage. Next, the measurement sample was placed in an oven at 40°C and stored for 30 days, after which the yellowing degree was measured again under the following measurement conditions. The value at this time was taken as the yellowing degree after storage. Each measurement was performed three times, and the average value was taken as the yellowing degree. The value obtained by subtracting the yellowing degree before storage from the yellowing degree after storage was taken as the change in yellowing degree due to storage, ΔYI.
Measurement conditions:
Color system: L*a*b*
Index: YI ASTM E313-96
Field of view: 10°
Main light source: D65
Secondary light source: None

<Monomer composition>
The monomer composition of the chlorinated vinyl polymers in the Examples , Reference Examples and Comparative Examples was evaluated by dissolving samples taken by the following method in tetrahydrofuran-d8 and carrying out NMR measurement.
10 mL of the aqueous dispersion was freeze-dried, and 0.5 g of the freeze-dried product was collected. The freeze-dried product was dissolved in 10 mL of tetrahydrofuran with a purity of 99.9% by mass or more, and 40 mL of acetone was dropped into the solution. The resulting precipitate was filtered, and the remaining insoluble matter was collected. The collected insoluble matter was used as a measurement sample.
The NMR measurement conditions are as shown in the table below.
Equipment: JEOL RESONANCE ECS400 (1H)
Bruker Biospin Avance600 (13C)
Observed nuclei: 1H (399.78MHz), 13C (150.91MHz)
Pulse program: Single pulse (1H), zgig30 (13C)
Accumulation count: 256 times (1H), 10,000 times (13C)
Lock solvent: THF-d8
Chemical shift reference: THF (1H: 180 ppm, 13C: 67.38 ppm)
The composition of the polymer was identified by integrating the peaks in the obtained NMR spectrum. The type of monomer contained was clear from the monomers charged.
For example, in the case of a polymer containing structural units derived from vinylidene chloride, methacrylonitrile, methyl methacrylate, and acrylic acid, the content of structural units derived from vinylidene chloride was determined by integrating from 80 to 90 ppm in the ¹³ C-NMR spectrum, the content of structural units derived from methacrylonitrile was determined by integrating from 110 to 130 ppm, the content of structural units derived from methyl methacrylate was determined by integrating from 170 to 180 ppm, and the content of structural units derived from acrylic acid was determined by integrating from 180 to 200 ppm, and the composition ratio of each monomer in the whole was calculated.
In the case of a copolymer containing structural units derived from methyl acrylate instead of methyl methacrylate, the calculation is performed by substituting methyl acrylate for methyl methacrylate in the above calculation method.
In the case of a copolymer containing structural units derived from acrylonitrile instead of methacrylonitrile, the calculation is performed by substituting acrylonitrile for methacrylonitrile in the above calculation method.
As a result of the above measurements, it was found that the polymers obtained in the Examples , Reference Examples and Comparative Examples had the same monomer composition as the charged composition.

The measurement results of the examples and comparative examples are shown.
The results in Table 1 demonstrate that the aqueous dispersion of the chlorinated vinyl polymer of the present invention can significantly suppress discoloration after film processing while maintaining high water vapor barrier properties of the film after coating. In particular, the result of ΔYI<0 in Example 1 and the like means that yellowing at 40° C. for one month can be completely suppressed.
There is a tendency for the discoloration of the film to increase when the pH of the aqueous dispersion is increased, but when compared at the same pH, it can be seen that the Examples are able to suppress discoloration compared to the Comparative Examples. Advantages of increasing the pH at the expense of discoloration include preventing corrosion of metal parts of the coating machine by acid and improving the aggregation stability of the aqueous dispersion, and it can be seen that yellowing can be reduced even in such cases by setting ΔE*ab to 1.0 or more.
In addition, when the same parts by mass of comonomers are copolymerized, MA is least prone to yellowing, and MAN, AN, and MMA tend to be more prone to yellowing than MA. However, it can be seen that for any of the comonomers, yellowing can be suppressed by setting ΔE*ab to 1.0 or more.
It is clear from Comparative Example 6 that, among substances generally used as bleaching agents, reducing bleaching agents are not only ineffective but also promote yellowing. In other words, it was demonstrated that not only a bleaching agent is sufficient, but also an oxidizing agent capable of making ΔE*ab 1.0 or more is necessary to suppress yellowing.

The aqueous dispersion of the chlorinated vinyl polymer of the present invention exhibits excellent water vapor barrier properties and yellowing resistance of the film after coating, and can therefore be suitably used as a coating for various materials such as food and pharmaceutical packaging films, paper, and general household goods.

Claims (10)

A water dispersion of vinylidene chloride polymer ,
The aqueous dispersion of the vinylidene chloride polymer contains an oxygen bleaching agent,
35 g of the vinylidene chloride polymer aqueous dispersion is added with 75 g of pure water and 10 mL of 1 mol/L hydrochloric acid, and stirred at 20° C. for 5 minutes at 300 rpm. The color of the mixture is used as a reference color. A mixture is then added with 65 g of pure water, 10 mL of 1 mol/L hydrochloric acid, and 10 mL of a 10 w/V % aqueous potassium iodide solution, and stirred at 20° C. for 5 minutes at 300 rpm. The aqueous dispersion of vinylidene chloride polymer is characterized in that, when the color difference of a mixture is measured by adding 65 g of pure water, 10 mL of 1 mol/L hydrochloric acid, and 10 mL of a 10 w/V % aqueous potassium iodide solution to 35 g of the vinylidene chloride polymer aqueous dispersion and stirring at 20° C. for 5 minutes at 300 rpm, ΔE*ab is 15 or more and 1,000 or less. 2. The aqueous dispersion of vinylidene chloride polymer according to claim 1 , wherein a mass ratio of structural units derived from vinylidene chloride is 70 mass% or more when the total mass of the vinylidene chloride polymer is taken as 100 mass%. 3. The aqueous dispersion of vinylidene chloride polymer according to claim 1, which has a solid content of 10% by mass or more as determined using a microwave solid content meter under an environment of 20°C and 50% RH. 4. The aqueous dispersion of vinylidene chloride polymer according to claim 1 , comprising a structural unit derived from vinylidene chloride and a structural unit derived from a copolymerizing monomer having a reactivity ratio r1 to vinylidene chloride of less than 0.7, wherein a mass proportion of the structural unit derived from the copolymerizing monomer having the reactivity ratio r1 of less than 0.7 is 1 mass% or more when a total mass of the structural unit derived from the vinylidene chloride , the structural unit derived from the copolymerizing monomer having the reactivity ratio r1 of less than 0.7, and the structural unit derived from the copolymerizing monomer having the reactivity ratio r1 of 0.7 or more is taken as 100 mass%. 5. The aqueous dispersion of vinylidene chloride polymer according to claim 4 , wherein the copolymerizable monomer having a reactivity ratio r1 of less than 0.7 is at least one selected from the group consisting of a monomer having a nitrile group, a monomer having a carboxyl group, and methyl methacrylate. 6. The aqueous dispersion of vinylidene chloride polymer according to claim 5 , wherein the monomer having a nitrile group is methacrylonitrile. 7. The aqueous dispersion of vinylidene chloride polymer according to claim 5, wherein a mass ratio of the structural units derived from the monomer having a nitrile group is 1 mass% or more when a total mass of the structural units derived from the vinylidene chloride, the structural units derived from the copolymerizable monomer having the reactivity ratio r1 of less than 0.7, and the structural units derived from the copolymerizable monomer having the reactivity ratio r1 of 0.7 or more is taken as 100 mass%. 8. The aqueous dispersion of vinylidene chloride polymer according to claim 5 , wherein the monomer having a carboxyl group is acrylic acid, itaconic acid, maleic acid or methacrylic acid. 9. The aqueous dispersion of vinylidene chloride polymer according to claim 4 , wherein a mass proportion of the structural units derived from a copolymerization monomer having a reactivity ratio r1 of less than 0.7 is 5 mass% or more and 20 mass% or less, when a total mass of the structural units derived from the vinylidene chloride- derived structural units, the structural units derived from the copolymerization monomer having a reactivity ratio r1 of less than 0.7 , and the structural units derived from the copolymerization monomer having a reactivity ratio r1 of 0.7 or more is taken as 100 mass%. A film comprising a layer coated with an aqueous dispersion of the vinylidene chloride polymer according to any one of claims 1 to 9 .