Preparation method of polyvinyl alcohol polymer, dispersion stabilizer and ethylene polymer

Abstract

The invention provides a polyvinyl alcohol polymer and the like. The polyvinyl alcohol polymer fully satisfies the following requirements 1, 2 and / or 3: wherein the requirement 1 has a polymerizable unsaturated bond; the yellowness index of a 24 mass% aqueous solution is 13 or less; and the yellowness index of the Remon 3 is 18 or less.

Description

Technical Field

[0001] The present invention relates to polyvinyl alcohol-based polymers, various uses of the polyvinyl alcohol-based polymers [such as a dispersion stabilizer [e.g., a dispersion stabilizer for suspension polymerization of vinyl monomers (especially vinyl chloride monomer)], a method for producing a vinyl polymer [especially a vinyl chloride polymer (resin)] using the polyvinyl alcohol-based polymer (or dispersion stabilizer), etc. Background Art

[0002] The industrial production method of vinyl chloride-based resins is usually carried out by batch suspension polymerization in which vinyl monomers such as vinyl chloride are dispersed in an aqueous medium in the presence of a dispersion stabilizer and polymerized using an oil-soluble polymerization initiator. As factors affecting the quality of vinyl chloride-based resins in the polymerization process, polymerization rate, ratio of aqueous medium to monomer, polymerization temperature, type and amount of polymerization initiator, form of polymerization tank, stirring speed, and type and amount of dispersion stabilizer can be cited. Among them, the influence of the dispersion stabilizer is very large.

[0003] The role of the dispersion stabilizer in suspension polymerization for obtaining vinyl chloride-based resins is to disperse the monomer in the aqueous medium, form stable droplets, uniformly adjust the size of the droplets that repeatedly disperse and coalesce, and at the same time control the cohesiveness of the polymerized particles. Therefore, the required properties of this dispersion stabilizer include:

[0004] <1> Controlling the particle size of the obtained vinyl chloride-based resin particles within an appropriate range;

[0005] <2> Increasing the plasticizer absorbability of the obtained vinyl chloride-based resin particles, thereby making the molding processability good;

[0006] <3> Keeping the porosity of the obtained vinyl chloride-based resin particles within a certain range to facilitate the removal of residual monomers;

[0007] <4> Making the hue of the obtained vinyl chloride-based resin particles good, etc.

[0008] That is, for the above dispersion stabilizer, it is required to exhibit, for example, excellent dispersing power (protective colloid property), control the particle diameter, particle shape, etc. of the vinyl chloride-based resin to an appropriate state, etc.

[0009] As the above dispersion stabilizer, polyvinyl alcohol-based resins (hereinafter sometimes abbreviated as PVA, etc.), cellulose derivatives, etc. are usually used alone or in combination.

[0010] For example, Non-Patent Document 1 describes a method of using a PVA having a viscosity-average degree of polymerization of 2000 and a saponification degree of 88 mol% or 80 mol% and having high emulsifying power, and a PVA having a viscosity-average degree of polymerization of 600 to 700 and a saponification degree of about 70 mol% as a dispersion stabilizer for suspension polymerization of vinyl chloride.

[0011] In addition, Patent Document 1 proposes a dispersion stabilizer for suspension polymerization, which is characterized in that it contains a polyvinyl alcohol-based polymer (B) having a double bond in the side chain, which is obtained by acetalizing a polyvinyl alcohol-based polymer (A) with a monoaldehyde having an olefinic unsaturated double bond.

[0012] Prior Art Documents

[0013] Patent Documents

[0014] Patent Document 1: Pamphlet of International Publication No. 2015 / 182567

[0015] Non-Patent Documents

[0016] Non-Patent Document 1: "Poval", published by Kobunshi Kankokai, in 1981 Summary of the Invention

[0017] (I) Technical Problem to be Solved

[0018] An object of the present invention is to provide a polyvinyl alcohol-based polymer (PVA) and the like.

[0019] (II) Technical Solution

[0020] As described above, when PVA is used as a dispersion stabilizer for suspension polymerization of vinyl chloride or the like, for the PVA used as the dispersion stabilizer or the like, technologies for further improving it are being developed.

[0021] In particular, Patent Document 1 relates to a technology developed by the inventors of the present application. It seems that by modifying (acetalizing) PVA with a monoaldehyde having an olefinic unsaturated double bond, the polymerization stability and dispersing power (protective colloid property) can be improved.

[0022] However, the inventors of the present application have found through research that the PVA used will affect the coloring (hue) of the obtained resin (vinyl chloride-based resin or the like), and may even cause the obtained resin to be colored. However, how the PVA affects the coloring of the resin is still unknown, and it is extremely difficult to explore PVA that can be used to reduce or suppress coloring.

[0023] Moreover, even if modification (acetalization) is carried out using a monoaldehyde having an olefinic unsaturated double bond as shown in Patent Document 1, the influence of such coloring still seems to remain (especially not improved), and it is still extremely difficult to explore a PVA that can improve polymerization stability and dispersibility and at the same time achieve improvement in coloring and suppression.

[0024] Among them, the inventors of the present application found that the coloring / hue (or the degree thereof) of PVA itself may affect the coloring of the resulting resin, and further studied this. As a result, it was found that according to PVA that sufficiently satisfies specific requirements (coloring characteristics), etc., improvement and suppression of the coloring of the resulting resin can be achieved. In particular, even for PVA having an unsaturated bond (unsaturated double bond) as in Patent Document 1, this tendency has not changed particularly, and even polymerization stability and dispersibility can be improved, and at the same time improvement and suppression of coloring can be achieved. The inventors of the present application further repeatedly studied, and thus completed the present invention.

[0025] That is, the present invention relates to the following inventions, etc.

[0026] [1] A polyvinyl alcohol-based polymer (A) that sufficiently satisfies the following Requirement 1 and the following Requirement 2 and / or Requirement 3:

[0027] Requirement 1: Having a polymerizable unsaturated bond;

[0028] Requirement 2: The YI (yellowness index) of a 4% by mass aqueous solution is 18 or less;

[0029] Requirement 3: The YI is 13 or less.

[0030] [2] The polyvinyl alcohol-based polymer (A) according to [1], wherein the proportion of the polymerizable unsaturated bond is 3 μmol / g or more.

[0031] [3] The polyvinyl alcohol-based polymer (A) according to [1] or [2], which sufficiently satisfies that the YI of a 4% by mass aqueous solution is 15 or less and / or the YI is 12 or less.

[0032] [4] The polyvinyl alcohol-based polymer (A) according to any one of [1] to [3], which further sufficiently satisfies the following Requirement 4:

[0033] Requirement 4: The transmittance at 430 nm of a 1% by mass aqueous solution is 90% or more.

[0034] [5] The polyvinyl alcohol-based polymer (A) according to any one of [1] to [4], wherein the proportion of the polymerizable unsaturated bond is 5 to 500 μmol / g,

[0035] the YI of a 4% by mass aqueous solution is 15 or less,

[0036] YI is 12 or less,

[0037] The transmittance at 430 nm of a 1 mass% aqueous solution is 95% or more.

[0038] [6] The polyvinyl alcohol polymer (A) according to any one of [1] to [5] contains an acetal skeleton (a) having a polymerizable unsaturated bond.

[0039] [7] The polyvinyl alcohol polymer (A) according to any one of [1] to [6] contains an acetal skeleton (a) having a polymerizable unsaturated bond,

[0040] The acetal skeleton (a) contains a skeleton represented by the following formula (a1).

[0041] [Chemical formula 1]

[0042]

[0043] In the formula, R' represents a group having a polymerizable unsaturated bond.

[0044] [8] The polyvinyl alcohol polymer (A) according to any one of [1] to [7] contains an acetal skeleton (a) having a polymerizable unsaturated bond,

[0045] The acetal skeleton (a) contains the skeleton represented by the formula (a1),

[0046] The content of the acetal skeleton (a) is 0.05 to 5 mol% per monomer unit.

[0047] [9] The polyvinyl alcohol polymer (A) according to any one of [1] to [9] further contains an ionic skeleton (b).

[0048]

[10] The polyvinyl alcohol polymer (A) according to any one of [1] to [9] further contains an ionic skeleton (b),

[0049] The content of the ionic skeleton (b) is 0.01 to 5 mol% per monomer unit.

[0050]

[11] In the polyvinyl alcohol polymer (A) according to any one of [1] to

[10] , the saponification degree of the polyvinyl alcohol polymer (A) is 50 to 90 mol%.

[0051]

[12] In the polyvinyl alcohol polymer (A) according to [1] to

[11] , the viscosity (20 °C) of a 4 mass% aqueous solution of the polyvinyl alcohol polymer (A) is 1 to 300 mPa·s (for example, 1 to 100 mPa·s, 2 to 100 mPa·s).

[0052]

[13] A dispersion stabilizer containing the polyvinyl alcohol-based polymer (A) described in any one of [1] to

[12] .

[0053]

[14] The dispersion stabilizer according to

[13] , which is a dispersion stabilizer for polymerization.

[0054]

[15] The dispersion stabilizer according to

[13] or

[14] , which is a dispersion stabilizer for suspension polymerization.

[0055]

[16] The dispersion stabilizer according to any one of

[13] to

[15] , which is a dispersion stabilizer for suspension polymerization of vinyl monomers containing vinyl chloride.

[0056]

[17] A method for preparing a vinyl polymer, which polymerizes a vinyl monomer in the presence of the polyvinyl alcohol-based polymer (A) described in any one of [1] to

[16] or a dispersion stabilizer.

[0057]

[18] The preparation method according to

[17] , wherein the polymerization is suspension polymerization.

[0058]

[19] The preparation method according to

[17] or

[18] , which suspension polymerizes vinyl monomers containing vinyl chloride.

[0059]

[20] Use of the polyvinyl alcohol-based polymer (A) described in any one of [1] to

[12] in a dispersion stabilizer (dispersant).

[0060]

[21] The use according to

[20] , wherein the dispersion stabilizer is a dispersion stabilizer for suspension polymerization.

[0061]

[22] The use according to

[20] or

[21] , wherein the dispersion stabilizer is a dispersion stabilizer for suspension polymerization of vinyl monomers containing vinyl chloride.

[0062]

[23] Use of the polyvinyl alcohol-based polymer (A) described in any one of [1] to

[12] in the polymerization of vinyl monomers.

[0063]

[24] The use according to

[23] , wherein the polymerization is suspension polymerization.

[0064]

[25] The use according to

[23] or

[24] , wherein the polymerization is suspension polymerization of vinyl monomers containing vinyl chloride.

[0065] (III) Beneficial effects

[0066] According to the present invention, PVA (novel or specific PVA) and its uses (such as dispersion stabilizers) can be provided.

[0067] This PVA (such as a dispersion stabilizer) has a specific hue (coloring property). In particular, this PVA (such as a dispersion stabilizer) has an unsaturated double bond and also has an excellent hue itself.

[0068] Moreover, this PVA also has the property of being a dispersion stabilizer. For example, it can exhibit excellent dispersibility (protective colloid property), achieve high polymerization stability, and obtain a resin (such as a vinyl chloride-based resin or other vinyl-based polymers) with excellent plasticizer absorbability and hue. Therefore, while having the above properties as a dispersion stabilizer, it can also balance the improvement and suppression of resin coloring. Detailed Embodiments

[0069] Hereinafter, the embodiments for implementing the present invention will be described in detail. In addition, the present invention is not limited to the embodiments described below.

[0070] The polyvinyl alcohol-based polymer of the present invention (polyvinyl alcohol-based polymer (A), PVA-based polymer (A), PVA (A), PVA) particularly satisfies (fully satisfies) the following Requirement 1 and at least one of the following Requirements 2 to 4:

[0071] Requirement 1: Having a polymerizable unsaturated bond [for example, a polymerizable unsaturated bond determined by bromine titration (detected or quantified by bromine titration)] (such as an unsaturated double bond);

[0072] Requirement 2: The YI of a 4% by mass aqueous solution is 13 or less;

[0073] Requirement 3: The YI is 18 or less;

[0074] Requirement 4: The transmittance at 430 nm of a 1% by mass aqueous solution is 90% or more.

[0075] In addition, the present invention also includes various uses of the above polyvinyl alcohol-based polymer (polyvinyl alcohol-based polymer (A)), particularly a dispersant (dispersion stabilizer, such as a dispersion stabilizer for suspension polymerization) containing the polyvinyl alcohol-based polymer (polyvinyl alcohol-based polymer (A)).

[0076] In the above various uses [such as a dispersant (dispersion stabilizer) such as a dispersion stabilizer for suspension polymerization], one or more than two kinds of PVA-based polymers (A) can be used.

[0077] Hereinafter, the present invention will be described in detail.

[0078] [Polyvinyl alcohol-based polymer (A)]

[0079] The PVA-based polymer (A) satisfies the following Requirement 1 and any one or more of the Requirements 2 to 4:

[0080] Requirement 1: having a polymerizable unsaturated bond;

[0081] Requirement 2: the YI of a 4% by mass aqueous solution is 13 or less;

[0082] Requirement 3: the YI is 18 or less;

[0083] Requirement 4: the transmittance at 430 nm of a 1% by mass aqueous solution is 90% or more.

[0084] In Requirement 1, examples of the polymerizable unsaturated bond include a double bond (unsaturated double bond), a triple bond (unsaturated triple bond), etc. The polymerizable unsaturated bond can usually be a double bond (especially a carbon-carbon double bond) [and may at least contain a double bond (especially a carbon-carbon double bond)].

[0085] In the PVA-based polymer (A), the proportion of the polymerizable unsaturated bond can be selected, for example, from a range of about 1 μmol / g or more (e.g., 2 μmol / g or more), preferably 3 μmol / g or more, and more preferably 5 μmol / g or more (e.g., it can be 8 μmol / g or more, 10 μmol / g or more, 12 μmol / g or more, 15 μmol / g or more, 20 μmol / g or more, etc.).

[0086] In the PVA-based polymer (A), the upper limit value of the proportion of the polymerizable unsaturated bond is not particularly limited, and can be, for example, 3000 μmol / g or less, 2000 μmol / g or less, 1000 μmol / g or less, 800 μmol / g or less, 600 μmol / g or less, 500 μmol / g or less, 450 μmol / g or less, 400 μmol / g or less, etc.

[0087] The proportion of the polymerizable unsaturated bond can also be set to a range obtained by appropriately combining the lower limit value and the upper limit value of the above range (hereinafter, the description of the range is the same).

[0088] Typically, in the PVA-based polymer (A), the proportion of the polymerizable unsaturated bond can be 1 to 2000 μmol / g, preferably 3 to 1000 μmol / g, and more preferably about 5 to 500 μmol / g.

[0089] In the PVA-based polymer (A) (the PVA-based polymer (A) that sufficiently satisfies Requirement 1), the proportion of the polymerizable unsaturated bond can sufficiently satisfy the proportion of the skeleton described later [for example, it can sufficiently satisfy the proportion of the acetal skeleton (a) (e.g., 0.001 mol% or more, 0.05 to 5 mol%, 0.1 to 3 mol%, 0.2 to 2 mol%, etc. per monomer unit)].

[0090] When the content of polymerizable unsaturated bonds (such as unsaturated double bonds) is within the above range, it is easy to effectively achieve the effects of the present invention. In particular, as long as it is not too small (such as 5 μmol / g or more, etc.), when used for suspension polymerization, etc., it is easy to achieve excellent polymerization stability, the adhesion of scale on the polymerization tank is suppressed, and the particle size of the obtained vinyl resin is not likely to become coarser, etc., so it is preferred. On the other hand, as long as the content of polymerizable unsaturated bonds (such as unsaturated double bonds) is not too large (such as 500 μmol / g or less, etc.), it is easy to obtain a vinyl resin with high plasticizer absorbability, so it is preferred.

[0091] The polymerizable unsaturated bonds contained in the PVA-based polymer (A) (possessed by the PVA-based polymer (A)) can be detected or quantified (to obtain its content (content ratio)), for example, by bromine titration. The method of bromine titration is not particularly limited. It utilizes the reaction between the polymerizable unsaturated bonds (such as unsaturated double bonds) contained in the PVA-based polymer (A) and bromine, and the amount (moles) of bromine that has reacted with the polymerizable unsaturated bonds (such as unsaturated double bonds) contained in the PVA-based polymer (A) can be used to calculate the polymerizable unsaturated bonds (such as unsaturated double bonds) (μmol / g) contained in the PVA-based polymer (A).

[0092] As described above, the PVA-based polymer (A) satisfies any one or more of the following requirements 2 to 4:

[0093] Requirement 2 The YI of the 4 mass% aqueous solution is 18 or less;

[0094] Requirement 3 The YI is 13 or less;

[0095] Requirement 4 The transmittance at 430 nm of the 1 mass% aqueous solution is 90% or more.

[0096] Typically, in most cases, the PVA-based polymer (A) fully satisfies Requirement 2 and / or Requirement 3. In particular, it is preferably to satisfy any two or more of Requirements 2 to 4, and more preferably to satisfy all of Requirements 2 to 4.

[0097] Requirement 2 limits the YI (yellowness, yellowness index) of the 4 mass% aqueous solution of the PVA-based polymer (A), and it is sufficient to be 18 or less. It can be preferably 16 or less (such as 15 or less, 13 or less, 12 or less), and more preferably 11 or less (such as 10 or less, 9 or less, 8 or less).

[0098] If Requirement 2 (YI of the 4 mass% aqueous solution) is within the above range, in addition to its excellent hue, when used as a dispersion stabilizer, it is easy to suppress and improve the coloring of the obtained vinyl resin, so it is preferred.

[0099] In addition, the YI of a 4% by mass aqueous solution of the PVA-based polymer (A) can be measured, for example, at 20°C using an ultraviolet-visible spectrophotometer to measure the UV-Vis spectrum of the 4% by weight aqueous solution (quartz cuvette with an optical path length of 10 mm), and calculated from the obtained data.

[0100] Requirement 3 defines the YI (yellowness, yellowness index) of the PVA-based polymer (A) (the polymer itself, in solid form), which can be 13 or less, preferably 12 or less, more preferably 11 or less (for example, 10 or less), and can be 9 or less, 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, etc.

[0101] If Requirement 3 (the YI of the polymer itself or in solid form) is within the above range, in addition to having excellent hue, when used as a dispersion stabilizer, it is easy to suppress and improve the coloring of the obtained vinyl resin, so it is preferred.

[0102] In addition, the YI of the PVA-based polymer (A) is obtained, for example, by measurement using a color difference meter. During the measurement, the PVA-based polymer (A) is usually in a powder state, and its particle size can be appropriately powdered or controlled according to its form for measurement. For example, the test powder obtained by passing PVA [such as powdered PVA (crushed PVA, etc.)] through a metal mesh (sieve) with a mesh size of 0.5 mm (30 mesh) can be measured using a color difference meter to obtain the YI value.

[0103] Requirement 4 defines the transmittance of a 1% by mass aqueous solution of the PVA-based polymer (A) at 430 nm, which can be 90% or more (for example, greater than 90%), preferably 91% or more (for example, 92% or more), more preferably 93% or more (for example, 94% or more, 95% or more, 96% or more, 97% or more).

[0104] If Requirement 4 (the transmittance of a 1% by mass aqueous solution at 430 nm) is within the above range, in addition to having excellent hue, when used as a dispersion stabilizer, it is easy to suppress and improve the coloring of the obtained vinyl resin, so it is preferred.

[0105] In addition, the transmittance of a 1% by mass aqueous solution of the PVA-based polymer (A) at 430 nm can be measured, for example, at 20°C using an ultraviolet-visible spectrophotometer to measure the transmittance at 430 nm of the 1% by weight aqueous solution (quartz cuvette with an optical path length of 20 mm, blank: pure water).

[0106] The PVA-based polymer (A) is not particularly limited as long as it fully satisfies the above requirements. As a solution (fully satisfying Requirement 1) having a polymerizable unsaturated bond, it may appropriately contain an acetal skeleton (a) having a polymerizable unsaturated bond (such as a vinylidene unsaturated double bond).

[0107] In the present invention, even though it contains such polymerizable unsaturated bonds (such as vinyl unsaturated double bonds, etc.) [for example, an acetal skeleton (a) having a polymerizable unsaturated bond (such as a vinyl unsaturated double bond)], it is easy to achieve excellent hue and it is easy to obtain an ethylene-based resin with excellent hue when used for suspension polymerization, etc.

[0108] [Acetal skeleton (a)]

[0109] In the acetal skeleton (a), the number of polymerizable unsaturated bonds is not particularly limited, and it may be 1 or more (for example, 1 to 5, 1 to 3, 1 to 2, 1, etc.).

[0110] In the acetal skeleton (a), the acetal may be any one of a cyclic acetal and an acyclic (chain-like) acetal, and a cyclic acetal is preferably used.

[0111] Among the representative acetal skeletons having a polymerizable unsaturated bond, a skeleton (structural unit) represented by the following formula (a1) is included. Therefore, the acetal skeleton (a) may include the skeleton represented by the following formula (a1).

[0112] [Chemical formula 2]

[0113]

[0114] In formula (a1), R'represents a group having a polymerizable unsaturated bond.

[0115] In the above formula (a1), R'is a group having a polymerizable unsaturated bond. R'may be the polymerizable unsaturated bond itself or a group containing a polymerizable unsaturated bond (such as a hydrocarbon group).

[0116] In addition, the group having a polymerizable unsaturated bond may have a substituent in addition to the polymerizable unsaturated bond. As the substituent, it can be appropriately selected according to the type of the group having a polymerizable unsaturated bond, and there is no particular limitation. For example, hydroxyl group, halogen atom, acyl group, ester group, alkoxy group, nitro group, substituted amino group, a group different from the basic group (such as an aromatic group such as an aryl group), etc. can be cited.

[0117] The substituents may be substituted alone or in combination of two or more.

[0118] Examples of the group having a polymerizable unsaturated bond [especially a double bond (olefinic double bond)] include a group having one polymerizable unsaturated bond {e.g., an alkenyl group [e.g., a vinyl group, an allyl group, a propenyl group (1-propenyl, 2-propenyl, etc.), a butenyl group, a pentenyl group, a 6-methyl-5-hexenyl group, a decenyl group, a 2-(dimethylamino)vinyl group, a cyclohexenyl group, a 2-phenylvinyl group, etc., a hydrocarbon group having 2 or more carbon atoms (e.g., 2 to 30, preferably 2 to 14, more preferably about 2 to 10) (a hydrocarbon group which may have a substituent), etc.]}, a group having two or more polymerizable unsaturated bonds {e.g., an alkanedienyl group [e.g., a 1,3-pentadienyl group, a 2,6-dimethyl-1,5-hexadienyl group, a cyclohexadienyl group, an allylcyclohexenyl group, etc., an alkanedienyl group having 4 or more carbon atoms (e.g., 4 to 30, preferably 4 to 14, more preferably 4 to 10)], an alkatrienyl group [e.g., an alkatrienyl group having 6 or more carbon atoms (e.g., 6 to 30, preferably about 6 to 24)], an alkatetraenyl group [e.g., an alkatetraenyl group having 8 or more carbon atoms (e.g., 8 to 30, preferably 8 to 24)], an alkapentaenyl group [e.g., an alkapentaenyl group having 10 or more carbon atoms (e.g., 10 to 30, preferably 10 to 24)], etc., a hydrocarbon group (a hydrocarbon group which may have a substituent, e.g., an alkapolyenyl group)}.

[0119] The acetal skeleton having a polymerizable unsaturated bond {e.g., the group represented by the formula (a1) (or R'-< in the formula (a1))} may be derived from a corresponding carbonyl compound (e.g., an aldehyde, its acetal, a ketone, etc.), especially an aldehyde [e.g., R'CHO (R' is an aldehyde of a hydrocarbon group having a polymerizable unsaturated bond), etc.]. Further, as described above, the carbonyl compound may have a substituent.

[0120] As such carbonyl compounds, for example, alkenals (e.g., acrolein, crotonaldehyde, methacrolein, 3-butenal, 3-methyl-2-butenal, 2-methyl-2-butenal, 2-pentenal, 3-pentenal, 4-pentenal, 2-hexenal, 3-hexenal, 4-hexenal, 5-hexenal, 2-ethylcrotonaldehyde, 2-methyl-2-pentenal, 3-(dimethylamino)acrolein, 10-undecenal, myristaldehyde, palmitaldehyde, olealdehyde, elaidin aldehyde, isolinolealdehyde, gadoleic aldehyde, erucic aldehyde, nervonic aldehyde, linoleic aldehyde, citronellal, cinnamaldehyde, etc., alkenals having 3 to 15 carbon atoms, preferably alkenals having 3 to 10 carbon atoms), alkadienals (e.g., 2,4-pentadienal, 2,4-hexadienal, 2,6-nonadienal, citral, perillaldehyde, etc., alkadienals having 5 to 15 carbon atoms, preferably alkadienals having 5 to 10 carbon atoms), alkatrienals (e.g., linolenaldehyde, eleostearic aldehyde, etc., alkatrienals having 7 to 30 carbon atoms, preferably alkatrienals having 7 to 25 carbon atoms), alkatetraenals (e.g., octadecatetraenal, arachidonoyl aldehyde, etc., alkatetraenals having 9 to 30 carbon atoms, preferably alkatetraenals having 9 to 25 carbon atoms), alkapentaenals (e.g., eicosapentaenal, etc., alkapentaenals having 11 to 30 carbon atoms, preferably alkapentaenals having 11 to 25 carbon atoms), etc., unsaturated aldehydes (especially monoaldehydes), ketones corresponding to them, acetals, etc.

[0121] In addition, when isomers (e.g., cis-trans isomers, etc.) exist in the carbonyl compound, any one of the isomers (e.g., both the cis form and the trans form, etc.) may also be included.

[0122] As described above, as the carbonyl compound, an acetal which is a condensate of an aldehyde and an alcohol may also be used. The acetal is not particularly limited, and examples thereof include condensates with primary alcohols (e.g., methanol, etc.).

[0123] These carbonyl compounds may be used alone or two or more of them may be used simultaneously.

[0124] In addition, from the viewpoint of water solubility, etc., the carbonyl compound is preferably composed of a monocarbonyl compound (monoaldehyde, etc.), and even when a polycarbonyl compound (e.g., polyaldehyde such as dialdehyde) is used, in most cases, its amount is reduced, and it is used at a level that can ensure water solubility, etc.

[0125] In addition, an acetal skeleton having a polymerizable unsaturated bond (for example, the acetal skeleton represented by the formula (a1)) may be a skeleton that can be introduced via a hydroxyl group. For example, it may be an acetal skeleton derived from two adjacent hydroxyl groups (for example, the hydroxyl groups of a vinyl alcohol unit) (introduced via two adjacent hydroxyl groups (for example, the hydroxyl groups of a vinyl alcohol unit)).

[0126] For example, when using a carbonyl compound (aldehyde, ketone, etc.) having a polymerizable unsaturated bond, for example, by acetalizing two adjacent OH groups in a PVA-based polymer with a carbonyl compound having a polymerizable unsaturated bond, a PVA-based polymer (A) containing an acetal skeleton (a) having a polymerizable unsaturated bond can be obtained.

[0127] The acetal skeleton having a polymerizable unsaturated bond (for example, the acetal skeleton represented by the formula (a1)) may have an ionic group (ionic skeleton) or may not have an ionic group (ionic skeleton).

[0128] The PVA-based polymer (A) may contain an acetal skeleton having a polymerizable unsaturated bond alone or may contain two or more kinds of acetal skeletons having a polymerizable unsaturated bond in combination.

[0129] In the PVA-based polymer (A), the content of the acetal skeleton (a) [or a polymerizable unsaturated bond, such as the skeleton represented by the formula (a1), etc.] can be selected from a range of 0.001 mol% or more (for example, 0.005 mol% or more) per monomer unit in the PVA-based polymer (A). For example, it can be 0.01 mol% or more, preferably 0.05 mol% or more, more preferably 0.1 mol% or more, and particularly can be 0.2 mol% or more, etc. It can also be 10 mol% or less [for example, 8 mol% or less (for example, 5 mol% or less, 3 mol% or less), preferably 2 mol% or less, more preferably 1 mol% or less].

[0130] In addition, as described above, the above ranges (upper limit value and lower limit value) can be appropriately combined to select a range (for example, 0.01 to 3 mol%, 0.05 to 5 mol%, etc.).

[0131] Specifically, the content of the acetal skeleton (a) (or a polymerizable unsaturated bond) in the PVA-based polymer (A) can be 0.05 to 5 mol% per monomer unit, preferably 0.1 to 3 mol%, and more preferably about 0.2 to 2 mol%.

[0132] In addition, a content of 1 mol% means that there is 1 acetal skeleton (a) (for example, the skeleton represented by the formula (a1)) relative to 100 monomer units (for example, the total of monomer units such as vinyl alcohol units and vinyl ester units).

[0133] When the content is as described above, the performance as a dispersant (dispersion stabilizer) can be effectively achieved (for example, a vinyl chloride resin with excellent polymerization stability, an appropriate average particle size, or excellent plasticizer absorbability can be effectively obtained).

[0134] In addition, by setting the upper limit value not too high, it is easy to make the preparation property and storage stability of the aqueous solution and the dispersibility in warm water good.

[0135] In addition, the method for measuring the content of the acetal skeleton (a) is not particularly limited. For example, it can be measured by NMR.

[0136] If specific examples are cited, for example, a PVA-based polymer (A) can be dissolved in a d6-DMSO solvent and measured by 1 1H-NMR. The signals from the polymerizable unsaturated bonds (such as vinyl double bonds) of the acetal skeleton (a) are analyzed to perform the measurement.

[0137] The PVA-based polymer (A) may contain an ionic skeleton (b). If the PVA-based polymer (A) contains an ionic skeleton (b), it is possible to easily prepare a PVA aqueous solution, and at the same time, the stability of the PVA aqueous solution (as well as the dispersibility in warm water) can be increased, and when storing the PVA aqueous solution using a tank or the like or adding the PVA aqueous solution to a polymerization machine (warm water at 40 to 70 °C), PVA will not precipitate in the polymerization machine. In addition, by introducing the ionic skeleton (b), the above effects [such as excellent dispersibility (for example, dispersibility in water or warm water)] can be exerted. However, if it is simply introduced, the hue may deteriorate. In the present invention, even if the ionic skeleton (b) is introduced as described above, at least any one of the requirements (2) to (4) can be fully satisfied, and excellent dispersibility and the like can even be achieved, and at the same time, an excellent hue can be effectively achieved.

[0138] [Ionic skeleton (b)]

[0139] The ionic skeleton (b) has an ionic group.

[0140] Examples of the ionic group include an anionic group {such as an acid radical [such as a carboxyl group, a sulfonate group (-SO3H), a phosphate group, etc.]}, a cationic group [such as an amino group, ammonium (ammonium cation)], and salts thereof (groups formed by forming salts).

[0141] Examples of the salt vary depending on anionic, cationic, etc. For example, metal salts [such as alkali or alkaline earth metals (such as lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts, etc.)], halides (such as chlorides, bromides, iodides, etc.) can be cited.

[0142] When the ionic group is a polybasic acid or the like, the salt can be a single (same) salt or a salt obtained by combining two or more kinds.

[0143] Among these ionic groups, acid radicals (especially carboxyl groups and sulfonic acid groups) and their salts {salts of acid radicals, such as carboxylates [e.g., -COOM (M is an alkali metal such as sodium (or its cation))], sulfonates [e.g., -SO3M (M is an alkali metal such as sodium (or its cation))]} are preferred.

[0144] As long as the ionic skeleton (b) has an ionic group, its embodiment is not particularly limited. For example, (1) an acetal skeleton (acetal group, acetal unit) having an ionic group, (2) a skeleton corresponding to (or derived from) a monomer having an ionic group, (3) a skeleton corresponding to (or derived from) a compound into which other ionic groups can be introduced {e.g., a chain transfer agent having an ionic group [e.g., an alcohol, a carbonyl compound (aldehyde, ketone, etc., especially aldehyde, etc.), a thiol, etc.]} can be cited.

[0145] In addition, the ionic skeleton (b) (one ionic skeleton (b)) only needs to have one or more ionic groups, and it can also have two or more ionic groups.

[0146] The PVA-based polymer (A) can have the above ionic skeleton (b) alone or in combination of two or more kinds of the above ionic skeletons (b).

[0147] In the PVA-based polymer (A), the content (proportion, content ratio) of the ionic skeleton (b) (e.g., the above skeletons (1), (2) and / or (3)) can be selected from a range of 0.001 mol% or more (e.g., 0.005 mol% or more) per monomer unit, for example, it can be 0.01 mol% or more, preferably 0.03 mol% or more, more preferably 0.05 mol% or more, etc., and it can also be 10 mol% or less [e.g., 8 mol% or less (e.g., 5 mol% or less, 3 mol% or less), preferably 2 mol% or less, more preferably 1 mol% or less].

[0148] Specifically, the content of the ionic skeleton (b) (e.g., the above skeletons (1), (2) and / or (3)) can be 0.01 to 5 mol% per monomer unit, preferably 0.03 to 2 mol%, more preferably about 0.05 to 1 mol%.

[0149] In addition, a content of 1 mol% means that there is one ionic skeleton (b) (e.g., the above skeletons (1), (2) and / or (3)) relative to 100 monomer units (e.g., the total of monomer units such as vinyl alcohol units and vinyl ester units).

[0150] When the content is as described above, it is easy to improve the preparation property and storage stability of the aqueous solution of the PVA-based polymer (A), and its dispersibility in warm water.

[0151] In addition, by setting the upper limit value not too high, the performance of the PVA-based polymer (A) as a dispersion stabilizer can be effectively achieved (for example, a vinyl chloride-based resin with excellent polymerization stability, a suitable average particle size, and excellent plasticizer absorbability can be effectively obtained).

[0152] In addition, the method for measuring the content of the ionic group can be selected according to the type of the skeleton having the ionic group, etc., and there is no particular limitation. For example, it can be measured by NMR, titration, UV absorbance, etc.

[0153] If specific examples are cited, the content of the skeleton represented by the following formula (b1-1) can be measured as follows: Dissolve the PVA-based polymer (A) in a d6-DMSO solvent, and use 1 1H-NMR for measurement, and analyze the signals of the substituents (such as hydrogen) from the benzene ring.

[0154] In addition to this, the PVA-based polymer (A) can also be completely saponified, the sample after Soxhlet extraction (for example, sodium acetate removed) is dissolved in water, a small amount of sodium hydroxide (NaOH) is added, and then conductometric titration is carried out with dilute hydrochloric acid, and thus the amount of carboxyl groups can be obtained from the titration amount of hydrochloric acid.

[0155] In addition, when the acetal skeleton having an ionic group is a structure that absorbs UV (ultraviolet rays), by measuring the UV absorbance of the aqueous solution containing the PVA-based polymer (A), the content of the acetal skeleton having an ionic group can be measured.

[0156] In addition, in the PVA-based polymer (A), with respect to 1 mole of the ionic skeleton (b) (such as the above-mentioned skeletons (1), (2) and / or (3)), the content of the acetal skeleton (a) (content per unit monomer unit) can be 50 moles or less (for example, 30 moles or less, 20 moles or less), preferably 15 moles or less, more preferably 10 moles or less, and can also be 0.05 moles or more (for example, 0.1 moles or more, 0.5 moles or more), preferably 1 mole or more, more preferably 2 moles or more, and particularly can be 3 moles or more.

[0157] When the ratio is such, it is easy to balance the excellent preparation property and storage stability of the aqueous solution, etc., and the excellent performance as a dispersion stabilizer.

[0158] In addition, the method for introducing the ionic skeleton (b) can be a known method according to its embodiment. As such an introduction method, for example, the following can be cited: (1) a method of obtaining a PVA-based polymer (sometimes referred to as a PVA-based polymer (C)) having an ionic group by acetalizing a PVA-based polymer with a carbonyl compound having an ionic group (aldehyde, its acetal, ketone, etc., particularly an aldehyde); (2) a method of copolymerizing a monomer having an ionic group with a vinyl ester to obtain a polyvinyl ester-based polymer having an ionic group, and then saponifying it to obtain a PVA-based polymer (B-3) having an ionic group; (3) a method of polymerizing a vinyl ester in the presence of a chain transfer agent having an ionic group (alcohol, aldehyde, thiol, etc.) and saponifying the resulting polyvinyl ester-based polymer (having an ionic group) to obtain a PVA-based polymer (B-4) having an ionic group, etc.

[0159] Hereinafter, each embodiment of the ionic skeleton (b) will be described in detail.

[0160] ((1) Acetal skeleton having an ionic group)

[0161] As described above, the acetal skeleton (acetal group, acetal unit) has an ionic group (the ionic group is substituted on the acetal skeleton).

[0162] The acetal can be either a cyclic acetal or an acyclic (chain-like) acetal, and preferably a cyclic acetal.

[0163] The representative acetal skeleton having an ionic group includes the skeleton (structural unit) represented by the following formula (b1). Therefore, the acetal skeleton having an ionic group can include the skeleton represented by the following formula (b1).

[0164] [Chemical formula 3]

[0165]

[0166] In formula (b1), R represents a group having an ionic group.

[0167] In the above formula (b1), R is a group having an ionic group. R can be the ionic group itself or a linking group having an ionic group (a group composed of an ionic group and the ionically substituted linking group).

[0168] As the linking group (basic group), for example, a hydrocarbon group can be cited. As the hydrocarbon group, an aliphatic hydrocarbon group can be cited [for example, an alkyl group [for example, a linear alkyl group (for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, etc., C 1-30 alkyl), a cycloalkyl group (for example, cyclopentyl, cyclohexyl, etc., C 3-10saturated aliphatic hydrocarbon groups such as (cycloalkyl), aromatic hydrocarbon groups [e.g., aryl (e.g., phenyl, tolyl, xylyl, naphthyl, etc., C 6-20 aryl), aralkyl (e.g., benzyl, phenethyl, etc., C 6-20 aryl-C 1-4 alkyl), etc.] etc.

[0169] In addition to ionic groups, the linking group (hydrocarbon group) may also have substituents (substituents that are not ionic groups). There is no particular limitation on the substituents, and examples thereof include a hydroxyl group, a halogen atom, an acyl group, an ester group, an alkoxy group, a nitro group, a group different from the basic group (e.g., an aromatic group such as aryl), etc.

[0170] The substituents may substitute the linking group (hydrocarbon group) alone or in combination of two or more.

[0171] In the linking group (hydrocarbon group, etc.) having an ionic group, the number of ionic groups may be one or more, and two or more ionic groups may also substitute the linking group.

[0172] As a specific acetal skeleton having an ionic group (the skeleton represented by formula (b1)), for example, a skeleton in which R in the formula (b1) is an ionic group (e.g., a carboxyl group and its salts, etc.), and a skeleton represented by the following formula (b1-1) can be cited.

[0173] [Chemical formula 4]

[0174]

[0175] In formula (b1-1), R1 to R5 represent a hydrogen atom or a substituent. Among them, at least one of R1 to R5 is an ionic group.

[0176] In the above formula (b1-1), as the ionic group and the substituent, the groups exemplified above can be cited. At least one of R1 to R5 is an ionic group, and any one can be preferably an ionic group. Representatively, one of R1 to R5 can be an ionic group (e.g., a carboxyl group, a sulfonate group, or their salts), and four are hydrogen atoms.

[0177] In addition, the acetal skeleton having an ionic group {e.g., the group represented by formula (b1) (or R-< in formula (b1))} can be derived from a corresponding carbonyl compound (e.g., an aldehyde, its acetal, a ketone, etc.), especially an aldehyde (e.g., RCHO). In addition, the carbonyl compound may have a substituent.

[0178] As such carbonyl compounds, for example, alkanals having an ionic group (e.g., glyoxylic acid, formylacetic acid, formylpropionic acid, salts thereof, etc., alkanals having an acid radical or its salt), arenecarbaldehydes having an ionic group [e.g., carboxybenzaldehyde (e.g., p-carboxybenzaldehyde), sulfobenzoaldehyde (e.g., o-sulfobenzoaldehyde, 4-formylbenzene-1,3-disulfonic acid), salts thereof, etc., aromatic aldehydes having an acid radical or its salt], etc. aldehydes (especially monoaldehydes), corresponding ketones, acetals, etc.

[0179] In addition, when isomers (e.g., cis-trans isomers, etc.) exist in the carbonyl compound, any one of the isomers (e.g., both the cis form and the trans form, etc.) may be included.

[0180] Furthermore, in the PVA-based polymer (A), as long as an ionic group can be formed, the ionic group in the carbonyl compound can be derivatized (esterification, anhydration, etc.).

[0181] For example, even if they are esters (e.g., alkyl esters) or acid anhydrides, as long as they can form (e.g., by hydrolysis) the corresponding acid radical (carboxyl group, sulfonic acid group) or its salt in the PVA-based polymer (A), they can still be used (hereinafter, the same applies to the ionic group).

[0182] These carbonyl compounds can be used alone or two or more of them can be used simultaneously.

[0183] In addition, from the viewpoint of water solubility, etc., the carbonyl compound is preferably composed of a monocarbonyl compound (monoaldehyde, etc.). Even when a polycarbonyl compound (e.g., polyaldehyde such as dialdehyde) is used, in most cases, its amount is reduced, etc., and it is used at a level that can ensure water solubility, etc.

[0184] In addition, the acetal skeleton having an ionic group (e.g., the acetal skeleton represented by the formula (b1)) can be a skeleton that can be introduced via a hydroxyl group. For example, it can be an acetal skeleton derived from two adjacent hydroxyl groups (e.g., the hydroxyl groups of vinyl alcohol units) (introduced via two adjacent hydroxyl groups (e.g., the hydroxyl groups of vinyl alcohol units)).

[0185] For example, when using a carbonyl compound having an ionic group (aldehyde, ketone, etc.), for example, two adjacent OH groups in the PVA-based polymer are acetalized with a carbonyl compound having an ionic group, whereby a PVA-based polymer (A) containing an acetal skeleton having an ionic group can be obtained.

[0186] The acetal skeleton having an ionic group (e.g., the acetal skeleton represented by the formula (b1)) may have a polymerizable unsaturated bond or may not have a polymerizable unsaturated bond.

[0187] The PVA-based polymer (A) may or may not contain an acetal skeleton having an ionic group.

[0188] The PVA-based polymer (A) may contain alone an acetal skeleton having an ionic group or may contain in combination two or more acetal skeletons having an ionic group.

[0189] The method for incorporating (introducing) an acetal skeleton having an ionic group (for example, an acetal skeleton having a carboxyl group, a sulfonate group, or a salt thereof) into the PVA-based polymer (A) is not particularly limited and conventional methods can be used.

[0190] As described later, in a representative method, the PVA-based polymer (C) can be acetalized using a carbonyl compound having an ionic group (aldehyde, its acetal, ketone, etc.).

[0191] In addition, by acetalizing the PVA-based polymer (C) using a carbonyl compound having an ionic group in the above manner, a PVA-based polymer (B-1) having an ionic group can be obtained. By making a carbonyl compound having a polymerizable unsaturated bond coexist during acetalization, a PVA-based polymer (A) having both an acetal skeleton (a) and an ionic group can be obtained, which is thus preferable.

[0192] Examples of the aldehyde having an ionic group include glyoxylic acid, o-carboxybenzaldehyde, p-carboxybenzaldehyde, sodium benzenesulfonate-2-carboxaldehyde, sodium benzenesulfonate-4-carboxaldehyde, disodium 4-formylbenzene-1,3-disulfonate, etc. p-Carboxybenzaldehyde or sodium benzenesulfonate-2-carboxaldehyde, etc. are preferred.

[0193] As described above, as the carbonyl compound, an acetal which is a condensate of an aldehyde and an alcohol can also be used. The acetal is not particularly limited, and examples thereof include condensates with primary alcohols (for example, methanol, etc.).

[0194] The carbonyl compounds can be used alone or in combination of two or more.

[0195] ((2) Skeleton corresponding to the monomer having an ionic group)

[0196] The monomer having an ionic group (monomer) is not particularly limited and can be appropriately selected according to the type of the ionic group.

[0197] As specific monomers, for example, monomers having an acid group can be cited [for example, monomers having a carboxyl group, such as monocarboxylic acids (such as aliphatic unsaturated monocarboxylic acids like acrylic acid, methacrylic acid, crotonic acid, etc.), polycarboxylic acids (such as aliphatic unsaturated dicarboxylic acids like itaconic acid, maleic acid, fumaric acid, etc.), their salts, etc.], monomers having a sulfonic acid group [such as alkenyl sulfonic acids (such as vinyl sulfonic acid, propene sulfonic acid), alkenyl aromatic sulfonic acids (such as styrene sulfonic acid), sulfonic acid group-containing amide monomers (such as 2-acrylamide-2-methylpropanesulfonic acid), their salts, etc.], monomers having other ionic groups [such as monomers having an amino group (such as (meth)acrylamidopropyldimethylamine, etc.), their salts, etc.].

[0198] In addition, as described above, as long as an ionic group can be introduced into the PVA-based polymer (A) (for example, as long as an ionic group is finally formed in the PVA-based polymer (A) through hydrolysis or the like), the above compounds can also be derivatives [such as acid anhydrides (such as maleic anhydride, etc.), esters (such as alkyl esters)].

[0199] In other words, the above derivatives can also be called derivatives capable of forming ionic groups. If specific examples are cited, even if acrylate is used, as long as acrylic acid or its salt is finally introduced into the PVA-based polymer (A). Therefore, acrylate can introduce a skeleton corresponding to acrylic acid or its salt into the PVA-based polymer (A).

[0200] These monomers can be used alone or in combination of two or more.

[0201] As described above, for example, by saponifying a polyvinyl ester-based polymer containing an ionic group obtained by copolymerizing a monomer having such an ionic group with a vinyl ester, a PVA-based polymer (B-3) containing an ionic group can be obtained.

[0202] ((3) Skeleton corresponding to a compound capable of introducing other ionic groups)

[0203] In this skeleton (3), as compounds capable of introducing ions, as described above, for example, alcohols having an ionic group, carbonyl compounds having an ionic group (aldehydes, ketones, etc., especially aldehydes, etc.), thiols having an ionic group, etc. can be cited. These compounds generally function as chain transfer agents.

[0204] Among them, from the perspective of high chain transferability (and thus easy introduction of ionic groups), thiols are preferred.

[0205] As thiols having ionic groups, for example, thiols having acid radicals can be mentioned [for example, thiols having carboxyl groups [for example, mercapto saturated fatty acids (for example, mercaptoalkanoic acids such as 3-mercaptopropionic acid, mercaptosuccinic acid, etc.)], thiols having sulfonic acid radicals [for example, mercaptoalkanesulfonic acids (for example, 3-mercapto-1-propanesulfonic acid)], their salts (for example, sodium 3-mercapto-1-propanesulfonate), etc.].

[0206] As described above, for example, by polymerizing vinyl esters in the presence of such a chain transfer agent having an ionic group (alcohol, aldehyde, thiol, etc.), an ionic group derived from the chain transfer agent can be introduced into the terminal of the vinyl ester-based polymer. Then, by saponifying the vinyl ester-based polymer, a PVA-based polymer (B-4) containing an ionic group at the terminal can be obtained.

[0207] In addition, the PVA-based polymer (A) may have other acetal skeletons (acetal groups, acetal units) that do not belong to the scope of the acetal skeleton (a) and the acetal skeleton having an ionic group.

[0208] As such other acetal skeletons, skeletons in which R' in the formula (a1) is a group having no ionic group and no polymerizable unsaturated bond (for example, an aliphatic group, an aromatic group, etc.) can be mentioned. As such a group, for example, an aliphatic group [for example, an alkyl group (for example, a C 1-30 alkyl group such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, etc.), a cycloalkyl group (for example, a C 3-20 cycloalkyl group such as cyclopentyl, cyclohexyl, etc.)], an aromatic group [for example, an aryl group (for example, a C 6-20 aryl group such as phenyl, naphthyl, etc.)], etc.

[0209] The method for introducing such other acetal skeletons is not particularly limited, and a conventional method can be used. For example, a method of acetalizing a PVA-based polymer (C) with an aldehyde corresponding to the other acetal skeleton can be mentioned. In addition, in this method, usually, other acetal skeletons are formed from two adjacent vinyl alcohol units.

[0210] As such an aldehyde, for example, an alkanal [for example, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, 2-methylbutyraldehyde, 2-ethylbutyraldehyde, 2-methylvaleraldehyde, 2-ethylhexanal], a cycloalkanecarbaldehyde [for example, cyclopentanecarbaldehyde (cyclopentyl aldehyde), cyclohexanecarbaldehyde (cyclohexyl aldehyde), etc.], etc., aliphatic aldehydes, and aromatic aldehydes such as arene formaldehyde (for example, benzaldehyde, naphthaldehyde, etc.) can be mentioned.

[0211] The PVA-based polymer (A) has at least vinyl alcohol units and may also have units that are not hydrolyzed (saponified) [such as vinyl ester units (or units derived from vinyl ester monomers, such as vinyl acetate units, etc.)].

[0212] In addition, the PVA-based polymer (A) may have other units as needed (units other than the vinyl alcohol units, the units that are not hydrolyzed, the acetal skeleton (a), the ionic skeleton (b), etc., as exemplified above). As such units, units derived from other monomers exemplified in the section on the PVA-based polymer (C) described below can be cited.

[0213] The saponification degree of the PVA-based polymer (A) can be, for example, 20 mol% or more (such as 25 mol% or more), preferably 30 mol% or more (such as 35 mol% or more), more preferably 40 mol% or more (such as 45 mol% or more), and particularly can be 50 mol% or more (such as 55 mol% or more, 60 mol% or more).

[0214] The upper limit value of the saponification degree of the PVA-based polymer (A) can be, for example, 95 mol% or less (such as 93 mol% or less), preferably 90 mol% or less (such as 88 mol% or less), more preferably 85 mol% or less (such as 80 mol% or less).

[0215] Specifically, the saponification degree of the PVA-based polymer (A) can be, for example, 20 to 90 mol% (such as 50 to 90 mol%), preferably 55 to 85 mol%, and more preferably around 60 to 80 mol%.

[0216] When the saponification degree is not too low, the preparation property, storage stability, and warm water dispersibility of the aqueous solution are excellent, so it is preferred. When the saponification degree is not too high, it is preferred in terms of several points such as being prone to exhibit excellent performance as a dispersant (such as excellent aggregation stability, appropriate average particle size, or being prone to effectively obtain a vinyl chloride-based resin with high plasticizer absorbability).

[0217] In addition, the saponification degree is determined, for example, by the method for measuring the saponification degree of PVA specified in JIS K 6726.

[0218] When the PVA-based polymer (A) has vinyl ester units, the proportion (proportion of monomer units) of the ionic skeleton (b) can be 10 mol or less, preferably 5 mol or less, more preferably 3 mol or less, and can be 0.01 mol or more (such as 0.05 mol or more, 0.1 mol or more), preferably 0.2 mol or more, and more preferably 0.3 mol or more, relative to 100 mol of vinyl ester units.

[0219] If it is such a ratio, it is easy to balance excellent preparation properties and storage stability of an aqueous solution, etc., and excellent properties as a dispersion stabilizer.

[0220] The viscosity (20 °C) of a 4 mass% aqueous solution of the PVA-based polymer (A) is not particularly limited. For example, it can be selected from the range of 1 mPa·s or more (e.g., 1.5 mPa·s or more), and can be 2 mPa·s or more (e.g., 2.2 mPa·s or more), preferably 2.5 mPa·s or more (e.g., 2.7 mPa·s or more), more preferably 3 mPa·s or more (e.g., 3.2 mPa·s or more, 3.4 mPa·s or more, 3.6 mPa·s or more), etc.

[0221] The upper limit value of the viscosity (20 °C) of a 4 mass% aqueous solution of the PVA-based polymer (A) is not particularly limited. For example, it can be selected from the range of 2000 mPa·s or less (e.g., 1500 mPa·s or less, 1000 mPa·s or less, 500 mPa·s or less), and typically, it can be selected from the range of 300 mPa·s or less (e.g., 250 mPa·s or less, 200 mPa·s or less, 150 mPa·s or less, 120 mPa·s or less, 100 mPa·s or less, 80 mPa·s or less, 50 mPa·s or less), and can be 30 mPa·s or less (e.g., 20 mPa·s or less), preferably 15 mPa·s or less (e.g., 10 mPa·s or less), more preferably 9 mPa·s or less (e.g., 8 mPa·s or less), etc.

[0222] Specifically, the viscosity (20 °C) of a 4 mass% aqueous solution of the PVA-based polymer (A) can be, for example, about 1 to 500 mPa·s (e.g., 2 to 300 mPa·s, 1 to 100 mPa·s, 2 to 100 mPa·s, 2.5 to 30 mPa·s), or can be about 20 mPa·s or less (e.g., 3 to 15 mPa·s, 3.2 to 10 mPa·s, 3.4 to 9 mPa·s, 3.6 to 8 mPa·s).

[0223] The (average) degree of polymerization of the PVA-based polymer (A) is not particularly limited. For example, it can be 100 or more (e.g., 120 or more), preferably 150 or more (e.g., 160 or more), more preferably 180 or more (e.g., 200 or more, 220 or more, 250 or more, 280 or more, 300 or more), etc.

[0224] The upper limit value of the (average) degree of polymerization of the PVA-based polymer (A) is not particularly limited. For example, it can be selected from the range of about 10,000 or less (e.g., 8,000 or less, 5,000 or less), can be 3,000 or less (e.g., 2,500 or less), preferably 2,000 or less (e.g., 1,500 or less), and more preferably 1,000 or less (e.g., 800 or less).

[0225] Specifically, the (average) degree of polymerization of the PVA-based polymer (A) can be, for example, 120 to 3,000 (e.g., 200 to 2,000), preferably 250 to 1,500, and more preferably about 300 to 1,000.

[0226] As long as the viscosity of the 4% by mass aqueous solution and the degree of polymerization of the PVA-based polymer (A) are not too small, it is advantageous in terms of polymerization stability, suppression of fouling adhesion, suppression of coarsening of the resulting vinyl-based resin, etc. In addition, as long as the viscosity of the 4% by mass aqueous solution and the degree of polymerization are not too large, it is advantageous in terms of excellent preparation property and storage stability of the aqueous solution, excellent warm water dispersibility, etc.

[0227] In addition, the viscosity of the 4% by mass aqueous solution (20 °C) is determined, for example, by the method specified in JIS K 6726. In addition, the degree of polymerization can be determined, for example, by the method specified in JIS K 6726, or can be a calculated (converted) value based on other analysis methods [e.g., a calculated value (converted value) based on the viscosity of the 4% by mass aqueous solution].

[0228] The cloud point of the 4% by mass aqueous solution of the PVA-based polymer (A) is preferably 20 °C or higher (e.g., higher than 20 °C, 22 °C or higher, 23 °C or higher, 24 °C or higher, 25 °C or higher), more preferably 27 °C or higher, and can be 30 °C or higher, etc.

[0229] The upper limit value of the cloud point of the 4% by mass aqueous solution of the PVA-based polymer (A) is not particularly limited. For example, it can be 75 °C, 70 °C, 65 °C, 60 °C, 55 °C, 50 °C, etc.

[0230] Typically, the cloud point of the 4% by mass aqueous solution of the PVA-based polymer (A) can be, for example, 25 to 50 °C, etc.

[0231] As long as it is the above cloud point, the preparation property and storage stability of the aqueous solution are excellent.

[0232] In addition, the cloud point of the 4% by mass aqueous solution can be adjusted according to the saponification degree, degree of polymerization, content of ionic skeleton (ionic group), etc. of the PVA-based polymer (A).

[0233] [Aqueous solution]

[0234] The PVA-based polymer (A) can be directly used as a dispersion stabilizer (dispersant), etc., or can be used in the form of an aqueous solution dissolved in water.

[0235] The aqueous solution of the present invention only needs to contain the PVA-based polymer (A) and water. The aqueous solution is formed, for example, by dispersing or dissolving the PVA-based polymer (A) as a dispersed substance in water.

[0236] In the aqueous solution, the content of the PVA-based polymer (A) is not particularly limited. For example, it can be about 1% by mass or more (e.g., 2% by mass or more, 3% by mass or more), and can be about 80% by mass or less (e.g., 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less).

[0237] The aqueous solution of the present invention has good stability.

[0238] From the perspective of improving the storage stability, a water-soluble organic solvent, etc. can be contained in the aqueous solution. Examples of the water-soluble organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; esters such as methyl acetate and ethyl acetate; and diol derivatives such as ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether. In addition, two or more of these organic solvents can be used in combination.

[0239] When a water-soluble organic solvent is contained, the proportion of the water-soluble organic solvent relative to the total solvent can be, for example, 70% by mass or less (e.g., 60% by mass or less), preferably 50% by mass or less, more preferably 30% by mass or less. In particular, from the perspective of environmental considerations and improvement of workability, the content of the organic solvent is preferably 5% by mass or less relative to the total solvent or the aqueous solution.

[0240] [Manufacturing method]

[0241] In the present invention, the method for preparing the PVA-based polymer (A) is not particularly limited. For example, the PVA-based polymer (A-1) can be obtained by acetalizing the PVA-based polymer (C) with an aldehyde having a polymerizable unsaturated bond.

[0242] When the PVA-based polymer (A) contains an ionic group, a carbonyl compound having a polymerizable unsaturated bond (e.g., a monoaldehyde) and a carbonyl compound having an ionic group (e.g., an aldehyde) are used, and at the same time, the PVA-based polymer (C) (without an ionic group) is subjected to an acetalization reaction, whereby the PVA-based polymer (A-2) containing an ionic group can be obtained.

[0243] In addition, by subjecting a PVA-based polymer (B-3 or B-4) having an ionic group to an acetalization reaction using a carbonyl compound having a polymerizable unsaturated bond (e.g., a monoaldehyde), a PVA-based polymer (A-3, A-4) containing an ionic group can be obtained.

[0244] Therefore, the process for preparing the PVA-based polymers (A-1, A-2, A-3, A-4) can be divided, for example, into: a process for preparing a PVA-based polymer (C) or a PVA-based polymer having an ionic group (B-3 or B-4), and a process for acetalizing any of these PVA-based polymers (acetalization process).

[0245] The method for preparing the PVA-based polymer (C) or the PVA-based polymer containing an ionic group (B-3 or B-4) is not particularly limited, and a conventionally known method can be used.

[0246] Hereinafter, the PVA-based polymers (B-3 or B-4) having an ionic group, the PVA-based polymer (C), and the acetalization process will be described in detail.

[0247] [PVA-based polymers (B-3), (B-4) and (C)]

[0248] The PVA-based polymer (C) is not particularly limited. For example, a PVA-based polymer obtained by saponifying (reacting) a vinyl ester-based polymer [saponified product of a vinyl ester-based polymer (a polymer containing a vinyl ester-based monomer as a polymerization component)] can be used.

[0249] In addition, the PVA-based polymers (B-3) and (B-4) can be obtained, for example, as described later by using other monomers containing monomers having an ionic group, chain transfer agents containing chain transfer agents having an ionic group, etc. in the preparation of the PVA-based polymer (C).

[0250] The vinyl ester-based polymer can be obtained by polymerizing at least a vinyl ester-based monomer (polymerizing as a polymerization component). The polymerization method is not particularly limited, and a conventionally known method can be used. For example, bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. can be mentioned. Considering the control of the degree of polymerization and the saponification reaction carried out after polymerization, solution polymerization using methanol as a solvent or suspension polymerization using water or water / methanol as a dispersion medium is preferred, but it is not limited thereto.

[0251] The vinyl ester-based monomers that can be used for the polymerization are not particularly limited. For example, fatty acid vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl octanoate, vinyl versatate, etc. can be mentioned. These vinyl ester-based monomers can be used alone or in combination of two or more. Among them, from an industrial perspective, vinyl acetate is preferred.

[0252] When polymerizing vinyl ester monomers, as long as the effects of the present invention are exerted, the vinyl ester monomers can be copolymerized with other monomers. In other words, the polymerization components of the vinyl ester polymer can include vinyl ester monomers and other monomers.

[0253] The other monomers that can be used are not particularly limited. For example, α-olefins (such as ethylene, propylene, n-butene, isobutene, etc.), (meth)acrylic acid and its salts, (meth)acrylic acid esters [such as (meth)acrylic acid alkyl esters (such as (meth)acrylic acid methyl ester, (meth)acrylic acid ethyl ester, (meth)acrylic acid n-propyl ester, (meth)acrylic acid isopropyl ester, (meth)acrylic acid n-butyl ester, (meth)acrylic acid isobutyl ester, (meth)acrylic acid tert-butyl ester, (meth)acrylic acid 2-ethylhexyl ester, (meth)acrylic acid dodecyl ester, (meth)acrylic acid octadecyl ester, etc. (meth)acrylic acid C 1-20 alkyl esters, etc.)], (meth)acrylamide, (meth)acrylamide derivatives (such as N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-hydroxymethyl(meth)acrylamide, etc.), vinyl ethers (such as methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tert-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. C 1-20 alkyl vinyl ethers, etc.), nitriles (such as acrylonitrile, methacrylonitrile, etc.), vinyl halides (such as vinyl chloride, vinyl fluoride, etc.), vinylidene dihalides (such as vinylidene dichloride, vinylidene difluoride, etc.), allyl compounds (such as allyl acetate, allyl chloride, etc.), vinyl silyl compounds (such as vinyltrimethoxysilane, etc.), fatty acid alkenyl esters (such as isopropyl acetate, etc.). These other monomers can be used singly or in combination of two or more.

[0254] Here, as the other monomers, by using other monomers containing monomers having ionic groups, the PVA-based polymer (B-3) can be obtained.

[0255] As monomers having ionic properties, the monomers exemplified above can be mentioned. For example, monomers having an acid group [for example, monomers having a carboxyl group, such as monocarboxylic acids (e.g., aliphatic unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, etc.), polycarboxylic acids (e.g., aliphatic unsaturated dicarboxylic acids such as itaconic acid, maleic acid, fumaric acid, etc.), their salts, etc.], monomers having a sulfonic acid group [for example, alkenyl sulfonic acids (e.g., vinyl sulfonic acid, propene sulfonic acid), alkenyl aromatic sulfonic acids (e.g., styrene sulfonic acid), amide-based monomers having a sulfonic acid group (e.g., 2-acrylamido-2-methylpropanesulfonic acid), their salts, etc.], monomers having other ionic groups [for example, monomers having an amino group (e.g., (meth)acrylamidopropyldimethylamine, etc.), their salts, etc.], etc.

[0256] When using other monomers, the content of the other monomers can be appropriately selected according to the monomers used, etc. For example, it can be, for example, 0.1 to 20% by mass relative to the total amount of the polymerization components.

[0257] In addition, when polymerizing vinyl ester monomers, a chain transfer agent can be made to coexist in order to adjust the degree of polymerization, etc. of the obtained vinyl ester polymer.

[0258] The chain transfer agent is not particularly limited. For example, aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, etc.; ketones such as acetone, methyl ethyl ketone, hexanone, cyclohexanone, etc.; thiols such as 2-hydroxyethanethiol, dodecyl mercaptan, 3-mercaptopropionic acid, mercaptosuccinic acid, sodium 3-mercapto-1-propanesulfonate, etc.; organic halides such as carbon tetrachloride, trichloroethylene, perchloroethylene, etc. can be mentioned.

[0259] Among them, according to the research of the inventors of the present application, it is known that if aldehydes or organic halides, etc. which are usually used as chain transfer agents are used, there seems to be a tendency for the hue to deteriorate (coloration) (although the reason is not certain, it is presumed that a structure that deteriorates the hue (coloration) is likely to be introduced at the terminal part, etc.). Therefore, even when aldehydes or organic halides are used, it is desirable to keep them at a level that fully satisfies requirements 2 to 4.

[0260] Here, as the chain transfer agent, by using a chain transfer agent containing a chain transfer agent having an ionic group, a PVA-based polymer (B-4) can be obtained.

[0261] As the chain transfer agent having an ionic group, the chain transfer agents exemplified above can be mentioned. For example, alcohols having an ionic group, carbonyl compounds having an ionic group, thiols having an ionic group {for example, thiols having an acid group [for example, thiols having a carboxyl group, such as mercapto saturated fatty acids (e.g., mercaptoalkanoic acids such as 3-mercaptopropionic acid, mercaptosuccinic acid, etc.)], thiols having a sulfonic acid group [for example, mercaptoalkanesulfonic acids (e.g., 3-mercapto-1-propanesulfonic acid)], their salts (e.g., sodium 3-mercapto-1-propanesulfonate), etc.}, etc.

[0262] The addition amount of the chain transfer agent is determined according to the chain transfer constant of the added chain transfer agent and the degree of polymerization of the target vinyl ester polymer. Generally, it is preferably 0.1 to 10% by mass based on the total amount of the polymerization components.

[0263] By subjecting the vinyl ester polymer obtained as described above to a saponification reaction, a PVA polymer (C) (and (B-3), (B-4)) can be prepared.

[0264] The method of the saponification reaction of the vinyl ester polymer is not particularly limited and can be carried out according to a conventionally known method. For example, an alcoholysis or hydrolysis reaction using an acidic catalyst such as hydroxides of alkali metals such as sodium hydroxide and potassium hydroxide, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid, and organic acids such as formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid can be applied.

[0265] Examples of the solvent used in the saponification reaction include alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; and aromatic hydrocarbons such as benzene and toluene. These solvents can be used alone or in combination of two or more.

[0266] When a gel-like product precipitates during the saponification reaction, a polyvinyl alcohol polymer can be obtained by crushing and drying the gel. It is preferable to neutralize the remaining catalyst before drying. When an alkali catalyst is used as the neutralizing agent, acidic substances such as acetic acid and phosphoric acid can be used, and when an acidic catalyst is used as the neutralizing agent, alkaline substances such as sodium hydroxide and potassium hydroxide can be used.

[0267] The drying of the polyvinyl alcohol polymer (C) (and (B-3), (B-4)) can be carried out in an oxidative atmosphere such as air or in an inert atmosphere (e.g., nitrogen).

[0268] In addition, the drying temperature can be normal temperature (natural drying), or it can be under heating or at a high temperature. From the perspective of effectively carrying out drying, the drying temperature can generally be 30°C or higher, 35°C or higher, 40°C or higher, 45°C or higher, 50°C or higher, 55°C or higher, 60°C or higher, 70°C or higher, etc. The upper limit value of the drying temperature is not limited. For example, it can be 250°C, 220°C, 200°C, 180°C, 160°C, 150°C, 140°C, 130°C, 120°C, 110°C, 100°C, 90°C, 80°C, etc.

[0269] Among them, according to the research of the inventors of the present application, it seems that there is a tendency for the hue to deteriorate (coloring) during drying in an atmosphere with a large amount of oxygen such as air or at high temperature (although the reason is uncertain, it is speculated that it is easy to introduce a structure that deteriorates the hue (colors) into the main chain, etc.). Therefore, even when drying in an oxidative atmosphere, under heating or at high temperature, it is desirable to remain at a level that fully satisfies Requirements 2 to 4.

[0270] From the above perspective, drying is preferably carried out in an inert atmosphere and is also preferably carried out at a temperature that is not too high (for example, 120 °C or lower, less than 120 °C, 115 °C or lower, 110 °C or lower, 100 °C or lower, 90 °C or lower, 70 - 110 °C, etc.).

[0271] In addition, the drying time is not particularly limited and can be selected according to the drying temperature, etc. For example, it can be about 1 to 12 hours.

[0272] [Acetalization]

[0273] In the present invention, for example, the method of acetalizing the PVA-based polymer [(C), (B-3), (B-4)] using a carbonyl compound having a polymerizable unsaturated bond (such as aldehyde) and a carbonyl compound having an ionic group is not particularly limited, and a known acetalization method can be adopted.

[0274] By acetalizing the PVA-based polymer (C) using a carbonyl compound having a polymerizable unsaturated bond, the PVA-based polymer (A-1) can be obtained. By acetalizing the PVA-based polymer (C) using a carbonyl compound having a polymerizable unsaturated bond and a carbonyl compound having an ionic group, the PVA-based polymer (A-2) can be obtained.

[0275] In addition, by acetalizing the PVA-based polymers (B-3, B-4) having an ionic group using a carbonyl compound having a polymerizable unsaturated bond, the PVA-based polymers (A-3, A-4) can be obtained.

[0276] In acetalization, the amount of the carbonyl compound used is not particularly limited. Relative to 100 parts by mass of the PVA-based polymer, the amount of the carbonyl compound used can be, for example, 0.05 - 50 parts by mass, preferably 0.1 - 20 parts by mass, and more preferably about 0.2 - 10 parts by mass.

[0277] In addition, the acetalization reaction is preferably carried out in the presence of an acidic catalyst. As the acidic catalyst, there is no particular limitation, and for example, inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; organic acids such as formic acid, acetic acid, oxalic acid, and p-toluenesulfonic acid, etc. can be cited.

[0278] The amount of the acidic catalyst is not particularly limited, and relative to 100 parts by mass of the PVA-based polymer, the amount of the acidic catalyst is, for example, 0.1 to 10 parts by mass.

[0279] As specific acetalization methods, for example, the following can be cited: (i) using an alkaline catalyst such as sodium hydroxide, saponifying an ethylene ester-based polymer in a solvent such as methanol to obtain a solution of the PVA-based polymer, then adding an aldehyde or the like and an acidic catalyst and performing acetalization, and then neutralizing with an alkaline substance to obtain a solution of the PVA-based polymer (A); (ii) in the presence of an acidic catalyst as a saponification catalyst, saponifying an ethylene ester-based polymer in a solvent such as methanol to prepare a PVA-based polymer, then adding an aldehyde or the like, directly using the acidic catalyst used in the saponification reaction to perform an acetalization reaction, and then neutralizing with an alkaline substance to obtain a solution of the PVA-based polymer (A); (iii) in the presence of an acidic catalyst and an aldehyde or the like, simultaneously performing a saponification reaction and an acetalization reaction on an ethylene ester-based polymer in a solvent, and then neutralizing with an alkaline substance to obtain a solution of the PVA-based polymer (A); (iv) adding an aldehyde or the like to an aqueous solution of the PVA-based polymer, reacting in the presence of an acidic catalyst, and then neutralizing with an alkaline substance to obtain an aqueous solution of the PVA-based polymer (A); (v) directly adding an aldehyde or the like to a pasty or powdery PVA-based polymer or adding a liquid obtained by dissolving or dispersing an aldehyde in an organic solvent or water, reacting in the presence of an acidic catalyst, then neutralizing with an alkaline substance, and further removing the excess solvent to obtain the PVA-based polymer (A); etc.

[0280] In the methods (i) to (iii), the solvent can be dried later and obtained in a solid form, or the solvent can be replaced with water to prepare an aqueous solution.

[0281] In the method (iv), the PVA-based polymer (A) can be obtained in the form of an aqueous solution, and thus can be directly used for suspension polymerization of vinyl chloride or the like.

[0282] The method of reacting in a paste state in (v) can easily obtain the PVA-based polymer (A) in a solid form, and thus is easy to operate.

[0283] In addition, in the methods (i) to (v), the method of preparing the PVA-based polymer into an aqueous solution, the methods of saponification, neutralization, dissolution, dispersion, and drying are not particularly limited, and conventional methods can be adopted.

[0284] In addition, as the alkaline substance for neutralization, there is no particular limitation, and for example, alkali metal hydroxides such as sodium hydroxide and potassium hydroxide can be cited.

[0285] From the perspective of reaction rate, the pH of the reaction solution during acetalization reaction is preferably 3.0 or less, more preferably 1.0 or less. In addition, the pH of the neutralized reaction solution is preferably 4.7 - 9.0, more preferably 7.0 - 8.5.

[0286] The drying of the polyvinyl alcohol polymer (A) can be carried out in the same manner as that of the polyvinyl alcohol polymer (C) (and (B-3), (B-4)). The drying conditions [drying atmosphere, drying temperature, drying time (such as 1 - 12 hours, etc.) etc.] and preferred options (and their reasons) are also preferably carried out under the conditions as described above (such as in an inert atmosphere like nitrogen, at a not-too-high temperature (such as 70 - 110 °C, etc.)).

[0287] [Use, preparation method of vinyl polymer, etc.]

[0288] The PVA-based polymer (A) can be used for various purposes (such as dispersant, film applications, etc.). As described above, it is particularly suitable for use as a dispersion stabilizer [or dispersant, for example, a dispersion stabilizer (dispersant) used in polymerization (such as suspension polymerization)].

[0289] Therefore, hereinafter, the use of the dispersion stabilizer based on the present invention (or the PVA-based polymer (A), the same hereinafter), and the preparation method of the vinyl polymer by polymerization of vinyl monomers (especially suspension polymerization) using this dispersion stabilizer will be described.

[0290] The suspension polymerization in the present invention refers to a polymerization method in which a vinyl monomer insoluble in an aqueous medium and an oil-soluble polymerization initiator are added to an aqueous medium and stirred, thereby forming fine droplets containing the vinyl monomer, and polymerization is carried out in these droplets. The aqueous medium that can be used here is not particularly limited, and examples thereof include water, an aqueous solution containing various additives, a mixed solvent of an organic solvent compatible with water and water, etc.

[0291] The above PVA-based polymer (A) in the present invention can be used as a dispersion stabilizer during the suspension polymerization of vinyl monomers. The vinyl monomer is not particularly limited, and for example, vinyl chloride, vinylidene chloride, styrene, acrylate, methacrylate, vinyl acetate, acrylonitrile, etc., which are commonly used in suspension polymerization, are preferred. Among them, vinyl chloride-based monomers are particularly preferred.

[0292] As vinyl chloride-based monomers, for example, vinyl chloride monomer (vinyl chloride) can be cited. In addition, mixtures of vinyl chloride monomer and other monomers copolymerizable with vinyl chloride monomer can be cited. As other monomers copolymerizable with vinyl chloride monomer, for example, monomers such as vinylidene chloride, vinyl acetate, ethylene, propylene, acrylic acid, acrylate, methacrylic acid, methacrylate, styrene, vinylalkoxysilane, maleic acid, hydroxyalkyl acrylate, propene sulfonic acid, vinyl sulfonic acid, etc. can be cited.

[0293] Therefore, the dispersion stabilizer of the present invention is suitable for the suspension polymerization of vinyl-based monomers containing vinyl chloride-based monomers (especially vinyl chloride), and can be particularly suitable for the homopolymerization of vinyl chloride by suspension polymerization. In addition, it can also be used for the binary or higher-order copolymerization of vinyl chloride with one or more of the known monomers copolymerizable with vinyl chloride by suspension polymerization. Among them, it can be particularly suitable as a dispersion stabilizer in the copolymerization of vinyl chloride and vinyl acetate by suspension polymerization.

[0294] By subjecting vinyl-based monomers containing vinyl chloride to suspension polymerization, vinyl chloride-based resins can be obtained. In the preparation of vinyl chloride-based resins, it is preferably 50 to 100 mol% (or 50 to 100% by mass) of vinyl chloride relative to the total amount of vinyl-based monomers used.

[0295] The polymerization initiator in the suspension polymerization of vinyl-based monomers can be a known polymerization initiator. For example, percarbonate compounds such as diisopropyl peroxydicarbonate, bis(2-ethylhexyl) peroxydicarbonate, bis(ethoxyethyl) peroxydicarbonate, perester compounds such as benzoyl peroxide, tert-butyl peroxyneodecanoate, cumyl peroxyneodecanoate, tert-butyl peroxydecanoate, peroxides such as acetyl cyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxybenzyloxyacetate, azo compounds such as 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), benzoyl peroxide, lauroyl peroxide, etc. can be cited. Further, potassium persulfate, ammonium persulfate, hydrogen peroxide, etc. can also be used in combination with them.

[0296] As the main function of the dispersion stabilizer in the suspension polymerization of vinyl-based monomers, it stabilizes the droplets composed of vinyl-based monomers and their polymers, preventing the polymer particles generated from the droplets from fusing with each other between the droplets and then forming larger lumps. Due to its excellent dispersion performance, the dispersion stabilizer of the present invention can form stable droplets with a smaller amount and can prevent the formation of lumps due to the above-mentioned fusion.

[0297] In addition, droplet stability means that droplets of small and substantially uniform size are stably dispersed in the dispersion medium of suspension polymerization.

[0298] In the suspension polymerization of vinyl monomers, the amount of the dispersion stabilizer (or PVA-based polymer (A)) of the present invention is not particularly limited, and is usually 5 parts by mass or less, preferably 0.005 to 1 part by mass, and more preferably 0.01 to 0.2 part by mass, relative to 100 parts by mass of the vinyl monomer. The dispersion stabilizer of the present invention is the same as a general dispersion stabilizer, and is usually dissolved in a dispersion medium for suspension polymerization by a conventional method before adding the vinyl monomer and then used.

[0299] As the dispersion stabilizer in the suspension polymerization of vinyl monomers, the dispersion stabilizer of the present invention can be used alone, or other dispersion stabilizers can be used simultaneously. As such other dispersion stabilizers, known dispersion stabilizers used in the suspension polymerization of vinyl monomers such as polyvinyl chloride in an aqueous medium can be cited. For example, PVA having an average degree of polymerization of 100 to 4500 and a saponification degree of 30 to 100 mol%, or modified PVA-based polymers other than the present invention, water-soluble cellulose ethers such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, water-soluble polymers such as gelatin, oil-soluble emulsifiers such as sorbitan monolaurate, sorbitan trioleate, glyceryl tristearate, and ethylene oxide-propylene oxide block polymers, and water-soluble emulsifiers such as polyoxyethylene glyceryl oleate and sodium laurate. These other dispersants can be used singly or two or more of them can be used simultaneously.

[0300] In the present invention, as the dispersion stabilizer, it is preferable to use in combination two or more PVA-based polymers having different degrees of polymerization and saponification degrees, and it is preferable to set one or more of them as the PVA-based polymer (A) which is the dispersion stabilizer of the present invention. More preferably, a PVA-based polymer having a high dispersion stability with a degree of polymerization of 1700 or more and a PVA-based polymer having a degree of polymerization of 1000 or less are used in combination, and one or more of them are set as the PVA-based polymer (A) of the present invention.

[0301] In the suspension polymerization using the dispersion stabilizer of the present invention, various known dispersion aids can also be used simultaneously. As the dispersion aid, low saponification degree PVA having a saponification degree preferably of 30 to 60 mol%, more preferably of 35 to 55 mol% can be used. In addition, as the dispersion aid, PVA having an average degree of polymerization preferably of 160 to 900, more preferably of 200 to 500 can be used.

[0302] In addition to the dispersion aid, various additives known in the suspension polymerization of vinyl compounds such as a chain transfer agent, a polymerization inhibitor, a pH adjuster, a fouling inhibitor, and a crosslinking agent can also be used simultaneously.

[0303] The polymerization temperature in suspension polymerization is not limited and can be arbitrarily selected according to the type of vinyl monomer used, the degree of polymerization of the target polymer, the polymerization yield, etc., but is usually preferably 40 to 70 °C. The polymerization time is not particularly limited either and can be appropriately set according to the target polymerization yield, etc.

[0304] The vinyl polymer obtained by the preparation method of the present invention described above can be processed into various molded articles, etc. In particular, for vinyl chloride resins, for example, vinyl chloride resins with an average particle size falling within a suitable range and excellent plasticizer absorbability can be effectively obtained, and in most cases, the processability into various molded articles is good.

[0305] Examples

[0306] Examples are listed below to further illustrate the present invention in detail and specifically, but the present invention is not limited by any of these examples.

[0307] In addition, in the following examples and comparative examples, unless otherwise specified, “%” and “parts” refer to “mass %” and “mass parts”.

[0308] First, the evaluation methods for the PVA polymer (A) and the vinyl chloride polymer (vinyl chloride resin) in this example are shown below.

[0309] (Method for measuring degree of polymerization and viscosity of 4% aqueous solution at 20 °C (4% viscosity))

[0310] The measurement is carried out according to the method specified in JIS K 6726.

[0311] (Method for measuring saponification degree)

[0312] The measurement is carried out according to the method specified in JIS K 6726.

[0313] (Method for measuring the content of polymerizable unsaturated bonds contained in PVA)

[0314] In an Erlenmeyer flask, a 0.5 mol / L bromine acetic acid solution is added dropwise to an aqueous solution obtained by dissolving 5 g of the sample (PVA) in 150 g of pure water, and the titration is carried out until the color of bromine (yellow) disappears. By dividing the amount of substance of bromine (μmol) required for titration by the weight (g) of PVA, the content of polymerizable unsaturated bonds (μmol / g) contained in PVA is calculated.

[0315] (Method for measuring YI of PVA aqueous solution)

[0316] Prepare a 4% aqueous solution, and measure its UV-Vis spectrum (quartz cuvette with an optical path length of 10 mm) at 20 °C using a UV-Vis spectrophotometer (manufactured by JASCO Corporation; V-730). Calculate the YI of the 4% aqueous solution from the obtained data.

[0317] (Method for measuring YI of PVA)

[0318] Measure the YI using a color difference meter (manufactured by NIPPON DENSHOKU INDUSTRIES Co., Ltd.; NW-12).

[0319] For the measurement sample (test powder), use the PVA (powder) obtained by passing the pulverized PVA (powder) through a metal mesh (sieve) with a mesh size of 0.5 mm (3 sieve).

[0320] (Method for measuring the transmittance of a PVA aqueous solution at 430 nm)

[0321] Prepare a 1% aqueous solution of PVA, and measure its transmittance at 430 nm at 20 °C using a UV-Vis spectrophotometer (manufactured by JASCO Corporation; V-730) (quartz cuvette with an optical path length of 20 mm, blank: pure water).

[0322] (Method for measuring the cloud point of a PVA aqueous solution)

[0323] Add a 4% PVA aqueous solution at 20 °C to a quartz cuvette with an optical path length of 10 mm, and use a UV-Vis spectrophotometer (manufactured by JASCO Corporation; V-730) to continuously measure the transmittance at 430 mm starting from a temperature of 20 °C at a heating rate of 2 °C per minute. Take the temperature at which the transmittance is 50% relative to the blank (pure water) as the cloud point.

[0324] (Method for evaluating the storage stability of a PVA aqueous solution)

[0325] Place a beaker containing a 4% PVA aqueous solution in a constant temperature water bath at 30 °C, visually confirm the state of the aqueous solution after 24 hours, and evaluate it according to the following criteria.

[0326] 〇: The aqueous solution maintains a uniform state.

[0327] ×: The aqueous solution separates into two layers.

[0328] (Evaluation of vinyl chloride polymer)

[0329] Evaluate the vinyl chloride polymer in the following manner.

[0330] <Average particle size>

[0331] The particle size distribution was measured using a Ro-Tap shaker (with JIS sieves), and the average particle diameter was determined.

[0332] <Plasticizer absorbability>

[0333] The obtained resin was added to a cylindrical container lined with glass fiber at the bottom, an excessive amount of dioctyl phthalate (hereinafter abbreviated as DOP) was added, and it was left for 30 minutes to allow DOP to penetrate the resin. Then, centrifugation was carried out at 3000 rpm to remove the excess DOP. Subsequently, the weight of the resin was measured, and the DOP absorption per 100 parts of the polymer was calculated. The larger the DOP absorption, the better the plasticizer absorbability and the more excellent the molding processability.

[0334] <Evaluation of the coloring property of vinyl chloride polymers>

[0335] 100 parts by weight of a vinyl chloride polymer, 50 parts by weight of di-2-ethylhexyl phthalate, 0.8 parts by weight of a dioctyltin mercapto stabilizer, 0.1 parts by weight of a polyethylene-based lubricant, and 0.8 parts by weight of a calcium-zinc-based composite (one pack) stabilizer were blended. The mixture was kneaded at 160 °C for 5 minutes using a test roll and formed into a sheet with a thickness of 0.45 mm.

[0336] Multiple sheets of the above-mentioned sheets were laminated and pressed at 160 °C for 5 minutes to produce a test piece of 40 mm × 40 mm × 15 mm (thickness). The YI of this test piece was measured using a color difference meter.

[0337] [Example 1]

[0338] (Synthesis of PVA-based polymer (C))

[0339] 55 parts of methanol and 45 parts of vinyl acetate monomer were pre-loaded into a reactor equipped with a stirrer, a condenser, a nitrogen inlet, and an initiator inlet. While circulating nitrogen in the system, the temperature was raised to 60 °C, and a 1% methanol solution of 5 parts of 2,2’-azobis(2,4-dimethylvaleronitrile) (ADVN) as an initiator was added to start the polymerization.

[0340] During polymerization, the system was maintained at 60°C while flowing nitrogen gas through the system. Immediately after the start of polymerization, 90 parts of vinyl acetate monomer were continuously added over 4 hours. At the 1-hour and 2-hour time points from the start of polymerization, 1 part of a 1% methanol solution of ADVN was added respectively. When the reaction yield of vinyl acetate reached 85%, the system was cooled to end the polymerization. In addition, the acetaldehyde concentration at the end of polymerization was 100 ppm. While introducing methanol vapor into the obtained polymer, the residual vinyl acetate monomer was removed by distillation to obtain a 50% methanol solution of polyvinyl acetate.

[0341] Next, 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide were added to 100 parts of the above-obtained 50% methanol solution of polyvinyl acetate and mixed well, and a saponification reaction was carried out at 40°C. The obtained gel-like substance was crushed and immersed in a mixed solvent (200 parts) of 100 parts of methanol and 100 parts of methyl acetate, and acetic acid was added for neutralization until the pH reached 9. Next, the sample obtained by solid-liquid separation was dried at 80°C for 5 hours under a nitrogen atmosphere. As a result of analysis, a powder of a PVA-based polymer (C) with a saponification degree of 76 mol% and a viscosity of a 4 mass% aqueous solution (20°C) of 5.5 mPa·s was obtained.

[0342] (Synthesis of PVA-based polymer (A-1))

[0343] 100 parts of the above-obtained powder of the PVA-based polymer (C) was immersed in a mixed solvent of 150 parts of methanol and 300 parts of methyl acetate, 0.8 part of acrolein was added, and it was directly maintained at 50°C for 1 hour, then 5 parts of a 50% methanol solution of p-toluenesulfonic acid was added, and the reaction was carried out at 50°C for 1 hour.

[0344] Next, it was neutralized with 10 parts of a 5% methanol solution of sodium hydroxide. The pH after neutralization was 7.5.

[0345] Next, the solvent was removed by centrifugation and then dried at 80°C for 5 hours under a nitrogen atmosphere to obtain a PVA-based polymer (A-1). The analytical values of this PVA-based polymer (A-1) were: saponification degree of 77 mol%, viscosity of a 4 mass% aqueous solution (20°C) of 5.8 mPa·s (average degree of polymerization was about 600), cloud point of a 4% aqueous solution was 35°C. In addition, the saponification degree and degree of polymerization were measured according to the method specified in JIS K 6726.

[0346] The content of double bonds derived from acrolein was 80 μmol / g, the YI of the PVA powder was 2, the YI of a 4 wt% aqueous solution was 7, and the transmittance at 430 nm was 98%. In addition, even when a 4% PVA aqueous solution was maintained at 30°C for 24 hours, the aqueous solution remained in a uniform state.

[0347] (Suspension polymerization of vinyl chloride)

[0348] The PVA-based polymer (A-1) obtained above was used as a dispersion stabilizer, and suspension polymerization of vinyl chloride was carried out under the conditions shown below.

[0349] 120 parts of deionized water and a 4% aqueous solution of 1.5 parts (0.06 part of the PVA-based polymer (A-1) relative to 100 parts of vinyl chloride monomer) of the PVA-based polymer (A-1) obtained above were placed in a pressure-resistant stainless steel polymerization machine. Then, the inside of the polymerization vessel was depressurized and degassed to 50 mmHg using a vacuum pump, 100 parts of vinyl chloride monomer was added, then 0.06 part of tert-butyl peroxypivalate as a polymerization initiator was added, and then stirring was started and the temperature was raised. Suspension polymerization was carried out while maintaining the internal temperature of the polymerization machine at 57 °C, and the polymerization reaction was stopped at the point when the conversion rate of vinyl chloride reached 88%. Then, the unreacted monomer was recovered using a pressure-reducing trap, and then the polymer slurry was taken out from the polymerization machine, dehydrated, and dried to obtain a vinyl chloride polymer (vinyl chloride resin).

[0350] [Examples 2 to 12]

[0351] The PVA-based polymer (A-1) shown in Table 1 was synthesized in the same manner as in Example 1, except that the polymerization conditions, saponification conditions, type and amount of aldehyde used for the acetalization reaction, etc. were appropriately changed.

[0352] Using the obtained PVA-based polymer (A-1), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0353] [Comparative Examples 1 to 4]

[0354] The PVA-based polymer (A-1) shown in Table 1 was synthesized in the manner described later, and using the obtained PVA-based polymer (A-1), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0355] The evaluation results of the PVA-based polymer (A-1) and the obtained vinyl chloride polymer are summarized in Table 1.

[0356] [Table 1]

[0357]

[0358] As shown in the above table, when the PVA-based polymers (A-1) obtained in Examples 1 to 12 were used for the suspension polymerization of vinyl chloride, vinyl chloride resins with excellent polymerization stability, an average particle size in an appropriate range, a large plasticizer absorption amount, reduced sheet coloring property, and excellent hue could be obtained.

[0359] [Comparative Example 1]

[0360] Except for drying the PVA-based polymer (C) at 150°C for 5 hours in an air atmosphere, the PVA-based polymer (A-1) was synthesized in the same manner as in Example 1. The hue of the obtained PVA-based polymer (A-1) deteriorated.

[0361] Attempted suspension polymerization of vinyl chloride in the same manner as in Example 1, and the sheet coloring property of the obtained vinyl chloride deteriorated.

[0362] [Comparative Example 2]

[0363] A PVA-based polymer (C) without double bonds having a 4 mass% aqueous solution viscosity (20°C) of 5.5 mPa·s (average degree of polymerization of about 600) and a saponification degree of 77 mol% was used as the PVA-based polymer (A-1), and suspension polymerization of vinyl chloride was attempted in the same manner as in Example 1, but the vinyl chloride resin caked (blocking) and the polymerization could not proceed normally.

[0364] [Comparative Example 3]

[0365] Polyvinyl acetate was obtained by polymerizing vinyl acetate in the presence of carbon tetrachloride, and then it was saponified according to Example 1 to obtain a PVA-based polymer having a 4 mass% aqueous solution viscosity (20°C) of 5.5 mPa·s (average degree of polymerization of about 600), a saponification degree of 77 mol%, a double bond content of 80 μmol / g, a YI of 35 for the PVA powder, a YI of 40 for the 4 wt% aqueous solution, and a transmittance of 80% at 430 nm for the 1 wt% aqueous solution. Using this PVA-based polymer, suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1, and the sheet coloring property of the obtained vinyl chloride resin deteriorated.

[0366] [Comparative Example 4]

[0367] Polyvinyl acetate was obtained by polymerizing vinyl acetate in the presence of acetaldehyde, and then it was saponified according to Example 1 to obtain a PVA-based polymer having a saponification degree of 77 mol% and a 4 mass% aqueous solution viscosity (20°C) of 5.5 mPa·s (average degree of polymerization of about 600). It was dried at 130°C for 5 hours in a nitrogen atmosphere to obtain a PVA-based polymer having a double bond content = 80 μmol / g, a YI of 45 for the PVA powder, a YI of 55 for the 4 wt% aqueous solution, and a transmittance of 65% at 430 nm for the 1 wt% aqueous solution. Using this PVA-based polymer, suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1, and the sheet coloring property of the obtained vinyl chloride resin deteriorated.

[0368] [Examples 13 to 15]

[0369] Except for appropriately changing the saponification conditions, the types (2 types) and amounts of aldehydes used in the acetalization reaction, etc., the PVA-based polymer (A-2) shown in Table 2 was synthesized in the same manner as in Example 1. Using the obtained PVA-based polymer (A-2), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer. The evaluation results of the PVA-based polymer (A-2) and the obtained vinyl chloride polymer are summarized in Table 2.

[0370] [Table 2]

[0371]

[0372] [Example 16]

[0373] (Synthesis of PVA-based polymer (B-3))

[0374] 55 parts of methanol and 45 parts of vinyl acetate monomer were pre-loaded into a reactor equipped with a stirrer, a condenser, a nitrogen inlet, and an initiator inlet. While flowing nitrogen through the system, the temperature was raised to 60 °C, and a 1% methanol solution of 6 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) as an initiator was added to start the polymerization.

[0375] During the polymerization, the system was maintained at 60 °C, and while flowing nitrogen through the system, 90 parts of vinyl acetate monomer and 2 parts of a 20% methanol solution of itaconic acid were continuously added for 4 hours immediately after the start of the polymerization. At the 1-hour and 2-hour time points from the start of the polymerization, 1.2 parts of a 1% methanol solution of ADVN were added respectively. The system was cooled at the time point when the reaction yield of vinyl acetate reached 85% to end the polymerization. While adding methanol vapor to the obtained polymer, the residual vinyl acetate monomer was distilled off to obtain a 50% methanol solution of polyvinyl acetate.

[0376] Next, 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide were added to 100 parts of the obtained 50% methanol solution of polyvinyl acetate and mixed well, and a saponification reaction was carried out at 40 °C. The obtained gel was crushed and immersed in a mixed solvent (200 parts) of 100 parts of methanol and 100 parts of methyl acetate, and acetic acid was added for neutralization until the pH reached 9. Then, the sample obtained by solid-liquid separation was dried in a nitrogen atmosphere at 80 °C for 5 hours. As a result of the analysis, a powder of PVA-based polymer (B-3) with a saponification degree of 71 mol%, a viscosity of 4 mass% aqueous solution (20 °C) of 5.5 mPa·s (average degree of polymerization of about 600), and an itaconic acid content of 0.2 mol% was obtained.

[0377] (Synthesis of PVA-based polymer (A-3))

[0378] The PVA-based polymer (A-3) shown in Table 3 was synthesized in the same manner as in Example 1.

[0379] (Suspension polymerization of vinyl chloride)

[0380] Using the obtained PVA-based polymer (A-3), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0381] [Examples 17 - 20]

[0382] Except for appropriately changing various conditions, the PVA-based polymer (A-3) shown in Table 3 was synthesized in the same manner as in Example 16.

[0383] Using the obtained PVA-based polymer (A-3), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0384] The evaluation results of the PVA-based polymer (A-3) and the obtained vinyl chloride polymer are summarized in Table 3. In addition, in the table, "AMPS" is sodium 2-acrylamido-2-methylpropanesulfonate.

[0385] [Table 3]

[0386]

[0387] [Example 21]

[0388] (Synthesis of PVA-based polymer (B-4))

[0389] 20 parts of methanol, 80 parts of vinyl acetate monomer, and 0.02 part of 3-mercaptopropionic acid were pre-charged into a reactor equipped with a stirrer, a condenser, a nitrogen inlet, and an initiator inlet. While flowing nitrogen through the system, the temperature was raised to 60°C, and a 1% methanol solution of 1.5 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) as an initiator was added to start the polymerization.

[0390] During the polymerization, the system was maintained at 60°C, and while flowing nitrogen through the system, a 1% methanol solution of 2 parts of 3-mercaptopropionic acid was continuously added for 4 hours immediately after the start of the polymerization. Then, at the 1-hour and 2-hour time points from the start of the polymerization, 0.5 part of a 1% methanol solution of ADVN was added respectively. The system was cooled at the time point when the reaction yield of vinyl acetate reached 80% to end the polymerization. While adding methanol vapor to the obtained polymer, the remaining vinyl acetate monomer was distilled off to obtain a 50% methanol solution of polyvinyl acetate.

[0391] Next, 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide were added to 100 parts of a 50% methanol solution of the above-obtained polyvinyl acetate, and the mixture was thoroughly mixed. A saponification reaction was carried out at 40°C. The resulting gel-like substance was pulverized and immersed in a mixed solvent (200 parts) of 100 parts of methanol and 100 parts of methyl acetate, and acetic acid was added for neutralization until the pH reached 9. Next, the sample obtained by solid-liquid separation was dried at 80°C for 5 hours under a nitrogen atmosphere. As a result of the analysis, a powder of a PVA-based polymer (B-4) having a saponification degree of 71 mol%, a viscosity of a 4 mass% aqueous solution (20°C) of 5.5 mPa·s (average degree of polymerization of about 600), and a 3-mercaptopropionic acid content of 0.2 mol% was obtained.

[0392] (Synthesis of PVA-based polymer (A-4))

[0393] The PVA-based polymer (A-4) shown in Table 4 was synthesized in the same manner as in Example 1.

[0394] (Suspension polymerization of vinyl chloride)

[0395] Using the obtained PVA-based polymer (A-4), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0396] [Examples 22 to 24]

[0397] Except for appropriately changing various conditions, the PVA-based polymer (A-4) shown in Table 4 was synthesized in the same manner as in Example 21.

[0398] Using the obtained PVA-based polymer (A-4), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1 to obtain a vinyl chloride polymer.

[0399] The evaluation results of the PVA-based polymer (A-4) and the obtained vinyl chloride polymer are summarized in Table 4. In addition, in the table, "MPS" is sodium 3-mercapto-1-propanesulfonate.

[0400] [Table 4]

[0401]

[0402] When the PVA-based polymers (A-2, A-3, A-4) obtained in Examples 13 to 24 were used for the suspension polymerization of vinyl chloride, vinyl chloride resins having excellent polymerization stability, an average particle size in an appropriate range, a large plasticizer absorption amount, reduced sheet coloring property, and excellent hue could be obtained.

[0403] Industrial applicability

[0404] The present invention can provide a specific polyvinyl alcohol-based polymer. Such a polymer can be suitably used as a dispersion stabilizer (dispersant) or the like.

Claims

1. A polyvinyl alcohol-based polymer (A) that fully satisfies the following Requirement 1 and the following Requirement 2 and / or Requirement 3: Requirement 1: Having polymerizable unsaturated bonds; Requirement 2: The yellowness index of a 4% by mass aqueous solution is 18 or less; Requirement 3: The yellowness index is 13 or less.

2. The polyvinyl alcohol-based polymer (A) according to claim 1, wherein, The proportion of polymerizable unsaturated bonds is 3 μmol / g or more.

3. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which fully satisfies that the yellowness index of a 4% by mass aqueous solution is 15 or less and / or the yellowness index is 12 or less.

4. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which further fully satisfies the following Requirement 4: Requirement 4: The transmittance at 430 nm of a 1% by mass aqueous solution is 90% or more.

5. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein, The proportion of polymerizable unsaturated bonds is 5 to 500 μmol / g, the yellowness index of a 4% by mass aqueous solution is 15 or less, the yellowness index is 12 or less, the transmittance at 430 nm of a 1% by mass aqueous solution is 93% or more.

6. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which contains an acetal skeleton (a) having polymerizable unsaturated bonds.

7. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which contains an acetal skeleton (a) having polymerizable unsaturated bonds, and the acetal skeleton (a) contains a skeleton represented by the following formula (a1), [Chemical formula 1] In formula (a1), R' represents a group having polymerizable unsaturated bonds.

8. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which contains an acetal skeleton (a) having polymerizable unsaturated bonds, the acetal skeleton (a) contains the skeleton represented by the formula (a1), and the content of the acetal skeleton (a) is 0.05 to 5 mol% per monomer unit.

9. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which further contains an ionic skeleton (b).

10. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, which further contains an ionic skeleton (b), and the content of the ionic skeleton (b) is 0.01 to 5 mol% per monomer unit.

11. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein, The saponification degree of the polyvinyl alcohol-based polymer (A) is 50 to 90 mol%.

12. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein, The viscosity of a 4% by mass aqueous solution of the polyvinyl alcohol-based polymer (A) at 20 °C is 2 to 100 mPa·s.

13. A dispersion stabilizer containing the polyvinyl alcohol-based polymer (A) according to claim 1 or 2.

14. The dispersion stabilizer according to claim 13, which is a dispersion stabilizer for polymerization.

15. The dispersion stabilizer according to claim 13, which is a dispersion stabilizer for suspension polymerization.

16. The dispersion stabilizer according to claim 13, which is a dispersion stabilizer for suspension polymerization of vinyl-based monomers containing vinyl chloride.

17. A method for preparing a vinyl-based polymer, which polymerizes vinyl-based monomers in the presence of the polyvinyl alcohol-based polymer (A) according to claim 1 or 2.

18. The preparation method according to claim 17, wherein, The polymerization is suspension polymerization.

19. The preparation method according to claim 17, which suspension polymerizes vinyl-based monomers containing vinyl chloride.

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