Polyvinyl alcohol-based polymer, dispersion stabilizer, and method for producing vinyl-based polymer

Abstract

Provided is a polyvinyl alcohol polymer.　The polyvinyl alcohol polymer satisfies requirements 1 and 2. Requirement 1: a polymerizable unsaturated bond is included. Requirement 2: the temperature at which the weight loss rate determined by thermogravimetric measurement is more than 0.5% / min in a temperature range of 150°C or higher is 255°C or higher.

Description

[Technical Field]

[0001] The present invention relates to polyvinyl alcohol polymers, various applications of these polyvinyl alcohol polymers [for example, dispersion stabilizers [for example, dispersion stabilizers for suspension polymerization of vinyl monomers (especially vinyl chloride monomers)], and methods for producing vinyl polymers [especially vinyl chloride polymers (resins)] using these polyvinyl alcohol polymers (or dispersion stabilizers). [Background technology]

[0002] The industrial manufacturing method for vinyl chloride resins is generally 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 polymerization is carried out using an oil-soluble polymerization initiator. Factors in the polymerization process that govern the quality of vinyl chloride resins include the polymerization rate, the ratio of aqueous medium to monomer, the polymerization temperature, the type and amount of polymerization initiator, the type of polymerization tank, the stirring speed, and the type and amount of dispersion stabilizer, but the influence of the dispersion stabilizer is particularly significant.

[0003] The role of dispersion stabilizers in suspension polymerization to obtain vinyl chloride resins is to disperse monomers in an aqueous medium, form stable droplets, ensure uniform droplet size during repeated dispersion and coalescence, and control the aggregation of polymerized particles. Therefore, the required properties of such dispersion stabilizers include: <1> To control the particle size of the resulting vinyl chloride resin particles within an appropriate range. <2> To increase the plasticizer absorption capacity of the resulting vinyl chloride resin particles and improve their moldability. <3> To maintain a certain porosity in the resulting vinyl chloride resin particles and facilitate the removal of residual monomers, <4> One example of this is improving the thermal stability of the resulting vinyl chloride resin particles.

[0004] In other words, the above-mentioned dispersion stabilizers are required to exhibit excellent dispersion power (protective colloidal properties), control the particle size and shape of the vinyl chloride resin to an appropriate state, and so on.

[0005] The above-mentioned dispersion stabilizers are generally polyvinyl alcohol-based resins (hereinafter sometimes abbreviated as PVA, PVA-based resin, PVA-based polymer, etc.), cellulose derivatives, etc., used alone or in appropriate combinations.

[0006] For example, Non-Patent Document 1 describes a method for using PVA with high emulsifying power, having a viscosity-average degree of polymerization of 2000 and a degree of saponification of 88 mol% or 80 mol%, or PVA with a viscosity-average degree of polymerization of 600-700 and a degree of saponification of around 70 mol%, as a dispersion stabilizer for suspension polymerization of vinyl chloride.

[0007] Furthermore, Patent Document 1 proposes a dispersion stabilizer for suspension polymerization that contains a polyvinyl alcohol polymer (B) having a double bond in its side chain, which is obtained by acetalizing a polyvinyl alcohol polymer (A) with an olefin-based monoaldehyde having an unsaturated double bond. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] International Publication No. 2015 / 182567 Brochure [Non-patent literature]

[0009] [Non-Patent Document 1] "Poval," published by Polymer Publication Society, 1981. [Overview of the project] [Problems that the invention aims to solve]

[0010] The object of the present invention is to provide polyvinyl alcohol-based polymers (PVA), etc. [Means for solving the problem]

[0011] As mentioned above, PVA is used as a dispersion stabilizer for suspension polymerization of vinyl chloride and other materials, and technologies are being developed to further improve PVA used as such a dispersion stabilizer.

[0012] In particular, Patent Document 1 relates to a technology developed by the present inventors, and it appears that polymerization stability and dispersion ability (protective colloidal properties) can be improved by modifying (acetalizing) PVA with a monoaldehyde having an olefinic unsaturated double bond.

[0013] On the other hand, the inventors' research has shown that the type of PVA used can affect the thermal stability of the resulting resin (such as a vinyl chloride resin), and consequently, reduce the thermal stability of the resulting resin. However, the factors that affect the thermal stability of the resin and how they affect it remain unknown, making the search for a PVA useful in terms of thermal stability extremely difficult.

[0014] Furthermore, this effect on thermal stability appears to persist (and not be particularly improved) even when modified (acetalized) with an olefin-based monoaldehyde having an unsaturated double bond, as described in Patent Document 1. Therefore, the search for a PVA that can improve both polymerizability and dispersion while simultaneously improving thermal stability (providing sufficient thermal stability) remains extremely difficult.

[0015] In this context, the inventors discovered that the thermal properties of PVA itself can affect the thermal stability of the resulting resin. Further investigations revealed that using PVA with specific thermal properties (thermal characteristics) can improve the thermal stability (provide sufficient thermal stability) of the resulting resin. In particular, they found that this tendency does not change even with PVA having unsaturated bonds (unsaturated double bonds) as described in Patent Document 1. Furthermore, they discovered that it is possible to improve thermal stability (provide sufficient thermal stability) while improving polymerizability and dispersion strength. Through further research, the inventors completed the present invention.

[0016] That is, the present invention relates to the following inventions, etc. [1] A polyvinyl alcohol polymer (A) that satisfies the following requirements 1 and 2. Requirement 1: having a polymerizable unsaturated bond Requirement 2: in a temperature range of 150°C or higher, the temperature at which the weight loss rate exceeds 0.5% / min, as determined from thermogravimetry, is 255°C or higher [2] The polyvinyl alcohol polymer (A) according to [1], wherein the content of the polymerizable unsaturated bond is 3 µmol / g or more. [3] The polyvinyl alcohol polymer (A) according to [1] or [2], wherein in a temperature range of 150°C or higher, the temperature at which the weight loss rate exceeds 0.5% / min, as determined from thermogravimetry, is 258°C or higher. [4] the content of the polymerizable unsaturated bond is 5 to 500 µmol / g, The polyvinyl alcohol polymer (A) according to any one of [1] to [3], wherein in a temperature range of 150°C or higher, the temperature at which the weight loss rate exceeds 0.5% / min, as determined from thermogravimetry, is 260°C or higher. [5] The polyvinyl alcohol polymer (A) according to any one of [1] to [4], which contains an acetal skeleton (a) having a polymerizable unsaturated bond. [6] which contains an acetal skeleton (a) having a polymerizable unsaturated bond, The polyvinyl alcohol polymer (A) according to any one of [1] to [5], wherein the acetal skeleton (a) comprises a skeleton represented by the following formula (a1).

Chemical Formula

[10] A polyvinyl alcohol-based polymer (A) as described in any of [1] to [9], wherein the degree of saponification is 50 to 90 mol%.

[11] A polyvinyl alcohol-based polymer (A) according to [1]-

[10] , wherein the viscosity of a 4% by mass aqueous solution (at 20°C) is 1 to 300 mPa·s (e.g., 1 to 100 mPa·s, 2 to 100 mPa·s).

[12] A dispersion stabilizer containing a polyvinyl alcohol polymer (A) as described in any of [1] to

[11] .

[13] The agent described in

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

[14] The agent described in

[12] or

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

[15] The agent described in any of

[12] to

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

[16] A method for producing a vinyl polymer, comprising polymerizing a vinyl monomer in the presence of a polyvinyl alcohol-based polymer (A) or agent described in any of [1] to

[15] .

[17] The method for producing polymers according to

[16] , wherein the polymerization is suspension polymerization.

[18] A method for producing vinyl monomers containing vinyl chloride, according to

[16] or

[17] .

[19] Use as a dispersion stabilizer (dispersant) for polyvinyl alcohol-based polymers (A) as described in any of [1] to

[11] .

[20] The use described in

[19] , wherein the dispersion stabilizer is a dispersion stabilizer for suspension polymerization. [twenty one] The use according to

[19] or

[20] , wherein the dispersion stabilizer is a dispersion stabilizer for suspension polymerization of vinyl monomers containing vinyl chloride. [twenty two] Use of polyvinyl alcohol-based polymer (A) described in any of [1] to

[11] for polymerization of vinyl monomers. [twenty three] The use described in

[22] , wherein polymerization is suspension polymerization. [twenty four] The use according to

[22] or

[23] , wherein the polymerization is a suspension polymerization of vinyl monomers containing vinyl chloride. [Effects of the Invention]

[0017] According to the present invention, PVA (novel or specific PVA) and its applications (dispersion stabilizer, etc.) can be provided.

[0018] Such PVA (dispersion stabilizers, etc.) possess specific thermal properties. In particular, such PVA (dispersion stabilizers, etc.) have excellent thermal stability despite having unsaturated double bonds.

[0019] Furthermore, such PVA also possesses properties as a dispersion stabilizer. For example, it exhibits excellent dispersive power (protective colloidal properties), enabling high polymerization stability and allowing for the production of resins with excellent plasticizer absorption and thermal stability (e.g., vinyl polymers such as polyvinyl chloride resins). Therefore, it is possible to achieve both the properties of a dispersion stabilizer and improved thermal stability in the resin (providing sufficient thermal stability). [Modes for carrying out the invention]

[0020] The embodiments for carrying out the present invention will be described in detail below. However, the present invention is not limited to the embodiments described below.

[0021] The polyvinyl alcohol-based polymers of the present invention (polyvinyl alcohol-based polymer (A), PVA-based polymer (A), PVA (A), PVA) particularly satisfy the following requirements 1 and 2. Requirement 1: Possesses polymerizable unsaturated bonds [e.g., polymerizable unsaturated bonds that can be determined by bromine titration (detected or quantified by bromine titration)] (e.g., unsaturated double bonds). Requirement 2: In the temperature range of 150°C or higher, the temperature at which the weight loss rate (determined from thermogravimetric measurements) exceeds 0.5% / min is 255°C or higher.

[0022] Furthermore, the present invention encompasses various applications of such polyvinyl alcohol-based polymers (polyvinyl alcohol-based polymer (A)), particularly dispersants (dispersion stabilizers, for example, dispersion stabilizers for suspension polymerization) containing polyvinyl alcohol-based polymers (polyvinyl alcohol-based polymer (A)). In these various applications [for example, dispersants such as dispersion stabilizers for suspension polymerization], one or more types of PVA polymers (A) may be used. The present invention will be described in detail below.

[0023] [Polyvinyl alcohol polymer (A)] PVA-based polymers (A) typically satisfy the following requirements 1 and 2. Requirement 1: Has polymerizable unsaturated bonds. Requirement 2: In the temperature range of 150°C or higher, the temperature at which the weight loss rate (determined from thermogravimetric measurements) exceeds 0.5% / min is 255°C or higher.

[0024] In requirement 1, examples of polymerizable unsaturated bonds include double bonds (unsaturated double bonds) and triple bonds (unsaturated triple bonds). Polymerizable unsaturated bonds may usually be double bonds (especially carbon-carbon double bonds) [at least double bonds (especially carbon-carbon double bonds)].

[0025] In the PVA-based polymer (A), the proportion of polymerizable unsaturated bonds can be selected from a range of, for example, 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., 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.

[0026] In the PVA polymer (A), the upper limit of the proportion of polymerizable unsaturated bonds is not particularly limited, but may 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.

[0027] The proportion of polymerizable unsaturated bonds can also be set to a range obtained by appropriately combining the lower and upper limits of the above range (the same applies to the description of the range below).

[0028] Typically, in a PVA-based polymer (A), the proportion of polymerizable unsaturated bonds may be 1 to 2000 μmol / g, preferably 3 to 1000 μmol / g, and more preferably about 5 to 500 μmol / g.

[0029] In a PVA-based polymer (A) (a PVA-based polymer (A) that satisfies requirement 1), the proportion of polymerizable unsaturated bonds may satisfy the proportion of the skeleton described below [for example, the proportion of acetal skeleton (a) may be satisfied (for example, 0.001 mol% or more, 0.05 to 5 mol%, 0.1 to 3 mol%, 0.2 to 2 mol%, etc. per monomer unit)].

[0030] When the content of polymerizable unsaturated bonds (e.g., unsaturated double bonds) is within the range described above, the effects of the present invention can be efficiently realized. In particular, if the content is not too small (e.g., 5 μmol / g or more), it is preferable because when used in suspension polymerization, it is easier to achieve excellent polymerization stability, suppression of scale adhesion to the polymerization tank, and less coarsening of the particle size of the resulting vinyl resin. On the other hand, if the content of polymerizable unsaturated bonds (e.g., unsaturated double bonds) is not too large (e.g., 500 μmol / g or less), it is preferable because it is easier to obtain a vinyl resin with high plasticizer absorption.

[0031] The polymerizable unsaturated bonds contained in the PVA polymer (A) can be detected or quantified by methods such as bromine titration [to determine their content (percentage)]. The method of bromine titration is not particularly limited, but it utilizes the reaction between the polymerizable unsaturated bonds (unsaturated double bonds, etc.) contained in the PVA polymer (A) and bromine. The amount of polymerizable unsaturated bonds (unsaturated double bonds, etc.) (μmol / g) contained in the PVA polymer (A) can be calculated from the amount of bromine (moles) that reacted with the polymerizable unsaturated bonds (unsaturated double bonds, etc.) contained in the PVA polymer (A).

[0032] In requirement 2, the temperature (T) at which the weight loss rate exceeds 0.5% / min is an indicator of the thermal stability of the PVA-based polymer (A), and a higher value indicates better thermal stability. T should be 255°C or higher, preferably 258°C or higher (for example, 260°C or higher), more preferably 262°C or higher (for example, 264°C or higher, 265°C or higher), and can also be 267°C or higher (for example, 268°C or higher, 269°C or higher, 270°C or higher), etc. The upper limit of T is not particularly limited and may be, for example, 450°C, 400°C, 350°C, 320°C, 300°C, 290°C, etc. Furthermore, in the measurement temperature range for thermogravimetric analysis, if the weight loss rate does not exceed 0.5%, T can be set to "greater than" the upper limit of the measurement temperature range (for example, if the upper limit of the measurement temperature range is 400°C, T is greater than 400°C).

[0033] Such a T makes it easier to efficiently realize the effects of the present invention (for example, when used in suspension polymerization, it is easier to efficiently obtain a vinyl resin with excellent thermal stability).

[0034] While this requirement 2 (temperature T) is not particularly limited, it can be efficiently satisfied by adjusting (selecting) the monomer composition of the PVA polymer (A), as well as by adjusting (selecting) the method of introducing polymerizable unsaturated bonds, drying conditions, etc., as described later.

[0035] Requirement 2 (weight loss rate) can be determined by performing thermogravimetric (TG) measurement. The conditions for thermogravimetric measurement (measurement conditions) are not limited, but for example, the heating rate may be a predetermined rate (e.g., 10°C / min). Other conditions (conditions other than heating rate) are also not limited and can be arbitrarily selected, but for example, under a nitrogen atmosphere, sample weight: 5-6 mg, measurement temperature range: 50°C or higher (e.g., 50-300°C, 50-400°C, 50-500°C), with other conditions being arbitrary.

[0036] In requirement 2, in thermogravimetric analysis (as a sample for thermogravimetric analysis), the PVA polymer (A) may be used as is, or it may be purified (extracted, etc.) as necessary. For example, in thermogravimetric analysis, the PVA polymer (A) may be used after Soxhlet extraction with methanol as the solvent (or it may be used after extraction).

[0037] PVA polymer (A) may contain impurities such as sodium acetate. While these impurities may affect thermogravimetric measurements, they can be removed by extraction (methanol extraction), making it easier to perform thermogravimetric measurements [the thermogravimetric measurement of the PVA polymer (A)] efficiently (making it easier to measure the inherent thermal stability of the PVA polymer (A) by eliminating the influence of impurities). Even if impurities such as sodium acetate are present, they do not function effectively when used as a dispersant (dispersion stabilizer), etc.

[0038] If the particle size of the measurement sample (PVA-based polymer (A)) is large, it may be used for thermogravimetric analysis after the particle size has been adjusted, for example, by grinding it in a pulverizer.

[0039] The PVA-based polymer (A) is not particularly limited as long as it satisfies requirements 1 and 2 above, but as an embodiment having polymerizable unsaturated bonds (satisfying requirement 1), it may preferably contain an acetal skeleton (a) having polymerizable unsaturated bonds (e.g., ethylenically unsaturated double bonds).

[0040] In the present invention, despite containing polymerizable unsaturated bonds (such as ethylenically unsaturated double bonds) [for example, an acetal skeleton (a) having polymerizable unsaturated bonds (such as ethylenically unsaturated double bonds)], it is easy to obtain a vinyl resin with excellent thermal stability when used in suspension polymerization.

[0041] [Acetal skeleton (a)] In the acetal skeleton (a), the number of polymerizable unsaturated bonds is not particularly limited, and it is sufficient if it is 1 or more (for example, 1-5, 1-3, 1-2, 1, etc.).

[0042] In the acetal skeleton (a), the acetal may be a cyclic acetal or an acyclic (chain-like) acetal, and preferably a cyclic acetal.

[0043] Typical acetal skeletons having polymerizable unsaturated bonds include the skeleton (structural unit) shown in formula (a1) below. Therefore, the acetal skeleton (a) may include the skeleton shown in formula (a1) below.

[0044] [ka] (In the formula, R' represents a group having a polymerizable unsaturated bond.)

[0045] In the above formula (a1), R' is a group having a polymerizable unsaturated bond. R' may be the polymerizable unsaturated bond group itself, or it may be a group containing a polymerizable unsaturated bond (for example, a hydrocarbon group). Furthermore, groups having polymerizable unsaturated bonds may also have substituents in addition to the polymerizable unsaturated bond. The substituents can be appropriately selected depending on the type of group having polymerizable unsaturated bonds and are not particularly limited. Examples include hydroxyl groups, halogen atoms, acyl groups, ester groups, alkoxy groups, nitro groups, substituted amino groups, and groups different from the base group (for example, aromatic groups such as aryl groups). Substituents may be substituted individually or in combination of two or more types.

[0046] Groups having polymerizable unsaturated bonds [especially double bonds (ethylenic double bonds)] include, for example, groups having one polymerizable unsaturated bond {for example, alkenyl groups [for example, vinyl groups, allyl groups, propenyl groups (1-propenyl groups, 2-propenyl groups, etc.), butenyl groups, pentenyl groups, 6-methyl-5-hexenyl groups, decenyl groups, 2-(dimethylamino)vinyl groups, cyclohexenyl groups, 2-phenylethenyl groups, etc., hydrocarbon groups (which may have substituents) having 2 or more carbon atoms (for example, 2 to 30, preferably 2 to 14, more preferably about 2 to 10 carbon atoms)], and groups having two or more polymerizable unsaturated bonds {for example, alkadienyl groups [for example, 1,3-pentadienyl groups, 2,6-dimethylamino)}, Examples include hydrocarbon groups (hydrocarbon groups that may have substituents, such as alkadienyl groups) such as 1,5-hexadienyl, cyclohexadienyl, propenylcyclohexenyl, etc., having 4 or more carbon atoms (e.g., 4 to 30, preferably 4 to 14, more preferably about 4 to 10); alkatrienyl groups [e.g., alkatrienyl groups with 6 or more carbon atoms (e.g., 6 to 30, preferably about 6 to 24)]; alkatetraenyl groups [e.g., alkatetraenyl groups with 8 or more carbon atoms (e.g., 8 to 30, preferably about 8 to 24)]; and alkapentaenyl groups [e.g., alkapentaenyl groups with 10 or more carbon atoms (e.g., 10 to 30, preferably about 10 to 24)].

[0047] The acetal skeleton having a polymerizable unsaturated bond {for example, the group represented by formula (a1) (or R'-< in formula (a1))} may be derived from the corresponding carbonyl compound (e.g., aldehydes, their acetals, ketones, etc.), particularly aldehydes [e.g., R'CHO (aldehydes in which R' is a hydrocarbon group having a polymerizable unsaturated bond)]. The carbonyl compound may have substituents as described above.

[0048] Examples of such carbonyl compounds include 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, myristreinaldehyde, palmitreinaldehyde, olealdehyde, elaidinaldehyde, vacenealdehyde, gadreinaldehyde, erukaaldehyde, nervonaldehyde, linolealdehyde, citronellal, cinnamaldehyde, and other C3-C15 alkenals, preferably C3-C10 alkenals], alkadienals [for example, Alkadienals having 5 to 15 carbon atoms, such as 2,4-pentadienal, 2,4-hexadienal, 2,6-nonadienal, citral, and perillaldehyde, preferably alkadienals having 5 to 10 carbon atoms], alkatrineals [for example, alkatrineals having 7 to 30 carbon atoms, such as linolenium aldehyde and eleostearin aldehyde, preferably alkatrienals having 7 to 25 carbon atoms], alkatetraenals [for example, S Examples include unsaturated aldehydes (especially monoaldehydes) such as thearidone aldehyde, arachidone aldehyde, and other C9-C30 alkatetraenals, preferably C9-C25 alkatetraenals, and alcapentaenals [for example, eicosapentaenaldehyde and other C11-C30 alcapentaenals, preferably C11-C25 alcapentaenals], as well as corresponding ketones, acetals, etc. Furthermore, if a carbonyl compound has isomers (e.g., cis-trans isomers), both isomers (e.g., both the cis and trans isomers) are included.

[0049] As mentioned above, acetals, which are condensates of aldehydes and alcohols, can also be used as carbonyl compounds. The acetals are not particularly limited, but examples include condensates with primary alcohols (e.g., methanol).

[0050] These carbonyl compounds can be used individually or in combination of two or more.

[0051] Furthermore, from the viewpoint of water solubility, carbonyl compounds are preferably composed of monocarbonyl compounds (such as monoaldehydes), and even when polyvalent carbonyl compounds (for example, polyvalent aldehydes such as dialdehydes) are used, they are often used in small amounts or at levels that ensure water solubility.

[0052] Furthermore, the acetal skeleton having polymerizable unsaturated bonds (for example, the acetal skeleton represented by formula (a1) above) may be a skeleton that can be introduced via hydroxyl groups, and may be an acetal skeleton derived from (or introduced via) two adjacent hydroxyl groups (for example, hydroxyl groups of vinyl alcohol units). For example, when using carbonyl compounds (aldehydes, ketones, etc.) having polymerizable unsaturated bonds, a PVA-based polymer (A) having an acetal skeleton (a) with polymerizable unsaturated bonds can be obtained by acetalizing two adjacent OH groups in a PVA-based polymer with a carbonyl compound having polymerizable unsaturated bonds.

[0053] The acetal skeleton having polymerizable unsaturated bonds (for example, the acetal skeleton represented by formula (a1) above) may or may not have ionic groups (ionic skeletons).

[0054] The PVA-based polymer (A) may have an acetal skeleton having polymerizable unsaturated bonds, either alone or in combination of two or more types.

[0055] In the PVA polymer (A), the content of the acetal skeleton (a) [or polymerizable unsaturated bond, for example, the skeleton shown in formula (a1)] may be selected from a range of about 0.001 mol% or more (for example, 0.005 mol% or more) per monomer unit in the PVA polymer (A), for example, 0.01 mol% or more, preferably 0.05 mol% or more, more preferably 0.1 mol% or more, particularly 0.2 mol% or more, and may 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].

[0056] As mentioned above, you may also select a range by appropriately combining these ranges (upper and lower limits) (for example, 0.01 to 3 mol%, 0.05 to 5 mol%, etc.).

[0057] Specifically, the content of the acetal skeleton (a) (or polymerizable unsaturated bond) in the PVA-based polymer (A) may be 0.05 to 5 mol%, preferably 0.1 to 3 mol%, and more preferably 0.2 to 2 mol% per monomer unit.

[0058] Note that a 1 mol% content refers to a case where there is one acetal skeleton (a) (for example, the skeleton shown in formula (a1)) for every 100 monomer units (for example, the total of monomer units such as vinyl alcohol units and vinyl ester units).

[0059] With the above-mentioned content levels, the performance as a dispersant (dispersion stabilizer) can be efficiently achieved (for example, a vinyl chloride resin with excellent polymerization stability, an appropriate average particle size, and excellent plasticizer absorption can be efficiently obtained).

[0060] Furthermore, by keeping the upper limit from being too high, it becomes easier to ensure good prepareability, storage stability, and dispersibility in hot water of the aqueous solution.

[0061] The method for measuring the acetal skeleton (a) content is not particularly limited, but for example, it can be measured using NMR. To give a specific example, for instance, dissolve a PVA-based polymer (A) in d6-DMSO solvent, and 1 The signal may also be measured by 1H-NMR and analyzed for signals originating from polymerizable unsaturated bonds (such as ethylenic double bonds) in the acetal skeleton (a).

[0062] The PVA-based polymer (A) may contain an ionic skeleton (b). The inclusion of an ionic skeleton (b) in the PVA-based polymer (A) facilitates the preparation of PVA aqueous solutions and improves the stability of the PVA aqueous solution (and further, its dispersibility in hot water). This also prevents PVA from precipitating in the polymer when storing the PVA aqueous solution in tanks or when adding it to a polymerizer (hot water at 40-70°C). While introducing an ionic skeleton (b) can provide such effects [e.g., excellent dispersibility (e.g., dispersibility in water and hot water)], simply introducing it may reduce thermal stability. In this invention, even with the introduction of an ionic skeleton (b), requirement (2) can be satisfied, and consequently, excellent dispersibility and other properties can be achieved while efficiently improving the thermal stability of the resin (providing sufficient thermal stability).

[0063] [Ionic skeleton (b)] The ionic skeleton (b) has ionic groups. Examples of ionic groups include anionic groups {for example, acidic groups [for example, carboxyl groups, sulfonic acid groups (-SO3H), phosphate groups, etc.]}, cationic groups [for example, amino groups, ammonium (ammonium cations)], and salts of these groups (groups that have formed salts).

[0064] Examples of salts include metal salts [e.g., alkali or alkaline earth metals (e.g., lithium salts, sodium salts, potassium salts, magnesium salts, calcium salts)] and halides (e.g., chlorides, bromides, iodides), depending on their anionic or cationic properties. When the ionic group is a polybasic acid, the salt may be a single (same type) salt or a salt formed by combining two or more types.

[0065] Among these ionic groups, acidic groups (especially carboxyl groups and sulfonic acid groups) and their salts {salts of acidic groups, for example, carboxylate salts [e.g., -COOM (where M is an alkali metal such as sodium (or its cation))], sulfonate salts [e.g., -SO3M (where M is an alkali metal such as sodium (or its cation))]}.

[0066] The ionic skeleton (b) is not particularly limited in form as long as it has an ionic group, and examples include (1) an acetal skeleton having an ionic group (acetal group, acetal unit), (2) a skeleton corresponding to (or derived from) a monomer having an ionic group, and (3) a skeleton corresponding to (or derived from) other compounds into which an ionic group can be introduced {for example, a chain transfer agent having an ionic group [for example, alcohols, carbonyl compounds (aldehydes, ketones, etc., especially aldehydes, etc.), thiols, etc.]}.

[0067] Furthermore, an ionic skeleton (b) (one ionic skeleton (b)) only needs to have one or more ionic groups, and may have two or more.

[0068] The PVA-based polymer (A) may have these ionic skeletons (b) individually or in combination of two or more types.

[0069] In the PVA polymer (A), the content (percentage, content ratio) of the ionic skeleton (b) (for example, the above skeletons (1), (2), and / or (3)) may be selected from a range of approximately 0.001 mol% or more (for example, 0.005 mol% or more) per monomer unit, for example, 0.01 mol% or more, preferably 0.03 mol% or more, more preferably 0.05 mol% or more, and may 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].

[0070] Specifically, the content of the ionic skeleton (b) (for example, the above skeletons (1), (2), and / or (3)) may be 0.01 to 5 mol%, preferably 0.03 to 2 mol%, and more preferably 0.05 to 1 mol% per monomer unit.

[0071] Note that a 1 mol% content means that for every 100 monomer units (for example, the total of monomer units such as vinyl alcohol units and vinyl ester units), there is one ionic skeleton (b) (for example, skeletons (1), (2), and / or (3) above).

[0072] With the above-mentioned content levels, it is easier to improve the prepareability, storage stability, and dispersibility in hot water of the aqueous solution of the PVA polymer (A).

[0073] Furthermore, by keeping the upper limit from being too high, the performance of the PVA-based polymer (A) as a dispersion stabilizer can be efficiently realized (for example, a vinyl chloride-based resin with excellent polymerization stability, an appropriate average particle size, and excellent plasticizer absorption can be efficiently obtained).

[0074] The method for measuring the ionic group content may be selected according to the type of skeleton containing ionic groups, etc., and is not particularly limited, but can be measured using methods such as NMR, titration, or UV absorbance. To give a specific example, the content of the skeleton shown in formula (b1-1) described below is obtained by dissolving the PVA polymer (A) in d6-DMSO solvent, and this1 The signal may also be measured by 1H-NMR and analyzed for signals originating from substituents (e.g., hydrogen) on the benzene ring. Alternatively, the amount of carboxyl groups can be determined from the titration volume of hydrochloric acid by completely saponifying the PVA polymer (A), dissolving the sample after Soxhlet extraction (for example, after removing sodium acetate), adding a small amount of sodium hydroxide (NaOH), and then titrating with dilute hydrochloric acid. Furthermore, if the acetal skeleton having ionic groups has a structure that absorbs UV (ultraviolet) light, the content of the acetal skeleton having ionic groups can be measured by measuring the UV absorbance of an aqueous solution containing the PVA polymer (A).

[0075] Furthermore, in the PVA polymer (A), the content of the acetal skeleton (a) (content per monomer unit) may 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, or 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 especially 3 moles or more, per mole of the ionic skeleton (b) (for example, the above skeletons (1), (2), and / or (3)), or 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 3 moles or more.

[0076] This ratio makes it easier to achieve both excellent aqueous solution preparation and storage stability, as well as superior performance as a dispersion stabilizer.

[0077] Furthermore, depending on the embodiment, known methods can be used for introducing the ionic skeleton (b). Examples of such introduction methods include: (1) a method to obtain a PVA-based polymer (B-1) having ionic groups by acetalizing a PVA-based polymer (sometimes called a PVA-based polymer (C)) with a carbonyl compound having ionic groups (aldehydes, their acetals, ketones, etc., especially aldehydes); (2) a method to obtain a polyvinyl ester polymer having ionic groups by copolymerizing a monomer having ionic groups with a vinyl ester, and then saponifying it to obtain a PVA-based polymer (B-3) having ionic groups; and (3) a method to obtain a polyvinyl ester polymer (having ionic groups) obtained by polymerizing a vinyl ester in the presence of a chain transfer agent having ionic groups (alcohol, aldehyde, thiol, etc.) and then saponifying it to obtain a PVA-based polymer (B-4) having ionic groups.

[0078] The following describes each aspect of the ionic skeleton (b) in detail.

[0079] ((1) Acetal skeleton having ionic groups) As mentioned above, the ionic group is present in the acetal skeleton (acetal group, acetal unit) (it is substituted onto the acetal skeleton).

[0080] The acetal may be a cyclic acetal or an acyclic (chain-like) acetal, and is preferably a cyclic acetal.

[0081] Typical acetal skeletons with ionic groups include the skeleton (structural unit) shown in formula (b1) below. Therefore, acetal skeletons with ionic groups may also include the skeleton shown in formula (b1) below.

[0082] [ka] (In the formula, R represents a group having an ionic group.)

[0083] In formula (b1) above, R is a group having an ionic group. R may be the ionic group itself, or it may be a linking group having an ionic group (a group composed of an ionic group and a linking group in which this ionic group is substituted).

[0084] Examples of linking groups (base groups) include hydrocarbon groups. Examples of hydrocarbon groups include aliphatic hydrocarbon groups [for example], alkyl groups [for example], linear alkyl groups (for example) such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and undecyl groups, etc. 1-30 C(alkyl groups), cycloalkyl groups (e.g., cyclopentyl group, cyclohexyl group, etc.) 3-10 Saturated aliphatic hydrocarbon groups such as cycloalkyl groups, aromatic hydrocarbon groups such as aryl groups (e.g., phenyl, tolyl, xylyl, naphthyl groups, etc.) 6-20 (aryl group), aralkyl group (e.g., benzyl group, phenethyl group, etc.) 6-20 Aryl-C 1-4 Examples include alkyl groups, etc.

[0085] The linking group (hydrocarbon group) may have substituents (non-ionic substituents) in addition to being an ionic group. Substituents are not particularly limited and include, for example, hydroxyl groups, halogen atoms, acyl groups, ester groups, alkoxy groups, nitro groups, and groups different from the base group (e.g., aromatic groups such as aryl groups). The substituents may be substituted for the linking group (hydrocarbon group) individually or in combination of two or more types.

[0086] In a linking group having an ionic group (such as a hydrocarbon group), the number of ionic groups only needs to be one or more, and two or more ionic groups may be substituted on the linking group.

[0087] Examples of acetal skeletons having specific ionic groups (skeletons represented by formula (b1)) include skeletons in which R in formula (b1) is an ionic group (e.g., a carboxyl group and its salts, etc.) and skeletons represented by the following formula (b1-1).

[0088] [ka] (In the formula, R1 to R5 represent hydrogen atoms or substituents. However, at least one of R1 to R5 is an ionic group.)

[0089] In the above formula (b1-1), the ionic group and substituent are as exemplified above. At least one of R1 to R5 is an ionic group, but preferably any one of them may be an ionic group. Typically, one of R1 to R5 may be an ionic group (for example, a carboxyl group, a sulfonic acid group, or a salt thereof), and the other four may be hydrogen atoms.

[0090] The acetal skeleton having an ionic group {for example, the group represented by formula (b1) (or R-< in formula (b1))} may be derived from the corresponding carbonyl compound (e.g., aldehydes, their acetals, ketones, etc.), particularly from aldehydes (e.g., RCHO). The carbonyl compound may have substituents.

[0091] Examples of such carbonyl compounds include aldehydes (especially monoaldehydes) such as alcanals having an ionic group (e.g., glyoxylic acid, formylacetic acid, formylpropionic acid, and alcanals having an acidic group or a salt thereof), arenecarbaldehydes having an ionic group [e.g., formylbenzoic acid (e.g., 4-formylbenzoic acid), formylbenzenesulfonic acid (e.g., 2-formylbenzenesulfonic acid, 4-formylbenzene-1,3-disulfonic acid), and arenecarbaldehydes having an acidic group or a salt thereof], and corresponding ketones, acetals, etc. Furthermore, if a carbonyl compound has isomers (e.g., cis-trans isomers), both isomers (e.g., both the cis and trans isomers) are included.

[0092] Furthermore, in the PVA polymer (A), if ionic groups can be formed, the ionic groups in the carbonyl compound may be derivatized (esterified, anhydrized, etc.). For example, even esters (e.g., alkyl esters) or acid anhydrides can be used if they can form the corresponding acid group (carboxyl group, sulfonic acid group) or a salt thereof in the PVA polymer (A) (for example, formed by hydrolysis) (the same applies to ionic groups below).

[0093] These carbonyl compounds can be used individually or in combination of two or more.

[0094] Furthermore, from the viewpoint of water solubility, carbonyl compounds are preferably composed of monocarbonyl compounds (such as monoaldehydes), and even when polyvalent carbonyl compounds (for example, polyvalent aldehydes such as dialdehydes) are used, they are often used in small amounts or at levels that ensure water solubility.

[0095] Furthermore, the acetal skeleton having an ionic group (for example, the acetal skeleton represented by formula (b1) above) may be a skeleton that can be introduced via a hydroxyl group, and may be an acetal skeleton derived from (or introduced via) two adjacent hydroxyl groups (for example, hydroxyl groups of a vinyl alcohol unit). For example, when using carbonyl compounds having ionic groups (aldehydes, ketones, etc.), a PVA polymer (A) having an acetal skeleton with ionic groups can be obtained by acetalizing two adjacent OH groups in a PVA polymer with a carbonyl compound having ionic groups.

[0096] The acetal skeleton having an ionic group (for example, the acetal skeleton represented by formula (b1) above) may or may not have polymerizable unsaturated bonds.

[0097] The PVA-based polymer (A) may or may not have an acetal skeleton having ionic groups.

[0098] The PVA-based polymer (A) may have an acetal skeleton having ionic groups, either alone or in combination of two or more types.

[0099] The method for incorporating (introducing) an acetal skeleton having ionic groups (for example, an acetal skeleton having a carboxyl group, a sulfonic acid group, or a salt thereof) into a PVA-based polymer (A) is not particularly limited, and conventional methods can be used.

[0100] In a typical method, as described later, the PVA-based polymer (C) may be acetalized with a carbonyl compound having an ionic group (aldehyde, its acetal, ketone, etc.). Furthermore, while it is possible to obtain a PVA-based polymer (B-1) having ionic groups by acetalizing the PVA-based polymer (C) with a carbonyl compound having ionic groups, it is preferable to include a carbonyl compound having polymerizable unsaturated bonds during acetalization, as this allows for obtaining both an acetal skeleton (a) and a PVA-based polymer (A) having ionic groups in one step.

[0101] Examples of aldehydes having an ionic group include glyoxylic acid, 2-formylbenzoic acid, 4-formylbenzoic acid, sodium 2-formylbenzenesulfonate, sodium 4-formylbenzenesulfonate, and disodium 4-formylbenzene-1,3-disulfonate, but 4-formylbenzoic acid or sodium 2-formylbenzenesulfonate are preferred.

[0102] As mentioned above, acetals, which are condensates of aldehydes and alcohols, can also be used as carbonyl compounds. The acetals are not particularly limited, but examples include condensates with primary alcohols (e.g., methanol).

[0103] Carbonyl compounds can be used alone or in combination of two or more.

[0104] ((2) Backbone corresponding to monomer having an ionic group) The monomer having an ionic group is not particularly limited and can be appropriately selected depending on the type of ionic group.

[0105] Specific monomers include, for example, monomers having an acidic group [e.g., monomers having a carboxyl group [e.g., monocarboxylic acids (e.g., aliphatic unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid), polycarboxylic acids (e.g., aliphatic unsaturated dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid), and salts thereof], monomers having a sulfonic acid group [e.g., alkenyl sulfonic acid (e.g., vinyl sulfonic acid, allyl sulfonic acid), alkenyl alen sulfonic acid (e.g., styrene sulfonic acid), amide monomers having a sulfonic acid group (e.g., 2-acrylamido-2-methylpropanesulfonic acid), and salts thereof], and monomers having other ionic groups [e.g., monomers having an amino group (e.g., (meth)acrylamidopropyldimethylamine), and salts thereof].

[0106] Furthermore, as described above, if ionic groups can be introduced into the PVA polymer (A) (for example, if ionic groups are ultimately formed in the PVA polymer (A) by hydrolysis or the like), these may be derivatives [for example, acid anhydrides (e.g., maleic anhydride, etc.), esters (e.g., alkyl esters)]. In other words, such derivatives can be described as derivatives capable of forming ionic groups. To give a specific example, even if an acrylic acid ester is used, it is sufficient that acrylic acid or a salt thereof is introduced into the final PVA-based polymer (A). Therefore, the acrylic acid ester introduces a skeleton corresponding to acrylic acid or a salt thereof into the PVA-based polymer (A).

[0107] These monomers may be used individually or in combination of two or more.

[0108] As described above, for example, a polyvinyl ester polymer containing ionic groups, obtained by copolymerizing such a monomer having ionic groups with a vinyl ester, can be saponified to obtain a PVA polymer (B-3) containing ionic groups.

[0109] ((3) Other skeletons corresponding to compounds into which ionic groups can be introduced) Examples of compounds that can introduce ionic properties into such a skeleton (3) include, as mentioned above, alcohols having an ionic group, carbonyl compounds having an ionic group (aldehydes, ketones, etc., especially aldehydes, etc.), and thiols having an ionic group. These may also function as chain transfer agents.

[0110] Among these, thiols are preferred due to their high chain mobility (and therefore ease of introducing ionic groups).

[0111] Examples of thiols having an ionic group include thiols having an acidic group [for example, thiols having a carboxyl group [for example, mercapto saturated fatty acids (e.g., mercaptoalkanoic acids such as 3-mercaptopropionic acid and mercaptosuccinic acid)], thiols having a sulfonic acid group [for example, mercaptoalkanesulfonic acid (e.g., 3-mercapto-1-propanesulfonic acid)], and salts thereof (e.g., sodium 3-mercapto-1-propanesulfonate)].

[0112] As described above, for example, by polymerizing vinyl esters in the presence of a chain transfer agent having such ionic groups (alcohol, aldehyde, thiol, etc.), ionic groups derived from the chain transfer agent can be introduced to the terminals of the vinyl ester polymer. Subsequently, by saponifying the vinyl ester polymer, a PVA polymer (B-4) containing ionic groups at its terminals can be obtained.

[0113] Furthermore, the PVA-based polymer (A) may have other acetal skeletons (acetal groups, acetal units) that do not fall within the category of the acetal skeleton (a) or an ionic group-containing acetal skeleton. Examples of such other acetal skeletons include skeletons in which R' in the above formula (a1) is a group having no ionic group or polymerizable unsaturated bond (e.g., an aliphatic group, an aromatic group, etc.). Examples of such groups include aliphatic groups [e.g., alkyl groups (e.g., C 1-30 alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, undecyl group, etc.), cycloalkyl groups (e.g., C 3-20 cycloalkyl groups such as cyclopentyl group, cyclohexyl group, etc.)], aromatic groups [e.g., aryl groups (e.g., C 6-20 aryl groups such as phenyl group, naphthyl group, etc.)], and the like.

[0114] The method for introducing such other acetal skeletons is not particularly limited, and conventional methods 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 such a method, other acetal skeletons are usually formed derived from two adjacent vinyl alcohol units.

[0115] Examples of such aldehydes include alkanals [e.g., acetaldehyde, propionaldehyde, butanal, pentanal, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, 2-methylbutanal, 2-ethylbutanal, 2-methylpentanal, 2-ethylhexanal], cycloalkane carbaldehydes [e.g., cyclopentane carboxaldehyde (cyclopentane carbaldehyde), cyclohexane carboxaldehyde (cyclohexane carbaldehyde), etc.] and other aliphatic aldehydes, and arene carbaldehydes (e.g., benzaldehyde, naphthaldehyde, etc.) and other aromatic aldehydes.

[0116] The PVA-based polymer (A) has at least vinyl alcohol units, but may also have vinyl alcohol units and units that have not been hydrolyzed (saponified) [for example, vinyl ester units (or units derived from vinyl ester monomers, for example, vinyl acetate units, etc.)].

[0117] In addition, the PVA-based polymer (A) may have other units as needed (units other than those exemplified above, such as vinyl alcohol units, unhydrolyzed units, acetal skeletons (a), and ionic skeletons (b)). Examples of such units include units derived from other monomers exemplified in the section on PVA-based polymer (C) described later.

[0118] The degree of saponification of the PVA-based polymer (A) may be, for example, 20 mol% or more (e.g., 25 mol% or more), preferably 30 mol% or more (e.g., 35 mol% or more), more preferably 40 mol% or more (e.g., 45 mol% or more), and particularly 50 mol% or more (e.g., 55 mol% or more, 60 mol% or more).

[0119] The upper limit of the degree of saponification of the PVA-based polymer (A) may be, for example, 95 mol% or less (e.g., 93 mol% or less), preferably 90 mol% or less (e.g., 88 mol% or less), and more preferably 85 mol% or less (e.g., 80 mol% or less).

[0120] Specifically, the degree of saponification of the PVA-based polymer (A) may be, for example, 20 to 90 mol% (for example, 50 to 90 mol%), preferably 55 to 85 mol%, and more preferably around 60 to 80 mol%.

[0121] A degree of saponification that is not too low is preferable because it provides excellent prepareability, storage stability, and dispersibility in hot water of the aqueous solution. A degree of saponification that is not too high is also preferable because it allows for the efficient acquisition of vinyl chloride resins that exhibit excellent dispersant properties (for example, those with excellent thermal stability, appropriate average particle size, and high plasticizer absorption).

[0122] The degree of saponification can be determined, for example, by the saponification method for PVA specified in JIS K 6726.

[0123] When the PVA polymer (A) has vinyl ester units, the proportion of the ionic skeleton (b) (proportion in monomer unit units) may be 10 moles or less, preferably 5 moles or less, more preferably 3 moles or less, per 100 moles of vinyl ester units, and may be 0.01 moles or more (for example, 0.05 moles or more, 0.1 moles or more), preferably 0.2 moles or more, more preferably 0.3 moles or more.

[0124] This ratio makes it easier to achieve both excellent aqueous solution preparation and storage stability, as well as superior performance as a dispersion stabilizer.

[0125] The viscosity (at 20°C) of a 4% by mass aqueous solution of the PVA polymer (A) is not particularly limited, but can be selected from a range of, for example, 1 mPa·s or more (e.g., 1.5 mPa·s or more), preferably 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), and 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.

[0126] The upper limit of the viscosity (at 20°C) of a 4% by mass aqueous solution of the PVA polymer (A) is not particularly limited, but may be selected from a range of approximately 2000 mPa or less (e.g., 1500 mPa·s or less, 1000 mPa·s or less, 500 mPa·s or less), typically from a range of approximately 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), preferably 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), and even more preferably 9 mPa·s or less (e.g., 8 mPa·s or less).

[0127] Specifically, the viscosity (at 20°C) of a 4% by mass aqueous solution of the PVA polymer (A) may be, for example, around 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 around 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).

[0128] The (average) degree of polymerization of the PVA polymer (A) is not particularly limited, but may be, for example, 100 or more (e.g., 120 or more), preferably 150 or more (e.g., 160 or more), and more preferably 180 or more (e.g., 200 or more, 220 or more, 250 or more, 280 or more, 300 or more), etc.

[0129] The upper limit of the (average) degree of polymerization of the PVA polymer (A) is not particularly limited, but may be selected from a range of, for example, 10,000 or less (e.g., 8,000 or less, 5,000 or less), 3,000 or less (e.g., 2,500 or less), preferably 2,000 or less (e.g., 1,500 or less), and even more preferably 1,000 or less (e.g., 800 or less).

[0130] Specifically, the (average) degree of polymerization of the PVA-based polymer (A) may be, for example, 120 to 3000 (for example, 200 to 2000), preferably 250 to 1500, and more preferably 300 to 1000.

[0131] If the viscosity and degree of polymerization of the 4% by mass aqueous solution of the PVA polymer (A) are not too low, it is advantageous in terms of polymerization stability, suppression of scale adhesion, and suppression of coarsening of the resulting vinyl resin. Furthermore, if the viscosity and degree of polymerization of the 4% by mass aqueous solution are not too high, it is advantageous in terms of ease of preparation of the aqueous solution, storage stability, and excellent dispersibility in hot water.

[0132] The viscosity of a 4% by mass aqueous solution (at 20°C) can be determined, for example, by the method specified in JIS K 6726. The degree of polymerization can also be determined, for example, by the method specified in JIS K 6726, or by a calculated (converted) value based on other analytical methods [for example, a calculated (converted) value based on the viscosity of a 4% by mass aqueous solution].

[0133] The cloud point of a 4% by mass aqueous solution of the PVA polymer (A) is preferably 20°C or higher (for example, greater 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 may also be 30°C or higher.

[0134] The upper limit of the cloud point of a 4% by mass aqueous solution of the PVA polymer (A) is not particularly limited, but may be, for example, 75°C, 70°C, 65°C, 60°C, 55°C, 50°C, etc. Typically, the cloud point of a 4% by mass aqueous solution of the PVA polymer (A) may be, for example, 25 to 50°C.

[0135] Such a cloud point results in excellent ease of preparation and storage stability of the aqueous solution.

[0136] The cloud point of the 4% by mass aqueous solution can be adjusted by the degree of saponification, degree of polymerization, and content of ionic skeletons (ionic groups) of the PVA-based polymer (A).

[0137] [Aqueous liquid] The PVA polymer (A) may be used as is as a dispersion stabilizer (dispersant), or it may be used as an aqueous solution dissolved in water. The aqueous solution of the present invention may contain a PVA-based polymer (A) and water. For example, the aqueous solution is obtained by dispersing or dissolving the PVA-based polymer (A) as a dispersed phase in water.

[0138] In aqueous solutions, the content of the PVA-based polymer (A) is not particularly limited, but may be, for example, 1% by mass or more (e.g., 2% by mass or more, 3% by mass or more), or 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).

[0139] The aqueous solution of the present invention has good stability.

[0140] The aqueous solution may contain water-soluble organic solvents to improve its stability during storage. Examples of water-soluble organic solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol; esters such as methyl acetate and ethyl acetate; and glycol derivatives such as ethylene glycol, ethylene glycol monomethyl ether, and ethylene glycol monoethyl ether. Two or more of these organic solvents may be used in combination.

[0141] When a water-soluble organic solvent is included, the proportion of the water-soluble organic solvent to the total solvent may be, for example, 70% by mass or less (for example, 60% by mass or less), preferably 50% by mass or less, and more preferably 30% by mass or less. In particular, from the viewpoint of environmental considerations and improved workability, it is preferable that the content of the organic solvent be 5% by mass or less relative to the total solvent or aqueous solution.

[0142] [Manufacturing method] In the present invention, the method for producing the PVA-based polymer (A) is not particularly limited, but for example, the PVA-based polymer (A-1) can be obtained by acetalizing the PVA-based polymer (C) with an aldehyde or the like having polymerizable unsaturated bonds.

[0143] When incorporating ionic groups into a PVA polymer (A), a PVA polymer (A-2) containing ionic groups can be obtained by simultaneously performing an acetalization reaction on a PVA polymer (C) (without ionic groups) using a carbonyl compound having polymerizable unsaturated bonds (e.g., monoaldehyde) and a carbonyl compound having ionic groups (e.g., aldehyde). Furthermore, by performing an acetalization reaction of a PVA polymer having an ionic group (B-3 or B-4) with a carbonyl compound having a polymerizable unsaturated bond (e.g., monoaldehyde), PVA polymers containing ionic groups (A-3, A-4) can be obtained. Therefore, the process for producing PVA-based polymers (A-1, A-2, A-3, A-4) can be divided into, for example, the process for producing a PVA-based polymer (C) or a PVA-based polymer having ionic groups (B-3 or B-4), and the process for acetalizing one of these PVA-based polymers (acetalization process). The method for producing PVA-based polymers (C) and PVA-based polymers containing ionic groups (B-3 or B-4) is not particularly limited, and conventionally known methods can be used. The following describes in detail the PVA polymer (B-3 or B-4) and PVA polymer (C) having ionic groups, and the acetalization process.

[0144] [PVA-based polymers (B-3), (B-4), and (C)] The PVA polymer (C) is not particularly limited, but for example, a PVA polymer obtained by saponifying (reacting) a vinyl ester polymer [saponified vinyl ester polymer (polymer with vinyl ester monomers as polymerization components)] can be used.

[0145] Furthermore, PVA-based polymers (B-3) and (B-4) can be obtained, for example, in the production of PVA-based polymer (C), as described later, by using other monomers containing monomers having ionic groups, or by using a chain transfer agent containing a chain transfer agent having ionic groups, respectively.

[0146] The vinyl ester polymer can be obtained by polymerizing at least a vinyl ester monomer (polymerizing it as a polymerization component). The polymerization method is not particularly limited, but may follow conventionally known methods, such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Considering the control of the degree of polymerization and the saponification reaction performed after polymerization, solution polymerization using methanol as the solvent or suspension polymerization using water or water / methanol as the dispersion medium is preferred, but is not limited to these.

[0147] The vinyl ester monomers that can be used in the polymerization are not particularly limited, but examples include vinyl acetate, vinyl formate, vinyl propionate, vinyl caprylate, vinyl versatate, and other fatty acid vinyl esters, and one or more of these vinyl ester monomers can be used. Among these, vinyl acetate is preferred from an industrial standpoint.

[0148] In polymerization of vinyl ester monomers, vinyl ester monomers may be copolymerized with other monomers as long as the effects of the present invention are achieved. In other words, the polymerization components of the vinyl ester polymer may include vinyl ester monomers and other monomers. Other monomers that can be used are not particularly limited, but include, for example, α-olefins (e.g., ethylene, propylene, n-butene, isobutylene, etc.), (meth)acrylic acid and its salts, (meth)acrylic acid esters [e.g., alkyl (meth)acrylates (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc., C (meth)acrylate] 1-20C(alkyl, etc.), (meth)acrylamide, (meth)acrylamide derivatives (e.g., N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide, etc.), vinyl ethers (e.g., methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc.) 1-20 Examples include alkyl vinyl ethers, nitriles (e.g., acrylonitrile, methacrylonitrile), vinyl halides (e.g., vinyl chloride, vinyl fluoride), vinylidenes (e.g., vinylidene chloride, vinylidene fluoride), allyl compounds (e.g., allyl acetate, allyl chloride), vinylsilyl compounds (e.g., vinyltrimethoxysilane), fatty acid alkenyl esters (e.g., isopropenyl acetate), etc. One or more of these other monomers can be used.

[0149] Here, by using other monomers, including monomers having ionic groups, a PVA-based polymer (B-3) can be obtained.

[0150] Examples of ionic monomers include those exemplified above, for example, monomers having acidic groups [for example, monomers having carboxyl groups [for example, monocarboxylic acids (e.g., aliphatic unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid), polycarboxylic acids (e.g., aliphatic unsaturated dicarboxylic acids such as itaconic acid, maleic acid, and fumaric acid), and salts thereof], monomers having sulfonic acid groups [for example, alkenyl sulfonic acids (e.g., vinyl sulfonic acid, allyl sulfonic acid), alkenylalene sulfonic acids (e.g., styrene sulfonic acid), amide monomers having sulfonic acid groups (e.g., 2-acrylamido-2-methylpropanesulfonic acid), and salts thereof], and monomers having other ionic groups [for example, monomers having amino groups (e.g., (meth)acrylamidopropyldimethylamine), and salts thereof].

[0151] When using other monomers, the content of the other monomers can be appropriately selected depending on the monomers used, for example, it may be 0.1 to 20% by mass relative to the total amount of polymerization components.

[0152] Furthermore, when polymerizing vinyl ester monomers, it is permissible to include a chain transfer agent in the presence of a chain transfer agent for purposes such as adjusting the degree of polymerization of the resulting vinyl ester polymer. Examples of chain transfer agents are not particularly limited, but include aldehydes such as acetaldehyde, propionaldehyde, butyraldehyde, and benzaldehyde; ketones such as acetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptans such as 2-hydroxyethanethiol, dodecyl mercaptan, 3-mercaptopropionic acid, mercaptosuccinic acid, and sodium 3-mercapto-1-propanesulfonate; and organic halogens such as carbon tetrachloride, trichloroethylene, and perchloroethylene. However, according to the inventors' research, when using common chain transfer agents such as aldehydes and organic halides, the temperature (T) at which the weight loss rate exceeds 0.5% / min tends to be lower (the reason is unclear, but it is thought that thermally unstable structures are more easily introduced to terminal parts, etc.). Therefore, even when using aldehydes or organic halides, it is desirable to keep the amount at a level that satisfies requirement 2.

[0153] Here, by using a chain transfer agent containing an ionic group as the chain transfer agent, a PVA-based polymer (B-4) can be obtained.

[0154] Examples of chain transfer agents having ionic groups include those exemplified above, such as alcohols having ionic groups, carbonyl compounds having ionic groups, and thiols having ionic groups {for example, thiols having acidic groups [for example, thiols having carboxyl groups [for example, mercapto saturated fatty acids (e.g., mercaptoalkanoic acids such as 3-mercaptopropionic acid and mercaptosuccinic acid)], thiols having sulfonic acid groups [for example, mercaptoalkanesulfonic acid (e.g., 3-mercapto-1-propanesulfonic acid)], and salts thereof (e.g., sodium 3-mercapto-1-propanesulfonate)]}.

[0155] The amount of chain transfer agent to be added 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, but generally, 0.1 to 10% by mass relative to the total amount of polymerized components is desirable.

[0156] By saponifying the vinyl ester polymer obtained as described above, PVA polymers (C) (and also (B-3), (B-4)) can be produced.

[0157] The method for the saponification reaction of vinyl ester polymers is not particularly limited, but conventionally known methods may be followed. For example, alcohol decomposition or hydrolysis reactions using acidic catalysts such as alkali metal hydroxides 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. Solvents used in saponification reactions 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 can be used individually or in combination of two or more.

[0158] If a gel-like product precipitates as the saponification reaction progresses, the polyvinyl alcohol polymer can be obtained by pulverizing and drying the gel-like substance. It is preferable to neutralize any remaining catalyst before drying. As a neutralizing agent, if a base catalyst is used, an acidic substance such as acetic acid or phosphoric acid is used; if an acidic catalyst is used, an alkaline substance such as sodium hydroxide or potassium hydroxide is used.

[0159] The drying of the polyvinyl alcohol polymer (C) (and also (B-3), (B-4)) may be carried out under an oxidizing atmosphere such as air, or under an inert atmosphere (e.g., nitrogen). Furthermore, the drying temperature may be at room temperature (natural drying), or under heating or high temperature conditions. However, from the standpoint of efficient drying, it is usually appropriate to use temperatures of 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. There is no upper limit to the drying temperature, but for example, it may 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. However, according to the inventors' research, drying in an oxygen-rich atmosphere such as air or at high temperatures tends to lower the temperature (T) at which the weight loss rate exceeds 0.5% / min (the reason is not clear, but it is thought that thermally unstable structures may be more easily introduced into the main chain, etc.). Therefore, even when drying in an oxidizing atmosphere, under heating, or at high temperatures, it is desirable to keep the drying level to one that satisfies requirement 2.

[0160] From this perspective, drying is preferably carried out under an inert atmosphere, and it is also preferable to dry at a temperature that is not too high (for example, 120°C or below, less than 120°C, 115°C or below, 110°C or below, 100°C or below, 90°C or below, 70-110°C, etc.).

[0161] The drying time is not particularly limited and can be selected according to the drying temperature, etc. For example, it may be around 1 to 12 hours.

[0162] [Acetalization] In the present invention, for example, the method of acetalizing the PVA-based polymer [(C), (B-3), (B-4)] with a carbonyl compound having polymerizable unsaturated bonds (such as an aldehyde) or a carbonyl compound having an ionic group is not particularly limited, and known acetalization methods can be used. PVA polymer (A-1) can be obtained by acetalizing PVA polymer (C) with a carbonyl compound having polymerizable unsaturated bonds. PVA polymer (A-2) can be obtained by acetalizing PVA polymer (C) with a carbonyl compound having polymerizable unsaturated bonds and a carbonyl compound having ionic groups. Furthermore, PVA polymers (A-3, A-4) can be obtained by acetalizing PVA polymers (B-3, B-4) having ionic groups with a carbonyl compound having polymerizable unsaturated bonds.

[0163] In acetalization, the amount of carbonyl compound used is not particularly limited, but may be, for example, 0.05 to 50 parts by mass, preferably 0.1 to 20 parts by mass, and more preferably 0.2 to 10 parts by mass, per 100 parts by mass of the PVA polymer.

[0164] Furthermore, the acetalization reaction is preferably carried out in the presence of an acidic catalyst. The acidic catalyst is not particularly limited, but examples include 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.

[0165] The amount of acidic catalyst used is not particularly limited, but is, for example, 0.1 to 10 parts by mass per 100 parts by mass of PVA polymer.

[0166] Specific acetalization methods include, for example, (i) saponifying a vinyl ester polymer in a solvent such as methanol with a basic catalyst such as sodium hydroxide to obtain a PVA polymer solution, then adding an aldehyde and an acidic catalyst to carry out acetalization, and then neutralizing with a basic substance to obtain a PVA polymer (A) solution; (ii) saponifying a vinyl ester polymer in a solvent such as methanol in the presence of an acidic catalyst as a saponification catalyst to obtain a PVA polymer, then adding an aldehyde, and using the same acidic catalyst used in the saponification reaction to carry out an acetalization reaction, and then neutralizing with a basic substance to obtain a PVA polymer (A) solution; (i (ii) A method of carrying out a saponification reaction and an acetalization reaction simultaneously in a solvent with an acidic catalyst and an aldehyde, etc., of a vinyl ester polymer, and then neutralizing with a basic substance to obtain a solution of PVA polymer (A); (iv) A method of adding an aldehyde, etc., to an aqueous solution of PVA polymer and reacting in the presence of an acidic catalyst, and then neutralizing with a basic substance to obtain an aqueous solution of PVA polymer (A); (v) A method of directly adding an aldehyde, etc., to a slurry or powdered PVA polymer, or adding a liquid dissolved or dispersed in an organic solvent or water, reacting in the presence of an acidic catalyst, then neutralizing with a basic substance, and further removing excess solvent to obtain PVA polymer (A); and so on. In methods (i) to (iii), the solvent can then be dried to obtain a solid, or the solvent can be replaced with water to obtain an aqueous solution. In method (iv), the PVA polymer (A) can be obtained as an aqueous solution and can be used directly in the suspension polymerization of vinyl chloride, etc. The method of reacting in a slurry state as in (v) is easy to handle because the PVA polymer (A) can be obtained as a solid. Furthermore, in methods (i) to (v), the methods for preparing the PVA polymer as an aqueous solution, saponification, neutralization, dissolution, dispersion, and drying are not particularly limited, and conventional methods can be used.

[0167] Furthermore, there are no particular restrictions on the basic substance used for neutralization, but examples include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide.

[0168] The pH of the reaction solution during the acetalization reaction is preferably 3.0 or lower from the viewpoint of reaction rate, and more preferably 1.0 or lower. Furthermore, the pH of the reaction solution after neutralization is preferably 4.7 to 9.0, and more preferably 7.0 to 8.5.

[0169] The drying of polyvinyl alcohol polymer (A) may be carried out in the same manner as for polyvinyl alcohol polymer (C) (and also (B-3), (B-4)). The drying conditions [drying atmosphere, drying temperature, drying time (e.g., 1 to 12 hours, etc.)] and preferred embodiments (and the reasons for them) are as described above (for example, it is preferable to dry under an inert atmosphere such as nitrogen at a temperature that is not too high (e.g., 70 to 110°C, etc.)).

[0170] [Applications, methods for producing vinyl polymers, etc.] PVA polymer (A) can be used for various applications (e.g., dispersants, film applications, etc.), but as mentioned above, it is particularly suitable for use as a dispersion stabilizer [or dispersant, for example, a dispersion stabilizer (dispersant) for polymerization (e.g., suspension polymerization)]. Therefore, the following describes a method for producing vinyl polymers by using the dispersion stabilizer of the present invention (or PVA-based polymer (A), hereinafter the same) or by polymerization of vinyl monomers (especially suspension polymerization) using the dispersion stabilizer.

[0171] The suspension polymerization method in this invention involves adding an insoluble vinyl monomer and an oil-soluble polymerization initiator to an aqueous medium and stirring to form tiny droplets containing the vinyl monomer, during which polymerization is carried out. The aqueous medium that can be used is not particularly limited, but examples include water, aqueous solutions containing various additive components, and mixed solvents of water and water-compatible organic solvents.

[0172] The PVA-based polymer (A) described above in the present invention can be used as a dispersion stabilizer when performing suspension polymerization of vinyl monomers. The vinyl monomer is not particularly limited, but vinyl monomers to which suspension polymerization is generally applied, such as vinyl chloride, vinylidene chloride, styrene, acrylic acid esters, methacrylic acid esters, vinyl acetate, and acrylonitrile, are preferred, and among these, vinyl chloride monomers are particularly preferred.

[0173] Examples of vinyl chloride monomers include vinyl chloride monomer (vinyl chloride), and mixtures of vinyl chloride monomer with other monomers copolymerizable thereto. Examples of other monomers copolymerizable with vinyl chloride monomer include vinylidene chloride, vinyl acetate, ethylene, propylene, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, vinylalkoxysilane, maleic acid, hydroxyalkyl acrylate, allyl sulfonic acid, and vinyl sulfonic acid.

[0174] Therefore, the dispersion stabilizer of the present invention is suitable for suspension polymerization of vinyl monomers, including vinyl chloride monomers (especially vinyl chloride), and can be used particularly suitably for the homopolymerization of vinyl chloride by suspension polymerization. It can also be used for binary or more multi-component copolymerization of vinyl chloride with one or more monomers selected from known monomers copolymerizable with vinyl chloride by suspension polymerization, and is particularly suitable as a dispersion stabilizer in the copolymerization of vinyl chloride and vinyl acetate by suspension polymerization.

[0175] A vinyl chloride resin can be obtained by suspension polymerization of vinyl monomers containing vinyl chloride. In the production of a vinyl chloride resin, it is preferable that 50 to 100 mol% (or 50 to 100% by mass) of the total amount of vinyl monomers used is vinyl chloride.

[0176] Polymerization initiators in the suspension polymerization of vinyl monomers can also be known ones, such as peroxide compounds like diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds like benzoyl peroxide, t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, and t-butyl peroxydecanoate; peroxides like acetylcyclohexylsulfonyl peroxide and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate; azo compounds like 2,2'-azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, and azobis(4-methoxy-2,4-dimethylvaleronitrile); benzoyl peroxide and lauroyl peroxide. Furthermore, these can be used in combination with potassium persulfate, ammonium persulfate, hydrogen peroxide, etc.

[0177] The main role of a dispersion stabilizer in the suspension polymerization of vinyl monomers is to stabilize droplets consisting of vinyl monomers and their polymers, and to prevent the polymer particles formed in the droplets from fusing together and forming large clumps. However, because the dispersion stabilizer of the present invention has excellent dispersion performance, it is possible to form stable droplets with a small amount of use and prevent the formation of clumps due to the aforementioned fusion. Furthermore, droplet stability means that fine, nearly uniformly sized droplets are stably dispersed in the dispersion medium of suspension polymerization.

[0178] In the suspension polymerization of vinyl monomers, there are no particular restrictions on the amount of the dispersion stabilizer of the present invention (or PVA polymer (A)) used, but it is usually 5 parts by mass or less per 100 parts by mass of vinyl monomers, preferably 0.005 to 1 part by mass, and more preferably 0.01 to 0.2 parts by mass. Similar to conventional dispersion stabilizers, the dispersion stabilizer of the present invention is generally dissolved in the dispersion medium of the suspension polymerization using a conventional method before charging the vinyl monomers.

[0179] As a dispersion stabilizer in the suspension polymerization of vinyl monomers, the dispersion stabilizer of the present invention may be used alone, or other dispersion stabilizers may be used in combination. Such other dispersion stabilizers include known dispersion stabilizers used when vinyl monomers such as vinyl chloride are suspended polymerized in an aqueous medium, such as PVA with an average degree of polymerization of 100 to 4500 and a degree of saponification of 30 to 100 mol%, modified PVA polymers other than those of the present invention, water-soluble cellulose ethers such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, water-soluble polymers such as gelatin, oil-soluble emulsions such as sorbitan monolaurate, sorbitan triolate, glycerin tristearate, and ethylene oxide propylene oxide block polymer, and water-soluble emulsifiers such as polyoxyethylene glycerin oleate and sodium laurate. One of these other dispersants may be used, or two or more may be used simultaneously.

[0180] In the present invention, it is preferable to use a combination of two or more PVA-based polymers with different degrees of polymerization and saponification as dispersion stabilizers, and it is preferable that one or more of these polymers be the PVA-based polymer (A) which is the dispersion stabilizer of the present invention. More preferably, a combination of a PVA-based polymer with a degree of polymerization of 1700 or higher and a PVA-based polymer with a degree of polymerization of 1000 or lower is used, and one or more of these polymers are the PVA-based polymer (A) of the present invention.

[0181] In suspension polymerization using the dispersion stabilizer of the present invention, various known dispersion aids can also be used in combination. As such dispersion aids, low-saponification PVA with a degree of saponification of preferably 30 to 60 mol%, more preferably 35 to 55 mol%, is used. Furthermore, the dispersion aid used is PVA with an average degree of polymerization of preferably 160 to 900%, more preferably 200 to 500.

[0182] In addition to dispersing agents, various additives known in the suspension polymerization of vinyl compounds, such as chain transfer agents, polymerization inhibitors, pH adjusters, scale inhibitors, and crosslinking agents, may also be used in combination.

[0183] There are no restrictions on the polymerization temperature in suspension polymerization, and it can be arbitrarily selected depending on the type of vinyl monomer used, the desired degree of polymerization of the polymer, the polymerization yield, etc. However, it is generally preferable to use a temperature of 40 to 70°C. There are also no particular restrictions on the polymerization time, and it can be set appropriately according to the desired polymerization yield, etc.

[0184] The vinyl polymer obtained by the manufacturing method of the present invention described above can be processed into various molded articles and the like. In particular, vinyl chloride resins can be efficiently obtained, for example, with an average particle size within an appropriate range and excellent plasticizer absorption, and often have good processability for various molded articles. [Examples]

[0185] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples. In the following examples and comparative examples, "%" and "parts" refer to "mass%" and "parts by mass," respectively, unless otherwise specified.

[0186] First, the evaluation methods for PVA and vinyl chloride polymer (vinyl chloride resin) in this example are described below.

[0187] (Method for measuring the degree of polymerization and viscosity of a 4% aqueous solution at 20°C (4% viscosity)) The measurements were performed in accordance with the method specified in JIS K 6726.

[0188] (Method for measuring the degree of saponification) The measurements were performed in accordance with the method specified in JIS K 6726.

[0189] (Method for measuring the amount of polymerizable unsaturated bonds contained in PVA) An aqueous solution of 5 g of PVA polymer was dissolved in 150 g of pure water in an Erlenmeyer flask. A 0.5 mol / L bromine acetic acid solution was added dropwise to this solution and the titration was continued until the bromine color (yellow) disappeared. The amount of polymerizable unsaturated bonds contained in the PVA (μmol / g) was calculated by dividing the amount of bromine (μmol) required for the titration by the weight (g) of PVA.

[0190] (Thermogravimetric measurement method) Measurements were performed using the NEXTA STA200RV manufactured by Hitachi High-Tech Science Co., Ltd. under the following conditions. • Nitrogen flow rate: 100 mL / min • Sample weight: 5-6 mg • Measurement temperature range: 50~500℃ • Heating rate: 10°C / min Using the results of thermogravimetric analysis, the polymerization loss rate (% / min) was calculated, and the temperature (T) at which this rate was 0.5% / min in the temperature range of 150°C or higher was determined. The temperature range was set to 150°C or higher, considering that weight loss at temperatures below 150°C may be mainly due to volatile components (residual volatile components of water, methanol, and methyl acetate) present in the sample. For the sample, a PVA-based polymer (A) was extracted using Soxhlet extraction with methanol as the solvent. The resulting sample was dried under reduced pressure at 120°C for 1 hour, pulverized, and then passed through a 60-mesh sieve.

[0191] (Method for measuring the cloud point of PVA aqueous solution) A 4% PVA aqueous solution at 20°C was placed in a quartz cell with a path length of 10 mm. Using a UV-Vis spectrophotometer (JASCO Corporation; V-730), the transmittance over 430 mm was continuously measured at a heating rate of 2°C / min starting from 20°C. The cloud point was defined as the temperature at which the transmittance was 50% of that of the blank (pure water).

[0192] (Method for evaluating the storage stability of PVA aqueous solution) A beaker containing a 4% PVA aqueous solution was placed in a 30°C constant temperature water bath, and the state of the aqueous solution was visually inspected after 24 hours and evaluated according to the following criteria. ○: The aqueous solution remained homogeneous. ×: The aqueous solution separated into two layers.

[0193] (Evaluation of vinyl chloride polymers) The vinyl chloride polymer was evaluated as follows.

[0194] <Average particle size> The particle size distribution was measured using a rotary vibrating screen (JIS screen used), and the average particle diameter was determined.

[0195] <Plasticizer absorption> The obtained resin was placed in a cylindrical container packed with fiberglass at the bottom, excess dioctyl phthalate (hereinafter abbreviated as DOP) was added, and the resin was left to stand for 30 minutes to allow the DOP to permeate it. After removing the excess DOP by centrifuging at 3000 rpm, the weight of the resin was measured, and the amount of DOP absorbed per 100 parts of polymer was calculated. A higher amount of DOP absorption indicates better plasticizer absorption and superior moldability.

[0196] <Evaluation of the thermal stability of vinyl chloride polymers> A blend of 100 parts by mass of vinyl chloride polymer, 0.5 parts by mass of dioctyl tin mercapto stabilizer, 0.8 parts by mass of fatty acid ester lubricant, and 0.5 parts by mass of calcium stearate was prepared. This mixture was then melt-kneaded using a plastograph (Laboplastmill, manufactured by Toyo Seiki Co., Ltd.) under conditions of a mixer temperature of 180°C and a rotor speed of 40 rpm. The time from the start of kneading until the resin blackened and the rotor torque began to increase was measured. A longer time indicates better thermal stability.

[0197] [Example 1] (Synthesis of PVA-based polymer (C)) A reactor equipped with a stirrer, condenser, nitrogen gas inlet, and initiator inlet was pre-charged with 55 parts methanol and 45 parts vinyl acetate monomer. The system was heated to 60°C while circulating nitrogen gas through it, and 5 parts of a 1% methanol solution of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) were added as an initiator to start polymerization. During polymerization, the system was maintained at 60°C, and nitrogen gas was flowed through the system while 90 parts of vinyl acetate monomer were continuously added from immediately after the start of polymerization for 4 hours. At 1 hour and 2 hours after the start of polymerization, 1 part each of a 1% methanol solution of ADVN was added. When the reaction yield of vinyl acetate reached 85%, the system was cooled and polymerization was terminated. The acetaldehyde concentration at the end of polymerization was 100 ppm. 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. Next, 100 parts of a 50% methanol solution of polyvinyl acetate obtained above were mixed with 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide, and the mixture was carried out at 40°C. The resulting gel was pulverized and immersed in a mixed solvent (200 parts) of 100 parts methanol and 100 parts methyl acetate, and acetic acid was added until the pH became 9 to neutralize it. Subsequently, the sample obtained by solid-liquid separation was dried under a nitrogen atmosphere at 80°C for 5 hours. Analysis revealed a PVA-based polymer (C) powder with a degree of saponification of 76 mol% and a viscosity of 5.5 mPa·s in a 4% by mass aqueous solution (20°C).

[0198] (Synthesis of PVA-based polymer (A-1)) 100 parts of the PVA polymer (C) powder obtained above were immersed in a mixed solvent of 150 parts methanol and 300 parts methyl acetate, 0.8 parts acrolein were added, and the mixture was held at 50°C for 1 hour. Then, 5 parts of a 50% methanol solution of p-toluenesulfonic acid were added, and the reaction was carried out at 50°C for 1 hour. Next, the solution was neutralized with 10 parts of a 5% methanol solution of sodium hydroxide. The pH after neutralization was 7.5. Next, the solvent was removed by centrifugation, and the mixture was dried under a nitrogen atmosphere at 80°C for 5 hours to obtain PVA-based polymer (A-1). The analytical values ​​of this PVA-based polymer (A-1) were a degree of saponification of 77 mol%, a viscosity of 5.8 mPa·s (average degree of polymerization approximately 600) in a 4% aqueous solution (20°C), and a cloud point of 35°C for a 4% aqueous solution. The degree of saponification and degree of polymerization were measured according to the method specified in JIS K 6726. The double bond content derived from acrolein was 80 μmol / g, and thermogravimetric analysis revealed that the temperature (T) at which the weight loss rate exceeded 0.5% / min was 272°C. Furthermore, the 4% PVA aqueous solution remained homogeneous even after being held at 30°C for 24 hours.

[0199] (Suspension polymerization of vinyl chloride) The PVA 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. In a pressure-resistant stainless steel polymerization reactor, 120 parts of deionized water and 1.5 parts of a 4% aqueous solution of the PVA-based polymer (A-1) obtained above (0.06 parts of PVA-based polymer (A-1) per 100 parts of vinyl chloride monomer) were charged. Next, the pressure inside the polymerization reactor was reduced to 50 mmHg using a vacuum pump, and after degassing, 100 parts of vinyl chloride monomer were charged, followed by 0.06 parts of t-butyl peroxyneodecanoate as a polymerization initiator. After that, stirring was performed and the temperature was increased. Suspension polymerization was carried out while maintaining the internal temperature of the polymerization reactor at 57°C, and the polymerization reaction was stopped when the conversion rate of vinyl chloride reached 88%. Then, after recovering the unreacted monomers using a vacuum trap, the polymer slurry was withdrawn from the polymerization reactor, dehydrated, and dried to obtain vinyl chloride polymer (vinyl chloride resin).

[0200] [Examples 2-12] 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 in the acetalization reaction were appropriately changed. 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.

[0201] [Comparative Examples 1-4] As described below, the PVA-based polymer (A-1) shown in Table 1 was synthesized, and using the obtained PVA-based polymer (A-1), a vinyl chloride polymer was obtained by suspension polymerization of vinyl chloride in the same manner as in Example 1.

[0202] Table 1 summarizes the evaluation results for the PVA-based polymer (A-1) and the resulting vinyl chloride polymer.

[0203] [Table 1]

[0204] As shown in the table above, when the PVA-based polymer (A-1) obtained in Examples 1 to 12 was used in the suspension polymerization of vinyl chloride, a vinyl chloride resin with excellent polymerization stability, an appropriate average particle size, high plasticizer absorption, and excellent thermal stability was obtained.

[0205] [Comparative Example 1] PVA polymer (A-1) was synthesized in the same manner as in Example 1, except that PVA polymer (C) was dried in an air atmosphere at 150°C for 5 hours. The obtained PVA polymer (A-1) had low thermal stability. Suspension polymerization of vinyl chloride was attempted in the same manner as in Example 1, but the thermal stability of the resulting vinyl chloride was low.

[0206] [Comparative Example 2] A PVA-based polymer (C) that does not contain double bonds, with a 4% by mass aqueous solution viscosity (20℃) of 5.5 mPa·s (average degree of polymerization approximately 600) and a degree of saponification of 77 mol%, was used as PVA-based polymer (A-1), and suspension polymerization of vinyl chloride was attempted in the same manner as in Example 1. However, the vinyl chloride resin became blocky, and polymerization could not be carried out normally.

[0207] [Comparative Example 3] Polyvinyl acetate was obtained by polymerizing vinyl acetate in the presence of carbon tetrachloride. This was then saponified according to Example 1 to obtain a PVA-based polymer with a viscosity (20°C) of 5.5 mPa·s (average degree of polymerization approximately 600) in a 4% by mass aqueous solution, a degree of saponification of 77 mol%, a double bond content of 80 μmol / g, and a temperature (T) of 220°C. Suspension polymerization of vinyl chloride was carried out using this PVA-based polymer in the same manner as in Example 1, but the thermal stability of the resulting PVC resin was low.

[0208] [Comparative Example 4] Polyvinyl acetate was obtained by polymerizing vinyl acetate in the presence of acetaldehyde. This was then saponified according to Example 1 to obtain a PVA-based polymer with a degree of saponification of 77 mol% and a viscosity (20°C) of 5.5 mPa·s (average degree of polymerization of approximately 600) in a 4% by mass aqueous solution. This was dried under a nitrogen atmosphere at 130°C for 5 hours to obtain a PVA-based polymer with a double bond content of 80 μmol / g and a temperature (T) of 252°C. Suspension polymerization of vinyl chloride was carried out using this PVA-based polymer in the same manner as in Example 1, but the thermal stability of the obtained PVC resin was low.

[0209] [Examples 13-15] Except for appropriately changing the saponification conditions, the type (2 types) of aldehyde used in the acetalization reaction, and the amount used, 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.

[0210] [Table 2]

[0211] [Example 16] (Synthesis of PVA-based polymer (B-3)) A reactor equipped with a stirrer, condenser, nitrogen gas inlet, and initiator inlet was pre-charged with 55 parts methanol and 45 parts vinyl acetate monomer. The system was heated to 60°C while circulating nitrogen gas, and 6 parts of a 1% methanol solution of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) were added as an initiator to start polymerization. During polymerization, the system was maintained at 60°C, and nitrogen gas was flowed through the system while 90 parts of vinyl acetate monomer and 2 parts of a methanol solution of 20% itaconic acid were continuously added from immediately after the start of polymerization for 4 hours. At 1 hour and 2 hours from the start of polymerization, 1.2 parts of a 1% methanol solution of ADVN were added, respectively. When the reaction yield of vinyl acetate reached 85%, the system was cooled and polymerization was terminated. 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. Next, 100 parts of a 50% methanol solution of polyvinyl acetate obtained above were mixed with 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide, and the mixture was carried out at 40°C. The resulting gel was pulverized and immersed in a mixed solvent (200 parts) of 100 parts methanol and 100 parts methyl acetate, and acetic acid was added until the pH became 9 to neutralize it. Subsequently, the sample obtained by solid-liquid separation was dried under a nitrogen atmosphere at 80°C for 5 hours. Analysis revealed a PVA-based polymer (B-3) powder with a degree of saponification of 71 mol%, a viscosity of 5.5 mPa·s (average degree of polymerization approximately 600) in a 4% by mass aqueous solution (20°C), and an itaconic acid content of 0.2 mol%.

[0212] (Synthesis of PVA-based polymer (A-3)) The PVA-based polymer (A-3) shown in Table 3 was synthesized in the same manner as in Example 1.

[0213] (Suspension polymerization of vinyl chloride) 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.

[0214] [Examples 17-20] The PVA-based polymer (A-3) shown in Table 3 was synthesized in the same manner as in Example 16, except that various conditions were changed as appropriate. 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. Table 3 summarizes the evaluation results for the PVA-based polymer (A-3) and the resulting vinyl chloride polymer. In the table, "AMPS" refers to sodium 2-acrylamido-2-methylpropanesulfonate.

[0215] [Table 3]

[0216] [Example 21] (Synthesis of PVA-based polymer (B-4)) A reactor equipped with a stirrer, condenser, nitrogen gas inlet, and initiator inlet was pre-charged with 20 parts methanol, 80 parts vinyl acetate monomer, and 0.02 parts 3-mercaptopropionic acid. The system was heated to 60°C while circulating nitrogen gas through it, and 1.5 parts of a 1% methanol solution of 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN) was added as an initiator to start polymerization. During polymerization, the system was maintained at 60°C, and nitrogen gas was flowed through the system while 2 parts of a 10% methanol solution of 3-mercaptopropionic acid were continuously added from immediately after the start of polymerization for 4 hours. Furthermore, 0.5 parts each of a 1% methanol solution of ADVN were added at 1 hour and 2 hours from the start of polymerization. When the reaction yield of vinyl acetate reached 80%, the system was cooled and polymerization was terminated. The remaining vinyl acetate monomer was distilled off while methanol vapor was added to the obtained polymer to obtain a 50% methanol solution of polyvinyl acetate. Next, 100 parts of a 50% methanol solution of polyvinyl acetate obtained above were mixed with 14 parts of methyl acetate and 6 parts of a 3% methanol solution of sodium hydroxide, and the mixture was carried out at 40°C. The resulting gel was pulverized and immersed in a mixed solvent (200 parts) of 100 parts methanol and 100 parts methyl acetate, and acetic acid was added until the pH became 9 to neutralize it. Subsequently, the sample obtained by solid-liquid separation was dried under a nitrogen atmosphere at 80°C for 5 hours. Analysis revealed a PVA-based polymer (B-4) powder with a degree of saponification of 71 mol%, a viscosity of 5.5 mPa·s (average degree of polymerization approximately 600) in a 4% aqueous solution (20°C), and a 3-mercaptopropionic acid content of 0.2 mol%.

[0217] (Synthesis of PVA-based polymer (A-4)) The PVA-based polymer (A-4) shown in Table 4 was synthesized in the same manner as in Example 1.

[0218] (Suspension Polymerization of Vinyl Chloride) Using the obtained PVA-based polymer (A-4), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1, whereby a vinyl chloride polymer was obtained.

[0219] [Examples 22 to 24] The PVA-based polymers (A-4) shown in Table 4 were synthesized in the same manner as in Example 21, except that various conditions were appropriately changed. Using the obtained PVA-based polymer (A-4), suspension polymerization of vinyl chloride was carried out in the same manner as in Example 1, whereby a vinyl chloride polymer was obtained.

[0220] The evaluation results of the PVA-based polymer (A-4) and the obtained vinyl chloride polymer are collectively shown in Table 4. In the table, "MPS" refers to sodium 3-mercapto-1-propanesulfonate.

[0221]

Table 4

[0222] When the PVA-based polymers (A-2, A-3, A-4) obtained in Examples 13 to 24 were used for suspension polymerization of vinyl chloride, it was possible to obtain a vinyl chloride resin excellent in polymerization stability, having an average particle diameter within an appropriate range, a large plasticizer absorption amount, and excellent thermal stability.

Industrial Applicability

[0223] 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 satisfies the following requirements 1 and 2 and has a degree of saponification of 60 mol% or more. Requirement 1: Contains an acetal skeleton (a) having polymerizable unsaturated bonds. Requirement 2: In the temperature range of 150°C or higher, the temperature at which the weight loss rate exceeds 0.5% / min, as determined by thermogravimetric measurements under a nitrogen atmosphere at a heating rate of 10°C / min, is 255°C or higher.

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, wherein the temperature at which the weight loss rate exceeds 0.5% / min, as determined by thermogravimetric measurement at a heating rate of 10°C / min under a nitrogen atmosphere in a temperature range of 150°C or higher, is 258°C or higher.

4. The proportion of polymerizable unsaturated bonds is 5 to 500 μmol / g. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the temperature at which the weight loss rate exceeds 0.5% / min, as determined by thermogravimetric measurement at a heating rate of 10°C / min under a nitrogen atmosphere in a temperature range of 150°C or higher, is 260°C or higher.

5. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the acetal skeleton (a) comprises a skeleton represented by the following formula (a1). 【Chemistry 1】 (In the formula, R' represents a group having a polymerizable unsaturated bond.)

6. The acetal skeleton (a) includes the skeleton represented by formula (a1), The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the content of the acetal skeleton (a) is 0.05 to 5 mol% per monomer unit.

7. Furthermore, the polyvinyl alcohol-based polymer (A) according to claim 1 or 2 contains an ionic skeleton (b).

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

9. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the degree of saponification is 60 to 90 mol%.

10. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the degree of saponification is greater than 60 mol%.

11. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the degree of saponification is 72 mol% or more.

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

13. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the viscosity of a 4% by mass aqueous solution (at 20°C) is 3 mPa·s or more.

14. The polyvinyl alcohol-based polymer (A) according to claim 1 or 2, wherein the average degree of polymerization is 250 or more.

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

16. The agent according to claim 15, which is a dispersion stabilizer for polymerization.

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

18. The agent according to claim 15, which is a dispersion stabilizer for suspension polymerization of vinyl monomers containing vinyl chloride.

19. A method for producing a vinyl polymer, comprising polymerizing a vinyl monomer in the presence of a polyvinyl alcohol polymer (A) according to claim 1 or 2.

20. The manufacturing method according to claim 19, wherein polymerization is suspension polymerization.

21. The method for producing a vinyl monomer containing vinyl chloride by suspension polymerization, as described in claim 19.

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