JP5779149B2 - White pigment dispersion composition for inkjet recording, method for producing AB block copolymer used in the composition, and white ink composition for inkjet recording - Google Patents

Description

  The present invention relates to an ink used for ink jet recording, a white pigment dispersion composition suitable for an ultraviolet or electron beam curable ink for ink jet recording, and production of an AB block copolymer used as a pigment dispersant for the composition. The present invention relates to a method and a white ink composition for ink jet recording comprising the above composition. More specifically, titanium pigment, a white pigment with excellent hiding power and heavy specific gravity, can be stably finely dispersed to a level suitable for ink for ink jet recording, and can easily return to its original dispersed state even when it settles. The present invention relates to a technique for providing an excellent pigment dispersant capable of producing

  In recent years, as an environmentally friendly printing method that reduces the burden on the environment, methods that use water-based ink, ultraviolet curable ink, or electron beam curable ink that do not use an organic solvent have been developed. Ink-jet printing methods that allow printing on various parts without using a plate with an inexpensive manufacturing facility have been adopted.

  In particular, inkjet printing performed using ultraviolet curable ink has the advantage that printing on a film, which is a plastic medium, can be suitably performed due to the high adhesion of the ink to the base material by ultraviolet curing. Its development is ongoing. However, many films are transparent, and unlike white paper, white ink is required to express white on the film. In this case, titanium oxide, a white pigment having a hiding power, is used for the white ink.

  However, titanium oxide has a high specific gravity, and white ink using titanium oxide as a white pigment tends to cause precipitation of titanium oxide, which is particularly problematic in inks for inkjet recording in which ink is ejected from the head for printing. Become. On the other hand, a polymer dispersant having a structure peculiar to a terminal for stably dispersing titanium oxide in an inkjet ink has been developed (Patent Document 1). Specifically, pigment dispersion obtained by dispersing titanium oxide in a UV-curable white ink for inkjet, a polymerizable compound represented by a curable polymerizable monomer, and a dispersant having a specific structure The liquid is going to be used.

JP 2007-270089 A

  However, according to the study by the present inventors, in a white ink obtained by dispersing titanium oxide having a heavy specific gravity as a white pigment, titanium oxide is likely to settle, and the above-described technique has not been sufficiently solved. In addition, when titanium oxide settles, it may be restored to the original dispersed state by stirring, but in many cases, it becomes a sticky gel-like sediment, or even a hard hard cake, There is also a problem that even if stirred, the original dispersion is not obtained. In addition, even if the precipitate disappears by stirring, the precipitated pigments adsorb each other to increase the particle size, which may cause clogging of the ink-jet head and cause problems such as being unable to print. is there. Under these circumstances, the present inventors have prevented the sedimentation of titanium oxide, which is a white pigment that is excellent in hiding power and useful for printing on a transparent film, which is a plastic medium, in the dispersion liquid, or settles. However, it has been recognized that it is necessary to develop a pigment dispersant that can be easily returned to the original dispersed state by stirring.

  Accordingly, an object of the present invention is to provide a white pigment dispersion composition in which titanium oxide, which is a white pigment, is stably dispersed to a particle size that can be used for inkjet printing. Furthermore, the object of the present invention is to prevent the titanium oxide in the white pigment dispersion from precipitating, or even if it settles, it can be easily returned to the original dispersed state by stirring again. An object of the present invention is to provide a white pigment dispersion composition suitable for inkjet printing on a film, and a white ink composition for inkjet recording using such a pigment dispersion.

  As a result of diligent investigations on the above-described problems of the prior art, the present inventors have been able to solve the above problems. Dispersibility, anti-settling property, and settling recovery property of titanium oxide used as a white pigment constituting white ink The present inventors have found a pigment dispersant comprising a copolymer having a specific structure capable of remarkably improving (hereinafter collectively referred to as “precipitation”). That is, a white pigment dispersion composition obtained by dispersing titanium oxide in such a pigment dispersant exhibits excellent pigment dispersibility and sedimentation, and an ink obtained using the white pigment dispersion is ink jet printing. It will be suitable for. Furthermore, the ink using the pigment dispersion exhibits high adhesion to a transparent substrate film in ink jet printing, and exhibits curability comparable to that of an ultraviolet curable ink. The headline and the present invention were completed.

The above object is achieved by the present invention described below. That is, in the present invention, 15 to 59% by mass of one or more polymerizable compounds (A) as a dispersion medium, 40 to 70% by mass of titanium oxide (B) as a white pigment, and 0.1% of a pigment dispersant (C). A polymer block comprising 7 to 12% by mass and 0 to 15% by mass of an organic solvent (D), wherein the pigment dispersant (C) comprises 90% by mass or more of a structural unit derived from a methacrylic acid monomer. and B is a-B block copolymer of the polymer block consisting of a-B block type, the a-B block copolymers, the B polymer block, a carboxyl group-containing methacrylic acid-based monomer and a phosphoric acid group having a carboxyl group An acid group-containing block comprising a structural unit derived from at least one of the acid group-containing methacrylic acid monomers of a phosphoric acid group-containing methacrylic acid monomer having Copolymers der is, the B polymer block, the acid value by a carboxyl group or a phosphoric acid group derived from the acid group-containing methacrylic acid-based monomer is a 50~500mgKOH / g, the molecular weight of said B polymer block (A- The number average molecular weight of the B block copolymer minus the number average molecular weight of the A polymer block) is in the range of 200 to 3,000, and the number average molecular weight of the AB block copolymer is 4,000 to 20 , 000, and its molecular weight distribution (weight average molecular weight / number average molecular weight) is 1.6 or less, and the acid group-containing methacrylic acid monomer is methacrylic acid, methacryloyloxyethylphthalic acid, and methacryloyloxy inkjet be at least one der characterized Rukoto ethyl phosphoric acid ester Preparative recording white pigment dispersion composition (hereinafter, referred to as white pigment dispersion) provides.

The following are mentioned as a preferable form of the said white pigment dispersion .
The average particle diameter of the titanium oxide being distributed (B) is 100 to 300 nm;
The polymerizable compound (A) is selected from the group consisting of cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, t-butylcyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, isobornyl acrylate and adamantyl acrylate. Be at least one selected ;
Monomers constituting the front Symbol A polymer block is poly (n = 2 or higher) alkylene (C2-C4) glycol methacrylate, poly (n = 2 or higher) alkylene (C2-C4) glycol monoalkyl (C1 - C18) ether methacrylate, and poly (n = 2 or more) hydroxyalkyl (C2-C18) is at least one kind of methacrylate acid, it is.

  Another embodiment of the present invention is a method for producing an acid group-containing AB block copolymer used in the pigment dispersant (C) constituting the white pigment dispersion, which comprises a polymerization initiating compound and a catalyst. In the presence, it has a step of living radical polymerization of a monomer component containing a methacrylic acid-based monomer, the polymerization initiating compound used in this step is at least one of iodine or iodine compound, and the catalyst used in this step is , Phosphorous halide, phosphite compound, phosphinate compound, imide compound, phenol compound, diphenylmethane compound and cyclopentadiene compound, and polymerization thereof Method for producing acid group-containing AB block copolymer, characterized in that the temperature is 30 to 50 ° C To provide.

As a preferable form of the method for producing the acid group-containing AB block copolymer, the monomer component containing a methacrylic acid monomer in the presence of the catalyst and the catalyst is living at a polymerization temperature of 30 to 50 ° C. after forming the a polymer block by radical polymerization, further, a monomer component containing at least one kind of the phosphoric acid group-containing methacrylic acid-based monomer having a carboxyl group-containing methacrylic acid-based monomer and a phosphoric acid group having a carboxyl group To obtain an AB block copolymer containing 90% by mass or more of a structural unit derived from a methacrylic acid monomer by forming a B polymer block by living radical polymerization at a polymerization temperature of 30 to 50 ° C. Is mentioned.

  As another embodiment of the present invention, there is provided a white ink composition for ink-jet recording comprising the above-mentioned white pigment dispersion composition. As a preferable form of the ink composition, an ultraviolet or electron beam curable ink further containing a photopolymerization initiator can be mentioned.

  According to the present invention described above, a white pigment dispersion obtained by stably finely dispersing titanium oxide, which can be used for an ink for ink jet printing, and is particularly suitable for an ink for ink jet printing of ultraviolet ray or electron beam type. Can be provided. This white pigment dispersion can stably disperse titanium oxide, which is a white pigment with a high specific gravity, in a fine state until it can be used for ink jet printing, and there is almost no sedimentation. It can be easily returned to the original dispersed state by a simple operation, and has excellent sedimentation recoverability. In addition, according to the present invention, the curability is excellent, and the adhesive property of the printed matter after being cured by printing on a plastic medium such as a transparent film is also obtained. An excellent ink for ink-jet printing can be provided.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments for carrying out the present invention.
The white pigment dispersion of the present invention comprises, on a mass basis, 15 to 59% of one or more polymerizable compounds (A) as a dispersion medium, 40 to 70% of white pigment titanium oxide (B), a pigment dispersant ( C) 0.7 to 12% and organic solvent (D) 0 to 15%, and the pigment dispersant is an acid group-containing block copolymer having the following specific structure: . Specifically, the block copolymer is an AB block type copolymer composed of an A polymer block and a B polymer block containing 90% or more of a structural unit derived from a methacrylic acid monomer, At least one of the B polymer blocks is an acid group-containing methacrylic acid, at least one of a carboxyl group-containing methacrylic acid monomer having a carboxyl group and a phosphate group-containing methacrylic acid monomer having a phosphate group. It comprises a structural unit derived from a system monomer. Hereinafter, components essential to the white pigment dispersion for inkjet recording of the present invention will be described.

<Pigment dispersant (C)>
As described above, the white pigment dispersion of the present invention contains titanium oxide having a high specific gravity as a white pigment, and is derived from a methacrylic acid monomer as a pigment dispersant (C) for dispersing the pigment. An AB block type copolymer containing 90% by mass or more of a structural unit, wherein at least the B polymer block contains a structural unit derived from a specific acid group-containing methacrylic acid monomer (hereinafter referred to as an “acid group-containing block copolymer”). It is also simply called an AB block copolymer).

  This AB block copolymer consists of a polymer block of A and a polymer block of B. As described below, the polymer blocks of A and B exhibit different functions due to the difference in configuration. Specifically, one A polymer block is a polymer block that dissolves and dissolves in the polymerizable compound (A) that is the dispersion medium constituting the white pigment dispersion of the present invention, and the other B polymer block is The polymer block adsorbs the acidic group of the polymer block to the surface of the pigment titanium oxide or the treated titanium oxide (B) by adsorption such as hydrogen bond or ionic bond. Further, the B polymer block is adsorbed with titanium oxide (B), and the A polymer block is dissolved in the polymerizable compound (A) which is a dispersion medium. The A polymer block causes steric repulsion, and titanium oxide ( It has a structure that maintains the dispersion stability of B).

  In addition, as described above, in the white pigment dispersion of the present invention, the pigment dispersant (C) having a specific structure can be adsorbed on the titanium oxide (B) to maintain the dispersion stability, but the oxidation with a heavy specific gravity. Titanium may sink due to the earth's gravity. However, the pigment dispersant (C), which characterizes the present invention, has a remarkably superior degree of adsorption of the B polymer block adsorbed to titanium oxide as compared with the conventional pigment dispersant even when it settles. Since the other A polymer block has an excellent affinity for the polymerizable compound (A) as a dispersion medium even if it settles and the titanium oxide adheres, it can be easily stirred and shaken. It works to return to the original dispersed state.

  The constituent component of the AB block copolymer which is the pigment dispersant (C) characterizing the present invention is 90% by mass or more, more preferably all of which is a methacrylic acid monomer. This is because the use of a methacrylic acid monomer as a raw material is particularly suitable for the specific living radical polymerization method used in the production method of the present invention, and the structure A and the functionally separated structure suitable for the purpose of the present invention. This is because an AB block copolymer composed of a polymer block of B can be easily obtained, and is therefore excellent in industrial applicability.

(A polymer block)
First, the polymer block A constituting the AB block copolymer characterizing the present invention is a polymer block that dissolves in the polymerizable compound (A), which is a dispersion medium, when used as a dispersant. Examples of the methacrylic acid monomer used for constituting the A polymer block include conventionally known monomers and are not particularly limited. Specific examples include the following.

For example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, 2-methylpropane methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, isodecyl Methacrylate, lauryl methacrylate, tetradecyl methacrylate, octadecyl methacrylate, behenyl methacrylate, isostearyl methacrylate, cyclohexyl methacrylate, t-butylcyclohexyl methacrylate, isobornyl methacrylate, trimethylcyclohexyl methacrylate, cyclodecyl methacrylate, cycl Decyl methyl methacrylate, such as tricyclodecyl methacrylate (cyclo) alkyl methacrylate;
Aryl methacrylates such as phenyl methacrylate, naphthyl methacrylate, benzyl methacrylate;
Alkenyl methacrylates such as allyl methacrylate;
Hydroxyl group-containing methacrylates such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, polyethylene glycol monomethacrylate;
Glycol monoalkyl ether methacrylates such as (poly) ethylene glycol monomethacrylate, (poly) ethylene glycol monomethyl ether methacrylate, (poly) ethylene glycol monolauryl ether methacrylate, (poly) propylene glycol monomethyl ether methacrylate;
Polyester methacrylates such as terminal methacrylates of poly-ε-caprolactone;
Halogen-containing methacrylates such as octafluorooctyl methacrylate and tetrafluoroethyl methacrylate;
Methacrylates that absorb ultraviolet rays, such as 2- (4-benzoxy-3-hydroxyphenoxy) ethyl methacrylate, 2- (2′-hydroxy-5-methacryloyloxyethylphenyl) -2H-benzotriazole;
And silicon atom-containing methacrylate having a trimethoxysilyl group and a dimethylsilicone chain.
Moreover, the macromonomer etc. which are obtained by introduce | transducing a (meth) acryl group into the one terminal of the oligomer obtained by superposing | polymerizing these monomers can be used.

  On the other hand, methacrylates having amino groups such as dimethylaminoethyl methacrylate are easily ionically bonded to carboxyl groups and phosphate groups, and epoxy groups, oxetanyl groups, and isocyanate groups react with carboxyl groups and phosphate groups. Should not be used because it may cause gelation and the like.

  Further, if necessary, in addition to the monomer or macromonomer listed above, methacrylic acid that is a methacrylic acid monomer having a carboxyl group (carboxyl group-containing methacrylic acid monomer) is added to the formation of the polymer block. May be included. Such a structure has a B polymer block to be described later and a methacrylate having a carboxyl group other than methacrylic acid, for example, a methacrylate ester of dibasic acid such as methacryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, or phosphoric acid. This is particularly useful when a monomer having a group is used. The reason is that when a dibasic acid or phosphoric acid group such as methacryloyloxyethylphthalic acid is introduced into the B polymer block, its acidity is compared with the pKa of methacrylic acid constituting the A polymer block, Because the pKa of the carboxyl group or phosphate group constituting the B polymer block is lower, that is, the B polymer block is more acidic than the A polymer block, the carboxyl group constituting the A polymer block This is because the carboxyl group and phosphate group of the B polymer block are selectively adsorbed with titanium oxide. The amount of methacrylic acid constituting the A polymer block is not particularly limited, and after printing, when development processing such as alkali development is necessary, the amount is introduced and adjusted.

  Particularly preferably, when forming the A polymer block, poly (n = 2 or more) alkylene (2 to 4 carbon atoms) glycol methacrylate, poly (n = 2 or more) alkylene (2 to 2 carbon atoms). 4) One or more kinds of glycol monoalkyl (having 1 to 18 carbon atoms) methacrylate and poly (n = 2 or more) hydroxyalkyl (having 2 to 18 carbon atoms) carboxylic acid methacrylate are used as one of the constituent components. It is preferable. When the monomer component as described above is introduced to form the A polymer block, when the obtained AB block copolymer is used as a pigment dispersant, high storage stability when titanium oxide having a high specific gravity is dispersed is used. Furthermore, even if titanium oxide settles, it can function to quickly return to the original dispersed state by shaking or stirring. That is, since the above-mentioned monomers have a large molecular weight and a long molecular length, the A polymer block formed by them contributes to dispersion stabilization due to steric repulsion when dispersed, and furthermore, oxidation When titanium is dispersed and stored, even if the titanium oxide settles, the steric repulsion and the molecular chain derived from these monomers solvate the polymerizable compound (A) as a dispersion medium, thereby cushioning material. It is considered that this serves to prevent the occurrence of hard agglomeration of titanium oxide and return to a state of being dispersed again by shaking or stirring. The introduction amount of the monomer mentioned as suitable above may constitute all of the A polymer block or may be copolymerized with the above-described monomer, and the constitutional amount is arbitrary.

  Specific examples of suitable monomers listed above include diethylene glycol monomethacrylate, triethylene glycol monomethacrylate, dipropylene glycol monomethacrylate, polyethylene glycol polypropylene glycol monomethacrylate, tri (tetramethylene glycol) monomethacrylate, methoxydiethylene glycol. Examples include methacrylate, ethoxytriethylene glycol monomethacrylate, methoxypolypropylene glycol methacrylate, polyethylene glycol monolauryl ether methacrylate glycol-based methacrylate, polylactic acid monomethacrylate, polyε-caprolactone methacrylate, poly12-hydroxystearic acid monomethacrylate, and the like. It is done. More specifically, poly ε-caprolactone obtained by ring-opening polymerization of ε-caprolactone using an alcohol such as lauryl alcohol as an initiator has a hydroxyl group at the end. Therefore, methacrylic acid chloride or anhydrous It can also be obtained by ring-opening polymerization of ε-caprolactone using ester methacrylate obtained by reacting methacrylic acid or hydroxyethyl methacrylate as an initiation compound. In addition, it can also be obtained by reacting isocyanatoethyl methacrylate or glycidyl methacrylate with a glycol or polyester having a hydroxyl group or amino group, which is a group capable of reacting with the isocyanate group or glycidyl group.

(B polymer block)
Next, the B polymer block constituting the AB block copolymer characterizing the present invention will be described. This is a polymer block that adsorbs to titanium oxide, which is a white pigment, when used as a dispersant, and is derived from these containing at least a methacrylic monomer containing an acid group having a carboxyl group or a phosphate group as a constituent component. It is a polymer block containing a structural unit. Examples of the monomer having a carboxyl group used in this case include methacrylic acid, methacryloyloxyethyl phthalate, methacryloyloxyethyl succinate, methacryloyloxyethyl maleate, methacryloyloxyethyl 1,2-cyclohexanedicarboxylate. 1,2-cyclohexene dicarboxylic acid methacryloyloxyethyl, methacryloyloxyethyl phthalate, methacryloyloxyethyl trimellitic acid, and the like. Among these, methacrylic acid and methacryloyloxyethyl phthalate are particularly preferable. Methacrylic acid can be used when the A polymer block does not have a carboxyl group for the reasons described above, but is a low-cost and highly versatile carboxyl group. Further, since methacryloyloxyethyl phthalate is a carboxyl group bonded to an aromatic group, it is preferred that it has high acidity and its aromatic ring has high affinity with the pigment and enhances its adsorptivity.

  Examples of the monomer having a phosphoric acid group used for forming the B polymer block include 2- (methacryloyloxy) ethyl phosphate, 3-chloro-2- (phosphonooxy) propyl methacrylate, 2- ( Examples include methacryloyloxy) propyl, 2- (phenoxyphosphonyloxy) ethyl methacrylate, acid phosphooxypolyoxyethylene glycol monomethacrylate, and acid phosphooxypolyoxypropylene glycol monomethacrylate. Bifunctional methacrylates such as bis (2-methacryloyloxyethyl phosphate) can also be used as long as the resulting phosphate group-containing block copolymer does not gel. In particular, 2- (methacryloyloxy) ethyl phosphate is suitable because of its versatility, commercial products, and the smallest molecular weight.

  Further, when forming the B polymer block constituting the AB block copolymer characterizing the present invention, homopolymerization of the above-mentioned monomer having a carboxyl group or a phosphoric acid group may be used, but other methacrylic acid monomers may be used together. It may be polymerized. This is the methacrylate listed above, and one or more are used.

  The amount of the acidic group forming the B polymer block containing the structural unit derived from the acid group-containing methacrylic acid monomer as described above is determined by the acid value due to the carboxyl group or phosphate group derived from the monomer used for the formation. 50-500 mgKOH / g. That is, if it is smaller than 50 mgKOH / g, the adsorptivity to the pigment may be deteriorated, and if it exceeds 500 mgKOH / g, the portion adsorbed to the pigment becomes excessive, so the pigment may rather aggregate. It is not preferable. More preferably, it is 70-250 mgKOH / g.

In the present invention, the molecular weight of the B polymer block is obtained by subtracting the number average molecular weight of the A polymer block from the number average molecular weight of the AB block copolymer used as the pigment dispersant (C). In the present invention, the molecular weight is preferably in the range of 200 to 3,000. If it is less than 200, the adsorptivity with respect to the pigment becomes weak, and if it exceeds 3,000, the molecular weight is large, so the particles can be adsorbed between the particles of the pigment and the particle diameter does not become fine or aggregates. This is not preferable because of its properties. In the present invention, the molecular weight of the B polymer block is more preferably in the range of 500 to 2,500.
That is, the B polymer block constituting the AB block copolymer characterizing the present invention is a monomer having various acidic groups alone or with these monomers so as to have the acid value and molecular weight as described above. It is preferable to prepare by copolymerizing with other monomers.

(Characteristics of AB block copolymer)
The pigment dispersant (C) constituting the white pigment dispersion of the present invention is an AB block copolymer composed of an A polymer block and a B polymer block as described above. The AB block copolymer preferably has a number average molecular weight of 4,000 to 20,000. If the molecular weight is less than 4,000, the molecular weight is so small that it may reduce the physical properties of the printed material formed with the ink containing the molecular weight. On the other hand, if it exceeds 20,000, the viscosity of the ink may be increased or aggregation due to adsorption of pigment particles may occur when the ink is dissolved and used because of its large molecular weight. This is not preferable. The molecular weight of the AB block copolymer used in the present invention is more preferably 4,000 to 10,000.

  Further, the AB block copolymer used as the pigment dispersant (C) characterizing the present invention preferably has a molecular weight distribution value of 1.6 or less obtained by dividing the weight average molecular weight by the number average molecular weight. More preferred according to the invention is a narrower molecular weight distribution of 1.5 or less. That is, this narrow distribution means that the molecular weight is uniform. Those having a wide molecular weight distribution include those having a low molecular weight to those having a large molecular weight, and those having a small molecular weight cause a decrease in the physical properties described above, while those having a large molecular weight cause an increase in viscosity or aggregation. Therefore, if the molecular weight distribution is wide, the performance as the pigment dispersant (C) may be deteriorated. Therefore, it is preferable to use one having a molecular weight distribution of 1.6 or less.

90% by mass or more of the constituent component of the AB block copolymer characterizing the present invention is a methacrylic acid monomer, and if necessary, other polymerizable monomers can be used at less than 10% by mass. Is not particularly limited. For example, acrylic monomers and vinyl monomers such as styrene can be used.
The above is the configuration of the AB block copolymer that functions well as a pigment dispersant (C) for titanium oxide (B), which is a white pigment, which is essential for achieving the effects of the present invention.

(Method for producing AB block copolymer)
The AB block copolymer having the above-described constitution characterizing the present invention can be easily obtained by living radical polymerization. Among them, a preferable production method includes a step of living radical polymerization of a monomer component containing a methacrylic acid monomer as described above in the presence of a polymerization initiating compound and a catalyst, and the polymerization initiating compound is at least either iodine or an iodine compound. And the catalyst is at least one selected from the group consisting of phosphorus halides, phosphite compounds, phosphinate compounds, imide compounds, phenol compounds, diphenylmethane compounds, and cyclopentadiene compounds. And a method of setting the polymerization temperature to 30 to 50 ° C.

  For living radical polymerization, various methods have been invented so far, such as nitroxide mediated polymerization (NMP method) utilizing dissociation and bonding of amine oxide radicals, copper, ruthenium, nickel, iron, etc. Atom transfer radical polymerization (ATRP method) that uses heavy metals and ligands that form complexes with these heavy metals and uses halogen compounds as starting compounds, dithiocarboxylic acid esters, xanthate compounds, etc. Reversible addition-fragmentation chain transfer (RAFT method) and Macromolecular Design via Interchange of Xanthate (MADIX), which are used as starting compounds and polymerized using addition polymerizable monomers and radical initiators Law), organic tellurium, organic bismuth, yes Antimony, antimony halides, organic germanium, a method of using a heavy metal such as germanium halide (Degenerative transfer: DT method).

  However, any of the above methods has a problem in obtaining an AB block copolymer having a configuration necessary for obtaining the effects of the present invention. That is, for example, in the NMP method, a tetramethylpiperidine oxide radical is used, but it is necessary to polymerize under a high temperature condition of 100 ° C. or higher, and when a methacrylate monomer is used, the polymerization does not proceed. There is also a problem.

  In addition, in the ATRP method, it is necessary to use a heavy metal, and since it is a polymerization method involving redox, it is necessary to remove oxygen, and in the method of polymerizing by forming a complex using an amine compound as a ligand, If an acidic substance is present, the formation of the complex is inhibited, so that it is difficult to polymerize the addition polymerizable monomer having an acid group as it is. Although it is necessary to polymerize the monomer which protected the acid group with the protecting group and to remove the protecting group after the polymerization, it is complicated and it is not easy to introduce the acid group into the polymer block.

  In addition, in the RAFT method and the MADIX method, first, special compounds such as dithiocarboxylic acid ester and xanthate compound are necessary, and these are sulfur-based compounds. Therefore, the resulting polymer has an unpleasant sulfur-based odor. It tends to remain and may be colored. For this reason, it is necessary to remove an odor and coloring from the obtained polymer. Polymerization of methacrylic acid monomers may not be successful.

  Further, in the DT method, it is necessary to use heavy metals as in the ATRP method. For this reason, there is a problem that it is necessary to remove heavy metals from the obtained polymer and to purify waste water containing the generated heavy metals.

  Under such circumstances, the living radical polymerization method used in the production method of the present invention does not require the use of heavy metal compounds, does not require purification of the polymer, and does not require the synthesis of special compounds. Therefore, it can be easily produced simply by using a relatively inexpensive material, and is extremely useful. Further, the polymerization conditions are mild, and the polymerization can be carried out under the same conditions as the conventional radical polymerization method. It should be noted that an acid group-containing monomer having a carboxyl group or a phosphate group is used as it is as a living radical. It can be polymerized.

  Specifically, the method for producing a block copolymer characterizing the present invention includes a step (polymerization step) of performing a living radical polymerization of a monomer component containing a methacrylic acid monomer in the presence of a polymerization initiating compound and a catalyst. And The polymerization initiating compound is required to be at least one of iodine and an iodine compound.

  The above-described polymerization step is a step of polymerizing a monomer component containing a methacrylic acid monomer by living radical polymerization using at least one of iodine and an iodine compound as a polymerization initiating compound. In the polymerization method used in the present invention, iodine radical is dissociated when heat or light is applied to iodine or iodine compound used as a polymerization initiating compound. Then, after the monomer is inserted in a state in which the iodine radical is dissociated, the iodine radical is immediately bonded again to the polymer terminal radical and stabilized, and the polymerization reaction proceeds while preventing the termination reaction.

  Specific examples of iodine compounds that can be used in the production method of the present invention include alkyl iodides such as 2-iodo-1-phenylethane and 1-iodo-1-phenylethane; 2-cyano-2-iodopropane 2-cyano-2-iodobutane, 1-cyano-1-iodocyclohexane, 2-cyano-2-iodo-2,4-dimethylpentane, 2-cyano-2-iodo-4-methoxy-2,4-dimethyl And cyano group-containing iodides such as pentane.

  As these iodine compounds, commercially available products may be used as they are, but those prepared by a conventionally known method can also be used. For example, an iodine compound can be obtained by reacting an azo compound such as azobisisobutyronitrile with iodine. Further, the iodine compound can be obtained by reacting an organic halide obtained by substituting iodine of the iodine compound with a halogen atom such as bromine or chlorine with an iodide salt such as quaternary ammonium iodide or sodium iodide, and performing halogen exchange. Can be obtained.

  In the polymerization step of the polymerization method used in the present invention, a specific catalyst capable of extracting iodine of the polymerization initiating compound is used together with the above-described polymerization initiating compound. Catalysts include phosphorus compounds such as phosphorus halides, phosphite compounds, phosphinate compounds; nitrogen compounds such as imide compounds; oxygen compounds such as phenol compounds; diphenylmethane compounds and cyclopentadiene compounds. It is preferable to use the following hydrocarbon compound. In addition, these catalysts can be used individually by 1 type or in combination of 2 or more types.

  Specific examples of the phosphorus compound include phosphorus triiodide, diethyl phosphite, dibutyl phosphite, ethoxyphenyl phosphinate, and phenylphenoxy phosphinate. Specific examples of the nitrogen compound include succinimide, 2,2-dimethylsuccinimide, maleimide, phthalimide, N-iodosuccinimide, and hydantoin. Specific examples of the phenolic compound that is an oxygen compound include phenol, hydroquinone, methoxyhydroquinone, t-butylphenol, catechol, and di-t-butylhydroxytoluene. Specific examples of the hydrocarbon compound include cyclohexadiene and diphenylmethane.

  The amount (number of moles) of the catalyst used is preferably less than the amount (number of moles) of the polymerization initiating compound. When the amount of the catalyst used (number of moles) is too large, the polymerization is controlled too much and the polymerization may not proceed easily. Moreover, it is preferable that the temperature (polymerization temperature) in the case of living radical polymerization shall be 30-50 degreeC. If the polymerization temperature is too high, iodine at the polymerization terminal may be decomposed by methacrylic acid, and the terminal may not be stable and living polymerization may not occur.

  In the polymerization step, a polymerization initiator that can generate radicals is usually added. As the polymerization initiator, conventionally known azo initiators and peroxide initiators are used. It is preferable to use a polymerization initiator that generates radicals sufficiently within the above polymerization temperature range. Specifically, it is preferable to use an azo initiator such as 2,2'-azobis (4-methoxy-2,4-dimethylvaleronitrile). The amount of the polymerization initiator used is preferably 0.001 to 0.1 mol times, more preferably 0.002 to 0.05 mol times with respect to the monomer. If the amount of the polymerization initiator used is too small, the polymerization reaction may not proceed sufficiently. On the other hand, if the amount of the polymerization initiator used is too large, a normal radical polymerization reaction that is not a living radical polymerization reaction may proceed as a side reaction.

  Living radical polymerization may be bulk polymerization that does not use an organic solvent, but is preferably solution polymerization that uses an organic solvent. The organic solvent is preferably one that can dissolve components such as a polymerization initiator compound, a catalyst, a monomer component, and a polymerization initiator. Specific examples of organic solvents include hexane, octane, decane, isodecane, cyclohexane, methylcyclohexane, toluene, xylene, ethylbenzene and other hydrocarbon solvents; methanol, ethanol, propanol, isopropanol, butanol, isobutanol, hexanol, benzyl alcohol Alcohol solvents such as cyclohexanol; ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, methyl cellosolve, ethyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol propyl ether, diglyme, triglyme, tetra Glyme, dipropylin glycol dimethyl ether, buty Carbitol, butyl triethylene glycol, methyl dipropylene glycol, methyl cellosolve acetate, propylene glycol monomethyl ether acetate, dipropylene glycol butyl ether acetate, glycol solvents such as diethylene glycol monobutyl ether acetate;

  Ether solvents such as diethyl ether, dipropyl ether, methylcyclopropyl ether, tetrahydrofuran, dioxane, anisole; ketone solvents such as methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, cyclohexanone, isophorone, acetophenone; methyl acetate, ethyl acetate, acetic acid Ester solvents such as butyl, propyl acetate, methyl butyrate, ethyl butyrate, caprolactone, methyl lactate, ethyl lactate, dimethyl oxalate, dimethyl adipate, dimethyl glutarate; halogenated solvents such as chloroform, dichloroethane; dimethylformamide, dimethylacetamide Amide solvents such as pyrrolidone, N-methylpyrrolidone, caprolactam, dimethyl sulfoxide, sulfolane, tetramethylurea, Ren carbonate, propylene carbonate, and dimethyl carbonate can be exemplified. In addition, these organic solvents can be used individually by 1 type or in combination of 2 or more types.

  Further, the organic solvent used in these polymerizations can be used as a constituent of the pigment dispersion as it is, and if necessary, the polymer can be taken out from the solution to be solid. This method is not particularly limited, and can be obtained as a solid polymer by, for example, precipitating in a poor solvent, filtering and drying, or drying the solution and taking out only the polymer. The obtained solid polymer may be used as a constituent of the white pigment dispersion of the present invention as it is, or a polymerizable compound (A that is another component constituting the white pigment dispersion of the present invention. ) Or an organic solvent (D) different from the polymerization solvent. Alternatively, after adding the polymerizable compound (A) or another organic solvent (D) to the obtained polymerization solution, when used for the polymerizable compound (A), a polymerization inhibitor or the like is added as necessary, The polymerization solvent may be distilled by vacuum or heating to form a dispersant solution of the polymerizable compound (A) or the organic solvent (D).

  In the case of solution polymerization, the solid content concentration (monomer concentration) of the polymerization solution is preferably 5 to 80% by mass, and more preferably 20 to 60% by mass. When the solid content concentration of the polymerization solution is less than 5% by mass, the monomer concentration may be too low to complete the polymerization. On the other hand, when the solid content concentration of the polymerization liquid is more than 80% by mass or bulk polymerization, the viscosity of the polymerization liquid is too high, and stirring tends to be difficult and the polymerization yield tends to decrease. Living radical polymerization is preferably carried out until the monomer runs out. Specifically, the polymerization time is preferably 0.5 to 48 hours, and more preferably 1 to 24 hours. The polymerization atmosphere is not particularly limited, and may be an atmosphere in which oxygen exists within a normal range or a nitrogen stream atmosphere. Moreover, the material (monomer etc.) used for superposition | polymerization may use what removed the impurity by distillation, activated carbon treatment, an alumina treatment, etc., and may use a commercial item as it is. Furthermore, polymerization may be performed under light shielding, or polymerization may be performed in a transparent container such as glass.

  The polymerization order of the AB block copolymer is as follows: (i) the monomer constituting the A polymer block is polymerized to form the A polymer block, and then (ii) the monomer constituting the B polymer block is added for further polymerization. It is preferable. When the monomer constituting the B polymer block is polymerized first, the polymerization may not be completed and the monomer having an acid group may remain in the reaction system. In such a case, the monomer having an acid group may be easily introduced into the A polymer block. On the other hand, if the monomer constituting the A polymer block is polymerized first, even if the polymerization is not completed and the monomer remains in the reaction system, If the B polymer block is introduced so that 90% by mass or more is a (meth) acrylate monomer, an AB block copolymer can be easily obtained. The polymerization rate is preferably 50% or more, more preferably 80% or more, and particularly preferably, the monomer constituting the A polymer block is polymerized to form the A polymer block until the polymerization rate reaches 100%. A polymer block monomer may be added to form a B polymer block.

In the production method of the present invention described above, the molecular weight of the resulting AB block copolymer can be controlled by adjusting the amount of the polymerization initiating compound used. Specifically, an AB block copolymer having an arbitrary molecular weight can be obtained by appropriately setting the number of moles of the monomer with respect to the number of moles of the polymerization initiating compound. For example, when 1 mol of a polymerization initiating compound is used and 500 mol of a monomer having a molecular weight of 100 is used for polymerization, an AB block copolymer having a theoretical molecular weight of “1 × 100 × 500 = 50,000” can be obtained. it can. That is, the theoretical molecular weight of the AB block copolymer can be calculated by the following formula (1). The above “molecular weight” is a concept including both the number average molecular weight (Mn) and the weight average molecular weight (Mw).
“Theoretical molecular weight of AB block copolymer” = “1 mol of polymerization initiating compound” × “monomer molecular weight” × “number of moles of monomer / number of moles of polymerization initiating compound” (1)

  In addition, since a polymerization process may involve a bimolecular termination or a disproportionation side reaction, an AB block copolymer having the above theoretical molecular weight may not be obtained. The AB block copolymer is preferably obtained without causing these side reactions. However, even if the molecular weight of the AB block copolymer obtained by coupling is somewhat increased, the molecular weight of the AB block copolymer obtained by stopping the polymerization reaction in the middle may be slightly decreased. The polymerization rate may not be 100%. Furthermore, once the polymerization is completed, the polymerization may be completed by adding a polymerization initiating compound or a catalyst and consuming the remaining monomer. That is, the AB block copolymer should just be produced | generated.

  The AB block copolymer obtained by the production method of the present invention may remain in a state in which iodine atoms derived from the polymerization initiating compound are bonded, but it is preferable to desorb iodine atoms. The method for desorbing iodine atoms from the AB block copolymer is not particularly limited as long as it is a conventionally known method. Specifically, the AB block copolymer may be heated or treated with an acid or alkali. Further, the AB block copolymer may be treated with sodium thiosulfate or the like. The detached iodine is preferably removed by treatment with an iodine adsorbent such as activated carbon or alumina.

  The pigment dispersant (C), which is an AB block copolymer having a specific structure used in the present invention, can be obtained by the steps as described above. The pigment dispersant (C) used in the present invention can be used for paints, inks, stationery, coating agents, etc., and in particular, fine particle formation and storage stability, ejection properties, sedimentation prevention or sedimentation recovery properties are required. Suitable for pigment dispersions for ultraviolet curable inkjet inks.

<Polymerizable compound (A)>
Next, one or more polymerizable compounds (A) to be contained as a dispersion medium, which is a component of the white pigment dispersion of the present invention, will be described. The object of the present invention is to provide a white pigment dispersion for use in ink jet recording, and more preferably UV curable ink for ink jet recording, so that the polymerizable compound (A) used in the present invention is used. As a preferable thing, the polymeric compound (A) which can be hardened | cured by ultraviolet irradiation is mentioned. Such a polymerizable compound (A) is used as a dispersion medium for titanium oxide as a pigment. Therefore, suitable polymerizable compounds (A) for use in the present invention include monomers and oligomers that can be cured by ultraviolet rays, are radically polymerizable compounds, and are cationically polymerizable compounds. It is preferable to use 1 or more types. Below, these compounds which can be used for the polymeric compound (A) which is a structural component of the white pigment dispersion liquid of this invention are illustrated.

  As the radical polymerizable compound, acrylic acid monomers and oligomers as listed below are suitable. Specific examples of monomers include butyl acrylate, 2-methylpropane acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, tetradecyl Acrylate, octadecyl acrylate, behenyl acrylate, isostearyl acrylate, cyclohexyl acrylate, t-butylcyclohexyl acrylate, isobornyl acrylate, trimethylcyclohexyl acrylate, cyclodecyl acrylate, cyclodecylmethyl acrylate, tricyclodecyl acrylate, benzyl acrylate, phenoxy Ethyl acrylate, phenyl Acrylate, naphthyl acrylate, benzyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, (poly) ethylene glycol monomethyl ether acrylate, (poly) ethylene glycol monolauryl ether acrylate, (poly) propylene glycol monomethyl ether acrylate, octafluoro Examples include octyl acrylate, tetrafluoroethyl acrylate, acrylate of ethylene oxide adduct of nonylphenol, acryloyloxyethyl phosphate, acryloyloxyphthalic acid, and the like. The above-mentioned methacrylate monomers can also be used.

  In the present invention, cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, t-butylcyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, isobornyl acrylate, and adamantyl acrylate are particularly preferable. This is because the cyclo ring has high adhesion to the film substrate. This is presumably because the distorted skeleton has a high affinity for polyolefin, PET, polyvinyl chloride, etc. of the film substrate. In addition, the skin irritation is small, and the odor is well tolerated. Further, since it has a large number of carbon atoms and is cyclic, the viscosity is low, the viscosity of the ink can be lowered, and it can contribute to the ejection stability of the ink.

  The radical polymerizable oligomer is a compound having two or more polymerizable groups in one molecule, and specific examples thereof include ethylene glycol, butanediol, hexanediol, nonanediol, cyclohexanedimethanol, butenediol. , Diacrylic acid ester of alkyl, alkenyl, cycloalkyl diol such as butynediol neopentyl glycol; poly (n = 2 or more) glycol ethers such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, ethylene oxide adduct of bisphenol A Diacrylates of poly (hexanediol adipate), polybutanediolsuccinic acid, polyacrylates of polyester diols such as polycaprolactone; Diacrylate of carbonate diol such as len carbonate; Polyacrylate of urethane polyol obtained by diisocyanate such as toluene diisocyanate and diol, triol, diamine, etc .; Polyacrylate of epoxy resin such as adduct of bisphenol A glycidyl ether; Polyglycerin , Polymethylated compounds of polyhydric hydroxyl group-containing compounds such as trimethylolpropane, pentaerythritol, dipentaerythritol and sorbitol, and their alkylene oxide adducts.

  As the cationically polymerizable compound, the above-mentioned acrylate and radical polymerizability can be contributed, but vinyl ethers can be used. Specific examples of vinyl ethers include monofunctional vinyl ethers such as ethyl vinyl ether, butyl vinyl ether, cyclohexyl vinyl ether, and hydroxyethyl vinyl ether; (poly) ethylene glycol divinyl ether, butanediol divinyl ether, hexanediol divinyl ether, trimethylolpropane trivinyl ether, etc. Can be used.

  These monomers and oligomers are conventionally used in consideration of the viscosity, ejection stability, adhesion, polymerization, curability, crosslink density, scratch resistance, scratch resistance, strength, and the like of the inkjet ink targeted by the present invention. One or more kinds of known blends are used and are not particularly limited.

<Titanium oxide pigment (B)>
Next, the pigment used in the present invention is for forming a white pigment dispersion or a white ink, and is a white pigment, particularly titanium oxide which is particularly excellent in concealment. Titanium oxide is not particularly limited, and can be used regardless of the crystal system such as rutile type, anatase type, brookite type, and production methods such as sulfuric acid method and chlorine method. Moreover, although it can be used even if surface treatment is not made, surface treatment which is organic treatment, such as silica treatment, alumina treatment, zirconia treatment, zinc treatment, silica alumina treatment, and silane coupling agent treatment, and inorganic treatment is made. Titanium oxide is also used. If necessary, a chromatic organic pigment or dye may be added as a reference color.
Further, for the purpose of the present invention, it is better that white has high hiding power, and the average particle diameter of the pigment itself is 50 to 300 nm, preferably 80 to 280 nm. If it is smaller than 50 nm, the concealing force is insufficient, and if it is more than 300 nm, it is not preferable because it does not become fine even if dispersed, or the filter or head is clogged. Moreover, since it is a large particle, it is easy to settle and it may be difficult to obtain dispersion stability.

  Further, the titanium oxide (B) preferably has an average particle diameter of 100 to 300 nm when it is dispersed as the white pigment dispersion of the present invention in order to exert concealing power. If it is less than 100 nm, the hiding power is insufficient, and if it exceeds 300 nm, it may cause clogging of the filter or head, settle in dispersion or ink, and may impair the smoothness and sharpness of the printed matter. Because. More preferably, it is 150-250 nm.

<Organic solvent (D)>
Next, the organic solvent (D) that may be contained in the white pigment dispersion of the present invention as necessary will be described. As described above, the organic solvent (D) may be blended as it is with the polymerization solvent when the pigment dispersant (B), which is an AB block copolymer characterizing the present invention, is formed. Need not be added separately. Moreover, the solvent (polymerization solvent) in this case is as described above, and is not particularly limited. The white pigment dispersion of the present invention is not limited to the above, and an organic solvent may be added separately to impart leveling properties, flexibility, and the like. The organic solvent can be the same as described above, and is not particularly limited. The amount of the organic solvent (D) constituting the white pigment dispersion of the present invention is 0 to 15% by mass, preferably 0 to 5% by mass. Those containing no organic solvent are preferable because they do not have a cost and a drying process. However, for the above reasons, the addition of an organic solvent is preferable in terms of viscosity adjustment and ease of handling according to the application conditions. You may add to the mass%. If it exceeds 15% by mass, the organic odor is strong, which is not preferable from the viewpoint of environmental problems and the necessity of a long drying process.

<Composition ratio of materials>
Next, the component ratio of each material constituting the white pigment dispersion of the present invention will be described. The ratio of the materials is 15 to 59% by mass of one or more polymerizable compounds (A) used as a dispersion medium, 40 to 70% by mass of titanium oxide (B) as a white pigment, and a pigment dispersant that characterizes the present invention ( C) is 0.7 to 12% by mass, and the organic solvent (D) added as necessary is 0 to 15% by mass. Titanium oxide, which is a pigment, occupies 40 to 70% by mass of the pigment dispersion, but if it is less than 40% by mass, there is a problem that viscosity is insufficient at the time of dispersion, and dispersion does not proceed, and if it exceeds 70% by mass, The viscosity may be too high to disperse. A more preferable ratio of titanium oxide (B) is 45 to 65% by mass.

  The pigment dispersant (C) characterizing the present invention is 0.7 to 12% by mass in the component ratio constituting the white pigment dispersion of the present invention, and 1 to 30% by mass with respect to titanium oxide as a pigment. Used in the range of%. If the amount is less than 1% by mass with respect to titanium oxide, the dispersion does not proceed due to insufficient dispersant, and if it is more than 30% by mass, the viscosity of the dispersion becomes high or the particles are aggregated when they settle. There is a possibility that it works like an adhesive. More preferably, it is in the range of 2 to 10% by mass with respect to titanium oxide, and is an amount balance that is adjusted according to the characteristics for ink jet recording and the cost.

  As described above, the polymerizable compound (A) constituting the white pigment dispersion of the present invention is useful when used as an ultraviolet or electron beam curable ink, for example, can be ultraviolet-cured and is radically polymerizable. Although a compound, a cationically polymerizable compound, etc. are used, it functions as a dispersion medium of titanium oxide (B) of a white pigment. The material ratio of the polymerizable compound (A) is required to be 15 to 59% by mass. The material ratio of the polymerizable compound (A) constituting the white pigment dispersion of the present invention is the amount of titanium oxide (B) used and the amount of pigment dispersant (C) required to disperse it. Therefore, if the ratio of the polymerizable compound (A) is less than 15% by mass, the function as a dispersion medium cannot be sufficiently exhibited even if the amount of titanium oxide (B) is as small as 40% by mass. . On the other hand, even when the ratio of titanium oxide (B) is as large as 70% by mass, it can be sufficiently dispersed if the ratio of the polymerizable compound (A) is 59% by mass. It may be adjusted appropriately within the range. As described above, the more preferable ratio of titanium oxide (B) is 45 to 65% by mass, but the material ratio of the polymerizable compound (A) to this range is 25 to 55% by mass. preferable.

  The ratio of the material constituting the white pigment dispersion of the present invention is the amount of titanium oxide (B) and pigment dispersant (C) that are white pigments satisfying the above ratio, and the polymerizable compound (A). And the organic solvent (D), and other additives used as necessary, so that the total amount is arbitrarily adjusted to 100% by mass.

<Other ingredients>
In addition, the white pigment dispersion of the present invention is produced by adjusting the essential material constituting the pigment dispersion and the material ratio as appropriate according to the purpose, but does not affect the quality. It is also a preferred form to use other additives. There is no particular limitation, and for example, a photopolymerization initiator, a photosensitizer, and a cosensitizer may be added in advance in order to have UV curability, and conversely, polymerization of a polymerizable compound during storage may be performed. In order to prevent this, a polymerization inhibitor or an antioxidant may be added. Other antifoaming agents, leveling agents, light stabilizers, ultraviolet absorbers, surface conditioners, colorants such as dyes, polymer components for improving film properties and adhesion, water repellents, oil repellents, chemicals One or more various additives such as a zinc oxide, an inorganic pigment, and a surfactant can be arbitrarily added as a cross-linking agent accompanied by a bond, a matting agent, a silane coupling agent, and other white pigments, and is not particularly limited.

<Distribution method>
As a method for obtaining the white pigment dispersion of the present invention using the above-mentioned materials, any dispersion method can be used, and it is not particularly limited. Examples of the disperser used at that time include a kneader such as a kneader, two rolls, three rolls, and Miracle KCK (Asada Steel Corporation, trade name), an ultrasonic disperser, and a microfluidizer that is a high-pressure homogenizer. (Trade name, Mizuho Industry Co., Ltd.), Nanomizer (trade name, Yoshida Kikai Kogyo Co., Ltd.), Starburst (trade name, Sugino Machine Co., Ltd.), G-Smasher (trade name, Rix Corporation), etc. . In the case of using a bead medium such as glass or zircon, a ball mill, a sand mill, a horizontal media mill disperser, a colloid mill, or the like can be used. The dispersion formulation is not particularly limited.

  In order to obtain a pigment dispersion having a desired particle size and distribution in the present invention, the size of the grinding media of the disperser is reduced, the filling rate of the grinding media is increased, the processing time is increased, and the discharge speed is increased. Methods such as slowing down and classification with a filter or centrifuge after pulverization are used. Or the combination of those methods is mentioned. Next, the obtained pigment dispersion may be used as it is, but it is preferable to remove coarse particles by centrifuging or passing through an arbitrary filter. As described above, the white pigment dispersion of the present invention can be obtained.

  Regarding the physical properties of the white pigment dispersion of the present invention obtained as described above, the physical properties such as viscosity are not particularly limited and are arbitrary. The viscosity range is 1 to 100 mPa · s, preferably 3 to 50 mPa · s. However, even if the viscosity is high, there is no particular limitation because it can be adjusted when ink is used. Other physical properties are not particularly limited.

<White ink composition for inkjet recording>
The present invention provides a white ink composition for ink jet recording comprising a white pigment dispersion obtained by using the pigment dispersant (C) that characterizes the present invention. The ink using the pigment dispersion of the present invention has very good physical properties such as precipitation, storage stability, ejection stability, ultraviolet curable, hardness, and adhesion to the substrate of the titanium oxide pigment. Give a good result. For example, the white pigment dispersion of the present invention can be used to prepare a white UV curable ink jet ink and can be used as a white ink composition for various other purposes.

  The composition and physical properties of the ink are arbitrary and are not particularly limited. This is determined by the specifications of the ink jet printer. As an example of blending, the white pigment dispersion, the polymerizable compound, the photopolymerization initiator, the photosensitizer, and the cosensitizer of the present invention are mainly used, and other additives can be added to make an ink. Preferably, the pigment content of titanium oxide in the ink is 5 to 30% by mass, and the white pigment dispersion liquid of the present invention can be blended so as to be the amount to make an ink. This pigment content is also optional.

Next, the present invention will be described in more detail with reference to synthesis examples, examples and comparative examples of the pigment dispersant (C) that characterizes the present invention. Hereinafter, “part” and “%” in the text are based on mass unless otherwise specified.

(Synthesis Example 1: UVP-1)
In a 2 L separable flask equipped with a reflux tube, a gas introduction device, a thermometer, and a stirring device, 312 parts of dibasic acid diester (trade name “DBE”, manufactured by Invista, hereinafter referred to as “DBE”), iodine 6. 1 part, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile) (hereinafter referred to as “V-70”) 29.4 parts, methyl methacrylate (hereinafter referred to as “MMA”) 96 parts 96 parts of butyl methacrylate (hereinafter referred to as “BMA”), 96 parts of 2-ethylhexyl methacrylate (hereinafter referred to as “EHMA”), 24 parts of benzyl methacrylate (hereinafter referred to as “BzMA”), and 3,5- 1.3 parts of di-t-butyl-4-hydroxytoluene (hereinafter referred to as “BHT”) was charged. Polymerization was carried out at 40 ° C. for 7 hours while flowing nitrogen to obtain a solution of A polymer block. The polymerization rate of the A polymer block calculated from the solid content was 97.0%. Moreover, Mn measured by GPC was 5,500, PDI was 1.23, and the molecular weight of the peak top was 6,800.

  A mixed solution of 18 parts of MMA, 38.8 parts of methacrylic acid (hereinafter referred to as “MAA”), 1.1 parts of V-70 and 139 parts of DBE was added to the solution of the obtained A polymer block. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The resulting polymer solution had a solid content of 44.0%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had a Mn of 6,800, a PDI of 1.30, and a peak top molecular weight of 8,000. Further, the polymer acid value calculated by titration with a 0.1 NKOH ethanol solution using ethanol / toluene as a solvent and phenolphthalein as an indicator was 70.3 mgKOH / g. Hereinafter, the acid value was measured by the same method as described above, and the value was shown. Also, the Mn of the B polymer block (“Mn of AB block copolymer: 6,800” − “Mn of A polymer block: 5,500”) was 1,300. As described above, the molecular weight (Mn) of the B polymer block was calculated by subtracting the number average molecular weight of the A polymer block from the number average molecular weight of the AB block copolymer. It is the calculated value obtained.

Furthermore, after diluting the above-obtained solution with 410 parts of DBE, 56 g of Shirakaba M (trade name, manufactured by Nippon Environmental Chemicals Co., Ltd., hereinafter the same) was added as activated carbon, and the mixture was stirred at room temperature for 12 hours to adsorb iodine. Then, the mixture was filtered through a filter to remove the activated carbon to obtain a yellow transparent liquid from which iodine was removed. After drying this liquid at 150 ° C. for 1 hour, the calculated solid content was 30.4%. Hereinafter, the final solid content is measured in the same manner as described above. Moreover, as for the polymer in the resin solution obtained as a yellow transparent liquid in the above, the molecular weight, the infrared spectrophotometer, and the acid value were measured by GPC. It was confirmed that it was not removed during the treatment. The same confirmation was performed in the following synthesis examples.
Hereinafter, the AB block copolymer obtained above is referred to as “UVP-1”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, the polymer block of A is a dispersant which is composed only of an aliphatic methacrylate, and the polymer block of B is an AB block copolymer having a carboxyl group derived from methacrylic acid.

(Synthesis Example 2: UVP-2)
In a 2 L separable flask equipped with a reflux tube, a gas introduction device, a thermometer, and a stirring device, 312 parts DBE, 6.1 parts iodine, 29.4 parts V-70, 96 parts MMA, 96 parts BMA, 48 parts EHMA, methacrylic 48 parts of acid methoxypolyethylene glycol (n = 3 to 5) (hereinafter referred to as “PME200”), 24 parts of BzMA, and 1.3 parts of BHT were charged. Polymerization was carried out at 40 ° C. for 7 hours while flowing nitrogen to obtain a solution of A polymer block. The polymerization rate of the A polymer block calculated from the solid content was 97.0%. Moreover, Mn measured by GPC was 5,300, PDI was 1.27, and the molecular weight of the peak top was 6,700.

  A mixed solution of 18 parts of MMA, 38.8 parts of MAA, 1.1 parts of V-70, and 139 parts of DBE was added to the solution of the obtained A polymer block. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The solid content of the polymer solution obtained above was 44.0%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had a Mn of 6,300, a PDI of 1.30, a peak top molecular weight of 8,200, and an acid value of 70.0 mgKOH / g. Further, the calculated Mn of the B polymer block was 1,000.

Furthermore, after diluting the solution with 410 parts of DBE, 56 g of Shirahige M was added as activated carbon, stirred at room temperature for 12 hours to adsorb iodine, filtered through a filter to remove activated carbon, and iodine was removed. A yellow transparent liquid was obtained. The measured solid content was 30.2%.
Hereinafter, the AB block copolymer obtained above is referred to as “UVP-2”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, the polymer block of A is composed of an aliphatic methacrylate and a methacrylate having a polyethylene glycol chain, and the polymer block of B is a dispersant that is an AB block copolymer having a carboxyl group derived from methacrylic acid. is there.

(Synthesis Example 3: UVP-3)
260 parts of DBE, 5.1 parts of iodine, 24.5 parts of V-70, 80 parts of MMA, 80 parts of BMA, 40 parts of EHMA, 40 methoxypolyethylene glycol methacrylate (n = 6 to 10) (hereinafter referred to as “PME400”) A polymer block solution was obtained in the same manner as in Synthetic Example 1 except that parts, BzMA20 parts, and BHT1.1 parts were used. The polymerization rate of the A polymer block calculated from the solid content was 98.5%. The A polymer block had a Mn of 5,400, a PDI of 1.28, and a peak top molecular weight of 6,900.

  In a solution of the obtained A polymer block, a mixed solution of 15 parts of MMA, 104.4 parts of 2-methacryloyloxyethylphthalic acid (hereinafter referred to as “MEPA”), 2.4 parts of V-70, and 204 parts of DBE. Added. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The solid content of the polymer solution obtained above was 43.9%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had an Mn of 7,800, a PDI of 1.31, a peak top molecular weight of 10,200, and an acid value of 40.0 mgKOH / g. Further, the calculated Mn of the B polymer block was 2,400.

Furthermore, after diluting the solution with 420 parts of DBE, 47 g of Shirasagi M was added as activated carbon, stirred at room temperature for 12 hours to adsorb iodine, filtered through a filter to remove activated carbon, and iodine was removed. A yellow transparent liquid was obtained. The measured solid content was 30.1%.
Hereinafter, the obtained AB block copolymer is referred to as “UVP-3”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, the polymer block of A is composed of an aliphatic methacrylate and a methacrylate having a polyethylene glycol chain, has a polyethylene glycol chain having a molecular weight larger than that of UVP-2, and the polymer block of B is derived from phthalic acid. The dispersant is an AB block copolymer having a carboxyl group bonded to the aromatic ring.

(Synthesis Example 4: UVP-4)
390 parts of tetraethylene glycol dimethyl ether (“trade name Hisolv MTEM”, manufactured by Toho Chemical Industries, Ltd., hereinafter referred to as “MTEM”), 5.1 parts of iodine, 24.5 parts of V-70, 120 parts of MMA, 120 parts of BMA, EHMA60 A polymer block solution was obtained in the same manner as in Synthesis Example 1 except that 60 parts of PME200, 30 parts of BzMA, and 1.1 parts of BHT were used. The polymerization rate of the A polymer block calculated from the solid content was 98.3%. The A polymer block had an Mn of 8,800, a PDI of 1.32, and a peak top molecular weight of 11,600.

  25. MMA 32.1 parts, 2- (methacryloyloxy) ethyl phosphate (trade name “Light Ester P-1M”, manufactured by Kyoeisha Chemical Co., Ltd., hereinafter referred to as “P1M”) 25. 2 parts, and a mixed solution of 156.7 parts of MTEM were added. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The solid content of the polymer solution obtained above was 43.9%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had an Mn of 10,300, a PDI of 1.34, a peak top molecular weight of 13,800, and an acid value of 28.3 mgKOH / g. Further, the calculated Mn of the B polymer block was 1,500.

  Furthermore, after diluting the solution with 497 parts of MTEM, 47 g of Shirasagi M was added as activated carbon, stirred at room temperature for 12 hours to adsorb iodine, filtered through a filter to remove activated carbon, and iodine was removed. A yellow transparent liquid was obtained. The measured solid content was 30.0%. Hereinafter, the AB block copolymer obtained above is referred to as “UVP-4”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, the polymer block of A is a dispersant composed of an aliphatic methacrylate and a methacrylate having a polyethylene glycol chain, and the polymer block of B is an AB block copolymer having an acidic group that is phosphoric acid. .

(Synthesis Example 5: UVP-5)
3 parts of DBE, 6.1 parts of iodine, 29.4 parts of V-70, 96 parts of MMA, 96 parts of BMA, 48 parts of EHMA, polycaprolactone modified (n = 5) 2-hydroxyethyl methacrylate (manufactured by Daicel, trade name “FM5 ”, Hereinafter referred to as“ FM5 ”), a solution of A polymer block was obtained in the same manner as in Synthesis Example 1 except that 48 parts, 24 parts of BzMA, and 1.3 parts of BHT were used. The polymerization rate of the A polymer block calculated from the solid content was 99.2%. The A polymer block had a Mn of 6,300, a PDI of 1.29, and a peak top molecular weight of 8,100.

  A mixed solution of 18 parts of MMA, 38.8 parts of MAA, 1.1 parts of V-70 and 138.8 parts of DBE was added to the solution of the obtained A polymer block. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The solid content of the polymer solution obtained above was 43.7%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had an Mn of 7,200, PDI of 1.30, a peak top molecular weight of 9,300, and an acid value of 69.3 mgKOH / g. Further, the calculated Mn of the B polymer block was 900.

  Furthermore, after diluting the solution with 420 parts of DBE, 56 g of white birch M was added as activated carbon, stirred at room temperature for 12 hours to adsorb iodine, filtered through a filter to remove activated carbon, and iodine was removed. A yellow transparent liquid was obtained. The measured solid content was 30.2%. Hereinafter, the AB block copolymer obtained above is referred to as “UVP-5”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, the polymer block A is composed of an aliphatic methacrylate and a methacrylate having a polyester chain, and the polymer block B is a dispersant that is an AB block copolymer having a carboxyl group derived from methacrylic acid.

(Synthesis Example 6: UVS-1)
Except for using MTEM 390 parts, iodine 2.5 parts, V-70 12.3 parts, MMA 120 parts, BMA 120 parts, EHMA 60 parts, PME200 60 parts, BzMA 30 parts, and BHT 1.1 parts. In the same manner as in Example 1, a solution of A polymer block was obtained. The polymerization rate of the A polymer block calculated from the solid content was 98.3%. The A polymer block had a Mn of 17,500, a PDI of 1.54, and a peak top molecular weight of 25,300.

  A mixed solution of 32.1 parts of MMA, 25.2 parts of P1M, and 156.7 parts of MTEM was added to the solution of the obtained A polymer block. And it polymerized for 4 hours at the same temperature, and formed B polymer block. After stopping the flow of nitrogen, the mixture was heated to 80 ° C. to release iodine bonded to the end of the polymer chain to obtain a polymer solution containing an AB block copolymer. It was confirmed that iodine was liberated when the polymer solution became a brown transparent liquid.

  The solid content of the polymer solution obtained above was 44.3%. Further, the polymerization rate of the B polymer block calculated from the solid content was almost 100%. The AB block copolymer had an Mn of 22,500, a PDI of 1.86, a peak top molecular weight of 38,500, and an acid value of 28.5 mgKOH / g. Moreover, Mn of the calculated B polymer block was 5,000.

  Furthermore, after diluting the solution with 497 parts of MTEM, 47 g of Shirasagi M was added as activated carbon, stirred at room temperature for 12 hours to adsorb iodine, filtered through a filter to remove activated carbon, and iodine was removed. A yellow transparent liquid was obtained. The measured solid content was 30.0%. Hereinafter, the AB block copolymer obtained above is referred to as “UVS-1”. This is a pigment dispersant (C) having a structure defined in the present invention. Specifically, a dispersant in which the polymer block of A is composed of an aliphatic methacrylate and a methacrylate having a polyethylene glycol chain, and the polymer block of B is an AB block copolymer having an acidic group that is phosphoric acid. However, the overall molecular weight is large, and the molecular weight of the polymer block of B which is the adsorbing portion is also large.

(Comparative Synthesis Example 1: UVH-1)
DBE547 part was thrown into the 2L separable flask equipped with the reflux tube, the thermometer, and the stirring apparatus, and it heated at 80 degreeC. 114 parts of MMA prepared by dissolving 12.5 parts of 2,2′-azobisisobutyronitrile, 96 parts of BMA, 48 parts of EHMA, 48 parts of PME200, BzMA prepared in a separate container in advance A monomer solution containing 20 parts and 38.8 parts of MAA was dropped into the 2 L separable flask over 1.5 hours. After completion of the dropwise addition, polymerization was further performed at the same temperature for 5 hours to obtain a polymer solution containing a polymer. The resulting polymer solution had a solid content of 40.5% and was diluted with DBE to adjust the solid content to 30%. The solid content was measured and found to be 30.0%. The polymer had a Mn of 6,700, a PDI of 2.0, and an acid value of 68.7 mgKOH / g. Hereinafter, the obtained polymer is referred to as “UVH-1”. This is, for example, a dispersant which is a copolymer having an ordinary random structure, which is not an AB block type copolymer defined in the present invention of Synthesis Example 2 synthesized from a similar monomer.

Tables 1 and 2 show the compositions and physical properties of the polymers obtained in the above synthesis examples.

The theoretical acid values shown in Table 1 are the molecular weights of the monomers used for the synthesis of each of the B polymer blocks, the molecular weight of MAA is 86.1, the molecular weight of MEPA is 278.3, and the molecular weight of P1M is 210. Assuming that the molecular weight of KOH is 56.1 and the case of Synthesis Example 1 is taken as an example, the calculation was performed as follows. Other examples were calculated in the same manner. Specifically, for example, since the weight percentage of MAA in the UVP-1 B polymer block is 68, it is calculated as described below, and the calculated value is 443.1 mgKOH / g.
(68 / 86.1) × 56.1 × 1,000 / 100 = 443.1 mgKOH / g

(Production Example 1: UVP-6)
A 5 L beaker was charged with 2 L of a mixed solution of water / methanol = 7/3 (volume ratio) and stirred with a disper at 1,000 rpm. Subsequently, 100 g of UVP-4 obtained in Synthesis Example 4 described above was gradually added to precipitate a UVP-4 polymer. The precipitate was a white powder. After further stirring for 1 hour, the solid was filtered off and washed well with a mixed solution of water / methanol = 1/1 (volume ratio). Subsequently, it was dried in a dryer at 50 ° C. for 24 hours to obtain 28.3 g of a polymer which was a slightly soft white powder. Next, 58.3 g of isobornyl acrylate as a dispersion medium was placed in a 200 mL beaker, and 25 g of the obtained polymer was gradually added while stirring with a stirrer, and stirred until this polymer was dissolved. A pale yellow polymer solution was obtained, and the solid content was measured and found to be 29.8%. The obtained polymer solution is a solution in which the pigment dispersant (C) defined in the present invention is contained in the polymerizable compound (A) which is a constituent of the white pigment dispersion of the present invention. . Hereinafter, this is referred to as “UVP-6”.

Example 1
24.7 parts (7.5 parts polymer, 5% based on pigment) of UVP-1, which is the pigment dispersant (C) obtained in Synthesis Example 1, and 125.3 parts of isobornyl acrylate as a dispersion medium Were mixed to obtain a homogeneous solution, 150 parts of alumina-treated titanium oxide (average particle size 210 nm) was added, and the mixture was stirred with a disper for 30 minutes to prepare a mill base. Next, using a horizontal media disperser “Dynomill 0.6 liter ECM type” (trade name, manufactured by Shinmaru Enterprises Co., Ltd., zirconia bead diameter 0.65 mm), dispersed at a peripheral speed of 10 m / s, in the mill base The pigment was sufficiently dispersed. The obtained mill base was filtered through a 10 μm membrane filter and then through a 5 μm membrane filter. At this time, no clogging of the filter was observed. A white pigment dispersion defined in the present invention was obtained. This is referred to as W-1.
The number average particle size of the pigment contained in the obtained W-1 was 180 nm and was finely dispersed when measured with a particle size measuring device “NICOMP 380ZLS-S” (trade name, manufactured by International Business Co., Ltd.). The viscosity was 9.7 mPa · s at 25 ° C. and 60 rpm when measured using an E-type viscometer.

Next, the storage stability test of W-1 obtained above was performed. The test method is to put W-1 in a light-shielded glass bottle and leave it in a thermostatic bath set at 60 ° C. for one month, change in viscosity and particle diameter, presence or absence of supernatant, presence or absence of sediment, its state, sediment Was tested for disappearance by stirring.
As a result, in W-1, the average particle diameter is 176 nm, the viscosity is 9.8 mPa · s, no change in physical properties due to storage is observed, and high dispersion stability is maintained. did it. The supernatant was not seen at all. Next, when the bottom of the bottle was scooped with a spatula, a slightly viscous sediment was observed. Subsequently, when the mixture was stirred with a spatula, almost no sediment was found and the original pigment dispersion was restored. When this average particle size was measured, it was 186 nm, and the average particle size was slightly increased due to the aggregation of the precipitate, but it was confirmed that the precipitate was dispersed again and became a good pigment dispersion state. .

(Examples 2-5 , 7, Reference Example 6, Comparative Example 1)
The pigment dispersant UVP-1 used in Example 1 was the same as Example 1 except that the pigment dispersant was changed to UVP-2 to 6, UVS-1, and UVH-1 obtained in the previous synthesis example, respectively. Thus, white pigment dispersions were obtained. Then, using each of the obtained white pigment dispersions, the dispersion state was evaluated and stored in the same manner as in Example 1. The results are summarized in Table 3.

As shown in Table 3, in the white pigment dispersions of Examples 1 to 5, 7 and Reference Example 6 , there was no clogging of the filter at the time of filtration performed after the dispersion treatment, and any dispersion liquid was used. As a result, the average particle size of the pigment in the dispersion was finely dispersed to 200 nm or less. From this, it was confirmed that the pigment dispersant (C) defined in the present invention is a dispersant having good dispersion performance even with respect to titanium oxide of a white pigment having a high specific gravity. In particular, the white pigment dispersions of Examples 2, 3, 4, 5, and 7 show almost no supernatant in the storage test, almost no precipitated pigment is observed, and the average particle diameter and viscosity are maintained. Further, good dispersion performance was given.

As described above, the white pigment dispersions of Examples 2 and 3 had almost no sediment, but a very small amount of sediment was observed. In addition, a small amount of sediment was confirmed in the white pigment dispersion of Example 1. However, in either case, it was confirmed that the original dispersion state was restored by stirring, and it was confirmed that the redispersibility was good. In the white pigment dispersion of Example 1, a larger amount of precipitate was confirmed than in the white pigment dispersions of Examples 2 and 3, which constitutes UVP-1 used as the pigment dispersant (C) in Example 1. This is probably because the A polymer block is not long side chain (polyethylene glycol chain or polycaprolactone chain), and thus there is not enough steric repulsion, and this causes aggregation.
Further, the white pigment dispersion of Reference Example 6 using UVS-1 obtained in Synthesis Example 6 as a dispersant showed good dispersibility, but sedimentation was observed in a storage test. The reason is that the molecular weight of UVS-1 used as the pigment dispersant (C) is larger than that of the other examples, so that it acts on the adsorption between the particles or the polymer molecules are entangled, and the dispersion is agglomerated. It is thought that sedimentation was observed in the preservation test. However, even in this case, it was confirmed that the original dispersion state was restored to some extent by stirring although it was not sufficient.

  On the other hand, the dispersant used in the white pigment dispersion of Comparative Example 1 was clogged with a filter when it was filtered, and sedimentation was observed in a storage stability test. This is because the polymer used for the dispersant of the white pigment dispersion of the comparative example is a random copolymer, so that adsorption points to the pigment are randomly present in the polymer molecule, and the molecular weight distribution is wide, i.e. high. It is thought that the dispersion of pigment worked in the direction of aggregation due to the presence of polymer molecules of molecular weight that acted on the adsorption between pigment particles or the presence of polymer molecules that did not contribute to dispersion. It is done. Moreover, the present inventors consider the reason why the redispersibility as in the white pigment dispersion of the example was not observed in the white pigment dispersion of Comparative Example 1, as follows. That is, the dispersant used in the white pigment dispersion of Comparative Example 1 does not cause steric repulsion with the solvent-soluble polymer chain like the dispersant defined in the present invention, but in the solvent-soluble portion in the polymer molecule. To give stability by solid repulsion. For this reason, the action of the steric repulsion is weak, and because there are polymer molecules that do not contribute to the dispersion, the precipitated material is compressed by the solvent-soluble portion or the polymer molecules that do not contribute to the dispersion by the high specific gravity titanium oxide. Thus, it is assumed that the solid agglomerates were fixed and did not return to the original dispersed state even when stirred.

(Examples 8 to 13)
The isobornyl acrylate used as the dispersion medium when preparing the white pigment dispersion of Example 4 containing UVP-4 as the pigment dispersant was respectively 1,9-nonane diacrylate (Example 8). , Cyclohexyl acrylate (Example 9), 3,3,5-trimethylcyclohexyl acrylate (Example 10), t-butylcyclohexyl acrylate (Example 11), dicyclopentenyl acrylate (Example 12), dicyclopentanyl acrylate A white pigment dispersion was obtained in the same manner except that it was changed to (Example 13). About each obtained dispersion liquid, it carried out similarly to the white pigment dispersion liquid of Example 4, and performed the evaluation about a dispersion state, and the storage test. All showed the same results as in the case of the white pigment dispersion of Example 4, and it was confirmed that fine particle dispersion and high storage stability were achieved. The details of the results are summarized in Table 4.

(Examples 14 and 15)
The amount of pigment dispersant (5%) relative to the pigment used in preparing the white pigment dispersion of Example 5 containing UVP-5 as the pigment dispersant was 3% (Example 14), A white pigment dispersion was obtained in the same manner except that the amount was changed to 10% (Example 15). Each of the obtained dispersions was subjected to a dispersion and storage test in the same manner as in Example 5. The obtained results are shown in Table 5 together with the white pigment dispersion of Example 5 for comparison.

As shown in Table 5, both the white pigment dispersions of Examples 14 and 15 had no filter clogging when filtered, and the average particle size after dispersion was 200 nm or less, and a good dispersion state was obtained. I was able to. As shown in Example 14, it is considered very preferable that the pigment dispersant can be dispersed well even if the amount of the pigment dispersant is as small as 3% with respect to the pigment. However, as shown in Table 5, in the case of the white pigment dispersion of Example 14, a trace amount of sediment was confirmed in the storage stability test. This indicates that in the white pigment dispersion of Example 14, the amount of the pigment dispersant was slightly insufficient with respect to the pigment, and sufficient dispersion stability could not be ensured in the storage state. However, it was confirmed that the dispersion can be returned to a good dispersion state by the stirring operation. As shown in Table 5, also in the case of the white pigment dispersion of Example 15, a trace amount of sediment was confirmed in the storage stability test. Precipitation generated in this case is considered to be due to the fact that the amount of the pigment dispersant was slightly excessive, and thus it acted on adsorption between the many particles. However, in the case of the white pigment dispersion of Example 15, it was confirmed that the original dispersion state was restored by stirring as in the case of the white pigment dispersion of Example 14 described above. Even if precipitation of titanium oxide may occur due to the use of the pigment dispersant that characterizes the present invention, these are excellent pigment dispersions that have good redispersibility and are sufficiently practical. It turns out that you can get.
As described above, by using a pigment dispersant comprising an acid group-containing AB block copolymer having a unique structure that characterizes the present invention, the white pigment dispersion of the present invention has a very fine white pigment titanium oxide. It was confirmed that even when dispersed, the storage stability was good, and even when some sedimentation occurred during storage, excellent redispersibility was achieved.

(Application example)
A white UV-curable inkjet ink was prepared using the white pigment dispersion of Example 4 prepared previously. Specifically, the components having the following composition were sufficiently stirred and then filtered through a membrane filter having a pore size of 10 μm and then through a 5 μm membrane filter to obtain an ink.
(Ink formulation)
White pigment dispersion of Example 4 40 parts Isoboronyl acrylate 17 parts 1,6-hexanediol diacrylate 25 parts Trimethylolpropane triacrylate 7 parts Dipentaerythritol hexaacrylate 3 parts Lucyrin TPO (manufactured by BASF) ) 3 parts Irgacure 819 (Photopolymerization initiator BASF) 2 parts Irgacure 127 (Photopolymerization initiator BASF) 3 parts

  When the pigment particle diameter in the ink prepared above was measured, it was 175 nm and the viscosity of the ink was 5.6 mPa · s. When the brown sample bottle was loaded with ink and tested for storage stability, the supernatant and sediment were not observed at all. The average particle size of the pigment in the ink after storage was 172 nm and the viscosity was 5.3 mPa.・ It was s. From the comparison with the following comparative application example, this is achieved by using the pigment dispersant that characterizes the present invention, the pigment adsorbing part is adsorbed without desorbing from the pigment, and the storage stability of the ink It was found that the properties were improved.

(Comparative application example)
As a comparative application example, an ink was prepared in the same manner except that the white pigment dispersion liquid of Comparative Example 1 was used instead of the white pigment dispersion liquid of Example 4 used in Example Application Example 1. In the case of the ink of this comparative application example, unlike the case of the ink of the application example 1, there is a slight resistance to the 10 μm membrane filter when filtering, and in addition, the 5 μm membrane filter performed next is a filter. I felt a strong resistance to pass through, that is, a clog occurred.

  The pigment particle diameter of the comparative application example prepared above was measured, and it was 258 nm and the viscosity of the ink was 6.3 mPa · s. Further, when a storage stability test was performed in the same manner as described above, a transparent supernatant was observed. Further, the ink of the comparative application example showed sedimentation, and there was a hard paste.

(Usage example 1)
Using the respective white inks obtained in the practical application examples and the comparative application examples, the following printing tests were performed by the inkjet recording method. Specifically, each white ink was loaded into a cartridge, and using an inkjet printer (trade name: EB100) manufactured by Konica Minolta, solid printing was continuously performed on a polyethylene terephthalate (PET) film for 1 hour for printing. . As a result, the ink of the application example using the white pigment dispersion liquid of Example 4 can be printed smoothly without clogging of the head, and the solid printing which is the image shows no streaks or twists, and is excellent. The discharge stability was shown. On the other hand, in the printing using the ink of the comparative application example using the white pigment dispersion liquid of the comparative example, the ink was stably ejected at the beginning, and the solid printing was good. After about 10 minutes, the discharge became unstable, streaks began to appear on the printed matter, and blurring occurred. This is considered to be caused by clogging at the head and a drop in the straightness of ink ejection.

  Furthermore, the printed matter formed by the ink containing the pigment dispersion of Example 4 obtained above was exposed by irradiating ultraviolet rays with a UV lamp to obtain a printed sample. The print sample was cut into a grid pattern with a cutter, and then an adhesive (fixing) test was performed by attaching a cello tape and peeling it off at once. As a result, the printed cured product did not peel off at all, and showed good adhesion to the film. Next, instead of the PET film, a vinyl chloride film and a surface-treated polypropylene film were used as the base film, respectively, printed in the same manner, and subjected to the same adhesion test. It was confirmed that the fixing property was exhibited.

(Usage example 2)
After the above-mentioned printing test performed using the ink of the example of application using the white pigment dispersion liquid of Example 4, it was left for one week, and the same continuous printing as described above was performed again for printing. As a result, no clogging of the head occurred, no streaks or kinks in the printed material were observed, and good dischargeability was exhibited. Since the white pigment dispersion of the embodiment of the present invention in which the white pigment titanium oxide is dispersed with the pigment dispersant having the specific structure defined in the present invention has a high degree of stability, the pigment aggregates or settles. Thus, the particle diameter does not increase, and it is considered that ink discharge was good even after lapse of time.

  In the same manner as described above, an ink was prepared using the white pigment dispersion liquid of another example, and the same test was performed using the ink using an ink jet printer. As a result, the same result is obtained when any ink is used, and the ink in which titanium oxide, which is a white pigment, is dispersed with the pigment dispersant defined in the present invention has good ejection stability, no streaking or distortion. It was confirmed that the printed matter gave high adhesion (high fixability).

  According to the present invention, an AB block copolymer having a specific structure defined in the present invention is used as a pigment dispersant, and a titanium oxide pigment having a high specific gravity is finely dispersed in the polymerizable compound (A) as a dispersion medium. In the ultraviolet curable ink-jet ink using the dispersed white pigment dispersion, the pigment is finely dispersed and the pigment particle diameter can be kept small. The pigment in the white pigment dispersion provided by the present invention has no sedimentation or aggregation when it is used as an ink, has high storage stability, and does not clog the head. No dripping, i.e., good ejection stability, good adhesion without hindering adhesion, especially suitable for printing on transparent plastic film, and further improved printing technology by inkjet printer. Can contribute to development.

Claims (8)

As a dispersion medium, 15 to 59% by mass of one or more polymerizable compounds (A), 40 to 70% by mass of titanium oxide (B) as a white pigment, 0.7 to 12% by mass of a pigment dispersant (C), And 0-15% by mass of organic solvent (D),
The pigment dispersant (C) is an AB block type AB block copolymer comprising an A polymer block and a B polymer block containing 90% by mass or more of a structural unit derived from a methacrylic acid monomer,
The A-B block copolymers, the B polymer block, a carboxyl group-containing methacrylic acid-based monomer and at least one kind of acid group-containing methacrylate of phosphoric acid group-containing methacrylic acid-based monomers having a phosphoric acid group having a carboxyl group comprising a constituent unit derived from an acid monomer, Ri acid group-containing block copolymer der,
The acid value of the B polymer block due to a carboxyl group or a phosphoric acid group derived from the acid group-containing methacrylic acid monomer is 50 to 500 mgKOH / g, and the molecular weight of the B polymer block (number of AB block copolymers) (Molecular weight obtained by subtracting the number average molecular weight of the A polymer block from the average molecular weight) is in the range of 200 to 3,000, and the number average molecular weight of the AB block copolymer is in the range of 4,000 to 20,000. Furthermore, the molecular weight distribution (weight average molecular weight / number average molecular weight) is 1.6 or less,
The acid group-containing methacrylic acid-based monomer, methacrylic acid, methacryloyloxyethyl phthalic acid, and methacryloyloxy-jet recording white pigment dispersion composition, wherein at least one Der Rukoto ethyl phosphoric acid ester. The white pigment dispersion composition for inkjet recording according to claim 1, wherein the dispersed titanium oxide (B) has an average particle diameter of 100 to 300 nm. The polymerizable compound (A) is selected from the group consisting of cyclohexyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, t-butylcyclohexyl acrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, isobornyl acrylate and adamantyl acrylate. jet recording white pigment dispersion composition according to claim 1 or 2 is at least one selected. The monomer constituting the A polymer block is poly (n = 2 or more) alkylene (C2 to C4) glycol methacrylate, poly (n = 2 or more) alkylene (C2 to C4) glycol monoalkyl (C1 to C18) ether. The white pigment dispersion composition for inkjet recording according to any one of claims 1 to 3 , which is at least one of methacrylate and methacrylate of poly (n = 2 or more) hydroxyalkyl (C2 to C18) carboxylic acid. object. It is a manufacturing method of the acid group containing AB block copolymer used for the pigment dispersant (C) which comprises the white pigment dispersion liquid composition for inkjet recording of any one of Claims 1-4 ,
Having a step of living radical polymerization of a monomer component containing a methacrylic acid monomer in the presence of a polymerization initiating compound and a catalyst, and the polymerization initiating compound used in the step is at least one of iodine or an iodine compound, The catalyst used in the step is at least one compound selected from the group consisting of phosphorus halides, phosphite compounds, phosphinate compounds, imide compounds, phenol compounds, diphenylmethane compounds and cyclopentadiene compounds. And a polymerization temperature thereof is 30 to 50 ° C., and a method for producing an acid group-containing AB block copolymer. A monomer block containing a methacrylic acid monomer in the presence of the polymerization initiation compound and the catalyst is subjected to living radical polymerization at a polymerization temperature of 30 to 50 ° C. to form an A polymer block, and further has a carboxyl group. A monomer component containing at least one of a carboxyl group-containing methacrylic acid monomer and a phosphoric acid group-containing methacrylic acid monomer having a phosphate group is added, and living radical polymerization is performed at a polymerization temperature of 30 to 50 ° C. The method for producing an acid group-containing AB block copolymer according to claim 5 , wherein an AB block copolymer containing 90% by mass or more of a structural unit derived from a methacrylic acid monomer is obtained by forming a B polymer block. A white ink composition for ink-jet recording, comprising the white pigment dispersion composition for ink-jet recording according to any one of claims 1 to 4 . The white ink composition for ink jet recording according to claim 7 , further comprising an ultraviolet ray or electron beam curable ink comprising a photopolymerization initiator.