JP2008213368A - Latex for ink jet recording medium and its manufacturing method, coated composition for ink jet recording medium and ink jet recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet recording medium capable of satisfying all of luster, ink absorbency (printing concentration), waterproofness and dampproofness at a sufficient level, a coated composition for ink jet recording medium to obtain that, a latex for ink jet recording medium, and the manufacturing method of latex for ink jet recording medium. <P>SOLUTION: The manufacturing method of latex for ink jet recording medium featured by carrying out polymerization of a first monomer under presence of nonionic surface active agent and a first monomer under presence of anionic surface active agent; then, alcoholic hydroxyl group containing alcoholic hydroxyl group containing water-soluble high-molecular compound and a second monomer are added to the obtained latex and further polymerization is contained. Thereby, the latex for ink jet recording medium is obtained. The latex is contained to compose the coated composition for ink jet recording medium. The coated composition is coated to compose the ink jet recording medium. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a latex for an inkjet recording medium, a method for producing the latex, a coating composition for an inkjet recording medium, and an inkjet recording medium. More specifically, a method for producing a latex for an ink jet recording medium by carrying out the polymerization of the monomer in at least two stages and causing each compound to exist in each step, and the ink jet recording medium obtained thereby The present invention relates to a latex, a coating composition for an ink jet recording medium containing the latex, and an ink jet recording medium formed by coating the latex.

The ink jet recording method is a method for recording characters, images, and the like by ejecting fine ink droplets from nozzles by various operating principles and attaching them to a recording medium. This recording method is characterized in that it is easy to increase the speed and color, and does not require processing such as development and fixing, and is rapidly spreading in recording apparatuses such as printers and plotters.
A recording medium used in such a recording method usually has a coating film formed by applying an aqueous resin composition on a support such as paper and drying it as an ink receiving layer.

In the ink jet recording system, there are strong demands for improving print quality and increasing the resolution of a printed image. For this reason, generally, a recording method using a low density ink and increasing the amount of ink used is employed.
However, at this time, there is a problem that the ink supplied in a large amount on the recording medium flows out without being absorbed by the receiving layer, and the recording portion such as printing becomes unclear or the strength of the ink receiving layer itself is lowered. Arise. Furthermore, when water droplets or the like adhere to the recording medium before and after ink jet recording, the ink receiving layer is deformed and the strength is reduced, or the recording part is eluted and bleeding occurs, so that the recording quality is remarkably deteriorated. Also occurs.

As a countermeasure against such a problem, a cationic substance comprising an oligomer or polymer comprising a monomer of a primary to tertiary amine or a quaternary ammonium salt that dissociates and exhibits cationic properties when dissolved in water, specifically, It is known to add dimethylamine / epichlorohydrin polycondensate, acrylamide / diallylamine copolymer, polyvinylamine copolymer, dicyandiamide / dimethyl / diallyl / ammonium chloride, polyethyleneimine and the like to the ink receiving layer.
For example, Patent Document 1 discloses a recording sheet in which an ink receiving layer composed of a cationic polymer having a crosslinkable group and a hydrophilic polymer is formed on at least one surface of a substrate. Yes. Patent Document 2 discloses that an ink jet recording sheet is directly or indirectly formed on at least one surface of a support using a binder composition comprising a cationic polymer, an inorganic filler, and a sulfosuccinic ester surfactant. The formation of a receiving layer is described.

  The ink receiving layer of the ink jet recording medium described in these publications meets the demand for achieving both ink absorbability and water resistance, which are contradictory properties, but the degree of improvement is sufficient. Needless to say, there is a need for further improvements in coating compositions that form recording media, particularly ink-receiving layers, in order to achieve higher quality ink jet recording.

By the way, it is necessary to provide a coating layer having a large void amount in order to ensure the absorption amount of the ink receiving layer. For this reason, a large amount of inorganic particles are contained in the ink receiving layer. However, as a result, the surface of the coating layer is very rigid and hard. Such a coating layer surface is easily cracked due to the generation of internal stress in the drying process of the coating liquid and the weak external force applied to the recording sheet after drying, and the smoothness and gloss are impaired. There is a point.
In order to bind these large amounts of inorganic particles, a hydrophilic polymer typified by polyvinyl alcohol is used as a binder. If a hydrophilic polymer is used as a binder, water can be used as the coating liquid, so there is no need to use an organic solvent, so there will be no problems with the working environment during the coating process or with the solvent remaining in the product. On the other hand, when the surface of the recording medium is touched with a finger, there is a problem that a fingerprint remains, and there are problems with water resistance and moisture resistance when printing with water-soluble ink.

For this reason, various studies have been made on binders for inkjet recording media containing a hydrophilic polymer such as polyvinyl alcohol.
In Patent Document 3, a vinyl alcohol polymer having a mercapto group at the molecular end is used as a dispersion stabilizer, and one or more single monomers selected from ethylenically unsaturated monomers and diene unsaturated monomers are used. A binder comprising an aqueous emulsion in which a polymer having a monomer as a constituent unit is used as a dispersoid is disclosed.
According to this document, it is said that an ink jet recording sheet having high gloss, excellent ink absorbability, and excellent water resistance, print density and crack resistance can be obtained. The effect is not enough.

In Patent Document 4, poly (vinyl alcohol) having a hydrophobic group at a molecular end is used as a dispersion stabilizer, and one or more monomers selected from monomers having an unsaturated double bond are used as constituent units. Resin for inkjet recording sheets comprising an aqueous emulsion having a coalesced dispersoid, or an aqueous emulsion imparted with a cationic property by using a cationic polymerization initiator or a combination of a cationic surfactant or a cationic monomer. A composition is described, and in practice, a latex is obtained by polymerization using a cationic initiator.
However, this method has a problem that when it is used in combination with a compound having an anionic surface such as silica fine particles, an ionic reaction occurs to form coarse particles, resulting in a significant decrease in glossiness.

  Patent Document 5 discloses an ink jet recording sheet which is an aqueous emulsion in which an anionic property is imparted by using an anionic polymerization initiator or a combination of an anionic surfactant and an anionic monomer in the same aqueous emulsion. An aqueous emulsion is disclosed. In the examples, polymerization was carried out using persulfate, but according to the study of the present inventor, this method still does not have sufficient polymerization stability and stability of the resulting latex. Addition of an anionic surfactant to this aqueous emulsion is said to reduce the bleeding resistance, and this is further deteriorated when polymerized using an anionic surfactant. Furthermore, there is also a problem that cation stability is lowered by imparting anionic property.

Japanese Patent Laid-Open No. 10-264511 JP 2000-309159 A Japanese Patent Publication No. 2003-251923 Japanese Patent Publication No. 2006-76249 Japanese Patent Publication No. 2006-346879

Accordingly, an object of the present invention is to provide an inkjet recording medium excellent in gloss, ink absorbability (print density) and water resistance, an inkjet recording medium coating composition for obtaining the same, and an inkjet recording medium excellent in cation stability. It is another object of the present invention to provide a latex and a method for producing the latex for an inkjet recording medium.
As a result of diligent research to achieve the above object, the present inventor has divided the polymerization into two stages, and the first stage polymerization is carried out in the presence of a combination of an anionic surfactant and a nonionic surfactant. Then, in the second stage, a specific hydrophilic polymer is additionally added and polymerization is performed to obtain a latex having excellent cation stability, and using this, an ink jet having excellent characteristics described above can be obtained. It has been found that a recording medium can be obtained, and the present invention has been completed based on this finding.

Thus, according to the present invention, the first monomer is polymerized in the presence of the nonionic surfactant and the anionic surfactant, and then the alcoholic hydroxyl group-containing aqueous solution having a hydrophobic group is added to the obtained latex. A method for producing a latex for an ink jet recording medium is provided, in which a polymerizable polymer compound and a second monomer are added and polymerization is further continued.
In the method for producing a latex for an ink jet recording medium of the present invention, the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group preferably has a hydrophobic group at its molecular end.
In the method for producing a latex for an ink jet recording medium of the present invention, a nonionic surfactant may be further added during the polymerization of the second monomer.

Moreover, according to this invention, the latex for inkjet recording media obtained by the manufacturing method of the said latex for inkjet recording media is provided.
Moreover, according to this invention, the coating composition for inkjet recording media formed by containing the latex for inkjet recording media of the said invention is provided.
Furthermore, according to this invention, the inkjet recording medium formed by coating the support body with the coating composition for inkjet recording media of the said invention is provided.

  According to the method for producing a latex for an ink jet recording medium of the present invention, a latex for an ink jet recording medium having a small particle size and excellent cation stability can be obtained. An ink jet recording medium obtained by coating a support with an ink jet recording medium coating composition obtained using the ink jet recording medium latex is excellent in gloss, ink absorbability, water resistance, and the like.

In the method for producing a latex for an inkjet recording medium of the present invention, the first monomer is polymerized in the presence of a nonionic surfactant and an anionic surfactant, and then a hydrophobic group is added to the obtained latex. The alcoholic hydroxyl group-containing water-soluble polymer compound and the second monomer are added, and the polymerization is further continued.
In the present invention, “monomer” is a concept including “monomer mixture”.

The monomer used in the present invention is not particularly limited, and those conventionally used for latexes for inkjet recording media can be used.
Examples of such monomers include olefins such as ethylene, propylene, 1-butene, and isobutene; vinyl halide monomers such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; vinyl formate, vinyl acetate, Carboxylic acid vinyl esters such as vinyl propionate, vinyl pivalate, isopropenyl acetate, vinyl versatate; styrene, α-methylstyrene, monochlorostyrene, dichlorostyrene, monomethylstyrene, dimethylstyrene, trimethylstyrene, hydroxymethylstyrene, p -Aromatic vinyl monomers such as styrenesulfonic acid and its sodium salt and potassium salt; ethylenically unsaturated monocarboxylic acids such as (meth) acrylic acid, crotonic acid and itaconic acid, and derivatives thereof such as esters and amides ; Fumaric acid, male Ethylenically unsaturated polyvalent carboxylic acids such as acid, itaconic acid, maleic anhydride, itaconic anhydride and derivatives thereof such as esters, anhydrides and amides; ethylenically unsaturated nitrile monomers such as (meth) acrylonitrile 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-ethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1; Conjugated dienes such as 1,3-pentadiene, 1,3-hexadiene, 2,4-hexadiene; vinyl ethers such as methyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether Monomer: Allyl acetate, methallyl acetate, allyl chloride, salt An allyl compound such as methallyl fluoride; a vinylsilane compound such as vinyltrimethoxysilane; a vinyl heterocyclic compound such as vinylpyridine and N-vinylpyrrolidone;
In the present invention, “(meth) acrylic acid” means “acrylic acid” and / or “methacrylic acid”. Similarly, “(meth) acrylonitrile” means “acrylonitrile” and / or “methacrylonitrile”.

  Among these monomers, ethylenically unsaturated monocarboxylic acids and derivatives thereof, ethylenically unsaturated polyvalent carboxylic acids and derivatives thereof, and ethylenically unsaturated nitrile monomers are preferable. Carboxylic acid and its derivatives are preferred.

Specific examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid and crotonic acid.
Specific examples of suitable ester derivatives of ethylenically unsaturated monocarboxylic acids include esters of ethylenically unsaturated monocarboxylic acids with alcohols having 1 to 12 carbon atoms. Specific examples thereof include (meth) acrylic. Methyl methacrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, (meth) Examples include 2-hydroxyethyl acrylate, dimethylaminoethyl (meth) acrylate, and the like.
Specific examples of amide derivatives of ethylenically unsaturated monocarboxylic acids include (meth) acrylamide, N-methylol (meth) acrylamide, N, N-dimethyl (meth) acrylamide, (meth) acrylamide-2-methylpropane Examples thereof include sulfonic acid and its sodium salt.

In the method for producing a latex for an ink jet recording medium of the present invention, first, a part of all monomers is polymerized in the presence of a nonionic surfactant and an anionic surfactant (this polymerization is carried out by “ Sometimes referred to as "first stage polymerization").
The ratio of the monomer used for the first stage polymerization is not particularly limited, but is 20 to 80% by weight, preferably 30 to 70% by weight, based on all monomers.
The composition of the monomer used for the first stage polymerization (hereinafter sometimes referred to as “first monomer”) is not particularly limited, but the glass transition temperature of the polymer obtained by the first stage polymerization is not particularly limited. Is preferably −85 to + 60 ° C.

It is essential that the first stage polymerization be carried out in the presence of a nonionic surfactant and an anionic surfactant.
The nonionic surfactant used in the first stage polymerization is not particularly limited.
Specific examples thereof include polyoxyalkylene alkyl aryl ether surfactants, polyoxyalkylene alkyl ether surfactants, polyoxyalkylene fatty acid ester surfactants, sorbitan fatty acid ester surfactants, silicone surfactants, acetylene alcohols Surfactant, fluorine-containing surfactant, etc. are mentioned.

Specific examples of the polyoxyalkylene alkyl aryl ether surfactant include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, and polyoxyethylene dodecyl phenyl ether.
Specific examples of the polyoxyalkylene alkyl ether surfactant include polyoxyethylene oleyl ether and polyoxyethylene lauryl ether.
Specific examples of the polyoxyalkylene fatty acid ester surfactant include polyoxyethylene oleate, polyoxyethylene laurate, and polyoxyethylene distearate.
Specific examples of the sorbitan fatty acid ester surfactant include sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, polyoxyethylene stearate and the like.

Specific examples of silicone surfactants include dimethylpolysiloxane.
Specific examples of the acetylene alcohol surfactant include 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, , 5-dimethyl-1-hexyne-3ol and the like.
Specific examples of the fluorine-containing surfactant include a fluorine alkyl ester.

  The amount of the nonionic surfactant used in the first stage polymerization is preferably 0.3 to 6.0 parts by weight with respect to 100 parts by weight of the monomer mixture in the first stage polymerization. The amount is more preferably 5 to 4.0 parts by weight, and still more preferably 1.0 to 2.5 parts by weight. If the amount used is less than the above lower limit, the resulting latex may be inferior in cation stability. On the other hand, if the amount used exceeds the above upper limit, the bleeding resistance of the ink jet recording medium obtained using latex may be lowered.

The anionic surfactant used in the first stage polymerization is not particularly limited, and specific examples thereof include carboxylate surfactants, sulfonate surfactants, sulfate ester surfactants, and phosphate ester surfactants. Can be mentioned.
Specific examples of the carboxylate surfactant include fatty acid salts, N-acylamino acids and salts thereof, polyoxyethylene alkyl ether carboxylates, acylated peptides, and the like.
Specific examples of the sulfonate surfactant include alkylbenzene sulfonate, alkyl naphthalene sulfonate, naphthalene sulfonate formalin condensate, melamine sulfonate formalin condensate, dialkyl sulfosuccinate ester salt, alkyl sulfoacetate salt, Examples thereof include α-olefin sulfonates and N-acyl alkyl sulfonates.

Specific examples of the sulfate ester surfactant include sulfated oil, higher alcohol sulfate ester salt, polyoxyethylene alkyl ether sulfate, higher alcohol ethoxy sulfate, polyoxyethylene alkyl phenyl ether sulfate, mono fatty acid glyceryl sulfate, Examples thereof include fatty acid alkylolamide sulfate salts.
Specific examples of the phosphate ester surfactant include an alkyl ether phosphate ester salt and an alkyl phosphate ester salt.

  The amount of the anionic surfactant used in the first stage polymerization is preferably 0.1 to 5.0 parts by weight with respect to 100 parts by weight of the monomer used in the first stage polymerization. 0.5 to 4.0 parts by weight is more preferable, and 0.5 to 3.0 parts by weight is even more preferable. If the amount used is less than the above lower limit, the particle size may increase, or the glossiness of the ink jet recording medium obtained using latex may be lowered. Latex may have poor cation stability.

The ratio of the amount of nonionic surfactant to the amount of anionic surfactant used in the first stage polymerization is not particularly limited, but usually the amount of nonionic surfactant / the amount of anionic surfactant The ratio is set to a range of 4/1 to 1/3.
Furthermore, the total amount of the nonionic surfactant and the anionic surfactant used in the first stage polymerization is 0.4 to 5.0 weights with respect to 100 parts by weight of the total monomers used in the polymerization. Part is preferable, 1.0 to 4.0 parts by weight is more preferable, and 1.5 to 3.0 parts by weight is still more preferable.
If the amount of the anionic surfactant used is too large, the cation stability of the resulting latex may be reduced. If the amount of the nonionic surfactant is too large, the particle size becomes too large, and the ink jet finally obtained. There is a possibility that the ink absorbability and glossiness of the recording medium are lowered.
In the present invention, it is important to use a nonionic surfactant and an anionic surfactant together in the first stage polymerization, thereby ensuring the cation stability of the latex for inkjet recording media obtained. Thus, it is possible to make each characteristic of the finally obtained ink jet recording medium excellent.

The first stage polymerization is preferably carried out by an emulsion polymerization method in an aqueous medium.
As the aqueous medium, water or a mixture of water and an organic solvent miscible with water can be used.
In the first stage polymerization, the ratio of the monomer to the aqueous medium is not particularly limited, but usually the monomer is 5 to 100 parts by weight, preferably 10 to 70 parts by weight with respect to 100 parts by weight of the aqueous medium. Parts, more preferably 10 to 55 parts by weight.

A polymerization initiator is not specifically limited, An inorganic peroxide, an organic peroxide, an azo compound etc. can be used.
Specific examples of the inorganic peroxide polymerization initiator include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; perphosphates such as potassium perphosphate; hydrogen peroxide; .
Specific examples of the organic peroxide polymerization initiator include hydroperoxides such as diisopropylbenzene hydroperoxide, cumene hydroperoxide, t-butyl hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, and the like. And peroxides such as di-t-butyl peroxide, isobutyryl peroxide, and benzoyl peroxide;
Specific examples of the azo compound polymerization initiator include azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, methyl azobisisobutyrate, and the like.
Among the initiators, a water-soluble radical polymerization initiator is preferable, and a persulfate is preferable, and potassium persulfate and ammonium persulfate are particularly preferable.
These polymerization initiators may be used alone or in combination of two or more.

The usage-amount of a polymerization initiator is 0.05-3 weight part normally with respect to 100 weight part of all the monomers used for superposition | polymerization, Preferably it is 0.1-2 weight part.
These polymerization initiators can be used as a redox polymerization initiator in combination with a reducing agent. The reducing agent is not particularly limited, and specific examples thereof include compounds containing metal ions in a reduced state such as ferrous sulfate and cuprous naphthenate; sulfonic acid compounds such as sodium methanesulfonate; dimethylaniline and the like An amine compound; and the like. These reducing agents may be used alone or in combination of two or more.
Although the usage-amount of a reducing agent changes with reducing agents, it is preferable that it is 0.03-10 weight part with respect to 1 weight part of polymerization initiators.

  A known chain transfer agent may be appropriately added to the polymerization reaction system in order to adjust the molecular weight of the polymer. In particular, when a monomer containing a conjugated diene monomer such as 1,3-butadiene is polymerized, it is preferable to use a chain transfer agent. In this case, the chain transfer agent is used in an amount of 0.2 to 5 parts by weight based on 100 parts by weight of the monomer mixture.

Specific examples of the chain transfer agent include α-methylstyrene dimer, mercaptan compound, sulfide compound, nitrile compound, thioglycolic acid ester, β-mercaptopropionic acid ester and the like.
Specific examples of the mercaptan compound include t-dodecyl mercaptan and n-dodecyl mercaptan.
Specific examples of the sulfide compound include dimethylxanthogen disulfide and diisopropylxanthogen disulfide.
Specific examples of the nitrile compound include 2-methyl-3-butenenitrile and 3-pentenenitrile.
Specific examples of the thioglycolic acid ester include methyl thioglycolate, propyl thioglycolate, octyl thioglycolate and the like.
Specific examples of the β-mercaptopropionic acid ester include methyl β-mercaptopropionate and octyl β-mercaptopropionate.
Among these, thioglycolic acid ester is preferable, and octyl thioglycolate is more preferable.
These chain transfer agents may be used alone or in combination of two or more.

Although polymerization temperature is not specifically limited, Usually, 0-100 degreeC, Preferably it is 5-95 degreeC.
In addition, the method for adding the monomer is not particularly limited, and the monomer used for the first stage polymerization may be added all at once, or all the amounts may be added sequentially, The remainder may be added all at once or sequentially.
From the viewpoint of stabilizing the polymerization and improving the stability of the resulting latex, the monomer is preferably added as an emulsion using an aqueous medium and a surfactant.
Furthermore, the stirring conditions during the polymerization are not particularly limited.

  In the first stage polymerization, the polymerization conversion rate is preferably 85 to 98.5% by weight. If this conversion rate is too low, there is a possibility that the cation stability of the resulting latex is lowered, and it is not economical to continue the polymerization until the conversion rate is higher than the above upper limit.

In the first stage polymerization, after the polymerization conversion rate reaches a certain level, the second stage polymerization is performed.
In the second-stage polymerization, the latex obtained by the first-stage polymerization was used in the first-stage polymerization among the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group and all monomers (hereinafter referred to as the remainder). , Sometimes referred to as “second monomer”), and polymerization is continued.
The monomer used in the first stage and the monomer used in the second stage may have the same composition or different compositions. The composition of the second monomer is not particularly limited, but the glass transition temperature of the polymer obtained when only the second monomer is polymerized is in the range of -20 to + 100 ° C. It is preferable. Further, it is preferable that the glass transition temperature in the second stage is higher than the glass transition temperature in the first stage.
In the second stage polymerization, a polymerization catalyst may be additionally added as necessary. The polymerization catalyst used may be the same as or different from that used in the first stage.
Note that the second stage polymerization may be carried out in two or more stages. That is, after polymerizing a part of the second monomer, the remainder may be further divided into several times.

In the present invention, the alcoholic hydroxyl group-containing water-soluble polymer compound refers to a water-soluble polymer compound containing 5 to 25 alcoholic hydroxyl groups per 1,000 molecular weight.
Specific examples thereof include vinyl alcohol polymers such as polyvinyl alcohol and various modified products thereof; saponified products of copolymers of vinyl acetate and acrylic acid, methacrylic acid or maleic anhydride; alkyl cellulose, hydroxyalkyl cellulose, alkyl Examples thereof include cellulose derivatives such as hydroxyalkyl cellulose; starch derivatives such as alkyl starch, carboxymethyl starch and oxidized starch; gum arabic, tragacanth rubber; polyalkylene glycol and the like. Of these, vinyl alcohol polymers are preferred from the viewpoint of easy availability of industrially stable products.

  The weight average molecular weight of the alcoholic hydroxyl group-containing water-soluble polymer compound is not particularly limited, but is usually 1,000 to 500,000, preferably 2,000 to 300,000. When the molecular weight is less than 1,000, the dispersion stabilizing effect at the time of polymerization becomes low. On the other hand, when the molecular weight is more than 500,000, the viscosity at the time of polymerization in the presence thereof increases, which may make the polymerization difficult.

In the present invention, the hydrophobic group means a hydrocarbon group having 5 or more carbon atoms. The hydrocarbon group may be an aliphatic group, an alicyclic group, or an aromatic group.
In the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group, the position of the hydrophobic group is not particularly limited, and even if it exists at the molecular end of the water-soluble polymer compound, it exists in the middle position of the molecular chain. However, those existing at the molecular ends are preferred.
In the present invention, the stability of the latex is improved by using the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group, and the resulting ink jet recording medium has excellent ink absorbability.

The alcoholic hydroxyl group-containing water-soluble polymer having a hydrophobic group can be obtained by introducing a hydrophobic group into the alcoholic hydroxyl group-containing water-soluble polymer by a known method.
For example, in the case of polyvinyl alcohol having a hydrophobic group, a method of introducing a hydrophobic group at one end of a molecular chain by the presence of a chain transfer agent having a hydrophobic group during polymerization of vinyl acetate, vinyl acetate and allyl glycidyl ether, A method of introducing a hydrophobic group at an intermediate position of a molecular chain by saponifying a vinyl acetate copolymer obtained by copolymerizing butadiene monoepoxide, N-glycidoxymethylacrylamide, etc. in the presence of a thiol compound Can be mentioned. According to the latter method, the amount of the hydrophobic group can be controlled by controlling the amount of the epoxy group-containing monomer used for the copolymerization.

  In the present invention, the amount of the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group used for the second stage polymerization is not particularly limited, but preferably, the monomer 100 used for the second stage polymerization is used. It is 3-50 weight part with respect to a weight part, More preferably, it is 5-25 weight part. When the amount used is within the above range, the dispersion stabilizing effect at the time of polymerization becomes high, the viscosity of the polymerization system becomes appropriate, the polymerization proceeds smoothly, and the inkjet recording medium using the resulting latex is used. The ink absorbency and water resistance are excellent.

  In the second stage polymerization, the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group may be added as an aqueous medium solution separately from the monomer used in the second stage polymerization. Using this as a dispersant, it is easy to prepare a monomer dispersion and add the three at the same time, which is also preferable from the viewpoint of maintaining polymerization stability.

  In the second stage, the amount of the aqueous medium to be used is not particularly limited, but usually, in the polymerization system in the second stage, the monomer (first monomer and second monomer) and the hydrophobic group are added. The total concentration with the alcoholic hydroxyl group-containing water-soluble polymer compound is 15 to 35% by weight. If the amount of the aqueous medium is too large, the concentration of the resulting latex may be lowered and an operation such as concentration may be required. Conversely, if it is too small, the polymerization stability may be lowered.

In the present invention, a nonionic surfactant may be newly added during the second stage polymerization.
By additionally adding a nonionic surfactant during the second stage polymerization, an effect of improving the cation stability of the obtained latex can be obtained.
As the nonionic surfactant, those similar to those used in the first stage polymerization can be used.
The amount of the nonionic surfactant added additionally in the second stage polymerization is not particularly limited, but is usually 3.0 parts by weight or less, preferably 100 parts by weight or less, preferably 100 parts by weight of the monomer used in the second stage. 1.5 parts by weight or less. If this amount is too large, the water resistance of the finally obtained inkjet recording medium may be lowered.
In the second stage polymerization, the additional nonionic surfactant is added as a dispersion or emulsion together with the monomer added in the second stage and the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group. Convenient.
In the second stage polymerization, it is not preferable to use an anionic surfactant or to add it to the latex after the polymerization because the cation stability of the resulting latex for ink jet recording medium is lowered.

  In the second stage polymerization, the polymerization temperature, the stirring conditions, the method for adding the monomer, etc. are not particularly limited. The polymerization is performed until the polymerization conversion finally becomes 90% by weight or more, preferably 93% by weight or more, more preferably 95% by weight or more. If the final polymerization conversion is too low, it may take a long time to remove unreacted monomers.

  After completion of the polymerization, the latex for an ink jet recording medium of the present invention is obtained by adjusting the concentration by removing, diluting or concentrating unreacted monomers, adjusting the pH, etc. by a conventional method.

  The solid content concentration of the latex for inkjet recording media is not particularly limited, but is usually 3 to 60% by weight, preferably 5 to 50% by weight, and more preferably 10 to 50% by weight.

The pH of the latex for ink jet recording media of the present invention is preferably adjusted in the range of 2.0 to 7.0.
The method for adjusting the pH is not particularly limited, and can be performed by adding a basic compound or an acidic compound to the latex.
The basic compound is not particularly limited, but ammonia or amine is preferably used.
The amine is preferably a tertiary amine, and specific examples thereof include trimethylamine, triethylamine, triethanolamine, dimethylethanolamine, diethylethanolamine, triisopropanolamine, butyldiethanolamine and the like.
These basic compounds may be used alone or in combination of two or more.
As the basic compound, alkali metal hydroxides such as potassium hydroxide, sodium hydroxide and lithium hydroxide; alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide can also be used. .
Moreover, what is necessary is just to use acidic compounds, such as a carbon dioxide gas, hydrochloric acid, nitric acid, a sulfuric acid, to reduce the pH of latex.
What is necessary is just to select the usage-amount of these basic compounds and acidic compounds so that pH can be set to the said range, and it is not specifically limited.

  The latex for an ink jet recording medium of the present invention thus obtained usually has a particle size of 10 to 150 nm, preferably 30 to 130 nm.

The weight average molecular weight of the tetrahydrofuran-soluble component of the polymer constituting the latex for the inkjet recording medium of the present invention is preferably in the range of 5,000 to 200,000, more preferably 15,000 to 200,000.
The glass transition temperature of the polymer constituting the latex for ink jet recording medium of the present invention is not particularly limited, but is usually 10 to 130 ° C.
Further, the polymer constituting the latex for ink jet recording medium of the present invention usually has a gel content (methylethyl insoluble matter) of 10 to 85% by weight when methylethylketone is used as a solvent.

  The coating composition for inkjet recording media of the present invention comprises the latex for inkjet recording media of the present invention. The latex for inkjet recording media functions as a medium for dispersing necessary components or optional components usually blended in this type of coating composition for inkjet recording media, and allows them to adhere to a suitably selected support. And has a binder function for forming an ink receiving layer.

In addition to the latex for inkjet recording medium of the present invention, the coating composition for inkjet recording medium of the present invention includes components usually used in this field, such as pigments, pigment dispersants, dyes, thickeners, fluidity. Improving agent, antifoaming agent, antifoaming agent, mold release agent, foaming agent, penetrating agent, fluorescent whitening agent, ultraviolet absorber, antioxidant, preservative, antifungal agent, water resistance agent, wet paper strength enhancer , Dry paper strength enhancer, dye fixing agent, etc. are blended.
The amount of these components used, the method of blending into the coating composition for inkjet recording media, and the like are appropriately selected within a range that does not impair the object of the present invention.

Examples of the pigment include silica, alumina, calcium carbonate, magnesium carbonate, kaolin, talc, titanium oxide, zinc oxide, aluminum oxide, barium sulfate, calcium sulfate, magnesium silicate, aluminum silicate, diatomaceous earth, zeolite, aluminum hydroxide, Inorganic pigments such as magnesium hydroxide; organic pigments such as hollow particles, styrene plastic pigments, and acrylic plastic pigments.
Among these, inorganic pigments are preferable, and silica is particularly preferable. The blending amount is usually in the range of 100 to 2,000 parts by weight, preferably 200 to 1,500 parts by weight with respect to 100 parts by weight of the solid content of the latex for inkjet recording media.
Among these, inorganic pigments are preferable, and pigments having a small particle diameter such as colloidal silica and colloidal alumina are particularly preferable. The blending amount is usually in the range of 100 to 5,000 parts by weight, preferably 200 to 2,000 parts by weight with respect to 100 parts by weight of the solid content of the latex for the ink jet recording medium.

  The method for preparing the coating composition for an inkjet recording medium is not particularly limited. Generally, a dispersion machine is used to add and disperse the latex for the inkjet recording medium, other compounding components, and water as required. In addition, the total solid content concentration of the coating composition for inkjet recording media is usually 5 to 50% by weight, preferably 10 to 40% by weight. Usually, it is 5 to 60% by weight, preferably 10 to 50% by weight.

The inkjet recording medium of the present invention is obtained by coating the above-described coating composition for an inkjet recording medium on a support.
The ink jet recording medium of the present invention can be obtained by applying a coating composition for an ink jet recording medium on at least one surface of a support and drying it to form a coating film as an ink receiving layer.

The support constituting the ink jet recording medium is not particularly limited, and may be appropriately selected according to the purpose of use of the ink jet recording medium and the recording apparatus. For example, base paper such as newspaper base paper, high-quality base paper, medium base paper, etc .; coated paper coated with polyvinyl alcohol, starch, etc. on the base paper; coated paper with a coating layer mainly composed of pigment, art paper Coated paper such as cast paper; synthetic paper (polypropylene resin-based multilayer film, paper with both sides covered with polyethylene); resin film such as polyester film and vinyl chloride film; metal, glass, ceramic, etc. And the like.
Of these, base paper, coated paper, and synthetic paper are preferable.

The method for applying the coating composition for an inkjet recording medium of the present invention on a support is not particularly limited. For example, it can apply | coat using common coaters, such as a roll coater, an air knife coater, a blade coater, a rod blade coater, a curtain coater, a bar coater, a die coater, a gravure coater.
The coating amount on the support is not particularly limited, but is usually 1 to 50 g / m ² , preferably 3 to 30 g / m ² . The thickness of the coating film is usually 10 to 40 μm.
After coating the coating composition for an inkjet recording medium on a support, the ink receiving layer can be formed by heating at an appropriate temperature in the range of 50 to 150 ° C., if necessary.

The ink jet recording medium of the present invention can impart smoothness and gloss to the ink receiving layer by calendering the obtained coating film as necessary. Further, it may be applied directly on the support to form a single ink-receiving layer, or a multilayer structure including an ink-receiving layer may be used as necessary. For example, an anchor layer may be provided below the ink receiving layer, and a gloss layer may be further provided on the ink receiving layer.
The ink jet recording medium of the present invention, if necessary, smoothes the obtained coating film by heat calendering with a super calendar, soft calender, etc., or by a heated dryer mirror surface while the coating film is in a wet state. Smoothness and gloss can be imparted to the surface by performing a so-called cast coating method in which the mirror surface smoothness is copied onto the surface of the coating layer. Further, the coating composition may be directly applied on the support to form a single ink-receiving layer, or a multilayer structure including an ink-receiving layer may be used as necessary. For example, an anchor layer may be provided below the ink receiving layer, and a gloss layer may be further provided on the ink receiving layer.

  The ink jet recording medium of the present invention is particularly useful as a recording medium (sheet) by an ink jet recording method in which droplets of ink are ejected and recorded, but it is also used as a sheet for water-based ink printing such as offset printing and flexographic printing. it can.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples. In the examples, “%” and “parts” are based on weight unless otherwise specified.
Moreover, the evaluation method of each characteristic is as follows.

[Average particle diameter of polymer latex]
Randomly select 300 polymer latex particles in an electron micrograph of the polymer latex, and determine the number average of the particle sizes.
[PH of polymer latex]
Using a pH meter (trade name “pH METER M-12”, manufactured by HORIBA), measurement is performed at 20 ° C.
[Viscosity of polymer latex]
Measured with a B-type viscometer under the conditions of 30 ° C. and 60 rpm.

[Glass transition temperature of polymer]
Polymer latex or aqueous solution is collected on an aluminum dish, dried at room temperature, and then vacuum dried at 40 ° C. to obtain a polymer sample. About this sample, it measures at a temperature increase rate of 10 degree-C / min using a highly sensitive differential scanning calorimeter (the Seiko Electronics Industry Co., Ltd. make, brand name "RDC220").
(Weight average molecular weight of polymer)
A polymer sample is obtained in the same manner as the glass transition temperature measurement sample. About this sample, it calculates | requires as a standard polystyrene conversion molecular weight by the gel permeation (GPC) measurement which uses tetrahydrofuran as an eluent.

[Cation stability]
After adding 1 part by weight of a cationic resin (manufactured by Sumitomo Chemical Co., Ltd., trade name “Smilease Resin 1001”) to 10 parts by weight of latex whose solid content is adjusted to 30% by weight, and sufficiently dispersing, The mixed state is observed and judged according to the following criteria.
○: There are aggregates.
Δ: Slightly aggregated.
X: There is a large amount of aggregates.

[Glossy]
Based on JIS Z8741, the glossiness at 75 ° of the recording sheet surface is measured using a variable angle gloss meter (trade name “GM-3D type” manufactured by Murakami Color Research Laboratory Co., Ltd.).

[Ink absorbency]
Using a commercially available inkjet printer (trade name “PM-G850” manufactured by Seiko Epson Corporation), the portrait (image identification number N1) of high-detail color digital standard image data (conforming to JIS X 9201-1995) Print with “Paper Mode Clean” and visually observe the bleeding of the image, and evaluate it according to the following criteria.
○: No blurring of the image and excellent ink absorbability.
Δ: Slight blurring of the image, but ink absorbability is at a practical level.
X: Image blurring is large and ink absorbency is below a practical level.

〔water resistant〕
Using a commercially available ink jet printer (trade name “PM-G850” manufactured by Seiko Epson Corporation), character printing is performed with black ink, and 30 ° C. water is dropped onto the printed portion and left for one hour. Thereafter, if there are remaining water droplets, they are sucked off with a waste cloth, and the printing state such as the surface state and blurring is visually observed and judged according to the following criteria.
○: Smudge, color density and surface state change are hardly observed.
Δ: Although there is a decrease in bleeding, color density and surface condition, it is at a practical level.
X: There is a decrease in blurring, color density and surface condition, which is below the practical level.

[Film transparency]
A coating solution is applied to a glass plate to a thickness of about 0.2 μm, and the state after drying at room temperature is visually observed and determined according to the following criteria.
○: High transparency.
Δ: Slightly cloudy.
X: It is cloudy.

[Example 1]
(Latex production example 1)
In a pressure-resistant container with a stirrer (preparation container for emulsion for the first stage polymerization), 50 parts of deionized water, 30 parts of 2-ethylhexyl acrylate, 10 parts of methyl methacrylate and sodium polyoxyethylene alkyl ether sulfate (anionic) Surfactant) (manufactured by Kao Corporation, trade name “Latemul E118B”) 0.6 part was added and stirred to obtain a monomer emulsion I.
In another pressure-resistant vessel with a stirrer (preparation vessel for the second stage emulsion), 50 parts of deionized water, 10 parts of 2-ethylhexyl acrylate, 50 parts of methyl methacrylate, polyoxyethylene lauryl ether (nonionic interface) Activator) (trade name “Emulgen 120” manufactured by Kao Corporation) 0.3 parts and 12 parts of polyvinyl alcohol having a hydrophobic group at one end (trade name “PVA-MP102” manufactured by Kuraray Co., Ltd.) are added and stirred. As a result, a monomer emulsion II was obtained.
Separately, in a pressure-resistant reaction vessel equipped with a stirrer, 250 parts of deionized water, 0.8 part of polyoxyethylene lauryl ether (nonionic surfactant) (trade name “Emulgen 120” manufactured by Kao Corporation) and polyoxyethylene alkyl ether Sodium sulfate (anionic surfactant) (trade name “Latemul E118B” manufactured by Kao Co., Ltd.) (0.4 parts) was added, and the temperature was raised to 75 ° C. and maintained at 75 ° C. Continuous addition of the monomer emulsion I was started, and then a polymerization initiator solution in which 0.2 part of potassium persulfate was dissolved in 5.0 parts of deionized water was added.
Continuous addition of monomer emulsion I was completed over 120 minutes. After completion of the addition, the reaction was further carried out for 60 minutes. The polymerization conversion rate at this time was 98.2%. Subsequently, a polymerization initiator solution in which 0.2 part of potassium persulfate was dissolved in 5.0 parts of deionized water was added, and the monomer emulsion II was continuously added to the reaction vessel over 180 minutes. Further, the reaction was carried out after 2 hours. Thereafter, the reaction was terminated by cooling. The polymerization conversion rate at this time was 98%, and the pH of the latex was 2.93.
After removing the unreacted monomer, the solid content concentration was adjusted to obtain a copolymer latex L1 having a solid content concentration of 24.1%. The viscosity of the obtained copolymer latex L1 was 95 mPa · s, the volume average particle diameter was 96 nm, and two points of −22 ° C. and 43 ° C. were observed as glass transition temperatures. The cation stability of this copolymer latex L1 was evaluated. The results are shown in Table 1.

(Preparation of inkjet recording sheet)
Using a disperser, 20 parts of copolymer latex L1 in terms of solid content was added to 100 parts of colloidal silica (manufactured by Nissan Chemical Industries, trade name “Snowtex”) and dispersed for 10 minutes. Further, after adding 3 parts of a cation resin (manufactured by Sumitomo Chemical Co., Ltd., trade name “Smilease Resin 1001”) in terms of solid content and sufficiently dispersing it, the solid content concentration is adjusted to 20% to prepare an ink jet recording medium. A coating composition was obtained.
After coating on both sides of a high-quality base paper having a basis weight of 70 g / m ^{2 so} that the weight after drying was 7 g / m ² per side, it was dried at 100 ° C. for 60 seconds. The obtained coated paper was conditioned overnight under an atmosphere of 23 ° C. and a relative humidity of 65%. Thereafter, the coated paper was calendered four times using a laboratory mini-calender under the conditions of 80 ° C. and linear pressure of 75 kg / cm to obtain an ink jet recording sheet. The recording sheet was evaluated for gloss, ink absorbability, water resistance and film transparency. The results are shown in Table 1.

[Examples 2 and 3]
(Latex production examples 2 and 3)
The monomer composition and the amount of deionized water in the first stage polymerization and the amount of deionized water were changed as shown in the table, and the nonionic surfactant and the anionic surfactant in the first stage polymerization and the second Latex L2 was prepared in the same manner as in Production Example 1 except that the amount of the polyvinyl alcohol having a hydrophobic group in the polymerization in the stage was changed as shown in the table, and the nonionic surfactant was not used in the second stage. And L3. The properties are shown in Table 1.

(Preparation of inkjet recording sheet)
A coating composition for an inkjet recording medium was obtained in the same manner as in Example 1 except that latexes L2 and L3 were used in place of the latex L1, and an inkjet recording sheet was obtained using this. The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
(Latex comparative production example 1)
In the second stage polymerization, polyvinyl alcohol having no hydrophobic group (trade name “PVA205” manufactured by Kuraray Co., Ltd.) was used in place of the polyvinyl alcohol having a hydrophobic group (the amount of water was changed). Polymerization was carried out in the same manner as in Production Example 1, but the polymerization system coagulated on the way, and latex could not be obtained.

[Comparative Example 2]
(Latex comparative production example 2)
In the second stage polymerization, 0.25 parts of polyoxyethylene lauryl ether (nonionic surfactant) (trade name “Emulgen 150” manufactured by Kao Corporation) was used without using polyvinyl alcohol having a hydrophobic group ( The amount of water in the first stage and the second stage was changed.) Other than that, polymerization was performed in the same manner as in Production Example 2 to obtain latex LC2. The properties are shown in Table 1.

(Preparation of inkjet recording sheet)
A coating composition for an inkjet recording medium was obtained in the same manner as in Example 1 except that latex LC2 was used instead of latex L1, and an inkjet recording sheet was obtained using this. The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
(Latex Comparative Production Example 3)
In addition to increasing the amount of anionic surfactant used in the first stage from 1.0 parts in total to 1.4 parts in total in the first and second stage polymerizations, without using a nonionic surfactant. Was polymerized in the same manner as in Production Example 1 to obtain latex LC3. The properties are shown in Table 1.

(Preparation of inkjet recording sheet)
A coating composition for an inkjet recording medium was obtained in the same manner as in Example 1 except that latex LC3 was used instead of latex L1, and an inkjet recording sheet was obtained using this. The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Note to Table 1)
* 1: Polyoxyethylene lauryl ether (trade name “Emulgen 120” manufactured by Kao Corporation)
* 2: Polyoxyethylene alkyl ether sulfate sodium salt (trade name “Latemul E118B” manufactured by Kao Corporation)
* 3: Polyvinyl alcohol having a hydrophobic group at one end (trade name “PVA-MP102” manufactured by Kuraray Co., Ltd.)
* 4: Polyvinyl alcohol having no hydrophobic group (Kuraray Co., Ltd., trade name “PVA205”)

[Comparative Example 4]
(Latex Comparative Production Example 4)
In the first stage polymerization, the same procedure as in Production Example 2 was conducted except that the nonionic surfactant was not used and the amount of the anionic surfactant was reduced from a total of 1.25 parts to a total of 1.0 parts. Polymerization was performed to obtain latex LC4. The properties are shown in Table 1.

(Preparation of inkjet recording sheet)
A coating composition for an inkjet recording medium was obtained in the same manner as in Example 1 except that latex LC4 was used instead of latex L1, and an inkjet recording sheet was obtained using this. The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 5]
(Latex comparative production example 5)
In the first stage polymerization, neither a nonionic surfactant nor an anionic surfactant was used, and instead of this, 15 parts of polyvinyl alcohol having a hydrophobic group was used (note that the first stage and the second stage). The amount of water in the stage was changed.) Polymerization was carried out in the same manner as in Production Example 2 to obtain latex LC5. The properties are shown in Table 1.

(Preparation of inkjet recording sheet)
A coating composition for an inkjet recording medium was obtained in the same manner as in Example 1 except that latex LC5 was used instead of latex L1, and an inkjet recording sheet was obtained using this. The characteristics were evaluated in the same manner as in Example 1. The results are shown in Table 1.

Table 1 shows the following.
In the second stage polymerization, when polyvinyl alcohol having no hydrophobic group is used instead of polyvinyl alcohol having a hydrophobic group, latex is not obtained (Comparative Example 1), and when any polyvinyl alcohol is not used. The obtained latex was inferior in cation stability, and the ink jet recording medium was inferior in gloss, ink absorbability and water resistance (Comparative Example 2).
In the first stage polymerization, when no nonionic surfactant is used, the cationic stability of the latex and the gloss, ink absorbability and film transparency of the ink jet recording medium are inferior (Comparative Example 4). Increasing the amount of surfactant improves the above properties of the ink jet recording medium, but cannot improve the cationic stability of the latex (Comparative Example 3). In addition, in the first stage polymerization, neither an anionic surfactant nor a nonionic surfactant is used, and when only a polyvinyl alcohol having a hydrophobic group is used instead of these, an ink jet recording medium is obtained. Was inferior in gloss (Comparative Example 5).
On the other hand, according to the present invention, a latex for an ink jet recording medium having excellent cation stability can be obtained, and an ink jet recording medium using the latex has gloss, ink absorbability, water resistance and film transparency. (Examples 1 to 3).

Claims (6)

  Polymerization of the first monomer is carried out in the presence of a nonionic surfactant and an anionic surfactant, and then the resulting latex contains an alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group and a second monomer. A method for producing a latex for an ink jet recording medium, wherein the monomer is added and the polymerization is further continued.   The method for producing a latex for an ink jet recording medium according to claim 1, wherein the alcoholic hydroxyl group-containing water-soluble polymer compound having a hydrophobic group has a hydrophobic group at its molecular end.   The method for producing a latex for an ink jet recording medium according to claim 1 or 2, wherein a nonionic surfactant is further added at the time of polymerization of the second monomer.   The latex for inkjet recording media obtained by the manufacturing method of any one of Claims 1-3.   The coating composition for inkjet recording media containing the latex for inkjet recording media of Claim 4.   An ink jet recording medium obtained by coating the coating composition for an ink jet recording medium according to claim 5 on a support.