JP5062451B2 - Binder for white pigment layer for recording sheet - Google Patents

Description

  The present invention relates to a binder for a white pigment layer for a recording sheet used in a recording system using water-based ink, and in particular, image storage due to high printing density, vividness, excellent resolution, and particularly excellent water resistance. The present invention relates to a binder for a white pigment layer that is used for a recording sheet that is good in performance and has a low adsorbent such as silica.

  In recent years, the ratio of recording methods using water-based ink has been increasing in printers for OA equipment such as personal computers. With this, the demand for recording materials is increasing, but on the other hand, the quality of printing, saturation, In order to further improve the appearance and image, a recording material having higher characteristics has been required. In particular, the use of confidential postcards, labels, and the like has been expanded and the usage conditions have been diversified, so that required characteristics such as water resistance have become more severe.

  For example, a recording sheet (Patent Document 1: Japanese Patent Laid-Open No. 55-51583) in which amorphous binder and a polymer binder such as polyvinyl alcohol are mixed and applied to a base paper, or porous pigment particles on the front and back of the base paper A recording sheet (Patent Document 2: Japanese Patent Application Laid-Open No. 56-148584) provided with an ink-receiving layer containing benzene has been proposed, and the vividness is much more chromatic than a conventional recording sheet using high-quality paper. Although the ink is irregularly spread when the coating amount is small, there is a problem that the blur of printing is large and the blur is small when the coating amount is large, but the coating layer is peeled off and powdered off.

  In order to solve this problem, if the amount of the binder is increased and the binding strength is improved, the ink absorption capacity becomes insufficient and the blurring becomes noticeable, resulting in a decrease in the image quality, and the desired resolution and intermediate color reproduction. It was difficult. Further, there is a proposal of a recording sheet (Patent Document 3: Japanese Patent Application Laid-Open No. 62-288076) having improved binding strength using a water-insoluble resin obtained by reacting polyvinyl alcohol, acrylic acid and methyl methacrylate. However, since the water-insoluble resin is anionic, the fixing property of the aqueous ink, which is also anionic, is poor, and it does not provide a solution for improving ink bleeding or water resistance. Furthermore, as a solution to these problems, a recording sheet containing a polycation polymer electrolyte (Patent Document 4: Japanese Patent Laid-Open No. 56-84992) and an ink mainly composed of a cationic polymer binder having ink adsorption properties are used. There are known methods such as a recording sheet provided with a receiving layer (Patent Document 5: Japanese Patent Laid-Open No. 58-24493). However, any of these methods has insufficient ink fixability, and light resistance of a printed image. However, there was a drawback that it was inferior.

  Further, a recording sheet containing a cationic acrylic resin emulsion obtained by copolymerizing an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester and an amino group-containing acrylic monomer in a white pigment layer (Patent Document 6: Japanese Patent Laid-Open No. 11-151867) -123867) is also known. However, since it is an essential condition that an amino group-containing acrylic monomer is included, the color developability is excellent, but the hydrophilicity of the polymer increases, and the water resistance is insufficient depending on the application. For this reason, there are problems such as an increase in dot diameter, lack of image storage stability, and layer separation during emulsion polymerization, which limits the polymerization method.

JP-A-55-51583 Japanese Patent Laid-Open No. 56-148584 JP-A-62-288076 JP 56-84992 A JP 58-24493 A Japanese Patent Laid-Open No. 11-123867

  The present invention has been made in order to improve the above circumstances, and in the quality characteristics of a printed image of a recording sheet using water-based ink, the print density is high, no blurring, the resolution is high, and the ink fixing property is good. Another object of the present invention is to provide a recording sheet binder suitable for a white pigment layer for a recording sheet that is excellent in water resistance.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have determined that a (meth) acrylic acid ester excluding an amino group-containing (meth) acrylic monomer is a specific cationic emulsifier in the white pigment layer for recording sheets. By using a cationic acrylic emulsion of a copolymer having a glass transition temperature in a specific temperature range and a particle diameter in a specific range, which is obtained by emulsion polymerization using Knowing that it provides excellent resolution, is excellent in water resistance, has good image storage stability, is less likely to lose adsorbents such as silica, and can solve the above-mentioned conventional problems, thus forming the present invention. It came to.

  Accordingly, the present invention provides a monomer mixture selected from the group consisting of (meth) acrylic acid esters excluding amino group-containing (meth) acrylic monomers as alkyl bis (2-hydroxyethyl) methylammonium chloride ( A white pigment layer recording comprising a cationic acrylic emulsion of a copolymer having a glass transition temperature of −40 to 80 ° C. and a particle diameter of 50 to 300 nm obtained by emulsion polymerization using EO = 2) The gist of the sheet binder.

  The recording sheet binder containing the cationic acrylic emulsion of the present invention has a high printing density, vividness, excellent resolution, and particularly excellent water resistance, so that it has good image storability, and recording with a small amount of adsorbent such as silica. Give a sheet. Due to this characteristic, the binder of the present invention is extremely advantageous in practice.

Hereinafter, the present invention will be described in more detail.
Examples of the (meth) acrylic acid ester used in the present invention include (meth) acrylic acid ester, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meta) with an alcohol having an alkyl group having 1 to 18 carbon atoms. ) Acrylate, methoxyethyl (meth) acrylate, butoxyethyl (meth) acrylate, glycidyl (meth) acrylate, allyl (meth) acrylate, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, etc. These monomers can be used alone or in combination of two or more. In the present invention, (meth) acrylates containing amino groups are not used. (Meth) acrylate is a general term for acrylate and methacrylate.

  In order to give the physical property which cannot be expressed only with the said component, the copolymerizable ethylenically unsaturated monomer can be used as needed. Examples of such monomers include acrylonitrile, vinyl acetate, vinyl propionate, styrene, acrylic acid, methacrylic acid, (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, and the like. it can. These are preferably used in an amount of 15% by weight or less of the total amount of monomers so as not to impair the object of the present invention.

  The emulsion copolymer can be produced by a known emulsion polymerization method using each of the above monomers. That is, the above-mentioned monomers are mixed, and an emulsifier, a polymerization initiator, etc. are added thereto to carry out emulsion polymerization in an aqueous system, such as a method for batch polymerization and a method for polymerization while continuously supplying each component. Various methods can be applied.

  As the emulsifier for emulsion polymerization used in the present invention, any one of the following two types of cationic emulsifiers is essential, and one of them is cocoalkyldimethylbenzylammonium chloride, tetradecyldimethylbenzylammonium chloride. And alkylbenzylammonium chloride such as octadecyldimethylbenzylammonium chloride, and the other is an alkyl group such as alkylbis (2-hydroxyethyl) methylammonium chloride and alkylpolyoxyethylenemethylammonium chloride having 8 to 18 carbon atoms. EO addition type | mold ammonium chloride whose EO addition mole number is 2-15 mol, From these, only 1 type or 2 types or more can be used in combination. The amount of these used is preferably 1 to 10 parts by weight, particularly 2 to 5 parts by weight, based on 100 parts by weight of the total amount of monomers.

  If cationic emulsifiers alone are insufficient in polymerization stability, mechanical and chemical stability, nonionic emulsifiers can be used in combination with polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene. Polyoxyethylene alkyl ethers such as ethylene stearyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene carboxylic acid ester, and nonionic reactive emulsifier having vinyl group in the molecule Etc., and it is preferably used in the range of 1 to 10 parts by weight, particularly 2 to 5 parts by weight with respect to 100 parts by weight of the total amount of monomers.

  Polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate, water-soluble types such as hydrogen peroxide, t-butyl hydroperoxide and azobisamidinopropane hydrochloride, benzoyl peroxide, diisopropyl peroxy Examples include oil-soluble types such as dicarbonate, cumylperoxyneodecanoate, cumylperoxyoctoate, and azobisisobutyronitrile, but use the hydrochloride of azobisamidinopropane, which is a cationic catalyst. It is preferable. What is necessary is just to let these usage-amounts be about 0.01-3 weight part with respect to 100 weight part of total amounts of a monomer.

  The polymerization reaction is usually carried out at a temperature of 35 to 90 ° C. with stirring, and the reaction time is usually about 3 to 40 hours. Further, by adjusting the pH by adding a basic substance at the start or end of emulsion polymerization, it is possible to improve the standing stability, freezing stability, chemical stability, etc. of the emulsion. In this case, the resulting emulsion is preferably adjusted to have a pH of 5 to 9, and therefore, a base such as ammonia, ethylamine, diethylamine, triethylamine, ethanolamine, triethanolamine, dimethylethanolamine, caustic soda or caustic potash. Sexual substances can be used.

The glass transition temperature of the copolymer obtained by polymerization needs to be in the range of -40 to 80 ° C, preferably -30 to 20 ° C. When the temperature is lower than −40 ° C., the resin film becomes too soft and the mechanical strength at the time of blending decreases, and when processed into a recording sheet, although a white pigment such as silica is added, The surface tack is strong and blocking occurs. When the temperature is higher than 80 ° C., there is a problem that even if another binder such as polyvinyl alcohol is used in combination, the film is too hard and white pigment such as silica is powdered off. This glass transition temperature Tg is obtained by the following formula based on the monomer used.
1 / Tg = Σ (wi / Tgi)
Tg: Glass transition temperature of copolymer (absolute temperature display)
Tgi: Glass transition temperature of homopolymer of monomer component (i) (absolute temperature display)
wi: weight fraction of component (i) in the copolymer

  The particle diameter of the copolymer obtained by polymerization needs to be in the range of 50 to 300 nm, preferably 70 to 250 nm. If it is smaller than 50 nm, the copolymer particles are adsorbed in the adsorbent pores such as silica, and sufficient color development as a cationic resin cannot be obtained, or the amount of the binder adsorbed is reduced and powder falling occurs. To do. The particle size was measured using a laser particle size analysis system PARIII manufactured by Otsuka Electronics.

  Examples of the white pigment for the white pigment layer used in the recording sheet of the present invention include silica, clay, talc, kaolin, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, silicon oxide, aluminum oxide, magnesium silicate, and calcium silicate. Examples thereof include inorganic substances such as aluminum silicate, aluminum hydroxide, and magnesium hydroxide, and plastic pigments such as polyethylene and polystyrene, which are used alone or in combination of two or more. In particular, silica is the most common because it is a porous pigment, does not contain impurities, and is relatively advantageous in terms of price, availability, and the like. In particular, fine powder silica having an average particle diameter of 3 to 6 μm is suitable.

  The cationic acrylic emulsion as a binder used in the present invention is 5 to 100 parts by weight, preferably 10 to 70 parts by weight, particularly preferably 30 to 50 parts by weight, in terms of dry solid content, with respect to 100 parts by weight of the white pigment. Part.

  In the present invention, a binder can be used together if necessary. Examples of the binder include copolymer latex of water-soluble polymers such as polyvinyl alcohol, methyl cellulose, and polyethyleneimine. These amounts can be replaced by 20 to 60% of the dry solid content of the cationic acrylic emulsion.

  EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example. In addition, the part and% in an example show a weight part and weight%, respectively.

[Synthesis Example 1] (Synthesis of Emulsion P1)
A polymerization vessel equipped with a stirrer, a condenser, a thermometer, and a nitrogen gas inlet is charged with 795 parts of deionized water and 6.5 parts of azobisamidinopropane hydrochloride, 558 parts of ethyl acrylate, 16-hydroxyethyl methacrylate 16 Parts, N-methylolacrylamide 45 parts, palm alkyldimethylbenzylammonium chloride 34 parts, alkylbis (2-hydroxyethyl) methylammonium chloride (alkyl group having 8 to 18 carbon atoms, EO addition mole number 2 moles) 18 parts, poly A solution obtained by mixing and emulsifying 21 parts of oxyethylene octylphenyl ether, 28 parts of sorbitan monolaurate and 546 parts of deionized water with a homogenizer, and 22.4 parts of 11% aqueous solution of Perbutyl H-69 (trade name, manufactured by NOF Corporation). And Super Light C (Mitsubishi Gas Chemical Co., Ltd.) Evenly added dropwise to the 8% aqueous solution of 22 parts of a trade name) over a period of 4 hours at separately above under stirring 60 ° C. to the polymerization vessel, allowed to react for 2 hours at further 80 ° C., to complete the polymerization. After cooling, 25% aqueous ammonia was added to adjust the pH to 6. The resulting emulsion (hereinafter referred to as P1) had a solid content concentration of 40.4%.

[Synthesis Examples 2 to 9] (Synthesis of emulsions P2 to P9)
The copolymer emulsion (P2 to P9) having a solid content concentration of 40 to 50% was obtained in the same manner as in Synthesis Example 1 by copolymerizing with the monomer types and the charged amount (%) shown in Table 1. For Synthesis Example 1, the monomer charge was rewritten in%.

乳化剤Ａ：ヤシアルキルジメチルベンジルアンモニウムクロライド
乳化剤Ｂ：アルキル（Ｃ₈〜Ｃ₁₈）ビス（２−ヒドロキシエチル）メチルアンモニウムク
ロライド
乳化剤Ｃ：ポリオキシエチレンノニルフェニルエーテル（ＥＯ付加モル数１７モル）
乳化剤Ｄ：ソルビタンモノラウレート
乳化剤Ｅ：ポリオキシエチレンラウリルエーテル（ＥＯ付加モル数１５モル）
乳化剤Ｆ：ラウリル硫酸ソーダ

Emulsifier A: Palm alkyl dimethyl benzyl ammonium chloride Emulsifier B: Alkyl (C ₈ -C ₁₈ ) bis (2-hydroxyethyl) methyl ammonium chloride
Loride emulsifier C: polyoxyethylene nonylphenyl ether (EO addition mole number 17 mol)
Emulsifier D: Sorbitan monolaurate emulsifier E: Polyoxyethylene lauryl ether (15 moles of EO added)
Emulsifier F: Sodium lauryl sulfate

[Example 1]
Emulsion P1 obtained in Synthesis Example 1 by gradually adding and dispersing 100 parts of finely powdered silica (manufactured by Tokuyama Soda Co., Ltd .; average particle diameter 4.5 μm, pore diameter 0.005 to 0.04 μm) in 400 parts of water while stirring. 100 parts is added, and after stirring, a paint is prepared, applied to a non-size paper with a Meyer bar so that the application amount is 5 g / m ² (dry weight solid content), dried, and then a recording sheet is formed through a super calendar. Thus, a test piece was obtained. The obtained test pieces were measured for print density, dot diameter, print image resolution and water resistance, ink absorbability, and dust-off properties. The results are shown in Table 2.

Each characteristic was measured as follows.
1. Print density For the dots printed with black ink by Canon printer BJC455J, the dot density was measured with Sakura Micro Densitometer PDM-5 (manufactured by Sakura Seiki Co., Ltd.).
2. Dot diameter Printed with Canon ink BJC455J using black ink, magnified 100 times, and measured dot diameter.
3. Print image resolution Black (B), magenta (M), cyan (C), and yellow (Y) were solid printed with a Canon printer BJC455J, and measured with a Macbeth densitometer RD-918 (manufactured by Macbeth).
4). Water resistance of the printed image Black, magenta, cyan, and yellow are printed on the Canon printer BJC455J, and after the printed part is immersed in water, the time for the occurrence of printing blur is measured.
5. Ink absorbability Black, magenta, cyan, and yellow are simultaneously ejected to the same location with Canon Printer BJC455J and rubbed with a paper presser plate after 1 second to measure ink stains.
○: No white portion of dirt △: Slightly dirty ×: Slightly dirty Powder fall-off The recording sheet test piece is bent and visually checked for powder fall-off.
○: No powder fall △: Slightly powder fall ×: Severe dirt

[Examples 2-3, Reference Examples 1-2, Comparative Examples 1-6]
A paint was prepared in the same manner as in Example 1 except that the type and amount of the copolymer emulsion shown in Table 2 and the kind and amount of fine powder silica were blended, and a test piece was prepared using the paint. The results are shown in Table 2. In Comparative Example 6, polyvinyl alcohol (manufactured by Kuraray Co., Ltd., trade name PVA-403) was used instead of the copolymer emulsion.

ａ：平均粒径４．５μｍ、徳山曹達社製
ｂ：平均粒径３．５μｍ、富士シリシア化学社製
Ａ：ポリビニルアルコール（ＰＡ−１５）、信越化学工業社製
Ｂ：ポリエチレンイミン、日本触媒社製

a: average particle size 4.5 μm, manufactured by Tokuyama Soda Co., Ltd. b: average particle size 3.5 μm, manufactured by Fuji Silysia Chemical Ltd. A: polyvinyl alcohol (PA-15), manufactured by Shin-Etsu Chemical Co., Ltd. B: polyethyleneimine, Nippon Shokubai Co., Ltd. Made

Claims (2)

  Using a monomer mixture selected from the group consisting of (meth) acrylic acid esters excluding amino group-containing (meth) acrylic monomers, using alkylbis (2-hydroxyethyl) methylammonium chloride (EO = 2) as a cationic emulsifier A binder for a white pigment layer for a recording sheet, comprising a cationic acrylic emulsion of a copolymer having a glass transition temperature of −40 to 80 ° C. and a particle size of 50 to 300 nm obtained by emulsion polymerization.   The binder for a white pigment layer for a recording sheet according to claim 1, wherein a water-soluble polymer selected from polyvinyl alcohol, methylcellulose, and polyethyleneimine is used in combination with the cationic acrylic emulsion.