JP4373110B2 - Method for producing wet method amorphous silica - Google Patents

Description

【００５８】
（実施例５〜８）
実施例１乃至４で得られた本発明によるシリカ粉末を填剤として下記組成からなる感熱記録層形成液を用いて感熱記録試験紙を作成した。この試験紙について下記に示す方法でそれぞれ評価した。結果を表４に示す。
【００５９】
（感熱記録試験紙の作成）
感熱塗液は各素材の固形分が以下の通りになるように調合した。尚、それぞれの素材はペイントシェンカー等により良く湿式粉砕した後に混合した。
ロイコ染料：ODB-2（3-ジエチルアミノ-6-メチル-7-アニリノフルオラン）１０部
顕色材：BPA（ビスフェノールA） ２０部
増感剤：PBBP （ポリベンジルビフェニル） ２０部
滑剤：ステアリン酸亜鉛 １０部
バインダー：PVA-117 （ポリビニルアルコール） 1５部
フィラー（表４参照） ２０部
上記感熱記録層形成液を市販PPC用紙上に乾燥重量が６g/m²となるように塗布後、室温で乾燥し、ロール圧１０ｋｇ／ｃｍ^２でカレンダリングを行い、試験用感熱記録試験紙とした。
【００６０】
（感熱紙の評価）
（１０）地汚れ濃度
塗布後２４時間経た感熱記録層形成液塗布紙の地汚れ濃度を富士写真フィルム（株）製標準濃度計FSD-103型でVフィルターを用いて測定し、これを肉眼観察により表２のような基準で評価した。
【表２】

【００６１】
（１１）動的発色画像濃度
（株）大倉電機製印字装置TH-PMDで記録し、（ヘッド電圧２４V、パルス幅１．３ｍｓｅｃ、パルス周期２ｍｓｅｃ、サーマルヘッド抵抗値１５７２Ω）、このときの発色画像濃度を標準濃度計FSD−１０３型（富士写真フィルム製）で測定し、これと肉眼観察により表３のような基準で評価した。
【表３】

【００６２】
（１２）カス付着防止試験
NTT FAX−５１０Tを用い、ベタ印字後のサーマルヘッドに付着するカスを肉眼で観察し以下のように評価した。
：優
：良
×：不良
【００６３】
【表４】

【００６４】
（実施例９〜１０）
実施例１乃至２で得られた本発明によるシリカ粉末を填剤として配合した、ポリプロピレン（ＰＰ）フィルムを作成した。このフィルムについて下記に示す方法でそれぞれ評価した。結果を表５に示す。
【００６５】
（フィルムの作成）
樹脂にＰＰを用いて、以下に示した配合原料を加工温度２３０℃で製膜し、厚さ３０μｍのフィルムを得た。

【００６６】
（フィルム確性試験環境）
ＩＳＯ ２９１：１９９７に準拠して、室温２３℃、湿度５０％に調節した環境中において試験フィルムを保存し、所定時間経過した試験片を各種フィルム確性試験に供した。
【００６７】
（１３）Ｈａｚｅ測定
Ｈａｚｅは、Ｇａｒｄｎｅｒ社製ｈａｚｅ−ｇａｒｄ ｐｌｕｓを使用し、ＡＳＴＭ Ｄ １００３−９５に準拠して測定した。Ｈａｚｅの値が小さいほど透明性に優れる。
【００６８】
（１４）Ｃｌａｒｉｔｙ測定
Ｃｌａｒｉｔｙは、ＡＳＴＭ Ｄ １０４４−９４に記載されている装置を用い、前記Ｈａｚｅ測定に用いたフィルムの試験片をそのまま測定した。Ｃｌａｒｉｔｙの値が大きいほど鮮明性に優れる。
なお、測定にはＧａｒｄｎｅｒ社製ｈａｚｅ−ｇａｒｄ ｐｌｕｓを使用した。
【００６９】
（１５）SCOF（静摩擦係数）測定
ＡＳＴＭ Ｄ １８９４−９５に準拠し、東洋精機製摩擦測定機ＴＲ−２を用いて、フィルム外表面同士の静摩擦係数を評価した。ＳＣＯＦの値が低いほど滑り性に優れる。
【００７０】
（１６）Gel数
ニコン製二光束干渉顕微鏡で得られた測定結果をMicromap 550及びSurface Explorerを使用し解析した。直径１００μｍ以上且つ突起高さ２μｍ以上の凸物をＧel（フィッシュアイ）と見なし、フィルム１6ｃｍ^２あたりのＧel数をカウントした。
【００７１】
（１７）アンチブロッキング性（ＡＢ性）測定
ＩＳＯ １１５０２：１９９５ ｍｅｔｈｏｄ Ｂに準ずる方法で、６kPaで６０℃、３日間圧着したフィルムについて、ブロッキング力の測定を行い、以下に示すように評価した。
○：問題なく剥れる
△：剥れにくい
×：剥れない
【００７２】
（比較例３）
ＰＰ−樹脂組成物配合表において、アンチブロッキング剤として比較例２を用いた。結果を表５に示す。
【００７３】
（比較例４）
ＰＰ樹脂に何も配合しないで、ＰＰ樹脂１００重量％とした。結果を表５に示す。
【００７４】
【表５】

【００７５】
【発明の効果】
本発明によれば、核生成反応及び核成長反応の二段の反応を用いることにより、湿式法によるものでありながら、微細化が容易な非晶質シリカを得ることができる。この非晶質シリカは、樹脂等に対する分散性が良好であり、例えば樹脂配合剤として好適である。また、比表面積も低く、ロイコ色素や顕色材等が入り込める空間が僅かである為、感熱記録用填剤として有用であり、更に不純金属成分含量が抑制されていることから、記録ヘッド等の腐食を防止することもできる。さらに、サブミクロンサイズまで微細化することで延伸フィルム等のフィラーとして利用できる他、樹脂中で微細なシリカの均一分散が可能となることによるガスバリアー性等の新たな機能を付与することも可能である。
【図面の簡単な説明】
【図１】粉砕スラリーの体積基準中位径（Ｄ_５０）と湿式粉砕時間の関係を示す図である。[0001]
BACKGROUND OF THE INVENTION
  The present invention is a wet method.Method for producing amorphous silicaMore specifically, a wet method that is easy to refine and useful as a resin compounding agent and a thermal paper fillerMethod for producing amorphous silicaAbout.
[0002]
[Prior art]
Amorphous silica is blended in various resins as an anti-blocking agent for preventing adhesion (blocking) between films on a resin film, for example (see, for example, Patent Document 1). Also, by blending amorphous silica as a filler in the recording layer of the thermal recording paper, the components in the recording layer (coloring of leuco dyes, etc.) during thermal recording (contact between the recording head and the recording layer). It is also known that inconveniences such as adhering to the recording head can be prevented (see Patent Document 2).
[0003]
[Patent Document 1]
JP 2001-131337 A
[Patent Document 2]
Japanese Patent Publication No. 2-1030
[0004]
[Problems to be solved by the invention]
By the way, amorphous silica is roughly classified into a wet process and a dry process (vapor phase process). Wet process amorphous silica is obtained by neutralizing an alkali silicate aqueous solution such as so-called water glass with mineral acid, and vapor phase process silica is obtained by hydrolyzing silicon tetrachloride in an oxygen flame. It is done.
[0005]
The amorphous silica as described above is used by a wet method or a gas phase method depending on required properties, etc., but the above method is easy because the manufacturing method is easy and the cost is low. In Patent Documents 1 and 2, amorphous silica obtained by a wet method is used.
[0006]
When amorphous silica is used as a resin compounding agent or a filler for heat-sensitive recording paper, the particle size is fine in order to uniformly disperse the resin and ensure surface smoothness and stable physical properties. In some cases, it is desired that the wet process silica has a drawback that when the particle size is smaller than a certain particle size, the cohesive force becomes dominant and a fine one cannot be obtained. In other words, fine particles can be formed by wet pulverization at the stage of an aqueous slurry, but they will aggregate when dried, and fine particles can be obtained even if further pulverization is performed under dry conditions. I can't.
[0007]
Further, when amorphous silica is used as a heat-sensitive recording paper filler, it is preferable that the content of impure metal components is suppressed in order to prevent corrosion of the thermal head. And alkaline earth metal salts are used, such a requirement cannot be satisfied and its practical use may be hindered.
[0008]
  Therefore, the object of the present invention is toWhile being an amorphous silica produced by a wet process,Easy to miniaturizeMethod for producing amorphous silicaIs to provide.
  Another object of the present invention is a wet process with a small amount of impure metal components.Method for producing amorphous silicaIs to provide.
[0009]
[Means for Solving the Problems]
  According to the present invention,A first stage in which alkali silicate and mineral acid are simultaneously added to water or an aqueous electrolyte solution while maintaining the pH in the region of 6 to 10 to produce silica core particles, and then the simultaneous injection is stopped and ripened. The process of
  Next, a second stage step of growing silica core particles while maintaining the pH in the region of 4 to 10 while simultaneously adding alkali silicate and mineral acid,
  A third stage of aging by stopping simultaneous pouring of alkali silicate and mineral acid; and
  Next, a fourth stage process for dealkalization, filtration, washing with water, drying and grinding,
A method for producing amorphous silica is provided.
[0010]
  The amorphous silica produced according to the present invention is, for example, the following formula (1):
    Pco = B / A (1)
  Where
    A is a 2 mmφ aqueous slurry of amorphous silica prepared to a concentration of 2 to 40% by weight.
  Laser of pulverized slurry obtained by limit pulverization by wet pulverization using alumina ball mill
  Volume-based median diameter by diffraction method (D ₅₀ )
    B is a powder of the limit by drying the pulverized slurry, followed by dry pulverization using a jet mill.
  Volume-based median diameter (D ₅₀ )
The degree of cohesion (Pco) defined in the above is in the range of 1.0 to 1.25, particularly 1.0 to 1.20, and can be dry pulverized to a level equivalent to wet pulverization by a jet mill. It has properties.
  The amorphous silica produced according to the present invention is
1. Volume-based median diameter (D₅₀) Is 2 μm or less,
2. The zeta (ζ) potential measured with the aqueous dispersion is −35 to −45 millivolts,
3. BET specific surface area is 80m²/ G or less,
4). The oil absorption is 150 cc / 100 g or less,
Having a refractive index greater than 5.15;
Is preferred.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
  In summary,The present inventionIt is completely different from the conventional case where the two-stage reaction process of the nucleation reaction and the nucleus growth reaction is an independent process.Amorphous silica is produced by a wet method.
[0012]
As already mentioned, even if normal wet silica can be refined by pulverization (wet pulverization) at the stage of wet slurry, it re-aggregates when it is dried, and further agglomerates when pulverized (dry). It is difficult to re-fine the resulting particles, and even if pulverized to the limit, it cannot be reduced to the particle size obtained by wet pulverization.
[0013]
  However,In the present inventionIn this method, the silica particles that form the nucleus are once generated by the nucleation reaction, and then the nucleus particles are gradually grown by the nucleus growth reaction.Amorphous silica is obtained, and amorphous silica having a small BET specific surface area is generally obtained.The reason why a silica having a small BET specific surface area can be obtained by the production method of the present invention is not clear, but is considered as follows. After the primary particle nuclei of silica are formed, the irregularities on the silica surface that increase the cohesiveness are densely filled in the nucleus growth process, resulting in non-porous secondary particles, resulting in a small BET specific surface area. It is guessed.In addition, as a result, the average particle size of the obtained aqueous slurry of amorphous silica having a predetermined concentration was subjected to limit pulverization by a wet pulverizer using alumina balls, and the slurry was dried to obtain a jet mill (dry type The agglomeration degree (Pco: see formula (1)) represented by the ratio to the average particle diameter of the powder obtained by limit pulverization with a pulverizer is very close to 1.
[0014]
In addition, the amorphous silica of the present invention is obtained by a wet method, and has the characteristics that the equilibrium moisture content at 25 ° C., 75% RH and 48 hours is 7% or less and the hygroscopic property is small. is doing. That is, the silica obtained by the above method has a BET specific surface area smaller than that obtained by the conventional method in which the silica particles are precipitated all at once, and therefore has a low hygroscopic property.
[0015]
In addition, when the reaction is divided into two stages as described above, the amount of electrolyte salt such as alkali metal salt or alkaline earth metal salt used may be small, and in some cases, the amount used may be zero. It is. Furthermore, since the resulting silica particles are densely nucleated, impurities derived from such electrolyte salts can be easily removed by washing. Therefore, such amorphous silica is very effectively applied not only as a resin compounding agent but also as a filler for heat-sensitive recording paper that dislikes the presence of impure metals.
[0016]
(Production of wet process amorphous silica)
Hereinafter, the present invention will be described in detail according to the production method.
The amorphous silica of the present invention comprises a nucleation step (first step), a nucleation growth step (second step), an aging step (third step), and a post-treatment step (fourth step). ) Is manufactured through.
[0017]
Nucleation process (first stage process):
In this step, first, alkali silicate and mineral acid are simultaneously poured into water or an aqueous electrolyte solution with stirring to produce silica core particles and aging. The aging time is not particularly limited as long as the nucleation time is generated.
[0018]
As the alkali silicate, sodium silicate, potassium silicate and the like can be used, but sodium silicate is usually used.
As the mineral acid, hydrochloric acid, nitric acid, sulfuric acid and the like can be used, but hydrochloric acid and sulfuric acid are generally used.
Further, the aqueous electrolyte solution to which the alkali silicate and the mineral acid are simultaneously added is not particularly limited, but sodium phosphate, ammonium sulfate, sodium chloride, sodium sulfate, lithium chloride, lithium sulfate, sodium carbonate, carbonate An aqueous solution of an electrolyte salt such as sodium hydrogen is used. In the present invention, since silica particles are not precipitated all at once, it is not necessary to use a high concentration aqueous solution of the electrolyte salt. For example, the amount of the electrolyte salt is the amount of alkali silicate used (SiO 2).₂The amount may be 50% by weight or less per conversion), and in some cases, the amount used may be zero (that is, simple water may be used).
[0019]
Silica is produced by metathesis reaction by simultaneous addition of alkali silicate and mineral acid. Control of pH in this reaction stage is important, and pH is adjusted to 6 to 10, preferably 8 during the simultaneous addition. To the range of 9.5. That is, when the pH is higher than the above range, the metathesis reaction does not proceed, and it becomes difficult to produce silica particles as a nucleus. On the other hand, if the pH is lower than the above range, the reaction proceeds all at once, silica particles precipitate all at once, and amorphous silica having the desired characteristics cannot be obtained. The reaction temperature in this step is preferably in the range of 50 to 100 ° C.
[0020]
After the completion of the above reaction, the simultaneous pouring is stopped and ripening is performed to precipitate amorphous silica particles as nuclei. In general, the pH at the time of aging is preferably 4 to 10, particularly 5 to 8. If the pH at this time is out of the above range, precipitation does not proceed effectively, and it may be difficult to obtain silica particles having the desired characteristics. Note that the pH adjustment at this stage can be easily performed by adding a predetermined amount of mineral acid as it is after, for example, stopping the addition of alkali silicate. In addition, this aging is generally carried out at a temperature of 50 to 100 ° C. for 10 to 60 minutes, although it varies depending on the amount of alkali silicate used.
[0021]
Nuclear growth process (second stage):
After the completion of the nucleation step, an alkali silicate and a mineral acid are simultaneously poured again to produce silica on the nuclei and grow silica nuclei. The pH in this step is adjusted to a range of 4 to 10, particularly 6.5 to 8.5. If the pH is higher than this range, the growth reaction of the core particles does not proceed effectively, and if the pH is low, the generation of new core particles is caused rather than the growth of the core particles. It becomes impossible to obtain silica particles.
[0022]
In this step, the pH adjustment can be easily performed by adjusting the injection acceleration of the mineral acid together with the injection acceleration. The reaction temperature in this step is preferably in the range of 50 to 100 ° C.
[0023]
Aging step (third step):
Next, the addition of alkali silicate and mineral acid is stopped, aging is performed in the above pH range, and silica particles on which the core particles generated in the previous step have grown are precipitated. That is, according to this method, amorphous silica particles in which silica core particles are densely grown can be precipitated. Such an aging step is generally performed at a temperature of 50 to 100 ° C. for 1 to 2 hours.
[0024]
Post-processing step (fourth step):
According to the present invention, the desired amorphous silica can then be obtained by carrying out dealkalization, filtration, washing with water, drying and grinding.
Dealkalization, filtration, and water washing are for removing by-product alkali salts, electrolyte salts, and the like, and are performed according to a conventional method. For example, dealkalization can be performed by adjusting the pH to about 2 to 4 by adding mineral acid. In the present invention, since the target silica particles are obtained by gradually growing the core particles, there is an advantage that the above-mentioned impure metal salt in the particles can be easily removed by the operation as described above. is doing. For example, according to the conventional method of precipitating silica particles all at once, the metal salt is contained in the particles and is difficult to remove by the above operation.
[0025]
Drying is performed by heat treatment at about 100 to 300 ° C., and the amorphous silica after washing and drying is made into a product by pulverizing to a predetermined particle size and classification according to the purpose. For such pulverization, jet pulverizer, impact pulverizer, vibration pulverizer, etc. are used. Gravity wind classifier, inertial wind classifier, centrifugal wind classifier, mechanical wind classifier are used for classification. A machine is used.
[0026]
(Amorphous silica)
Since the amorphous silica obtained as described above has undergone two-stage reaction steps of nucleation and nucleation, it has characteristics not found in conventionally known wet-process silica.
[0027]
  That is, the amorphous silica obtained by the production method of the present invention has the following formula (1):
    Pco = B / A (1)
    Where
    A represents the aqueous slurry of amorphous silica prepared to a concentration of 2 to 40% by weight.2mm
  Wet grinding machine using φ ball millDiffraction of pulverized slurry obtained by limit pulverization with
  Volume-based median diameter (D₅₀)
    B, drying the crushed slurry, thenDry milling using a jet millLimit powder
  Volume-based median diameter (D₅₀)
Cohesion degree defined by (Pco)Indicates a value close to 1, for exampleIt is in the range of 1.0 to 1.25, particularly 1.0 to 1.20, and can be dry pulverized to a level equivalent to wet pulverization. This also means that even if the particles refined to a predetermined particle size once aggregate, they can be atomized again by pulverization, which is extremely advantageous industrially. Here, limit pulverization means pulverization to the limit value and refinement, and as an example, FIG. 1 shows the volume-based median diameter (D₅₀) And wet grinding time. From the figure, when the wet pulverization is carried out, the volume-based median diameter (D₅₀) Is constant, and it can be seen that further miniaturization is impossible. Therefore, the volume-based median diameter (D₅₀) Is to grind until a certain value is reached.
[0028]
For example, the amorphous silica of the present invention is used by being blended with various substrates such as a resin compounding agent and a heat-sensitive recording paper filler. For this reason, the volume-based median diameter of the pulverized slurry by the laser diffraction method ( D₅₀) Is preferably 2 μm or less. Moreover, even if it aggregates and enlarges after drying, it can return to the original fine particle easily by carrying out dry grinding again.
[0029]
Further, the amorphous silica of the present invention has an equilibrium moisture content of 7% or less at 25 ° C., 75% RH and 48 hours, and has low hygroscopicity. The silica obtained by the above-described method is believed to have low hygroscopicity because the core particles grow densely. Therefore, this amorphous silica has few problems of condensate, and for example, the problem of foaming accompanying the separation of moisture when kneaded into a resin or when heat-sealing a film is also solved.
[0030]
The wet process amorphous silica of the present invention also has a characteristic that the zeta (ξ) potential measured with respect to the aqueous dispersion is in the range of −35 to −45 millivolts by the method of Examples described later. .
In addition, since the value of the zeta (ξ) potential varies depending on conditions such as the pH of the solution, it was measured under the following conditions in the present invention. A value obtained when 0.15 g of the sample was suspended in 200 ml of ion-exchanged water was used as an origin value, and then pH adjustment was performed using a diluted hydrochloric acid solution.
The suspension was ultrasonically dispersed for 5 minutes, and the zeta potential at pH 5 was measured with a Zevernizer 3000Hsa manufactured by Malvern.
[0031]
The wet process amorphous silica of the present invention has a BET specific surface area of 80 m.²/ G or less, preferably 30 m²/ G or less, particularly preferably 10 m²/ G or less, and is useful as a resin compounding agent or a thermal paper filler.
[0032]
Furthermore, since the wet-process amorphous silica of the present invention is produced through two reaction stages of generation of core particles and growth of core particles, the oil absorption is a relatively small value of 150 cc / 100 g or less. Furthermore, the refractive index is larger than 1.45 and shows a value close to that of a resin. Therefore, it has the advantage that the transparency can be maintained when blended with the resin.
[0033]
In the present invention, an impure metal component derived from an alkali metal or an electrolyte salt is effectively removed by washing. Therefore, for example, the specific resistance measured after boiling a 5% suspension for 5 minutes shows a high value of 5 kΩ · cm or more.
[0034]
[Usage]
The above-described amorphous silica of the present invention is excellent in dispersibility in a resin, and can be imparted with, for example, anti-blocking properties by being blended with various resins as a resin compounding agent. Moreover, even if it adds to a stretched film etc. by refinement | miniaturization, a stretch whitening phenomenon can be suppressed.
[0035]
In addition, when used as a resin compounding agent, it can be compounded into the resin as it is, but it can be used for various purposes by performing post-treatment such as coating with organic and inorganic auxiliaries as necessary.
[0036]
For example, calcium soap such as stearic acid, palmitic acid, lauric acid, metal soap such as zinc salt, magnesium salt, barium salt, silane coupling agent, aluminum coupling agent, titanium coupling agent, zirconium coupling It can be surface-treated with an organic auxiliary such as an agent, various waxes, various unmodified or modified resins (eg, rosin, petroleum resin, etc.) and used for various applications. These organic auxiliaries are preferably used in amounts of 0.5 to 10% by weight, in particular 1 to 5% by weight, per amorphous silica.
[0037]
Examples of the inorganic auxiliary agent include fine particle silica such as aerosil and hydrophobically treated aerosil, silicates such as calcium silicate and magnesium silicate, metal oxides such as calcia, magnesia and titania, magnesium hydroxide and aluminum hydroxide. Metal hydroxides such as calcium carbonate, metal carbonates such as calcium carbonate, fluorides such as magnesium fluoride and ammonium fluoride, synthetic zeolites such as A-type and P-type, and acid-treated products thereof or metal ion-exchange products thereof Particles can be used, and these can be blended or mashed with amorphous silica. These inorganic auxiliaries are preferably used in an amount of 0.5 to 10% by weight, particularly 1 to 5% by weight, per amorphous silica.
[0038]
The thermoplastic resin to which the amorphous silica of the present invention is blended is not particularly limited, but olefin-based resins for film formation are particularly suitable, for example, low-, medium- or high-density. Polyethylene, isotactic polypropylene, syndiotactic polypropylene, or polypropylene polymers that are copolymers of these with ethylene or α-olefin, linear low density polyethylene, ethylene-propylene copolymer, polybutene-1, Ethylene-butene-1 copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, ion-crosslinked olefin copolymer (ionomer), ethylene-acrylic Acid ester copolymers, and the like. These may be used alone or in combination of two or more. It can also be used in the form of a blend. Of course, the amorphous silica of the present invention can be blended with other known film forming resins such as nylon 6, nylon 6-6, nylon 6-10, nylon 11 and nylon 12. It can also be blended with thermoplastic polyesters such as polyamide, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polysulfone, vinyl chloride resin, vinylidene chloride resin, vinyl fluoride resin and the like.
[0039]
Particularly when blended in a resin to impart antiblocking properties, the amorphous silica of the present invention is in an amount of 0.05 to 1 part by weight, especially 0.1 to 0.5 part by weight per 100 parts by weight of the resin. It is good to use.
[0040]
In addition, the amorphous silica of the present invention is subjected to nucleation by simultaneous two-stage reaction, and it is believed that the silica is closely bonded, the specific surface area is low, and leuco Since there is little space for pigments and developer to enter, it is also useful as a thermal paper filler. Furthermore, since the impure metal component content is suppressed, there is no concern of causing thermal head corrosion or the like, and it can be incorporated into a composition for forming a thermal recording layer formed on a support such as paper. it can. In this composition, a colorant such as a leuco dye, a color former such as phenols, a binder such as a water-soluble resin, and a sensitizer are blended. The amorphous silica of the present invention has a solid content. It can be contained in an amount of 10 to 60% by weight, in particular 20 to 40% by weight.
[0041]
【Example】
The present invention will be described with reference to the following examples, but the present invention is not limited to these examples. The measurement of the Example was performed by the following method.
[0042]
(1) Volume-based median diameter (D₅₀)
Measurement was performed using a MasterSizer2000 manufactured by Malvern.
[0043]
(2) Zeta (ξ) potential
A value obtained when 0.15 g of the sample was suspended in 200 ml of ion-exchanged water was used as an origin value, and then pH adjustment was performed using a diluted hydrochloric acid solution. The suspension was ultrasonically dispersed for 5 minutes, and the zeta potential at pH 5 was measured with a Zevernizer 3000Hsa manufactured by Malvern.
[0044]
(3) Specific surface area, pore volume
ASAP2010 manufactured by Micromeritics was used, and measurement was performed by the BET method.
[0045]
(4) Equilibrium moisture content
About 2 g of a sample is placed in a 40 × 40 mm weighing bottle previously weighed, dried for 2 hours in an electric constant temperature dryer at 110 ° C., and then allowed to cool in a desiccator. Next, the weight of the sample was precisely weighed, placed in a desiccator previously adjusted to a relative humidity of 75% with a saturated saline solution, and the weight increase after 48 hours was measured to obtain the equilibrium moisture content.
[0046]
(5) Specific resistance
A sample of 5 g was suspended in 95 g of ion-exchanged water and then boiled for 5 minutes. Next, the suspension was cooled with water and measured with an electric conductivity meter (DS-14) manufactured by Horiba, Ltd.
[0047]
(6) pH
A sample of 5 g was suspended in 95 g of ion-exchanged water and then boiled for 5 minutes. Next, the suspension was cooled with water and then measured using a pH meter (HM-30G) manufactured by Toa Denpa Kogyo.
[0048]
(7) Oil absorption
Measured according to JIS K5101-1991
[0049]
(8) Bulk density
It measured based on JISK6220-1995.
[0050]
(9) Refractive index
Optical Mineralology Vol. 1 1987 Blackwell Scientific Publications Measured according to the Becke test described in P18-P25.
[0051]
Example 1
(Nucleation process)
Sodium silicate solution (SiO2) in 0.5% ammonium sulfate aqueous solution₂: 24.3%, Na₂O: 7.8%, S.I. G. = 1.33) and a 13% aqueous hydrochloric acid solution were added simultaneously until the silica concentration reached 0.3% while maintaining pH 9 at a reaction temperature of 85 ° C. After the pH was lowered to pH 5, the simultaneous pouring was once stopped and the mixture was aged and stirred for 15 minutes.
(Nuclear growth process)
Next, a sodium silicate solution and a 13% hydrochloric acid aqueous solution were simultaneously added while maintaining the pH at 7.5 until the silica concentration reached 4.5%. After completion of the addition, the mixture was aged and stirred for 1 hour to complete the nucleus growth reaction, and a 13% hydrochloric acid aqueous solution was added to lower the pH to 2.5. Thereafter, according to a conventional method, after filtration and washing with water, instantaneous drying was performed, and dry pulverization and classification were performed to obtain Sample 1A.
(Miniaturization)
Sample 1A was redispersed in water to prepare a suspension having a silica concentration of 20%. The suspension was wet-ground for 5 hours using a ball mill (2 mmφ alumina ball). The obtained pulverized slurry was instantaneously dried with a spray dryer, and the dry powder was dry pulverized to obtain Sample 1B.
The physical properties were measured and the results are shown in Table 1.
[0052]
(Example 2)
Synthesis was carried out under the same reaction conditions at a reaction temperature of 60 ° C. using 1.5% saline in place of the 0.5% aqueous ammonium sulfate solution of Example 1 to obtain Sample 2A. Further, miniaturization was performed under the same conditions to obtain Sample 2B.
The physical properties were measured and the results are shown in Table 1.
[0053]
(Example 3)
A 2.0% sodium sulfate aqueous solution was used in place of the 0.5% ammonium sulfate aqueous solution of Example 1, and synthesis was carried out under the same reaction conditions at a reaction temperature of 70 ° C. to obtain Sample 3A. Further, miniaturization was performed under the same conditions to obtain Sample 3B.
The physical properties were measured and the results are shown in Table 1.
[0054]
(Example 4)
The synthesis was carried out under the same reaction conditions without using the ammonium sulfate of Example 1, and Sample 4A was obtained. Moreover, refinement | miniaturization was implemented on the same conditions and 4B was obtained.
The physical properties were measured and the results are shown in Table 1.
[0055]
(Comparative Example 1)
(Nucleation process)
Sodium silicate solution (SiO2) in 0.5% ammonium sulfate aqueous solution₂: 24.3%, Na₂O: 7.8%, S.I. G. = 1.33) and a 13% aqueous hydrochloric acid solution were simultaneously added at a reaction temperature of 60 ° C. while maintaining pH 9 until the silica concentration reached 0.3%. After the pH was lowered to pH 6.5, the simultaneous pouring was once stopped and the mixture was aged and stirred for 15 minutes.
(Nuclear growth process)
Next, a sodium silicate solution and a 13% hydrochloric acid aqueous solution were simultaneously added while maintaining the pH at 3 until the silica concentration reached 4.5%. After completion of the addition, the mixture was aged and stirred for 1 hour to complete the nucleus growth reaction, and a 13% hydrochloric acid aqueous solution was added to lower the pH to 2.5. Then, according to a conventional method, after filtering and washing with water, instant drying was performed, and dry pulverization and classification were performed to obtain Sample 5A.
(Miniaturization)
Sample 5A was redispersed in water to prepare a suspension having a silica concentration of 20%. The suspension was wet-ground for 5 hours using a ball mill (2 mmφ alumina ball). The obtained pulverized slurry was instantaneously dried with a spray dryer, and the dry powder was dry pulverized to obtain Sample 5B.
The physical properties were measured and the results are shown in Table 1.
[0056]
(Comparative Example 2)
Sodium silicate solution in SiO 2 (SiO 2₂: 24.3%, Na₂O: 7.8%, S.I. G. = 1.33) and a 13% aqueous sulfuric acid solution were simultaneously added at a reaction temperature of 75 ° C. while maintaining a pH of 8 until the silica concentration reached 4.5%. After completion of the addition, the mixture was aged and stirred for 1 hour, and a 13% sulfuric acid aqueous solution was added to lower the pH to pH 2. Then, according to a conventional method, after filtration and washing with water, instant drying was performed, and dry pulverization and classification were performed to obtain Sample 6A.
(Miniaturization)
Sample 6A was redispersed in water to prepare a suspension having a silica concentration of 15%. The suspension was wet-ground for 5 hours using a ball mill (2 mmφ alumina ball). The obtained pulverized slurry was instantaneously dried with a spray dryer, and the dry powder was dry pulverized to obtain Sample 6B.
The physical properties were measured and the results are shown in Table 1.
[0057]
[Table 1]

[0058]
(Examples 5 to 8)
A thermal recording test paper was prepared using a thermal recording layer forming liquid having the following composition using the silica powder according to the present invention obtained in Examples 1 to 4 as a filler. The test papers were evaluated by the methods shown below. The results are shown in Table 4.
[0059]
(Creation of thermal recording test paper)
The heat-sensitive coating liquid was prepared so that the solid content of each material was as follows. In addition, each raw material was mixed after wet-grinding well with a paint schenker or the like.
Leuco dye: ODB-2 (3-diethylamino-6-methyl-7-anilinofluorane) 10 parts
Developer: 20 parts BPA (bisphenol A)
Sensitizer: PBBP (polybenzylbiphenyl) 20 parts
Lubricant: 10 parts of zinc stearate
Binder: PVA-117 (polyvinyl alcohol) 15 parts
Filler (see Table 4) 20 parts
Drying weight of the above thermal recording layer forming liquid on commercial PPC paper is 6g / m²After coating, the film is dried at room temperature, and the roll pressure is 10 kg / cm.²Was subjected to calendering and used as a test thermal recording test paper.
[0060]
(Evaluation of thermal paper)
(10) Contamination density
The scumming density of the heat-sensitive recording layer forming liquid coated paper 24 hours after coating was measured with a standard densitometer FSD-103 manufactured by Fuji Photo Film Co., Ltd. using a V filter. Evaluated by criteria.
[Table 2]

[0061]
(11) Dynamic color image density
Recorded with a printing apparatus TH-PMD manufactured by Okura Electric Co., Ltd. (head voltage 24 V, pulse width 1.3 msec, pulse period 2 msec, thermal head resistance value 1572Ω), and the color image density at this time was determined as a standard densitometer FSD-103 It was measured with a mold (manufactured by Fuji Photo Film) and evaluated according to the criteria shown in Table 3 by observation with the naked eye.
[Table 3]

[0062]
(12) Waste adhesion prevention test
Using NTT FAX-510T, debris adhering to the thermal head after solid printing was observed with the naked eye and evaluated as follows.
: Excellent
: Good
×: Defect
[0063]
[Table 4]

[0064]
(Examples 9 to 10)
A polypropylene (PP) film was prepared by blending the silica powder according to the present invention obtained in Examples 1 and 2 as a filler. The films were evaluated by the methods shown below. The results are shown in Table 5.
[0065]
(Create film)
Using PP as the resin, the following blended raw materials were formed at a processing temperature of 230 ° C. to obtain a film having a thickness of 30 μm.

[0066]
(Film accuracy test environment)
In accordance with ISO 291: 1997, the test film was stored in an environment adjusted to a room temperature of 23 ° C. and a humidity of 50%, and the test piece after a predetermined time was subjected to various film accuracy tests.
[0067]
(13) Haze measurement
Haze was measured in accordance with ASTM D 1003-95 using a Gardner-made haze-gard plus. The smaller the value of Haze, the better the transparency.
[0068]
(14) Clarity measurement
Clarity measured the test piece of the film used for the said Haze measurement as it was, using the apparatus described in ASTM D 1044-94. The greater the value of Clarity, the better the clarity.
In addition, Gardner's haze-gard plus was used for the measurement.
[0069]
(15) SCOF (Static Friction Coefficient) measurement
Based on ASTM D 1894-95, the coefficient of static friction between the outer surfaces of the film was evaluated using a friction measuring machine TR-2 manufactured by Toyo Seiki. The lower the SCOF value, the better the slipperiness.
[0070]
(16) Gel number
Measurement results obtained with a Nikon two-beam interference microscope were analyzed using a Micromap 550 and Surface Explorer. Convex objects with a diameter of 100 μm or more and a protrusion height of 2 μm or more are regarded as Gel (fish eye), and the film is 16 cm.²The number of Gel per count was counted.
[0071]
(17) Measurement of anti-blocking property (AB property)
With respect to the film pressure-bonded at 6 kPa at 60 ° C. for 3 days by the method according to ISO 11502: 1995 method B, the blocking force was measured and evaluated as shown below.
○: Peel without problems
Δ: Hard to peel
×: not peeled
[0072]
(Comparative Example 3)
In the PP-resin composition formulation table, Comparative Example 2 was used as an antiblocking agent. The results are shown in Table 5.
[0073]
(Comparative Example 4)
Nothing was added to the PP resin, and the PP resin was 100% by weight. The results are shown in Table 5.
[0074]
[Table 5]

[0075]
【The invention's effect】
According to the present invention, by using a two-stage reaction of a nucleation reaction and a nucleation growth reaction, it is possible to obtain amorphous silica that is easily refined while being based on a wet method. This amorphous silica has good dispersibility with respect to a resin or the like, and is suitable, for example, as a resin compounding agent. In addition, since the specific surface area is low and there is little space for the leuco dye or developer to enter, it is useful as a heat-sensitive recording filler. Corrosion can also be prevented. Furthermore, it can be used as a filler for stretched films, etc. by miniaturizing to sub-micron size, and it can also add new functions such as gas barrier properties by enabling uniform dispersion of fine silica in the resin. It is.
[Brief description of the drawings]
FIG. 1 Volume-based median diameter (D₅₀) And the wet pulverization time.

Claims (1)

A first stage in which alkali silicate and mineral acid are simultaneously poured into water or an aqueous electrolyte solution while maintaining the pH in the region of 6 to 10 to produce silica core particles, and then the simultaneous pouring is stopped and ripening is performed. The process of
Next, a second step of growing silica core particles while maintaining the pH in the region of 4 to 10 while simultaneously adding alkali silicate and mineral acid,
A third step for aging by stopping simultaneous pouring of alkali silicate and mineral acid, and then a fourth step for dealkalization, filtration, washing, drying and grinding,
A process for producing amorphous silica, comprising:

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