Titanium dioxide pigment and resin composition containing the same

The present invention relates to a titanium dioxide pigment for a polycarbonate resin composition and a resin composition containing the same.

Polycarbonate resin has excellent impact resistance, heat resistance, electrical characteristics, transparency, and high processing accuracy, and is therefore used in mechanical parts, parts and housings of electrical and electronic equipment, medical instruments, optical parts, and the like. Many of these polycarbonate resin compositions are required to have concealing properties, and usually contain a titanium dioxide pigment having a high refractive index of visible light. Since the polycarbonate resin generally has a high melting temperature, it is necessary to process the polycarbonate resin at a high temperature when trying to blend the titanium dioxide pigment into the polycarbonate resin. However, since titanium dioxide is originally hydrophilic and has high hygroscopicity, when it is processed at a high temperature, the moisture-absorbing moisture volatilized from the titanium dioxide pigment and the polycarbonate resin undergo a hydrolysis reaction, and the resin composition becomes yellowish. The color changes to a polycarbonate color, or the molecular weight decreases, resulting in impaired strength.

In order to deal with this phenomenon, for example, in a polycarbonate resin composition containing a titanium dioxide pigment, methyl hydrogen polysiloxane or a copolymer of dimethylsiloxane represented by the following formula 2 and methylhydroxanesiloxane is mixed with the polycarbonate resin. (See Patent Document 1). Further, a technique of coating a needle-shaped titanium dioxide compounded in a polycarbonate resin composition with a polyorganohydrogensiloxane such as methylhydrogenpolysiloxane is also known (see Patent Document 2). Equation 2: (CH₃)₃SiO (SiO (CH)₃)₂)_x(SiOHCH₃)_ySiO (CH₃)₃[x = 103, y = 22, or x = 17.5, y = 3.2]

<patcit num="1"><text>JP-A-54-102351 (Claims)</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 8-59976 (Claims)</text></patcit>

However, the copolymer described in Patent Document 1 has insufficient discoloration resistance and an effect of suppressing a decrease in molecular weight. Further, although the methyl hydrogen polysiloxane described in the same document and Patent Document 2 is effective in discoloration resistance and reduction of molecular weight, when a titanium dioxide pigment is blended in a high concentration, streaks are formed on the surface of the resin composition. There is a problem that the pattern of is generated. This phenomenon is called silver streak, which greatly impairs the commercial value of the resin composition.

<p> The present invention provides a titanium dioxide pigment in which discoloration and a decrease in molecular weight of the polycarbonate resin are suppressed even when the polycarbonate resin composition is blended in a high concentration, and silver streak is unlikely to occur, and a resin composition containing the same. ..</p>

<p> As a result of diligent research, the present inventors have found that if the surface of a titanium dioxide pigment is coated with a copolymer obtained by copolymerizing dimethylsiloxane and methylhydroxanesiloxane at a specific polymerization ratio, discoloration resistance in a polycarbonate resin is obtained. The present invention has been completed by finding that the composition is excellent in quality, does not impair properties such as strength of the composition, and has improved silver streak resistance.</p><p> That is, the present invention is a titanium dioxide pigment for a polycarbonate resin composition, which comprises having a coating layer of an organopolysiloxane represented by the following formula 1 on the surface of titanium dioxide particles. Equation 1: (CH₃)₃SiO (SiO (CH)₃)₂)_n(SiOHCH₃)_mSiO (CH₃)₃[n and m are integers that satisfy 0.8 m / n 1.2. ]</p>

<p> The titanium dioxide pigment of the present invention can obtain a polycarbonate resin composition which hardly causes discoloration even when blended at a high concentration, has high strength, and has almost no surface defects such as silver streaks.</p>

The present invention is a titanium dioxide pigment for a polycarbonate resin composition, and is characterized by having a coating layer of polyorganosiloxane represented by the following formula 1 on the surface of titanium dioxide particles. Organohydrogen polysiloxane is said to have a high effect of making the titanium dioxide pigment hydrophobic because its hydrogen group and the hydroxyl group of the titanium dioxide pigment are hydrogen-bonded to seal the hydroxyl group. Therefore, the amount of adsorbed water of titanium dioxide can be suppressed, the polycarbonate resin is less likely to be hydrolyzed even when processed at a high temperature, and the obtained resin composition hardly turns yellow, and the polycarbonate resin. The original characteristics are not impaired. However, on the other hand, if the hydrogen group of the organohydrogen polysiloxane is not bonded to the hydroxyl group of the titanium dioxide pigment, it becomes hydrogen gas at high temperature and is easily desorbed. Therefore, the titanium dioxide pigment coated with the organohydrogen polysiloxane is used. When blended at a high concentration, it is presumed that hydrogen gas volatilized from the surface of the resin composition during processing causes silver streaks. In the present invention, the hydrophobicity of the titanium dioxide pigment is improved and the hydrogen group is formed by coating the titanium dioxide pigment with a copolymer obtained by copolymerizing the dimethylsiloxane represented by the formula 1 with approximately the same amount of methylhydroxanesiloxane. It suppresses the detachment of the polymer and improves the silver streak resistance. Equation 1: (CH₃)₃SiO (SiO (CH)₃)₂)_n(SiOHCH₃)_mSiO (CH₃)₃[n and m are integers that satisfy 0.8 m / n 1.2. ]

In the present invention, it is important to use a copolymer obtained by copolymerizing dimethylsiloxane and methylhydroxanesiloxane at a polymerization ratio in the above range. For example, dimethylpolysiloxane so that the addition amount ratio is within this range. Even if and methylhydroxane polysiloxane are treated with a titanium dioxide pigment, the effect of the present invention cannot be obtained, probably because the methyl hydrogen polysiloxane is preferentially coated with the titanium dioxide pigment. Further, although Patent Document 1 discloses a polycarbonate resin composition containing a copolymer represented by the following formula 2, it is not suggested to coat it with a titanium dioxide pigment. By the way, even if the copolymer of the formula 2 is coated with the titanium dioxide pigment, the bond with the titanium dioxide pigment is weak when the amount of polymerization of such dimethylsiloxane is large, so that the copolymer is not sufficiently hydrophobized. No effect is obtained. Equation 2: (CH₃)₃SiO (SiO (CH)₃)₂)_x(SiOHCH₃)_ySiO (CH₃)₃[x = 103, y = 22, or x = 17.5, y = 3.2]

As the organopolysiloxane used in the present invention, a copolymer in which n and m in the above formula 1 satisfy 50 n + m 300 is preferable. If n + m is smaller than this range, the molecular weight becomes too small, so that it is difficult to form a dense organopolysiloxane coating, and if it is large, the molecular weight becomes too large, and it is difficult for the organopolysiloxane and the titanium dioxide pigment to come into contact with each other. It becomes difficult to seal the hydroxyl group, and it is difficult to obtain the effect of the present invention. A more preferred organopolysiloxane is one with m / n = 1 and n + m = 100 (ie, n = 50, m = 50). The coating amount of the organopolysiloxane is preferably in the range of 0.5 to 5% by weight, more preferably in the range of 1 to 3% by weight, based on the titanium dioxide pigment.

The titanium dioxide pigment of the present invention preferably has an average particle size (electron micrograph) in the range of 0.1 to 0.4 μm, and more preferably in the range of 0.1 to 0.25 μm. The crystal form may be either anatase type or rutile type, and may be a mixture of both, and amorphous titanium dioxide is partially contained within the range in which the object of the present invention is not impaired. May be good. The titanium dioxide pigment may be obtained, for example, by the so-called sulfuric acid method of hydrolyzing a titanium sulfate solution, or by the so-called chlorine method of vapor phase oxidation of titanium halide, and is not particularly limited.

In the present invention, in addition to the organopolysiloxane, various inorganic compounds and organic compounds are coated on the surface of the titanium dioxide pigment according to desired properties such as imparting weather resistance, light resistance, etc., and improving productivity. May be good. For example, examples of such an inorganic compound include oxides known in the art such as aluminum, silicon, tin, zirconium and antimony, and phosphates thereof such as aluminum phosphate, which may be coated as a mixture. Two or more types may be combined and coated by laminating or the like. The oxide used as an inorganic compound in the present invention includes not only ordinary oxides but also hydrated oxides and hydroxides. Examples of the organic compound include polyols such as trimethylolpropane and trimethylolethane, alkanolamines such as triethylamine, and derivatives thereof.

Since the titanium dioxide pigment has high catalytic activity and has a property of accelerating the deterioration of the organic resin component, in the present invention, as titanium dioxide particles, aluminum oxide is oxidized on the surface thereof in advance so as not to impair the durability of the polycarbonate resin composition. It is preferable to use titanium dioxide particles having a coating layer of a substance and / or a silicon oxide. To obtain titanium dioxide particles having a coating layer of aluminum oxide and / or silicon oxide, aluminum oxide and silicon oxide can be coated individually, or they can be coated as a mixture or laminated. You may. When laminating aluminum oxide and silicon oxide, the coating order is not limited, but coating aluminum oxide on the outer shell facilitates operations such as dehydration, drying, and pulverization in the titanium oxide pigment manufacturing process. Therefore, it is preferable. Since aluminum oxide and silicon oxide are usually coated on titanium dioxide pigments as hydrated oxides (or hydroxides), the coating amount can be durable in order to reduce the amount of volatile water. It is preferable to reduce the amount as much as possible. Specifically, the coating amount of aluminum oxide is Al with respect to the titanium dioxide pigment.₂O₃The range is preferably 0.05 to 5% by weight, more preferably 0.5 to 2.5% by weight, and the coating amount of silicon oxide is SiO.₂The range is preferably 0.05 to 5% by weight, more preferably 0.2 to 2% by weight.

To coat the titanium dioxide pigment with the organopolysiloxane represented by the above formula 1, a dry crusher such as a fluid energy crusher or an impact crusher or a high-speed stirrer such as a Henschel mixer or a super mixer is used to obtain titanium dioxide particles. And the organopolysiloxane are stirred and mixed. It is preferable to use a dry crusher such as a fluid energy crusher because the organopolysiloxane can be coated more uniformly while pulverizing the titanium dioxide pigment, and the manufacturing process can be rationalized by simultaneously performing the pulverization step and the coating step. .. Among the fluid energy crushers, it is even more preferable to use a swirl type device such as a jet mill because the crushing efficiency is good and the mixing property is also excellent.

To coat the titanium dioxide particles with aluminum oxide and silicon oxide in advance before coating the organopolysiloxane, the following known methods can be used. For example, (1) an aqueous solution of a silicon compound is added to an aqueous slurry in which titanium dioxide particles are dispersed, the pH is adjusted to 4 to 9 using an aqueous solution of an acidic compound or a basic compound, and then an aluminum compound is further added. An aqueous solution is added and the pH is adjusted to 4 to 9 using an aqueous solution of an acidic compound or a basic compound. (2) An aqueous solution of an acidic compound or a basic compound is added to an aqueous slurry of titanium dioxide particles to the above range. A method of adding an aqueous solution of a silicon compound to the slurry and then adding an aqueous solution of an aluminum compound in the same manner while maintaining the pH of the above can be mentioned. After coating with aluminum oxide and silicon oxide, filtration, washing, and drying may be performed, if necessary.

The solid content concentration of the titanium dioxide particles in the aqueous slurry is in the range of 50 to 800 g / liter, preferably in the range of 100 to 500 g / liter. If the concentration is higher than 800 g / liter, the viscosity of the aqueous slurry becomes too high, and it becomes difficult to uniformly coat the aluminum oxide and the silicon oxide. Also, if it is lower than 50 g / liter, industrial operability is reduced. Examples of the aluminum compound include sodium aluminate, aluminum sulfate, aluminum nitrate, aluminum chloride and the like, and examples of the silicon compound include sodium silicate and potassium silicate.

When coating aluminum oxide and silicon oxide, inorganic acids such as sulfuric acid and hydrochloric acid or organic acids such as acetic acid and formic acid are used as acidic compounds for adjusting pH, and sodium hydroxide and hydroxide are used as basic compounds. Known compounds such as potassium and ammonia can be used.

The following invention is a polycarbonate resin composition, which comprises a titanium dioxide pigment having a coating layer of the organopolysiloxane and a polycarbonate resin. The resin composition of the present invention has almost no processing defects such as silver streaks, and has excellent strength and whiteness. Therefore, it is useful for molded products such as mechanical parts, parts of electric / electronic devices, housings, and automobile parts. Further, the present invention can be applied not only to such molded products but also to intermediate products such as master batches and color pellets, and is particularly useful for master batches because it has excellent silver streak resistance at high pigment concentrations. .. The blending ratio of the titanium dioxide pigment and the polycarbonate resin is not particularly limited, but the titanium dioxide pigment is usually in the range of 1 to 80 parts, more preferably 1 to 60 parts by weight, based on 100 parts by weight of the polycarbonate resin. For batches, the range is 10 to 900 parts by weight, more preferably 50 to 500 parts by weight. Further, depending on the application, a reinforcing material such as glass fiber known to those skilled in the art, and various additives such as stabilizers, dispersants, lubricants, antioxidants, ultraviolet absorbers, fillers, etc. may be added. It is also possible to add a resin component other than the polycarbonate resin such as polyester resin, ABS resin, acrylic resin, polyolefin resin, polyamide resin and elastomer to the extent that the effect of the present invention is not impaired, and use the resin as an alloy.

The resin composition of the present invention is obtained by blending a molten polycarbonate resin with a titanium dioxide pigment coated with the organopolysiloxane using a kneader. The kneading machine may be a generally used one, and examples thereof include a single-screw extruder, a twin-screw extruder, an intensive mixer such as a Banbury mixer, and a roll forming machine.

Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are provided solely for illustration purposes and are not intended to limit the scope of the invention.

Example 1 (Coating with Silicon Oxide and Aluminum Oxide) Rutile-type titanium dioxide particles having an average particle diameter of 0.2 μm were mixed with water to prepare an aqueous slurry having a weight of titanium dioxide of 300 g / liter. While holding this slurry at 60 ° C, enter sodium silicate while stirring.₂Add 1% to the weight of the titanium dioxide particles, then neutralize the pH to about 5 with sulfuric acid, coat with silicon oxide, and then add sodium aluminate to Al with stirring.₂O₃As a result, 2% was added to the weight of the titanium dioxide particles, and then the pH was neutralized to 5 with sulfuric acid to coat the aluminum oxide. Then, it was separated by filtration, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill to obtain titanium dioxide particles (sample a) coated with silicon oxide and aluminum oxide.

(Coating with Organopolysiloxane) Organopolysiloxane in which n and m of Equation 1 are n = 50 and m = 50 with respect to titanium dioxide particles while stirring the above sample a at 1800 rpm using a Henschel mixer. KF-9901 (manufactured by Shin-Etsu Chemical Industry Co., Ltd.) was added to coat the surface of titanium dioxide particles in an amount of 2% by weight. The obtained titanium dioxide pigment is used as sample A.

Example 2 (Coating of Silicon Oxide and Aluminum Oxide) In Example 1, the amount of silicon oxide covered was set to SiO.₂Titanium dioxide particles coated with silicon oxide and aluminum oxide (Sample b) in the same manner as in Example 1 except that the weight of the titanium dioxide particles was 0.5% and the coating amount of aluminum oxide was 0.5%. Got

(Coating with Organopolysiloxane) The titanium dioxide pigment of the present invention was obtained by the same treatment as in Example 1 except that sample b was used instead of sample a as titanium dioxide particles. This is referred to as sample B.

Comparative Examples 1 to 4 The organopolysiloxane coating in Example 1 was coated with methyl hydrogen polysiloxane (KF-99: manufactured by Shin-Etsu Chemical Co., Ltd.) in an amount of 2% by weight (Comparative Example 1), dimethylpolysiloxane (KF-96: Shin-Etsu). Chemical Industry Co., Ltd.) 2% by weight (Comparative Example 2), 1% by weight of methyl hydrogen polysiloxane (same as above) and 1% by weight of dimethylpolysiloxane (same as above) (Comparative Example 3), (CH₃)₃SiO (SiO (CH)₃)₂)₇₅(SiOHCH₃)₂₅SiO (CH₃)₃Dimethylpolysiloxane-methylhydroxanesiloxane copolymer of 2% by weight (Comparative Example 4) was treated in the same manner as in Example 1 to obtain a titanium dioxide pigment as a comparative sample. Let each be samples C to F.

Comparative Examples 5 to 7 Titanium dioxide pigments of Comparative Samples were obtained in the same manner as in Comparative Examples 1 to 3 except that Sample b was used instead of Sample a as the titanium dioxide particles in Comparative Examples 1 to 3. , Each of the obtained comparative samples is designated as Samples G to I.

Evaluation 1 (Silver streak resistance, whiteness) 40 g each of Samples A to I obtained in Examples 1 and 2 and Comparative Examples 1 to 7 and 400 g of polycarbonate resin (Iupilon S-2000: manufactured by Mitsubishi Gas Chemical Company, Inc.) Was placed in a polyethylene bag and hand-blended for 5 minutes. This product is melt-extruded over 7 minutes using a twin-screw extruder (manufactured by Ikegai Corp.: PCM-30 type) at a resin temperature of 300 ° C, and comes out of the T-die mounted on the discharge side. The melt was formed into a sheet having a thickness of about 0.8 mm using a sheet roll. The state of the molded sheet surface was visually observed to determine the superiority or inferiority of silver streak resistance. The judgment criteria are as follows. In addition, the YI value (yellow index) of the sheet was measured using a color computer (SM-7 type: manufactured by Suga Test Instruments Co., Ltd.). The smaller the YI value, the smaller the discoloration to yellow and the better the discoloration resistance. Judgment : No silver streak is found. Judgment : Slight silver streak is observed. Judgment : Silver streak is partially recognized. Judgment ×: Silver streak is recognized throughout.

Evaluation 2 (Karl Fischer Moisture) Samples A to I obtained in Examples 1 and 2 and Comparative Examples 1 to 7 were left to stand at a constant temperature and constant humidity of 25 ° C. and 55% relative humidity for 24 hours to achieve an equilibrium state. Then, 1 g of the sample was measured for Karl Fischer moisture at 100 ° C and 300 ° C using a Karl Fischer moisture measuring device and a moisture vaporizer attached to it (both manufactured by Mitsubishi Chemical Corporation), and the difference (the difference) Δ_300-100) Was calculated. Δ_300-100It is considered that the smaller the value of, the smaller the amount of volatile water when actually molding the polycarbonate resin.

The above evaluation results are shown in Table 1. It can be seen that the titanium dioxide pigment of the present invention has a small amount of volatile moisture and is excellent in discoloration resistance and silver streak resistance in the polycarbonate resin system.

<tables num="1"><img file="JP2005290137A_D0001.tif" /></tables>

The titanium dioxide pigment of the present invention is useful for a polycarbonate resin composition, and this resin composition is suitable for use as a mechanical part, a part or housing of an electric / electronic device, an automobile member, or the like.