JPS61215633A - Precipitation-process synthetic silica for reinforcing and filling elastomer - Google Patents

Abstract

PURPOSE:To obtain the titled silica low in bound water content, excellent in dispersibility, effect of imparting strength, etc., and capable of giving an elastomer excellent in efficiency, operability and processability, obtained by reacting an alkali metal silicate with a mineral acid under a specified condition to form a precipitate. CONSTITUTION:An alkali metal silicate (e.g., sodium silicate) is reacted with a mineral acid (e.g., sulfuric acid) with intense agitation at a high temperature >=90 deg.C and a pH of 7-9 to form a precipitate so that the amount of silica formed per unit time may be 30g/l.min or below and the silica concentration at the end of the reaction may be 70g/l or below. The obtained silica is heated, if necessary, at 250-500 deg.C to obtain precipitation-process silica which has a low value of dry basis ignition loss I (%) of formula I (JIS K-5101), a relationship of equation II (wherein a=5.3X10<-3>, 1.77<=b<=3.00 and 100<=S<=300) between I and a BET nitrogen adsorption method surface area S (m<2>/g) (JIS K-8885).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a precipitated synthetic silica used as a nidistomer reinforcing filler.

[Background of the invention]

Synthetic silica produced by a precipitation method (hereinafter referred to as precipitation silica) is used in a wide variety of fields. For example, agrochemicals with the purpose of imparting high oil absorption, paint matting agents that utilize an appropriate agglomerated particle size, finely powdered thickeners for paints and resins, and thixotropic agents are well-known. In addition, it is widely used as the main nidistomer reinforcing filler, which is the object of the present invention.

In addition to the precipitated silica, carbon black, silicates, silicic anhydride (fumed silica), etc. are also used as elastomer reinforcing fillers, but carbon black, for example, has high reinforcing performance and dynamic properties. However, due to reasons such as the product being black and lacking in so-called free coloring, silicic anhydride being expensive, and silicates lacking sufficient reinforcing performance, their application has been restricted to limited use of nidistomers. It is limited.

For these reasons, precipitated silica, which has relatively excellent reinforcing performance and is produced at low cost, that is, obtained by the reaction of an alkali metal silicate with a mineral acid or a third substance, is called the Nidistomer reinforcing filler. Currently, it is widely used as

However, although such precipitated silica for filling Nistomer reinforcement exhibits relatively high reinforcing performance, it tends to be inferior to general vulcanizate properties such as tensile strength and abrasion resistance compared to carbon black. , it has been pointed out that there is a need for improvement regarding high reinforcing properties.

By the way, if we compare the mechanism of elastomer reinforcement by applying precipitated silica to that of carbon black, in carbon black, the hydroxyl groups, carboxyl groups, quinone groups, etc. present on the particle surface are chemically bonded to the elastomer. In addition to bonding, the structure based on the chains between particles further enhances the reinforcing effect and is said to strongly reinforce the Nistomer, whereas silica-based materials have silanol groups on the surface (5t-OH). It is said that the reinforcing effect on the elastomer is due to the hydrogen bond between the silanol group and the nidistomer and van der Waals attraction.

From the above reinforcement mechanism, the reinforcing effect becomes greater as the specific surface area of silica increases, that is, as the number of silanol groups on the surface increases.

However, in reality, the reinforcing effect of precipitated silica cannot be solved simply as described above.

In other words, silica with a high specific surface area has a large number of silanol groups, so the self-cohesive force due to hydrogen bonds between particles acts too strongly, resulting in poor dispersion inside the nidistomer. This is understood to be due to the fact that only a portion of it comes into contact with the nidistomer, which actually reduces the reinforcing effect.

As another method for improving the reinforcing performance of precipitated silica, a method of combining a silane coupling agent and other organic compounds has been proposed.

For example, for a silane coupling agent, a preparation method consisting of a chloro-substituted silane and a silicate filler (JP-A-56
-303443) or a method using a mixture of oligosulfide and silicate and a mixture of mercaptosilane and silicate (West German Patent Publication Nos. 2255577 and 2528134), etc. An example of blending is a method using a rubber compound blended with acrylic polymerizable monomers (Japanese Unexamined Patent Publication No. 79812/1983).

However, although the combination method of blending these compounds has a considerable improvement effect on the reinforcing properties, it is not sufficient compared to the reinforcing properties of carbon black, especially the abrasion resistance.

[Purpose of the invention]

The present invention was made in view of the various problems described above, and its purpose is to provide a precipitated silica which is industrially useful as an elastomer reinforcing filler and has been improved to exhibit a high reinforcing effect. It provides:

[Summary of the invention]

Therefore, the characteristics of the precipitated silica of the present invention, which has been made to achieve the above object, are the dry weight ignition loss rate (
4): BET specific surface area (m”/?) by nitrogen adsorption method: S
The relationship is within a range that satisfies the relational expression (i): 1 = as + b...0 In the present invention, the dry amount is used as a reference because the attached moisture changes depending on the relative humidity. This is to eliminate the influence of (105°C evaporation).

The reason why the precipitated silica that exhibits the excellent reinforcing effect of the present invention is within the range specified by the above relational expression (i) is as follows.

In other words, according to the inventor's study of the reinforcing mechanism of precipitated silica and the correlation between the reinforcing effect, an increase in the specific surface area (-
A reduction in the diameter of secondary particles) increases the number of silanol groups on the particle surface, increases the self-cohesive force on the other side, and causes poor dispersion inside the elastomer, which has a contradictory character in that it does not lead to an increase in the reinforcing effect. As already mentioned, it has . A more detailed study of this problem shows that if the specific surface area of precipitated silica and the degree of presence of silanol groups on the particle surface can be adjusted appropriately, precipitated silica particles with a sufficiently large specific surface area can be dispersed well inside the elastomer. It can be understood that it can be obtained. The inventors of the present invention have repeatedly conducted tests and considerations from this viewpoint, and have discovered that the precipitated silica within the above-specified range exhibits an excellent reinforcing effect, leading to the present invention.

Although the detailed mechanism by which silica falling within the range of relational expression (i) of the present invention exhibits superior dispersibility and reinforcing properties to conventional precipitated silica is not fully clear, it is inferred as follows. .

Since precipitated silica is synthesized in an aqueous solution, it exhibits a significantly higher loss on ignition than so-called fumed silica, which is synthesized in the gas phase and by decomposing silicon tetrachloride at high temperatures. In general, for silica, the loss on ignition on a dry basis is also referred to as bound water, but precipitated silica has a unique twin silanol group>Si<81 compared to fumed silica.
It is said that it has a high density distribution of silanol groups on the surface due to the presence of silane, and therefore has a high weight ratio of bound water. This high-density silanol group distribution and the excessive amount of bound water caused by it not only make it difficult to disperse in the silica because it strengthens the cohesive force of the silica itself, but also makes it difficult to disperse the silica into the silica itself. This will adversely affect the bonding with silane coupling agents and the like.

The precipitated silica of the present invention has improved dispersibility because its self-cohesive force can be weakened due to the reduced surface silanol group concentration.
This facilitates the bonding of the nidistomer itself and other drugs in the nidistomer, and due to the reduced surface-bound water, hydrogen bonds within the nidistomer and weak bonds between silica molecules based on van der Waals forces generate structural properties. It is presumed that the reinforcing property is improved due to the above factors.

One of the characteristics of the precipitated silica of the present invention specified as the range described above is that it has a dry weight ignition value of This is where the weight loss rate shows a low value. Specifically speaking, the first
In contrast to the precipitated silica of the present invention in the range shown by the shaded area in the figure, the conventional precipitated silica for elastomer reinforcement filling has a BFiT specific surface area of 50 to 220 l? The dry weight ignition loss rate = 1 is higher than the upper limit of the specific range.

The precipitated silica in the present invention is specified as a range within the shaded area in Figure 1 determined by the above formula (i), and if the dry weight ignition loss rate: ■ is lower than the lower limit in Figure 1, it is reinforced. In addition, when I is higher than the upper limit shown in FIG. 1, the effect of imparting reinforcing properties to the elastomer cannot be sufficiently obtained.

The above formula (i) for indicating such a specific range was obtained based on statistical organization of data through repeated experiments. If the coefficient is less than 1.77, the concentration of silanol groups is too low, so the reinforcing property decreases, and 3.0
If it is 0 or more, the reinforcing property cannot be sufficiently improved, probably because the concentration of silanol groups is not much different from that of conventional ones.

The specific surface area S is determined from the balance between reinforcing properties and dispersibility, and is generally 100 pre/? ≦S≦300 Heima,
Preferably, 150d<S<250d. S is 100mM? If it is less than 300 i/P, the reinforcing property will be insufficient even if the dispersibility is good, and if it is more than 300 i/P, the dispersibility will be poor. The primary particle diameter in this case is generally about 12 to 25 nm.

The precipitated silica of the present invention is produced, for example, according to the following method.

One method is to specify the reaction conditions in the commonly used reaction between an alkali metal silicate and a mineral acid, and the other is the precipitation method of a reinforcing filler of a commercially available nidistomer. This is a method for modifying silica or newly prepared precipitated silica having a wide range of specific surface area values by heat treatment.

Regarding the preparation under the former reaction conditions, it is basically similar to the conventionally known method of reacting an alkali metal silicate with a mineral acid such as sulfuric acid or hydrochloric acid, but special attention must be paid to the following points: Compared to commonly performed reactions, for example, the temperature is high (90°C or higher), the stirring is strong to give high shear properties, the pFI during the reaction is near neutrality (pH 7 to 9), and the The amount of silica produced per unit time is small (301/1.- or less), or the silica concentration during the reaction is low (the concentration at the end of the reaction is 70%).
f/l or less), etc. Other steps for producing precipitated silica, ie, filtration, washing with water, drying, and, if necessary, appropriate pulverization, are carried out by known methods and do not require any special attention.

For the latter improved heat treatment method, commercially available precipitated silica for elastomers such as N1psil V
N3 (manufactured by Nippon Sirikani Gyo Co., Ltd.; product name), His
il 233 (two product names manufactured by PPG in the United States) etc. to 250
This is achieved by heat treatment at a temperature of 500°C to 500°C, preferably 350°C to 450°C. The former reaction and this heat treatment may be combined. Examples of equipment used for heat treatment include a temperature-controlled dryer, a kiln, or a method of passing through a burner that emits a flame. , it is not necessary to undergo a particularly long thermal history. Regarding the heat treatment temperature: Precipitated silica treated at a temperature of 250°C or lower or 500°C or higher does not meet the range of formula (1) above, and therefore the reinforcing properties of the nidistomer are not improved. Those heated to 500°C or higher are significantly inferior to those that are not heat treated.

The silica to which the precipitated silica of the present invention can be applied includes almost all commercially available products.
For example, natural rubber, organic synthetic rubber, silicone rubber, etc. can be mentioned.

[Embodiments of the invention]

Examples of the present invention and measurement examples of reinforcing effects when various elastomers are filled with the examples will be shown below, in comparison with comparative examples having characteristics outside the range shown in FIG.

Note that there is no need to take special precautions when applying elastomers, but as a general matter, the amount of compounding and other compounding agents that suit the purpose should be appropriately selected and Needless to say, a kneading operation that can sufficiently disperse the precipitated silica should be selected and carried out appropriately.

Example 1 931 t of hot water was charged into a 2001 stainless steel reaction tank equipped with a flow meter for each raw material of IJ (silicic acid) and sulfuric acid, a temperature controller using steam, and a stirrer with a rotation speed of 180 Orpm and a two-stage propeller with a diameter of 18 crIL. Mi, Sodium silicate (Nano 0.75 noV1%SiO, /N
a2O molar ratio 3.30, specific gravity 1.14)'i and p
Adjusted to H13. Sodium silicate 14.81/hr.

Sulfuric acid (18.4 mol/l) approximately 510 ml/h
The pH was adjusted to 7 to 8 by flowing down at a ratio of r 2 , and the reaction was carried out for 300 minutes. The temperature during the reaction was maintained at 95°C. Subsequently, sulfuric acid was added to the reaction-completed solution to adjust the pH'i to 2.5. The silica concentration of this precipitated silica suspension is 50 f
/l. The suspension was filtered with a filter press, washed with water, and the by-produced sulfuric acid was removed over the sulfuric acid used for acidification. Some water was added to the resulting wet cake, stirred to form a slurry, and dried in a spray dryer (inlet heated air 250°C, outlet temperature 110°C). Approximately 9 ktj was obtained as product. The B specific surface area of the obtained product is 2
33Wt'/? .

The dry weight loss rate on ignition was 4.1 inches.

Example 2 The same reaction tank as in Example 1 was used, the stirring conditions were the same, the same concentration of raw materials was used, and the hot water was heated at 100 A! t-Preparation, pH 8
sodium silicate at 9.98 l/hr,
Add sulfuric acid K at 340ml/hr for 400 minutes,
I reacted. The reaction temperature was maintained at 90°C. Acidification and subsequent treatments were carried out in exactly the same manner as in Example 1. The weight of the obtained product is approximately 9 kg? Met.

Is the BET specific surface area of the product 268rt? /? The ignition loss rate on a dry basis was 4.3 inches.

Example 3 The product obtained in Example 2 was heat-treated for 1 hour in an electric furnace maintained at 430°C. After heat treatment, the product was left unsealed in the air for 40 hours to allow natural moisture absorption. Is the BET specific surface area of this thing 240ttV'? Therefore, the dry weight ignition loss rate decreased to 3.1%.

Comparative Example 1 Using the same reaction tank as in Example 1, the rotation speed of the stirrer was set to zoo
rpm and using both raw materials at the same concentration, hot water 1001
ft While adjusting the preparation pH to 12-13, add silicic acid (f)
”) Rum t 40 rhr, sulfuric acid about 1360 m
The reaction was carried out at a flow rate of 1 Ar. The temperature during the reaction was 80°C. Acidification and subsequent treatments were performed in the same manner as in Example 1. The weight of the obtained product was about 9 yu. The IT specific surface area of the product is 210nVt, and the dry weight loss rate is 4.9.
%Met.

Example 4 The product obtained in Comparative Example 1 was heat-treated for about 1 hour in a constant temperature dryer maintained at 450°C. After the heat treatment, the product was naturally sucked for 14 hours and left in a constant temperature and humidity chamber for about 30 hours at a temperature of 25° C. and a relative humidity of 70° C. to moisten the product. This product had a BET specific surface area of 135 i/r and a dry weight loss rate of 3.0%.

Example 5 The product obtained in Comparative Example 1 was heat-treated for about 1 hour in an electric furnace maintained at 250°C. After the heat treatment, the same moisture absorption operation as in Example 4 was performed. The BET specific surface area of the obtained product is 1
89 m''/7. The ignition loss rate on a dry basis was 3.4%.

Comparative Example 2 In the same reaction tank and under the same stirring conditions as Comparative Example 1, warm water 1
081 and commercially available No. 3 sodium silicate 30iO 1 (Si029%, 2/'Na2O molar ratio 3.2
) After charging i and raising the temperature to 80°C, for a total reaction time of 80 minutes, sulfuric acid (18.4 mol/l) was added, and the pH for t-
．． It was added continuously until it reached 0. Reaction temperature is 80℃±
It was maintained at 2°C. The reaction completed liquid was aged for 30 minutes at 80°C to obtain a precipitated silicic acid slurry.

This slurry was filtered, washed with water, and dried in the same manner as in Example 1 to obtain a product-like product. The iT specific surface area of the obtained product was 145→'1, and the ignition loss rate on a dry basis was 4.1%.

Example 6 The product obtained in Comparative Example 2 was heat-treated in a small kiln with a diameter of about 150 mm and a length of 3 m at an outlet temperature of 350°C. After the heat treatment, the sample was left in the air at room temperature for 48 hours for natural moisture absorption. The BET specific surface area of the product was 139 m1, and the ignition loss rate on dry basis was 3.0 cm.

Example 7 Precipitated silica Nipgil AQ having a BET specific surface area of 198 net t” (manufactured by Nippon Silikani Gyo Co., Ltd.)
(trade name) was kept at 350° C. in an electric furnace and heat-treated for 1 hour. After the heat treatment, the same natural moisture absorption as in Example 6 was performed. The BET specific surface area of the obtained product is 162 d/f
The dry weight ignition loss rate was 3.6%.

Comparative Example 3 The same precipitated silica as in Example 7 N1 psil AQ f was maintained at 600° C. for about 1 hour in an electric furnace. The moisture absorption treatment was also performed in the same manner as in Example 6. The obtained product had a BET specific surface area of 142 dm and a dry weight ignition loss rate of 1.8 dm.

Example 8 BET specific surface area 165, current precipitation method silica N1 psil
NS (manufactured by Nippon Shirigani Gyo Co., Ltd.: trade name) was treated at 450° C. in the same small kiln as in Example 6. After the heat treatment, it was maintained at 25° C. and a relative humidity of 90 in a constant temperature and humidity chamber for 24 hours.

The BET specific surface area of this product was 159 inches, and the dry weight ignition loss rate was 2.7 inches.

Comparative Example 4 Precipitated silica Njpsil having a specific surface area of 98 nitrates
It was treated at 500° C. for 1 hour in an ER (trade name, manufactured by Nihon Shirikani Gyo Co., Ltd.) electric furnace. After the treatment, it was left open to the atmosphere for 40 hours. The specific surface area of this product is 96d/
7. The dry weight loss on ignition was 2.0%.

Table 1 shows the BET comparative surface area and dry weight ignition loss of the precipitated silicas of Examples 1 to 8, Comparative Examples 1 to 4, and three other comparative examples.

Next, as Examples 1 to 8, Comparative Examples 1 to 4, and other comparative examples as described above, commercially available precipitated silica N1 psil AQ% N1 psil NS (manufactured by Nippon Silikani Gyo Co., Ltd.: trade name) and Hisil 23
Comparison of elastomer reinforcing effect and tests on dispersibility of No. 3 (trade name, manufactured by PPG, USA) were conducted in accordance with the following procedures, and the measurement results are shown in Table 1 above.

(1) Compounding test for styrene-butadiene rubber SBR1502 100 parts by weight Various precipitated silica 4ol Stearic acid 2I Anti-aging agent (2%/ferraphenol PEG (polyethylene glycol) 3I ZnO (zinc white) 5I Accelerator DPG (dicarg L) 2I accelerator DM (dibenzothiazyl disulfide) 1.5# Silane coupling agent (S 1-6g Degussa product name) 41 Sulfur 0.51 or more, set at 80℃ with circulating water capacity 1,
In a 71OB Banbury mixer, the ingredients excluding sulfur were sequentially added and kneaded at 40 revolutions for 5 minutes. The mixture taken out from the Banbury mixer was mixed with sulfur using an 8-inch test roll, kneaded for 5 minutes, and then formed into a sheet. The crystal was vulcanized by steam heating press at 150° C. for 30 minutes. The vulcanizate was measured for elongation, tensile strength, and 200% tensile stress in accordance with JISK 6301.

(2) Compound test composition for nitrile rubber Compound Hyfka-1i42 (product name manufactured by Nippon Zeon Co., Ltd.) 1
00 parts by weight Stearic acid II
Zinc white No. 3 51 Io
cormorant
2I Accelerator DM (-8/Sobi Kakaku M. Phyto) 1.5 1 Accelerator TS (Tetramethylthiuram monosulfide) 0.5'TEA () Reethanolamine) 21 Various silica
50 1 Silankatugunon Denj (Si-59: mentioned above) 21 Cross-wire conditions Using 8 inch x 1 finch test roll, Rotating board ratio 1:
1.2, front roll l 7 rpm, roll temperature 50-6
The mixture was kneaded at 0° C. for about 15 minutes.

Vulcanization conditions A steam heating press was used, and the vulcanization temperature was 150°C; the vulcanization time was 20 minutes.

The physical properties of the vulcanized product were measured in accordance with J-S K-6301, and the abrasion test was performed using an Akron type, 15o% inclination, 6-bond load, 400 pre-slips, and abrasion volume reduction after 1000 rotations in the main test. did.

(3) Compounding test mix for butadiene rubber
Combined JSRBROI (product name manufactured by Japan Synthetic Rubber Co., Ltd.) 1
00 parts by weight Stearic acid 11 Zinc white No. 3 5I accelerator D(-
)'7: Resistance -?)11 Accelerator DM (dibenzothiazyl disulfide)
1.5#DEC (diethylene glycol) 3
1 Shirankatugunonk 1f (St-6c+: mentioned above)
2g various silica
50 1
1.51 Crosstalk conditions Same as nitrile rubber test.

Vulcanization conditions: 150℃ x 1 using the same vulcanization press as nitrile rubber.
Vulcanization was performed for 5 minutes.

The physical properties of the vulcanizate are measured in the same manner as for nitrile rubber.

<4) Compounding test mix for silicone rubber
The mixture was mixed with various types of silica, 40' processing aid (methoxy group-containing polydimethylsiloxane), 21 mixed wire conditions, and kneaded on a 6 inch x 13 inch test roll at 20°C for 5 minutes.

Vulcanization conditions Primary vulcanization was performed at 160°C for 10 minutes using a steam vulcanization press, and secondary vulcanization was performed at 200°C for 4 hours using an electric oven.

Measurement of physical properties of vulcanizates It was conducted in accordance with JIS K 6301.

(5) Test for dispersibility Regarding the dispersibility of the filler in the elastomer, the mixing time of the blend is compared with the measurement of the physical properties of the vulcanizate, and the time required to reach complete mixing is used as a measure of dispersibility. Measured using

Specifically, according to the styrene-butadiene rubber compound listed in (1), a B-type Banbury mixer (capacity i11.71) was used.
After setting the inside of the rubber to 80°C, the rubber was put in and masticated for 30 seconds, and in the next 15 seconds, the precipitated silica of Example 1.3.4.6 and Comparative Example 1.2.3 ~ and others were mixed. All of the compounding agents were changed to input sand. Each of the removed formulations was sheeted out for molding using an 8 inch x 1 finch test roll. The training time by roll was unified to 2 minutes.

The sheets were press-vulcanized at 150° C. for 30 minutes using a steam heating press, and their tensile strengths were measured and compared in accordance with JIS K 6301.

The results are shown in Table 2 and FIG.

Table 2 The results of the above examples, comparative examples, and nidistomer formulation examples can be summarized as follows.

According to this example, the relationship between the BIT specific surface area and the ignition loss rate on a dry basis is included in the present invention.The precipitated synthetic silica has a reduced amount of bound water compared to commercially available or commonly synthesized precipitated synthetic silica. It has been demonstrated that by blending this material into an elastomer, it has a high reinforcing effect, and it has also been demonstrated that the dispersibility is improved.

This unprecedented high reinforcing property provides a high quality, freely colorable elastomer, and the improved dispersibility is expected to improve workability.

〔Effect of the invention〕

The precipitated silica that falls within the scope of the present invention has the property of having reduced bound water compared to commercially available or commonly synthesized precipitated silica, and by blending this into an elastomer, it has a high Has a reinforcing effect.

Further, dispersibility is improved.

By using this unprecedented highly reinforcing precipitated silica, a freely colorable elastomer-vulcanized product is provided, and dispersibility is improved, resulting in improved efficiency in terms of vulcanization properties, workability, and processability. Improvements such as these can be obtained, and its usefulness is extremely significant.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing specific ranges regarding the properties of the precipitated silica of the present invention, and FIG. 2 is a diagram showing the measurement results of a dispersion test regarding styrene-butadiene rubber. Figure 1 BET Shell - Maru A #Dragon Figure 2 012.54,5 滉諌@l'! ! 'l (intermediate)

Claims (1)

[Claims] Ignition loss rate (%) on a dry weight basis measured in accordance with JIS K-5101 and K-8885: I = ([105°C 2 hours dry weight (g)] - [900°C
1 hour ignition weight (g)])/[105°C 2 hour dry weight (g)] x 100 BET specific surface area by nitrogen adsorption method (m
^2/g): Precipitation method synthetic silica I for elastomer reinforcement filling, characterized in that the relationship of S satisfies the following formula:
aS+b where a=5.3×10^-^3 1.77≦b≦3.00 100≦S≦300