Silicones and Silicone-Modified Materials - American Chemical Society

Chapter 36

TOSPEARL: Silicone Resin for Industrial Applications 1

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on June 14, 2016 | http://pubs.acs.org Publication Date: May 4, 2000 | doi: 10.1021/bk-2000-0729.ch036

Robert J . Perry and Mary E . Adams

2

2

1General Electric Company Silicones, 260 Hudson River Road, Waterford, N Y 12188 General Electric Company C R D , P.O. Box 8, Schenectady, N Y 12301

Tospearl particles are crosslinked siloxanes made by the controlled hydrolysis and condensation of methyltrimethoxysilane. Their spherical nature, narrow particle size distribution and chemical and thermal stability make them ideal for use in wear resistance, antiblocking and light diffusing applications.

Tospearl is a spherical silicone resin particle made by the controlled hydrolysis and condensation of alkyl trialkoxysilanes (equation 1) and produced by Toshiba Silicones, a joint venture of G E Silicones. The first report of these materials appeared in 1985 when the aqueous amine catalyzed condensation of methyl trimethoxysilane was described (1). Since the initial disclosure, a number of other patents have issued in this area (2-8). The product is a three-dimensional network that is intermediate between inorganic and organic particles. This paper describes the physical and chemical properties of this network as well as its utility in a number of applications.

Me RO-Si-OR

H 0

NH

Me 3

2

OR

-H Q

HO-Si-OH

2

OH l

i O

I

OH

Me l

Me - S i - O - S i - 0 i OH

0 1

V

l

'

-Si-O-V Me

Me

-fo-si-o} o (1) Preparation There are a number of grades of Tospearl produced with sizes ranging form submicron to 12pm.

Each of these materials has its own characteristic production process but the

© 2000 American Chemical Society

Clarson et al.; Silicones and Silicone-Modified Materials ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

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common thread is that reaction to form the Tospearl particle occurs at the silane/water interface (Figure 1). As the silane hydrolyzes, it becomes soluble in the aqueous phase where it undergoes condensation. As the silanol condenses, it becomes insoluble and precipitates. The particle size and distribution are affected by base concentration, stirring rate, paddle shape, vessel size, temperature and solids concentration. When the correct balance between all these parameters is achieved, monodisperse, spherical beads form.

interface Tospearl particles

Figure 1. Tospearl kettle. Figure 2 shows the effect of stirring rate and ammonia concentration on the particle size. The stirring rates increase from 1 to 4 (a range of 2-60 rpm) and at the slower rates smaller particles are formed. As the rate increases, the particles become larger. At a constant stirring rate, the particles grow to a larger size at lower ammonia concentrations.

c o o J ,

•

Ratel

•

Rate 2

A Rate 3

CD N

•

55

Rate 4

Q

o '€ 0. I

I

I I 11

10

100

N H Concentration (10 N) 2

3

Figure 2. Effect of Stirring Rate and N H 3 Concentration on Particle Size.

In a separate set of experiments, Figure 3 illustrates the effect the methyltrimethoxysilane/ water ratio has on the particle size. The largest particles were formed at high silane/water rations at a given base concentration. However, a maximum was seen in the base range examined.



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Figure 4 outlines the process for product isolation. After the particles are formed, the reaction mixture is filtered to remove gel from the suspension. The filtrate is then subjected to another, finer filtration and the resulting filter cake is dried at ~ 2 0 0 ° C to give the isolated resin. During drying, some fusing of particles occurs resulting in a loose network structure. This is broken up by jet milling the clusters; a process in which aggregates are propelled at a conical ceramic plate at high speeds. MeSi(OR)

1

k.

3

Hydrolysis filter filter and Condensation

Wet Resin

dry

Dry Resin

jet milling p

TOSPEARL

NH,

Figure 4. Tospearl Process

Properties Table 1 shows some of the characteristics of the various grades of Tospearl that can be produced by this method. Diameters from 0.5m to 12 m can be obtained with the smaller particles having high specific surface areas and low bulk specific gravities. With the exception of 2000B and 240, all the particles have narrow particle spheres. Tospearl 2000B is still spherical, but has a broader size distribution centered at 6m. The amorphous 240 grade has a rounded, irregular shape. These materials are pH neutral and have low moisture content.


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Table 1. Characteristics of Commercial Tospearl Grades Tospearl

Diameter (|im)

Bulk sp. gr.

Specific Surface Area (m /g)

105 120 130 145 3120 240

0.5 2.0 3.0 4.5 12.0 4.0 (amorphous)

0.25 0.35 0.36 0.43 0.46 0.17

70 30 20 20 18 35

2

Figure 5. Particle Size Distribution for Tospearl. 120.

Electron micrographs o f these materials are shown in Figure 6. One can see the spherical nature o f the particle as well as the mono-disperse nature of the beads. A s expected for a material that is primarily inorganic, the thermal stability o f the silicone resin spheres is extremely high, especially when compared to fine organic particles, as shown i n Figure 7. Tospearl 120 was stable to 4 0 0 + ° C in air and at 800°C, there was only 10% weight loss. The weight loss seen at 450 °C is attributed to further condensation within the particle with loss o f water and/or methanol. Tospearl particles are also readily dispersed i n a variety o f solvents. Table 2 shows the dispersion viscosity o f Tospearl 120 i n polar and nonpolar solvents. In polar ketone, alcohol and ether solvents, the viscosities are quite low. When nonpolar or chlorinated solvents are used, the dispersion viscosities rise by an order o f magnitude. The polar solvents more readily associate with the residual silanol groups on the Tospearl particles effectively isolating them from self-association. In non-polar solvents, self-association is possible and the viscosity rises accordingly.



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Figure 6. Micrographs of Tospearl Particles.

&

W

o _J

o-

—

20-

i

•

40-

Tospearl 120

-C

i

60"m 55 -> 80-

1

":

- - - Acrylic Resin powder

\ 200

400

600

800

Temperature (°C)

Figure 7. Thermogravimetric Analysis of Tospearl 120 and Organic Resin Fine particles.



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Table 2. Dispersion Viscosities of Tospearl 120 at 50 wt % . Solvent Dispersion Viscosity (cP) 5-10 Ketone-based Ester-based 15-20 10 Alcohol-based (CI-2) Alcohol-based (C3-4) 20-28 Glycol-ether-based 20-25 25 Diacetone alcohol Tetrahydrofuran 20 220-230 Aromatic Hydrocarbon-based 370 n-Hexane Kerosene Perchloroethylene

280 260

Chloroform

640

Applications Tospearl particles have found widespread use in a number of varied applications. These materials improve wear, water and chemical resistance and modify the slip properties of rubber surfaces. In the paint and ink arena, Tospearl has been used as a dispersing agent and to adjust viscosity as well as to prevent blocking and pigment hardening and as luster control. The cosmetic industry uses these particles to improve the feel of foundations, to prevent the caking in lipsticks and in hand and body creams. Figure 8 gives a brief overview of the particle sizes commonly used in a variety of applications. Table 3 also shows the specific types of Tospearl that have been utilized in lubrication, anti-blocking and light diffusing environments. The "A" designation indicates a Tospearl grade suitable for personal care applications.

Particle Diameter (urn) 0.5!

1.0

2.0

10

5.0 < Plastic sponge >

.

< Plastic film and sheet >

< Cosmetics >

_ < Paint and ink >

< Lubricating oil >

< Back coating > ~"

^

• ^

< Delustering coating > < Household products > ^ ^< Gas barrier coating > ^ < Light diffusing plate >^

Figure 8. Application vs. Particle Size.


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Table 3. Function and Applications of Tospearl particles. Function Matting

Application Paint, Ink, SHC Back coat for color ribbon Gravure ink Gas barrier coating Car wax Organic photoconductor drum OPP Film Cosmetics (foundations) Weatherstrip coating Gas barrier coating Paint, ink Liquid crystal display Acrylic resin Polycarbonate resin PET resin Cosmetics (foundations) Cosmetics (foundations)


Lubrication

Anti-blocking

Light Diffusing

Flowability Anti-agglomeration

Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl Tospearl

Product 120, 130, 145,240 105, 120 105, 120 120, 130, 145 120, 130, 145 120 120, 130, 145 120A, 130A, 145A 120, 130, 145 120, 130, 145 120, 240 120, 130, 145 120, 130, 145 120, 130, 145 120, 130, 145 120A, 130A, 145 A 120A, 130A, 145A

Tospearl has also been used to increase the abrasion resistance o f weather stripping (Table 4). Untreated E P D M base rubber abraded easily. When treated with a curable silicone, the abrasion resistance increased by an order o f magnitude and the friction was halved, but a glossy rather than the desired matte finish was obtained. Addition o f Tospearl 120 or 145 improved the abrasion resistance another 6-8 fold and the friction coefficient decreased 4-8 times. In addition, the rubber took on a matte appearance. If the particles were too large, as with Tospearl 3120, the abrasion resistance decreased.

Table 4. Results of Treating Weatherstripping with Tospearl. Weatherstrip Condition Untreated Treated Treated w/120 Treated w/145 Treated w/3120

Appearance matte glossy matte matte matte

Friction STATIC 2.1 1.5 0.4 0.2 0.1

Coefficient DYNAMIC 2.0 1.3 0.3 0.2 0.1

Abrasion Resistance* 500 5,000 30,000 40,000 20,000

* number of strokes

Tospearl has been used as a plastic film additive i n polypropylene (PP). A specific example is shown i n Table 5 where Tospearl 120 was incorporated into a single P P sheet. One third less Tospearl was required when compared to silica to obtain the same anti blocking properties. In addition, the static slip was half as large.


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Table 5. Evaluation of Tospearl in a Single PP Sheet, Properties Base Resin Antiblocking Agent Particle Size


Particle Content Thickness

New Formulation Homo PP Tospearl 120 2 nm 240 ppm

Old Formulation Homo PP Silica 1 fim 900 ppm

30 urn

30 pm 1.8% (ASTM D 1003) 0.50 (ASTM D 1894) 780g/10cm2

Haze Static Slip (Film/Film) Antiblocking Property

1.4% 0.25 800g/10cm2

In a coextruded film (Figure 9) with the same Tospearl loading as silica, the resulting material had a two-fold increase in anti-blocking properties and a 70% reduction in static slip (Table 6). ,

TOSPEARL

Random PP

!

)

/ •

•

a • •

•

• \

Homo PP Random PP

Figure 9. Coextruded Polypropylene Film.

Table 6. Evaluation of Tospearl in a Coextruded PP Film. Properties Core Layer Skin Layer Antiblocking Agent Particle Size Particle Content Thickness haze Static Slip (Film/Film) Antiblocking Property

New Formulation Homo PP Random PP Tospearl 120

Old Formulation Homo PP Random PP Silica

2 iim 2000 ppm 22 jim 1.8% 0.15 150g/10cm2

3 nm 2000 ppm 22 jam 1.6% (ASTM D 1003) 0.48 (ASTM D 1894) 360g/10cm2

Table 7 shows a polycarbonate (PC) resin which was treated with Tospearl to provide an improved light diffusing sheet (9). At only 40% of the barium sulfate level, the Tospearl treated sheet allowed more light through and the light was better dispersed than the conventional additive. The mechanical integrity of the PC sheeting was also retained as shown by the mechanical measurements.


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Table 7. Evaluation of Tospearl in a Polycarbonate Film. Properties Polycarbonate Resin Antiblocking Agent Particle Content Thickness Izod (kg.cm/crm) Tensile Strength (kg/cni2) Haze Light Transmission

Old Formulation 100 parts CaCCb 2 parts 1 mm 80.0 630 80.2% 70.5%

New Formulation 100 parts Tospearl 120 0.2 parts 1mm 89.0 630 92.4% 75.9%

Table 8 also shows a light diffusing application using acrylic sheeting. Again, more light is transmitted and is more diffuse (10). Table 8. Evaluation of Tospearl in a P M M A Sheet Properties Base Resin Antiblocking Agent Particle Content Thickness Total luminous transmittance Diffusing luminance Parallel luminance

New Formulation PMMA Tospearl 120 1.0% 1 mm 95.6% 90.3% 5.0%

Old Formulation PMMA BaS04 2.5% 1 mm 83.7% (ASTM D 1003) 78.4% 5.1%

In addition to the examples noted above, these spherical silica particles have found use as additives i n other P M M A (11-13), PP (14-15), P E T (16), P V C (17) and P E (18) formulations. A l l applications described thus far have utilized untreated Tospearl particles. Although extensive condensation occurs during the synthesis o f these particles, some silanol groups remain on the surface. The following two examples illustrate the ease with which the Tospearl surface can be modified. The surface o f Tospearl 120 can be rendered more hydrophobic by treatment with hexamethyldisilazane ( H M D Z ) or trimethylchlorosilane (TMSC1) as shown i n Table 9. Hydrophobicity is determined by the amount o f material that is "wetted" by the solvent mixture and settles out during centrifugation. 4 5 % o f the untreated particles are wetted by a 60/40 methanol/water mixture. After hydrophobizing the surface, less than 5% were "wetted" (19). Table 9. Treatment of Tospearl 120 with Hydrophobizing Agents. Methanol/Water Ratio 60/40 80/20

HMDZ 25°C/15 h 3 50

HMDZ 160°C/6 h 0 30

TMSCI 25°C/16 h 4 51

Untreated


45 100

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In another application, the surface charge could be altered by treatment with aminoethylaminopropyltrimethoxysilane as seen i n Table 10 (20). The greater the amine loading o n the surface, the greater the positive charge. Numerous other examples o f surface treatments have also been reported (21-25).


Table 10. Treatment of Tospearl with Aminoethylaminoproptltrimethoxysilane. Surface Treating Agent Solution Aminosilane (parts) Methanol (parts) Contact Charge (pC/g)

Example 1

Example 2

Example 3

Untreated

1 19 +150

2 18 +270

10 10 +330

-950

Summary The spherical silicone resin particles described above are made by the hydrolysis and condensation o f methyltrimethoxysilane. These materials are chemically inert, thermally stable and available i n a variety o f sizes with a narrow particle distribution. Specific examples have illustrated how a number o f diverse industries have used these particles for wear resistance, anti-blocking properties and light diffusing ability and h o w the surface characteristics can be modified. Other applications can also be favorably impacted by these unique materials. The options are only limited by your imagination.

Acknowledgments W e thank H . Kimura, A . Takagi, M . Y o y a , M . Nishida, M . Iwasaki, T. Sugito, Y . Kasahara, M . Matsumoto, A . Home, J. Russell and K . Murthy for supplying valuable reference and application information.

References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Kimura, H., U S 4,528,390 to Toshiba Silicone Co., Ltd., 7/9/85. Jpn. K o k a i Tokkyo Koho, JP 61221520 to Toshiba Silicone Co., Ltd., 9/19/86. Jpn. K o k a i Tokkyo Koho, JP 61247345 to Toshiba Silicone Co., Ltd., 10/29/86. Jpn. K o k a i Tokkyo Koho, JP 62129840 to Toshiba Silicone Co., Ltd., 5/28/87. Jpn. K o k a i Tokkyo Koho, JP 63069712 to Toshiba Silicone Co., Ltd., 3/25/88. Jpn. K o k a i Tokkyo Koho, JP 05239365 to Toshiba Silicone Co., Ltd., 2/26/91. Jpn. K o k a i Tokkyo Koho, JP 03047840 to Toshiba Silicone Co., Ltd., 2/28/91. Jpn. K o k a i Tokkyo Koho, JP 05140314 to Toshiba Silicone Co., Ltd., 6/8/93. Ohtsuka, U.; Fugiguchi, T.; Oishi, K. U S 5,352,747, to GE Plastics, Japan, Ltd., 10/4/94. Jpn. K o k a i Tokkyo Koho, JP 9316002 B to Asahi Chemical Co., Ltd., 1993 Jpn. K o k a i Tokkyo Koho, JP 3207743 to Misubishi Rayon., 11/11/91.


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12. 13. 14.


15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

Jpn. K o k a i Tokkyo Koho, JP 3273046 to Misubishi Rayon., 12/4/91. Jpn. K o k a i Tokkyo Koho, JP 3294348 to Misubishi Rayon., 12/25/91. M i z u n o , H.; Fujiwara, K . U S 4,769,418 to Misubishi Petrochemicals C o . , Ltd., 9/6/88. Jpn. K o k a i Tokkyo Koho, JP 9020845 to Mitsui Toatsu Chemical C o . , Ltd., 1/21/97. Etchu, M.; Murooka, H., U S 5,620,774 to Teijin Ltd., 4/14/97. Jpn. K o k a i Tokkyo Koho, JP 1103440 to Kohjin C o . , Ltd., 4/20/89. Jpn. K o k a i Tokkyo K o h o , JP 9059457 to Mitsui Toatsu Chemicals C o . , L t d . , 3/4/97. Saitoh, K.; Kimura, H., U S 4,895,914 to Toshiba Silicones C o . , Ltd., 1/23/90. K i m u r a , H.; Takagi, A., U S 4,871,616 to Toshiba Silicones C o . , Ltd., 10/3/89. Sumida, H.; Kimura, H., U S 4,652,618 to Toshiba Silicones Co., Ltd., 3/24/87. Saito, K.; Kimura, H., U S 4,996,257 to Toshiba Silicones C o . , Ltd., 2/26/91. Saito, K.; Kimura, H., U S 5,034,476 to Toshiba Silicones C o . , Ltd., 7/23/91. Saito, K.; K i m u r a , H., U S 5,106,922 to Toshiba Silicones C o . , Ltd., 4/21/92. Saito, K.; Kimura, H., U S 5,204,432 to Toshiba Silicones C o . , Ltd., 4/20/93.


Silicones and Silicone-Modified Materials - American Chemical Society

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