DE1230562B - Process for the production of polysiloxane elastomers - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

C08g

German class: 39 b -22/10

Number: 1230 562

File number: D 43776IV c / 39 b

Filing date: February 29, 1964

Opening day: December 15, 1966

The invention relates to a process for the production of polysiloxane elastomers of high aging resistance in non-closed systems and with improved mechanical properties below Use of finely divided oxides of silicon.

To obtain useful mechanical properties of polysiloxane elastomers, - is similar as with many other types of synthetic rubber - an addition of reinforcing fillers is necessary. The best Results are according to known methods with highly active silica fillers, which optionally can still have a content of titanium dioxide, achieved.

It is also known to make the hydrophilic surface of a precipitated, hydrated silica hydrophobic, by treating them in the precipitation suspension with organohalosilanes or directly and precipitates from water glass solution with the addition of mineral acid. The pyrogenic route, e.g. B. from the Vapor phase hydrolysis of silicon tetrachloride or by reducing quartz with carbon in an electric arc furnace and by subsequent oxidation with hot air gases, leave silicon dioxide produced transform into hydrophobic fillers by vaporising organohalosilanes. As a result of her Hydrophobicity can then be incorporated into elastomers relatively easily and lead to them to vulcanizates with relatively good mechanical properties.

When determining these property values, however, it often turns out that one obtains large scatter, which make reproducibility difficult. This applies in particular to the aging resistance required in practice of polysiloxane elastomers in storage. However, this resistance to aging is at the previously used fillers are not yet available to a satisfactory extent. According to experience they are stored for some time before vulcanization and age, become tight, and have to then replasticized, d. H. the previous plastic state must be restored by rolling and kneading getting produced.

In order to avoid the aforementioned disadvantages and to improve the rubber properties according to a known method the use of rare earth oxides as heat stabilizers together with highly dispersed silicic acid and diphenylsilanediol as anti-lock protection in mixtures recommended with polysiloxanes.

The invention was based on the object of providing a process for the production of polysiloxane elastomers of high aging resistance in a non-closed process for the production of
Polysiloxane elastomers

Applicant:

German gold and silver refinery
formerly Roessler, Frankfurt / M.

Named as inventor:

Dr. Hanns Biegler, Wesseling;

Dr. Helmut Brünner, Rheinfelden (Bad.);

Dr. Horst Ferch, Hanau;

Gottfried Kallrath, Brühl-Vochem

These systems using such finely divided oxides of silicon from organopolysiloxanes, organic Peroxides and usual additives indicate which the vulcanizate one of the requirements of the Aging resistance adapted to practice in non-closed systems with simultaneous improvement give the mechanical properties without any special additions of z. B. Oxides Rare earths are required as heat stabilizers.

The characteristic is to be seen in the fact that highly dispersed oxides of silicon, which by treatment have been made hydrophobic with organic silicon halogen compounds in such a way that they only have a low silanol group density can be used.

It has been found that when silicon dioxides modified in this way are used In polysiloxanes that are detrimental to elastomers, the replasticizing work is unnecessary because the mass does not change during storage. With the use of such hydrophobized silicas but it is also possible to increase the degree of filling compared with the use of unmodified fillers achieve and thereby also improve the mechanical properties of the vulcanizate, advantages, which are not or only slightly

609 747/354

3 4

Sufficiently hydrophobized silicon dioxides by no means niche values in the case of air aging were not to be expected so strongly. The possibility of a higher sink rate than when using non-hydrophobic fillings in elastomers is fillers with the same Shore hardness,
possible, which is also little affected by aging. The one with a hydrophobized silica 5 example
Acid-filled polysiloxane elastomers together

in storage less than those with non-hydro- I _n per 100 parts of a commercially available silicone

phobic fillers. rubber raw material at roller temperatures

Can be incorporated between 20 to 30 ° C with the addition of dicumyl fillers than usual therefore to the same Shore hardness more and receives at these i ° peroxide (95 ° / _o solution) 35 parts of a fumed recovered higher-filled vulcanizates the same Tear - hydrophilic silica (A), in a second batch strength, higher elongation at break and almost 35 parts of a pyrogenically obtained hydrophobic double tear strength. In addition to the improvements in silica (B), 35 parts in a third batch in terms of aging resistance and in the mechanically hydrophobic, non-tempered, fine-particle silica properties, the higher filling acid (C) and in a fourth batch also make it cheaper to the same extent of the end product. Mixing ratio the same but tempered one used for the filling of silicone rubber product (D) incorporated.

expedient silicon dioxides which, according to the German Auslegeschriften, deliberately dispensed with these four comparative substances, 20 the differences between the individual fillers and is based on precipitated or thermal substances produced to stand out more clearly.
Silicon dioxides with a specific surface area to fluctuate in the determination of the eigenfrom 50 to 300 m ^a / g. To exclude the complete dependency values in vulcanizates, saturation of a silica with, for example, 200m ² / g, the mixtures were stored at room temperature for at least 8 days before vulcanization, determined according to BET-25, plasti method for short (surface dimension according to Brunauer The mixtures were E mm et and Teller [see I. Amer. Chem. Soc, 25 minutes at 150 ^° C. under a specific 60, p. 309, 1938]. The BET surface area is determined plate pressure of 70 kg / cm ^2. Then, by measuring the temperature of the liquid ßend, the vulcanizates were post-vulcanized for 6 hours in the circulating nitrogen in the high vacuum of the surface adsorber cabinet at 200 ° C,
bated nitrogen or noble gas), are z. B. about In the table below, with the same 14 g of dimethyldichlorosilane per 100 g of the hydro-filling degree, the different behavior of the phobating silica or corresponding amounts of different silicas in polysiloxane elastomers of other organosilanes is required. That corresponds to the expression. There are silicone vulcanizates with a trap of dimethylchlorosilane about 2.2% C in the hydro- 35 a hydrophilic fumed silica (A), the phobic product. Such a hydrophobized silica described above has a specific acid (B) and the hydrophobic precipitated unge surface of 144 m ² / g after tempering and still has a silanol tempered (C) and tempered silica group density within the range from 0.1 to other compared.

1.0 / 100 Å ² , preferably from 0.21 OH / 100 Å ² . 40 When using the latter two

For the mentioned range of 0.1 to 1.0 OH / 100 Å ² silicas (C) and (D) observed effects, the

If the carbon content in the hydrophobic product was not to be expected without further ado, go out

when using dimethylchlorosilane between 1 lines II, 3, 8, 10. It must be surprising

and 3% vary. By using others that after a circulating air aging at 275 ° C after

Halosilanes can have a higher carbon 45 6 days or such a high elongation at break of 220%

content obtained without giving the silanol group density.

is significantly influenced and without the mechanical properties. If one compares the tensile strength according to this

frilled properties of the vulcanizate are essential to the aging process, so one finds for the product (A)

to be changed. However, it is preferable to use extremely high values. However, these numbers are

Dimethylchlorosilane. 50 fictitious insofar as the material is largely embrittled

The benefits that result from the incorporation of and for practical purposes due to this are high

Almost completely hydrophobic and tempered silica brittle can no longer be used,

acid during processing with silicone rubber, tensile strength and elongation at break were after

result, are explained using an example in which the DIN 53 504 according to St II by means of an electronic

different behavior of pyrogenically obtained tearing machine was determined at room temperature. the

hydrophilic silica (A), obtained from pyrogenic extraction speed was 100 mm / min. the

Nener and hydrophobized silica (B), the Shore hardness was determined according to DIN 53 505,

a precipitated, hydrophobized but unannealed With the same degree of filling (26 percent by weight)

Silicic acid (C) and finally the same, but the vulcanizate (D) only gives a Shore hardness of 37. Tempered silica (D) in polysiloxane elasto- 60 um to the Shore hardness of the vulcanizates (A) and (B)

mers with the same degree of filling facing each other, it is possible to use considerably more filler

is posed. to interfere. The strength of such more highly filled

This clearly results in the better behavior of a vulcanizate (D), experience has shown that it is quite the same

hydrophobized and tempered at 400 to 600 ° C, the tensile strength of the vulcanizate (A), however Silicic acid in the so-called air aging and 65 increases the tear resistance again, so that a

the better temperature resistance in not nearly doubling the tear resistance

closed systems compared to the other silicon room temperature is observed. This point is

dioxide fillers. It shows that the mecha- for practice is particularly important.

1 230 562
5
Table I. dimension Tensile strength
Elongation at break
Shore hardness A kp / cm ^a
0 /
/O
i. E. Tensile strength
Elongation at break
Shore hardness A kp / cm ²
O/
/ 0
i. E. Tensile strength
Elongation at break
Shore hardness A kp / cm ²
O/
/ 0
iE Tear resistance
Tear strength after 1 day at ⁰ to +275 C kp / cm
kp / cm A.
35 teU Values of
B.
35 teU 6th elastomer «
D ₁
35 teU 1
D ₂
45 teU Test conditions Minutes
Minutes 1 day of air aging 6 days of air aging unaged 12th
10 10
2 PolysUoxan
C.
35 parts 8th
0.5 10
0.5 I.
II Mixing time
Plasticizing time after 12 days unaged 8th
0.5 70
280
54 75
350
45 55
600
42 70
550
59 1
2
3 + 275 ° C 50
400
45 34
160
48 45
200
40 36
450
41 35
400
52 4th
5
6th + 275 ° C 32
340
43 50
20th
80 35
30th
80 30th
220
52 35
200
65 7th
8th
9 30th
200
46 10
10 12th
13th 16
13th 18th
14th 10
11 co co
T-I T-I

The table shows the different behavior of hydrophilic (A) and hydrophobic (B) and (C) silicas particularly evident in the aging behavior in non-closed systems, with between Pyrogenic and precipitated hydrophobic silicas also show a different behavior is.

In a further comparative experiment, the modes of action of an application of oxides became less frequent Earth together with highly disperse silica by the known method mentioned at the beginning investigated the procedure according to the invention, the results of which are shown in Table II.

For this experiment, cerite oxide, type A 1, obtained from monazite sand was used (supplier: Auer-Remy sales group rare earths. H. Blum & Co., K. G., Hamburg).

This cerite oxide type consists of:

CeO ₂ 46.5 to 48.5 ° / ₀

Pr ₆ O ₁₁ 5 to 6%

Nd ₂ O ₃ 17 to 20%

Sm ₂ O ₃ 2 to 3.5%

La ₂ O ₃ and other rare species
Earth rest

based on the total oxide content of the goods of 99%

Filler, cerite oxide and diphenylsilanediol were worked into the silicone rubber on the mixing roller and the mixtures were stored in a heating cabinet at 110 ° C. for 1 hour. After cooling, the peroxide was added. After another 24 hours storage time, the mixtures were plasticized, pressed into sheets and vulcanized in the press 100 minutes at 125 ⁰ C. The secondary curing was carried out for 1 hour at 15O ⁰ C and 24 hours at 25O ⁰ C. The test specimens according to DIN 53 504 (Normstab II) punched out of these plates were then stored in desiccators for 6 days at 25 ° C. and 75% relative humidity. The following was checked:

1. after the samples have been taken from the desiccator (lines 1, 2 and 3 of the table)

2. after melting the samples in glass tubes and heating them to 250 ^° C. for 24 hours (lines 4, 5 and 6 of the table) and

3. after 3 days of aging in a circulating air cabinet at 275 ° C (lines 7, 8 and 9 of the table).

From the table it can be seen that with the glass tube aging (lines 4 to 6) by adding either Diphenylsilanediol (D) or from cerite oxide (E) each hydrophilic pyrogenically obtained by itself Silicic acid no improvement compared to the mixtures that do not contain additives (C) and (F), is to be determined. By combining the two additives (I), (K) and (L), the expansion values after glass tube aging can be determined noticeably improve, with an optimum at 6 to 8% cerite oxide. The use of a hydrophobized Silicic acid (column M and N of the table) gives poorer results in this test. It is however, it is already known that non-hydrophobic precipitated silicas can also be aged in a closed environment System produce poorer mechanical properties than pyrogenic silicas.

In contrast, at an aging in a circulating air cabinet after 3 days at 275 ⁰ C a significant improvement in elongation at break and the hardness when using a hydrophobicized precipitated silica in place of pyrogen-derived hydrophilic silica is added.

(Compare columns D and F with M and N in rows 7, 8 and 9, respectively). Similar improvements can be made but also by adding diphenylsilanediol (D) or cerite oxide (E) and (H) or both Achieve additions together (I) and (K). In the latter case, one again recognizes a from the experiments Optimal at 6 to 8% (I) and (K) cerite oxide. At 10% cerite the ductility falls to a very low level Value from (L).

The soft rolling times (plasticizing times) determined on the test mixtures that result from a use of diphenylsilanediol as protection against hardening of the unvulcanized mixtures

IO

Shortest plasticizing times can be reduced, can be seen from line 10 of the table. As can be seen, this advantage is also achieved according to the invention Use of hydrophobized, precipitated silica instead of pyrogenic silica, even without it other additives achieved.

The additives required according to the prior art can be used by the method according to the invention to achieve improved manufacturing conditions and properties of silicone elastomers under stress ceased to exist in non-closed systems, which is an essential labor and Material savings are guaranteed.

Table II

A. B. C. D. E. F. G H I. K L. M. N I. Trial number 4193 4190 4192 4194 4189 4191 4186 4187 4188 4201 4200 II degassed dimethyl polysiloxane with ge low content reactive groups Teüe 100 92 100 100 92 100 92 92 92 100 100 III pyrogenic hydrophilic Parts 40 40 40 40 40 40 40 40 40 SiO ₈ IV precipitated hydrophobic Parts 40 40 bated SiO ₂ V Diphenylsilanediol Teüe 16 16 16 16 16 (50 ° / oiginSiloprene) VI Ceria type Al Parts 6th 6th 6th 8th 10 VII Dicumyl peroxide (95%) Parts 1 1 1 1 VIII Benzoyl peroxide (50%) Parts 2 2 2 2 2 2 2

Mechanical values after post-vulcanization for 24 hours at 250 ° C

Tensile strength
Elongation at break
Shore hardness A

Tensile strength
Elongation at break
Shore hardness A

Kp / cm ² 45 57 50 49 55 64 53 62 60 57 0 /
/O 320 540 330 240 390 320 470 500 500 440 i. E. 57 38 45 50 41 50 39 44 46 40

after 24 hours of aging in a glass tube at 250 ° C

Kp / cm ² 20th 14th 13th 20th 19th 10 13th 12th 13th 2 ° / o 280 310 310 270 350 240 430 390 360 50 LE. 46 27 24 35 30th 30th 27 33 36 3

after 3 days of aging in a circulating air oven at 275 ⁰ C.

Tensile strength
Elongation at break
Shore hardness A

Peat times after
24 hour storage

Kp / cm '
O/

/ 0

Minutes

41 49 47 50 300 290 91 53 57

29
80
85

50

190

60

57

190

70

180

Ibis 3

Obisl

2 to Ibis 2 Obisl

Ibis 2 Obisl

200

Obisl

25th
80
68

38

300

42

Obisl Obisl

Obisl

Claims (2)

Patent claims: 1. Process for the production of polysiloxane elastomers of high aging resistance in not closed systems using highly dispersed silicon oxides from organopolysiloxanes, organic peroxides and usual additives, characterized that highly disperse oxides of silicon, which are produced by treatment with organic silicon halogen compounds have been rendered hydrophobic in such a way that they only have a low density of silanol groups have, which is known per se Way is subjected to vulcanization. 2. The method according to claim 1, characterized in that highly disperse oxides of silicon are used, which have been hydrophobized by treatment with preferably dimethylchlorosilane so far that they are at a carbon content of 1.00% ° i ^s 3.00% and a BET specific surface area of 50 to 300 m ^a / g only have a silanol group density ^{of 0.1 to 1.0 / 100 Å 2.} Considered publications:
French Patent No. 1,284,864.