RU2041905C1 - Composition for protective coating and a method of its preparing - Google Patents

Abstract

FIELD: protective compositions. SUBSTANCE: composition has, polymethylphenylsiloxane solution in toluene (as dry matter) 25-34; tetrabutoxytitanium 5-11; silicate 42-60; metal oxide 1-5; silicon carbide 3-10; Composition is prepared by mixing polymethylphenylsiloxane solution in toluene with tetrabutoxytitanium, addition of metal oxide, silicon carbide to the mixture, and mechanical working prepared suspension in ball mill. Properties: drying time up to degree 3 is 0.5 h; coating adhesion by lattice cutting method is 1 point; impact strength of coating is 3.5-4.0 H x m; bending strength is 1-3 mm; hardness by device M-3 is 0.4-0.6. Composition is used for coating large-size equipment. EFFECT: enhanced quality of composition. 3 cl, 2 tbl

Description

 The invention relates to the field of materials science of protective coatings, in particular to compositions based on polyorganosiloxanes hardening at ambient temperature. The composition is intended to produce weather-resistant anticorrosive coatings on metal surfaces and can be used in cases where it is impossible to form coatings at high temperatures, for example, when painting large equipment in shipbuilding, car building, automotive, and hydraulic engineering.

 Known compositions based on polyorganosiloxanes, consisting of three components: a polymer binder, silicates and oxides [1] After curing, the composition forms a single spatially cross-linked structure, which can be considered as a system of thin polymer films fixed between particles of other components. A set of properties that ensure reliable use of coatings is largely achieved due to the introduction of silicate components that form siloxane-silicate bonds with the polymer, as well as oxides that catalyze this process and improve adhesive performance.

Si-O

Si

+

Si-O

Si

__→ поверхность силиката (с) молекула полимера (п)
__→

Реакции

^__→

^{+ H}2^O

i-OH+R-

i

__→

i-O-Si

+ RH протекают с достаточной полнотой при нагревании или в присутствии сшивающих агентов и относятся главным образом к стадии пространственной сшивки (отверждения) композиции на основе полиорганосилоксанов.The breaking of siloxane bonds in the silicate lattice and the polymer molecule is carried out under the influence of external energy influences, including mechanical ones:

Si-O

Si

+

Si-O

Si

__ → surface of silicate (s) polymer molecule (p)
__ →

Reactions

^{__ →}

^{+ H} 2 ^O

i-OH + R-

i

__ →

iO-Si

+ RH proceed with sufficient completeness when heated or in the presence of crosslinking agents and relate mainly to the stage of spatial crosslinking (curing) of a polyorganosiloxane-based composition.

In the manufacture of the composition during the processing of a suspension containing polyorganosiloxane, silicate and oxide in a ball mill, the most likely reaction proceeding according to the first scheme is the formation of primary chemical bonds between the polymer base and silicate components. Subsequent crosslinking, leading to the formation of a single spatial structure, is carried out in the process of curing the composition under the influence of high temperatures or in the presence of crosslinking additives at a temperature of 10-30 ^o C.

In the case of curing the known composition under the influence of high temperatures, it is possible to obtain high-quality coatings with high physical and mechanical properties. However, the formation of such coatings is a labor and energy intensive process, since the heat treatment requires a special program: temperature rise at a rate of 1.5-2 ^{° C} per minute to 270 ^{° C,} isothermal hold at this temperature for 2.5-3 h and subsequent cooling at a speed of up to 5 ^° C per minute. Failure to comply with the heat treatment leads to the formation of internal defects and bubbles due to the release of intramolecular and condensation water, which causes the destruction of polyorganosiloxanes and, as a consequence, the deterioration of physical and mechanical properties. The disadvantages of the composition also include its limited use in the high-temperature curing of applied coatings: the composition is not suitable for painting large-sized parts and metal structures.

Closest to the composition of the invention is a known composition for a protective coating comprising a solution of polymethylphenylsiloxane in toluene, tetrabutoxytitanium (0.6 wt.), Silicate and metal oxide. A method of manufacturing the composition involves the introduction of tetrabutoxytitanium in a composition that was previously used only as an independent composition. In this case, the hardener is introduced into it immediately before coating [2]
However, the coating obtained on the basis of the known composition has low strength characteristics, hardness and adhesion to the substrate and is inferior in physicomechanical properties to coatings based on compositions cured by high temperatures.

 An object of the invention is to improve the physico-mechanical properties of the coating, which consists in increasing the strength characteristics, hardness and adhesion to the substrate.

 The increase in strength characteristics, hardness and adhesion of the coating to the substrate is achieved by the fact that the composition for a protective coating, including a solution of polymethylphenylsiloxane in toluene, tetrabutoxytitanium, silicate and metal oxide, additionally contains silicon carbide, in the following ratio, wt.

Polymethyl
nilsiloxane in toluene,
calculated on the dry matter 25-34 Tetrabutoxytitanium 5-11 Silicate 42-60 Metal oxide 1-5 Silicon carbide 3-10
The increase in strength characteristics, hardness and adhesion to the substrate is also achieved by the fact that in the method of manufacturing the composition, which consists in mixing a solution of polymethylphenylsiloxane in toluene, tetrabutoxytitanium and inorganic components and machining the resulting suspension in a ball mill, according to the invention, the solution of polymethylphenylsiloxane in toluene is first mixed with tetrabutoxy titanium, and then inorganic components are introduced into the mixture.

 It is an unconventional sequence of mixing the components of the composition when tetrabutoxy titanium is used in significant concentrations that leads to the formation of a uniform gel and its final processing in a ball mill provides a high-quality composition with a characteristic consistency for the paint.

.The high concentration of tetrabutoxytitanium in the composition after it is applied to the metal surface as the organic solvent evaporates provides a more active reaction of transesterification of tetrabutoxytitanium with polymethylphenylsiloxane, both the first and second stages. In addition, the concentration of tetrabutoxy titanium is sufficient to bind OH groups located on the surface of silicates and oxides. As a result of such chemical interactions, a highly structured coating with high physicomechanical properties is formed with a significant content of a compound of the formula: Me _x Ti _m Si _n O _{m + n} +

.

 The use of tetrabutoxy titanium in high concentrations is not an obvious solution, since earlier the concentration of tetrabutoxy titanium was limited, trying to avoid what happens when mixing tetrabutoxy titanium with a suspension containing polymethylphenylsiloxane, silicate and oxide, gelation. It was believed that gelation makes the composition unsuitable for intended use. However, the use of tetrabutoxy titanium in sufficiently high concentrations is possible due to a special method of mixing the components in the manufacture of the composition. The addition of inorganic components to the pre-prepared mixture of tetrabutoxy titanium with a solution of polyorganosiloxane in toluene during the mixing process leads to uniform gelation of the suspension without the formation of hard-to-grind clots and guarantees after preparation in a ball mill to obtain the finished composition with a characteristic consistency for coloring.

 The presence of silicon carbide in the composition, which during machining is capable of grinding not to a particle size of 10-20 μm, such as silicate, but to 1-2 μm, ensures its uniform distribution as a filler in the smallest voids of the spatially crosslinked structure of the resulting coating, increasing its hardness.

 It was found that the optimal content of tetrabutoxytitanium in the composition should be 5-11 wt. When the content of tetrabutoxytitanium is less than 5 wt. the composition dries slowly and the resulting coatings have a low hardness index. The increase in the concentration of tetrabutoxytitanium over 11 wt. leads to the formation of a very hard coating with high internal stresses, with low adhesion to the substrate.

 Exceeding the upper limit of the recommended range of concentrations of polymethylphenylsiloxane in the composition increases the drying time and causes a decrease in hardness of the coating. When the concentration of polymethylphenylsiloxane is less than 25 wt. the strength characteristics of the coating are significantly deteriorated, its hardness and adhesion to the substrate are reduced.

 Limitations in the composition of the concentration of silicate and silicon carbide at the upper limit, respectively, 60 and 10 wt. due to the observed tendency to decrease the values of strength characteristics. The choice of the lower limit of the content of the component in the composition for silicate 42 wt. and for silicon carbide 3 wt. due to considerations of maintaining sufficient hardness of the coating.

 The limits of the content of metal oxide are selected in accordance with the practice of its introduction into organosilicate materials to impart color. When the content of metal oxide is less than 1 wt. the composition has no pronounced color. With the introduction of metal oxide in an amount exceeding 5 wt. the staining effect remains at the achieved level, in addition, the coating becomes less elastic, which is reflected in a decrease in bending strength.

 The composition is prepared as follows.

 A solution of polymethylphenylsiloxane in toluene is loaded into a ball mill and tetrabutoxy titanium is introduced into it with gentle stirring. The remaining components are then added in powder form to the mixture. The resulting gel is subjected to processing in a ball mill for 1-3 days. After machining, the composition is ready and has a characteristic consistency for the paint. It is poured into tightly closed glass or metal dishes.

In the laboratory, studies were conducted on the properties of coatings obtained from compositions, distinguished by the quantitative content of the components. To this composition was applied to a metal substrate (Art. 3) and dried at 20 ° ^C. The coating thickness was 100 microns.

 PRI me R s 1-14. The compositions of the examples are prepared as described above. The compositions of the examples are given in table. 1, the properties of coatings based on them in table. 2.

 The use of the composition according to the invention and the method for its preparation makes it possible to produce coatings cured at ambient temperature that are comparable in their physical and mechanical properties to the physical and mechanical properties of coatings cured at high temperatures. In addition to high strength characteristics, hardness and adhesion to the substrate, coatings based on the composition of the invention also have good electrophysical properties.

Claims (1)

 1. The composition for a protective coating, comprising a solution of polymethylphenylsiloxane in toluene, tetrabutoxytitanium, silicate and metal oxide, characterized in that it additionally contains silicon carbide in the following ratio, wt. A solution of polymethylphenylsiloxane in toluene calculated on the dry matter 25 34
Tetrabutoxy titanium 5 11
Silicate 42 60
Metal oxide 1 5
Silicon Carbide 3 10
2. A method of obtaining a composition for a protective coating, which consists in mixing a solution of polymethylphenylsiloxane in toluene, tetrabutoxytitanium and inorganic components and machining the resulting suspension in a ball mill, characterized in that the solution of polymethylphenylsiloxane in toluene is mixed with tetrabutoxytitanium, and then inorganic components are introduced into the mixture , while the components are taken in the following ratio, wt. A solution of polymethylphenylsiloxane in toluene calculated on the dry matter 25 34
Tetrabutoxy titanium 5 11
Inorganic components:
Silicate 42 60
Metal oxide 1 5
Silicon Carbide 3 10

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