HRP950513A2 - Activator for the depolymerisation of optionally filled crosslinked and/or non-crosslinked polysiloxanes - Google Patents

Description

The invention relates to activators for the depolymerization of cross-linked polysiloxanes which, if necessary, contain a filler and/or non-cross-linked polysiloxanes, processes for the depolymerisation of cross-linked polysiloxanes which, if necessary, contain a filler and/or non-cross-linked polysiloxanes and their use.

Silicone products, such as joining materials, elastomers, resins or adhesives, have a wide range of applications due to their excellent resistance against environmental influences. Their insolubility, their resistance against chemical corrosion and their resistance to temperature loads make them desirable materials. However, the insolubility of the once created network of silicone bonding material can also bring with it a disadvantage. Thus, for example, contamination with silicone joining materials must be removed using a work method that is not clean, or old joining materials are usually removed mechanically. At the same time, silicone rubber residues are often left behind on the substrate, which often opposes cleaning efforts.

DE 43 00 168 shows how hardened silicone rubber residues can be removed by means of alkylbenzenesulfonic acids, which can also be used as catalysts already in the production of polysiloxane. With many substrates, it can be harmful that they are strong acids, which prove to be corrosive and corrosive.

The task of the proposed invention was, therefore, to prepare a mild, non-corrosive activator and depolymerization agent that acts as quickly as possible.

It has now surprisingly been found that phosphoric acid and/or certain phosphoric acid esters enable the rapid depolymerization of cross-linked and non-cross-linked polysiloxanes.

The object of the proposed invention is therefore an activator of depolymerization of cross-linked polysiloxanes, which if necessary contain fillers, which contains phosphoric acid and/or mono- and/or diester of phosphoric acid of the following general formula (I)

O=P(OH)n(OR)3-n

and polycondensation products derived from it, in which n is 1, 2 or 3, and the residue R represents aromatic residues, for example phenyl, toluyl or mesityl residues, saturated, unsaturated, straight or branched aliphatic hydrocarbon residues with 1 to 20 carbon atoms,

and with n = 1, the residues of R can be the same or different from each other.

In addition, the subject of the proposed invention are depolymerization activators of cross-linked and/or non-cross-linked polysiloxanes, which contain phosphoric acid and/or mono- and/or diester of phosphoric acid of the following general formula (I)

O=P(OH)n(OR)3-n

and polycondensation products derived from it, in which n is 1, 2 or 3, and the residue R has the meaning of aromatic saturated, unsaturated, straight or branched aliphatic hydrocarbon residues with 1 to 20 carbon atoms,

and with n = 1, the R residues can be the same or different from each other, and contain at least one additional auxiliary substance.

Cross-linked and/or non-cross-linked polysiloxanes, which can be depolymerized, in the sense of the invention are all known linear siloxanes, such as for example α,ω-dihydroxypolydimethylsiloxanes, polydimethylsiloxanes terminated at the end with dimethylvinylsiloxy or trimethylsiloxy, all known silicone resins and all known addition, condensation and radically cross-linked polysiloxanes, which if necessary contain fillers, such as cross-linked silicone joining materials.

Examples of phosphoric acid esters according to the invention are:

dibutyl phosphate, monobutyl phosphate, bis-(2-ethylhexyl)-phosphate or mono-isononyl phosphate. The use of phosphoric acid alone is less advantageous due to its highly viscous consistency. In a preferred embodiment of the proposed invention, the activator is a phosphoric acid mono- and/or diester.

Activators can also correspond to several monoesters or several diesters.

In one embodiment of the proposed invention, the activator contains one or more excipients. The type and quantity of excipients is the same. depending on the respective application, i.e. whether the activator must be pasty, liquid or gelatinous.

Auxiliary substances in the sense of the invention are, for example, acidic or neutral fillers, such as pyrogenic or precipitable, if necessary hydrophobicized silicon acid, paraffins and other rheological auxiliary substances, such as layered silicates (bentonites) in combination with a solvent.

As a solvent, many organic solvents are suitable, such as halogenated hydrocarbons, esters, ethers, saturated, unsaturated, aliphatic and aromatic branched C7-C30 hydrocarbons and carboxylic acids. These are primarily liquid carboxylic acids, especially primarily carboxylic acids with at least 6 carbon atoms, for example 2-ethylhexanoic acid, since they accelerate the dissolution process.

As auxiliary substances of particular advantage, especially with cross-linked and/or non-cross-linked polysiloxanes, are mixtures of aliphatic, naphthenic and aromatic hydrocarbons, such as crystal oil K 60 or short-chain polysiloxanes of the general formula

[image]

with R = C1-C6-alkyl or phenyl, preferably R = methyl, whereby the residues within the molecule may be the same or different, and X = 0 to 20, preferably 0 to 10.

In the preferred embodiment, the proposed invention contains the activator mono- and/or diester of phosphoric acid and/or phosphoric acid, at least one filler and/or solvent. ethylhexanoic acid.

For the production of the activator according to the invention, phosphoric acid and/or mono- and/or diester of phosphoric acid is mixed directly with auxiliary substances present as necessary. If necessary, it is degassed by short evacuation after mixing.

Pasty actuators can be produced by adding fillers, for example pyrogenic or precipitable, hydrophobized silicic acid, if necessary, or a rheological aid, for example layered silicates (bentonite). Phosphoric acid esters, according to the invention, can be directly processed with fillers into pasty masses, and they are however, they can also be previously dissolved in one of the above-mentioned solvents. The rheological behavior of pastes thickened, for example, with pyrogenic silicic acid is influenced by the amount of water introduced with the silicic acid. 0.1 to 5% of water can be added for thickening, i.e. creating consistency.

Depending on the application, the activators according to the invention can be produced within wide limits regarding their chemical composition.

The subject of the proposed invention is also the process of depolymerization of cross-linked, which if necessary contain fillers and/or non-cross-linked polysiloxanes, after which the activator according to the invention is brought into contact with the polysiloxanes and at least one auxiliary substance.

The contact time of the polysiloxane with the activator depends on the thickness of the polysiloxane and its degree of cross-linking.

The process according to the depolymerizer invention can be carried out in a wide temperature range. The depolymerization of silicone is accelerated by increasing the temperature. At room temperature, it takes between 1 and 4 hours to melt a thin silicone layer. For the depolymerization of cross-linked polysiloxanes, which contain basic fillers, an activator based on the neutralization reaction should be placed in a clear excess. For thicker layers, multiple applications are beneficial. In the case of silicone materials for joining, most of the silicone material is removed mechanically, usually before applying the removal agent.

At the same time, depending on the need, the activator can be used with or without auxiliary substances. Efficiency is primarily determined by the concentration of phosphoric acid or phosphoric acid ester. As a rule, the activator mixture contains at least 5% phosphoric acid ester. Preferably, between 1 and 25% of pyrogenic silicic acid is used for thickening, especially preferably 5 to 15%. For the production of stable phases, the addition of 0.5 to 2% water proved to be particularly advantageous.

The object of the proposed invention is also the use of the activator according to the invention for the depolymerization of cross-linked and/or non-cross-linked polysiloxanes. In its embodiment, the proposed activator according to the invention is used for depolymerization of hardened silicone materials for joining.

The following examples serve to explain the invention, which, however, does not have a limiting effect.

Performance examples

1.) Decomposition of cross-linked polysiloxanes

Example 1

34.0 wt. is dissolved in the mixer. part of bis-(2-ethylhexyl)-phosphate in 50.5% wt. parts in 50.5 wt. parts of isoeicosane, one saturated, branched hydrocarbon (isoparaffin, C20 content > 90%). At the end, 15.5 parts by weight of pyrogenic silicic acid (150 m2 /g) are mixed in three portions, mixed for another 10 minutes and the mixture is degassed under 50 mbar A transparent product between paste and jelly is obtained.

Example 2

10 wt. parts of pyrogenic silicic acid with a surface area of 150 m2/g are mixed in three portions in 90 wt. parts of a mixture of mono- and diisononyl phosphate with an approximate molar composition of 1:1. At the end, it is mixed for another 10 minutes and the mixture is degassed under 50 mbar. The resulting product is a medium viscosity liquid.

Example 3

In a mixture of 27.0 wt. parts of bis-(2-ethylhexyl)-phosphate and 63.0 wt. part of 2-ethylhexanoic acid is mixed in three portions of 10.0 wt. parts of pyrogenic silicic acid. At the end, the mixture is mixed for another 10 minutes. Then 0.5 wt. parts of water and the mixture is degassed under 50 mbar. A pasty, stable product is obtained.

Example 4

(comparison)

The procedure is as in example 3 with the only difference that instead of the mixture of bis-(2-ethylhexyl)-phosphate 1 2-ethyl-hexanoic acid, 90.0 wt. parts of 2-ethyl-hexanoic acid.

Activators from examples 1, 2, 3 and 4 were tested as follows:

A transparent silicone bonding material, hardened with acetic acid, consisting of 60.2 wt. parts of polydimethylsiloxane, stopped with OH-end groups, viscosity 50 pascal, 25.0 wt. parts of polydimethylsiloxane closed with trimethylsiloxy end groups, viscosity 1 pascal, 4.0 wt. parts of ethyltriacetoxylan, 9.5 parts by mass of pyrogenic silicic acid with a specific surface area of 150 m2/g and 0.01 mass. of diisobutyltin diacetate and cured for a week. The test samples were 1 cm wide and 2 mm thick. Activators from examples 1 to 4 were applied with a layer 1 to 2 mm thick. Depending on the time of action, it was tested using a scraper whether the silicone elastomer could be easily removed mechanically.

The results of the experiment are listed in the following table 1:

[image]

Example 5

Proceed analogously to example 1 and produce a silicone remover paste of 45 wt. parts of bis-(2-ethylhexyl)-phosphate, 45 wt. parts of crystal oil K 60 (a mixture of aliphatic, naphthenic and aromatic hydrocarbons, CAS No. 64742-88-7, which can be obtained from Grüssing GmbH, Filsum), 9.5 wt. parts of pyrogenic silicic acid with a specific surface area of 150 m2/g and 0.5 wt. parts of water. The test results are listed in Table 2.

Example 6

Proceeding analogously to example 5, a paste of 42.5 wt. parts of bis-(2-ethylhexyl)-phosphate, 42.5 wt. parts of short-chain polydimethylsiloxane of average chemical composition (CH3)3SiO[Si(CH3)2O]4Si(CH3)3 and 15 wt. parts of paraffin (solidification temperature 69 to 73°C, obtainable from Merck, Darmstadt). To produce a homogeneous mass, it was necessary to heat the mixture to approx. 100°C (see test results in table 2).

[image]

1) The tests were carried out with a transparent vulcanized material for bonding with a layer thickness of approx. 2 mm.

Example 7

In the following, a series of different experiments were conducted, during which the production of silicone removal paste was not abandoned, and only the depolymerizing effect of the chemical composition was evaluated. First, a mixture of the composition listed in Table 3 was produced, and finally, in a small glass tube with a volume of approx. 8 ml layer of vulcanized transparent bonding material thickness approx. 2 mm, length 25 mm and width 5 mm coated with approx. 5 ml of the appropriate mixture and after the specified time the effect was evaluated.

The experiments serve as proof that catalysts, which are known to have a degrading effect on silicone polymers, are not without further ado also suitable for the depolymerization of vulcanized silicone elastomers. This particularly applies to the conditions under which silicone removal pastes would be used in practice, i.e. at room temperature by applying the paste to the layers of silicone elastomer to be removed.

[image]

Siloxane 1: Short-chain polydimethylsiloxane of average chemical composition (CH3)3SiO[Si(CH3)2O]4Si(CH3)3.

2) Comparative experiment.

As can be seen from Table 3, under these conditions only chemical compositions with bis-(2-ethylhexyl)-phosphate degrade vulcanized silicone elastomers. Furthermore, it can be determined that the decomposition effect is enhanced by the addition of a solvent such as cyclohexane.

2.) Decomposition of non-crosslinked polysiloxane

With the experiments listed below, the decomposing effect of phosphoric acid ester and sodium hydroxide, which is a known catalyst for the decomposition of silicone polymers (eg DE OS 40 22 661), should be demonstrated. At the same time, the experiments were carried out with polymethylsiloxane, stopped at the end with dimethylvinylsiloxane, with a viscosity of approx. 65 pascals at 25°C (available from Bayer AG as Silopren® U 65). The degradation action was documented by measuring the viscosity of the corresponding catalyst/silicone polymer mixture over time. The decrease in viscosity is a clear indication of the polymer degradation effect of the corresponding catalyst. Viscosity measurements were performed with a Haake rotary altimeter, where only relative changes in viscosity were determined and were reported in units of scale divisions. The corresponding corresponding results can be seen in Table 4.

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Mixture 1; 98% methanol, 2% NaOH.

Mixture 2: 48% methanol, 48% methyltrimethoxysilane, 2% NaOH.

As the test results show, the phosphoric acid ester used, as well as the sodium hydroxide, immediately decomposes the silicone polymer. At the same time, from the relative change in viscosity, it becomes clear that bis-(2-ethylhexyl)-phosphate causes a stronger decrease in viscosity after a short time, and compared to pure bis-(2-ethylhexyl)-phosphate, the combination with auxiliary substances according to the invention, such as cyclohexane and 2 -ethylhexanoic acid, clearly enhances the degradation effect on silicone polymer (examples 8 to 10).

Claims (9)

1. Activator for depolymerization of cross-linked polysiloxanes containing phosphoric acid and/or mono- and/or phosphoric acid diester of the following general formula (I) O=P(OH)n(OR)3-n and polycondensation products derived therefrom, in which n is 1, 2 or 3, and the residue R has the meaning of aromatic residues, for example phenyl, toluolyl or mesityl residues, saturated, unsaturated, straight or branched aliphatic hydrocarbon residues with 1 to 20 carbon atoms , and with n = 1, the residues of R can be the same or different from each other. 2. Activator according to claim 1, characterized in that the activator is monoester and/or diester of phosphoric acid. 3. Activator according to claims 1 to 2, characterized in that the activator contains one or more auxiliary substances. 4. Activator according to claim 3, characterized in that the auxiliary substance is at least one filler and/or one solvent. 5. Activator according to claim 4, characterized in that the filler is pyrogenic citric acid, and the solvent is 2-ethylhexanoic acid. 6. Activator for depolymerization of cross-linked and/or non-cross-linked polysiloxanes, which contains phosphoric acid and/or monoester and/or diester of phosphoric acid of the following formula (I) O=P(OH)n(OR)3-n and polycondensation products derived from it, in which n is 1, 2 or 3, and the residue R has the meaning of aromatic, saturated, unsaturated, straight chain or branched aliphatic hydrocarbon residues with 1 to 20 carbon atoms, and with n = 1, the residues of R can be mutually equal or different. 7. Activator according to claim 6, characterized in that the auxiliary substance is 2-ethylhexanoic acid, a mixture of aliphatic, naphthenic and aromatic hydrocarbons and/or short-chain polysiloxane of the general formula R3Si-[OSi(R)2]x-OSiR3 with R = C1-C6-alkyl or phenyl, where the residues within the molecule can be equal or unequal, and x = 0 to 20. 8. Process for the depolymerization of cross-linked, which if necessary contain a filler and/or non-cross-linked polysiloxanes, characterized in that during the depolymerization the activator according to one of claims 1 to 7 is brought into contact with the polysiloxanes. 9. Use of an activator according to one of claims 1 to 6, characterized in that for the depolymerization of hardened silicone joining materials.