GB2270522A

GB2270522A - Two-part siloxane elastomer-forming composition

Info

Publication number: GB2270522A
Application number: GB9318139A
Authority: GB
Inventors: Peter Otto Bentz; Monika Mitter
Original assignee: Dow Corning GmbH
Current assignee: Dow Silicones Deutschland GmbH
Priority date: 1992-09-10
Filing date: 1993-09-01
Publication date: 1994-03-16
Anticipated expiration: 2013-09-01
Also published as: GB9219208D0; JPH06166821A; FR2695396A1; JP3485602B2; DE4330605A1; GB2270522B; GB9318139D0; FR2695396B1; DE4330605B4

Abstract

Elastomer-forming composition which gives unprimed adhesion to a wide range of supports and consists of (A) a vinyl polyorganosiloxane, (B) a Si-H containing organosilicon compound, (C) a noble metal catalyst, (D) a silane or siloxane having at least one epoxy-functional group and one alkoxy-functional group and (E) aluminium acetyl acetonate, iron acetyl acetonate, zinc acetyl acetonate or an aluminium salt of a fatty acid, is made storage stable by placing (C) only in the first part and (D) only in the second part of the composition.

Description

PM ^^ 122700zd! ELASTOMER-FORMING COMPOSITION This invention relates to

an elastomer forming silicone composition having good unprimed adhesion. It more particularly relates to compositions provided as a two part composition.

Two part elastomer forming silicone compositions have been known for some time. A particularly useful type of silicone elastomer forming composition is the type where the elastomer is formed via an addition reaction. This type of composition has the advantage that upon curing no by-products are formed, hence the resulting elastomer product has substantially the same dimension as the uncured elastomer, and is thus particularly useful in applications where precision is very important. Constancy of dimension upon cure is not the case, for example with products which cure by condensation reactions where the evolution of a by-product, e.g. alcohol, will cause the product to shrink to some extent upon curing.

Many addition reaction silicone elastomer-forming compositions require priming of the surface onto which they are applied in order to ensure good adhesion thereto. This is particularly true where the surface is metal or a plastic.

Attempts have been made to produce addition reaction elastomer-forming compositions which have improved unprimed adhesion to metal or plastic substrates. For example U.S. specification 4,087,585 discloses self-adhering silicone compositions comprising certain hydroxylated vinylcontaining polysiloxanes, vinyl-containing polydiorgano- siloxanes, organosilicon compounds having at least 3 silicon-bonded hydrogen atoms, a platinum catalyst and a silane having at least an epoxy- containing organo group and an alkoxy group. The material is shown to give good unprimed adhesion on aluminium when heated for at least 15 minutes at 1500C. It was found that most similar compo sitions require heating at a temperature of at least 1000C in order to achieve unprimed adhesion to many substrates.

The abstract of Japanese application J60101146 describes a composition which is claimed to give improved unprimed adhesion, even when cured at lower temperatures. The application discloses compositions comprising 100 parts by weight of a polyorganosiloxane containing at least 2 units per molecule, wherein the silicon atom has an alkenyl substituent, polyorganohydrogen siloxane having at least two silicon-bonded hydrogen atoms per molecule, 0.1 to 20 parts by weight of an epoxy compound, 0.01 to 10 parts by is weight of an organic aluminium compound and a catalytic amount of a platinum, palladium or rhodium compound which shows improved adhesion.

European Application 240 333 discloses a curable thermosetting resin composition which comprises a conti- nuous phase of a thermosetting resin and a finely dispersed cured composition prepared by reacting an organopolysiloxane, a curing agent, an alkoxy group-containing organosilicon compound and a compound of Al or Z r- The dispersed phase shows improved adhesion to the continuous phase.

European Application 493 791 describes a curable organopolysiloxane composition with improved adhesion which comprises an organopolysiloxane having alkenyl radicals, an organohydrogensiloxane, a Pt-containing catalyst, an organosilicon compound having alkoxy groups, and possibly epoxy groups, and a zirconium compound.

It has been found, however, that the compositions according to the cited specifications, J60101146, E.P.

3 240 333 and 493 791 though very effective in improving some adhesion, are not stable when stored for some time. There is also no indication as to how these compositions could be made stable. There is therefore a need to improve the compositions in such a way that they will become stable.

We have now found that by making the composition into. a two part system, and separating the catalyst and the epoxy functional silane, a stable composition is obtained.

The invention accordingly provides storage stable elastomer-forming composition consisting of a first and a second part and comprising (A) a polyorganosiloxane having an average of about two silicon-bonded vinyl groups per molecule, (B) an organosilicon compound having on average at least 3 silicon-bonded hydrogen atoms per molecule, (C) is a noble metal catalyst, (D) a silane having at least one epoxy- functional group and one alkoxy-functional group, or an organosilicon compound of the general formula (R.0) RO_ SiO(R.SiO) (R1R.SiO) (R11R.SiO) SiRO_ (OR") C 3 c 2 X y Z 3 c c wherein RO denotes a monovalent hydrocarbon or substituted hydrocarbon radical having no more than 8 carbon atoms and which may contain ether oxygen, Rf denotes a hydrocarbon group having olefinic unsaturation and having at least 6 carbon atoms, R" denotes a monovalent hydrocarbon or hydrocarbonoxy group or a halogenated hydrocarbon or hydrocarbonoxy group or a hydrocarbon or hydrocarbonoxy group which contains oxygen in the form of an ether linkage or a hydroxyl group, said R" containing an epoxy group, 2 has a value of 0, 1, 2 or 3, A, y and z have a value of at least 1, with z being at least 2 if c is 0 and (E) metal compound selected from aluminium acetyl acetonate, iron acetyl acetonate, zinc acetyl acetonate, or an aluminium salt of a fatty acid, wherein Component (C) is only present in the first part of the composition and Component (D) is only present in the second part of the composition.

Component (A) of the composition of the invention is a polyorganosiloxane which preferably has the general formula Vi-[SiR 2 0] n-SiR 2 Vi, wherein Vi denotes a vinyl group, R denotes an organic group, which is selected from monovalent hydrocarbon or halogen-substituted hydrocarbon groups having at most 8 carbon atoms per group, and wherein n is an integer. These preferred polyorganosiloxanes are substantially linear polymers, but small amounts of trifunctional siloxane groups or tetrafunctional siloxane groups may also be present. Such groups would result in a certain amount of branching in the polymer. Although preferred polyorganosiloxanes are endblocked with vinyldiorganosiloxane units, it is also possible that vinyl groups only occur along the chain of the polymer. Suitable polymers will have a viscosity in the range of from 20mPa.s to 2000Pa.s, preferably 10OmPa.s to 50Pa.s. Suitable groups R include alkyl, alkenyl, aryl, chlorine or fluorine substituted alkyl groups, alkaryl and aralkyl groups. Examples of suitable groups R are methyl, ethyl, propyl, hexyl, phenyl, vinyl, butenyl, hexenyl, methylphenyl, trifluoropropyl and P(perfluoropropyl)ethyl. It is most preferred that at least 80% of all groups R are methyl groups. Most preferred polyorganosiloxane (a) is therefore a a,w-vinyl end-blocked polydimethylsiloxane. Suitable polyorganosiloxanes (A) are well known and commercially available polymers.

Component (B) is preferably an organohydrogen siloxane having on average at least 3 silicon-bonded hydrogen atoms per molecule, any remaining substituents of the silicon atoms being monovalent hydrocarbon groups having up to 8 carbon atoms. These materials are also well known in the art. The silicon- bonded hydrocarbon substituents are preferably selected from alkyl groups having from 1 to 6 carbon atoms and phenyl groups. The organohydrogen siloxanes can be homopolymers, copolymers or mixtures thereof which comprise units such as R 2 Sio, R 3 Si%1 RHSiO, HSiO 3/2' RSiO 3/2' R 2 HSiO, and S'02' wherein R is as defined above. No more than 1 hydrogen atom should be linked to any one silicon atom. It is preferred that at least 80% of all R groups are lower alkyl groups, most preferably methyl groups. Specific examples of suitable organosilicon compounds (B) are copolymers of trimethyl- siloxane, dimethylsiloxane and methylhydrogensiloxane units, cyclic methylhydrogensiloxanes and copolymers of dimethylhydrogensiloxane units, dimethylsiloxane units and methylhydrogensiloxane units. The organosilicon compounds (B) preferably have at least 5 silicon-bonded hydrogen is atoms per molecule and are most preferably copolymers of trimethylsiloxane units, methylhydrogensiloxane units and optionally dimethylsiloxane units, and have a viscosity of from 2 to about 50OmPa.s at 250C.

The noble metal catalyst, which is used as Component (C) of the composition of the invention, is a group VIII metal or a complex or compound thereof. Preferably Component (C) is a platinum compound or complex. This component is effective in catalysing the addition reaction between the vinyl groups of Component (A) and the silicon- bonded hydrogen atoms of Component (B). This addition reaction is well known and has been described in a number of textbooks and publications. Suitable platinum compounds and complexes include chloroplatinic acid, platinum acetylacetonate, complexes of platinous halides, with unsaturated compounds such as ethylene, propylene, organovinylsiloxanes and styrene, hexamethyldiplatinum, Ptcl 2 Ptcl 3 and Pt(CN) 3 The preferred platinum catalysts are complexes of platinum compounds and vinyl siloxanes, e.g. those formed by the reaction of chloroplatinic acid and divinyltetramethyl disiloxane. Sufficient of the catalyst should be employed to provide a homogenous and effective cure of the composition. The preferred proportion of platinum catalyst is usually that which will provide from about 1 to about 40 parts by weight of Pt per million parts by weight of Components (A) and (B) combined.

Component (D) for use in the compositions of the invention is a silane having at least one epoxy-functional group and one alkoxy-functional group, or an organosilicon compound of the general formula (R.0) RO_ SiO(R.Sio) (R1R.SiO) (R11R.SiO) SiRO_ (OR.) c 3 c 2 X y z 3 c c wherein RO denotes a monovalent hydrocarbon or substituted hydrocarbon radical having no more than 8 carbon atoms, and which may contain ether oxygen, R' denotes a hydrocarbon group having olefinic unsaturation and having at least 6 carbon atoms, W' denotes a monovalent hydrocarbon or hydrocarbonoxy group or a halogenated hydrocarbon or hydrocarbonoxy group or a hydrocarbon or hydrocarbonoxy group which contains oxygen in the form of an ether linkage or a hydroxyl group, said W' containing an epoxy group, p has a value of 0, 1, 2 or 3, x, v and z have a value of at least 1, with z being at least 2 if c is 0. This latter type has been disclosed and described in detail in G.B. patent specification 2 208 650.

Suitable silanes for use as Component (D) are mole cules with the general formula W' a R2 b SiR 4-a-b wherein W' and R are as defined above, R2 is an alkoxy group having up to 8 carbon atoms, A has a value of 1 or 2, 12 has a value of 1, 2 or 3 and a+b has a value of 2, 3 or 4. Examples of suitable groups R 2 include methoxy, ethoxy, propoxy or butoxy. It is preferred that all groups R2 are methoxy or ethoxy groups. The groups R are as defined above for Component (A), including the preferred groups for R. Groups W' are epoxy containing groups which may have the general formula 0 0 0 -XCH-CH 2' -OXCH-CH 21 -OX-O/ or -X where X is a divalent hydrocarbon group, halogenate hydrocarbon group or ether oxygen or hydroxyl containing hydrocarbon group. Examples of X include methylene, ethylene, propylene, phenylene, chloroethylene, -CH 2-0-(CH 2)3-1 -CH 2-0-(CH 2)2-0-(CH 2)3_ and CH 2 CH(OH)CH 2_ Preferably W' has the formula / 0 \ / 0 -XCH-CH 2 or -OXCH-CH 2 and most preferably X is alkylene or alkyleneoxyalkylene, for example -(CH 2) 3 -OCH 2 -, -(CH 2)4_ is or -CH 2_ It is preferred that a has a value of 1 and b a value of 3.

Component (E) is a metal compound, selected from aluminium acetyl acetonate, iron acetyl acetonate, zinc acetyl acetonate, or an aluminium salt of a fatty acid.

Suitable examples wherein acac denotes acetylacetonate, are Al(acac) 3, Fe(acac) 31 Zn(acac)4 and Al[OC(O)(CH 2)16 CH 313Particularly preferred is Al(acac) 3 Additional ingredients may also be used in compositions according to the invention. These include fillers, flame retardant additives, heat stabilising additives, pH stabilising agents, mildewicides, colorants, pigments and solvents. For example suitable fillers include reinforcing silica fillers such as pyrogenically produced silica and precipitated silica, resinous materials, for example those comprising units of the formula R 3 Sio, and units of the formula SiO 2, alumina, finely divided quartz, calcium carbonate, zinc oxide, titania and zirconium silicate. Fillers which are added to the compositions of this invention are preferably treated with filler treating agents to improve their compatibility with the other components of the composition. Such agents are generally known in the art and include for example hexamethyldisilazane, alkylalkoxysilanes, methylhalogenosilanes and short chain silanol endblocked polydimethylsiloxanes. The filler may constitute up to about 50% by weight of the total composition, but preferably constitutes from 5 to 40% by weight of the composition. The preferred filler is a reinforcing silica.

Compositions according to the present invention preferably have 100 parts by weight of Component (A), sufficient of Component (B) to give from 0.5 to 3 siliconbonded hydrogen atoms per vinyl group present in component (A), from 0.5 to 20 parts by weight of Component (D) and from 0.1 to 10 parts by weight of component (E) as well as the appropriate amount of catalyst as mentioned above.

The crucial aspect of the invention is that the compositions are stored, prior to mixing for application purposes, in two parts, of which only one part contains Component (C) and only the other part contains Component (D). It is preferred that Component (A) is present in both parts of the composition. Component (B) is preferably only present in the part which does not contain Component (C), unless a cure inhibitor is also included, in which case it could be present in either or both parts. Component (C) must only be present in one part, preferably not the part where Component (B) is present, and definitely not the part where Component (D) is present. Component (E) may be in either part but is preferably present in the part which does not include Component (D). Each part of the composition is stored separately till immediately prior to use, at which time they are to be mixed thoroughly, and applied.

Mixing of the two parts may be achieved by placing the materials in a third container and stirring them. More suitably the two components are mixed in an extrusion device which is linked up to the containers which contain the two parts. Each part is preferably prepared in such a way that mixing can be done in an easy ratio, e.g. 1:1 or 10:1. Said ratios are usually preset on the extrusion devices. During storage it is preferred that each part is placed in a moisture impermeable package which does not contain any materials which may be detrimental, e.g. to the platinum catalyst.

Compositions according to the invention are curable at relatively low temperatures and still provide good unprimed adhesion to a large number of substrates. Suit- is able substrates include aluminium, polyvinylchloride, polycarbonate, polyetherimide, poly(phenyleneoxide) and poly (phenylene sulfone).

There now follow some examples which illustrate the invention, and some comparative examples to show the improvement of the invention.

Preparation of base compositions Part I of the base composition was prepared by mixing 52 parts by weight of a dimethylvinylsiloxane end-blocked polydimethylsiloxane having a viscosity of 450mPa.s, 46.3 parts by weight of an inert ground quartz filler, 1 part by weight of zinc oxide, 0.5 part by weight of carbon black and 0.2 part by weight of a solution of a platinum complex in a vinylsiloxane, resulting in 12ppm of platinum in the composition of Part I. Part II was prepared by mixing 46.8 parts by weight of a dimethylvinylsiloxane end-blocked polydimethylsiloxane having a viscosity of 450mPa.s, 46.8 parts by weight of an inert ground quartz filler and 6.3 parts by weight of a trimethylsiloxane end-blocked polydimethylsiloxane, having 37.5 mole% dimethylsiloxane units and 62.5% methylhydrogensiloxane units.

Example 1

To 100 parts by weight of Part I, was added 1.6 parts by weight of a solution of 10% aluminium acetylacetonate in toluene. To 100 parts by weight of Part II was added 5.6 parts by weight of 3-2,3epoxypropoxy-propyl trimethoxysilane. After mixing thoroughly, each mixture was placed in a separate closed container and stored for one week in an oven at 500C. After one week, the content of the two containers were mixed in a ratio of 1:1, and heated to SOOC for 4 hours. The resulting elastomer was satisfactory, and was only slightly softer than the comparative example, based on JP 60101146, without any storage.

Example 2

To 100 parts by weight of Part I, was added 1.6 parts by weight of a solution of 10% aluminium acetylacetonate in toluene and 0.1 part of a solution of a platinum complex in a vinylsiloxane, resulting in 24ppm of platinum in the composition of Part I. To 100 parts by weight of Part II was added 5.6 parts by weight of 3-2,3-epoxypropoxy-propyl trimethoxysilane. After mixing thoroughly each mixture was placed in a separate closed container and stored for one week in an oven at 500C. After one week the content of the two containers were mixed in a ratio of 1:1 and heated to 800C for 4 hours. The resulting elastomer was harder than for Example 1 and was identical to the comparative example, based on JP 60101146, without any storage. Example 3 30 The composition of Example 2 was applied to the following substrates: polyvinylchloride, poly(phenylene sulfone), polycarbonate, poly(penyleneoxide), poly(oxymethylene), polyetherimide, poly(ethylenetera- phthalate), poly(butyleneteraphthalate), glass fibre reinforced epoxy resin, aluminium and polyether sulfone. The substrates were placed in an oven at 700C for 4 hours in which time the silicone composition was completely cured. The substrates with cured compositions were stored at room temperature overnight and tested for adhesive and cohesive adhesion. This was done cutting a small section of the cured composition away from the substrate with a razor blade, gripping this loosened section and pulling it away from the substrate. If the cured composition came completely away from the substrate a 100% adhesion failure was recorded, if the composition tore, without coming away from the substrate, a 0% adhesion failure was recorded. The latter is the desired outcome. Intermediate results is were recorded as the percentage of the total area where cured composition was totally removed from the substrate. Table I gives the results for each substrate in % adhesion failure.

TABLE I % Adhesive Substrate failure polyvinylchloride 0 poly(phenylene sulfone) 40 polycarbonate 0 poly(phenyleneoxide) 0 poly(oxymethylene) 0 polyetherimide 10 poly(ethyleneterephthalate) 0 poly(butyleneterephthalate) 0 glass fibre reinforced epoxy resin 0 aluminium 0 polyether sulfone 100 Comparative Example 1 To 100 parts by weight of Part I was added 5.6 parts by weight of 3-2,3epoxypropoxy-propyl trimethoxysilane. To 100 parts by weight of Part II was added 1.6 parts by weight of a solution of 10% aluminium acetylacetonate in toluene. After mixing the ingredients thoroughly, each of the two Parts were placed separately in a closed container and stored for one week in an oven at 500C. After one week the content of the container with Part I had discoloured.

The two containers were mixed in a ratio of 1:1 and heated to 800C for 4 hours. Surprisingly only a soft rubbery gel was obtained which was not useful. This example shows the deterioration of the composition when stored in a way which is different from the present invention.

Comparative Example 2 A composition according to the teaching of JP60101146 was prepared by mixing 93.1 parts by weight of a dimethylvinylsiloxane end-blocked polydimethylsiloxane having a viscosity of 450 mPa.s, 93.1 parts by weight of an inert ground quartz filler, 7.2 parts by weight of a black past, containing 80. 1% by weight of a dimethylvinylsiloxane endblocked polydimethylsiloxane having a viscosity of 450mPa.s, 13.3% by weight of zinc oxide and 6.6% by weight of carbon black, 0.2 part by weight of a solution of a platinum complex in a vinylsiloxane, providing 0.6% by weight of Pt in the solution, 6.3 parts by weight of a trimethylsiloxane end-blocked polydimethylsiloxane, having 37.5 mole% dimethylsiloxane units and 62.5% methylhydrogensiloxane units, 0.1 part by weight of polymethylvinylcyclo- siloxane having from 3 to 7 siloxane units per molecule, 1.6 parts by weight of a solution of 10% aluminium acetyl acetonate in toluene and 5.6 parts by weight of (3-glycidoxypropyl) trimethoxysilane. The composition was stored at room temperature and was no longer pourable after 5 hours. After 24 hours the composition was cured to a solid block of silicone elastomer.

Claims

1. A storage stable elastomer-forming composition comprising (A) a polyorganosiloxane having an average of about two siliconbonded vinyl groups per molecule, (B) an organosilicon compound having on average at least 3 silicon-bonded hydrogen atoms per molecule, (C) a noble metal catalyst, (D) a silane having at least one epoxy-functional group and one alkoxy-functional group, or an organosilicon compound of the general formula (R-0) RO_ SiO(R-SiO) (R1ROSiO) (R11R.SiO) SiRO_ (ORO) wherein RO C 3 C 2 X y z 3 C C denotes a monovalent hydrocarbon or substituted hydrocarbon radical having no more than 8 carbon atoms and which may contain ether oxygen, R' denotes a hydrocarbon group having olefinic unsaturation and having at least 6 carbon atoms, W' denotes a monovalent hydrocarbon or hydrocarbonoxy group or a halogenated hydrocarbon or hydrocarbonoxy group or a hydrocarbon or hydrocarbonoxy group which contains oxygen in the form of an ether linkage or a hydroxyl group, said W' containing an epoxy group, c has a value of 0, 1, 2 or 3, x, y and z have a value of at least 1, with z being at least 2 if c is 0 and (E) metal compound selected from aluminium acetyl acetonate, iron acetyl acetonate, zinc acetyl acetonate, or an aluminium salt of a fatty acid, characterised in that the composition consists of 2 parts and that Component (C) is only present in the first part of the composition and Component (D) is only present in the second part of the composition.

2. A composition according to Claim 1 characterised in that Component (A) is a substantially linear polymer end-blocked with vinyldiorganosiloxane units having a viscosity of from 20mPa.s to 2000Pa.s.

- A composition according to any one of the preceding claims characterised in that Component (A) is a a,w-vinyl end-blocked polydimethylsiloxane having a viscosity of from 100 inPa.s to 50 Pa.s.

4. A composition according to any one of the preceding claims characterised in that Component (B) has at least 5 siliconbonded hydrogen atoms per molecule and is a copolymer of trimethylsiloxane units, methylhydrogensiloxane units and optionally dimethylsiloxane units, having a viscosity of from 2 to about 50OmPa.s at 250C.

5. A composition according to any one of the preceding claims characterised in that in Component (D) W' has the formula / 0 \ / 0 \ -XCH ---2 -- -OXCH--CH 2 and X is selected from -(CH 2)3 -OCH 2-1 -(CH 2)4_ and -CH 2_ groups and a has a value of 1 and b a value of 3.

6. A composition according to any one of the preceding claims characterised in that Component (E) is aluminium acetyl acetonate.

7. A composition according to any one of the preceding claims characterised in that it comprises 100 parts by weight of Component (A), sufficient of Component (B) to give from 0.5 to 3 silicon-bonded hydrogen atoms per vinyl group present in Component (A), from 0.5 to 20 parts by weight of Component (D) and from 0.1 to 10 parts by weight of component (E).

8. A composition according to any one of the preceding claims characterised in that Component (A) is present in both parts of the composition, Component (B) is only present in the part which does not contain Component (C) and Component (E) is present in the part which does not include Component (D).

9. A composition according to any one of the preceding claims characterised in that each part of the composition is stored separately in a moisture impermeable package.

10. A method of making a composition storage stable, said composition comprising (A) a polyorganosiloxane having an average of about two silicon-bonded vinyl groups per molecule, (B) an organosilicon compound having on average at least 3 silicon-bonded hydrogen atoms per molecule, (C) a noble metal catalyst, (D) a silane having at least one epoxyfunctional group and one alkoxy-functional group, or an organosilicon compound of the general formula (R.0) Ro- SiO(R.SiO) (R,Rosio) (R11ROSiO) SiRO_ (ORO) wherein RO C 3 C 2 X y z 3 C C denotes a monovalent hydrocarbon or substituted hydrocarbon radical having no more than 8 carbon atoms, and which may contain ether oxygen, R' denotes a hydrocarbon group having olefinic unsaturation and having at least 6 carbon atoms, W' denotes a monovalent hydrocarbon or hydrocarbonoxy group or a halogenated hydrocarbon or hydrocarbonoxy group or a hydrocarbon or hydrocarbonoxy group which contains oxygen in the form of an ether linkage or a hydroxyl group, said W' containing an epoxy group, jg has a value of 0, 1, 2 or 3, x, y and z have a value of at least 1, with z being at least 2 if c is 0 and (E) metal compound selected from aluminium acetyl acetonate, iron acetyl acetonate, zinc acetyl acetonate, or an aluminium salt of a fatty acid, characterised in that the composition is provided in a first and a second part whereby Component (C) is only present in the first part of the composition and Component (D) is only present in the second part of the composition.