Moisture curing conformal coating composition

Abstract

The present invention relates to moisture curing conformal coating compositions with improved mechanical and adhesion properties as well as thermal stability. The conformal coating composition comprises (A) one or more linear hydroxyl-terminated organopolysiloxanes, (B) one or more organopolysiloxane resins, (C) one or more organosilicates, (D) one or more alkoxysilanes having at least one tertiary amino group, (E) one or more alkoxysilanes having at least one primary or secondary amino group, and (E) one or more organosilanes having at least one primary or secondary amino group. And (F) one or more UV fluorescent pigments. The invention further relates to a process for preparing such a moisture-curable conformal coating composition.

Description

[0001] This application is a divisional application of the Chinese patent application with application number 202080102398.3, filed on June 24, 2020. Technical Field

[0002] The present invention relates to moisture-curable conformal coating compositions having improved mechanical and adhesion properties, as well as thermal stability. The conformal coating compositions comprise (A) one or more linear, hydroxyl-terminated organopolysiloxanes, (B) one or more organopolysiloxane resins, (C) one or more organosilicates, (D) one or more alkoxysilanes having at least one tertiary amino group, (E) one or more alkoxysilanes having at least one primary or secondary amino group, and (F) one or more UV fluorescent pigments. The present invention further relates to methods for preparing such moisture-curable conformal coating compositions. Background Art

[0003] Conformal coatings are thin polymer films that conform to the contours of a printed circuit board to protect its components. Specifically, conformal coatings are used to protect electronic components from the environmental factors to which they are exposed. Examples of these factors include moisture, dust, salt, chemicals, temperature fluctuations, and mechanical abrasion. There are many available conformal coating chemistries, including acrylics, epoxies, polyurethanes, silicones, fluorinated or non-fluorinated parylenes, and amorphous fluoropolymers. It is important to select a coating chemistry that meets the needs of the application.

[0004] The conformal coatings of the present invention are preferably solvent-free, one-component, and, due to a unique crosslinking chemistry, are stable and fast curing at ambient temperatures. They are also preferably free of metal catalysts. Furthermore, due to the reactive silane used as component (D), curing is very fast (<15 minutes tack-free time) without adversely affecting shelf life. Current conformal coatings have one or more undesirable characteristics, such as high solvent or volatile organic content, the need for mixing, long cure times, or problems with anchoring and adhesion to circuit boards. Many earlier prior art publications, such as US4424252A, US5179134A, US5300608A, and US6828355B1, focus on UV-curable or dual UV / moisture-curable conformal coatings for fast cure process times (UV curing is typically the method of choice for fast curing), however, herein, conformal coating applications are described that cure with moisture in minutes. There are limited publications on new conformal coating systems, such as EP0510608A1, JP7252420A2, US2009123703A1, US2015175863A1, and US2020002535A1. However, these compositions either do not contain catalysts or are not single-component systems, which require premixing in most cases. The conformal coating composition of the present invention is preferably a single-component composition. Preferably, the conformal coating composition does not contain a catalyst (due to the presence of the silane crosslinker (D)).

[0005] Therefore, it is an object of the present invention to provide a conformal coating composition that is sprayable and preferably solvent-free and metal catalyst-free. The conformal coating composition should adhere well to printed circuit boards and be suitable for automated optical inspection. Furthermore, conformal coatings made from such compositions should preferably have a low tack-free time, elastomeric to elastoplastic properties, good thermal stability, good electrical insulating properties, and good anchoring and adhesion properties in the presence of flux residues. DETAILED DESCRIPTION

[0006] The term "conformal coating" refers to a polymer film that conforms to the contours of a printed circuit board to protect the board's components from environmental factors such as moisture, dust, chemicals, mechanical abrasion, and temperature changes.

[0007] The present invention relates to a moisture-curable conformal coating composition comprising:

[0008] (A) one or more linear hydroxyl-terminated organopolysiloxanes;

[0009] (B) one or more organopolysiloxane resins;

[0010] (C) one or more organosilicates;

[0011] (D) one or more alkoxysilanes having at least one tertiary amino group;

[0012] (E) one or more alkoxysilanes having at least one primary or secondary amino group; and

[0013] (F) One or more UV fluorescent pigments.

[0014] Optionally, the moisture-curable conformal coating composition further comprises (G) one or more additives.

[0015] Component (A):

[0016] Component (A) is a typical crosslinkable base polymer that forms a base film. It is OH-functional and is used for moisture curing with alkoxyorganosilanes. Suitable compounds are known in the art and are described, for example, in US Pat. No. 7,074,875 B2. They are commonly used in formulating RTV-1 compositions and are generally made from polymers having OH end groups.

[0017] One-component silicone rubber mixtures (RTV-1) are widely known, which can be stored if water is excluded, but vulcanize in the presence of moisture at room temperature to give elastomers and sealants. They generally consist of polymeric or oligomeric, mainly linear siloxanes, crosslinkers which must contain readily hydrolyzable groups, plasticizers which are mainly methyl-terminated polydimethylsiloxane fluids (e.g. available from Wacker Chemie AG). AK 50), and, if appropriate, other additives such as curing catalysts, pigments, processing aids, and fillers. The vulcanization of the mixture can be carried out under acidic conditions (for example, in the presence of acetoxysilanes), under alkaline conditions (for example, with the aid of aminosilanes), or under neutral conditions (for example, with the aid of compounds having oxime groups or alkoxy groups). RTV-1 systems that crosslink under neutral conditions are required, in particular when the cleavage products produced during the curing of the mixture must not affect the substrate, such as in conformal coating applications where acetic acid can corrode printed circuit boards. In many applications, systems that crosslink under neutral conditions are preferred, as the odor of the elimination product in acetoxy and amine compositions is unpleasant. In addition, due to the toxicology of the cleavage products, oxime compositions are increasingly being replaced by corresponding alkoxy compositions.

[0018] To formulate RTV-1 compositions, polymers with OH end groups (component (A)) are typically used. The reaction of the crosslinker component with the OH polymer (preferably a trialkoxyorganosilane in the case of alkoxy compositions) can occur during the compounding process, with or without plasticizers and other fillers. Since these compositions are often difficult to produce and subject to limited mixing specifications (transparent compositions are almost impossible to obtain), polymers pre-terminated with alkoxy end groups are typically used. Alkoxy termination of the OH groups can be achieved during the mixing step. Therefore, premixing of components (A) and (D) and / or (E) is not necessary. However, for these reasons, components (A) and (D) are preferably added to the container first, as the reaction is very rapid, and the termination occurs in the container before the other components are added. Their preparation is disclosed, for example, in EP 0 559 045 B1 and is typically carried out by reacting a hydroxyl-terminated polydiorganosiloxane of a specific viscosity with an alkoxysilane in the presence or absence of a metal catalyst. The desired polymer (i.e., an alkoxy-terminated polymer, essentially the reaction product of component (A) with components (D) and / or (E)) is formed during this condensation process with the elimination of alcohol. The other mixture components are then added after this preparation of the alkoxy-terminated polymer. However, a disadvantage of all the methods described so far is that a sufficient degree of conversion of the OH-terminated polymer is only achieved when methoxysilanes are used. If ethoxysilanes known to date are used to prepare the polymer, the conversion of the OH groups may not be complete. Consequently, curing (gelation) of the composition may occur before the preparation of the RTV-1 mixture is complete, or even during storage of the final mixture, and this means that the resulting product has insufficient storage stability. To eliminate this problem, the formulation should be optimized with an excess of the alkoxysilane crosslinker component (D). Even if component (D) is ethoxysilane, no gelation is observed due to the excess proportion and the fact that component (D) is very reactive.

[0019] Exemplary compounds are commercially available and are described, for example, in US8507618B2 and US7074875B2. Such compounds are available from WACKER Chemie AG under the name CT601 is available as an OH-terminated polydimethylsiloxane having a viscosity of 300 mPa·s (measured based on standard test method ASTM D4652 performed at room temperature (25° C.) using a Brookfield DV-1 digital viscometer instrument equipped with a type LV-2 (62) spindle at a speed of 50 rpm).

[0020] Preferably, the linear hydroxyl-terminated organopolysiloxane (A) has the following general formula (I):

[0021]

[0022] Each R 0 are independently selected from C1-C10 alkyl, preferably methyl, and n is a number from 5 to 5,000, preferably from 10 to 3,000. The number average molecular weight (M) is measured by size exclusion chromatography (SEC) in THF at 25°C. n ) is preferably in the range of 50 to 300,000, more preferably 100 to 200,000, even more preferably 5,000 to 50,000, in particular 5,000 to 20,000. A suitable measurement system is a ThermoFisher Scientific Ultimate U3000 HPLC system equipped with a RefractoMax 521 refractive index detector using a mixed bed and 1000 AAgilent 5 μm 300×7.5 mm columns connected in series.

[0023] The conformal coating composition preferably comprises 40 to 70 wt%, more preferably 50 to 60 wt% of component (A), based on the total weight of the moisture-curable conformal coating composition.

[0024] Component (A) is preferably different from the other components of the conformal coating composition.

[0025] Component (B):

[0026] The role of component (B) is to provide hardness and mechanical strength. An additional benefit is that it is easy to react with other components of the composition via its residual OH and / or alkoxy functional groups. Therefore, component B is very suitable for moisture curing systems.

[0027] Exemplary compounds are available from WACKER Chemie AG, e.g. under the name MQ803 resin (which contains >3% alkoxy groups and -0.3% hydroxyl groups) is commercially available. This resin has proven to be very useful in these applications.

[0028] Preferably, the organopolysiloxane resin (B) comprises the following units:

[0029] R3SiO 1 / 2 (Unit M)(IIa)

[0030] SiO 4 / 2 (Unit Q)(IIb)

[0031] wherein each R is independently selected from an alkyl group, preferably a C1-C10 alkyl group, more preferably a methyl group; an alkoxy group, preferably a C1-C10 alkoxy group, more preferably an ethoxy group; a hydroxy group; or an alkenyl group, preferably a C2-C10 alkenyl group, more preferably a vinyl group. In a particularly preferred embodiment, each R is independently selected from a methyl group, a methoxy group, an ethoxy group, and a hydroxy group.

[0032] A preferred component of the reaction mixture for preparing the coating composition is a functional MQ resin, preferably an OH functional MQ resin, i.e. a highly crosslinked resin containing M, D, Q and / or T moieties. In other words, the MQ resin comprises primarily M units (R3SiO 1 / 2 ), and Q units in which each silicon atom is linked to four other oxygen atoms (SiO 4 / 2 ), thus producing a high level of cross-linked matrix. In some MQ resins, there are also small amounts of difunctional D units (R2SiO 2 / 2 ) and trifunctional T units (RSiO 3 / 2 ), wherein R is each as defined above. MQ resins are typically produced by hydrolysis and condensation of silanes such as tetraethoxysilane, vinyldimethylethoxysilane and trimethylethoxysilane. As a result of their preparation process, the resulting MQ resins often retain some residual alkoxy functionality and may also contain other functional groups, such as silanol functionality. Preferably, the organopolysiloxane resin (B) comprises at least 80%, more preferably at least 90%, even more preferably at least 95%, in particular at least 99% of M and Q units, based on the total number of M units and Q units. Preferably, the ratio of the number of M units to Q units, based on the total number of M units and Q units, is in the range of 30:70 to 70:30, preferably 35:65 to 65:35.

[0033] Exemplary compounds are described in, for example, US Pat. No. 6,365,670 B1.

[0034] The conformal coating composition preferably comprises 10 to 30 wt%, more preferably 15 to 25 wt% of component (B), based on the total weight of the moisture-curable conformal coating composition.

[0035] Component (B) is preferably different from the other components of the conformal coating composition.

[0036] Component (C):

[0037] The role of component (C) is to improve mechanical properties and increase crosslinking density.

[0038] Preferably, the organosilicate (C) has the following general formula (III):

[0039]

[0040] Each R 1 are independently selected from C1-C10 alkyl, preferably C2-C5 alkyl, more preferably ethyl; or C2-C20 alkoxy-alkyl, and n is a number from 1 to 10, preferably 5 to 7.

[0041] Preferably, each R1 Independently selected from C1-C10 alkyl, preferably C2-C5 alkyl, more preferably ethyl.

[0042] The organosilicate (C) may be partially hydrolyzed.

[0043] A preferred organosilicate of formula (III) is partially hydrolyzed tetraethyl silicate.

[0044] Exemplary compounds are described, for example, in US Pat. No. 3,531,424 A. In particular, component (C) is preferably a polyalkoxy compound, for example ethyl orthosilicate or a partially hydrolyzed ethyl silicate, such as "ethyl silicate 40", which is approximately decaethyl tetrasilicate.

[0045] Exemplary compounds are available from WACKER Chemie AG under the name SILICATE TES 40WN, which is an ethyl silicate polymer, is commercially available. It is a low viscosity liquid that provides approximately 41% silicon dioxide (silica) when fully hydrolyzed.

[0046] The conformal coating composition preferably comprises 3 to 20 wt%, more preferably 5 to 15 wt% of component (C), based on the total weight of the moisture-curable conformal coating composition.

[0047] Component (C) is preferably different from the other components of the conformal coating composition.

[0048] Component (D):

[0049] The role of component (D) is to quickly build a very strong network.

[0050] There are various commercially available products, for example from WACKER Chemie AG.

[0051] Exemplary compounds are described in WO 03 / 018658 A1 and WO 03 / 014226 A1. In particular, functionalized alkoxysilanes are described in which the alkoxysilyl group is separated from a heteroatom (e.g., oxygen or nitrogen) by a methylene spacer, and the reactivity of the silane with respect to hydrolysis and condensation of the silyl unit is significantly increased by the spatial proximity of these two groups used to functionalize the organopolysiloxane and the organic polymer. The increased reactivity of such "α-silanes" with methylene spacers is also described in Monatshefte für Chemie 2003, 134, 1081-1092.

[0052] Such highly reactive α-silanes have hitherto been used to prepare silane-functional (pre)polymers which have a correspondingly increased reactivity toward moisture and are therefore suitable for the preparation of compositions which cure in the presence of atmospheric moisture.

[0053] Preferably, the alkoxysilane (D) having one or more tertiary amino groups has the following general formula (IV):

[0054] R 3 R 4 N-(CR 5 2)-Si(R 2 ) 3-x (OR 1 ) x (IV),

[0055] in

[0056] x is 2 or 3, preferably 3.

[0057] Each R 1 and R 2 are independently selected from hydrocarbon groups having 1 to 12 carbon atoms or alkoxy-alkyl groups having a total of 2 to 20 carbon atoms. 1 and R 2 Independently selected from hydrocarbon groups having 1 to 5 carbon atoms.

[0058] R 1 and R 2 Examples are alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl (such as n-hexyl), heptyl (such as n-heptyl), octyl (such as n-octyl and isooctyl such as 2,2,4-trimethylpentyl), nonyl (such as n-nonyl), decyl (such as n-decyl), dodecyl (such as n-dodecyl); alkenyl groups such as vinyl and allyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl; aryl groups such as phenyl and naphthyl; alkaryl groups such as o-, m- and p-tolyl, xylyl and ethylphenyl; aralkyl groups such as benzyl, α- and β-phenylethyl.

[0059] Group R 1 Preferably it is a hydrocarbon group having 1 to 5 carbon atoms, more particularly an alkyl group having 1 to 3 carbon atoms. 1 More preferably, it is methyl or ethyl. 1 More preferred is ethyl.

[0060] R 2 Preferred is methyl or ethyl.

[0061] Each R 3 and R 4independently selected from alkyl, cycloalkyl, alkenyl or aryl groups, each having up to 12 carbon atoms, which may be optionally substituted with halogen atoms and / or organic functional groups, or divalent alkyl, cycloalkyl, alkenyl or aryl groups, each having up to 12 carbon atoms, which may be optionally substituted with halogen atoms and / or other functional groups such as nitro, thiol, carboxyl, carbonyl, ester, hydroxyl and ether groups.

[0062] R 3 and R 4 Examples are alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, hexyl (such as n-hexyl), heptyl (such as n-heptyl), octyl (such as n-octyl and isooctyl such as 2,2,4-trimethylpentyl), nonyl (such as n-nonyl), decyl (such as n-decyl), dodecyl (such as n-dodecyl); alkenyl groups such as vinyl and allyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, cycloheptyl and methylcyclohexyl; aryl groups such as phenyl and naphthyl; alkaryl groups such as o-, m- and p-tolyl, xylyl and ethylphenyl; aralkyl groups such as benzyl, α- and β-phenylethyl.

[0063] Group R 3 and R 4 Preferably it is a hydrocarbon group having 1 to 6 carbon atoms, more particularly an alkyl group having 1 to 4 carbon atoms. 3 and R 4 Preferred is methyl, ethyl, propyl or butyl.

[0064] Component (D) preferably has no primary amino functions.

[0065] In formula (IV), R 5 is hydrogen or an alkyl, cycloalkyl, alkenyl or aryl group having up to 12 carbon atoms, which may be optionally substituted by halogen atoms and / or other functional groups such as nitro, mercapto, carboxyl, carbonyl, ester, hydroxyl and ether groups. 5 Preferred is hydrogen.

[0066] In an alternative embodiment, N and Si (R 2 ) 3-x (OR 1 ) x The methyl bonds between them can be propyl (so-called gamma-silane) or ethyl.

[0067] Preferred alkoxysilanes of formula IV are

[0068] N,N-diethylaminomethyl-triethoxysilane,

[0069] N,N-diethylaminomethyl-methyldiethoxysilane,

[0070] N,N-dibutylaminomethyl-triethoxysilane,

[0071] N,N-dibutylaminomethyl-methyldiethoxysilane,

[0072] N-(triethoxysilylmethyl)piperazine,

[0073] N-(methyldiethoxysilylmethyl)piperazine,

[0074] N-(triethoxysilylmethyl)morpholine,

[0075] N-(methyldiethoxysilylmethyl)morpholine,

[0076] N-(3-acryloyloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane,

[0077] N-(N-acetylphenyl)-3-aminopropyltriethoxysilane,

[0078] 3-(N-allylamino)propyltrimethoxysilane,

[0079] 4-aminobutyltriethoxysilane,

[0080] N-(6-aminohexyl)aminomethyltriethoxysilane,

[0081] N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane,

[0082] 11-aminoundecyltriethoxysilane,

[0083] (N,N-diethylaminomethyl)triethoxysilane,

[0084] 3-(1,3-dimethylbutylene)aminopropyltriethoxysilane,

[0085] N-phenylaminomethyltriethoxysilane,

[0086] (Cyclohexylaminomethyl)triethoxysilane,

[0087] tris(triethoxysilylmethyl)amine,

[0088] 3-(2,4-dinitrophenylamino)propyltriethoxysilane,

[0089] 3-Mercaptopropyltriethoxysilane.

[0090] The conformal coating composition preferably comprises 3 to 15 wt%, more preferably 5 to 15 wt% of component (D), based on the total weight of the moisture-curable conformal coating composition.

[0091] Component (D) is preferably different from the other components of the conformal coating composition.

[0092] Component (E):

[0093] The function of component (E) is to impart additional adhesion strength on various substrates (eg, polymer-coated printed circuit boards, flexible boards, ceramics, silicones, and glass).

[0094] Exemplary compounds are described, for example, in US Pat. No. 4,644,074A. In particular, the amino-functionalized siloxanes used in the methods of the present invention are well known in the art. They can be prepared according to the method described in U.S. Pat. No. 2,947,771 to Bailey, wherein an amino-functionalized silane is equilibrated with a siloxane in the presence of an alkali metal hydroxide. Furthermore, they can be prepared according to the method described in U.S. Pat. No. 3,598,853 to Friedman et al., wherein an amino-functionalized silane is condensed with a silanol-terminated polydiorganosiloxane. Other methods for preparing amino-functionalized siloxane fluids are described in U.S. Pat. Nos. 3,890,269 to Martin; 2,930,809 to Jex et al.; and 3,045,036 to Jex et al. The amino-functionalized siloxanes and their methods of preparation described in these references are incorporated herein by reference.

[0095] Preferably, the at least one alkoxysilane (E) having one or more primary or secondary amino groups has the following general formula (V):

[0096] R 6 HN-R 7 -Si(OR 1 )3(V),

[0097] where R 6 is selected from hydrogen or hydrocarbon groups, preferably hydrogen, and R 7 is an alkyl linking group comprising at least one carbon atom, preferably at least 2 carbon atoms, preferably,

[0098] -CH2-CH2- or –CH2-CH2-CH2-, and R 1 As defined above, methyl or ethyl is preferred.

[0099] Preferred alkoxysilanes of the general formula (V) are:

[0100] β-Aminopropyltriethoxysilane,

[0101] γ-aminopropyltriethoxysilane,

[0102] γ-aminopropyl-dimethoxysilane,

[0103] Methyl-β-(aminoethyl)-γ-aminopropyldimethoxysilane,

[0104] ω-aminohexyltributylmethoxysilane,

[0105] β-(Aminoethyl)propyltrimethoxysilane,

[0106] β-(Aminoethyl)-hexyltriethoxysilane,

[0107] β-(Aminopropyl)butyltributoxysilane,

[0108] (Trimethylsilylpropyl)ethylenediamine,

[0109] (Trimethylsilylisobutyl)-ethylenediamine, and

[0110] γ-3-Aminopropyltrimethoxysilane.

[0111] The conformal coating composition preferably comprises 0.001 to 10 wt%, more preferably 0.5 to 5 wt% of component (E), based on the total weight of the moisture-curable conformal coating composition.

[0112] Component (E) is preferably different from the other components of the conformal coating composition.

[0113] Component (F):

[0114] The function of component (F) is to facilitate visual and automated optical inspection of surface defects under UV light.

[0115] It is well known in the industry to incorporate pigments and dyes into polymer systems. The dye / pigment can be pre-dispersed in one or more components of the coating composition, or can be added as a separate part. The dye / pigment can also be functionalized or covalently bonded to siloxanes, silanes, other silicone-compatible and incompatible polymers, or can simply be physically blended. The carrier polymer can be functional or non-functional.

[0116] Preferably, the UV-fluorescent pigment (F) is selected from UV marking whitening solutions comprising one of the proprietary whitening agents which are fluorescent under UV or black light. Preferably a material is used which is soluble or dispersible into the polydimethylsiloxane (PDMS) polymer and network.

[0117] In a preferred embodiment, the ColourPaste FL UV fluorescent dyes are incorporated into the coating compositions of the present invention to provide autofluorescence, which is crucial for automated inspection of the final PCB (printed circuit board). In addition, solubilization or grafting of other fluorescent markers such as TINOPAL OB (BASF), KB-140 and KB-6002 (KUSTOM GROUP), fluoranthene, coumarin 120, pyrene derivatives, and perylene is also possible.

[0118] The dye / pigment may be covalently bonded to the silicone, silane or other polymer, or may be physically blended.The optional carrier polymer may be functional or non-functional PDMS or any other silicone compatible polymer, copolymer or oligomer.

[0119] Preferably, component (F) comprises 1 to 10 parts of TINOPAL OB or UVITEX optical brighteners designed for various applications. These dyes are incorporated into 100 parts of functional or non-functional silicones.

[0120] The resulting fluid can be further diluted or used as is in the conformal coating formulations of the present invention to aid in automatic defect detection under UV or black light.Combinations of different pigments, dyes, optical brighteners and fluorescent markers are also possible.

[0121] The conformal coating composition preferably comprises 0.001 to 10 wt%, more preferably 0.5 to 5 wt% of component (F), based on the total weight of the moisture-curable conformal coating composition.

[0122] Component (F) is preferably different from the other components of the conformal coating composition.

[0123] Component (G):

[0124] Component (G) serves to further adjust physical and mechanical properties, such as hardness and softness, increase wear resistance, promote adhesion and anchoring, and may include additional components. This component may be reactive and covalently bonded to the moisture-curing matrix (as in the case of, for example, phenyltriethoxysilane) or may be blended and remain unbonded in the polymer matrix (as in the case of, for example, non-reactive polydimethylsiloxane (PDMS) fluid).

[0125] A preferred functional compound is phenyltriethoxysilane, commercially available from WACKER Chemie AG as SILANE P-TRIETHOXY or from GELEST, Inc as PHENYL TRIETHOXY SILANE.

[0126] A preferred non-functional compound is polydimethylsiloxane, AK fluids such as AK 50 is commercially available and is a non-reactive polydimethylsiloxane having a viscosity of about 50 mPa·s, as measured based on standard test method ASTM D4652 performed at room temperature (25° C.) using a Brookfield DV-1 digital viscometer instrument equipped with a type LV-2 (62) spindle at a speed of 50 rpm.

[0127] Preferably, the moisture-curable conformal coating composition further comprises (G) one or more additives selected from viscosity modifiers or mechanical property and adhesion enhancers.

[0128] Preferred additives are:

[0129] Trimethylsilyl terminated non-functional PDMS fluid or other well known reactive diluents, resins or silanes.

[0130] Preferred functional additives are; ethyltrimethoxysilane, methylbutoxysilane, propyldipropoxysilane, methyltriethoxysilane, ethyltriethoxysilane, ethyl orthosilicate and n-butyl orthosilicate or polyethyl silicate, isopropyl polysilicate, butyl polysilicate, dimethyltetraethoxysilane, trimethylpentabutoxytrisiloxane, phenyltriethoxysilane, phenyltributoxysilane, diphenyldiethoxysilane, propyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, propyltriethoxysilane and methyltriethoxysilane and partially hydrolyzed silicates such as ethyl silicate.

[0131] In addition, the following functional additives can be used in combination with the above silanes for performance enhancement: α-aminomethylsilanes such as aminomethyl-triethoxysilane, aminomethylmethyldiethoxysilane, N-cyclohexyl-aminomethyl-triethoxysilane, N-cyclohexylaminomethyl-methyldiethoxysilane, N-ethylaminomethyl-triethoxysilane, N-ethylaminomethyl-methyldiethoxysilane, N-butylaminomethyl-triethoxysilane, N-butylaminomethyl-methyldiethoxysilane, N-phenylaminomethyl-triethoxysilane, N-phenylaminomethyl-methyldiethoxysilane, O-methyl

[0065] Examples of the present invention include methylcarbamate methyl-triethoxysilane, O-methylcarbamate methyl-methyldiethoxysilane, N-phenyltriethoxysilane, N,N-diethylamino-methyl-triethoxysilane, N,N-diethylaminomethyl-methyl-diethoxysilane, N,N-dibutylaminomethyl-triethoxysilane, N,N-dibutylaminomethyl-methyldiethoxysilane, N-(triethoxysilylmethyl)piperazine, N-(methyldiethoxysilyl-methyl)piperazine, N-(triethoxysilylmethyl)morpholine, and N-(methyldiethoxysilylmethyl)morpholine. In addition, α-oxymethylsilanes such as methacryloxymethyl-triethoxysilane, methacryloxymethyl-methyldiethoxysilane, methoxy-methyl-triethoxysilane, methoxymethyl-methyldiethoxysilane, glycidyloxymethyl-triethoxysilane, and glycidyloxymethyl-methyldiethoxysilane are also used. In addition, α-phosphonomethylsilanes such as diethylphosphonate-methyl-triethoxysilane and diethylphosphonate-methyl-methyldiethoxysilane are also used. In addition to the silanes having ethoxysilyl groups listed here, the corresponding methoxysilanes can also be used.

[0132] Component (G) is preferably different from the other components of the conformal coating composition.

[0133] The conformal coating composition preferably comprises 0 to 25 wt%, more preferably 1 to 10 wt%, even more preferably 5 to 7 wt% of component (G), based on the total weight of the moisture-curable conformal coating composition.

[0134] The moisture-curable conformal coating composition according to the present invention preferably comprises, and more preferably consists of, the following materials based on the total weight of the moisture-curable conformal coating composition:

[0135] - 40 to 70% by weight, preferably 50 to 60% by weight, of component (A),

[0136] - 10 to 30% by weight, preferably 15 to 25% by weight, of component (B),

[0137] - 3 to 20% by weight, preferably 5 to 15% by weight, of component (C),

[0138] - 3 to 15% by weight, preferably 5 to 15% by weight, of component (D),

[0139] - up to 10% by weight, preferably from 0.5 to 5% by weight, of component (E),

[0140] - up to 10% by weight, preferably from 0.5 to 5% by weight, of component (F),

[0141] Optionally,

[0142] 0 to 25% by weight, preferably 1 to 10% by weight, of component (G).

[0143] Preferably, the moisture-curable conformal coating composition is sprayable.

[0144] Preferably, the viscosity of the conformal coating composition is in the range of 50 to 10,000 mPa·s, more preferably in the range of 100 to 6,000 mPa·s, and particularly in the range of 500 to 4,000 mPa·s. The viscosity can be measured by a Brookfield viscometer instrument based on standard test method ASTM D4652 using a spindle type LV-2 (62) at a speed of 50 rpm.

[0145] The conformal coating compositions of the present invention should preferably meet the desired flow properties without the need for additional diluents and / or viscosity modifiers (agents), such as softeners.

[0146] Thus, the conformal coating composition of the present invention does not include diluents and / or viscosity modifiers.

[0147] The conformal coating composition of the present invention is preferably an RTV-1 composition, ie, it is a one-part composition that cures at room temperature (about 25°C).

[0148] Preferably, the composition of the present invention has a low volatile organic compound content to avoid atomization to adapt to high pressure spraying processes. In addition, due to environmental and health safety regulations, low volatile organic compound content products are desirable and required in the coatings industry.

[0149] The percentage of volatile matter can be determined gravimetrically using the international standard test method ASTM D-2369. More precisely, the volatile organic content can also be determined by gas chromatography using the international standard test method ASTM D-2369.

[0150] Furthermore, the present invention relates to a process for preparing the composition according to any one of claims 1 to 10, which comprises mixing components (A), (B), (C), (D), (E), (F) and optionally component (G).

[0151] Preferably, the method according to the present invention comprises the following steps

[0152] (a) first mixing components (A), (B) and (D);

[0153] (b) homogenizing the composition of step (a);

[0154] (c) Components (C), (E), (F) and optionally (G) are mixed into the composition of step (b).

[0155] Preferably, step (b) comprises heating the composition.

[0156] Mixing and homogenization can be performed by any known method, preferably by planetary mixing equipment, such as PCLaborsystem model LA G2.

[0157] Example

[0158] Invention Example 1:

[0159] The following compounds have been used to prepare moisture-curable conformal coating compositions:

[0160] A: OH-functional silicone fluid ( CT 601M, WACKER Chemie AG),

[0161] B: Silicone resin containing Q units and M units ( MQ 803TF, Wacker Chemie AG),

[0162] C: Partially hydrolyzed ethyl silicate polymer ( SILICATE TES 40WN, Wacker Chemie AG),

[0163] D: N,N,-di(butyl)aminomethyltriethoxysilane (SILAN DBA-TEO, Wacker Chemie AG),

[0164] E: 3-aminopropyltrimethoxysilane ( GF 96, Wacker Chemie AG),

[0165] F: Fluorescent pigment paste ( UV FL, Wacker Chemie AG),

[0166] G1: Phenyltriethoxysilane (SILANE P-TRIETHOXY, Wacker Chemie AG),

[0167] G2: Linear non-reactive polydimethylsiloxane ( AK 50, Wacker Chemie AG)

[0168] Use the following weight ratios:

[0169] Components weight% A 54.1 B 23.2 C 7.5 D 7.4 E 1 F 1 G1 1.8 G2 4 total 100

[0170] Add component D first for use at all times during mixing. Start nitrogen flow to establish a nitrogen blanket (a moisture-free mixing environment). Add component A, followed by the slow addition of powdered component B while mixing. Continue mixing until the composition is uniformly dispersed (appearance: turbid dispersion - solid resin particles dispersed in a fluid). Alternatively, components A and B can be premixed separately and this premix added over component D. Optionally, heat the mixture to 45°C (homogenization time is approximately 1 hour at 45°C, or approximately 2 hours at room temperature; for small-scale laboratory samples prepared in a speed mixer, 10 minutes at 70°C is sufficient to completely dissolve components A and B). Then, add the remaining components in the following order while stirring under a nitrogen blanket: component G2, component C, component G1, component E, component F (alternatively, a speed mixer can be used for small-scale laboratory sample preparation). Continue mixing until a homogeneous (translucent) formulation is obtained. A vacuum (0-200 mbar, preferably 0-100 mbar, or more preferably 0-50 mbar) may be applied (vacuum application may be initiated at any point after all ingredients have been added). Mixing is continued under vacuum for a minimum of 30 minutes, followed by breaking the vacuum with a nitrogen blanket. The resulting product is moisture sensitive. Therefore, a vacuum and / or nitrogen blanket is necessary for long-term storage and larger-scale samples.

[0171] The properties of the conformal coating compositions of the present invention were compared with commercially available compositions:

[0172] Comparative Example 1: 964 (WACKER Chemie AG), an RTV-1 amine curing system that cures to a translucent coating upon contact with moisture in the air.

[0173] Comparative Example 2: Dow 3-1965 Conformal Coating (Dow Corning)

[0174] Comparative Example 3: ECC3050S Conformal Coating (Momentive)

[0175] The results are summarized as follows:

[0176]

[0177] The following test methods have been applied:

[0178] Hardness: Test method standard ASTM D2240,

[0179] Adhesion and anchoring: Test method standard ASTMD3359,

[0180] Volatile matter: Test method standard ASTM D-2369,

[0181] Tensile strength: Test method standard ASTMD638,

[0182] Elongation: Test method standard ASTMD412.

[0183] The conformal coatings of the present invention are odorless and have improved mechanical properties to absorb physical stresses and respond to thermal cycling (low and high temperature fluctuations).

Claims

1. A moisture-curable conformal coating composition comprising, based on the total weight of the moisture-curable conformal coating composition: (A) 40 to 70 weight percent of one or more linear hydroxyl-terminated organopolysiloxanes; (B) 10 to 30 weight percent of one or more organopolysiloxane resins; (C) 3 to 20 weight percent of one or more organosilicates; (D) 3 to 15 weight percent of one or more alkoxysilanes having at least one tertiary amino group; (E) 0.001 to 10 weight percent of one or more alkoxysilanes having at least one primary or secondary amino group; and (F) 0.001 to 10% by weight of one or more UV fluorescent pigments, The alkoxysilane (D) having one or more tertiary amino groups has the following general formula (IV): R 3 R 4 N-(CR 5 2)-Si(R 2 ) 3-x (OR 1 ) x (IV), in x is 2 or 3, R 1 and R 2 are each independently selected from a hydrocarbon group having 1 to 12 carbon atoms or an alkoxy-alkyl group having C2 to C10 carbon atoms, R 3 and R 4 are each independently selected from alkyl, cycloalkyl, alkenyl or aryl groups, each having up to 12 carbon atoms and each optionally substituted, R 5 is hydrogen or an optionally substituted alkyl, cycloalkyl, alkenyl or aryl group each having up to 12 carbon atoms, and The organic silicate (C) has the following general formula (III): Each R 1 are independently selected from C1-C10 alkyl, or C2-C20 alkoxy-alkyl, and n is a number from 1 to 10, and wherein the organopolysiloxane resin (B) comprises at least 80% of M and Q units based on the total number of M, Q, D and T units, in M unit refers to R3SiO 1 / 2 , D unit refers to R2SiO 2 / 2 , T unit refers to RSiO 3 / 2 , Q unit refers to SiO 4 / 2 , wherein each R is independently selected from alkyl, alkoxy, hydroxy, or alkenyl, and The conformal coating composition does not contain a metal catalyst.

2. The moisture-curable conformal coating composition according to claim 1, wherein the linear hydroxyl-terminated organopolysiloxane (A) has the following general formula (I): Each R 0 are independently selected from C1-C10 alkyl groups, and n is a number from 5 to 5,000.

3. The moisture-curable conformal coating composition according to any one of claims 1 to 2, wherein the alkoxysilane (E) having one or more primary or secondary amino groups has the following general formula (V): R 6 HN-R 7 -Si(OR 1 )3(V), where R 6 is selected from hydrogen or hydrocarbon groups, and R 7 is an alkyl linking group containing at least two carbon atoms, and R 1 Independently selected from C1-C10 alkyl or C2-C20 alkoxy-alkyl.

4. The moisture-curable conformal coating composition according to any one of claims 1 to 3, further comprising (G) one or more additives selected from viscosity modifiers or mechanical property and adhesion enhancers.

5. The moisture-curable conformal coating composition according to any one of claims 1 to 4, wherein the moisture-curable conformal coating composition comprises, based on the total weight of the moisture-curable conformal coating composition: - 50 to 60% by weight of component (A), - 15 to 25% by weight of component (B), - 5 to 15% by weight of component (C), - 5 to 15% by weight of component (D), - 0.5 to 5% by weight of component (E), - 0.5 to 5% by weight of component (F), and Optional, 0 to 25% by weight, preferably 1 to 10% by weight, of component (G).

6. The moisture-curable conformal coating composition of any one of claims 1 to 5, wherein the moisture-curable conformal coating composition is sprayable.

7. The moisture-curable conformal coating composition according to any one of claims 1 to 6, wherein the conformal coating composition has a viscosity measured at 25°C in the range of 50 to 10,000 mPa·s, preferably in the range of 100 to 6,000 mPa·s, more preferably in the range of 500 to 4,000 mPa·s.

8. A process for preparing the composition of any one of claims 1 to 7, comprising mixing components (A), (B), (C), (D), (E), (F) and optionally component (G).

9. The method according to claim 8, comprising: (a) first mixing components (A), (B) and (D); (b) homogenizing the composition of step (a); (c) Components (C), (E), (F) and optionally (G) are mixed into the composition of step (b).

10. The method of claim 9, wherein step (b) comprises heating the composition.

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