CA1116771A - Flexible coating resins from siloxane resins having a very low degree of organic substitution - Google Patents
Flexible coating resins from siloxane resins having a very low degree of organic substitutionInfo
- Publication number
- CA1116771A CA1116771A CA000311613A CA311613A CA1116771A CA 1116771 A CA1116771 A CA 1116771A CA 000311613 A CA000311613 A CA 000311613A CA 311613 A CA311613 A CA 311613A CA 1116771 A CA1116771 A CA 1116771A
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- weight percent
- composition
- acid
- resins
- silanol
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Classifications
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
- C09D183/04—Polysiloxanes
Abstract
ABSTRACT OF THE DISCLOSURE
Abrasion resistant siloxane resins having a low degree of organic substitution thereby tending to be brittle can be made flexible by including some degree of phenyl substitution into the organic substitution.
Such resins are useful as coatings on optical lenses and skylights.
Abrasion resistant siloxane resins having a low degree of organic substitution thereby tending to be brittle can be made flexible by including some degree of phenyl substitution into the organic substitution.
Such resins are useful as coatings on optical lenses and skylights.
Description
~ ~ 67 ~ ~
The avaiiability of ligh~weight plastics has led to the replacement of glass by such plastics for numerous uses. Over the past several years, new plastics have been developed which find use in window glazing, lenses, clear face shields, aircraft canopies and the like.
Although such plastics have many outstanding properties, they are deficient in their resistance to scratching. An outstanding e~ample is the deterioration of plastic sunglass lenses by common everyday use because such glasses are frequently removed from the face and laid on hard substrates, lens down.
Thus, in order to better utili~e the advantageous properties of today's plastics, there is a need to render such plastics scratch and abrasion resistant.
In order to obtain abrasion resistant sur~aces, such as, for example, polycarbonate surfaces, investigators have tended to coat very thin coats of organic or silicone ; resins on the surface of the plastics. The intent was to obtain abrasion resistance without losing the optical properties of the plastic substrate, Such an organic coating is disclosed in U.S~
Patent No. 4,018,941. Such an organic coating is prepared from polyols and urethanes and is cured via melamine crosslin~ers. Although some degree of abrasion resistance is afforded by the melamine coating, it has a tendency to be affected by outdoor exposure and eventually the coating deteriorates.
In view of the above9 silicone coatings which exhibit good weather resistance were developed. Such resins are shown in U.S~ Patents 3,389,114, 3,389,121, 3,634,3~1, 3,642,698 and 3,935,346, all assigned to Owens-Illinois.
The latter patent teaches a method of making an abrasion resistan~ coating from an alkylated melamine-formaldenyde resin and a hydroly7ate of CH3Si~OR)3. These resins all have good wea-ther resistance but only moderate abrasion resistance.
A siloxane resin having a low degree of organic substitution has been developed. The coating had hardness and therefore good abrasion resistance. Such resins are disclosed in U.S. Patent 3,986,997 issued October 19, 1976 to Harold A. Clark. The ClarX resins are very versatile materials and find utility as abrasion resistant coatings on a number oE substrates which requi.re good abrasion resistance.
The only disadvantage of the Clar~ resins is the fact that they tend to be inflexiblel~ that is, under certain circumstances the coatings tend to cra~e.
It is well Xnown in the silicone art that flexibility can be built into a siloxane resin coating by incorporating a dimethyl containing hydrolyzable silane in the formulation when the resin is first prepared (see Canadian Patent No. 1,015,888). Unfortunately, the presence of dimethyl siloxane in any siloxane resin tends to also soften the coating so that the abrasion resistance alls off. Thus, for purposes of obtaining an abrasion resistant coatin$ with flexibility, one would not suggest using the above approach in preparing the resins.
What is needed is a weather resistant, abrasion resistant, flexible, c ear coating.
There has now been discovered a means of improving the flexibility of siloxane resins having a low degree of organic substitution without undue sacrifice of the abrasion resistance of the coating.
What is disclosed herein is an improvemen~ in the flexibility of the Clark resins shown in the U.S.
Patent No. 3,986,997 set out above.
Such improved flexibility can be obtain~d by incorporating in the original formulation for the Clark resin a certain amount of monophenylsilsesquioxane structure.
It has been found that the incorporation of C6H5Si~OH)3 in the Clark resin gives increased flexibility to the resin without significant loss of abrasion resistance of the cured coating.
In accordance with the present teachings, a pigment-free aqueous coating composition is provided which comprises 1) a dispersion of colloidal silica in
The avaiiability of ligh~weight plastics has led to the replacement of glass by such plastics for numerous uses. Over the past several years, new plastics have been developed which find use in window glazing, lenses, clear face shields, aircraft canopies and the like.
Although such plastics have many outstanding properties, they are deficient in their resistance to scratching. An outstanding e~ample is the deterioration of plastic sunglass lenses by common everyday use because such glasses are frequently removed from the face and laid on hard substrates, lens down.
Thus, in order to better utili~e the advantageous properties of today's plastics, there is a need to render such plastics scratch and abrasion resistant.
In order to obtain abrasion resistant sur~aces, such as, for example, polycarbonate surfaces, investigators have tended to coat very thin coats of organic or silicone ; resins on the surface of the plastics. The intent was to obtain abrasion resistance without losing the optical properties of the plastic substrate, Such an organic coating is disclosed in U.S~
Patent No. 4,018,941. Such an organic coating is prepared from polyols and urethanes and is cured via melamine crosslin~ers. Although some degree of abrasion resistance is afforded by the melamine coating, it has a tendency to be affected by outdoor exposure and eventually the coating deteriorates.
In view of the above9 silicone coatings which exhibit good weather resistance were developed. Such resins are shown in U.S~ Patents 3,389,114, 3,389,121, 3,634,3~1, 3,642,698 and 3,935,346, all assigned to Owens-Illinois.
The latter patent teaches a method of making an abrasion resistan~ coating from an alkylated melamine-formaldenyde resin and a hydroly7ate of CH3Si~OR)3. These resins all have good wea-ther resistance but only moderate abrasion resistance.
A siloxane resin having a low degree of organic substitution has been developed. The coating had hardness and therefore good abrasion resistance. Such resins are disclosed in U.S. Patent 3,986,997 issued October 19, 1976 to Harold A. Clark. The ClarX resins are very versatile materials and find utility as abrasion resistant coatings on a number oE substrates which requi.re good abrasion resistance.
The only disadvantage of the Clar~ resins is the fact that they tend to be inflexiblel~ that is, under certain circumstances the coatings tend to cra~e.
It is well Xnown in the silicone art that flexibility can be built into a siloxane resin coating by incorporating a dimethyl containing hydrolyzable silane in the formulation when the resin is first prepared (see Canadian Patent No. 1,015,888). Unfortunately, the presence of dimethyl siloxane in any siloxane resin tends to also soften the coating so that the abrasion resistance alls off. Thus, for purposes of obtaining an abrasion resistant coatin$ with flexibility, one would not suggest using the above approach in preparing the resins.
What is needed is a weather resistant, abrasion resistant, flexible, c ear coating.
There has now been discovered a means of improving the flexibility of siloxane resins having a low degree of organic substitution without undue sacrifice of the abrasion resistance of the coating.
What is disclosed herein is an improvemen~ in the flexibility of the Clark resins shown in the U.S.
Patent No. 3,986,997 set out above.
Such improved flexibility can be obtain~d by incorporating in the original formulation for the Clark resin a certain amount of monophenylsilsesquioxane structure.
It has been found that the incorporation of C6H5Si~OH)3 in the Clark resin gives increased flexibility to the resin without significant loss of abrasion resistance of the cured coating.
In accordance with the present teachings, a pigment-free aqueous coating composition is provided which comprises 1) a dispersion of colloidal silica in
2) a solution which has as cosolvent ether esters of ethylene or propylene glycol and water and has as solute
- 3) a partial condensate of a silanol of the formula RSi(OH)3 in which R is an alkyl radical of 1 to 3 carbon atoms and phenyl wherein at least 70 weight percent of the silanol is CH3Si(OH)3, wherein the composition contains 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 50 percent of the partial condensater and wherein the composition contains sufficient acid to provide a pH in the range of 2.8 to 6Ø
1 ~ 6~ ~ ~
Not only can one obtain flexibility in siloxane resins having a low degree o~ substitution, one can obtain control over the degree of flexibility given to such resins by merely controlling the amount of monophenyl silanol put into the formulation, i.e., the degree of flexibility built into the cured coating of the resin is linearly dependent on the amount of monophenyl silanol actually incorporated in the ~ormulation. The control is such that flexibility + 5% can be estimated from the amount of monophenyl silanol incorporated.
At least 1 weight percent of C6H5Si(OH)3, based on the weight of total RSi(OH)3 present in the composition, is required to get the flexibility effect. Up to 30 weight percent of C6H5SitOH)3 can be utilized. Generally, greater than 30 weight percent of C6H5Si~OH)3, even though giving increased fle~ibility, does not retain the required abrasion resistance.
The resins are prepared by the methods found in the above Clark patent and the only di~ference is that C6H5Si~OCH3)3, in the proper proportions, is mixed with the CH3Si~OH)3 befoTe the hydrolysis and contact with ~he colloidal silica. The C6H~Si~OCH3)3 can be pre-hydrolyzed before mixing with the CH3Si~OH)3 but no significant advantage is obtained thereby.
The silica component of the composition is present as colloidal silica. Aqueous colloidal silica dispersions generally have a particle size in the range of 5 to 150 millimicrons in diameter. These silica dispersions are prepared by methods well-known in the ` art and are commercially a~aila~le, It is preferred to use colloidal silica of 10-3Q millimicron par~icle si~e in order to obtain dispersions having a greater stability and to provide coatings having superior optical properties.
Colloidal silicas of this type are relatively free of Na2O
and other alkali metal oxides, generally containing less than 2 weight percent, preferably less than 1 weight percent Na2O. They are available as both acidic and basic hydrosols. Colloidal silica is distinguished from other water dispersable forms of SiO2, such as nonparticulate polysilicic acid or alkali metal silicate solutions, which are not operative in the practice of the present invention.
The silica is dispersed in a solu~ion of the siloxanol carried in a lower aliphatic alcohol-water, or ether ester-water, cosolvent. Suitable lower aliphatic alcohols include methanol, ethanol, isopropanol, and t-butyl alcohol. Mixtures of such alcohols can be used. Isopropanol is the preferred alcohol and when mixtures of alcohol are utilized it is preerred ta utilize ~it least 50 weight percent of isopropanol in the mixture to obtain optimum adhesion of the coating. Suitable etheT esters are ether esters of ethylene or propylene glycol such as CH3cOOtcH2cH2o)2c2H5~ CH3COO~CH2CH2)2 4 9' ; CH3COOCH~CH2OC2H5~ CHjCOOCH~CH2OCH3 and CH3COOC~2CH2OC4Hg and analogs o~ such materials prepared from propylene glycol.
The solvent system should contain from about 20 to 75 weight percent of alcohol or ether ester to ensure solubility o the siloxanol. Optionally one can utilize an additional water-miscible polar solvent, such as acetone, butyl cellosolve and the like in a minor amount, for example, no more than 20 weight percent of the cosolvent system.
~ 6~7~
To obtain optimum properties in the coating and to prevent immediate gellation of the coating composition, sufficient acid to provide a pH of from 2.8 to 6.0 must .
be present. Suitable acids include both organic and inorganic acids such as hydrochloric, acetic, chloroacetic~ citric, benzoic, dimethylmalonic, formic, glutaric, glycolic, maleic, malonic, toluene-sulfonic, oxalic and the like. The specific acid utilized has a direct effect on the rate of silanol condensation which in turn determines shelf life of ~he composition. The stronger acids, such as hydrochloric and toluenesulfonic acid, give appreciably shortened shelf or bath life and require less ageing to obtain the described soluble partial condensate. It is preferred to add sufficient water-miscible carboxylic acid selected from the group consisting of acetic, formic, propionic and maleic acids to provide pH in the range of 4 to 5.5 in ~he coating composition. In addition to providing good bath life, the alkali metal salts of these acîds are soluble, thus allowing the use of these acids with silicas containing a substantial Z0 ~greater than 0.2% Na20) amount of alkali metal or metal oxide.
The composition is easily prepared by adding the trialkoxysilanes, such as R'Si(OCH3)3, to colloidal silica hydrosols and adjusting the pH to the desired level by addition of the organic acid. The acid can be added to either the silanes or the hydrosol prior to mixing the two components pro~ided that the mixing is done rapidly The amount of acid necessary to obtain the desired pH
will depend on the alkali metal content of the silica but is usually less than one weight percent of the composition.
Alcohol is generated by hydrolysis of the alkoxy substituents of the silane, for example, hydrolysis of one mole of -Si(OC2H5)3 generates 3 moles of ethanol. Dependins upon the percent solids desired in- the final composition~
.. , , .~
additional alcohol e~her ester, water or a water-miscible solvent can be added. The composition should be ~-ell mi~ed and allowed to age for a short period of time to ensure formation of the partial condensate. The coating composition thus obtained is a clear or slightly hazy low viscosity fluid which is stable for several days.
Buffered latent condensation catalysts can be added to the composition so that milder curing conditions can be utilized to obtain the optimum abrasion resis~ance in the final coating. Alkali metal salts of carboxylic acids, such as potassium formate, are one class of such latent catalysts. The amine carboxylates and quaternary ammonium carboxylates are another such class of la~ent catalysts. O~ course the catalysts imust be soluble or at least miscible in the cosolvent system. The catalysts are latent to the extent that at room temperature they do not appreciably shorten the bath life of the composition, but upon heating the catalyst dissociates and generates a catalytic species ac~ive to promote condensation.
Buffered catalysts are used to avoid effects on the pH
of the composi~ion. Certain of the commercially a~ailable colloidal silica dispersions contain free alkali metal base which reacts with the organic acid during the adjustment of pH to generate the carboxylate catalysts in situ. This is particularly true when starting with a hydrosol having a pH of 8 or 9. The compositions can be cataly~ed by addition of carboxylates such as dimethylamine acetate~ ethanolamine acetate, dimethylaniline formate, te~raethylammonium benzoate, sodium acetate, sodium propionate, sodium formate or benzyltrimethylammonium acetate. The amount of catalyst can be varied depending upon the desired curing condition, but at about 1.5 weight percent catalyst in the composition, the bath life is shortened and optical properties of the coating may be impaired. It is preferred to utilize from about 0.05 to 1 weight percent of the catalyst.
To provide the grea~est stability in the dispersion form while obtaining optimum properties in the cured coatin~, it is preferred to utilize a coating composition having a pH in the range o 4-5 which contains 10-35 weight percent solids; the silica portion having a pàrticle size in the range of 5-30 millimicrons, the partial condensate CH3Si(OH)3 and C6H5Si(OH)3 being present in an amount in the range of 35 to 55 weight percent of the total solids in a cosolvent oE methanol, isopropanol and water or CH3COOCH2CH20CH3 and water or ether esters, the alcohols representing from 30 to 60 weight percent of the cosolvent and a catalyst selected from the group consisting of sodium acetate and benzyltrimethylammonium acetate being present in an amount in the range of 0.05 to 0.5 weight percent of the composition. Such a composition is relatively s~able and, when coated onto a substrate, can be cured in a relatively short time at temperatures in the range of 75-1~5C. to provide a transparent abrasion resistant surface coating.
The coating compositions of the invention can be applied to solid substrates by conventional methods, such as flowing, spraying or dippin~T to ~orm a continuous surface ~1~ 6'7~
film. Although substrates of soft plastic sheet material show the greatest improvement upon application of the coating, the composition can be applied to other substrates, such .
as wood, metal, printed surfaces, leatker, glass, ceramics and textiles. The compositions are especially useful as coatings for dimensionally stable synthetic organic polymeric substrates in sheet or film form, such as acrylic polymers, for example, poly~methylmethacrylate), polyesters, for example poly(ethyleneterephthalate) and polycarbonates, such as poly(diphenylolpropane)carbonate, polyamides, polyimides, copolymers o acryloni~rile-styrene, styrene-acrylonitrile-butadiene copolymers, polyvinyl chloride, butyrates, polyethylene and the li~e. Transparent polymeric materials coated with these compositions are us,e~ul as flat or curved enclosures, such as windows, skylight:s and l~indshields, especially for transportation equipme:nt. Plastic lenses, such as acrylic or polycarbonate opht:halmic lenses, can be coated ~-ith the compositions of the invention In certain applications requiring high optical resolution, it may be desirable to filter the coating composition prior to applying it to the substrate. In other applications, such as cor~rosion-resistant coatings on metals, the slight haziness ~less than 5~) obtained by the use of certain formulations 3 such as those containing citric acid and sodium citrate, is not detrimental and filtration is not necessary.
By choice of proper formulation, including solvent, application conditions and pretreatment of the substrate, the coatings can be adhered to substantially all solid surfaces. A hard solvent-resistan~ surface coating is ~ ~ 6~
obtained by removal of the solvent and volatile materials.
The composition will air dry to a tack-free condition, but heating in the range of 50 to 150~ is necessary to obtain condensation of residual silanols in ~he partial condensate.
This final cure results in the formation of silsesquioxanes of the formula 0SiO3/2 and RSiO3/2 and greatly enhances the abrasion resistance of the coating. The coating thickness can be varied by means of the particular application technique, but coatings of about 0.5 to 20 micron preferably 2-10 micron thickness are generally utilized.
BspecialIy thin coatings can be obtained by spin coating.
Now so that those skilled in the art can better understand and appreciate the invention, the following examples are presented, In the e~amples and elsewhere in this disclosure, ~he use of the symbols ~ and Me mean "phenyl" and "methyl"
respectively.
Example 1 - Preparation of phenyl containing resins of this invention.
Six resins were prepared for evaluation.
Sample 1 was prepared according to the procedure of Example 1 of U.S. 3,986,997 and was used for comparison purposes.
Samples 2-6 were prepared according to the following procedure. Samples 2, 3 and 4 fall within the scope of this invention and Samples 5 and 6 fall outside the scope of the claims.
5% ~Si(OH)3/45 CH3Si~OH)3 To a three-nec.~ed, round-bottomed flask was added 154.5 grams of a colloidal sllica having an initial pH of 3.1 containing 34% SiO2 of approximately 22 millimicron particle size and having an Na2O content of less than 0.01 weight percent. It was cooled to 8C and 5.3 grams o~
., . . ~ . . ........... , . . - . . . . - - - - ..
glacial acetic acid was added. 96.0 grams of CH3Si(OMe)3 and 8.1 grams of 0Si(OMe)3 were premixed and slowly added to the colloidal silica with vigorous st rring and external cooling. The methoxy silanes were allowed to hydrolyze with the formation of methanol. After the hydrolysis was complete, 2.7 grams of a 10% solution of sodium acetate and 132.4 grams of isopropanol were added.
After seven days standing, 66.2 grams additional alcohol was added and the solution filtered.
Samples 3 through 6 were prepared in the same manner as Sample 2 but with appropriate adjustment of the relative amounts o~ ~CH3)SiO~CH3)3 and C6H5Si~OCH3)3 employed to give:
Sample 3:
10~ C6H5Si(OH)3/40% CH3sitoH)3;
Sample 4:
15~ C6H5Si~OH)3/35% CH~Si~OH)3;
Sample 5:
20% C6H5Si~OH)3/30% CH3Si(OH)3; and Sample 6:
25% C6HSSi(OH)3/25% CH3si~O )3 Exam~le 2 Plexiglas~ panels 4" x 4" x 1/8" (10.16 cm x 10.16 cm x 0.32 cm) after being cleaned with isopropanol and air dried, were flow coated with a 22.5% solids resin, allowed to air dry and then cured for 18 hours at 75C.
Similar l" x 4" x 1/8" ~2.54 cm x 10.16 cm x 0.32 cm) strips were prepared to test the flexibility. The test for flexibility is relatiue and was ca~ried out in ~he following manner.
The 1" (2.5~ cm) wide strips were placed in a vise-like device so that the longest i.e. ~" ~10,16 cm) axis was horizontal. A strong light was placed on the opposite side of the strip from ~here the observation was being made, so that the craze marks when they formed, were more easily seen. The vise-like device is manipulated by hand to draw the vise jaws together slowly so that the plastic strip irst humps in the center and then begins to form a semi circle with the coating on the outside of the semi circle. While observing the coating, the jaws are moved slowly together (decreasing the radius of curvature) until craze marks are propogated in the coating. When the craze marks show across the entire width of the plastic strip, the end point has been reached.
The degree of flexibility is then calculated in the following manner. The initial length of ~he st~ip before compression is designated AB. The distance between the vise jaws at the end of compression is designated AB.
Prior measurements of angle of ~ plotted versus AB
give a graph i.e. ~ = ~B from which ~ can be easily determined.
AB
The radius of curvature ~r) can then be calculated.
r = AB 1~0 __ 'IT ~ o ~ 6~ ~ ~
One has to assume that ~ is an arc of a circle.
The actual shape of the semi-circle in this test is a parabola which suggests that this is a more severe test than a test which had a true semi-circular shape.
The abrasion resistance was determined according to ASTM ~ethod Dl0~4-~6. The instrument ~as the Tabor A braser. A 500 gram ~est load was used with CS-lOF
abrasive wheels and the test panels subjected to 500 revolutions on the abraser turntable~ The percent change in haze which is the criterion for determining the abrasion resistance of the coatlng is determined by measuring the di~-ference in haze of the unabrased and abrased coatings.
Haze is defined as that percentage of transmitted light which in passing through the specimen deviates from the incident beam by forward scattering. In this method, only light flux that deviates more than 2,5 degrees on the arerage is considered to be haze. The ~ Haze on the coatings was determined by ASTl~ Method D1003-61. A
Hunter Haze Meter: Gardner Laboratory, Inc~ was used.
The ~ Haze was calculated by measuring the amount of diffused light dividing by the amount of transmit~ed light and multiplying by one hundred.
The adhesion test was the 1/8" crossha*ch tape pull test in which the cured coating is crosshatched in 1/8" squares using a sharp object, over a square inch area. Adhesive tape ~#600 Adhesive - 3M Company) is firmly pressed onto the crosshatched area and sharply pulled away.
If all of the coating remains, the adhesion is 100~.
~Lfi~
o~
.,, ~ o~oo~o o\O o~o o\O o~o n t~ ~ o . .
U~ ¢ ~
1 ~ 6~ ~ ~
Not only can one obtain flexibility in siloxane resins having a low degree o~ substitution, one can obtain control over the degree of flexibility given to such resins by merely controlling the amount of monophenyl silanol put into the formulation, i.e., the degree of flexibility built into the cured coating of the resin is linearly dependent on the amount of monophenyl silanol actually incorporated in the ~ormulation. The control is such that flexibility + 5% can be estimated from the amount of monophenyl silanol incorporated.
At least 1 weight percent of C6H5Si(OH)3, based on the weight of total RSi(OH)3 present in the composition, is required to get the flexibility effect. Up to 30 weight percent of C6H5SitOH)3 can be utilized. Generally, greater than 30 weight percent of C6H5Si~OH)3, even though giving increased fle~ibility, does not retain the required abrasion resistance.
The resins are prepared by the methods found in the above Clark patent and the only di~ference is that C6H5Si~OCH3)3, in the proper proportions, is mixed with the CH3Si~OH)3 befoTe the hydrolysis and contact with ~he colloidal silica. The C6H~Si~OCH3)3 can be pre-hydrolyzed before mixing with the CH3Si~OH)3 but no significant advantage is obtained thereby.
The silica component of the composition is present as colloidal silica. Aqueous colloidal silica dispersions generally have a particle size in the range of 5 to 150 millimicrons in diameter. These silica dispersions are prepared by methods well-known in the ` art and are commercially a~aila~le, It is preferred to use colloidal silica of 10-3Q millimicron par~icle si~e in order to obtain dispersions having a greater stability and to provide coatings having superior optical properties.
Colloidal silicas of this type are relatively free of Na2O
and other alkali metal oxides, generally containing less than 2 weight percent, preferably less than 1 weight percent Na2O. They are available as both acidic and basic hydrosols. Colloidal silica is distinguished from other water dispersable forms of SiO2, such as nonparticulate polysilicic acid or alkali metal silicate solutions, which are not operative in the practice of the present invention.
The silica is dispersed in a solu~ion of the siloxanol carried in a lower aliphatic alcohol-water, or ether ester-water, cosolvent. Suitable lower aliphatic alcohols include methanol, ethanol, isopropanol, and t-butyl alcohol. Mixtures of such alcohols can be used. Isopropanol is the preferred alcohol and when mixtures of alcohol are utilized it is preerred ta utilize ~it least 50 weight percent of isopropanol in the mixture to obtain optimum adhesion of the coating. Suitable etheT esters are ether esters of ethylene or propylene glycol such as CH3cOOtcH2cH2o)2c2H5~ CH3COO~CH2CH2)2 4 9' ; CH3COOCH~CH2OC2H5~ CHjCOOCH~CH2OCH3 and CH3COOC~2CH2OC4Hg and analogs o~ such materials prepared from propylene glycol.
The solvent system should contain from about 20 to 75 weight percent of alcohol or ether ester to ensure solubility o the siloxanol. Optionally one can utilize an additional water-miscible polar solvent, such as acetone, butyl cellosolve and the like in a minor amount, for example, no more than 20 weight percent of the cosolvent system.
~ 6~7~
To obtain optimum properties in the coating and to prevent immediate gellation of the coating composition, sufficient acid to provide a pH of from 2.8 to 6.0 must .
be present. Suitable acids include both organic and inorganic acids such as hydrochloric, acetic, chloroacetic~ citric, benzoic, dimethylmalonic, formic, glutaric, glycolic, maleic, malonic, toluene-sulfonic, oxalic and the like. The specific acid utilized has a direct effect on the rate of silanol condensation which in turn determines shelf life of ~he composition. The stronger acids, such as hydrochloric and toluenesulfonic acid, give appreciably shortened shelf or bath life and require less ageing to obtain the described soluble partial condensate. It is preferred to add sufficient water-miscible carboxylic acid selected from the group consisting of acetic, formic, propionic and maleic acids to provide pH in the range of 4 to 5.5 in ~he coating composition. In addition to providing good bath life, the alkali metal salts of these acîds are soluble, thus allowing the use of these acids with silicas containing a substantial Z0 ~greater than 0.2% Na20) amount of alkali metal or metal oxide.
The composition is easily prepared by adding the trialkoxysilanes, such as R'Si(OCH3)3, to colloidal silica hydrosols and adjusting the pH to the desired level by addition of the organic acid. The acid can be added to either the silanes or the hydrosol prior to mixing the two components pro~ided that the mixing is done rapidly The amount of acid necessary to obtain the desired pH
will depend on the alkali metal content of the silica but is usually less than one weight percent of the composition.
Alcohol is generated by hydrolysis of the alkoxy substituents of the silane, for example, hydrolysis of one mole of -Si(OC2H5)3 generates 3 moles of ethanol. Dependins upon the percent solids desired in- the final composition~
.. , , .~
additional alcohol e~her ester, water or a water-miscible solvent can be added. The composition should be ~-ell mi~ed and allowed to age for a short period of time to ensure formation of the partial condensate. The coating composition thus obtained is a clear or slightly hazy low viscosity fluid which is stable for several days.
Buffered latent condensation catalysts can be added to the composition so that milder curing conditions can be utilized to obtain the optimum abrasion resis~ance in the final coating. Alkali metal salts of carboxylic acids, such as potassium formate, are one class of such latent catalysts. The amine carboxylates and quaternary ammonium carboxylates are another such class of la~ent catalysts. O~ course the catalysts imust be soluble or at least miscible in the cosolvent system. The catalysts are latent to the extent that at room temperature they do not appreciably shorten the bath life of the composition, but upon heating the catalyst dissociates and generates a catalytic species ac~ive to promote condensation.
Buffered catalysts are used to avoid effects on the pH
of the composi~ion. Certain of the commercially a~ailable colloidal silica dispersions contain free alkali metal base which reacts with the organic acid during the adjustment of pH to generate the carboxylate catalysts in situ. This is particularly true when starting with a hydrosol having a pH of 8 or 9. The compositions can be cataly~ed by addition of carboxylates such as dimethylamine acetate~ ethanolamine acetate, dimethylaniline formate, te~raethylammonium benzoate, sodium acetate, sodium propionate, sodium formate or benzyltrimethylammonium acetate. The amount of catalyst can be varied depending upon the desired curing condition, but at about 1.5 weight percent catalyst in the composition, the bath life is shortened and optical properties of the coating may be impaired. It is preferred to utilize from about 0.05 to 1 weight percent of the catalyst.
To provide the grea~est stability in the dispersion form while obtaining optimum properties in the cured coatin~, it is preferred to utilize a coating composition having a pH in the range o 4-5 which contains 10-35 weight percent solids; the silica portion having a pàrticle size in the range of 5-30 millimicrons, the partial condensate CH3Si(OH)3 and C6H5Si(OH)3 being present in an amount in the range of 35 to 55 weight percent of the total solids in a cosolvent oE methanol, isopropanol and water or CH3COOCH2CH20CH3 and water or ether esters, the alcohols representing from 30 to 60 weight percent of the cosolvent and a catalyst selected from the group consisting of sodium acetate and benzyltrimethylammonium acetate being present in an amount in the range of 0.05 to 0.5 weight percent of the composition. Such a composition is relatively s~able and, when coated onto a substrate, can be cured in a relatively short time at temperatures in the range of 75-1~5C. to provide a transparent abrasion resistant surface coating.
The coating compositions of the invention can be applied to solid substrates by conventional methods, such as flowing, spraying or dippin~T to ~orm a continuous surface ~1~ 6'7~
film. Although substrates of soft plastic sheet material show the greatest improvement upon application of the coating, the composition can be applied to other substrates, such .
as wood, metal, printed surfaces, leatker, glass, ceramics and textiles. The compositions are especially useful as coatings for dimensionally stable synthetic organic polymeric substrates in sheet or film form, such as acrylic polymers, for example, poly~methylmethacrylate), polyesters, for example poly(ethyleneterephthalate) and polycarbonates, such as poly(diphenylolpropane)carbonate, polyamides, polyimides, copolymers o acryloni~rile-styrene, styrene-acrylonitrile-butadiene copolymers, polyvinyl chloride, butyrates, polyethylene and the li~e. Transparent polymeric materials coated with these compositions are us,e~ul as flat or curved enclosures, such as windows, skylight:s and l~indshields, especially for transportation equipme:nt. Plastic lenses, such as acrylic or polycarbonate opht:halmic lenses, can be coated ~-ith the compositions of the invention In certain applications requiring high optical resolution, it may be desirable to filter the coating composition prior to applying it to the substrate. In other applications, such as cor~rosion-resistant coatings on metals, the slight haziness ~less than 5~) obtained by the use of certain formulations 3 such as those containing citric acid and sodium citrate, is not detrimental and filtration is not necessary.
By choice of proper formulation, including solvent, application conditions and pretreatment of the substrate, the coatings can be adhered to substantially all solid surfaces. A hard solvent-resistan~ surface coating is ~ ~ 6~
obtained by removal of the solvent and volatile materials.
The composition will air dry to a tack-free condition, but heating in the range of 50 to 150~ is necessary to obtain condensation of residual silanols in ~he partial condensate.
This final cure results in the formation of silsesquioxanes of the formula 0SiO3/2 and RSiO3/2 and greatly enhances the abrasion resistance of the coating. The coating thickness can be varied by means of the particular application technique, but coatings of about 0.5 to 20 micron preferably 2-10 micron thickness are generally utilized.
BspecialIy thin coatings can be obtained by spin coating.
Now so that those skilled in the art can better understand and appreciate the invention, the following examples are presented, In the e~amples and elsewhere in this disclosure, ~he use of the symbols ~ and Me mean "phenyl" and "methyl"
respectively.
Example 1 - Preparation of phenyl containing resins of this invention.
Six resins were prepared for evaluation.
Sample 1 was prepared according to the procedure of Example 1 of U.S. 3,986,997 and was used for comparison purposes.
Samples 2-6 were prepared according to the following procedure. Samples 2, 3 and 4 fall within the scope of this invention and Samples 5 and 6 fall outside the scope of the claims.
5% ~Si(OH)3/45 CH3Si~OH)3 To a three-nec.~ed, round-bottomed flask was added 154.5 grams of a colloidal sllica having an initial pH of 3.1 containing 34% SiO2 of approximately 22 millimicron particle size and having an Na2O content of less than 0.01 weight percent. It was cooled to 8C and 5.3 grams o~
., . . ~ . . ........... , . . - . . . . - - - - ..
glacial acetic acid was added. 96.0 grams of CH3Si(OMe)3 and 8.1 grams of 0Si(OMe)3 were premixed and slowly added to the colloidal silica with vigorous st rring and external cooling. The methoxy silanes were allowed to hydrolyze with the formation of methanol. After the hydrolysis was complete, 2.7 grams of a 10% solution of sodium acetate and 132.4 grams of isopropanol were added.
After seven days standing, 66.2 grams additional alcohol was added and the solution filtered.
Samples 3 through 6 were prepared in the same manner as Sample 2 but with appropriate adjustment of the relative amounts o~ ~CH3)SiO~CH3)3 and C6H5Si~OCH3)3 employed to give:
Sample 3:
10~ C6H5Si(OH)3/40% CH3sitoH)3;
Sample 4:
15~ C6H5Si~OH)3/35% CH~Si~OH)3;
Sample 5:
20% C6H5Si~OH)3/30% CH3Si(OH)3; and Sample 6:
25% C6HSSi(OH)3/25% CH3si~O )3 Exam~le 2 Plexiglas~ panels 4" x 4" x 1/8" (10.16 cm x 10.16 cm x 0.32 cm) after being cleaned with isopropanol and air dried, were flow coated with a 22.5% solids resin, allowed to air dry and then cured for 18 hours at 75C.
Similar l" x 4" x 1/8" ~2.54 cm x 10.16 cm x 0.32 cm) strips were prepared to test the flexibility. The test for flexibility is relatiue and was ca~ried out in ~he following manner.
The 1" (2.5~ cm) wide strips were placed in a vise-like device so that the longest i.e. ~" ~10,16 cm) axis was horizontal. A strong light was placed on the opposite side of the strip from ~here the observation was being made, so that the craze marks when they formed, were more easily seen. The vise-like device is manipulated by hand to draw the vise jaws together slowly so that the plastic strip irst humps in the center and then begins to form a semi circle with the coating on the outside of the semi circle. While observing the coating, the jaws are moved slowly together (decreasing the radius of curvature) until craze marks are propogated in the coating. When the craze marks show across the entire width of the plastic strip, the end point has been reached.
The degree of flexibility is then calculated in the following manner. The initial length of ~he st~ip before compression is designated AB. The distance between the vise jaws at the end of compression is designated AB.
Prior measurements of angle of ~ plotted versus AB
give a graph i.e. ~ = ~B from which ~ can be easily determined.
AB
The radius of curvature ~r) can then be calculated.
r = AB 1~0 __ 'IT ~ o ~ 6~ ~ ~
One has to assume that ~ is an arc of a circle.
The actual shape of the semi-circle in this test is a parabola which suggests that this is a more severe test than a test which had a true semi-circular shape.
The abrasion resistance was determined according to ASTM ~ethod Dl0~4-~6. The instrument ~as the Tabor A braser. A 500 gram ~est load was used with CS-lOF
abrasive wheels and the test panels subjected to 500 revolutions on the abraser turntable~ The percent change in haze which is the criterion for determining the abrasion resistance of the coatlng is determined by measuring the di~-ference in haze of the unabrased and abrased coatings.
Haze is defined as that percentage of transmitted light which in passing through the specimen deviates from the incident beam by forward scattering. In this method, only light flux that deviates more than 2,5 degrees on the arerage is considered to be haze. The ~ Haze on the coatings was determined by ASTl~ Method D1003-61. A
Hunter Haze Meter: Gardner Laboratory, Inc~ was used.
The ~ Haze was calculated by measuring the amount of diffused light dividing by the amount of transmit~ed light and multiplying by one hundred.
The adhesion test was the 1/8" crossha*ch tape pull test in which the cured coating is crosshatched in 1/8" squares using a sharp object, over a square inch area. Adhesive tape ~#600 Adhesive - 3M Company) is firmly pressed onto the crosshatched area and sharply pulled away.
If all of the coating remains, the adhesion is 100~.
~Lfi~
o~
.,, ~ o~oo~o o\O o~o o\O o~o n t~ ~ o . .
U~ ¢ ~
- 4~,. .
,.-.~.. ..... . ........o,, .... - . ~ . . -, `
~ a~ .
~ ~ :~
a~ o C ~t~ ~ ~ ~ o E~ ~1 ~oo ~
~ o r ~ :
.~ .
.~ ~
o ~C
o\ o\ o\ o\O o\o o\o O O O o o o o o o o o o ~-1 ~1 ~ ~1 ¢ o ,. .
~: `:
o o o o o o ~ ~ ~ o ,,(~.
E~
,1 ~n ~d ~,1 h C~ ~: :.
' `.
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t~ o U~ ~ L~ o U~ `
' ~ ~1 ~1 ~ ~
O ;;
:
a~
~z ~
u~
,.-.~.. ..... . ........o,, .... - . ~ . . -, `
~ a~ .
~ ~ :~
a~ o C ~t~ ~ ~ ~ o E~ ~1 ~oo ~
~ o r ~ :
.~ .
.~ ~
o ~C
o\ o\ o\ o\O o\o o\o O O O o o o o o o o o o ~-1 ~1 ~ ~1 ¢ o ,. .
~: `:
o o o o o o ~ ~ ~ o ,,(~.
E~
,1 ~n ~d ~,1 h C~ ~: :.
' `.
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Claims (5)
1. A pigment-free aqueous coating composition comprising (1) a dispersion of colloidal silica in (2) a solution which has as cosolvent ether esters of ethylene or propylene glycol and water and which has as solute (3) the partial condensate of a silanol of the formula RSi(OH)3 in which R is selected from the group consisting of an alkyl radicalof 1 to 3 carbon atoms and phenyl wherein at least 70 weight percent of the silanol is CH3Si(OH)3 and from 1 to 30 weight percent of the silanol is C6H5Si(OH)3 wherein the composition contains 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 50 weight percent of the partial condensate, and wherein the composition contains sufficient acid to provide a pH in the range of 2.8 to 6Ø
2. A composition in accordance with claim 1 wherein the cosolvent additionally contains a water-miscible polar solvent in an amount up to 20 weight percent based on the weight of suspending medium.
3. A composition in accordance with claim 1 or claim 2 wherein the acid is water-miscible organic acid selected from the group consisting of acetic acid, formic acid, propanoic acid and maleic acid.
4. A composition in accordance with claims 1 or 2 containing from about 0. 05 to 1. 5 weight percent of a buffered latent silanol condensation catalyst.
5. An article comprising a solid substrate coated with a pigment-free coating composition in accordance with claim 1 or claim 2.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US86397077A | 1977-12-23 | 1977-12-23 | |
| US863,970 | 1977-12-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1116771A true CA1116771A (en) | 1982-01-19 |
Family
ID=25342228
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000311613A Expired CA1116771A (en) | 1977-12-23 | 1978-09-19 | Flexible coating resins from siloxane resins having a very low degree of organic substitution |
Country Status (6)
| Country | Link |
|---|---|
| JP (2) | JPS5487736A (en) |
| BE (1) | BE873005A (en) |
| CA (1) | CA1116771A (en) |
| DE (1) | DE2855792C2 (en) |
| FR (1) | FR2412595A1 (en) |
| GB (1) | GB2010879B (en) |
Families Citing this family (17)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1116771A (en) * | 1977-12-23 | 1982-01-19 | Ronald H. Baney | Flexible coating resins from siloxane resins having a very low degree of organic substitution |
| EP0048114A1 (en) * | 1980-09-12 | 1982-03-24 | Dow Corning Limited | Siloxane resin compositions and preparation and use |
| JPS5968377A (en) * | 1982-10-14 | 1984-04-18 | Toshiba Silicone Co Ltd | Coating composition and its preparation |
| JPH036989Y2 (en) * | 1984-12-18 | 1991-02-21 | ||
| JPS60221702A (en) * | 1985-01-23 | 1985-11-06 | Toray Ind Inc | Molding having transparent coating layer |
| JP2653023B2 (en) * | 1988-04-22 | 1997-09-10 | 大阪有機化学工業 株式会社 | Coating composition |
| GB9816269D0 (en) * | 1998-07-27 | 1998-09-23 | Pilkington Plc | Plastic glazings |
| EP1087001B1 (en) * | 1999-09-24 | 2004-12-01 | General Electric Company | Curable abrasion-resistant coating compositions |
| US8015970B2 (en) * | 2007-07-26 | 2011-09-13 | 3M Innovative Properties Company | Respirator, welding helmet, or face shield that has low surface energy hard-coat lens |
| EP2374836A1 (en) * | 2010-04-07 | 2011-10-12 | Nuplex Resins B.V. | Crosslinkable composition crosslinkable with a latent base catalyst. |
| KR102131463B1 (en) | 2011-10-07 | 2020-07-08 | 알넥스 네덜란드 비. 브이. | Crosslinkable composition |
| BR112015025624B1 (en) | 2013-04-08 | 2021-09-08 | Allnex Netherlands B.V | RETICULABLE COMPOSITION, KIT, METHOD FOR PREPARING A RETICULABLE COMPOSITION, AND, COATING COMPOSITIONS |
| CN107667151A (en) | 2015-04-17 | 2018-02-06 | 欧尼克斯荷兰有限公司 | RMA cross-linkable compositions with improved adhesiveness |
| US10767074B2 (en) | 2015-04-17 | 2020-09-08 | Allnex Netherlands B.V. | Process for the manufacture of a crosslinkable composition |
| WO2016166361A1 (en) | 2015-04-17 | 2016-10-20 | Nuplex Resins B.V. | Floor coating compositions |
| AU2016250029B2 (en) | 2015-04-17 | 2020-12-24 | Allnex Netherlands B.V. | RMA crosslinkable compositions and RMA crosslinkable resins for easy to clean coatings |
| DE102021129250A1 (en) | 2021-11-10 | 2023-05-11 | EXXERGY GmbH | Improving glass strength and fracture toughness with a non-brittle coating |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1241236A (en) * | 1969-05-01 | 1971-08-04 | Owens Illinois Inc | Process of coating plastics with organopolysiloxanes and articles made thereby |
| IL37707A (en) * | 1970-09-25 | 1974-10-22 | Stauffer Chemical Co | Binder composition,its preparation and coating compositions containing it |
| GB1391850A (en) * | 1971-04-28 | 1975-04-23 | Matsushita Electric Ind Co Ltd | Nonflammable coating composition for electronic parts |
| BE793556A (en) * | 1971-12-30 | 1973-06-29 | Stauffer Chemical Co | COATING COMPOSITIONS PROVIDING GALVANIC PROTECTION |
| BE793558A (en) * | 1971-12-30 | 1973-06-29 | Stauffer Chemical Co | COATING COMPOSITIONS PROVIDING GALVANIC PROTECTION |
| GB1390270A (en) * | 1972-11-06 | 1975-04-09 | Monsanto Ltd | Coating compositions |
| US3986997A (en) * | 1974-06-25 | 1976-10-19 | Dow Corning Corporation | Pigment-free coating compositions |
| CA1116771A (en) * | 1977-12-23 | 1982-01-19 | Ronald H. Baney | Flexible coating resins from siloxane resins having a very low degree of organic substitution |
-
1978
- 1978-09-19 CA CA000311613A patent/CA1116771A/en not_active Expired
- 1978-11-17 JP JP14216678A patent/JPS5487736A/en active Granted
- 1978-12-21 FR FR7835958A patent/FR2412595A1/en not_active Withdrawn
- 1978-12-21 GB GB7849484A patent/GB2010879B/en not_active Expired
- 1978-12-22 BE BE192502A patent/BE873005A/en unknown
- 1978-12-22 DE DE19782855792 patent/DE2855792C2/en not_active Expired
-
1980
- 1980-08-18 JP JP11332480A patent/JPS5641267A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS5487736A (en) | 1979-07-12 |
| GB2010879A (en) | 1979-07-04 |
| GB2010879B (en) | 1982-08-04 |
| DE2855792C2 (en) | 1982-03-25 |
| DE2855792B1 (en) | 1981-01-29 |
| FR2412595A1 (en) | 1979-07-20 |
| BE873005A (en) | 1979-06-22 |
| DE2855792A1 (en) | 1979-06-28 |
| JPS5618626B2 (en) | 1981-04-30 |
| JPS5641267A (en) | 1981-04-17 |
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