JPS5857508B2 - Method of producing an adhesive metal surface on a substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION There are many applications where it is desirable to produce thin metal films or coatings on a variety of solid substrates.

One example of such an application is the production of silvered mirrors in which very thin films or coatings of metallic silver are deposited from solutions of chemicals onto glass or similar substrates.

Also, large reflectors for solar applications have been produced from silver or aluminum deposited on a solid substrate.

Some problems with prior art methods of producing thin metal coatings on solid substrates include cumbersome application methods, for example in the manufacture of silvered mirrors from chemical solutions, and the difficulty of producing metal coatings on solid substrates over long periods of time. It is something that cannot be maintained.

Also, in vapor deposition, vacuum metallization, ion blasting, spraying, and similar methods, when a solid substrate is pretreated with some composition agents that can hide or eliminate its scratches, divots, and voids. For the first time, a metallized surface can retain its aesthetic value.

Such materials are generally curable organic coatings that are first applied to a solid substrate at a thickness that physically fills scratches, depressions, and voids, and then cured.

This metallization then takes place on the surface of the organic coating.

Unfortunately, these organic "baseco"
Due to the existence of at, s ) J, manufacturers are faced with various adhesion problems between the basecoat and the solid substrate, and between the basecoat and the thin metal film or coating.

This problem is greatly exacerbated when manufactured articles are intended for outdoor use and are exposed to the ravages of the weather.

Accordingly, there is a need for improved methods and improved metallization materials for producing adherent metal films or coatings on solid substrates.

In accordance with the present invention, an improved method of adhering thin (metallic films or coatings) to solid substrates is disclosed.

This improved method utilizes specific silanes or mixtures of silanes to strongly adhere thin metal films or coatings to solid substrates.

Silanes have long been known to be useful for bonding many materials to many types of surfaces.

It is generally recognized that silane coupling agents are not universal coupling agents such that any silane will bond any material to any substrate.

Alternatively, certain silanes can be used to bond certain materials to certain substrates, i.e., silanes with
It is generally accepted that each silane must be suitable for each application, and therefore not all silanes are considered suitable for all applications.

Recent British Patent No. 1,550,532, issued Letters Patent on August 15, 1979, describes alkoxysilanes, alkyl silicates, and alkyl acrylates or alkyl methacrylates and hydroxyalkyl acrylates or hydroxy It has been disclosed that a combination of alkyl methacrylate copolymers can be used to adhere thin films or coatings of metal to plastic substrates.

It is disclosed in this patent that the inventive composition serves two purposes: the polymeric material is the film-forming element and the silane increases the adhesion of the metal overcoat. ing.

The alkoxysilane shown here has the formula (where n is 1
．． 2, or 3, R is a hydrocarbon group having 1 to 6 carbon atoms, and R' is an alkyl group having 1 to 4 carbon atoms.

This prior art material and method appears to serve extremely well as long as the article is intended for indoor use.

It has been observed that this material does not have sufficient adhesion to the deposited polymeric film of metal, resulting in a loss of adhesion of the thin metal film.

The adhesion of thin metal films to various substrates can be increased by the use of certain silanes and silane mixtures on certain substrates, and articles made using this inventive method are durable, It has now been found to be weather resistant and to have gloss and high specularity.

Disclosed herein are methods of producing a cohesive thin continuous metal surface on a substrate and articles made thereby.

That is, (I) a solid substrate is composed of at least one organofunctional silane having the general formula or a partial hydrolyzate thereof, or said organofunctional silane or a partial hydrolyzate thereof and the general formula (wherein the formula R is 1 an alkyl group having 1 to 4 carbon atoms, R' is a difunctional hydrocarbon group having 1 to 12 carbon atoms or a group -CH2CH2CH2NHCH2CH2-1X is -NH
2, OH or Ct group, R// is phenyl group, or 1
Alkyl groups having from 1 to 4 carbon atoms, a and b
have a value of 2 or 3 respectively, C has a value of O or 1, and (6) a mixture of a second silane or its partial hydrolyzate with a+c=3); The silanized surface was dried until the volatiles were removed and then (I
Disclosed is a method of producing an adherent metal surface on a substrate by depositing the metal on a silanized surface with n) to produce a thin continuous film or coating on the surface.

The organofunctional silane used in step (2) has the general formula (wherein R is an alkyl group having 1 to 4 carbon atoms, and R' is a difunctional carbonized Hydrogen group or group -CH2CH2CH2NHCH2CH2-1X is -NH
2, OH or Ct group, R is preferably a methyl group, a has a value of 2 or 3, C has a value of O or 1, a+c=3).

Therefore, contemplated within the formula * is (CH30)3Si(CH2)3NH(CH2)2NH
2, an organofunctional silane such as

Contemplated within the scope of this invention are partial hydrolysates of these organofunctional silanes.

The present inventor defines the "partial hydrolyzate" in the text by treating all or one organofunctional silane with water.
It is contemplated that the water-soluble or water-miscible products formed when the alkoxy groups of moieties are hydrolyzed.

Sometimes a small amount of acid is needed along with water to carry out the hydrolysis.

When "hydrolyzate" or "partially hydrolyzate" is used in the text, it always refers to hydrolyzed silane,
Or it means containing silanes, water for hydrolysis, and an alcoholic solvent produced by cleavage of an alkoxy group from the silane.

Although treatment of the substrate can be carried out with only organofunctional silanes or partial hydrolysates thereof, it is contemplated within the scope of this invention that the treatment of the substrates is carried out with organofunctional silanes or partial hydrolysates thereof with the general formula (RO). bSi
R″4-b (wherein R has the same meaning as R, R// is a phenyl group or an alkyl group having 1 to 4 carbon atoms, and b has a value of 2 or 3. It is a mixture of organosilanes with

For the above formulas, partial hydrolysates of (RO)BSiR''4-b are also part of the invention.

R is preferably a methyl group.

The organofunctional silanes and organosilanes are known commercially available silanes and their preparation is well demonstrated in the art and need not be repeated in the text.

Whenever it is necessary to use mixtures of silanes, this is done by simple mixing techniques.

The pure silanes may be mixed first and then co-hydrolyzed, or they may be hydrolyzed separately and the hydrolysates may then be mixed.

If a mixture of silanes is required for the purposes of the invention,
It is generally preferred to mix these in a ratio of organofunctional silane to organosilane of 1:10 to 10:1 by weight.

This ratio applies to the weight of the silane before hydrolysis.

As mentioned above, some silanes require the presence of small amounts of acid to enhance hydrolysis.

Such acids are, for example, hydrochloric acid and acetic acid.

This acid requirement is known in the silane hydrolysis art.

It is generally preferred that the silane be hydrolyzed prior to mixing.

After hydrolysis of the silane, simply shaking the hydrolysis vessel, ie, bottle or flask by hand, is sufficient to drive the hydrolysis reaction.

Generally, the hydrolysis mixture is used without further modification or purification at this point.

The amount of total silane in the hydrolysis mixture may be from 0.01 to 35 parts by weight.

If the silane is used without partial hydrolysis,
It can be dissolved in water-soluble or water-miscible solvents such as isopropanol, methanol, butanol, methyl cellosolve.

Mixtures of this type of solvent are contemplated within the scope of this invention.

These solvents can also be used with hydrolyzed silanes to increase film forming ability.

The silane or silane solution can be applied to the substrate by any method convenient to the user.

Methods such as dipping, spreading, and spraying are most suitable for the present invention.

Substrates useful in the present invention are solid substrates.

Thus, almost any useful solid material that constitutes an article can serve as a substrate for the present invention.

Such substrates include, for example, acrylonitrile-butadiene-styrene copolymer, 5ioplas cross-linked polyethylene (Dow Corning Corporation,
ionlMidlandlMichigan), polycarbonate, Mylar (E.

1, Dupont, Wilmingt, on, Del.
polyethylene terephthalate, such as Kapt, On ■ (E.

1, polyimides such as Dupont, Nory
l■-(General Elect, ric Co,
,Pit,t,5fie ld.

Polyphenylene oxide such as Massachusetts, t, s), Ryt, on■ (Phillips
Chemical Co., Chicago, II
Polyphenylene sulfide such as 1nois) and Minlon■ (E, 1. Dupont, )
Minerals such as optical fibers can be nylon, acrylic, urethane, epoxy and polyester to name but a few.

Wood, cardboard, glass, metal, silicone rubber, and resins, urethane foam and polyvinyl chloride foam are examples of other useful substrates.

One method described herein is to treat a solid substrate with an organofunctional silane or a mixture of organofunctional silanes and organosilanes, and then treat the treated surface with It consists of giving a dry assignment.

By volatile materials we mean solvents, water, and low molecular weight products produced by hydrolysis.

A "majority" of volatile materials means that the surface must be tack-free or nearly tack-free to the touch.

This can be achieved in many ways.

For example, the treated surface can be placed at room temperature for a period of time, perhaps several days, to allow volatile materials to gradually evaporate into the atmosphere.

However, typically in commercial manufacturing, time is a factor and the article can be heated to remove volatile materials.

Vacuum can be applied to reduce pressure and increase volatilization.

In this text, the inventor used a number of methods to remove volatile substances in a short time, such as 1 to 5 seconds, by simultaneously applying heat and removing a vacuum.

Any method of removing volatile materials that is compatible with the manufacturer's procedures in manufacturing is contemplated herein.

After removing the volatiles, a thin metal coating is applied.

Generally, any method by which a thin continuous metal coating can be applied is satisfactory for the present invention.

Methods such as vapor deposition, electroplating, sputtering, ion blasting, atomization, and the like are preferred.

However, thin continuous metal coatings can be achieved by this chemical solution application method without deleterious effects on the adhesion promoting coating.

Metals useful in the present invention are any metals that can be vapor deposited, electroplated, sputtered, ion blasted, sprayed, or applied from a chemical solution.

copper, nickel, tin, silver, silver solder, gold, aluminum,
Metals such as platinum, titanium, zinc, and chromium are preferred.

For purposes of this invention, "thin" means the thickness of the metal film necessary to provide a continuous coherent film or coating.

Generally, the thickness of these coatings is less than 30 microns.

Articles made according to the present invention can be coated with a transparent protective coating such as the silicone resins described in U.S. Pat. No. 3,986,997.

Generally, these substances are covered with a "topcoat".
) J and is known in the art.

As mentioned above, the surfaces of some substrates are soft enough to be damaged by gouges or scratches during the manufacture of the article, and the surface of some substrates is soft enough to be damaged by gouges or scratches during the manufacture of the article, and the scratches must be overgrown in order to finally obtain an aesthetically pleasing product. If you simply plate metal with a thin coating or film, scratches will be visible through it.
This wound must be removed.

A common method of covering over these scratches is to prime the substrate with a material such as a curable organic polymer.

This organic polymer fills the wound and provides a smooth, flat, intact surface onto which a thin metal coating can be applied.

Accordingly, other inventions herein contemplate the use of such primer materials in conjunction with the methods and materials of the present invention.

That is, the present invention also provides for treating a substrate with an undercoat,
The present invention also relates to applying the silane or silanes of the present invention to the undercoat.

This metal is then applied to a silanized basecoat.

Preferred for this invention are certain silicone basecoats.

For further details, this undercoat was published on October 19, 1976.
Preferred are those selected from the siloxane coatings disclosed in U.S. Pat. No. 3,986,997 issued to Harold A. C1ark v.

The siloxane coatings disclosed in this patent are referenced in the text.

If a basecoat is used, the substrate is cleaned by any conventional method, then the basecoat is applied and cured.

General [6 at 150°C for C1ark coating
8 hours are required.

Some basecoats simply require a few minutes of air drying time.

In some cases, a primer may be required, depending on the substrate and undercoat.

For example, 7 runs of the present invention may be used as such a primer.

The cured basecoat is then surface treated with a silane or mixture of silanes, dried and protectively coated with the selected metal.

Accordingly, contemplated within the claims of the present invention are the substrates mentioned herein that are protectively coated with an organic or silicone basecoat and then treated with the inventive silane or silane mixture.

A third feature of the invention is the use of the silanes of the invention for certain curable coatings to increase the adhesion of thin metal films or coatings.

While the essence of the invention first described herein is the treatment of certain substrates or the treatment of certain substrates primed with organic or silicone curable coatings, another aspect of the invention is Features relate to metallization of curable organic or silicone basecoats containing the inventive silane or silanes disclosed herein prior to curing.

The invention therefore also consists of incorporating the silane of the invention into a curable basecoat and then depositing the metal to form a film or coating thereon.

Therefore, the present invention & DI) also combine a solid substrate with at least one organo-functional silane having the general formula or a partial hydrolyzate thereof, or such an organosilane-functional silane or a partial hydrolyzate thereof and a solid substrate having the general formula , formula R is an alkyl group having 1 to 4 carbon atoms, R' is a difunctional hydrocarbon group having 1 to 12 carbon atoms or the group -CH2CH2CH2NHCH2CH-1X is -NH2
, OH or Ct group, R'' is a phenyl group or an alkyl group having 1 to 4 carbon atoms, a and b each have a value of 2 or 3, C has a value of O or 1 , a+c=3) with a curable organic or silicone basecoat containing a second silane mixture having (6) drying of this basecoat until most of the volatiles are removed, and then (e)
It consists of a method of producing an adherent metal surface on a substrate by depositing the metal onto the basecoat to produce a thin continuous film or coating.

The organic basecoats useful herein are those commonly used as basecoats for metal deposition on solid articles.

These materials are air-dried acrylics or urethanes that can be used with or without heat curing.

Such substances include, for example, Red 5pot, Pa1
nt and Varnish Co, tIn
c, Evansville, Indiana
Trade name of acrylic polymer manufactured by VC, E
It is B-1.

The amount of silane or silanes incorporated into the basecoat ranges from 0.1 to 10% based on the weight of the silane(s) and basecoat.
He is in charge of weight.

Simple mixing of silane into the base coat is all that is required.

It should be noted that such mixing need not be carried out under anhydrous conditions as good adhesion effects are obtained even if the silane is used in its pure or prehydrolyzed state.

The basecoat is dried and/or cured, depending on the intended application, and then a metal overcoat is applied by one of the methods described above.

Articles produced by the method of the invention described herein have excellent adhesion, weather resistance, durability, and whenever the metal surface is mirror-like, high efficiency and mirror-like properties.

The following examples are not to be construed as limiting the invention as claimed.

In the present invention, several types of silanes were evaluated by observing the adhesion of metal coatings.

Appearance was measured based on subjective characteristics of film continuity, gloss, specularity, and presence/absence of cracks, pockmarks, etc.

A good film is continuous, free of voids and/or pockmarks, and has gloss and a high degree of specularity.

Specularity is a term used in the specular wave technique and refers to the degree of light transmitted from the surface of a mirror, that is, the quality of the mirror.

Adhesion was measured subjectively by rubbing the metal surface with a cloth saturated with acetone, methanol or isopropanol, using moderate pressure unless a different method was indicated.

Report the degree to which the metal surface survived this treatment.

, those in which no coating is removed are considered "excellent".

"Good" is when some slight wear occurs.

"Slightly good" means that metals are significantly removed.

"Bad" means essentially all metallization is removed.

"None" means all coatings are removed.

Example 1 The following samples were prepared to see which silane or combination of silanes provided the best adhesion between a given substrate and a type of metal.

Silanes or combinations of silanes were prepared at the concentrations indicated by a method that included hydrolysis of each silane and final combination of the silanes to obtain the adhesion promoter used on the substrate.

Table 1 of this example shows the various silanes tested.

Silane 1i(CH30)3Si(CH2)3NH(CH
2) 2NH2.

Silane B is (CH30)3si(CH2)3sH. Silane C is.

Silane D is (CH30)3Si(CH2)3Ct, silane E is phenyl Si(OCH3)3, silane F is propyl5i(OCH3)3, and silane G is CH2
=CH8i (OCH3) 3, Shira7 HHAHO(C
H2) 3 S i (OCH3) 3.

The results are shown in Table 2.

IPA is an isoproper tool.

MeOH is methanol. GMS is Durham.

Primer Production Silane A (8 gms), IPA (8 gms), in a small 1 oz glass bottle with a screw top lid.
and 1.12 gm5 of water were mixed with stirring.

The bottle was left overnight (approximately 16-20 hours).

This substance is then transferred to a larger bottle and at the same time
Diluted with 0gm5 IPA.

Silane B (12,35gm5), IPA (717,
65gm5), glacial acetic acid (30gms) and 4(Ni'
of water were mixed together in the order indicated in the text.

Silane C (24 gms) and 1.2 gm of water were mixed and left overnight (16-20 hours).

This material was then diluted with 800 gm5 of MeOH and all silanes D, E, F and G were treated similarly.

3 gms of silane was treated with 27 gms of MeOH, then a small amount of acetic acid and enough water for complete hydrolysis were added, the mixture was shaken until clear, and then used without extensive aging.

By the same method as D, E, F and G, H was converted into MeOH
I was in charge of 20 out of 20 middle school classes.

All primers were filtered before use. All samples were manually dipped into the primer solution and excess material allowed to drip off.

The samples were then dried as described in the table.

Table 1 shows the silanes or combinations of silanes used in the examples.

"Sample N (LJ is the reference number of the experiment performed on these examples.

"Silane N (LIJ) is the organofunctional silane used in the sample.

"Silane N (L2J is the organosilane used in the sample.

"Acid addition" and "H20 addition" mean that the substance was used as a hydrolyzate in the hydrolysis water together with the alcohol produced as a by-product during hydrolysis.

Pure silanes, ie, when used without prehydrolysis, are so described.

In Table 2, Sample N (L9) from Table 1 shows the silane and silanes used in the particular experiment.

If more than one experiment was performed with the same silane but with different substrates or deposited metals, the experiments were designated as a, b, c, etc.

For example, from Table 1, sample 4 is a primer consisting of clans C and B.

Sample 4a of Table 2 used a 2.4:1 ratio of silanes, with 1.3 parts by weight of total silane present in the primer;
The substrate during the experiment was glass, indicating that the deposited metal was silver solder.

Sample 4b of Table 2 is the primer of Sample 4 of Table 1 with the same ratio of silane at the same weight solids, but indicates that the substrate is now an acrylic sheet and the deposited metal is aluminum. ing.

All samples in Table 2 are from Thermionics La
Bora t, ories, Haywa
rd, Mikros Vacuum Ev made by CA1
It was deposited using aporat, or Model VE-10.

Example 2 In order to compare the materials described in GB 1,550,532 with the present invention, the following materials were prepared.

1,80 gms of silicate-based polymer containing methyltrimethoxysilane was mixed with 20 gm5 of Ac
ryloid OL-42 (Rohm & Haas
Co, Ph1ladelphia, PA) mixed with?
= A e rylo 1 dOL-42 is an acrylic polymer similar to that described in British Patent Example 1.

Acryloid is 80% solids in Cellosolve Acetate.

Igram's hexamethylenetetramine catalyst was also added with stirring.

**800gm5 diluted with IPA
5 gm of H8(CH2)3S1(OCH3)3 was mixed with a further 800 gm5 of MeOH in 40 parts diluted with MeOH and a small amount of acetic acid and water and the mixture was stirred until clear.

Lexan■ (General Electric.

A polycarbonate slide was abraded with sandpaper to simulate an article that had been abused since its manufacture.

After cleaning the slide, section it into four equal parts,
The marked portion was dipped from above into a solution of Primer P, and then air-dried for 20 minutes at room temperature.

A solution of acrylate polymer, silicate, and alkoxysilane similar to that described in Example 1 of GB 1,550,532 is then applied to/on the slide. The primed area was thereby provided with a protective coating and then allowed to air dry.

The coating was then heated at 70°C for 15 minutes and at 100°C.
It was cured for 20 minutes.

Next, 4 of the slides (2) and (2) were immersed in the P solution and air-dried for 10 minutes at room temperature.

Finally, all slides were evaporated with metallic silver and heated to 100°C.
It was cured for 15 minutes.

If the slide were placed upright and a coating or layer was observed on the surface of the slide, the leftmost ζ portion (labeled A) would have only a silver coating.

Moving to the right, the next four sections (labeled B) are now British Patent No. 1,550, which covers the polycarbonate slide.
It would have a top layer of silver overlying the layer of polymer described in the '532 patent.

The third section (labeled C) has a top layer of silver which in turn covers a layer of P primer which also coats the polymer described in British Patent No. L550,532 which coats the polycarbonate slide. Dew.

The last part (labeled D) is the top layer of silver, Primer P.
a second layer of P, a third layer as described in GB 1,550,532, and finally a fourth layer of Primer P.

Sections B, C1 and D were scored with a sharp instrument into orthogonal parallel squares to obtain 25 equal squares.

Next, 5cotch trademark adhesive tape +650 (3M
Co,, St, Paul, Minne 5ota)
was forced into this square with orthogonal parallel lines and forcibly removed.

Although acknowledging that optimal conditions were not found, the test was considered passed if at least 50 parts or more of metallic silver remained intact.

Table 3 shows the results. ”Example 3 of adhesion loss that occurs at the silver/undercoating interface H8(CH2)3Si(OCH
3) There are 10 deuterons of 3, CH35i (OCH3)
A silicone resin was prepared according to Example 2 of US Pat. No. 4,173,553, except that 40 weight molecules of 3 were present and 50 weight molecules of colloidal silica were present.

This material is designated as "A" in the text. Other silicone resin samples were prepared as described in Example IK of US Pat. No. 3,986,997.

That is, it is the same substance as above except for H8(CH2)3S1(OCH3)3, and is designated as "B".

These two types of materials were compared side-by-side in terms of their ability to receive and adhere to metal deposited thereon.

Both materials were diluted with isopropanol to approximately 10% solids.

Clean square sample of Laxan polycarbonate 1 was/soaked in rAJ.

The remainder, )/2, was immersed in "B".

The sample was then air-dried for 40 minutes at 25°C.

This sample was then evaporated with silver.

The sample was then cured for 1 hour at 125°C.

Both samples had excellent specularity.

This sample was subjected to methanol friction to test the adhesion of silver.
The material rAJ was clearly superior in retaining metallic silver.

Example 4 The silicone resin designated as rBJ in Example 3 above was applied to square samples of clean Lexan ■ polycarbonate and cured for 25 minutes at 100'C.

4 of the coated slides was then coated with Primer P of Example 2.
25°C.
and dried for 2 minutes.

This square sample was then evaporated with silver to give 125
The fourth side of the slide, which was cured for 1 hour at 50°C and primed with Example 20 Primer P, had excellent retention of silver deposited thereon.

The means of metal deposition described herein and in the claims are conventional means of metal deposition, and a detailed description of such methods is not considered necessary to those skilled in the art.

The embodiments of the invention for which exclusivity is claimed are set forth in the claims.

Claims (1)

[Scope of Claims] At least one organofunctional silane or a partial hydrolyzate thereof having the general formula (wherein the formula R is 1 to 4 R' is a difunctional hydrocarbon group or group -8H, OH or Ct having 1 to 12 carbon atoms, R11 is a phenyl group, or a second silane or a partial hydrolyzate thereof having a carbon atom-containing alkyl group, a and b each having a value of 2 or 3, C&'!, O or having a value of 1, a+c=3) (6) drying the silanized surface until most of the volatiles are removed; and (e) depositing metal onto the 7-run treated surface. A method of producing a cohesive metal surface on a substrate by producing a thin continuous film. 2 (■) treating the solid substrate with a curable organic or silicone undercoat and then curing the undercoat; (6) applying the cured undercoat to at least one organofunctional silane having the general formula or partially hydrated thereof; decomposition product, or the organofunctional silane or its partial hydrolyzate and the general formula (wherein R is an alkyl group having 1 to 4 carbon atoms and π has 1 to 12 carbon atoms a difunctional hydrocarbon group or group -8H, OH or Ct, R// is a phenyl group or an alkyl group having 1 to 4 carbon atoms, ! and each have a value of 2 or 3; , C is 0 or 1
(e) drying the silane-treated surface until most of the volatiles are removed; , then 4. A method of producing an adherent metal surface on a substrate by depositing the metal on the silanized surface to produce a thin continuous film or coating on the surface. 3(■) The solid substrate is composed of at least one organofunctional silane having the general formula or a partial hydrolyzate thereof, or the organofunctional silane or the hydrolyzate thereof and the general formula (wherein the formula R is one or more an alkyl group having 4 carbon atoms, π is a difunctional hydrocarbon group having 1 to 12 carbon atoms or a group -CH2CH2CH2NHCH2CH2-X is -NH2
, -SH, OH1 or a Ct group, R// is a phenyl group or an alkyl group having 1 to 4 carbon atoms, a and b each have a value of 2 or 3, C is O or 1 (6) with a curable organic or silicone primer containing a mixture of a second silane or its partial decomposition products having a value a + c = 3) until most of the volatiles are removed; A method of producing an adherent metal surface on a substrate by drying the basecoat and then (e) depositing metal onto the basecoat to produce a thin continuous film or coating on the basecoat.