CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation-in-part application of copending patent application Serial No. 237,118 filed 8/26/88. Technical Field

This invention relates to a resinous article, such as a PVC resinous article, having its surface modified with a modifier ingredient, such as a U.V. stabilizer. Background Art

Photodegradation of many types of solid polymeric articles by U.V. light has been a continual problem confronting the industry. Such U.V. degradation causes discoloration, embrittlement and deterioration of the article. Accordingly, U.V. absorber compounds have been incorporated into such polymeric articles in an attempt to provide effective stabilization to U.V. light.

However, photodegradation is known to be a surface phenomenon. Accordingly, incorporation of U.V. stabilizers into the polymeric material prior to shaping the resin into solid form has been largely uneconomical and inefficient because the stabilizer is present substantially in the interior of the shaped article, where it cannot function effectively to prevent surface photodegradation.

Accordingly, surface treatments have been proposed to provide more effective U.V. protection for resins such as PVC. These surface treatments are based on the ability of various organic solvents to swell the resin and to direct the ultraviolet light stabilizer material dissolved in the solvent principally into the surface region of the resin body.

The swelling method is described in detail, for example, by Katz, et al. in articles appearing in the

"Proceedings of the A.S.C. Div. of Org. Coatings and Plastics" 16, (1) p. 202-205 (1976), entitled "Ultraviolet Protection of Transparent PVC by Diffusion Coating"; and in Soc. Plast. Eng., Tech. Papers (1976), .22., 511-512. Katz uses a dip method to impregnate a transparent PVC sheet with a non-migrating ultraviolet light absorber. The dip technique comprises swelling the polymer with a carrier solvent, e.g. 3-6.5% by wt. of stabilizer in the carrier, and thereafter heating the treated polymer in air at an elevated temperature to drive the stabilizer below the surface of the polymer and to remove residual solvent. The disclosed solvents are toluene, tetrachloroethane, chloroform and 1,2-dichloroethane, and mixtures of chloroform and 1,2-dichloroethane.

Jochanan, in Israel Patent No. 39,037, published Nov. 10, 1975, entitled "U.V.-and Oxidation-Proof Products from Organic Plastics and their Manufacture", describes various methods of applying a 5% by wt. solution or suspension of an ultraviolet light absorber in methylene chloride to the surface of a plastic sheet. The methods disclosed by Jochanan include immersion, spraying, brushing, roller-printing and curtain-coating. However, with such application methods, a large amount of residual stabilizer and solvent is left on the surface of the article, whereupon the modified surface is observed to be streaky, hazy, and has runs or pockmarks thereon. In fact, at a stabilizer concentration of 12.5% by wt., the resultant surface was found to become white and opaque.

Amborski, in U.S. Patent No. 3,043,709, discloses an organic polymeric article having an ultraviolet light absorber compound adjacent to the surface of the article. The article is treated by several methods, including dipping- coating a PVC film in a 2 1/2% by wt. stabilizer solution in ethanol, and, thereafter, heating the coated film in air at 130°C. to drive the absorber below the surface of the film and to remove the solvent.

Solvay and Cie, in Belgian Patent No. 612,206, discloses a process for surface treating rigid polyvinyl chloride objects. The method comprises immersing the object in a swelling solvent containing a very small amount of light stabilizer, e.g. a 0.5% by wt. solution, and then evaporating the solvent in air. The solvents disclosed are THF, cyclohexanone, DMF, acetone and carbon disulfide.

Bristol, et al. , in U.S. Patent No. 3,519,462, describes the treatment of polyvinyl chloride and other polymers with a solution of a U.V. stabilizer in a diol or triol, e.g. propylene glycol.

Lempkowicz, in U.S. Patent No. 4,126,600, describes a solution process of surface modifying PVC sheets by applying a stabilizer solution in air to a PVC sheet heated to 120°C. (Example 1) and then vaporizing the solvent remaining in the sheet. The amount of U.V. agent present in the treatment solution is disclosed to vary between 5 and 40% by weight of the solution, preferably between 10 and 30% by wt. Suitable solvents are disclosed as being chlorinated solvents derived from hydrocarbons having from 1 to 3 carbon atoms.

Baumgartel, et al., in FRG Patent Applications 28 08 005 and 38 08 036, both filed February 24, 1978, laid-open August 30, 1979, describe a process for rejuvenating installed, weathered PVC siding by spraying, brushing or roller-coating the siding with a solution of U.V. absorber in an organic solvent or mixture of solvents. The concentration of U.V. stabilizer in such solution was between 0.5 and 5 wt.%, preferably 0.5 to 2.5 wt.%. The preferred solvent system was a mixture of liquids, particularly methylene chloride and a second liquid, such as acetone, ethyl acetate, methyl acetate, THF cyclohexanone, DMF and methyl alcohol.

These processes in the prior art, however, fail to provide a resinous article that is both stabilized only in the surface region of the article and substantially planar. Particularly for resinous articles, such as PVC siding,

curvature or bending in the article from the application of a modifier composition renders the article less than satisfactory for commercial application. For example, if house siding has a substantial bend or curvature, it will not lie flat against the house and moisture can seep under the siding.

Furthermore, it is preferable that the U.V. stabilizing composition provide a surface modified article having only a minimum and constant amount of solvent in the PVC resin after surface modification. This amount preferably does not affect the physical appearance of the treated article, particularly the planarity of the article, e.g. a residential siding sheet.

Disclosure of the Invention

The present invention, which solves the problems of the prior art, relates to a stabilized article comprising a resinous body. The resinous body has incorporated into the surface region of at least one surface of the article (i) a stabilizing amount of a surface modifier ingredient in a concentration decreasing from the surface and (ii) a solvent in a concentration of less than 0.7 wt.% of the weight of the resinous body.

By limiting the amount of solvent retained within the surface of the article after surface modification, the appearance of the modified surface, particularly its surface perfection and planarity, is unaffected. A curvature of less than 0.3 may be obtained when the concentration of solvent retained is less than 0.7 wt.% of the modified resinous article. Such surface perfection and planarity enhances the use and commercial value of the resinous article. Brief Description of the Drawings

The invention will be more clearly understood by referring to the following drawings.

Fig. 1 is a graph of the change in the Yellowness Index (delta YI) vs. the U.V. stabilizer, in g/m 2' incorporated into the surface region of a PVC sheet.

Fig. 2 is a graph of the curvature of a surface modified PVC siding sheet, in inches, vs. the wt.% retained solvent therein.

Figs. 3a and 3b show surface modified PVC siding articles made using (a) U.V. stabilizer compositions having low concentrations of stabilizer, and (b) U.V. stabilizer compositions having concentrations of stabilizer within the range of the invention, to illustrate the effect of solvent upon curvature of the modified article.

Fig. 4 is a plot of the wt.% retained solvent in a PVC article vs. the concentration, in wt.%, of U.V. stabilizer in

2 the applying composition, based on 1.8 g/m incorporation of

UV stabilizer into a 35 mil sheet.

Fig. 5 is a graph of the amount of U.V. stabilizer, in 2 g/m , incorporated into the sur ace region of a PVC sheet vs. the concentration of U.V. stabilizer in the applying composition at a contact time of 7.5 seconds.

Best Mode for Carrying Out the Invention

Reference will now be made in detail to the present preferred embodiment of the invention. It should be understood that while the description that follows primarily focuses on a PVC resinous material, any suitable substrate material may be used to enjoy the advantages of the present invention.

In accordance with the present invention, a stabilized article comprising a resinous body is provided. The resinous body has incorporated into the surface region of at least one surface of the body (i) a stabilizing amount of a surface modifier ingredient in a concentration decreasing from the surface and (ii) a solvent in a concentration of less than 0.7 wt.% of the weight of the resinous body.

The resinous body can be made of any polymer or plastic material. Exemplary materials include polyvinyl chloride (PVC), polycarbonate, polyethylene, polypropylene, acrylonitrile/butadiene/styrene (ABS), rubber, polyacrylates,

polymethacrylates, and polyesters (e.g. polyethylene terephthalate and polybutylene terephthlate) . The resin substrate can be transparent, translucent, opaque or pigmented.

The resinous body can be an entire article or only part of an article. The article can be of any shape. Exemplary articles include residential and commercial siding and window frames.

The surface modifier ingredient can be any ingredient with which one skilled in the art would desire to modify the properties of the surface region of the resinous body. Exemplary modifier ingredients include U.V. radiation stabilizers, anti-oxidants, anti-static agents, pigments and dyes. Preferred U.V. radiation stabilizers are benzophenones and triazoles.

A stabilizing amount of U.V. stabilizer is defined herein as being that amount of a U.V. stabilizer incorporated into an article which affords substantially maximum U.V. protection for the article with a substantially minimum amount of U.V. stabilizer therein. That is, higher amounts of U.V. stabilizer incorporated into the surface region of the article would not materially enhance the U.V. protection obtained with the economically effective, stabilizing amount of U.V. stabilizer already incorporated into the article.

To be an economically effective, as well as a stabilizing amount of U.V. stabilizer, the stabilizer should be incorporated within the resinous article, such as PVC siding sheet, within the available contact time of the process, as determined by the swelling rate of the solvent, the line speed, e.g. the feed rate of PVC residential siding, and the requirement that a reasonable distance of separation be maintained between the application and solution displacement zones in the process.

One way of making the stabilized article of the present invention is by the method as claimed in U.S. Patent No. 4,770,905, issued September 13, 1988, the disclosure of which

is incorporated herein by reference, a process is described for producing a U.V. stabilized, surface modified PVC resin body. The U.V. stabilized article is made by a continuous process in which the resin body is contacted with a solution of U.V. stabilizer in a resin-swellable organic solvent. Thereafter, residual stabilizer and solvent are displaced from the modified surface. Both steps are preferably carried out under conditions which are non-evaporative of the solvent.

In a typical embodiment of this process, the resin body is immersed in a suitable liquid media, such as water, and the surface to be modified is contacted through the liquid media with a solution of a U.V. stabilizer in the resin- swellable organic solvent. A jet of water is directed against the modified surface to displace any residual stabilizer and solvent thereon. The liquid is one which is nonagressive toward the surface and which is immiscible with the solvent. That is, the liquid media, such as water, should not dissolve, swell or otherwise react with the surface.

The solution should be immiscible with the liquid. For example, if the liquid is water, then the solution can be water-immiscible organic solvents, such as halogenated hydrocarbons having up to six carbon atoms in the chain, ketones, and aliphatic esters. Examples of such solutions include methylene chloride, chloroform, 1,2-dichloroethane, 2-chloro-2-methylpropate, 2-pentanone, 3-pentanone, 2-hexanone, 2,4-pentanedione, diethyl ether, dipropyl ether, dimethoxy ethane and furan.

The preferred arrangement in this process is a two- layer, two-phase system, wherein water is the upper layer, and the stabilizer composition is the lower layer. The resin body is immersed in the upper layer and the stabilizer composition is pumped from the lower layer and directed onto the surface of the body to be modified. Excess stabilizer solution then falls off the surface of the body by gravity

and returns to the lower layer. During the time of application of the stabilizer composition, the solvent mixture in the composition is prevented from evaporating into the atmosphere by the blanket of liquid above it, which is advantageous for producing a modified surface having a high degree of surface perfection, and for ecological reasons.

In operation, a continuous resin strip, for example of polyvinyl chloride (PVC), is fed onto the upper layer at a predetermined rate from below a roller which is positioned below the surface of the water. In the "application zone" a series of applicator nozzles are oriented below the surface level of the water with their orifices directed towards the surface strip. The applicator nozzles continuously direct a stream of stabilizer composition over the upper surface of the moving resin strip. The thus-applied stabilizer solution remains on the surface of the strip whereupon the surface region is modified effectively with stabilizer.

Downstream of the applicator zone is a "displacement zone", in which residual stabilizer solution is removed in situ from the thus-treated surface of the strip. The term "in situ" means that the displacement step is carried out without exposing the treated surface to the ambient atmosphere; rather, the surface remains under water so that the solvent cannot evaporate. The duration of passage from the applicator zone to the displacement zone is defined as the "contact time" of the process. In the displacement zone, a jet element directs a spray of displacing liquid, preferably water, at a pressure sufficient to displace residual stabilizer solution from the treated surface of the strip.

A second roller is located ahead of the displacement zone and below the level of the water to accept the thus- treated resin strip after it leaves the displacement zone. Variable speed nip roller pullers are positioned outside the tank to move the strip at a predetermined speed through and out of the tank.

The preferred solvent is water-immiscible, has a boiling point of less than 85°C, and is non-aggressive towards the resin. Methylene chloride is preferred (b.p.

40°C).

In order to provide a diffusion process for surface modification of residential PVC siding, for example, it is necessary to provide a U.V. stabilizer composition which will incorporate a predetermined, effective, stabilizing amount of

U.V. within the surface region of the sheet, i.e. to a depth stabilizer of up to about 200 microns, without leaving an appreciable amount of solvent in the treated article, or stabilizer on its treated surface, and within a contact time which will allow for reasonable separation of application and displacement zones, particularly in a continuous process.

The advantages which flow from limiting the amount of retained solvent within the surface of the article after surface modification include that the appearance of the modified surface, particularly its surface perfection and planarity, is substantially unaffected. For example, when the concentration of retained solvent within a planar article is less than 0.7 wt.% of the resinous article, a curvature of less than 0.3 may be obtained.

Referring now to the drawings, Fig. 1 is a plot of weathering data reported as changes in Yellowness Index

2 (delta YI) vs. the amount of U.V. stabiliser, in g/m , present in the surface region of a surface modified PVC siding sheet. The data shows that economically effective

U.V. protection is achieved when about 1.8-2.8 g/m of the

U.V. stabilizer is present in the surface region. Lower amounts give substantially poorer protection, i.e. the ascending portion of the curve, and higher amounts afford very little improvement in weathering and is economically unjustified. Accordingly, it is desirable to provide a stabilizer composition which will provide such a useful amount of U.V. material in the surface region.

Fig. 2 is a plot of the curvature of the siding article in inches of height from the level vs. the wt.% retained solvent in the article after incorporation of the U.V. stabilizer. For commercial use as a siding material, it is necessary that the siding article be substantially planar. Accordingly, a curvature of greater than 0.3 inches is considered unacceptable for the industry. Less than 0.3 inches of a curvature can be achieved if the solvent incorporation is less than 0.7 wt.%.

Fig. 3 is a representation of siding sheets which have been surface modified by the process described herein. The sheets show (a) acceptable curvature and (b) unacceptable curvatures, that is, below and above 0.3 inches of curvature.

Fig. 4 is a plot of wt.% retained solvent in the PVC siding article after surface modification vs. the U.V. stabilizer concentration in wt.% in the applying composition. The data shows that less than 0.7% retained solvent is achieved at a stabilizer concentration of 18 wt.% or more. Within a stabilizer concentration range of 18-40 wt.%, the amount of retained solvent is about 0.2-0.4 wt.%. This range represents a substantially minimum and constant amount where the slope of wt.% solvent vs. stabilizer concentration is substantially zero.

Accordingly, it would be desirable to use this stabilizer concentration to achieve the desired low amount of retained solvent, and thereby achieve low curvature values.

However, it is preferred that this concentration satisfy the other condition of providing an economically effective amount

2 of 1.8-2.8 g/m of U.V. stabilizer within the region of the sheet, that is, down to 200 microns from the surface, and at least 70% of this amount within the first 100 microns from the surface. This degree of incorporation also is preferably achieved within contact times allowable by the process itself for production of residential PVC siding, that is, at a feed rate of 60 ft/sec. and within a reasonable separation of application and displacement zones. In practice, a contact time of about 2-10 seconds is required.

The graph in Fig. 5 shows that, unexpectedly, the amount of U.V. stabilizer incorporated into the surface region of the article increases with the stabilizer concentration in the applying composition only for dilute solutions, that is, below 18 wt.% stabilizer. Thereafter, the amount of U.V. stabilizer incorporated into the article actually decreases with concentration, i.e. the relationship of the amount of U.V. stabilizer incorporated vs. the concentration has a negative slope for compositions having a stabilizer concentration of greater than 18 wt.%.

Accordingly, this discovery enables the use of high concentrations of stabilizer in the applying solution to achieve all of the desirable parameters simultaneously,

2 namely; (1) 1.8-2.8 g/m of stabilizer incorporation,

(2) less than 0.7 wt.% retained solvent in the treated sheet,

(3) a contact time of 2-10 seconds, and (4) a feed rate of 60 ft/sec. of siding.

More particularly, Fig. 5 shows that the use of a range of 18-40 wt.% stabilizer composition will achieve the desired amount of U.V. incorporation of 1.8 g/m 2 to 2.8g/m2 within a contact time of 7.5 seconds, and leave less than 0.7 wt.% solvent therein. A concentration of less than 18 wt.%, or greater than 40 wt.% stabilizer, in the composition cannot provide these improved results.

Table I below shows the effect of the concentration of the treating solution upon the retained solvent in the treated article immediately after impregnation of different amounts of stabilizer. The article treated was standard 9" double 4 extruded PVC siding. The data demonstrates again that for impregnation of a stabilizing amount of U.V. stabilizer, a stabilizer concentration of 18-40 wt.% will provide a retained solvent level of less than 0.7 wt.%.

TABLE I

Wt. % Retained Solvent in a PVC Resinous Body at Increasing

Stabilizer Levels from Treatment Solutions of Various

Stabilizer Concentrations

Wt. % Stabilizer (g/m ² . Solution Solvent: Stabilizer 0.9 1.8 2.7 3.6 (Wt. % Stab. ) Ratio

Wt. % Retained Solvent

10 20 30

Table II below correlates the data in Table I above with the resultant curvature of the siding as shown pictorially in Fig. 2. For application as siding for building, a curvature of less than 0.3 inches is obtained with a retained solvent of less than 0.7 wt.%, i.e. a stabilizer concentration of 18-40 wt.%. The preferred concentration is an about 30 wt.% stabilizer concentration. The degree of curvature is measured by the "curling" of the originally planar siding to the condition wherein, when one edge of siding is held on a flat surface, the opposite edge is lifted off the flat surface. This curvature is measured in "inches of curvature" as shown in Fig. 2. In practice, the curvature is observed to occur in a direction perpendicular to the direction of extrusion of the PVC siding, which is indicated by the arrows in Fig. 2.

TABLE II

Curvature of PVC Siding Surface Modified at Increasing

Stabilizer Levels from Treatment Solutions of Various

Stabilizer Concentrations

2 Solution Wt. % Stabilizer g/m J_

(wt. % Stab.) 0.9 1.8 2.7 3.6

Curvature (Inches )

10 20 30

While a siding article has been shown to illustrate the principles of the invention with respect to the effect of retained solvent upon curvature, it will be understood that other polymer articles may be treated effectively as well. For example, sheets, films, rods, tubes, and other simple and complex shaped articles may be used. Soffit sheets in the siding industry, polymer articles in the construction industry, and lineals used in window enclosures also will benefit from the retention of shape for a treated surface when the retained solvent level is below 0.7 wt.%.

It will be apparent to those skilled in the art that various modifications and limitations can be made in producing stabilized articles according to the present invention. Thus, it is intended that the present invention cover the modifications and limitations of the invention provided they come within the scope of the appended claims and their equivalents.