WO2014062371A1 - Sealant for capped wood-plastic composites - Google Patents

Abstract

WPC, especially with capstock thereon, is vulnerable to delamination during useful life of because of ingress of moisture from precipitation or humidity at uncapped surfaces. Use of a two component, aliphatic polyurethane coating which cures over the uncapped surface reduces incidence of "flare-up" delamination.

Description

SEALANT FOR CAPPED WOOD-PLASTIC COMPOSITES

CLAIM OF PRIORITY

[0001] This application claims priority from U.S. Provisional Patent

Application Serial Number 61/715,918, bearing Attorney Docket Number 12012022 and filed on October 19, 2012, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] This invention concerns a sealant for composites made from a mixture of biofiber and thermoplastic, shaped into construction articles.

BACKGROUND OF THE INVENTION

[0003] Plastic has taken the place of other materials in a variety of industries. In the packaging industry, plastic has replaced glass to minimize breakage, reduce weight, and reduce energy consumed in manufacturing and transport. In other industries, plastic has replaced metal to minimize corrosion, reduce weight, and provide color-in-bulk products. Recently, an entire industry has arisen called "wood-plastic composites" ("WPC"). The acronym WPC is used even if the functional filler is not wood but another material, usually bio- derived.

[0004] WPC has begun to replace wood in building and other construction materials where the wood is susceptible to rotting, warping, or discoloration. The advent of thermoplastic biofiber composites has made outdoor decks, porches, railings, windows and stairways more durable. With structural issues resolved, the next key to growing this market is making the plastic composite look like naturally-colored or stained wood.

[0005] The ability of WPC to simulate the appearance of natural wood, including its surface texture and wood grain coloration, and to provide greater durability compared to wood, are critical to WPC materials successfully replacing the natural wood itself. The colorants and additives used to achieve these characteristics, however, significantly add to the WPC products' costs. To reduce these costs, manufacturers have begun to incorporate various colorants and additives into a thinner outer layer, or "capstock", which covers the core construction material, thus reducing the total amount of colorants and additives per linear foot of product.

[0006] "Wood-plastic composite" or WPC is a general term used in the building construction industry for the mixture of biofiber or other particles into thermoplastic, followed by shaping by extrusion or molding into a variety of end use articles, among them, decking, railings, fences, etc., in circumstances in which the composite is intended to simulate the use of wood but have the durability of thermoplastics.

[0007] WPC itself is not immune to the effects of heat, humidity, sunlight, precipitation, or the freeze/thaw cycles of outdoor usage. For this reason, there has been inventive activity to include the option of providing a cover layer or "capstock" to the WPC article.

[0008] WPC itself has two very different types of surfaces, finished and unfinished. The finished surface results from polymer/biofiber extrusion or molding events and is not susceptible to moisture ingress. The unfinished or post-formation exposed surface is uncapped, usually an end cut or other abrasion of the finished surface and is susceptible to moisture ingress.

SUMMARY OF THE INVENTION

[0009] It has been found that WPC, especially with capstock thereon, is prone to swelling or "water flare-up" of ends and end cuts of boards or other uncapped structures of the WPC. It is estimated that there are about 150 end cuts generated in fabricating a deck of 16 feet by 12 feet dimensions (192 square feet or 17.63 square meters). Water flare-up has not been an issue with uncapped boards because all six sides will pick up water and the entire board would swell uniformly. With capstock being a different material from the WPC substrate, delamination is possible and has been noticed over useful life of the WPC. Articles in technical literature, such as "Question & Answer: Swelling Capstock Decking" in Professional Deck Builder (September/October 2011) report the extent of the problem.

[00010] "With capstock decking, you have sealed a WPC— which wants to absorb water— in a protective wrapper. This offers many advantages, but the uncapped ends of the boards are free to pick up water just like before. Since only the ends of capstock decking take on much water, that's where the swelling happens. I've measured the water absorption rate through the ends of a capped WPC and found it to be more than six times higher than through the cap.

Unfortunately, the real kicker is that once the decking flares, the flare never fully goes away. Even if you completely dry the deck, the swelling may go down some, but the board will never be the same."

[00011] This problem has been solved in which unfinished exposed surfaces or post-formation exposed surfaces ("uncapped surfaces") are treated with a polyurethane coating, especially at those locations adjacent the capstock laminated thereto.

[00012] One aspect of the present invention is a method of using a two component, aliphatic polyurethane ("PUR") coating to protect WPC, comprising applying the coating to an uncapped surface of the WPC.

[00013] Another aspect of the present invention is the two-component, aliphatic polyurethane composition used as the coating.

[00014] A feature of the invention is that the two part PUR coating cures at the surface of uncapped surface. This feature results in the advantage that the uncapped surface has a protective layer generated from curing of the PUR coating, which adheres to both the biofiber and the thermoplastic at that uncapped surface and reduces water flare up in capped WPC.

[00015] More about the invention is explained in the embodiments with reference to the Drawing. [00016] DRAWING

[00017] Fig 1. is a end view of a WPC substrate, such as a decking board, with a capstock layer laminated to the WPC.

[00018] EMBODIMENTS

[00019] WPC and Capstock

[00020] WPC in the building and construction industries use

thermoplastics to serve as the matrix, including polyolefins, poly(vinyl halides), polystyrenes, polycarbonates, and other engineering grade polymers suitable for use in the particular shape of construction. Of these choices, polyethylene is preferred because of the compatibility of that polymer resin with compounds serving as the capstock.

[00021] The polymer composite of the WPC, as the substrate to a capstock, can include fillers to reduce cost of polymer. Fillers can be metallic, ceramic, or bio-derived. Among possible fillers are wood fiber, wheat straw, fly ash, granulated rubber particles, rice hulls, kenaf, and any other small size product of commerce which needs to be recycled in a sustainable way.

[00022] The capstock can be made separately from the substrate and subsequently fused or adhered to the substrate. Alternatively, the capstock can be co-extruded with the substrate.

[00023] The shape of the substrate, and hence the purpose of the capstock, can vary according to choice of architects and other building designers. Capstocks can be employed as the outer surface in windows and doors, decking and fencing, railings and spindles, stairways and steps, posts and pillars, shutters and fascia, etc. Currently, the largest volume of wood plastic composites used as substrates are deck planks and other lumber construction pieces. Capstocks can be utilized to provide both a better durable surface than wood itself and a more aesthetically pleasing surface than the substrate itself.

[00024] Moreover, with the capstock covering the exposed surface(s) of the substrate, there need not be coloration or other finishing ingredients in the substrate. The substrate can be made with less expense, resulting in the overall construction item having all of the structural properties needed for the substrate and all of the durability and non-glossy appearance properties of the capstock.

[00025] General contractor home construction and do-it-yourself home improvement home owners both can benefit from composite substrates which have cap stocks.

[00026] The thickness of the capstock depends on the thickness and construction purpose of the substrate. Generally, the thickness of the capstock can range from about 1 mm to about 4 mm and preferably from about 1.5 mm to about 3 mm. Stated another way, the thickness of the capstock relative to the thickness of the substrate can range from about 3% to about 20% and preferably from about 5% to about 10%.

[00027] The capstock can cover only the surface exposed to the most viewing by users of the construction item or can cover any other portion or the entire remainder of all surfaces of the substrate. The capstock should cover at least all surfaces which are exposed to sunlight, in order that the substrate not be exposed to ultra-violet light and fade to a different color than the capstock which has weathering agent protection as described above.

[00028] Coloration of the capstock can mimic colors of popular wood species, such as redwood or cedar. Alternatively, the coloration can be chosen to be any color according to design choice for decorative or informative effect.

[00029] The outer surface of the capstock can be smooth or textured as desired, with a preference for some texturing if used where foot traffic is likely. Desirably, the capstock texture can resemble wood grain or other tactile effect to enhance its simulation of finished wood structures.

[00030] With capstocks such as those disclosed in PCT Publications WO

2012/103378 and WO 2012/109489, both incorporated by reference herein, one of ordinary skill in building materials can protect substrates with a non-glossy capstock in an economical way with aesthetically pleasing results, preferably also with years of durability to outdoor uses. [00031] The capstock of PCT Publication WO 2012/103378 is a low gloss capstock compound, comprising (a) polyethylene in both pellet form and powder or flake form; (b) polyolefin elastomer (such as ethylene- octene copolymer); (c) gloss inhibiting agents comprising silica and barium sulfate; wherein when a surface of a strip of the compound is tested according to ASTM D523, D2457, the surface has a Gloss Angle at 85° of less than 10 GU.

[00032] The capstock of PCT Publication WO 2012/109489 is A low gloss capstock compound, comprising (a) polyethylene in both pellet form and powder or flake form; (b) metal-based ionomer thermoplastic resin, wherein the metal is selected from the group consisting of magnesium and zinc; (c) acid scavenger for the metal-based ionomer thermoplastic resin; (d) gloss inhibiting agents comprising silica and barium sulfate; wherein, when a surface of a strip of the compound is tested according to ASTM D523, D2457, the surface has a Gloss Angle at 85° of less than 10 GU.

[00033] Coating Material

[00034] Based on the experimental results identified below, it has been found that an acceptable coating material to serve as the sealant for WPC has the following properties:

[00035] Two part aliphatic polyurethane system with a Part A comprising aliphatic ester(s) and a Part B comprising an aliphatic isocyanate in which the mixture of Parts A and B have (a) sufficient viscosity to minimize dripping of the coating material when applied as a sealant to the WPC; (b) a coating drying time of less than three hours; and (c) a percentage increase in thickness after four weeks of immersion in water of less than two percent.

[00036] Preferably the coating drying time needs to be less than 3 hours and the percentage dimensional increase of less than about 3 percent.

[00037] Protective Industrial Polymers Inc. of Cleveland, Ohio ("PIP") is a commercial source of coating materials satisfying the requirements of viscosity, drying time, and minimize water-based expansion. [00038] Xylene is a suitable solvent for clean up of the coating material on tools or spills.

[00039] Method of application

[00040] Any conventional method of applying a thick liquid to a solid surface can be used as the coating step of the invention.

[00041] The two parts of the coating material need to be thoroughly mixed together and used less than 25 minutes after mixture, and preferably as quickly as possible. Mixture can be common agitation without raised temperature.

[00042] The mixed coating material can then be applied to form the sealant on the WPC surface. Application can use any type of conventional tool or apparatus, with a paint brush is the most common.

[00043] A sufficient amount of coating material is needed to thoroughly provide a sealing layer over the exposed WPC surface. The thickness of the sealing layer can range from about 2 to about 6 mils (0.05 - 0.15 mm) and preferably from about 3 to about 4 mils (0.07 - 0.10 mm).

[00044] As stated above the coating drying time should be less than three hours, but it is also recognized that coating drying time is a function of coating thickness.

USEFULNESS OF THE INVENTION

[00045] The coating of uncapped surfaces reduces and preferably minimizes incidences of delamination of capstock from the WPC substrate.

[00046] Fig 1. shows an end cross-sectional view of a typical WPC board

10 having a capstock 12 as described above laminated to a substrate 14 of thermoplastic in which many pieces of biofiber particulate 16 are dispersed.

[00047] The coating described above is adhered to the entire end cross- section of the board, resulting in the requirement of the coating to adhere to the composition of the capstock 12, the composition of the thermoplastic in the substrate 14, and the composition of the biofiber. [00048] In the experiments below, commercial products, including both one part and two part polyurethane systems, were tried without success. It is believed that the unusual combination of thermoplastic and biofiber in WPC adversely affected the sealing properties.

[00049] While product literature for Protect 21000 UR, a one part polyurethane system, is indicated for use with "concrete, wood or other approved polymer surfaces", there is no indication that Protect 21000 UR would provide sealing capability for an uncapped surface, in which the material is a blend of both polymer and biofiber such as wood. Indeed, the disparate types of WPC components creates on a microscale two totally different interfaces with which the coating material must successfully adhere. As the product literature for Protect 21000 UR indicates that "contaminates" must be removed before application of the coating. At the interfacial chemical level, the biofiber could be considered a contaminate of the polymer. But also, the polymer could be considered a contaminate of the biofiber.

[00050] Moreover, the sealant composition must adhere to the capstock itself and at the location of greatest stress to flare-up, the interface between the capstock and the WPC. The capstock will be virtually immune to water absorption if there is no biofiber in the capstock, but the WPC is significantly affected by water absorption as identified above. The minimization of delamination at the interface of capstock and WPC can be fulfilled by use of the sealant composition described above.

[00051] The sealant composition can be packaged in a twin cartridge container, which dispenses 2 parts of A and 1 part of B and eliminates the need of weighing either part. This twin cartridge can benefit from use of a dispensing gun which releases about 250 ml of the sealant composition.

Alternatively, one can use a caulk gun in which a single tube is placed with dual components for the proper ratio of part A and part B dispensing.

[00052] It is surprising that a single coating material, whether prepared from a pre-mixed single dispenser or a double dispenser and mixed soon before application could effectively seal a blend of two different types of materials in the substrate, contrary to anything suggested by the Protect 21000 UR product literature, the closest commercial literature from Protective Industrial Polymers Inc., the supplier of the coating material used successfully in this invention.

[00053] Examples demonstrate the conditions for success.

EXAMPLES

[00054] The Examples and Comparative Examples were established by experiments in five series, identifying how and why the mixture of the present invention is unexpectedly superior to the other compositions tested. Table 1 shows the commercially available WPC which were used for the testing. PE means polyethylene.

[00055] All Examples and Comparative Examples were tested according to the following procedures.

[00056] Application Method

[00057] The container or containers holding the mixtures were shaken for

30 seconds and then loaded on the dispensing gun. Whether in a single Part or in two Parts, the composition(s) was(were) dispensed to a 4 oz paper cup and mixed for 30 seconds using a wooden stick. In the case of the two Part embodiment, the twin cartridge has a cap that allows the product to be dispensed and resealed.

[00058] Each mixture was applied to only one end cut of each board

(cleaned with a rag to remove any dirt) using a paint brush of one inch in width. The coating thickness varied between about 3 and about 6 mils (between 0.0762 mm and 0.1524 mm).

[00059] For testing, the board was positioned in either in the horizontal or vertical position.

[00060] The coating was allowed to dry for about 3 to 6 hours before testing began. Temperature and relative humidity will have an effect on the drying times, and a person having ordinary skill in the art should be able to accommodate the ambient conditions or taken action to control them.

[00061] In the two Part embodiment, it was found that the mixture of Part

A and B had a shelf life of about 25 minutes. A fresh batch had to be dispensed after that duration.

[00062] Testing Method

[00063] After 24 hours following the coating of one end cut of each board, the boards having both sealed end cuts and unsealed end cuts were measured for the thickness increase, width increase, and in some instances, weight gain to establish baseline values. Then the boards were immersed in a water bath at a depth of one inch (2.54 cm) for a continuous period of four weeks, except for retrieval at weekly intervals for measurements of each end of each board for the thickness increase, width increase, and in some instances, weight gain. After four weeks duration, the percentage change from the baseline control value was calculated. All measurements were in inches.

[00064] Series 1:

[00065] Experiments were performed upon a variety of commercially available WPC boards identified in Table 1 using a commercially available wood sealer (Anchor Seal from U.C. Coatings of Buffalo, NY), a commercially available clear cosmetic nail polish (Clear 201 from Calvin Klein), and commercially available 2000 UR two-part polyurethane system from Protective Industrial Polymers Inc. applied at a volume ratio of 0.5 Part A and 2.0 Part B. Table 2 shows the results. The Anchor Seal product and the clear nail polish did not work. The 2000 UR two-part polyurethane performed very well as a sealant. While acceptable in sealing performance, the application drying time of more than six hours did not make 2000 UR two-part polyurethane a preferred solution to the problem.

[00066] Series 2 and 3:

[00067] The next two experiments used 21000 UR one part polyurethane system from Protective Industrial Polymers Inc. As Table 3 shows for Series 2, this commercial product had acceptable sealant performance with two popular and commercially available WPC boards, as measured by low percentage changes after four weeks of immersion relative to the control measurements. But it was also determined that this 21000 UR product had insufficient viscosity, which caused dripping. Also the 21000 UR product was too foamy for acceptable use.

[00068] Series 3 used the following WPC boards with 21000UR and thickness was measured at three different locations. The acceptable sealing performance shown in Table 4 was overshadowed by the dripping and foamy problems.

[00069] Series 4:

[00070] Series 4 used five different formulations from Protective

Industrial Polymers Inc. of a two part polyurethane system, identified in Table 5 for the first two formulations and Table 6 for the latter three formulations. The ratio of mixing, viscosity assessment, shelf life, and drying time are identified for each formulation in Table 7. The trio of formulations 3, 4, and 5 were designed for a faster curing time of the mixture on the WPC end cuts, as compared to the commercially available 2000 UR product. All five

formulations designed to have a higher viscosity to reduce dripping, as compared to the commercially available 21000 UR product.

[00071] For each of the five formulations, Part A was mixed as follows:

[00072] Charge Item #1 into a mixing vessel of suitable batch size using a sawtooth Cowles dissolver blade of a width of at least 33% of the diameter of the vessel.

[00073] Turn on mixer at medium speed (1200-1600 rpm) and add Item

#2 into vortex. Mix for a minimum of 10 minutes to assure a homogenous blend

[00074] Add Item #3 with mixer running at low speed (600-800 rpm).

Continue at low speed.

[00075] Add Item #4 with mixer running at low speed. Continue at low speed.

[00076] Add Item #5 for Formulations 3-5 with mixer running at low speed. Continue at low speed.

[00077] Add Item #5 for Formulations 1 and 2 or Add Item #6 for

Formulations 3-5 with mixer running at low speed. Continue at low speed for a minimum of 15 minutes.

[00078] Submit Sample to QC. After QC approval, re-blend at low speed for a minimum of 5 minutes prior to packaging.

[00079] Part B need not have any additional preparation because it is used "as is" from the manufacturer.

[00080] All tests were performed on capped WPC from TimberTech.

The first and second formulations had no data because they did not cure rapidly enough. Table 8 reports the results for formulations 3-5 upon the increase in thickness and width as in the prior Series but also length in inches and mass in grams, at each weekly interval of testing being compared to the baseline initial measurements. An unsealed board was tested also as a control.

[00081]

[00082] Both Desmophen™ NH 1420 resin and NH 1520 resin are low viscosity amine functional resins, reported to be aspartic ester amines, developed for use in the formulation of high solids two-component

polyurethane/urea coatings. Both resins are solvent-free, amine-functional co- reactants for polyisocyanates. Each can be blended with other amine functional resins in order to customize characteristics.

[00083] Desmophen™ NH 1420 resin has an amine value of 199-203 and a viscosity at 25°C of 900-2000 mPa- sec, whereas Desmophen™ NH 1420 resin has an amine value of 189-193 and a viscosity at 25°C of 800-2000 mPa- sec.

[00084] Desmodur™ N 100 is an aliphatic polyisocyanate (HDI biuret) used as the hardener component for lightfast polyurethane coating systems. The polyisocyanate has a NCO content of about 22 %.

[00085] VESTAMIN A 139 aldimine is a liquid, blocked crosslinker for polyisocyanate resins based on a cycloaliphatic diamine. As supplied the product exhibits a very low reactivity towards isocyanate groups. The aldimine has an amine number of about 40 mg KOH/g.

[00086] These data show the ability to use any of formulations 3-5 as a sealant composition for use in the invention, with a preference for formulation 4 because of viscosity, shelf life, time to dry, and sealing performance.

[00087] After four weeks of the immersion testing, the acceptable amount of increase of board width can range from about 0.5% to about 1.5% and preferably from about 0.5% to about 1.2%.

[00088] After four weeks of the immersion testing, the acceptable amount of increase of board thickness can range from about 0.5% to about 3% and preferably from about 0.5% to about 2.0%.

[00089] After four weeks of the immersion testing, the acceptable amount of increase of board weight can range from about 0% to about 3% and preferably from about 0% to about 1.3%.

[00090] Series 5:

[00091] This experiment showed the results of end cuts of WPC sealed with Rhinodeck Armadillo Sealer from MasterMark, using the Timbertech WPC board identified above. The sealant is a one part system and appeared to be oil based. Table 9 shows the results.

[00092] The results of the Series 5 experiment showed that the

MasterMark sealant product was inadequate compared to the sealant compositions of Series 4, Formulations 3-5.

[00093] The invention is not limited to the above embodiments. The claims follow.

Claims

1. A method of using a two component, aliphatic polyurethane coating to protect wood-plastic composites, comprising applying the coating to an uncapped surface of the wood-plastic composite.

2. The method of Claim 1, wherein wood-plastic composite has a capstock laminated thereto and wherein the uncapped surface is an unfinished surface or a post-formation exposed surface of wood-plastic composite adjacent the capstock laminated thereto.

3. The method of Claim 1 or Claim 2, wherein the coating adheres to and cures on both the wood-plastic composite and the capstock laminated thereto.

4. The method of Claim 1 or Claim 2, wherein the wood-plastic composite comprises thermoplastics and fillers, wherein the fillers are selected from the group consisting of metallic, ceramic, and bio-derived materials.

5. The method of Claim 4, wherein the thermoplastic is selected from the group consisting of polyolefins, poly(vinyl halides), polystyrenes, and polycarbonates, and combinations of them, and wherein the filler is selected from the group consisting of wood fiber, wheat straw, fly ash, granulated rubber particles, rice hulls, kenaf and combinations of them.

6. The method of Claim 5 wherein the thermoplastic is polyethylene and the filler is wood fiber.

7. The method of any one of Claims 1-6, wherein the capstock is a low gloss compound, comprising:

(a) polyethylene in both pellet form and powder or flake form; (b) polyolefin elastomer (such as ethylene- octene copolymer);

(c) gloss inhibiting agents comprising silica and barium sulfate; wherein when a surface of a strip of the compound is tested according to ASTM D523, D2457, the surface has a Gloss Angle at 85° of less than 10 GU.

8. The method of any one of Claims 1-6, wherein the capstock is a low gloss compound, comprising:

(a) polyethylene in both pellet form and powder or flake form;

(b) metal-based ionomer thermoplastic resin, wherein the metal is selected from the group consisting of magnesium and zinc;

(c) acid scavenger for the metal-based ionomer thermoplastic resin;

(d) gloss inhibiting agents comprising silica and barium sulfate; wherein, when a surface of a strip of the compound is tested according to ASTM D523, D2457, the surface has a Gloss Angle at 85° of less than 10 GU.

9. The method of Claim 1 or Claim 2, wherein, after immersion in water for four continuous weeks, wood-plastic composite in the form of a board having capstock laminated thereto has an increase in board width of from about 0.5% to about 1.5%, an increase in board thickness of from about 0.5% to about 3%, and an increase in board weight of from about 0% to about 3%.

10. The method of Claim 1 or Claim 2, wherein the two component, aliphatic polyurethane coating comprises a Part A and a Part B, wherein Part A comprises an aspartic ester amine and wherein Part B comprises an aliphatic polyisocyanate.

11. The method of any one of Claims 1-9, wherein the two component, aliphatic polyurethane coating comprises a Part A and a Part B, wherein Part A comprises an aspartic ester amine and wherein Part B comprises an aliphatic polyisocyanate, and wherein the two component, aliphatic polyurethane coating is mixed in a weight ratio of 2: 1 of Part A:Part B.

12. The method of Claim 11, wherein the aspartic ester amine is present in Part A in a weight percent ranging from about 14 to about 41 weight percent to the total weight of Part A.

13. A capped wood-plastic composite article having uncapped surfaces treated using the method of any one of Claims 1-12.

14. The article of Claim 13, wherein the article is shaped as a part of an outdoor deck, a porch, a railing, a fence, a window, or a stairway.

15. A two component, aliphatic polyurethane compound useful as a coating for the method of any one of Claims 1-9, comprising a Part A comprising an aspartic ester amine and a Part B comprising an aliphatic polyisocyanate.

16. The two component, aliphatic polyurethane compound of Claim 15, coated on a capped wood composite article.

17. The compound of Claim 16, wherein the two component, aliphatic polyurethane coating is mixed in a weight ratio of 2:1 of Part A:Part B.

18. The compound of Claim 17, wherein the aspartic ester amine is present in Part A in a weight percent ranging from about 14 to about 41 weight percent to the total weight of Part A.

19. The compound of Claim 18, wherein Part A further comprises an aldimine.

20. The compound of Claim 19, wherein the compound has a drying time of about 3 hours.