WO2008054613A1

WO2008054613A1 - Method of preparing artificial turf

Info

Publication number: WO2008054613A1
Application number: PCT/US2007/021478
Authority: WO
Inventors: Linda Kim-Habermehl; Nicoletta Piccolrovazzi
Original assignee: Dow Global Technologies Inc.
Priority date: 2006-10-30
Filing date: 2007-10-05
Publication date: 2008-05-08

Abstract

A method of preparing artificial turf, using a high solids backing compound formulation comprising a synthetic latex having a bimodal particle size distribution and filler. Surprisingly, the backing compound of the invention provides at least one of improved dry tuft lock, improved wet tuft lock, and improved tuft retention, when compared to existing commercial backing compounds.

Description

METHOD OF PREPARING ARTIFICIAL TURF

Cross-Reference to Prior Application

This application claims the benefit of U.S. Provisional Application No. 60/855,246 filed October 30, 2006. Background of the Invention

The present invention relates to the manufacture of synthetic grass.

The synthetic grass market has traditionally been segmented into "sports" and "residential/landscaping" categories. The advantages of synthetic grass relative to natural grass fields include the following: ability to withstand more intensive use, year- round usage, consistently good playing qualities, and a low maintenance/expenditure requirement (e.g., no watering requirements). Performance requirements of synthetic grass include the following: softness (low coefficient of friction, low modulus), resiliency, durability, wear resistance, UV stability, tear resistance, water drainage, mold and mildew growth control, recycleability, and cost. Synthetic grass typically consists of tufts (sometimes referred to as yarn or fiber), a polypropylene primary backing, and loose infill which consists of rubber granules and silica sand. The use of polyethylene monofilaments in tufts is increasing due to the more natural appearance and lower sliding resistance that it imparts. These monofilaments are thinner relative to the fibers previously used (thus requiring higher tuft lock) and seem to exhibit properties that are closer to natural grass. Some of the newer monofilaments can be easily realigned after prolonged use to an upright position using rotating brushes, thereby ensuring a permanently open surface. The rubber granules present in the infill typically comprise reground, recycled styrene-butadiene-rubber tires.

In the manufacturing process, synthetic grass can be coated with a latex- based backing compound, the main function of which is to bind the tufts to the primary polypropylene backing. Performance requirements for synthetic grass backing compound include the following: tuft lock, performance maintenance after water immersion, performance maintenance at low temperature, backstitch coverage, dimensional stability, faster drying, and cost. Higher dry tuft lock, wet tuft lock, and tuft retention are desired, as these properties lead to increased durability of the synthetic grass for sports play. For example, the minimum durability for A Series soccer fields is 15 years (with twice a week play).

It would be desirable to have a backing compound that would, compared to existing compound formulations, provide one or more of the following: faster drying time during manufacture, lower cost, improved dry tuft lock, improved wet tuft lock, and improved tuft retention. Faster drying is desirable because of the productivity improvements from faster line speeds that can be realized. Lower energy costs may also be realized. Reduction or elimination of any synthetic grass backing compound formulation ingredients, without any detrimental impact on synthetic grass performance, is also desirable for reduced cost.

Summary of the Invention

The present invention can provide one or more of the desired benefits listed above, and includes a method of preparing artificial turf, the method comprising: binding artificial turf tufts to an artificial turf backing using a binding amount of a backing compound formulation, the backing compound formulation comprising the following components: a. 100 weight parts binder comprising a synthetic latex having a bimodal particle size distribution, b. 20 to 500 weight parts filler, based on 100 dry weight parts of the binder; c. optionally, a dispersing amount of a dispersing agent , d. optionally, a coloring amount of a colorant, and e. optionally, a thickening amount of a thickener, with the proviso that the solids content of the formulation is at least 79% by weight, based on the total weight of the formulation.

Other embodiments of the invention include an artificial turf having a wet tuft lock property value of at least 2 kg, an artificial turf having a dry tuft lock property value of at least 3.5 kg, and an artificial turf having a wet tuft lock retention value of at least 60%. Surprisingly, the backing compound of the invention provides at least one of improved dry tuft lock, improved wet tuft lock, and improved tuft retention. Detailed Description of the Invention

The terms artificial turf, artificial grass, synthetic grass, synthetic turf, and artificial pitch are used interchangeably herein to refer to a synthetic material that is especially useful for replacing grass, such as on sports fields, race tracks, etc., but is not limited to that use.

The method of the invention comprises preparing artificial turf using a backing compound formulation. The formulation comprises at least a filler, a binder, but can contain other components or ingredients.

For the purposes of the present invention, the term "dry" means in the substantial absence of liquids and the term "dry basis" refers to the weight of a dry material.

For the purposes of the present invention, the term "copolymer" means a polymer formed from at least 2 monomers.

The binder employed in the backing compound formulation advantageously comprises a synthetic latex. A synthetic latex, as is well known, is an aqueous dispersion of polymer particles prepared by emulsion polymerization of a combination of monomers. For the purposes of the invention, a latex is employed such that the binder has sufficient adhesive properties for use in the manufacture of synthetic grass. Preferably, the latex has a bimodal particle size distribution.

Advantageously, the minimum film formation temperature of the latex is less than about 30°C. Representative monomers useful in preparing the latexes of this invention and methods for preparing the individual separate particles are described in U.S. Patents 3,404,1 16 and 3,399,080, the teachings of which are incorporated herein by reference. Examples of monomers suitable for preparing the latexes of this invention include butadiene, styrene, acrylonitrile, vinyl acetate, alkyl acrylates, hydroxyalkyl acrylates, alkyl methacrylates, hydroxyalkyl methacrylates, acrylamide, and n-methylolacrylamides. Mixtures of monomers can be employed. Especially preferred latexes include modified styrene/butadiene latexes such as, for example, styrene/butadiene/acrylic acid, styrene/butadiene/acrylic acid/itaconic acid, styrene/butadiene/β-hydroxyethyl acrylate, styrene/butadiene/β-hydroxyethylacrylate/acrylic acid, styrene/butadiene/acrylonitrile/acrylic acid, styrene/n-butylacrylate/acrylic acid, methylmethacrylate/n-butylacrylate/acrylic acid, vinyl acetate/acrylic acid, vinyl acetate/n- butylacrylate/acrylic acid, styrene/butadiene/methylmethacrylate/acrylic acid, styrene/butadiene/methylmethacrylate/acrylonitrile/acrylic acid, and styrene/n-butyl acrylate/butadiene/acrylic acid. Mixtures of latexes can be employed. It is desirable that the latex be carboxylated in order to increase colloidal stability and, hence, the degree of binding efficiency. Examples of suitable carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid and fumaric acid. Mixtures of carboxylic acid monomers can be employed in the aforementioned latexes. The amount of carboxylic acid monomer advantageously is from about 1.5 to about 4 weight percent, based on the total weight of monomers employed, preferably is from about 1.8 to about 3%, and more preferably is from about 2 to about 2.4%.

The bimodal latex comprises large-size polymer particles and small-size polymer particles. The volume average diameter of the small-size particles advantageously is in the range of from about 35 to about 75 nm, and preferably is from about 45 to about 70 nm. The volume average diameter of the large-size polymer particles advantageously is in the range of from about 120 to about 180 nm, and preferably is from about 130 to about 170 nm. Volume average particle diameter is measured using hydrodynamic chromatography.

The weight percentage of the large-size polymer particles in the latex advantageously exceeds the weight percentage of the small-size polymer particles. Advantageously, the weight ratio of the small particles to the large particles is within the range of from about 5/95 to about 40/60, preferably from about 10/90 to about 30/70

Bimodal latexes and methods for their preparation are well known to those skilled in the art. The bimodal latex can be prepared by blending two polymer dispersions that each have just one of the two desired peaks in the particle size distribution. See, e.g., WO 02/070615, the teachings of which are incorporated herein by reference. Alternatively, bimodal latexes can be prepared by intermediate addition of a seed latex during the emulsion polymerization process. For example, the large size particle can be prepared, and either simultaneously to or after the large size particle is formed, the seed latex can be added in order to provide the small size polymer particles. It is also possible to prepare the bimodal latex by a polymerization in the presence of two (seed) latexes containing particles with different average diameters as disclosed in German Pat. Appl. 31 47 008. East German Pat. Appl. 274 229 describes a further preparation process wherein the bimodal particle size distribution is controlled by the presence of an emulsifier (surfactant). This can also be applied to the present invention. Any of the latexes can be concentrated, if desired.

The bimodal latex is advantageously a high solids latex, i.e. has a solids content of at least about 53 weight percent, based on the weight of the latex. Preferably, the solids of the latex is at least about 55%, and more preferably is at least about 56%. High solids latexes typically are composed of particles of relatively large size and that have a broad particle size distribution. As a result, higher coating formulation solids can be attained with the bimodal latexes compared to formulations prepared with the corresponding monodisperse latex.

The filler employed can be essentially any filler suitable for use in synthetic grass manufacture. Such fillers are widely commercially available. Examples of mineral fillers or pigments include those known in the art, such as calcium carbonate clay, kaolin, talc, titanium dioxide, calcium aluminum pigments, satin white, synthetic polymer pigment, zinc oxide, barium sulphate, gypsum, fly ash, silica, alumina trihydrate, mica, hollow polymer pigments, and diatomaceous earth. The amount of pigment that is employed can vary depending upon the density of the filler and the coating properties desired. The average particle size of the filler advantageously is within the range of from about 1 to about 100 μm, and preferably is from about 10 to 80 μm. The dispersant, if employed, can be essentially any dispersant suitable for use in synthetic grass manufacture. Such dispersants are widely commercially available. Examples of dispersants include those known in the art such as polyacrylate dispersing agents or polyphosphate dispersing agents. A dispersing amount of the dispersant is employed. The amount of dispersant employed can vary depending upon the pigment level used in the formulation, and the desired degree of dispersion and stability.

Preferred backing formulations comprise an aqueous medium, a finely divided mineral filler or pigment, and a bimodal latex, and may further optionally include one or more of the following: carbon black, a dispersing agent, and a thickener. Advantageously, backing formulations comprise about 20 to about 500 parts pigment, 100 parts of bimodal latex, 0 to about 0.7 parts carbon black, 0 to about 2.5 parts of a dispersing agent, and 0 to about 0.6 parts thickener, all parts being on a dry weight basis. Preferred backing formulations comprise about 100 to about 350 parts pigment, 100 parts of bimodal latex by weight, 0 to about 0.5 parts carbon black, 0.3 to about 0.7 parts of a dispersing agent, and 0 to about 0.2 parts thickener, all parts being on a dry weight basis. Advantageously, the formulation of the invention contains at least about 60 percent solids by weight based on the weight of the formulation, preferably at least about 76.5 percent, more preferably at least about 79%. In one embodiment of the invention, the solids content of the formulation is from about 60 to about 82 percent. Advantageously, coating formulations of this invention are higher in solids than comparable formulations comprising monodisperse or highly multi-disperse latexes. Preferably, the backing compounds of this invention are at least about 4% higher in solids than comparable formulations prepared using only one monodisperse latex or only one highly multi-disperse latex.

It is also understood that additives known in the art, which include colorants, such as carbon black, cobinders, thickeners, water retention aids and the like, can be added to the coating formulation. Examples of such additives are disclosed in the aforementioned U.S. Patent 3,399,080. In a preferred embodiment of the invention, the backing formulation is substantially free of added organopolysiloxane. In another embodiment of the invention, the backing formulation is substantially free of added thickener.

The formulation of this invention offers a combination of advantages, which can include the following: high wet tuft lock, high tuft lock retention of the coated synthetic grass, possible reduction or elimination of external thickening agents, and significantly faster drying of the formulation. For example, synthetic grass backing compound formulations of the invention containing a high solids latex do not necessarily require a thickener; thus, cost savings from reduction or elimination of thickener is an additional benefit. Techniques for the preparation of synthetic grass are well known to those skilled in the art, and the method employed is largely a matter of the manufacturer's preference. For example, grass backing compound can be applied frothed or unfrothed, by lick roll or direct spread application at a coat weight of from about 500 to about 2,000 grams per square meter (gsm), with 800 gsm being typical for residential/landscaping applications and about 1000 gsm being typical for sports field applications. The applied coat weight is controlled by lick roll speed, scraping knife angle, and compound viscosity, as is well known in the art. Some grass backing compound is applied via a direct spread application method using a knife roller or brush to increase penetration of the compound.

The coated backing is then dried, advantageously at a speed of 6 to 8 meters per minute (mpm), through ovens in which the backing side and pile side can be heated at different temperatures according to methods well known to those skilled in the art. When polyethylene monofilaments are employed as the tufts, they tend to shrink and shrivel at higher temperatures.

Synthetic grass is typically specified by the following parameters: mass per unit area, tufts per unit area, pile weight, fiber identification, and in-fill materials. The numerous and varied styles of synthetic grass differ in length of the tuft, number of tufts, thickness of the tufts, tuft shape, tuft structure tuft arrangement, etc. It is not unusual for synthetic grass producers to manufacture 50 to 70 different styles of synthetic grass using only one or two backing compounds with one latex. Appropriate installation and maintenance of the synthetic grass surface is critical to achieve optimum playing characteristics.

Advantageously, a synthetic grass prepared by the process of the invention has a wet tuft lock of at least about 2 kg, preferably at least about 2.5 kg, and more preferably at least about 3 kg. Advantageously, a synthetic grass prepared by the process of the invention has a dry tuft lock of at least about 3.5 kg, preferably at least about 3.8 kg and more preferably at least about 4.1 kg. Advantageously, a synthetic grass prepared by the process of the invention has a tuft lock retention value of at least about 60%, preferably at least about 70%, and more preferably at least about 80%.

The following performance characteristics of synthetic grass surfaces are typically evaluated by the producers: Tuft withdrawal force / pile anchorage

Player / surface interaction: shock absorbency, slip resistance, sliding distance, abrasiveness

Ball / surface interaction: vertical ball rebound, ball roll, angled ball behaviour Resistance to wear: shock absorbency, vertical deformation, ball rebound, angled ball behaviour, etc.

Resistance to ultraviolet, water, heat, and frost Color fastness, dimensional stability Specific Embodiments of the Invention

The following examples are given to illustrate the invention and should not be construed as limiting in scope. All parts and percentages are by weight unless otherwise indicated.

Test Methods Note that synthetic grass testing methods are frequently the same testing methods used to measure the properties of carpet products. Accordingly, reference to "carpet" in the following methods is not inconsistent with the invention.

1. Dry Tuft Lock Or Dry Pile Anchorage Measurement

Of a carpet sample (ca. 20cm x 32cm), a loop (loop pile carpet) is hooked or one end of a tuft (cut pile carpet) is gripped and pulled using a WIRA tuft withdrawl tensometer (available from Wira Instrumentation, Ltd., Bradford, UK). The needle is positioned on 0, and the speed setting is automatic.

Operating Procedure:

The maximum force registered during the removal process is recorded. The method is applicable to loop pile and cut pile tufted synthetic grass.

1.1. Cut Pile Carpets:

Condition the carpet in defined conditions, typically 23 ⁰C and 50% relative humidity for 24 hours for dry tuft lock (record relative humidity, temperature and conditioning time). Select one tuft and attach the tuft grip in the middle of the tuft. Clamp the carpet in the tuft withdrawl apparatus. Attach the tuft grip vertically to the upper jaw. The force reading should be 0. Set the apparatus in motion by turning the switch down (The chain and grip go up) and withdraw the tuft completely. Once the tuft has been removed, turn the switch up for the grip to come back to its original position. Check that only one tuft was withdrawn and record the maximum force (if additional fibres from another tuft were gripped or if only part of the tuft was removed, ignore the result and repeat the measurement). 1.2. General

Repeat the procedure for a maximum of 10 tufts or loops, spread evenly through the available samples, making sure there is at least 25 mm distance between a previously withdrawn tuft or loop and the new one, and that all tufts and loops are at least 25 mm away from the edge. If the pile yarn breaks without pulling out the tuft or loop, record this separately, marked 'broken' .

Include this result in the number of valid tests, and use it separately in calculations. Where both cut and loop pile are present, they should be tested separately, and care should be taken to ensure that where possible the tufts or loops tested are surrounded by those of the same type. Only completely uncut loops should be tested.

1.3. Specific Cases

1.3.1. Multi-layer woven carpet

For woven carpets in which tufts are placed on several layers, the tuft lock of each layer should be recorded separately. The outer tufts can be identified after testing by the hole they leave on the carpet backing.

1.3.2. For some types of synthetic grass, it is recommended to attach the several filaments of one tuft together before conditioning and testing.

1.4 Calculations and Reporting:

Calculate the mean tuft withdrawl force in kg force, and the standard deviation for all the results, excluding any marked 'broken.'

Wet Tuft Lock Or Wet Pile Anchorage Measurement

The procedure to test for wet tuft lock is the same as that to test for dry tuft lock except that the synthetic grass samples are immersed in water at 25°C for a set time. After 3 hours, they are removed from the water, tapped dry on the surface, i.e. shaken to remove most excess water such that the surface is still wet and may be dripping, and measured immediately for tuft lock.

Tuft Retention

Tuft retention (%) is calculated as follows: 100 - (((dry tuft lock- wet tuft lock) / dry tuft lock)* 100).

Brookfield Viscosity

The viscosity is measured using a Brookfield RVT viscometer (available from Brookfield Engineering Laboratories, Inc., Stoughton, Massachusetts, USA). For viscosity determination, 600 ml of a sample are poured into a 1000 ml beaker and the viscosity is measured at 25°C at a spindle speed of 20 rpm using a #4 spindle.

Materials Employed

Latex 1 : XZ 92241.00, carboxylated styrene-butadiene latex, 56.5% solids in water, available from The Dow Chemical Company, Midland, MI, USA.

Latex 2: BASF 332S. CARBOCIA 80 : calcium carbonate, available from Carbocia, 440 Rue Louis Marga,

59830, Louvil, France.

RX 3300: polyacrylic dispersant, available from EOC GROUP, Industriepark "De Bruwaan" 24, B9700 Oudenaarde, Belgium.

RX 810: acrylic thickener, available from EOC Group. RX 3300: polyacrylic dispersant, available from EOC Group.

Carbon Black: carbon black, dispersed in water, available from Lefatex Chemie GmbH, Stiegstr. 64, 41379 Brϋggen, Nordrhein-Westfalen, Germany

Example 1 and Comparative Experiment A Compounds are formulated using 100 parts latex, 200 parts CARBOCIA 80,

0.5 parts RX 3300, 0.35 parts carbon black dispersion, and 0.5 parts RX 3300. Formulation 1 uses Latex 1 and no thickener. Formulation 2 uses Latex 2 and 0.45 parts RX-810 (thickener). These formulations have a Brookfield viscosity of approximately 4350 mPa- seconds. Compounds are applied onto uncoated synthetic grass (monofilament type) using a lab coater operating at a speed of 1.7 mpm. The gap between the rolls is 0.5 mm and the weight of the back pressure disc (which determines the amount of pressure applied between the two rolls and thus to the synthetic turf) is 630 g. The synthetic grass is passed through the tandem roll coater a total of 6 times, 3 times to apply the compound and an additional 3 times so that the compound is worked into the turf. The coated area is approximately 0.093 m², respectively. The samples are then dried in an oven at 1 10⁰C for 12 minutes with a fan speed of 2000 rpm for air flow.

The resulting synthetic grass has the properties shown in Table 1.

Claims

WHAT IS CLAIMED IS:

1. A method of preparing artificial turf, the method comprising: binding artificial turf tufts to an artificial turf backing using a binding amount of a backing compound formulation, the backing compound formulation comprising the following components: a. 100 weight parts binder comprising a synthetic latex having a bimodal particle size distribution, b. 20 to 500 weight parts filler, based on 100 dry weight parts of the binder; c. optionally, a dispersing amount of a dispersing agent, d. optionally, a coloring amount of a colorant, and e. optionally, a thickening amount of a thickener, with the proviso that the solids content of the formulation is at least 79% by weight, based on the total weight of the formulation.

2. The method of Claim 1 wherein the latex has a solids content of at least 56% based on the total weight of the latex and is formed from at least the following monomers: i. a monoolefinically unsaturated monomer, ii. a conjugated diene, and iii. from about 1.5 to 4 weight percent of a carboxylic acid monomer, based on the total weight of the monomers.

3. The method of Claim 2 wherein the acid monomer comprises acrylic acid and/or itaconic acid.

4. The method of Claim 1 wherein the solids content of the latex is at least about 53%.

5. The method of Claim 1 wherein the solids content of the latex is at least about 55%.

6. The method of Claim 1 wherein the latex is polymerized from monomers comprising styrene and butadiene.

7. An artificial turf having a dry tuft lock property value of at least 3.5 kg.

8. An artificial turf having a wet tuft lock property value of at least 2 kg.

9. An artificial turf having a wet tuft lock retention value of at least 60%.

10. The method of Claim 2 wherein the latex is polymerized from monomers comprising styrene and butadiene.