Development of soft feel coatings with waterborne polyurethanes.Soft feel coatings applied over plastic substrates are widely used in automotive interiors and consumer products. These coatings provide a luxurious look and leather-like texture to hard plastic surfaces. Traditionally, two-component solvent-based polyurethanes polyurethanes (pŏl'ēy  r`əthānz), group of plastics that may be either thermosetting or thermoplastic. Polyurethane can be made into both flexible and rigid foams. have been used
in these applications. In recent years, waterborne polyurethane polyurethaneAny of a class of very versatile polymers that are made into flexible and rigid foams, fibres, elastomers (elastic polymers), surface coatings, and adhesives. formulations with lower volatile organic compounds volatile organic compound Environment Any toxic cabon-based (organic) substance that easily become vapors or gases–eg, solvents–paint thinners, lacquer thinner, degreasers, dry cleaning fluids have become the choice for soft feel coatings. In this article, the development of soft feel coatings with waterborne polyurethane technology will be presented. The performance of soft feel coatings based on waterborne polyisocyanates with polyester, acrylic acrylic, artificial fiber made from a special group of vinyl compounds, primarily acrylonitrile. Acrylic fibers are thermoplastic (i.e., soften when heated, reharden upon cooling), have low moisture regain, are low in density, and can be made into bulky fabrics. polyols, and/or polyurethane dispersions will be discussed. [ILLUSTRATION OMITTED] INTRODUCTION Soft feel coatings are coatings which provide a soft touch and leather-like feeling. They are applied over plastic substrates and are widely used in automotive interiors, such as instrument panels, airbag covers, armrests, and interior door panels. Soft feel coatings are also used in consumer electronics, including cell phones, computers, vacuum cleaners vacuum cleaner, mechanical device using a draft of air to remove dust, loose dirt, or other particulate matter from dry surfaces. It is especially useful on highly textured surfaces, such as carpets and upholstery, that are difficult to clean by wiping or brushing. , etc. The coatings used in automotive industries Automotive Industries, Ltd. (Hebrew: תעשיות רכב נצרת עלית, תע"ר for soft feel applications have to meet the following requirements: * Soft touch feeling and pleasant handle * Resistance to chemicals--suntan lotion lotion /lo·tion/ (lo´shun) a liquid suspension, solution, or emulsion for external application to the body. lo·tion n. 1. and insect repellent insect repellent, substance applied to the skin in order to provide protection against biting insects, primarily mosquitoes, ticks, chiggers, fleas, and certain flies. ; acids, bases, water, and other cleaners * Physical durability--adhesion, impact, scratch resistance, wear, and abrasion abrasion /abra·sion/ (ah-bra´zhun) 1. a rubbing or scraping off through unusual or abnormal action; see also planing. 2. a rubbed or scraped area on skin or mucous membrane. resistance * Low gloss * Weather stability * Ambient Surrounding. For example, ambient temperature and humidity are atmospheric conditions that exist at the moment. See ambient lighting. or low temperature cure Recently, many efforts have been made to develop waterborne polyurethane coatings for soft feel applications. These include the development of specifically designed waterborne polyols, functional and nonfunctional polyurethane dispersions (PUD PUD abbr. peptic ulcer disease Peptic ulcer disease (PUD) A stomach disorder marked by corrosion of the stomach lining due to the acid in the digestive juices. ), and hydrophilic hydrophilic /hy·dro·phil·ic/ (-fil´ik) readily absorbing moisture; hygroscopic; having strongly polar groups that readily interact with water. hy·dro·phil·ic adj. modified polyisocyanates, as well as development of additives to enhance soft feel properties. The challenge is to improve chemical resistance, such as suntan lotion suntan lotion sun n → lotion f or lait m solaire suntan lotion sun n → Sonnenmilch f resistance, without compromising the softness of the coatings. [ILLUSTRATION OMITTED] To make a polyurethane, one normally reacts a polymer containing hydroxyl hydroxyl /hy·drox·yl/ (hi-drok´sil) the univalent radical OH. hy·drox·yl n. The univalent radical or group OH, a characteristic component of bases, certain acids, phenols, alcohols, carboxylic functionality (polyol) with a polyisocyanate. Waterborne polyurethanes involve more complicated chemistry compared to traditional solvent-borne systems due to the presence of water. Water can compete with the reaction of the isocyanate i·so·cy·a·nate n. Any of a family of nitrogenous chemicals that are used in industry and can cause respiratory disorders, especially asthma, if inhaled. to the polyol. The relative reactivity of aliphatic aliphatic /al·i·phat·ic/ (al?i-fat´ik) pertaining to any member of one of the two major groups of organic compounds, those with a straight or branched chain structure. al·i·phat·ic adj. isocyanate with various active hydrogen-containing compounds is listed in Table 1. The slower reaction rate of aliphatic isocyanate with water compared to hydroxyl functions of polyols is the key for the success of 2K waterborne polyurethane technology. The reactions which take place in waterborne polyurethane system are shown in Figure 1. Water reacts with isocyanate groups generating carbon dioxide carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. gas. At the same time, a primary amine (Chem.) an amine containing the amido group, or a derivative of ammonia in which only one atom of hydrogen has been replaced by a basic radical; - distinguished from See also: Primary In this article, we examined the impact of polyurethane chemistries on soft feel performance. This was accomplished by formulating various waterborne polyol types and PUDs with a water-dispersible aliphatic polyisocyanate from Rhodia. EXPERIMENTAL Four types of waterborne polyurethane coating formulations with different combinations of polymer resins Versatlie liquid plastic coating. It self-levels and hardens to produce a thick, clear, durable and glossy finish. have been evaluated for soft feel applications. The binders evaluated include waterborne polyester polyols, polyurethane dispersions (PUD), combination of polyester polyol with PUD, and combination of acrylic polyol with PUD. Rhodocoat[R] WT 2102, a hydrophilic aliphatic isocyanate, was used as the crosslinker for the various polymer resins. A general formulation for soft feel coating in this study is given in Table 2, in which combinations of polyester polyols with PUDs were used as an example. For the other three types of formulations, the binders and crosslinkers were adjusted according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. the suppliers' recommendations. The effect of NCO/OH ratio was also evaluated in this study. Coated ABS (Automatic Backup System) See backup program. panels were prepared by conventional spray techniques. The panels were flashed off at ambient conditions for 10 to 15 min after spraying. The coatings were cured at 180[degrees]F (8[degrees]C) for 30 min, and allowed to stand for one week prior to testing. The following test methods were used in this study: Soft feel was measured subjectively by hand touch and rated on a scale from 1 to 5, with 1 being poor soft feel (hard feel) and 5 being good soft feel. Gloss was measured at 20[degrees] and 60[degrees] by ASTM ASTM abbr. American Society for Testing and Materials D 523 test method. Persoz hardness was measured by ASTM D 4366 test method and reported in seconds. Adhesion adhesion /ad·he·sion/ (ad-he´zhun) 1. the property of remaining in close proximity. 2. the stable joining of parts to one another, which may occur abnormally. 3. was measured by ASTM D 3359B test method. Pencil hardness was used as an indicator for scratch resistance and was measured by ASTM D 3363 test method. MEK Noun 1. MEK - a terrorist organization formed in the 1960s by children of Iranian merchants; sought to counter the Shah of Iran's pro-western policies of modernization and opposition to communism; following a philosophy that mixes Marxism and Islam it now attacks the double rub resistance was measured by rubbing rubbing, v creating friction and heat by drawing the hands across the body at varying speeds, rhythms, and depths. Benefits include muscle elongation, tension release, and increased flexibility. the surface of the cured coating with an MEK soaked soak v. soaked, soak·ing, soaks v.tr. 1. a. To make thoroughly wet or saturated by or as if by placing in liquid. b. To immerse in liquid for a period of time. 2. wiper and reported as the number of rubs without observation of adverse effect on the coating. Reverse impact strength was measured by ASTM D 2794 test method by using cold rolled steel panels and reported in inch-pounds force (in.-lb). Chemical resistance (resistance to 10% sulfuric acid sulfuric acid, chemical compound, H2SO4, colorless, odorless, extremely corrosive, oily liquid. It is sometimes called oil of vitriol. Concentrated Sulfuric Acid , 10% acetic acid acetic acid (əsē`tĭk), CH3CO2H, colorless liquid that has a characteristic pungent odor, boils at 118°C;, and is miscible with water in all proportions; it is a weak organic carboxylic acid (see carboxyl group). , and 10% ammonium hydroxide ammonium hydroxide n. A colorless, basic, aqueous solution of ammonia, NH4OH, used as a household cleanser and in the manufacture of a wide variety of products, including textiles, rayon, rubber, fertilizer, and plastic. ) was measured by visual observation after one hour spot application of the chemical to the surface of a cured coating specimen and rated on a scale from 1 (poor) to 5 (good). [FIGURE 1 OMITTED] Suntan lotion resistance was measured by visual inspection after one hour spot application of ethylhexyl p-methoxycinnamate-containing suntan lotion with an SPF (1) (Stateful Packet Firewall) See stateful inspection. (2) (Sender Policy Framework) An e-mail authentication system that verifies that the message came from an authorized mail server. of 45 to the surface of a cured coating specimen and rated on the following scale: (1) No visual effect (2) Repairable with no visual effect (3) Spotting discoloration dis·col·or·a·tion n. 1. a. The act of discoloring. b. The condition of being discolored. 2. A discolored spot, smudge, or area; a stain. Noun 1. observed (4) Softening/slight dissolution of top layer observed (5) Blistering blis·ter·ing n. See vesiculation. delamination delamination /de·lam·i·na·tion/ (de-lam?i-na´shun) separation into layers, as of the blastoderm. de·lam·i·na·tion n. 1. A splitting or separation into layers. 2. observed (6) Coating dissolved [FIGURE 2 OMITTED] Elevated temperature suntan lotion resistance testing was conducted and rated in the same manner as suntan lotion resistance testing, except that the temperature of the test specimen was maintained at 74[degrees]C during the one hour spot application of suntan lotion. Insect repellent resistance was measured by visual inspection after one hour spot application of insect repellent containing 20 wt% N,N-diethyl-meta-toluamide (DEET) to the surface of a cured coating specimen and rated on the same scale as that used with suntan lotion. RESULTS AND DISCUSSION Although many additives can reinforce the soft feel properties of soft feel coatings, the polymer resins in the coating formulations played key roles for providing the leather feel and meeting the requirements for soft feel applications. Therefore, four types of waterborne polyurethane coating formulations with different resin combinations, as shown in Figure 2, were evaluated for soft feel applications in this study. Soft Feel I: Polyester Polyol A water dispersible polyester polyol was formulated with the hydrophilic aliphatic isocyanate and evaluated for soft feel applications. In this formula, only polyester polyol and isocyanate were used as the binder binder: see combine. An earlier Microsoft Office workbook file that let users combine related documents from different Office applications. The documents could be viewed, saved, opened, e-mailed and printed as a group. . As shown in Figure 3, the coating based on polyester polyol easily passed suntan lotion and insect repellent resistance testing (rating 3). However, the coating exhibited higher hardness, hence, it showed less soft touch. With NCO/OH ratio increased, the hardness increased, so did the chemical resistance, while the softness feeling was lost due to increased crosslinking density. The data in Table 3 indicated that the coating gave very good low gloss, good adhesion, and scratch resistance. Soft Feel II: PUD Several industrial available polyurethane dispersions were formulated with hydrophilic polyisocyanate Rhodocoat WT 2102 for soft feel applications (Soft Feel II). The data in Figure 4 and Table 4 listed one example from this formula. The PUD contained very low level amine amine (əmēn`, ăm`ēn): see under amino group. amine Any of a class of nitrogen-containing organic compounds derived, either in principle or in practice, from ammonia (NH3). functionality, which could be used for crosslinking in addition to carboxyl groups carboxyl group (kärbŏk`sĭl), in chemistry, functional group that consists of a carbon atom joined to an oxygen atom by a double bond and to a hydroxyl group, OH, by a single bond. . Weight of polyisocyanate per hundred parts of component A instead of NCO/OH ratio was used in preparation of the formulation. As seen in Figure 4, the coating based on PUD system provided very good soft feeling. However, good suntan lotion and DEET resistance was obtained only when a very high isocyanate concentration was used. With increases in isocyanate concentration, hardness, and chemical resistance significantly increased, while softness was lost. However, this coating system provided good low gloss and adhesion. [FIGURE 3 OMITTED] [FIGURE 4 OMITTED] [FIGURE 5 OMITTED] [FIGURE 6 OMITTED] [FIGURE 7 OMITTED] Soft Feel III: Combination of Polyester Polyol with PUD An additional study was carried out to combine polyester polyol with PUD and formulated with hydrophilic polyisocyanate for soft feel applications (Soft Feel III). A blending ratio of polyester polyol to PUD of 50/50 and 25/75 based on solids are shown as examples. The results are given in Figures 5 and 6 and Tables 5 and 6. It was found that coatings with good soft feel and suntan lotion resistance were obtained in this polyester polyol/PUD blended system. Soft touch properties were increased when PUD concentration in the formulation increased. As expected, the isocyanate level increased hardness and suntan lotion resistance increased, while the soft feeling characteristic decreased. The coatings showed very good low gloss and adhesion. Therefore, by adjusting the blend ratio of polyol to PUD and NCO/OH ratio, the properties between softness and chemical resistance could be balanced. In this study, good soft feel coatings were obtained when polyester polyol/PUD ratio between 50/50 to 25/75 and NCO/OH ratio between 2 to 4 were used. Soft Feel IV: Combination of Acrylic Polyol with PUD A combination of acrylic polyol with polyurethane dispersions was formulated with hydrophilic isocyanates and evaluated in soft feel coating applications. Very similar results were obtained as in the prior example (Soft Feel III). A higher NCO/OH ratio was needed to balance the soft feel properties with suntan lotion and DEET resistance. Data in Table 7 showed good low gloss, adhesion, and flexibility as well. Why Choose a Combination of Polyol with PUD? The challenge for soft feel coating applications is to balance the soft-touch properties and the resistance to chemicals. The former requires softness of the coating film, which is inherently low in glass transition temperature The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). ([T.sub.g]) and low in crosslinking density. The latter requires increased crosslinking density and higher [T.sub.g], which hardens the film and strengthens the coating from attack by the solvents and other aggressive reagents. The system of the combination of polyester polyol with PUD crosslinked with polyisocyanates optimized the performance, and provided the balance between the softness of coating films and crosslinking density, or resistance to chemicals. Soft feel coating was designed to simulate the feeling of the natural leather. The modulus See modulo. of plastics, leathers, and rubbers or elastomers is schematically sche·mat·ic adj. Of, relating to, or in the form of a scheme or diagram. n. A structural or procedural diagram, especially of an electrical or mechanical system. illustrated in Figure 8. At ambient conditions, plastic materials give very high modulus, while rubber or elastomers show very low modulus. Natural leather is a partially crosslinked natural polymer and shows medium modulus between plastics and elastomers. It usually shows two glass transition temperatures as well. Soft feel coating films were analyzed via thermal mechanical analysis (TMA TMA Turnaround Management Association TMA Texas Medical Association TMA Transportation Management Association TMA Training and Management Assistance (a component of OHRD, which is a component of OWR) TMA Tooling & Manufacturing Association ) and one of the examples is given in Figure 9. The coating film based on the combination of polyester polyol with PUD system shows two glass transition temperatures, -39[degrees]C and 57[degrees]C, which correspond to PUD and crosslinked polyol in the film. The similarity of thermal mechanical properties between soft feel coatings based on the combination of polyester polyol with PUD and the natural leather may explain the optimized performance of this type of coating for soft feel application. Characteristics of Soft Feel Measurement of the haptic haptic /hap·tic/ (hap´tik) tactile. hap·tic adj. Of or relating to the sense of touch; tactile. haptic tactile. properties (feeling of softness) of coatings by instrument is not a simple task. While great efforts have been made by many research groups, none of them showed good correlation between the data obtained by instrument and the data based on the personal sensation of test subjects. The most popular method is still to test the coating subjectively by hand feel of individuals. However, we found that a simple test, measurement of Persoz hardness, could give useful information for initial screening of soft feel coating development. We measured the soft feel coating developed in our lab and other commercially available products and found that coatings which gave both soft touch feeling and resistance to chemicals had Persoz hardness of 60 to 100 sec, and preferred 70 to 90 sec. These values are much lower compared to polyurethane topcoats (150-250 sec), and plastic substrate such as ABS (~270 sec) and polycarbonates polycarbonates, group of clear, thermoplastic polymers used mainly as molding compounds (see plastic). Polycarbonates are prepared by the reaction of an aromatic difunctional phenol with either phosgene or an aromatic or aliphatic carbonate. (~290 sec). We observed a good correlation between Persoz hardness and soft feel rating in our studies. [FIGURE 8 OMITTED] [FIGURE 9 OMITTED] [FIGURE 10 OMITTED] CONCLUSION Standard polyol systems (Soft Feel I) provided coatings with very good chemical resistance, but reduced soft feel due to high hardness and crosslinking density. Polyurethane dispersion dispersion, in chemistry dispersion, in chemistry, mixture in which fine particles of one substance are scattered throughout another substance. A dispersion is classed as a suspension, colloid, or solution. system (Soft Feel II) offered coatings with very good soft touch feel, but less resistance to chemicals. The combination of polyol with PUD (Soft Feel III and IV) balanced the chemical resistance and soft feel characteristics. As a result, optimum performance of soft feel coatings was achieved in systems combining an acrylic or polyester polyol with PUDs specifically designed for soft feel application and crosslinked with Rhodocoat WT 2102, a water dispersable polyisocyanate.
Table 1 -- Relative Reactivity of Aliphatic Isocyanate with Active
Hydrogen-Containing Compounds (a)
% NCO Reacted, % NCO Reacted,
Compounds 20[degrees]C 80[degrees]C
Aliphatic amine Very high 100
Aromatic amine 10-20 100
Primary OH 2-4 30
Secondary OH 1 15
Water 0.4 6
Tertiary OH 0.01 --
Phenol 0.01 --
Urea -- 2
Carboxylic acid -- 2
Urethane -- 0.02
(a) Determined after 30 min of reaction.
Table 2 -- An Example Formulation (Soft Feel III) for Soft Feel Coatings
Raw Materials Weight % Suppliers
Component I
Witco UCX 8256-148N 10.57 Crompton
Witcobond[R] W290H 23.86 Crompton
Aurasperse[R] W7114 20.83 Engelhard
Pergopak[R] M3 4.62 Lonza
Surfynol[R] 104DPM 0.51 Air Products
BYK[R] 346 0.28 Byk
Tinuvin[R] 292 0.29 Ciba
Tinuvin[R] 1130 0.29 Ciba
Deionized water 30.81
Component II
Rhodocoat WT 2102 7.93 Rhodia
Total 100.00
Table 3 -- Coating Properties of Soft Feel I
NCO/OH 1.5 2.0 2.5 3.0
Film thickness (mil) 1.6 1.7 1.6 1.7
Gloss (20[degrees]/60[degrees]) 0.2/2.5 0.2/2.6 0.2/2.2 0.2/1.8
Adhesion 100% 100% 100% 100%
Scratch resis, (pencil hardness) 2H 2H 3H 4H
MEK rubs resistance >200 >200 >200 >200
Reverse impact (in.-lb) >160 >160 >160 >160
1 hr spot test (5=good, 1=poor)
10% Sulfuric acid 4-5 4-5 4-5 4-5
10% Acetic acid 4-5 4-5 4-5 4-5
10% Ammonium hydroxide 5 5 5 5
Table 4 -- Coating Properties of Soft Feel II
WT 2102 weight per hundred
Component A 4 8 12 16 20
Film thickness (mil) 1.4 1.3 1.4 1.4 1.4
Gloss (20[degrees]/
60[degrees]) 0.3/3.4 0.3/3.3 0.3/3.5 0.3/3.2 0.3/3.2
Adhesion 100% 100% 100% 100% 100%
Scratch resis. (pencil
hardness) H H 2H 2H 2H
MEK rubs resistance 150 200 >200 >200 >200
Reverse impact (in.-lb) >160 >160 >160 >160 >160
1 hr spot test (5=good,
1=poor)
10% Sulfuric acid 5 5 5 5 5
10% Acetic acid 4-5 4-5 4-5 4-5 4-5
10% Ammonium hydroxide 5 5 5 5 5
Table 5 -- Coating Properties of Soft Feel III (polyol/PUD 50/50)
NCO/OH 1.5 2.0 2.5 3.0 4.0
Film thickness (mil) 1.3 1.4 1.4 1.5 1.4
Gloss (20[degrees]/
60[degrees]) 0.2/2.7 0.2/2.6 0.2/2.4 0.2/2.5 0.1/2.2
Adhesion 100% 100% 100% 100% 100%
Scratch resis. (pencil
hardness) H H 2H 2H 2H
MEK rubs resistance >200 >200 >200 >200 >200
Reverse impact (in.-lb) >160 >160 >160 >160 >160
1 hr spot test (5=good,
1=poor)
10% Sulfuric acid 4-5 4-5 4-5 4-5 5
10% Acetic acid 4-5 5 5 5 5
10% Ammonium hydroxide 4-5 5 5 5 5
Table 6 -- Coating Properties of Soft Feel III (polyol/PUD 25/75)
NCO/OH 1.5 2.0 3.0 4.0 5.0
Film thickness (mil) 1.4 1.4 1.5 1.5 1.4
Gloss (20[degrees]/
60[degrees]) 0.3/3.2 0.3/3.1 0.3/2.6 0.3/2.5 0.2/2.1
Adhesion 100% 100% 100% 100% 100%
Scratch resis. (pencil
hardness) F H H 2H 2H
MEK rubs resistance 150 200 >200 >200 >200
Reverse impact (in.-lb) >160 >160 >160 >160 >160
1 hr spot test (5=good,
1=poor)
10% Sulfuric acid 4-5 4-5 4-5 4-5 4-5
10% Acetic acid 4-5 4-5 4-5 5 5
10% Ammonium hydroxide 4-5 5 5 5 5
Table 7 -- Coating Properties of Soft Feel IV
NCO/OH 1.5 2.5 3.5 4.5 5.5
Film thickness (mil) 1.5 1.4 1.5 1.6 1.5
Gloss (20[degrees]/
60[degrees]) 0.3/3.4 0.3/3.4 0.3/3.4 0.3/3.5 0.3/3.6
Adhesion 100% 100% 100% 100% 100%
Scratch resis. (pencil
hardness) F F H 2H 2H
MEK rubs resistance >200 >200 >200 >200 >200
Reverse impact (in.-lb) >160 >160 >160 >160 >160
1 hr spot test (5=good,
1=poor)
10% Sulfuric acid 4-5 4-5 4-5 4-5 4-5
10% Acetic acid 4 4 4 4-5 4-5
10% Ammonium hydroxide 5 5 5 5 5
Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, Chicago, IL, October 27-29, 2004. References (1) Melchiors, M., Sonntag, M., Kobusch, C., and Jurgens, E, "Recent Developments in Aqueous aqueous /aque·ous/ (a´kwe-us) 1. watery; prepared with water. 2. see under humor. a·que·ous adj. Two-Component Polyurethane (2K-PUR) Coatings," Prog. Org. Coat., 40(1-4), 99-109 (2000). (2) Yasuda, K., Imada, M., Koike, E., and Kozu, K., "Quantitative Evaluation of Textures in Coating Materials--Quantitation of Feelings on Soft Feel Coatings," Toso Kogaku, 36(2), 40-45 (2001). (3) Thomas, P., Waterborne and Solvent Based Surfacing Coating Resins and Their Applications, John Wiley John Wiley may refer to:
by Lichang Zhou and Bernard Koltisko Rhodia Inc.* * 259 Prospect Plains Rd., Cranbury, NJ 08512. |
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