Acrylic-urethane IPN plastisol

Abstract

Plastisol compositions having a two-resin interpenetrating polymer network (IPN) are disclosed. The compositions begin with blocked isocyanate grafted acrylic polymer, blocked isocyanate urethane prepolymer, plasticizer, optionally pigment, and optionally thixotropic agent. When subjected to a thermal cure, the isocyanate groups on the acrylic polymer and urethane prepolymer both become unblocked and both react with the crosslinking agent to form an interpenetrating acrylic-polyurethane network. The two-resin IPN offers improved storage stability, hand-feel characteristics, and processing properties for textile printing among other uses. Preferably these plastisol compositions are essentially free of polyvinyl halides and phthalates restricted for regulatory reasons.

Claims

1. A plastisol composition, comprising: (a) acrylic polymer; (b) urethane prepolymer; (c) plasticizer; (d) crosslinking agent; (e) optionally a thixotropic agent; and (f) optionally a pigment; wherein the crosslinking agent is multifunctional, and wherein the acrylic polymer and urethane prepolymer contain blocked isocyanate groups that become unblocked when subjected to heat and react with the crosslinking agent to form an interpenetrating acrylic-polyurethane network.

2. The plastisol composition of claim 1, wherein the acrylic polymer is a core-shell acrylic polymer.

3. The plastisol composition of claim 2, wherein the core-shell acrylic polymer has a glass transition temperature of between about 65 C. to about 125 C.

4. The plastisol composition of claim 1, wherein the isocyanate content of the acrylic polymer is about 0.02% to about 10.0% by weight.

5. The plastisol composition of claim 1, wherein the crosslinking agent is a latent amine curative.

6. The plastisol composition of claim 1, wherein the blocked isocyanate groups of the acrylic polymer and the urethane prepolymer become unblocked when subjected to a thermal cure at temperatures of about 130 C. to about 170 C.

7. The plastisol composition of claim 1, wherein the composition is essentially free of polyvinyl halides and restricted phthalates.

8. The plastisol composition of claim 1, wherein the plasticizer is selected from the group consisting of dioctyl terephthalate, benzoate esters, polyadipates, citrates, alkylsulfonic acid phenyl esters, esters of 1,2-cyclohexane dicarboxylic acid, and combinations thereof.

9. The plastisol composition of claim 1, wherein the thixotropic agent contains at least one of the following: castor oil derivative, high molecular weight polyolefin, attapulgite, montmorillonite clay, organo-clay, fumed silica, fibrated mineral, calcium sulphonate derivative, polyamide resin, polyester amide, alkyds, or oil-modified alkyd.

10. The plastisol composition of claim 1, wherein the additional additives are selected from the group consisting of lubricants, dispersants, fillers, optical brighteners, puff matting agents, antioxidants, chemical and physical blowing agents, stabilizers, moisture scavengers, air release agents, oxidizers, reducers, surfactants, processing aids, and combinations thereof.

11. The plastisol composition of claim 1, wherein the composition in weight percent comprises: (a) the acrylic polymer in the range of 10 to 50%; (b) the urethane prepolymer in the range of 10 to 50%; (c) the plasticizer in the range of 50 to 75%; (d) the crosslinking agent in the range 0.5 to 5%; (e) the pigment in the range of 0 to 40%; (f) the thixotropic agent in the range of 0 to 10%; and (g) an additive in the range of 0 to 40%.

12. The plastisol composition of claim 1, wherein the ratio of the acrylic polymer resin and the urethane prepolymer to the plasticizer is in the range from about 2:1 to about 1:3.

13. The plastisol composition of claim 1, wherein the ratio of the acrylic polymer resin to the urethane prepolymer is in the range from about 1:1 to about 4:1.

14. A method of making the plastisol composition of claim 1, comprising the steps of: (a) blending, into a mixture, blocked isocyanate grafted acrylic polymer, plasticizer, and optionally the pigment together using a rotary mixer with jacketed cooling tub until the mixture is homogeneous; (b) de-agglomerating the mixture using a 3-roll mill, for a sufficient duration to ensure a Hegman fineness of grind value 4; and (c) adding crosslinking agent wherein the urethane prepolymer with blocked isocyanate functional groups is added during step (a) or step (c); and wherein optionally the thixotropic agent is added during any of the above steps to achieve the desired viscosity target.

15. The method of claim 14, wherein the plastisol composition is cured by (d) heating the plastisol composition to unblock the isocyanate groups on the acrylic polymer and the urethane prepolymer so that the isocyanate groups will react with the crosslinking agent to form an interpenetrating acrylic-polyurethane network.

16. The method of claim 15, wherein the plastisol composition is heated in step (d) at temperatures of about 130 C. to about 170 C. for at least about 0.5 minutes.

17. A printed textile article comprising a textile article having an image graphic printed thereon from the plastisol composition of claim 1.

18. The printed textile article according to claim 17, wherein the textile article is a garment and wherein the image graphic from the plastisol composition is applied by a screen-printing technique.

19. A coated article, comprising a substrate wherein the coating consists of the plastisol composition of claim 1.

20. The coated article of claim 19 wherein the coating of the article has been applied by spin casting, slush molding, rotational molding, spray coating, or dip coating.

Description

EXAMPLES

General Experimental Materials Examples

(1) Table 2 shows the list of ingredients for Comparative Examples A-G and Examples 1 and 2.

(2) TABLE-US-00002 TABLE 2 Commercial Brand Name Ingredient Purpose Source Dianal LP 3202 Acrylic core-shell Base polymer Dianal resin resin America (Tg 84 C., acid value = 16.6 mg KOH/g determined by acid titration) Kane Ace Blocked Base polymer Kaneka UC521 isocyanate grafted resin acrylic-core shell polymer Takenate B- Blocked Base polymer Mitsui 7030 isocyanate resin Chemicals urethane prepolymer Mesamoll Alkylsulphonic Plasticizer Laxness acid ester with Deutschland phenol (ASE) GmbH Eastman 168 Dioctyl Plasticizer Eastman terephthalate Chemical Hallstar Polyester adipate Plasticizer Hallstar Dioplex 7017 Adipic dihydrazide Crosslinking Tokyo (Amine equivalent agent Chemical weight = 87.1%) Industry Acematt TS 100 Fumed Silica Thixotropic Evonik agent Industries Expancel 920 Unexpanded Thixotropic AkzoNobel DU-80 microspheres (dry) agent Tiona RCL-4 Hydrophobic Inorganic white Millennium organically-treated pigment Chemicals titanium dioxide

(3) The base polymer resin(s), plasticizer, color pigment and thixotropic agent were all combined in the first step (except for the blocked isocyanate urethane prepolymer in Examples 1-2, and Comparative Example E as noted below) by mixing in a KitchenAid stand mixer. The plasticizer for each example was selected based on its optimal solubility with the polymer base resin. The resulting blend was milled in a 3-roll mill, to achieve a Hegman Fineness of Grind (ASTM D1210) of approximately 6.

(4) To this pre-blended mixture, the crosslinking agent was added for Comparative Examples B, D, E, and F, and Examples 1-2. No crosslinking agent was added to Comparative Examples A and C. In Examples 1-2, and Comparative Example E, the blocked isocyanate urethane prepolymer was added to the pre-blended mixture after milling.

(5) The recipes for Comparative Examples A-G and Examples 1-2 by weight percent of the plastisol ink composition are in Table 3. Table 4 shows performance characteristics of the plastisol according to the tests described in the following section.

(6) General Experimental Testing Procedures

(7) The ball-burst penetration test was conducted on Comparative Examples A-F, and Example 1. The plastisol compositions of these examples were each drawn-down as a 10-mil film onto a smooth and flat Teflon sheet using a Multiple Clearance Square Applicator (Byk-Gardener). The films were cured for three minutes in an electrically heated oven set to 140 C. After cooling, the respective films were carefully peeled from the Teflon sheet, cut to size and clamped between two large steel washers (internal diameter=1.7 cm). The films were then subjected to a micro ball burst strength test, modeled on ASTM D3787-01, using a 0.8 cm polished steel ball to apply a controlled load (i.e. the peak force) at 90 degrees to the plastisol film, and having a constant rate of traverse=3 mm/min. The strain was measured by the perpendicular distance traveled by the ball point from touching the plastisol film unstrained to the point of the plastisol film tearing. The modulus of toughness was calculated in millijoules (mJ) by multiplying the peak force (in Newtons) by the strain (in millimeters). A summary of data from these tests, including the modulus of toughness, is provided in Table 4.

(8) Storage stability and print screen testing for haptic appeal, opacity and wash fastness were performed on Comparative Example G and Example 2, which contained white pigment. The plastisol ink formulations for Comparative Example G and Example 2 were printed onto 100% black cotton tee-shirts (Gildan Heavy Cotton) using a Challenger II automatic screen printing press from M&R Company, equipped with 110 mesh screen in the design of a large number 8. The print procedure was as follows: the shirts were printed once using a double squeegee stroke, flashed dried under a quartz heater (Red Chili from M&R Co.) for 8 sec, 180 C., and then reprinted using a double stroke. The shirts were removed from the pallet, and then fully cured in a 12-foot gas-fired conveyor dryer (M&R Sprint series) set to 160 C. and a belt speed of 6 feet/min. After cure, the shirts were inspected for haptic appeal and opacity of the prints. The haptic hand properties of the printed swatches were determined subjectively by feeling the swatch for roughness and any tackiness (i.e. stickiness) of the printed ink.

(9) Then, the shirts printed with the plastisol inks of Comparative Example G and Example 2 were laundered using a Miele PT 7136 Plus wash machine set to a water temperature of 60 C. and a spin velocity of 1000 rpm, and a Miele PW 6065 Plus drier, set to the cotton cycle. The laundry detergent used was Tide Ultra (Proctor & Gamble, Cincinnati, Ohio). After 5 laundry cycles, the shirts were examined for cracking and loss of adhesion using optical microscopy.

(10) To test for ink stability, Comparative Example G and Example 2 were aged in an oven at 46 C. (114.8 F.) for 5 days. The initial and aged viscosity was determined on an AR2000ex rheometer (TA instruments), using 20 mm parallel-plate geometry under flow conditions at a shear rate of 1 sec.sup.1 and a temperature of 25 C. A summary of the results for haptic appeal, opacity, wash fastness and storage stability is provided in Table 5.

(11) TABLE-US-00003 TABLE 3 Example Ingredients A B C D E F G 1 2 Blocked isocyanate 38.46% 37.42% 29.07% 31.18% 23.60% grafted acrylic core- shell polymer Acid-functionalized 38.46% 37.42% 31.18% core-shell acrylic resin Polyester adipate 37.50% 36.48% 28.34% 30.40% 23.00% plasticizer Dioctyl terephthalate 20.19% 19.64% 15.26% 16.37% 12.38% plasticizer Alkyl-sulphonic acid 57.69% 56.13% 46.77% ester with phenol plasticizer Urethane prepolymer 15.59% 88.11% 15.59% 11.80% w/ blocked isocyanate functional groups Latent curative 2.71% 2.71% 3.35% 3.08% 3.35% 2.54% Hydrophobic 23.84% 23.88% organically-treated titanium dioxide Fumed silica 3.85% 3.74% 3.85% 3.74% 3.12% 8.81% 2.90% 3.12% 2.35% Unexpanded 0.58% 0.47% microspheres Total 100% 100% 100% 100% 100% 100% 100% 100% 100%

(12) TABLE-US-00004 TABLE 4 Example Property Units A B C D E F 1 Peak force N 2.97 3.52 2.83 3.11 4.50 10.91 7.63 strain Mm 23.25 21.50 20.00 21.75 16.25 23.50 27.75 Modulus of N * mm 27.06 37.60 24.85 33.62 30.54 98.23 77.56 Toughness (mJ)

(13) TABLE-US-00005 TABLE 5 Comparative Property Example G Example 2 Haptic appeal (subjective Slightly sticky, Smooth, soft and dry. hand feel) tacky. No tack or stickiness Opacity Excellent Excellent Storage Stability, Good: (5 days)/ Excellent: (5 days)/ accelerated aging test (initial) = 2.5 (initial) = 1.7 (7 days at 46 C.); (5 days)/(initial) Wash fastness, 5 cycles Poor: film cracking Excellent: no cracking, and surface abrasion with minor roughening of the surface

(14) Performance Results

(15) Comparative Example A demonstrated that the plastisol of the blocked isocyanate grafted acrylic core-shell polymer, without the use of any crosslinking agent, has a very poor modulus of toughness (i.e. less than 30 mJ). When a crosslinking agent was added to the blocked isocyanate grafted acrylic core-shell polymer in Comparative Example B, the cured plastisol composition showed an improved toughness modulus.

(16) Comparative Examples C and D replaced the isocyanate grafted acrylic core-shell polymer with an acid-functionalized core-shell acrylic resin. Again, no crosslinking agent was added to Comparative Example C, whereas Comparative Example D included a crosslinking agent. Similar to the previous examples, the cured plastisol of Comparative Example C had very poor modulus of toughness, and the cured plastisol of Comparative Example D had a comparatively better modulus of toughness.

(17) Because polyurethane is known in the art for its toughness as a result of the crosslinking when cured, in Comparative Example F the acrylic polymer was replaced by a urethane prepolymer with blocked isocyanate groups and crosslinking agent. The result was a cured plastisol having a very high modulus of toughness. Comparative Example E then included both an acid-functionalized core-shell acrylic resin and a blocked isocyanate urethane prepolymer with a crosslinking agent. Surprisingly, the cured plastisol of Comparative Example E demonstrated a very poor modulus of toughness, which was even lower than the crosslinked acid-functionalized core-shell acrylic polymer alone (i.e. Comparative Example D).

(18) Example 1 substituted the acid-functionalized core-shell acrylic resin of Comparative Example E with a blocked isocyanate grafted acrylic core-shell polymer, which was then blended together with a blocked isocyanate urethane prepolymer. In contrast to Comparative Example E, Example 1 unpredictably demonstrated a high modulus of toughness similar to the toughness of the cured urethane composition of Comparative Example F.

(19) These examples demonstrate that the covalent bonds formed by crosslinking generally increase the modulus of toughness for the cured acrylic polymer plastisols compared to the uncrosslinked acrylic polymer plastisols. However, in Comparative Example E, the two-resin plastisol of a blocked isocyanate urethane prepolymer and an acid functionalized core-shell acrylic still resulted in a lower modulus of toughness. This poor toughness is likely the result of the plastisol forming separate interpenetrating polymer networks (or domains)one domain formed by the acrylic polymer and another domain formed by the polyurethanewhich causes the cured plastisol of the heterogeneous composition to be weaker than a homogenous composition of either of the respective polymer resins alone.

(20) Unexpectedly, the cured plastisol of urethane prepolymer with blocked isocyanate groups and isocyanate grafted core-shell acrylic polymer for Example 1 had a high modulus of toughness of more than 2 the toughness of the crosslinked isocyanate grafted acrylic core-shell polymer alone (i.e. Comparative Example B). The excellent modulus of toughness for Example 1 indicates there is crosslinking between the polyurethane and acrylic polymer segments, forming an acrylic-polyurethane interpenetrating polymer network.

(21) In Example 2, a formulation similar to Example 1 also containing additional additives and white pigment, was used as a screen printing ink plastisol. In comparison, Comparative Example G contained isocyanate grafted acrylic core-shell polymer with no crosslinking agent or urethane prepolymer. Although both plastisol formulations had excellent opacity for screen printing, Comparative Example G had a less desirable haptic appeal being slightly sticky and tacky versus the smoothness and dryness of Example 2. Furthermore, Example 2 showed improved storage stability and much improved wash fastness compared to Comparative Example G. Therefore, the acrylic-polyurethane interpenetrating polymer network of Example 2 resulted in greater stability of the plastisol, as well as an improved haptic appeal and wash fastness compared to the uncrosslinked isocyanate grafted acrylic core-shell polymer.

(22) For Examples 1 and 2, the isocyanate groups of the urethane prepolymer and acrylic resin would have the same relative reaction rate with the amine of the adipic dihydrazide; so the crosslinking reactions on the acrylic polymer and urethane prepolymer would occur simultaneously. The relative reaction rate for the isocyanate (based on an uncatalyzed reaction rate at 80 C.) is 100,000 with the aliphatic amine of the adipic dihydrazide and between about 20,000 to about 50,000 with a secondary aliphatic amine of the adipic dihydrazide according to the Handbook of Adhesive Technology, 2.sup.nd Edition, edited by A. Pizzi, K. L. Mittal, CRC Press, 2003. p. 699.

(23) On the other hand, the reaction between a primary hydroxyl group and an amine is only 100, according to the Handbook of Adhesive Technology for an uncatalyzed reaction rate at 80 C., which would represent the relative reaction rate of the acid-functionalized core-shell acrylic polymer. As a result the acid functionalized core-shell acrylic polymer would take longer to react with the crosslinking agent compared to the urethane prepolymer.

(24) In the Examples it is likely that the although the urethane prepolymer isocyanate groups of Comparative Example E formed crosslinks with adipic dihydrazide, the acid-functionalized core-shell acrylic polymer did not have time under normal screen printing curing conditions to form similar crosslinkages with adipic dihydrazide, thus resulting in separate polymer domains that lead to a weaker cured composition. So, the functional groups of the acrylic polymer and urethane prepolymer are preferably the same or have similar relative reaction rates with the crosslinking agent selected.

(25) The invention is not limited to the above embodiments. The claims follow.