WO2014209963A1

WO2014209963A1 - Crosslinked acrylic plastisol inks

Info

Publication number: WO2014209963A1
Application number: PCT/US2014/043812
Authority: WO
Inventors: James M. Hurley
Original assignee: Polyone Corp
Current assignee: Avient Corp
Priority date: 2013-06-25
Filing date: 2014-06-24
Publication date: 2014-12-31
Anticipated expiration: 2015-12-25

Abstract

Plastisol ink compositions that are essentially free of both polyvinyl halides and phthalate plasticizers are disclosed. The compositions contain acid functionalized acrylic core-shell resin, non-phthalate plasticizer, pigment, thixotropic agent, and optionally, filler and additional additives. The acrylic acid functionalized acrylic core-shell resin is crosslinked using a polyaziridine to result in a plastisol ink having storage stability, hand-feel characteristics and processing properties comparable to polyvinyl-halide-based plastisol inks.

Description

CROSSLINKED ACRYLIC PLASTISOL INKS

CLAIM OF PRIORITY

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

Application Serial Number 61/838,988 bearing Attorney Docket Number 12013026 and filed on June 25, 2013, which is incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention concerns plastisol ink compositions that are essentially free of vinyl halide and phthalate plasticizer, in which an acrylic core-shell polymer resin is crosslinked. This crosslinking results in improved storage stability, hand-feel characteristics, and processing properties.

BACKGROUND OF THE INVENTION

[0001] Plastisol ink compositions are well known for their ability to be screen-printed or otherwise applied to textiles and then be heated to form graphics and other images on the textiles. Most common among these imaged textiles are T-shirts with images of famous entertainers, college names, witty sayings, etc.

[0002] The ink composition is a plastisol, because the means of application of the colorful liquid ink utilizes the fluid properties of the plastisol before heating and/or pressure causes the base resin in the plastisol to cure into a colorful solid on the surface of the textile.

[0003] Historically, most plastisols were a combination of polyvinyl chloride (PVC) resin particles dispersed in and swelled by phthalate-based plasticizers. However, due to environmental and health safety concerns, the composition of these inks is under increasing scrutiny. [0004] The use of acrylic resins in place of PVC, together with non- phthalate plasticizers is especially attractive and has been extensively researched. Nonetheless, non-phthalate, acrylic resin plastisol inks continue to have shorter storage stability, less desirable hand-feel characteristics of softness without tackiness, and can be more difficult to process using the processes and techniques used for PVC plastisol, which continues to be prevalent in the industry.

[0005] To address some of the problems associated with acrylic -based plastisol resins, a number of patents and patent applications have proposed the use of acrylic core-shell polymers, namely: US 4,199,486 (Boessler et al.); US5,324,762 (Overend et al.); US 6,355,712 (Schultes et al.); US 6,433,048 (Kasai); and US 2010/0069566 (Mae). These patents and published patent applications teach that a core-shell structure is effective in improving the storage stability of acrylic plastisol. Unfortunately, improvements in storage stability of the core-shell acrylic resins are usually accompanied by a decrease in certain physical properties significant to the use of acrylic resins as a plastisol resin, such as the visco-elastic characteristics of the cured resin.

[0006] A rather different approach is discussed in US 6,495,626

(Overend et al.) which discloses the use of a blend of a plasticizer incompatible acrylic resin with a plasticizer compatible resin. Despite improvements reported, the storage stability and physical properties of these compositions remain unsatisfactory.

[0007] To address the poor strength, elongation and durability issues of plastisols made with acrylic core-shell resins, several persons have described creating an interpenetrating polymer networks (IPNs) by adding reactive blocked isocyanate-functional polyurethane to produce a dispersed polyurethane or polyurea phase in the final cured composition. Examples of this approach are US 6,916,869 Eto et al.; US 2006/0173110 (Baba); and US 7,332,539

(Nakayama et al.). [0008] While the presence of an interpenetrating polyurethane or polyurea network in the acrylic plastisol might increase the strength, toughness etc. of the resulting cured film, the rate of cure of the blocked isocyanates is typically too slow for normal oven curing conditions (150°C, 1-2 minutes) used in the textile screen-printing industry, and so the full benefits of the cured phase are not achieved. In addition, blocked isocyanates could pose health risks, because the blocking agents themselves are often irritants or could be carcinogenic.

[0009] An interesting new approach to these problems in the industry has been described in US 7,622,525 (Ukai et al.). In this patent, Ukai et al. forego the requirement of a one-pack system and instead, the acrylic plastisol components are split into two storage-stable parts: Part A (a mixture of the thermoplastic resin in a poor solvating plasticizer along with dicyandiamide curing agent), and Part B (a mixture of a strong solvating plasticizer along with a very strongly solvating acrylic or methacrylic monomer and fillers).

[00010] Parts A and B are blended prior to use to create a fast reacting and adherent coating. This approach helps solve the storage stability problem, but the composition, after blending, gels too quickly at room temperature (0.5 - 60 minutes) for screen printing applications. In addition, the acrylic or methacrylic monomers used are volatile irritants with a strongly objectionable odor.

[00011] Therefore, the industry still lacks a solution to the deficiencies of the various prior approaches to a non-PVC/non-phthalate plastisol ink which meets all the requirements for screen-printing of textiles.

SUMMARY OF THE INVENTION

[00012] What the art needs is a plastisol ink that is essentially free of vinyl halide and phthalate plasticizer, exhibits fast cure (i.e. 1-3 minutes at temperature between 138-160° ), stores well for acceptable shelf life, has acceptable visco-elastic properties, and has a good hand-feel characteristic. "Essentially free" means that there is no intention to include any vinyl halide material or phthalate plasticizer material in the plastisol ink compositions.

[00013] One aspect of the invention are plastisol ink compositions that are essentially free of both polyvinyl halides and phthalate plasticizers, comprising: (a) acid functionalized acrylic core-shell resin; (b) non-phthalate plasticizer; (c) crosslinking agent; (d) pigment; (e) thixotropic agent, (g) optionally, filler, and (g) optionally additional additives. The crosslinking agent is a polyaziridine that reacts with the functionalized acid groups on the acrylic core- shell polymer and links one acrylic core- shell polymer to another acrylic core- shell polymer.

[00014] The ratio of (a) acid functionalized acrylic core-shell resin to (b) non-phthalate plasticizer can range from 2: 1 to about 1:3, whereas ratios of between 1: 1 and 1:2 respectively are preferred.

[00015] The plastisol composition after curing is preferable lightly crosslinked as represented by an average theoretical molecular weight between cross links (Mc) of between about 50,000 g/mol to about 10,000,000 g/mol, and more preferably between about 100,000 g/mol and about 5,000,000 g/mol, and most preferably between about 1,000,000 g/mol and about 3,000,000 g/mol.

[00016] Another aspect of the present invention is a method of making plastisol ink compositions that are essentially free of polyvinyl halides and phthalate plasticizers by (a) blending, into a mixture, acid functionalized acrylic core-shell resin, non-phthalate plasticizer, pigments, and optionally, dispersant, together using a rotary mixer with jacketed cooling tub until the mixture is homogeneous (b) de-agglomerating the mixture using a 3-roll mill, with a gap setting of between 1-2 mils to ensure a Hegman fineness of grind value > 4 and (c) adding crosslinking agent to crosslink the acrylic core-shell polymer forming the plastisol ink composition. Typically, the bulk of the thixotropic agent may be added either during step (a), with the remainder added during step (c) to adjust the final viscosity of the plastisol ink composition to within a range of about 500,000 to about 1,300,000 centipoise when measured at 2.5 revolutions per minute on a Brookfield LVT rheometer.

[00017] A feature of the present invention is that the plastisol

compositions of the present invention have hand-feel characteristics and processing properties, comparable to polyvinyl-halide-based plastisol inks, which minimize the necessity of changes in equipment or training of use of equipment. An advantage of the present invention is that the plastisol ink compositions can be used as inks for placing, such as by screen-printing, graphics and other images on textiles virtually in the same manner as conventional polyvinyl halide-based plastisol inks.

[00018] Other aspects of the invention will become apparent from a description of the embodiments.

EMBODIMENTS OF THE INVENTION

[00019] Functionalized Acrylic Core-shell Resin

[00020] Acrylic core-shell polymer resins are useful in plastisol solutions, because their shells can have a different chemical compatibility compared to their cores. This difference can be exploited to increase shelf life of the plastisol by selecting a plasticizer that is incompatible with the shell polymer resin, but is compatible with the core polymer resin.

[00021] Acceptable resins for the invention are an acid-functionalized acrylic having a core-shell resin structure. Preferred is a core resin based primarily on methylmethacrylate-co-butyl acrylate-co-acrylic acid and a shell resin based primarily on methylmethacrylate or methyl methacrylate-co-acrylic acid. Preferentially, the acid comonomers are contained within the core portion of the core-shell structure.

[00022] The shell is preferably comprised primarily of polymethyl methacrylate (PMMA). The acid number of the resin (ASTM D664), which is an indication of the carboxylic acid content, is preferably between about 0.2 and about 20 mg KOH/g. Preferably, the acrylic core-shell polymer resin is made by a spray-dried emulsion process. [00023] The volume ratio of the core-to-shell is in the range 1:3 to 3: 1.

The number average molecular weight, M_n, of the acrylic core- shell polymer can range from about 300,000 to about 4,000,000 g/mol. The grains of the acrylic polymer resin consist of secondary particles in the range of about 20 μιη to about 80 μιη in diameter, which themselves are aggregates of primary particles of approximately 1 mm diameter. The particle size distribution of the aggregated secondary particles is dependant on the spray drying and

temperature conditions. The glass transition temperature (T_g) for the core-shell polymer resin is between about 75°C to about 125°C and preferably between about 85°C to about 120°C.

[00024] A preferred acrylic core- shell polymer resin for the invention is

LP 3202 brand acrylic in powder form, manufactured commercially by Dianal America.

[00025] Crosslinking Agent

[00026] The plastisol composition of the invention includes a

crosslinking agent that reacts with the functionalized acid groups on the acrylic core- shell polymer and links one acrylic core- shell polymer to another acrylic core-shell polymer in the plastisol. Any crosslinking agent known by a person having ordinary skill in the arts can be used in this invention. Preferred are polyaziridines, which contain saturated rings with nitrogen atoms in the ring. Of the different types of polyarziridines, propyleneimines are preferred to ethyleneimines. Because the ring of the polyaziridine is unstable, the oxygen of the carboxyl group on the functionalized acrylic core-shell polymer opens the ring, while the hydrogen atom of the carboxyl group protonates the nitrogen, and forms an aminoester as shown below.

[00027] In order to achieve optimal crosslinking efficiency,

polyaziridines will crosslink at multiple sites, creating a network of interconnected acrylic core-shell polymers. An example of polyaziridine is trimethylolpropane-tris-(N-methylazridinyl)-propionate manufactured by DSM Corporation under the trade name Neocryl CX-100™.

[00028] For the present invention, preferably the crosslinking agent is used in an amount to create a lightly crosslinked plastisol. For a lightly crosslinked plastisol, the crosslinking is preferably added in an amount calculated to have an average theoretical molecular weight between cross links (M_c) of between about 50,000 g/mol to about 10,000,000 g/mol, and more preferably between about 100,000 g/mol and about 5,000,000 g/mol, and most preferably between about 1,000,000 g/mol and about 3,000,000 g/mol.

[00029] Plasticizer

[00030] The plasticizers for the plastisol composition may be selected from a wide number of non-phthalate plasticizers, including benzoate esters, citrates, alkylsulfonic acid phenyl esters, and esters of 1,2-cyclohexane dicarboxylic acid. Preferred for the invention is Mesamoll^®, a plasticizer reported to be phthalate-free, commercially manufactured by LANXESS.

[00031] Thixotropic Agent

[00032] The plastisol ink composition (in particular, an underbase white ink that will be printed on a dark garment) needs to include a thixotropic agent, in order that the shear stress vs. shear rate curve of the plastisol used as an ink, (measured using e.g. a oscillatory frequency sweep at 25°C with a cone and plate rheometer then data-transformed using the Cox-Merz Rule, or measured using a high shear extrusion viscometer as discussed in ASTM D1823) conforms approximately to a Herschel-Bulkley fluid T=To+K(y)ⁿ where τ is the shear stress, τ₀ is the yield stress of about 500-100 Pa, K is the consistency of about 2000 Pa.s, y is the shear rate and n (exponential factor) is between about 0.5 and 0.9. In addition, it is important that the plastisol ink display a creep strain < 0.05 when subjected to a static strain of 50 Pa in a creep test, using a cone and plate rheometer. When conforming to these requirements, the plastisol ink possesses a thick, buttery and "short" texture which allows for good printability, while at the same time producing printed images possessing good opacity and a soft, smooth "hand", a word used in the art to denote a comfortable haptic or feeling of the image on the textile when touched and manipulated in multiple and complex directions.

[00033] If no thixotropic agent is present in plastisol inks of the present invention, then the printed garment will have a rough "hand." The rough "hand" is caused by the unevenness of the surface deposit, primarily determined by surface roughness and coefficient of friction.

[00034] Thixotropic agent may contain castor oil derivative, high molecular weight polyolefin, attapulgite, montmorillonite, organo-clay, fumed silica, fibrated mineral, calcium sulphonate derivative, polyamide resin, polyester amide, alkyds, and oil-modified alkyd.

[00035] Preferably the thixotropic agent is a fumed silica such as

Aerosil^® 200 particles commercially available from Evonik Degussa, or hydrogenated castor oil such as Thixcin^® wax commercially available from Elementis Specialties, or combinations thereof.

[00036] Additional Additives

[00037] A variety of additives known to those skilled in the art can be included in plastisol ink compositions of the present invention to increase processing or performance properties.

[00038] Non-limiting examples of additives include dispersants, lubricants, 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.

[00039] These additives are commercially available from a wide variety of sources and are very well known by those skilled in the art desiring formulations that mix and process well (dispersants, lubricants, air release agents, etc.) as well as provide valuable performance properties (optical brighteners, puff matting agents, antioxidants, etc.)

[00040] Range of Ingredients

[00041] Table 1 shows acceptable, desirable, and preferred ranges of the ingredients identified above: resin, plasticizers, crosslinking agent, pigment, filler, thixotropic agent, and optional additives. The invention can be based on a blend comprising these ingredients, consisting essentially of these ingredients, or consisting of these ingredients.

[00042] Water is not used as a solvent for mixing the ingredients above; so the plastisol ink composition is essentially free of water.

[00043] The variation of pigment concentration depends greatly on how much pigment is needed to achieve the desired color. Some intense fluorescent colors require multiple pigments in significant concentrations. Also, pigment concentration is dependent on the location of color within three-dimensional color-space, especially with respect to the lightness/darkness axis.

[00044] The variation in additive concentration depends on which additives are being added and for what purpose. Those skilled in the art would not require undue experimentation to develop a collection of preferred additives and their concentrations to achieve flowable plastisol inks with lasting appearance on the textile.

[00045] Because of the necessity of intimately mixing particulates

(resin(s), pigment(s), certain additives) into the plasticizer, it is preferable to apportion the amount of plasticizer for introduction into a mixing chamber at various times. More preferably, for economy of color generation as known to those skilled in the art, one can develop a masterbatch of base ingredients and then have a separate pigment concentrate(s) that are compatible with the masterbatch but do not require the inventory of having a full complement of colors of plastisol ink compositions, so long as the masterbatch can be mixed with a selected pigment concentrate at the appropriate time.

[00046] In respect of processing of plastisol ink compositions of the present invention, a feature of the invention is that the ingredients selected for the compositions unexpectedly provide very similar processing conditions for use by one skilled in the art of using polyvinyl halide plastisol ink compositions. Thus, it is very advantageous via the present invention to have an entirely new line of possible plastisol inks with virtually the same mechanics and techniques of use to make imaged graphics on textiles.

[00047] Method of preparing masterbatches and pigment concentrates are well known to those skilled in the art. The method of preparation of plastisol inks of this invention is identical to that of plastisol inks made from vinyl halides and phthalate esters. However, it has been found that use of three-roll milling aids in reducing particle size of the particulates in the inks to improve delivery of the inks in the screen-printing process to the textile to be imaged.

[00048] Preferably, one can blend the core/shell copolymer resin, plasticizers, fillers, pigments, and optional processing / performance aids together using a rotary mixer with jacketed cooling tub until the resulting mixture is homogeneous. [00049] Then, in a second step, the mixture is de-agglomerated using a 3- roll mill, for a sufficient duration to ensure a Hegman fineness of grind value >4. The crosslinking agent can be added before the roll-milling step, immediately after roll-milling or immediately prior to screen printing.

[00050] Thixotropic agents can be added in step one, or as the last step so as to achieve the final viscosity target.

USEFULNESS OF THE INVENTION

[00051] The resulting plastisol compositions are suitable for the screen printing of textiles. When subjected to a thermal cure at oven temperatures of 130 - 170^°C for about 0.5 minutes to about 2 minutes, the acrylic core-shell polymer in the plastisol reacts with the crosslinking agent to produce a crosslinked acrylic plastisol with excellent tensile strength, elongation, wash fastness and haptic (soft-hand) appeal.

[00052] Plastisol inks of the present invention provide comparable processing and performance as conventional plastisol inks containing polyvinyl halide resins and phthalate plasticizers, but are essentially free of both of them. For example, one can use the same squeegees, ovens, cure temperatures, dwell times, screens, emulsions, and clean up techniques as those employed for polyvinyl chloride/phthalate plastisol inks. In this respect, the inks of the present invention can be considered "drop-in replacements" for the

conventional vinyl/phthalate inks.

[00053] The viscosity of plastisol inks is acceptably from about 100,000 to about 1,600,000 centipoise, desirably from about 250,000 to about 1,400,000 cps and preferably from about 500,000 to about 1,300,000 centipoise, when measured at 2.5 revolutions per minute on a Brookfield LVT rheometer. The inks are printable via screen printing techniques, including without limitation, high speed automatic presses, manual printing, and high speed rotary printers.

[00054] Multiple plastisol inks can be used with different pigments in order to generate multi-colored image graphics according to techniques well known in the art. Further information about printing image graphics can be found at the website for Wilflex™ inks: wilflex.com.

[00055] It is an advantage of the invention that one can continue to use known techniques with new plastisol ink formulations that process and perform in an essentially like manner to conventional vinyl halide plastisol ink formulations. Thus, printers are not required to learn new techniques, yet the screen-printed image graphics are made from new plastisol ink formulations.

[00056] The viscosity of these plastisol compositions could also be modified by a person having ordinary skill in the art to meet the requirements of differing modes of application and usage, such as for sealants and underbody coatings.

[00057] Examples further demonstrate the utility of the invention.

EXAMPLES

[00058] General Experimental Materials Examples

[00059] Table 2 shows the list of ingredients for Comparative Example A and Examples 1-3.

Table 2

Brand Name Ingredient Type Purpose Commercial

Source

Aerosil^® A-200 Fumed Silica Powder Thixotropic Evonik

agent Industries

Disperplast^®1150 Polar acidic NonDispersant BYK

ester of long aqueous Chemie chain alcohols liquid

[00060] The acid functionalized acrylic core- shell polymer resin, non- phthalate plasticizer, color pigment, dispersant, and thixotropic agent were combined by mixing in a KitchenAid stand mixer. The resulting blend was milled in a 3-roll mill, to achieve a Hegman Fineness of Grind (ASTM D1210) of approximately 6.

[00061] To this mixture, the crosslinking agent was added in the amount of 0.017% in Example 1, 0.165% in Example 2, and 1.65% in Example 3.

Comparative Example A had no crosslinking agent added. The amount of crosslinking agent used resulted in different crosslinking densities that can be represented by the average theoretical molecular weight between cross links (M_c) on the acrylic polymer chains. The M_c is calculated by the number of crosslink junctures (based on the stoichiometry of the crosslinking agent and reactive sites of the acrylic polymer), multiplied by number average molecular weight (M_n) of the acrylic polymer.

[00062] The calculation of M_c is further described in the published article

Hurley, James M. "Estimating the Engineering Properties of Electronic

Packaging Materials." IEEE Transactions on Components and Packaging Technologies Vol. 31, No.2, June 2008, p. 417-424, which is incorporated herein only to the extent that the calculation of M_c is described within this reference.

[00063] The recipes for Comparative Example A and Examples 1-3 by weight percent of the plastisol ink composition are in Table 3 below. Wilflex™ Sprint White- 11335 ink, a commercial white PVC plastisol ink available from PolyOne Corporation, was used as Comparative Example B.

[00065] The uncured plastisol ink composition was tested for storage stability at a temperature of 46°C (114.8°F) using a Brookfield LVT rheometer and a number 7 spindle. A 0 to 10% increase in relative viscosity after 18 hours indicates the plastisol ink will be stable under normal storage conditions for several weeks.

[00066] Comparative Examples A and B, and Examples 1-3 were also manually screen printed through a 110-mesh screen onto a black 100% cotton swatch, flash-dried under a quartz infra-red heater for 6 seconds, and then reprinted. The printed samples were cured in a 12-foot M&R Sprint Series textile gas-fired oven. The temperature was set at 177°C, and the belt speed was set at 6 ft/min. The printed area measured 6 x 10.5 cm.

[00067] 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. [00068] Finally, the visco-elastic properties of the cured plastisol inks were determined using a creep test on an AR2000ex rheometer from TA Instruments. The sample geometry was defined by the instrument settings to be a cylinder of 20 mm diameter x 1 mm height. The compositions were cured at 135°C for 5 minutes and then cooled to 25°C. A torque of 10,000 μΝ.ιη was applied, from which an applied creep strain of 6.37 Pa was calculated. Sample strain versus time curves were recorded. After 5 minutes (300 seconds), the creep strain was removed and the sample was allowed to recover for 1 minute.

[00069] The creep results were analyzed using the mechanical 4-element

Burgers model with the values of the 2 spring constants G_1; G₂ and the two dashpot viscosities η_1; η₂ obtained from a non-linear least-squared analysis.

[00070] The chart below represents creep curves fitted to the 4-element

Burgers model for Comparative Examples A and B, and Examples 1-3. The strain is an absolute number with no units. The time is shown in seconds.

Example A

» Example B

Example 1

Example 2

Example 3

0 60 120 180 240 300 360

time (sec)

[00071] Performance Results

[00072] Table 5 shows performance characteristics of the plastisol according to the tests described earlier. For comparative purposes, Comparative Example B, Wilflex Sprint White-11335, was tested because this ink is known for its desirable smooth, soft hand and low tackiness. The data in Table 4 is derived from the chart above.

Table 4

Examples A 1 2 3 B

Subjective Very soft, Soft, Smooth, harsh, stiff Soft, haptic feel tacky smooth, slightly smooth,

(printed non-tacky stiff non-tacky swatch)

Storage Good Good Good Good Good stability, of (minimal (minimal (minimal (minimal (minimal ink 18 hrs. / viscosity viscosity viscosity viscosity viscosity

46°C increase) increase) increase) increase) increase)

[00073] Comparative Example B represented the optimal standard for a plastisol ink composition: good storage stability; soft-smooth feel and no tackiness; and known ease of processing which is closely related to its visco- elastic properties. The uncrosslinked acrylic plastisol, Comparative Example A, had acceptable storage performance. However, the swatch of Comparative Example A was very soft and tacky, indicating the ink surfaces will stick together after multiple hot wash cycles. In addition, Comparative Example A had a much higher visco-elastic creep strain compared to Comparative Example B.

[00074] The crosslinking of Examples 1-3, maintained the storage stability of the plastisol ink. In addition, the swatch samples for Examples 1-3 did not display any tackiness. Example 3 was rougher, compared to Examples 1 and 2, which displayed a more desirable smoothness. Example 1 also displayed a desirable softness. The increased crosslinking density from Example 1 to Example 3 across two orders of magnitude correlated to progressively stiffer and rougher printed swatches. Examples 1 to 3 fit within acceptable visco- elastic properties, with Examples 1 and 2 displaying a fitted creep curve closer to the creep curve for Comparative Example B compared to Example 3. The low and high values for Gl, G2 and/or η _{1 ;} η₂ are represented in Table 5. Table 5

low high

Gi (Pa) 1.00E+03 8.0E+03

G₂ (Pa) 1.60E+03 1.5E+04 ru (Pa.s) 4.00E+05 6.5E+07 η₂ (Pa.s) 4.00E+04 1.7E+05

[00075] Unexpectedly, crosslinking the acrylic polymer shell of the resin plastisol ink resulted in improved hand-feel and visco-elastic characteristics of the ink plastisol in Examples 1-3. Moreover, by controlling the crosslinking density, one can control the visco-elasticity characteristics and haptic feel of the plastisol ink. The average theoretical molecular weight between cross links (M_c) for Examples 1-3 are shown in Table 6 below.

[00076] At a lower density of crosslinking (i.e. lightly crosslinked), e.g.

Example 1, there is more flexibility in the polymer chains, which is manifested in a softer ink, and as there is increased crosslinking in Examples 2 and 3, the material becomes stiffer and more brittle.

[00077] The invention is not limited to the above embodiments. The claims follow.

Claims

What is claimed is:

1. A plastisol ink composition that is essentially free of both polyvinyl halides and phthalate plasticizers, comprising:

(a) acid functionalized acrylic polymer core-shell resin;

(b) non-phthalate plasticizer;

(c) crosslinking agent;

(d) pigment;

(e) thixotropic agent;

(g) optionally, filler;

(g) optionally additional additives; and

wherein the crosslinking agent reacts with functionalized acid groups on the acrylic core-shell polymer and links one acrylic core-shell polymer to another acrylic core- shell polymer, and

wherein the crosslinking agent is a polyaziridine.

2. The composition of Claim 1, wherein the core of the acid

functionalized acrylic core-shell polymer resin contains 50% by mass or more of at least one polymer selected from the group consisting of

methylmethacrylate-co-butyl acrylate-co-acrylic acid, and combinations thereof.

3. The composition of Claim 1 or Claim 2, wherein the shell of the acid functionalized acrylic core-shell resin contains 50% by mass or more of at least one polymer selected from the group consisting of methylmethacrylate, methyl methacrylate-co-acrylic acid, and combinations thereof.

4. The composition of any one of the above claims, wherein the acid functionalized core-shell polymer resin contains carboxylic acid groups and has an acid number value of about 0.2 to about 20 mg KOH/g.

5. The composition of any one of the above claims, wherein a volume ratio of core to shell of the acrylic polymer resin is in the range of 1:3 to 3: 1.

6. The composition of any one of the above claims, wherein the acrylic core-shell polymer resin has a glass transition temperature of more than about 75°C and a number average molecular weight of more than about 500,000 g/mol.

7. The composition of any one of the above claims, wherein the acrylic resin has a primary particle size range of about 20 μιη to about 80 μιη in diameter.

8. The composition of any one of the above claims, wherein the non- phthalate plasticizer is selected from the group consisting of benzoate esters, citrates, alkylsulfonic acid phenyl esters, esters of 1,2-cyclohexane dicarboxylic acid, and combinations thereof.

9. The composition of any one of the above claims, wherein the polyaziridine crosslinking agent is a propyleneimine.

10. The composition of any one of the above claims, wherein the pigment is titanium dioxide.

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

12. The composition of any one of the above claims, wherein the additional additives are selected from the group consisting of lubricants, 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.

13. The composition of any one of the above claims, wherein the composition in weight percent comprises:

14. The composition of any one of the above claims, wherein after curing the composition is lightly crosslinked as represented by an average theoretical molecular weight between cross links (M_c) of between about 50,000 g/mol to about 10,000,000 g/mol.

15. The composition of any one of the above claims, wherein the ratio of the acid functionalized acrylic core-shell resin to non-phthalate plasticizer has a range from about 2: 1 to about 1:3.

16. The composition of any one of the above claims, wherein the ratio of the acid functionalized acrylic core-shell resin to non-phthalate plasticizer has a range from about 1: 1 to about 1:2.

17. A method of making the plastisol ink composition of any of Claims 1-16, comprising the steps of: (a) blending, into a mixture, acid functionalized acrylic core-shell resin, non-phthalate plasticizer, pigments, and optionally, dispersant, 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;

(c) adding crosslinking agent to crosslink the acrylic core-shell polymer forming the plastisol ink composition; and

wherein the bulk of the thixotropic agent is added during step (a), with smaller additional amounts added during step (c) to achieve the desired viscosity target.

18. The method of Claim 17, wherein thixotropic agent is added until the viscosity of the plastisol ink composition has a range of about 500,000 to about 1,300,000 centipoise when measured at 2.5 revolutions per minute on a Brookfield LVT rheometer.

19. A textile article having an image graphic printed thereon from the plastisol ink composition of any of Claims 1-16.

20. The textile article according to Claim 19, wherein the article is a garment and wherein the image graphic of plastisol is applied by a screen- printing technique.