PROCESS FOR MAKING EXPANDABLE POLYVINYL CHLORIDE PASTE CONTAINING TRIMELLITATE PLASTICIZERS

Abstract

The present disclosure relates to the processing of a flexible polyvinyl chloride foam having predetermined characteristics formed from a polyvinyl chloride emulsion including polyvinyl chloride resin and a plasticizer by controlling one or more of the following: a concentration of stabilizer in the final foam, a heating rate during processing, a maximum temperature during fusion, and/or a total residence time during heating. Predetermined characteristics of interest for a flexible PVC foam may include, for example, low yellowness, uniform density, high compression modulus and/or a uniform cell morphology.

Claims

1. A process for making a polyvinyl chloride foam, the process comprising: providing a formulation further comprising: a polyvinyl chloride resin; a stabilizer; a plasticizer; and a chemical blowing agent; providing heat to the formulation at temperature in a range from about 15 C. to 25 C. above a fusion temperature of the plasticizer; wherein the heat is provided for a predetermined duration or less to form a plastisol; and wherein the stabilizer has a concentration in a range between 0.1-0.5% by weight in the plastisol.

2. A process for making a polyvinyl chloride foam, the process comprising: providing a polyvinyl chloride formulation further comprising: polyvinyl chloride resin; and a tris (2-ethylhexyl) trimellitate plasticizer; at least one zinc-based stabilizer; and an azodicarbonamide chemical blowing agent; providing heat to the polyvinyl chloride formulation at a temperature in a range between 15 C. to 25 C. above a fusion temperature of the tris (2-ethylhexyl) trimellitate plasticizer and for a total oven residence time of less than five minutes to form a plastisol; and wherein a concentration of at least one mixed metal stabilizer in the polyvinyl chloride plastisol is in a range between 0.1-0.5% by weight.

3. The method of claim 1, wherein the plasticizer can comprise of at least one of a Di-2-ethylhexyl terephthalate (Eastman 168) or TOTM (Plasthall Hallstar).

4. The method of claim 1, wherein the stabilizer can comprise of at least one of a Zinc octoate, Plastistab 2275 (AM Stabilizers), Barium or Zinc mixed metal stabilizer (Plastistab 2483, AM Stabilizers), Calcium or Zinc mixed metal stabilizer (Plastistab 3013, AM Stabilizers) or Barium Ricinoleate (City Chemical LLC).

5. The method of claim 2, wherein the mixed metal stabilizer comprises at least one of a barium or zinc stabilizer.

6. The method of claim 2, wherein the mixed metal stabilizer comprises at least one of a calcium or zinc stabilizer.

7. The method of claim 2, wherein the temperature settings on the oven are configured to simulate conditions in a continuous production oven.

8. The method of claim 2, further configured to use high speed centrifugation to remove air bubbles from the plastisol.

9. A process for making a flexible foam, having predetermined characteristics forming a polyvinyl chloride emulsion including a polyvinyl chloride resin and a plasticizer, wherein the process is further configured to control: a concentration of stabilizer in the final foam; a heating rate during processing; a maximum temperature during a fusion; and a total residence time during the heating.

10. The method of claim 9, wherein the predetermined characteristics includes low yellowness, uniform density, high compression modulus and/or a uniform cell morphology.

11. A foamed sports article comprising the polyvinyl chloride foam composition of claim 1.

12. A foamed sports article comprising the polyvinyl chloride foam composition of claim 1 embedded over a textile substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The following detailed description, given by way of example, but not intended to limit the invention solely to the specific embodiments described, may best be understood in conjunction with the accompanying drawings.

[0020] FIG. 1 depicts the calculated profiles according to Poppe for an air oven temperature setting of 213 C.; and

[0021] FIG. 2 shows 14 reference color standards for ASTM D848.

DETAILED DESCRIPTION OF THE INVENTION

[0022] In theory, the problem of creating an acceptable foam with a high molecular weight, and slower fusing plasticizer might be addressed by reducing the rate of azodicarbonamide decomposition (i.e., blowing), through eliminating any activators, or kickers, and raising the oven temperature. However, it is a challenge to implement such theory in practice because of the following reasons: First, many of the traditional PVC stabilizers, for example, zinc/cadmium and zinc/lead soaps, as well as tin stabilizers (e.g. butyl tin maleate) are increasingly under government and regulatory scrutiny due to health concerns. Replacements of traditional PVC stabilizers, such as zinc-based stabilizers, for example, zinc, calcium/zinc-, and barium/zinc-stabilizers act to various degrees as activators for azodicarbonamide, as well as, increase the process temperature and/or oven residence time. Zinc based stabilizers may include calcium/zinc-soaps and/or barium/zinc-soaps. Use of these soaps may cause thermal. stress on the plastisol resulting in an increase in foam yellowness. Thus, there is increasing demand for thermal stabilizers.

[0023] In an earlier report, Poppe., (A. C. Poppe, Verfahrenstechische and energetische Gesichtspunkte bei der Auswahl von Phthalat-Weichmachern zur Herstellung von Beschichtungspasten, Kunststoffe 72, p. 13-16 (1972) Translation: Process engineering and energetic aspects in the selection of phthalate plasticizers for the production of coating pastes.), discussed the benefits of increased processing temperature for the phthalate plasticizers DINP and DIDP compared to faster-fusing DOP, while Exelby et. al. recommended reducing the activation of the blowing agent when using slower fusing phthalates. (J. H. Exelby, R. R. Puri and D. M. Henshaw, Handbook of Vinyl Formulating, Chapter 20: Blowing agents, p. 536.) However, no comprehensive approach has yet been devised for improving the quality of foams made with high molecular weight, non-phthalate plasticizers, particularly trimellitates. In particular, TOTM is of special interest, because of its very high molecular weight (546.8 daltons) and low migration tendencies. A challenge of using TOTM is its high fusion temperature.

[0024] In an embodiment, a PVC foam made with TOTM plasticizer along with a azodicarbonamide chemical blowing agent is provided. The process to formulate such a foam includes providing a plastisol paste that includes PVC. For example, a mixer speed may have a value in range between 1000-3000 rpm. In particular, a mixer speed of 2000 rpm may be used. The plastisol is heated using an oven having a set temperature greater than 10 C., preferably greater than 15 C. to 25 C., above the fusion temperature of the TOTM plasticizer. In some instances, the following variables may be predetermined, in particular the total residence time for heating and/or use of mixed metal stabilizer in predetermined amounts, for example, mixed metal soaps. For example, in an embodiment, the total oven residence time, not considering cooling time, should be less than five (5) minutes and the amount mixed metal stabilizers, in particular barium/zinc and calcium/zinc, should be controlled such that the total concentration of zinc-soaps in the plastisol is in a range between 0.1-0.5% by weight.

[0025] The present invention discloses compositions containing a desirable range of zinc-containing additives, used together with specific heating profiles consisting of a heating rate, maximum fusion temperatures and a total residence time. The above processes allow for making TOTM-plasticized PVC foams, which exhibit low yellowness, uniform density, high compression modulus and a uniform cell morphology. The following materials are used as part of such process:

1. Stabilizers:

[0026] 1.1. Zinc octoate, Plastistab 2275 (AM Stabilizers)

[0027] 1.2. Barium/Zinc mixed metal stabilizer, 5:1 ratio (Plastistab 2483, AM Stabilizers)

[0028] 1.3. Calcium/Zinc mixed metal stabilizer, 10:1 ratio (Plastistab 3013, AM Stabilizers)

[0029] 1.4. Barium Ricinoleate (City Chemical LLC)

2. PVC:

[0030] 2.1. Solvin 370 HD emulsion grade resin, K value=70 (Inovyn)

[0031] 2.2. Solvin 367 NF micro-suspension grade resin, K value=67 (Inovyn)

3. Plasticizers:

[0032] 3.1. Di-2-ethylhexyl terephthalate (Eastman 168)

[0033] 3.2.TOTM (Plasthall Hallstar)

4. Kicker:

[0034] 4.1. Zinc Oxide USP 10 (Zinc Oxide LLC)

5. Processing and Dispersing Aids:

[0035] 5.1. BYK 4100 (Altana)

[0036] 5.2. Disperplast 1150 (Altana)

6. Blowing Agent:

[0037] 6.1. Azodicarbonamide (Celogen AZ 130)

7. Masterbatches 7.1. Azodicarbonamide Masterbatch: 100 g Celogen AZ-130 was slowly added to a mixture of 98 g Eastman 168 and 2 g Disperplast 1150 under intensive Cowles blade mixing to produce a bright orange paste. Azodicarbonamide concentration=50%

[0038] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims.

[0039] The present invention will be further illustrated in the following Examples which are given for illustration purposes only and are not intended to limit the invention in any way.

[0040] The formulations and relative quantities of the raw materials used in the examples of the present disclosure are set forth in Table 1 below.

TABLE-US-00001 TABLE 1 Compositions investigated. Comp. A B C (claimed) D (claimed) E (claimed) F Solvin 370 HD 70 70 70 70 70 70 Solvin 367 NF 30 30 30 30 30 30 Plasthall 100 100 100 100 100 100 TOTM Plas-Chek 3 3 3 3 3 3 770 Plastistab 3 1 2275 Plastistab 3 2483 Plastistab 3 3013 Ba-ricinoleate 3 BYK P4100 1 1 1 1 1 1 Azo 3.2 3.2 3.2 3.2 3.2 3.2 Masterbatch Total parts 207.2 210.2 208.2 210.2 210.2 210.2 % azo 0.77 0.76 0.77 0.76 0.76 0.76 % Zn-soap 0.0 1.45 0.48 0.24 0.13 0.0 Note: quantities are listed in phr, based on a combined 100 parts resins.

[0041] Samples of various foamable PVC formulations were prepared to evaluate the characteristics of the foamable PVC formulations. A 200 g sample of each of the various example PVC formulations were prepared. The plastisol pastes were prepared using a high-speed lab mixer equipped with a 2.5 inch Cowles blade. At 2000 rpm mixer speed, a maximum tip speed of 2.5**2000/12=1308 feet/min is calculated. The azodicarbonamide blowing agent and the zinc-oxide kicker (when used) were added to the formulations in the form of concentrated master batches. The Hegman finesse-of-grind of all finished pastes was found to be 5 or lower (<38 microns). After mixing, air bubbles were removed through high-speed centrifugation. Then, 5 gram samples of the various example plastisols were weighed into small aluminum weighing dishes (2.5-inch diameter), and cured for various lengths of time in a Quincy model 10 electrically heated batch-type oven. Various oven settings were investigated as part of the process.

[0042] Oven Cure Profiles: The temperature settings on the oven were adjusted to simulate conditions in a continuous production oven. Specifically, Poppe showed that the temperature of a coating in a continuous oven can be approximated by an equation derived from Newton's law of heating:

[00001]$\frac{.Math.T}{{.Math.T}_0}=e^{-.Math.t/\mathrm{cp}.Math.g}$

where T is the temperature difference between the hot oven air and the paste layer, T.sub.0 is the initial temperature difference between the oven air and the paste layer when entering the gelling tunnel (oven), is the heat transfer coefficient, C.sub.p is the specific heat of the paste and g is the coating weight per m.sup.2. Expanding this equation, the temperature T.sub.t of the paste at time t (seconds) is calculated:

T.sub.t=T.sub.0T.sub.0.Math.exp(.Math.t/c.sub.p.Math.g)

For the relevant case of a thick (0.6 cm) foam yoga mat, the following parameters were used:
Initial coating weight g: 2.35 kg/m.sup.2.
Specific heat of the plastisol C.sub.p: 1800 W/(m.sup.2.Math.K)
Heat transfer coefficient (high efficiency oven): 58 W/(m.sup.2.Math.K)
Initial paste temperature: 35 C.

[0043] FIG. 1 shows the calculated profiles according to Poppe for an oven air temperature setting of 213 C.: high temperature condition (red line) and 190 C.: low temperature condition (blue line), are compared to actual temperature readings from the batch oven (red diamonds and blue dots, respectively) as measured with a thermocouple embedded in a plastisol sample. It is observed that a good agreement is obtained, i.e., the batch oven conditions used are compatible to a continuous manufacturing process.

[0044] Further, samples of different composition were heated in the oven for various lengths of time using the high and low temperature conditions. After cooling, the samples were evaluated in terms of the foam density (ASTM D1622), Asker C durorneter hardness (JIS K 6301), Foam structure (optical microscopy and ASTM D3576) and yellowness (visually assessment versus liquid standards according to ASTM D848). The color numbers of the 14 reference color standards in ASTM D848 (Acid Wash Color of Industrial Aromatic Hydrocarbons) are depicted in FIG. 2.

[0045] The results are compiled in Table 2 shown below:

TABLE-US-00002 TABLE 2 Residence Foam Asker C Foam Cell Foam Exp. Composition Oven setting time Density Hardness Structure Color 1 A H 2 1.10 74 NA 6 2 A H 3 0.87 64 NA 4 3 A H 4 0.56 50 + 2 4 A H 5 0.44 44 + 2 5 A H 5.5 0.42 43 +/ 4 6 B H 2 0.54 48 ++ 1 7 B H 3 0.39 42 ++ 1 8 B H 4 0.37 41 +/ 6 9 B H 5 0.35 40 11 10 F H 3 0.87 64 NA 4 11 F H 4 0.56 50 +/ 3 12 F H 5 0.44 44 +/ 3 13 F H 5.5 0.42 43 5 14 C H 3 0.46 45 ++ 1 15 C H 4 0.39 42 ++ 1 16 C H 5 0.38 42 +/ 2 17 D H 3 0.60 52 ++ 1 18 D H 4 0.41 43 ++ 1 19 D H 5 0.39 42 ++ 1 20 E H 5 0.40 44 + 2 21 B L 2 0.98 69 NA 4 22 B L 0 0.50 47 +/ 1 23 B L 4 0.40 43 4 24 B L 5 0.39 42 11

[0046] In Table 2, under low temperature oven conditions with composition B (experiments #21-24), the majority of the azodicarbonamide reacts before the TOTM fusion temperature of approximately 192 C. has been reached. The foam has a poor morphology, exhibiting a non-uniform, coarse cell structures with sink marks and craters. In addition, even with a high concentration of the kicker stabilizer zinc-soap (1.5%), a residence time of 4-5 minutes is needed to achieve complete foaming. The long residence time, together with the high zinc-soap stabilizer content, leads to discoloration (a result of the so-called zinc-sensitivity of some PVC compositions).

[0047] On the other hand, under the high temperature oven condition, the TOTM fusion temperature is reached after about 160 seconds. In the case of the highly activated formula B (experiments #6-9), the majority of the azodicarbonamide has already reacted, (concomitant development of melt strength and foaming reaction). All foaming is essentially complete after 3 minutes and the end product is a high quality foam. However, this composition is sensitive to any additional oven residence time because the foams will quickly discolor with a coarsening of the cell structure (over-blowing). This high sensitivity and narrow process window makes it difficult to achieve a good quality uniform cell structure at the target density, without foam discoloration.

[0048] In addition, by using a zinc-free stabilizer such as barium-ricinoleate in composition F (experiments #10-13) or even in formulation A (no heat-stabilizer at all, experiments #1-5), the activity of the azodicarbonamide is greatly reduced, and complete foaming can be achieved in 5 minutes or more. And while the complete absence of zinc-soaps yields lighter colors even after a longer than preferred oven residence time, the foam structure formed is of lower quality than experiment #7 (i.e. where an activator is present and the residence time is short).

[0049] More satisfying results are obtained in the compositions C, E and especially D (experiments #14-16, 20, and 17-19, respectively) with a reduced concentration of zinc-soap as compared to composition B. An excellent foam structure is achieved after about 4 minutes of oven residence time, thereby allowing a wider process window for melt strength to develop. In addition, the zinc-sensitivity is drastically reduced resulting in lower foam yellowness and better color retention.

[0050] Having thus described in detail preferred embodiments of the present invention, it is to be understood that the invention defined by the above paragraphs is not to be limited to particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope of the present invention.