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Void-containing polyester shrink film with improved density retention

Inactive Publication Date: 2006-06-08
EASTMAN CHEM CO
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0014] The void-containing films of the present invention have high shrinkage and maintain their low density after exposure to temperatures typically present during recycling processes. The films may be used as roll-fed or traditional shrink-sleeve labels, can be printed easily, and seamed by traditional means. Our void-

Problems solved by technology

If these labels are not removed prior to the sink/float step by some other means such as, for example, by air elutriation or by manually tearing them off of the bottle, they will sink with the PET and eventually cause color and haze contamination.
For labels made from PVC, this contamination is particularly undesirable as PVC emits corrosive hydrochloric acid at PET processing temperatures.
The presence of small amounts of polystyrene with recycled PET, however, can cause offgassing and release of hazardous styrene monomer during subsequent PET processing.
Polyester shrink labels, by contrast, are usually more compatible with reprocessed PET, but still present contamination problems from printing inks and glues.
Foaming is effective for decreasing the density, but the resulting film is difficult to print an

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples

[0053] General—Test methods followed standard ASTM procedures wherever possible. Film densities were obtained by immersing small pieces of the film (cut using a hole punch) in fluids of known density. The fluid density which caused the film sample to “hang” without sinking or floating was taken to be the film density. For densities from 0.80 g / cc to 1 g / cc, these fluids were produced from blends of ethanol and water and calibrated against a hydrometer. For densities above 1 g / cc, the control fluids were blended in a similar manner using salt and water.

[0054] General film quality and aesthetics were based on subjective evaluation and are shown in Table II. An excellent film was one with uniform dispersion of voids / additives, high opacity, no high / low spots, good strength, and no streaking from poor mixing. Film tactile qualities (i.e. “hand”) were also included with stiff, noisy films being rated more poorly, and softer “low-noise” films being preferred. Poor films generally exhibit...

examples 1-8

Annealing Experiments

[0062] Films in this example were made in the same manner as Comparative Examples 1-7; however, stretching conditions were varied to try and balance the post-wash density with shrinkage. It was found that annealing temperatures in the vicinity 100° C. worked best. Samples containing lower levels of concentrate (e.g., Examples 1 and 2) had the narrowest processing window, but were also the toughest and least likely to tear. Stretch ratios had to be run higher on these films to get the most possible voiding (they were also less likely to tear during the stretching process than films with higher levels of concentrate).

[0063] Increasing the level of concentrate to 30% (Examples 6-8) resulted in a film with excellent shrinkage and low density under a very wide range of processing conditions. However, the film was also more prone to tearing because of the high level of voiding. Although this film would be acceptable for many applications, it is less preferred for pa...

example 9

Curve Fitting and Optimization of Trial Data

[0064] The data from Examples 1-8 and Comparative Examples 1-7 were statistically fit to an equation to better understand trends and interactions (included in this analysis was other trial data on the same tenter frame not reported above). The variables in the model were stretch ratio, average stretch temperature (i.e. the average of preheat and stretch temperature), % clip retraction, anneal temperature, and % concentrate. The responses to be predicted were 5 seconds shrink at 95° C. and density after 15 minutes at 85° C. Analysis and optimization was performed using JMP™ statistical analysis software and a linear model fit.

[0065] Optimization was performed in order to find the best combination of conditions that would yield high shrinkage (>60%) and a density less than 1.05 g / cc after the 85° C. wash. Constraints to the optimization were that the concentrate level had to be less than 30 wt % to minimize brittleness, and the stretch con...

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Abstract

Disclosed are void-containing polyester shrink films which show excellent density retention upon exposures to high temperatures. The films have high shrinkage and retain their low density after processing under conditions of temperature and moisture used in typical recycling processes. The films are useful for sleeve label and other shrink film applications, and their lower density allows them to be readily separated from soft drink bottles, food containers and the like during recycling operations. Also disclosed is a process for void-containing polyester shrink films having high shrinkage and low density after exposure to elevated temperatures.

Description

CROSS REFERENCES TO RELATED APPLICATIONS [0001] This application claims the benefit of U.S. Provisional Application Ser. No. 60 / 633,765, filed Dec. 7, 2004.FIELD OF THE INVENTION [0002] This invention pertains to void-containing, polyester shrink films. More particularly, this invention pertains to void-containing, polyester shrink films that have high shrinkage and maintain a low density after shrinkage. The invention further pertains to a process for a void-containing shrink film that has high shrinkage and good density retention after shrinkage. The films may be used to produce labels for packaging applications. BACKGROUND OF THE INVENTION [0003] Films produced from polymers such as polyolefins, polystyrene, poly(vinyl chloride), polyesters and the like, are used frequently for the manufacture of labels for plastic beverage or food containers. Because these labels are often recycled, it is desirable that the label materials are compatible with the recycling process streams and no...

Claims

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Application Information

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IPC IPC(8): F16B4/00
CPCC08J5/18C08J2367/02C08K3/00C08L67/02B29C67/20B29C55/005B29C47/0057Y10T428/1328C08L101/00C08L2666/02B29C48/0018C08L67/00
Inventor SHELBY, MARCUS DAVIDTANNER, CANDACE MICHELETINCHER, MARK ELLIOTTLITTLE, RONDELL PAUL JR.
Owner EASTMAN CHEM CO
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