JPH0651810B2 - Method for producing partially crystalline polyester products - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a method of making a polyethylene terephthalate / polyolefin blend sheet material for use in thermoforming partially crystalline, heat-set products. In particular, the present invention describes a method of adding an antioxidant to paraffin polyolefin before it is combined with polyethylene terephthalate.

BACKGROUND OF THE INVENTION With the increasing popularity of microwave ovens, there has been a general interest in producing low cost, microwave transparent, disposable food packaging containers. The cooked food is placed in this container and then frozen. The consumer places the frozen food package in a microwave oven or conventional convection oven for final cooking prior to its use. This type of dual oven cookable tray (dual oven
There are a wide variety of requirements on the container for an able tray). First, the container must be able to withstand prolonged high temperature exposure without significant loss of impact strength or dimensional stability. Second, the container must retain a uniform color and be resistant to any decomposition or degradation that may cause discoloration during prolonged high temperature exposure in a microwave oven or conventional oven. US Patent No. 4,
No. 463,121 is a partially crystalline polyester product for producing a product composed of polyethylene terephthalate (PET) as a major component and polyolefin as a minor component with a total crystallinity of about 10 to about 30%. It describes a method of manufacturing. These products can be used as containers and exhibit stable impact strength and dimensional stability due to limitations on crystallinity achieved during thermoforming. Approximately 0.0% in PET / polyolefin blends to stabilize the intrinsic viscosity of the above US patents or products
It teaches that it is desirable to add from 5 to about 2% by weight of heat stabilizer.

U.S. Pat. No. 3,960,807 has three essential components: (1) a crystallizable polyester, (2) a crack stopping agent, preferably a polyolefin, and (3) a nucleating agent. It teaches a method of thermoforming a product from the composition. The method disclosed in this patent improved the impact resistance of the product and the crystallization rate during thermoforming.

In an attempt to produce thin products such as microwave double oven cookable trays or containers made without antioxidants, US Pat. No. 4,463,121
It has been found that when trays made according to No. 3 or No. 3,960,807 undergo thermal aging, they always encounter three prominent problems. That is, all of these problems are related to high temperature exposure, (1) decrease in tray intrinsic viscosity, (2) the color tends to discolor to brown or yellow, (3) irregular touch surface, especially touched tray surface. There are three areas in which a yellow or brown mottled part appears. This last phenomenon will be referred to herein as fingerprinting. The method of the present invention effectively eliminates the above three thermal degradation phenomena by incorporating an effective heat stabilizer or antioxidant into the polyolefin prior to compounding it with the PET resin. This method is one tenth or more of the level required when antioxidants are added to polyester or polyester / polyolefin blends.
An antioxidant level of 1/100 gives effective protection to the substance.

It is therefore an object of the present invention to provide a method for producing thermally stable sheet material from polyethylene terephthalate and polyolefins during subsequent thermoforming operations on the sheet material. An advantage obtained using the method of the invention is that thin products or trays can be produced that resist discoloration or fingerprint formation during high temperature heat aging. An advantage of the present invention is that the trays for electronic ovens or conventional ovens produced by the method of the present invention can withstand more than 1 hour at 200 ° C without discoloration, fingerprint formation or substantial reduction in intrinsic viscosity. is there. Yet another advantage is that low levels of antioxidant provide adequate tray protection.

BRIEF DESCRIPTION OF THE INVENTION The purpose and advantages of the present invention are to stabilize the following (a) melt blending of an effective amount of a heat stabilizer with a polyolefin derived from an olefin monomer having 2 to 6 carbon atoms. (B) polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 in a dry atmosphere at least 150 ° C.
Up to 0.02 in water content in polyethylene terephthalate
Form a dry polyethylene terephthalate by heating for a time sufficient to reduce to below wt%; (c) mixing a small amount of the stabilized polyolefin with a large amount of the dry polyethylene terephthalate to form a homogeneous molten melt blend; (d) forming a sheet from the homogeneous melt blend; and (e) cooling the sheet to form a substantially amorphous sheet; an amorphous, thermal process characterized by the following steps: It can be achieved by using a method for producing a thermally stable polyolefin-modified polyethylene terephthalate sheet.

Another aspect of the present invention is to provide the following (a) an effective amount of a heat stabilizer melt-blended with a polyolefin derived from an olefin monomer having 2 to 6 carbon atoms to obtain a stabilized polyolefin. And (b) polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 in a dry atmosphere of at least 150 ° C.
Up to 0.02 in water content in polyethylene terephthalate
Heated for a time sufficient to reduce to below wt% to form dry polyethylene terephthalate; (c) simultaneously conveying the dry polyethylene terephthalate and the stabilized polyolefin to the melt compounding means; (d) a small amount of the stabilization Polyolefin is mixed with a quantity of the dry polyethylene terephthalate to form a homogeneous molten melt blend; (e) a sheet is formed from the homogeneous melt blend; (f) the amorphous sheet is placed on a mold. (G) 15% to 35% of the sheet in a heated mold
Thermoforming to form a product for a time sufficient to achieve a crystallinity of: (h) removing the product from the heated mold; and (i) cutting the product from the sheet; A method of making a thermally stable, partially crystalline, heat-set, non-oriented product characterized by comprising steps.

Yet another aspect of the present invention provides the following (a) an effective amount of a heat stabilizer which is melt blended with a polyolefin derived from an olefin monomer having 2 to 6 carbon atoms to provide a stabilized polyolefin. (B) sufficient time to reduce the water content of polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 ° C. in a dry atmosphere to 0.02% by weight or less. Heat to form dry polyethylene terephthalate; (c) simultaneously convey the dry polyethylene terephthalate and the stabilized polyolefin to a melt compounding means; (d) mix a small amount of the stabilized polyolefin with a large amount of the dry polyethylene terephthalate. Forming a mixture; (e) melt blending the mixture to form a homogeneous molten melt blend; (f) the homogeneous melt blend. (G) cooling the sheet to form a substantially amorphous sheet; (h) placing the amorphous sheet on a mold; (i) the sheet. Thermoforming in a heated mold for a time sufficient to achieve partial crystallization of the amorphous sheet; (j) removing the partially crystalline sheet from the heated mold; (k) ) Cutting away the portion of the sheet that was in contact with the surface of the mold leaving the matrix of the amorphous sheet; and (l) crushing the matrix to form a regrind and the regrind step (b). ) And then mixing the regrind with the mixture formed in step (d),
Then, the steps (e) to (l) are repeated at least once more; a method for producing a recycled polyolefin-modified polyethylene terephthalate sheet, which comprises each step.

DETAILED DESCRIPTION OF THE INVENTION In order to produce a product or container that can be used in applications where high service temperatures are applied, polyester in crystalline state rather than in a very poor state is required. Among the known crystallizable thermoplastic polyesters, polyethylene terephthalate (hereinafter referred to as PET) has good high temperature dimensional stability, resistance to chemicals, oils and solvents and without absorbing or reflecting microwaves. It has desirable properties such as the ability to pass through. These properties make the polymer the choice for use in high temperature food containers.

Polyethylene terephthalate polymer is terephthalic acid or its lower alkyl ester (dimethyl terephthalate)
And ethylene glycol by any known polymerization technique. That is, terephthalic acid or dimethyl terephthalate is esterified or transesterified and then polycondensed with ethylene glycol to convert to a high molecular weight product. For use in the present invention, the polyester thus produced has a viscosity of about 0.6, measured at 30 ° C. in a 60/40 vol. Volume phenol / tetrachloroethane mixed solvent.
It should have an intrinsic viscosity in the range of 5 to about 1.2, preferably about 0.80 to about 1.05. Known intrinsic polymerization methods can be used to achieve this higher intrinsic viscosity.

In order to utilize polyethylene terephthalate in workable commercial molding processes such as thermoforming, it is essentially necessary to achieve the desired level of crystallinity with very short cycle times. Approximate cycle time is about 5
The fully unmodified polyethylene terephthalate polymer, which is ~ 7 seconds, has too slow a crystallization rate to achieve the required cycle time. Overcoming this slow crystallization rate,
And a nucleating agent can be added in order to increase the number of produced crystallites. Most known nucleating agents are inorganic materials with an average particle size of 2-10 microns. Other known nucleating agents are carbonaceous materials, such as carbon black and graphite. Common nucleating agents are talc, gypsum, silica,
Calcium carbonate, alumina, titanium dioxide, pyrophylite silicate, finely divided metal, powdered glass, carbon black and graphite. The above-mentioned characteristic of the known nucleating agent is involved in that the nucleating agent is formed by a polyester having a crystal structure of 100.
It exists in the solid form within the temperature range of 300 ° C. All these granular nucleating agents can be used, giving the advantage of goodness, but leveling of the crystallinity (levell
ing off) occurs if these particulate nucleating agents are reduced or eliminated.

The second essential ingredient of this invention is polyolefin, which must be present with polyethylene terephthalate. The polyolefin used in the present invention has 2 carbon atoms.
~ 6 olefin monomers.
The resulting polymer contains repeating units derived from the original monomer units. These repeating units are no longer carbon-
It differs from a monomer in that it does not contain a carbon double bond. Such polymers include low density polyethylene, high density polyethylene, linear low density polyethylene, polypropylene, polyisopropylene, polybutene, polypentene, polymethylpentene. Polyolefins are generally present at levels of 0.5 to 15% by weight of the total composition. It has been found that the preferred range is 1 to 5% by weight. The most preferred range is 2 to 4% by weight. A preferred group of polyolefins are polyethylenes, the most preferred type being linear low density polyethylene (LLDP) such as the products marketed by Dow Chemical under the tradenames DOWLEX 2045 and 2035.
E). When compared to unmodified PET, all the polyolefins give the final product improved impact strength and improved release in the thermoforming process. Polyethylene and polypropylene have a wider operating temperature range, faster crystallization rates and lower temperatures for onset of crystallization. These improvements result in faster cycle times, higher throughput (parts / minute) and lower cost end products.

When polyolefin is used with PET, US Pat. No. 3,9 containing both polyolefin and an additional nucleating agent.
It has been found to give crystallization rates at least as fast as PET compositions as described in 60,807.

It is known to add heat stabilizers or antioxidants to polyethylene terephthalate, but this thermoplastic blend will be heated in an environment where the PET / polyolefin blend is subjected to heating at a temperature of approximately 200 ° C for a time close to one hour. The problem of protecting against decomposition has become particularly difficult. This is particularly noticeable because it is desirable to minimize the presence of stabilizers or antioxidants when the product to be made from PET / polyolefin blends comes into contact with food. Unexpectedly, PE
It has been discovered that T / polyolefin blends can be optimally protected by directly adding relatively low levels of antioxidants or stabilizers to the polyolefin component prior to making the blend. This method of incorporating a heat stabilizer prior to compounding PET with polyolefin (1) minimizes the loss of intrinsic viscosity during processing and subsequent heat aging,
A method is provided that ensures (2) the discoloration of the blend during high temperature exposure and (3) the absence of fingerprinting or discoloration smear areas during high temperature aging. The heat stabilizer used in the present invention is a compound that clearly exhibits antioxidative properties, and its most important property is its ability to suppress oxidation. Thermal stabilizers useful in the practice of this invention must be capable of protecting the heat-formed, heat-set polyester product during exposure to elevated temperatures. US Pat. Nos. 3,987,004 and 3,904,57
8 and 3,644,482 disclose many examples of known heat stabilizers. The following compounds are representative thermal stabilizers useful in the practice of this invention: alkylated substituted phenols, bisphenols, substituted bisphenols, thiobisphenols, polyhydric phenols, thiobisacrylates, aromatic amines, organic phosphites. And polyphosphite. Primary aromatic polyamines, diarylamines, bisdiarylamines, alkylated diarylamines, ketones-specific aromatic amines which clearly show specific heat-stabilizing ability
There are diarylamine condensation products, aldehyde-amine condensation products and aldehyde amines. The conditions considered severe in the practice of this invention are that the thermoformed, heat-set product is exposed to temperatures near 200 ° C for more than 30 minutes. A preferred heat stabilizer for such severe high temperature applications, especially where stains or discoloration due to the heat stabilizer are undesirable, is a polyvalent phenol, which has more than two phenol ring structures therein. Tetrakis (methylene 3-
(3,5-Di-tert-butyl-4-hydroxyphenyl) -propionate) methane and 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-) Hydroxybenzyl) benzene, but is not limited thereto. The latter polyvalent phenols are most preferred. Thermal stabilizers can be advantageously added at levels up to 2% by weight, but levels up to 0.05% by weight, based on the total PET / polyolefin / stabilizer composition, are more preferred. The most preferred level is 0.005-0.03% by weight.

The antioxidant is added by melt blending directly into the polyolein component of the polymer blend. Thus, it can be seen that the polyolefin component contains the appropriate antioxidant in a final weight ratio of PET to polyolefin in a greater weight percent than is applicable. The particular level of use will depend on the degree of protection required, the nature or type of the particular stabilizer selected, the severity of heat exposure and the solubility limit of the polyolefin chain. If the food tray is a product produced by the method of the present invention, appropriate adjustments must be considered with respect to the materials that come into contact with the food, which adjustments are generally made to either component and to the final polymer blend. There is an upper limit to the amount of antioxidant that can be added.

This process for the production of polyolefin modified polyethylene terephthalate sheet comprises the steps of (1) melt blending a suitable heat stabilizer with a polyolefin derived from a monoolefin having 1 to 4 carbon atoms to form a stabilized polyolefin. including. (2) Polyethylene terephthalate with an intrinsic viscosity of 0.65 to 1.2 is heated above its glass transition temperature in dry air or nitrogen atmosphere, and in that state, degradation degradation due to hydrolysis is reduced during the step of the next method. It must be held until a low enough moisture content is reached. (3) The stabilized polyolefin and dried polyethylene terephthalate resin, in suitable proportions, are simultaneously conveyed to an extruder where both components are melt compounded to form a homogeneous melt blend. (4) Form a sheet from this homogeneous melt blend. (5) Cool the sheet to form a substantially amorphous sheet.

Melt compounding of the heat stabilizer may be carried out in a post polymerization stage of the polyolefin preparation, or optionally, the antioxidant is adequately dispersed throughout the melted polyethylene in the barrel of a conventional thermoplastic mixing extruder. It may be carried out using such an extruder. The process step of heating the polyethylene terephthalate resin in a dehumidified nitrogen or air atmosphere requires maintaining the resin's intrinsic viscosity level. Any level of moisture content that maintains a sufficiently high intrinsic viscosity level during the remaining processing steps of the process is suitable. It is advantageous to keep the moisture content at the lowest practicable. Generally, a water content of 0.02% or less is required. A moisture content of less than 0.005% is most preferred for PET with high intrinsic viscosity. Due to the need to keep its impact resistance and dimensional stability good for the containers to be made in the present invention, it is essential that PET be handled carefully to maintain its high intrinsic viscosity. Mixing of the polyolefin containing the antioxidant with the dried PET can be accomplished by any of the film extrusion techniques known in the art, in which the polyolefin and PET are heated above their glass transition temperature to melt the molten material. Blended in shear to form a homogeneous blend of two different plastics. At this time, polyolefin is dispersed throughout PET, but each is considered to be retained in a separate phase. The sheet can be formed by any conventional film forming technique. The sheet used in the Examples below is a Prodex film extruder in which the molten sheet is extruded onto a chill casting roll and immediately cooled to minimize the increase in crystallinity.
m extruder). Table I shows the extrusion conditions of the sheets used to make the amorphous sheet material used to make the trays in those examples.

Heat-set thin trays made from sheet material made from stabilized polyolefin / PET may be manufactured using any of the known thermoforming methods including vacuum assist molding, air assist molding, mechanical plug assist molding or matt molding. Can also be done. The mold, or mold, should be preheated to a temperature sufficient to achieve the desired crystallinity. The selection of the optimum mold temperature depends on the type of thermoformer, the shape, the wall thickness of the product to be molded and other factors. The operable mold temperature range is 150-215 ° C. A preferable range is 170 to 190 ° C.

Heat setting is a term that describes a process that thermally induces partial crystallization of a polyester product with less orientation. In the practice of the present invention, heat-setting involves contacting the product film or sheet with the heated mold surface for a time sufficient to achieve a level of crystallinity that imparts the appropriate physical properties to the final part. Will be achieved. The desired level of crystallinity has been found to be about 1 to about 35%. 15% for containers that should be used for high temperature food applications
It has been found that the above crystallinity levels are necessary for proper dimensional stability during part removal and exposure to ovens.

The heat-set component can be stripped from the mold cavity by known removal means. One method is the blow back method, which involves breaking the vacuum created between the mold and the forming sheet with the introduction of compressed air.
Once the heat set is removed from the mold, the remaining flat sheet material is cut off to obtain the final tray. Most commercial thermoforming molds have multiple cavities to make multiple trays from a single sheet, so die punching (dinking ou
t) and the flat matrix of the original sheet with the contours of the removed tray remains. Roughly 10 to 60% of the original sheet is the matrix, and the matrix must be recycled in order to allow the thermoforming operation to be carried out economically. This cyclic use of the matrix means imparting a considerable amount of heat history to the sheet material. When 40% sheet material is recycled, it is believed that some portion of the polyolefin / PET blend is subjected to 5 complete recycle steps. These recirculation steps include (1) crushing, (2) heating in a dry atmosphere, melt compounding with virgin material entering the system, (4) forming into a sheet, (5) ) Cooling, (6)
Then reheat before entering the thermoforming mold, (7) companding and heat setting in a thermoforming machine, (8) subsequently cooling the part and (9) the part. Includes stripping. All these steps are repeated 5 times. Thus, the resin will be subjected to very high sheet making and thermoforming temperatures for a much longer time than initially thought necessary in such cases. Recognized that this extreme high temperature exposure is detrimental to the intrinsic viscosity of PET and the stability of the polyolefin component, and that protecting PET / polyolefin blends is critically important, especially when circulation utilization approaches 40%. What was done was not before the present invention. In the following examples, the intrinsic viscosity is 1.
No. 04 polyethylene terephthalate was used either alone or in combination with linear low density polyethylene (LLDPE) available from Dow Chemical Company under the trade name Dow Rex 2045. PET containing LLDPE was dried and extruded according to the conditions in Table 1 and then a thickness of 0.
The 76mm sheet is a Comet Lovemaster thermoforming machine (Co
met Labmaster thermoformer) 13 cm x 13 cm square,
Thermoformed into a 2.5 cm deep tray. In the examples, percentages are weight percentages based on the total weight of the composition, polymer sheet or tray unless otherwise stated.

Unstabilized Food Trays Examples 1-2 A polyethylene terephthalate sheet material having an intrinsic viscosity of 1.04 was molded into a tray. Intrinsic viscosities were measured after the thermoforming of the trays was completed and then the trays were aged at 200 ° C. for 1 hour in a circulating air oven. next,
The intrinsic viscosity was measured again. The results are shown in Example 1 in Table II. Example 2 is 97% PET with no antioxidant (AO)
It was a 3% LLDPE sheet. From the results shown in Table II, PET alone or blended with polyolefin, e.g. linear low density polyethylene, has an intrinsic viscosity during high temperature aging when not protected with antioxidant or stabilizer systems. It is clear that it will be substantially reduced. This reduction in intrinsic viscosity is completely unacceptable for food trays. In addition, Example 3 is US Pat. No. 4,463,
This is a feature of products made in accordance with the teachings of No. 121 without the inclusion of antioxidants.

Comparative Experiment Results All of the samples of Examples 3 to 7 below are the most preferable polyhydric phenolic antioxidants.
1,3,5-trimethyl-2,4, sold under the tradename Ethanox 330 by
PET / LL containing various levels of 6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene
Manufactured from DPE. The AO percentages given in the sheet forming formulations in Table II are the percentages of antioxidants by weight of the total sheet composition. In this series of experiments, the purpose was to evaluate the effect of heat aging at 200 ° C. on three important properties of trays that can be used in microwave ovens and conventional ovens. These characteristics are as follows: (1) Fingerprinting-this term refers to the phenomenon that appears as irregular, widely-spaced discolored areas on aged tray samples. Discoloration typically occurs on the surface of a tray that is touched by human hands. The sporadic stains in Table II are “Yes” in the column for fingerprint formation regarding the effect of aging.
Or, it is represented by either "none". The description is "Yes"
In this case, it should be understood that the fingerprint forming part appeared after aging. A "no" entry indicates that the tray retained its original uniform appearance. (2) Color /
The term "color" indicates whether or not the original color of the tray is retained after aging for 1 hour at 200 ° C. The occurrence of discoloration is a uniform change in the shade of the tray. If the entry in the color column says "Stable," it indicates that the color did not change after aging. If the entry says "Discoloration," a discernible change in color resulted from thermal aging. (3) Intrinsic viscosity-Intrinsic viscosity tends to decrease when PET is exposed to high temperature The original intrinsic viscosity was measured and compared with the intrinsic viscosity value after aging at 200 ° C. for 1 hour. Variables 3 to 7 are AO levels and AO
Including components added and AO addition method.

Example 3 In Example 3, 0.1% AO was added to the melt phase PET during the manufacture of the polyethylene terephthalate polymer. The intrinsic viscosity remained satisfactory, but the relatively high levels of AO in PET contributed to the discoloration of the PET polymer used in the blend. This discoloration was a general yellowing phenomenon in which the color of unused PET resin changed from normal milky white to brown. PET
It is presumed that all of the holding at high temperature for a long time while the base resin having a high temperature and a high intrinsic viscosity (1.04) received during the production is in a solid state contributes to the total discoloration. This discoloration is very sensitive to applications such as food trays. Moreover, the aged sample also showed unsatisfactory fingerprint formation.

Example 4 Example 4 is a blend with the same polymer composition as Example 3, but with 0.19% antioxidant added. The antioxidant was added to both the PET in the reaction vessel and the linear low density polyethylene in the master batch. 77/23 wt% PET / LLDPE is shown in the column of AO addition method indicated as master batch
Illustrates the operation of employing the original master-batching step in which was mechanically compounded in the form of granular pellets to form a master-batch.

This master batch blend of PET and linear low density polyethylene was subsequently fed simultaneously with PET resin at a ratio of 13 to 87% by weight to a Prodex film extruder for LLDPE.
A final product of 3% and PET 97% was obtained. This masterbatch method achieves improved dispersion throughout the PET of polyethylene even in situations where the feed from the hopper to the film extruder must handle low percentages of resin, such as 3%, without accurate calibration. . The intrinsic viscosity was retained and there was clearly no fingerprint formation. However, tray discoloration was noticeable with this higher level of antioxidant. Antioxidants have a pronounced tendency to yellow when added to PET / polyolefin blends at relatively high levels.

Examples 5-7 Film sheet materials were made using PET / LLDPE in a 97/3 wt% ratio with varying percentages of antioxidant.
This series of experiments utilized the method of the present invention in which an antioxidant was added to linear low density polyethylene prior to compounding with PET. No antioxidant is added to PET. This method is shown in Table II under "LLDPE".
In this method, the antioxidant remelts the particulate polyolefin and uniformly blends the desired level of antioxidant into the polyolefin, and then melts the resin into the desired particulate form, eg, It was added to the polyolefin by finishing it into pellets, pill beads or other desired morphology, this formulation being a Sterling Transfermix extruder.
ruder), in which case the barrel temperature was kept at about 195 ° C and the die temperature was kept at 175 ° C. The screw speed is 84 rpm
It was. This linear low density polyethylene was then accurately compounded with dry PET at the throat inlet to the film extruder. The film extruder uniformly blended PET with the stabilized linear low density polyethylene to form a homogeneous melt blend. The results shown in Table II for the aging properties of trays made with this polyolefin stabilized blend show that even with very low levels of antioxidant,
The intrinsic viscosity is retained during aging at 00 ° C. for 1 hour, and the color of the tray is stable. 0.00
Example 5 with 9 wt% antioxidant shows fingerprint formation, while Example 6 with slightly higher levels of antioxidant has barely discernible traces. It only indicates that there is fingerprint formation. 0.0
Example 7 using 24% by weight of AO shows no signs of fingerprint formation. This result required almost eight times as much antioxidant level to eliminate fingerprint formation, yet the resin exhibited a yellowish tint after aging Example 3.
In sharp contrast to.

Cycling Tests Examples 8-22 When making trays from flat sheet material by thermoforming, a typical thermoforming process yields approximately 40% scrap sheet material after each forming and trimming cycle. This sheet material must be reground and mixed with incoming virgin PET / polyolefin material for reuse. This cyclical use adds significant thermal history to the polymer blend, causing problems of discoloration, fingerprint formation, loss of intrinsic viscosity and change in crystallinity and degradation degradation. In order to produce an acceptable thermoformed food tray, all of the above properties must be stabilized and removed in a commercial process with a substantial proportion of regrind. In a typical thermoforming process, it is reground to 40%. A simulation of steady-state operation of such a thermoforming system assumed that this regrind means that the same resin must be used approximately 5 consecutive times throughout the sheet manufacturing and tray thermoforming system. ing. Therefore, in the next experimental plan, a 40% regeneration and a 5-cycle system are simulated in order to evaluate thermal stability. The resin used is 97% PET (limited viscosity 1.0
4) 3% linear low density polyethylene, Dow Rex 2045 commercially available from Dow Chemical Company and 0.015% Ethanox 330 commercially available from Ether. The antioxidant was melt compounded into LLDPE using a Stirling Transfer Mix Extruder and then 1.7
For 5 inch (45 mm) Prodex Film Extruder
Pelletized for feeding and compounding with PET. The steps of this method are as follows.

(1) Conair dehumidifyi a resin / regrind blend with a dry nitrogen atmosphere.
ng hopper) at 170 ° C. for 4 hours.

(2) After drying, each sample was placed in a wet oven at 100 ° C to keep it dry and equilibrated to a temperature of 100 ° C.

(3) 100 ° C. resin was placed in the extruder hopper and mixed with antioxidant-stabilized LLDPE to obtain the correct proportion of blend.

(4) The compounded materials were extruded according to the specifications in Table I above to form amorphous sheets.

(5) The test tray was thermoformed under the following conditions using a Comet Lovemaster thermoforming machine.

Preheating in the furnace 12 seconds Furnace temperature Upper 315 ° C Bottom 225 ° C Molding time 8 seconds Molding temperature 160 ° C An extra unmolded sheet part was cut out from the thermoformed tray to obtain a recycled matrix for reprocessing.

(6) Remove the remaining unformed matrix sheet at 150 ℃
Crystallize with, cool, crush with 0.6mm screen,
It was then mixed with virgin 97/3 PET / LLDPE resin at a new resin / regrind ratio of 60/40. The resin / regrind blend was dried according to step (1) and the experimental steps (1)-(6) were repeated for 5 cycles. The following properties were taken for each tray from each of the 5 cycles: (1)
Intrinsic viscosity, (2) Hunter clor value
Crystallinity (%) calculated from the density of "B" and (3) tray. All results are shown in Table III.

The data shown in Table III shows that a tray made from a film having a polyolefin component added with an antioxidant has excellent intrinsic viscosity retention, good color retention and excellent crystallization over 5 regrind cycles. Demonstrating that it had a degree of controllability. This stability indicates that materials using this method of stabilizing polyolefin prior to the addition of PET can be recycled multiple times without sacrificing the strength and appearance properties of the final tray. This recycle capacity is critical in commercial thermoforming operations where matrix waste is above 40%.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display area C08L 23:02) 7107-4J B29K 67:00

Claims (18)

[Claims] 1. (a) melt blending an effective amount of a heat stabilizer with polyethylene to form a stabilized polyethylene; (b) drying polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2. At least 150 ℃ in the atmosphere
The water content in polyethylene terephthalate is 0.02
Heating for a time sufficient to reduce to less than or equal to wt% to form dry polyethylene terephthalate; (c) conveying the dry polyethylene terephthalate and the stabilized polyethylene simultaneously to a melt compounding means; (d) a small amount of the stabilizing (E) melt blending the mixture to form a homogenous melt melt blend; (f) forming a sheet from the homogenous melt blend; (e) melt blending the mixture to form a mixture; g) cooling the sheet to form a substantially amorphous sheet; (h) placing the amorphous sheet on a mold; (i) placing the sheet in a heated mold. Thermoforming for a time sufficient to achieve partial crystallization of the amorphous sheet; (j) removing the partially crystalline sheet from the heated mold; (k) on the surface of the mold. Cut off the part of the sheet that was in contact Leaving the matrix; and triturated with (l) the matrix to form a regrind,
Heating the regrind according to step (b), then mixing the regrind with the mixture formed in step (d), and repeating steps (e) to (l) at least one more time; A method for producing a polyethylene-modified polyethylene terephthalate sheet which can be recycled and is characterized by comprising: 2. The method of claim 1 wherein said polyethylene is a linear low density polyethylene. 3. The polyethylene is linear low density polyethylene and the heat stabilizer is 1,3,5-trimethyl-2,
4,6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and tetrakis (methylene 3-)
(3,5-di-t-butyl-4-hydroxyphenyl)-
A process according to claim 1 which is a polyhydric phenol selected from the group consisting of propionate) methane. 4. The method of claim 1 wherein the effective amount of said heat stabilizer is less than 0.05% by weight. 5. An effective amount of the heat stabilizer is about 0.005% by weight.
The method of claim 1 wherein the amount is from about 0.03% by weight. 6. The heat stabilizer is 1,3,5-trimethyl-
Claim 2, which is 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene.
Method described in section. 7. (a) Melt blending an effective amount of a heat stabilizer with polyethylene to form a stabilized polyethylene; (b) Dry polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2. At least 150 ℃ in the atmosphere
The water content in polyethylene terephthalate is 0.02
(C) Mix a small amount of the stabilized polyethylene with a large amount of the dry polyethylene terephthalate to form a homogeneous melt-melt blend by heating for a time sufficient to reduce to less than or equal to wt.%; d) forming a sheet from the homogeneous melt blend; and (e) cooling the sheet to form a substantially amorphous sheet; an amorphous, characterized in that it comprises: A method for producing a thermally stable polyethylene-modified polyethylene terephthalate sheet. 8. The method of claim 7 wherein said polyethylene is a linear low density polyethylene. 9. The polyethylene is linear low density polyethylene and the heat stabilizer is 1,3,5-trimethyl-2,
4,6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzyl and tetrakis (methylene 3-)
(3,5-di-t-butyl-4-hydroxyphenyl)-
A method according to claim 7 which is a polyvalent phenol selected from the group consisting of propionate) methane. 10. The method of claim 7 wherein the effective amount of said heat stabilizer is less than 0.05% by weight. 11. The method of claim 7 wherein the effective amount of said heat stabilizer is from about 0.005% to about 0.03% by weight. 12. The heat stabilizer is 1,3,5-trimethyl-
The compound is 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene.
Method described in section. 13. (a) Melt blending an effective amount of a heat stabilizer with polyethylene to form a stabilized polyethylene; (b) Dry polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2. At least 150 ℃ in the atmosphere
The water content in polyethylene terephthalate is 0.02
Heating for a time sufficient to reduce to less than or equal to wt% to form dry polyethylene terephthalate; (c) conveying the dry polyethylene terephthalate and the stabilized polyethylene simultaneously to a melt compounding means; (d) a small amount of the stabilizing Polyethylene is mixed with a quantity of the dry polyethylene terephthalate to form a homogeneous melt melt blend; (e) a sheet is formed from the homogeneous melt blend; (f) the amorphous sheet is placed on a mold. (G) thermoforming the sheet in a heated mold for a time sufficient to achieve a crystallinity of 15% to 25% to form a product; (h) heating the product to the heated mold. Removing from the mold; and (i) cutting the product from the sheet; thermally stable, partially crystalline;
Manufacturing method for heat-set non-oriented products. 14. The method of claim 13 wherein said polyethylene is a linear low density polyethylene. 15. The polyethylene is a linear low density polyethylene and the heat stabilizer is 1,3,5-trimethyl-.
2,4,6-Tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and tetrakis (methylene)
14. The method of claim 13 which is a polyhydric phenol selected from the group consisting of 3- (3,5-di-t-butyl-4-hydroxyphenyl) -propionate) methane. 16. The method of claim 13 wherein the effective amount of said heat stabilizer is less than 0.05% by weight. 17. The method of claim 13 wherein the effective amount of heat stabilizer is from about 0.005% to about 0.03% by weight. 18. The heat stabilizer is 1,3,5-trimethyl-
Claim 2, which is 2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene.
The method according to item 3.