FR2578547A1 - PROCESS FOR THE MANUFACTURE OF PARTIALLY CRYSTALLINE ARTICLES OF POLYOLEFIN MODIFIED ETHYLENE POLYTEREPHTHALATE - Google Patents

Abstract

ACCORDING TO THE INVENTION, A MIXTURE OF ETHYLENE POLYTEREPHTHALATE AND POLYOLEFIN IS PREPARED BY MIXING A THERMAL STABILIZER ONLY WITH POLYOLEFIN BEFORE ITS INCORPORATION OF ETHYLENE POLYTEREPHTALATE. AND POLYOLEFIN, HAVING IMPROVED COLOR STABILITY AND CAN BE RECYCLED SEVERAL TIMES WHICH ARE EXTRUDED INTO A SHEET THEN HOT FORMED IN USEFUL ARTICLES IN PARTICULAR AS CONTAINERS FOR FOOD RESISTANT TO MICROWAVE OVENS.

Description

The present invention relates to a method of manufacturing articles

  partially crystalline in polyester. More particularly, the invention relates

  a method of manufacturing a sheet made of a metal

  polyethylene terephthalate / polyolefin diaper for

  the use in hot forming of thermoset articles

  partially crystalline cis. In particular the invention

  describes a process for adding the exclusive antioxidant-

  polyolefin before mixing with polyt-

ethylene rephthalate.

  The growing popularity of microwave ovens has aroused general interest in: the production of inexpensive disposable microwave transparent containers for food packaging. Prepared pre-cooked food can be placed in the container and then frozen. The consumer completes the cooking in

  the packaging of frozen food in a microwave oven

  waves or in a conventional convection oven before consuming it. The requirements that the use of this type of

  ovens required to containers are many and diverse.

  First, the container must be able to withstand prolonged exposure to elevated temperatures without noticeable decrease in impact strength or dimensional stability. Also, the container must

  maintain a uniform color and resist any

  gradation which may alter the color during exposure

  prolonged at a high temperature in a microwave or conventional oven. US Patent 4,463

  121 describes a method of manufacturing an article by

  partly crystalline polyester made up of

  major layer of polyethylene terephthalate (PET) and as a minor component of a polyolefin to produce an article having a total crystallinity of about 10 to about 30%. Such articles can be used as containers and exhibit consistency in impact resistance and dimensional stability due to the limitation of the degree of crystallinity obtained during hot forming. This patent also indicates that it is desirable to add from about 0.05 to about 2% by weight of a thermal stabilizer to the PET / polyolefin mixture to stabilize the intrinsic viscosity

of the article.

  US Pat. No. 3,960,807 describes a process for the hot forming of articles from a composition containing three essential components (1) a crystallizable polyester, (2) a crack-arresting agent,

  preferably a polyolefin and (3) a nucleating agent

  tion. The process described in this patent improves the re-

  impact strength of the article and the speed of crystalli-

  sation during hot forming.

  In an attempt to produce thin-walled articles such as tubs or containers which can be heated in a microwave oven or a conventional oven containing no antioxidant, it has been discovered that, during thermal aging of the tubs prepared according to the processes of US Pat. Nos. 4,463,121 or 3,960,807, we regularly encounter three distinct problems which are all linked to exposure to a high temperature: (1) a decrease in the intrinsic viscosity of the tank, (2) a tendency to show browning or yellowing and (3) the appearance of irregular yellow or brown spots on the surface of the container, particularly where the hands touched the container. This latter phenomenon is here called the formation of fingerprints. The method of the invention effectively eliminates the three phenomena of

  thermal degradation listed above thanks to the

  polyolefin effective corporation of a stabilizer

  thermal or antioxidant effective before the po-

  lyolefin is mixed with the PET resin. The process provides effective protection of the material with

  antioxidant concentrations between the di-

  tenth and one hundredth of those required when

  add antioxidant to polyester or ooly- mix

  ester / polyolefin. An object of one aspect of the invention is to

  provide a manufacturing process, starting from polyté-

  athene rephthalate and a polyolefin, a film

  which is thermally stable during subsequent hot forming operations. An additional advantage of using the inventive method is the production

  Weatherproof Thin Walled Items or Tubs

  tint ration or fingerprint formation

  during thermal aging at elevated temperature.

  One of the advantages of the invention is that a bins which can

  be heated in a microwave or conventional oven

  sique, manufactured according to the process of the invention, can

  resist 2000C for more than one hour without deterioration

  shade ration, formation of fingerprints or significant decrease in intrinsic viscosity. Another

  advantage is that very low concentrations of anti

  oxidant effectively protect the tank.

  The purposes and advantages of an aspect of innovation

  tion can be obtained by using a

  manufacture of a thermostable amorphous sheet of poly-

  ethylene terephthalate modified with a compressed olefin

  the stages of: (a) mixing in the molten state an effective amount of a thermal stabilizer with a derived polyolefin

  olefinic monomers containing 2 to 6 carbon atoms

  bone 'to form a stabilized polyolefin; (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 1500C in a dry atmosphere for a time sufficient to reduce the moisture content of the polyethylene terephthalate below 0.02% by weight to form a dry polyethylene terephthalate (c) mixing a small amount of the stabilized polyolefin with a major amount of dry polyethylene terephthalate to form a homogeneous molten mixture; (d) forming a sheet from the homogeneous molten mixture; (e) cooling said sheet to form

  an essentially amorphous leaf.

  Another aspect of the invention relates to a

  process for manufacturing a thermostable article by-

  partially thermoset crystalline and not oriented

taking the stages of:

  (a) mix in the molten state an effective amount

  ce of a thermal stabilizer with a polyoltfin

  derived from olefinic monomers containing 2 to 6 ato-

  carbon to form a stabilizing polyolefin

  sée; (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 C in a dry atmosphere for a time sufficient to reduce the moisture content of the polyethylene terephthalate below 0.02% by weight to form a dry polyethylene terephthalate; (c) simultaneously conduct the polyterephthalate

  dry ethylene and the fine polyol stabilized at a dis-

  positive melt mixing;

  (d) mixing a small amount of the polyolefin

  not stabilized with a major amount of polytere-

  dry ethylene phthalate to form a homogeneous molten mixture; (e) forming a sheet from said homogeneous molten mixture; (f) placing said amorphous sheet on a mold; (g) hot forming said sheet into an article in a heated mold for a time sufficient to obtain a crystallinity between 15 and 35%; (h) unmolding the article from the heated mold; and

  (i) separating the article from said sheet.

  According to another aspect, the invention relates

  a process for manufacturing a polytere sheet-

  ethylene phthalate modified by a polyolefin and re-

  cyclable, comprising the steps of: (a) mixing in the melt an effective amount of a thermal stabilizer with a derived polyolefin

  olefinic monomers containing 2 to 6 carbon atoms

  bone to form a stabilized polyolefin; (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 C in a known atmosphere for a

  sufficient time to reduce the humidity of the soil

  ethylene lyterephthalate below 0.02% by weight to form a dry polyethylene terephthalate; (c) simultaneously conduct the polytrephthalate

  dry ethylene and the polyolefin stabilized to a dispo-

  mixture sitive in the molten state; (d) mixing a small amount of the polyolefin

  stabilized with a major amount of polyterephthala-

  te of dry ethylene to form a mixture; (e) mixing the mixture in the molten state to form a homogeneous molten mixture; (f) forming a sheet from the homogeneous molten mixture;

  (g) cooling said sheet to form a sheet

  the essentially amorphous; (h) placing the amorphous sheet on a mold; (i) hot forming said sheet in a heated mold for a time sufficient to obtain partial crystallization of the amorphous sheet; (j) demolding the partially crystalline sheet from the heated mold; (k) separate the portion of the leaf that has been

  contact with the mold surface to leave a

  trice of the amorphous leaf; and (1) grinding the matrix to form ground waste and heating the ground waste according to stage (b), then mixing the ground waste with the mixture formed in stage (d) and repeating at least one more

times stages (e) to (1).

  The invention will now be described in detail.

detailed lesson.

  To produce items or containers

  useful in applications where working temperatures

  high plies are encountered, a crystalline rather than amorphous polyester is required. Among the polyesters

  known crystallizable thermoplastics, polytere-

  ethylene phthalate (hereinafter abbreviated as PET) has the desirable properties of good dimensional stability at elevated temperatures,

  resistance to chemical agents, oil and sol-

  and transparent in the microwave without the ab-

  sorb or reflect them. These properties make this po-

  lymer particularly useful for use in

  high temperature resistant food containers

  vee. The polyethylene terephthalate polymer is obtained according to known polymerization techniques, either from terephthalic acid, or from one of its lower alkyl esters (dimethyl terephthalate) and ethylene glycol. We are esterifying or

  transesterifies terephthalic acid or terephthala-

  te dimethyl then polycondense with ethylê-

  ne-glycol to obtain a high molecular weight product. For use in the invention, the polyester thus produced must have an intrinsic viscosity

  between about 0.65 and about 1.2, preferably

  between about 0.80 and about 1.05 as measured in a mixed solvent consisting of a 60/40 mixture by volume of phenol and tetrachloroethane at 30 C. The known solid state polymerization methods can be used to obtain high intrinsic viscosities. To use polyethylene phthalate in viable industrial forming processes, such as hot forming, it is essential that the desired level of crystallinity is obtained in a very short cycle. An acceptable cycle time is approximately 5 to 7 seconds. Polyethylene terephthalate polymer

  totally unmodified has crystal speeds-

  far too low for the required cycle times to be obtained. To compensate for this slowness of

  crystallization, nucleating agents can be added

  o05 tion to increase the number of crystallites formed.

  Most known nucleating agents are ma-

  mineral particles having an average particle size

  them from 2 to 10 micrometers. Other known nucleating agents are carbonaceous materials such as carbon black

  carbon and graphite. The nucleating agents

  rants can be talc, gypsum, silica, car-

  calcium bonate, alumina, titanium dioxide,

  pyrophylite type silicates, finely divided metals

  glass powder, carbon black and grit

  phite. The common characteristic of nuclear agents-

  tion known above is that they exist in a solid form in the temperature range from 100 C to 300 C in which the polyesters form crystal structures. On- can use with good results

  any of these particular nucleating agents

  res although stabilization of the degree of crystallinity

  appears when these particular nucleating agents

res are reduced or eliminated.

  The second essential component of the invention

  is a polyolafine which must be present with the po-

  ethylene lyterephthalate. Polyole-

  fines which are produced from olefin monomers

  ques having 2 to 6 carbon atoms. The polymer obtained

  contains repeating patterns derived from monomeric patterns

  original res. These repeating patterns differ from monomv -

  res in that they no longer contain double bonds

  carbon-carbon. These polymers include polyethylene

  lLow density, high density polyethylene linear low density polyethylene, polypropylene, polyisopropylene, polybutin, polypentene and polymnethylpentene. The polyolefin can be present at concentrations of 0O5 to 15% of the total weight of the composition. The preferred range has been found to be 1 to 5% by weight. Particularly preferred is 2 to 4% by weight. A preferred category of polyolefins

  consists of polyethylenes, the type of which

  Particularly preferred is linear low density polyethylene (LLDPE) as represented by the products marketed by Dow Chemical under the brand names DOWLEX 2045 and 2035. By comparison with non-PET

  modified all polyolefins improve resistance

  this to shock the finished article and improve demolding in the hot forming operation. Polyethylene and polypropylene have the widest ranges of operating temperatures, the highest rates of crystallization and the lowest temperatures of onset of crystallinity. These improvements

  lead to shorter cycle times, to a number of

  increased number of parts per minute and at a lower cost of

the finished article.

  The use of polyolefins with PET has been shown to ensure crystallization rates at least

  as high as those of PET compositions containing

  providing both the polyolefin and a nucleating agent

  additional as described in US Patent 3,960,807.

  We know that thermal stabilizers or

  antioxidants can be added to polyterephta-

  ethylene late, however the problem of protecting PET / polyolefin blends against degradation

  thermal, in environments where the thermal mixture

  plastic is subjected to heating at temperatures

  res close to 200 C for a neighboring period

  1 hour becomes particularly difficult. This problem

  is especially important to me when the article,

  which must be made from the mixture of PET / polyole-

  fine, must come into contact with food because it

  desirable to minimize the amount of stabil

  iisants or antioxidants present. We discovered that,

  quite unexpectedly, the mixture of PET / po-

  lyolefin can be optimally protected by ad-

  addition of a relatively low concentration of anti

  oxidant or stabilizer directly to the poly-

  olefinic before the preparation of the PET / poly blend

  olefin. This process of incorporating the stabilizer

  thermal, before mixing PET and polyole-

  fine, provides a method for ensuring (1) a decrease

  minimum intrinsic viscosity when

  transformation and thermal aging

  laughing; (2) the elimination of the alteration of the hue

  of the mixture during exposure to high temperature

  vee; and (3) elimination of the formation of traces

  fingers or regions with spots of tint

  altered during aging at high temperature. The thermal stabilizers that are used here are compounds that have antioxidant properties, the most important of which is the capacity

  to inhibit oxidation. An effective thermal stabilizer

  this in the practice of the invention must be able to

  protect the hot formed and thermoset poly article

  ester during exposure to high temperatures

  vee. US patents 3,987,004, 3,904,578 and 3,644,482

  describe many examples of thermal stabilizers

  what are known. The following compounds are

  representative examples of thermal stabilizers used

  in the practice of the invention: alkyl phenols,

  bisphenols, substituted bisphenols, thiobis-

  phenols, polyphenols, thiobisacrylates, ami-

  aromatic nes, organic phosphites and poly-

  phosphites. Particular aromatic amines which exhibit specific thermal stabilization properties include: primary polyamines,

  diarylamines, bisdiarylamines, diarylamines al-

  kyleas, ketone-diarylami- condensation products

  nes, aldehyde-amine condensation products and

  aldehyde-amines. The conditions considered

  me severe in the practice of the corresponding invention

  tooth on exposure of the hot formed article and ther-

  cured at temperatures close to 200 C for a period exceeding 30 minutes. Stabilizers

  preferred thermal for these applications at temperatures

  severe high erasures, especially when any

  coloring or any change in color due to sta-

  thermal binder is undesirable, are polyphenol type compounds having more than two structures

  cyclic phenolics. Useful polyphenols include

  not limited to: tetrakis (3- (3,5-di-tert-bu-

  tyl-4-hydroxyphenyl) methylene propionate) methane and

  1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hy-

  droxybenzyl) benzene. The latter polyphenol is particularly preferred. Thermal stabilizers

  can advantageously be added to

  concentrations up to 2% by weight, but particularly preferred the concentrations less than 0.05% by weight relative to the totality of the composition PET / polyolefin / stabilizer. The most preferred concentration is between 0.005 and

0.03% by weight.

  The antioxidant is added by mixing in the molten state directly in the polyolefin component of the

  polymer blend. It is therefore understood that the com-

  polyolefinic posing appropriately contains a

  higher percentage of antioxidant by weight

  requested in the final PET to polyolefin report. The con-

  particular concentration used is determined by the degree of protection required, the nature of the particular stabilizer chosen, the severity of exposure to

  heat and any limitation of solubility in the

  lyolefin. When the article produced according to the process

  of the invention is a food container, the regulations

  appropriate information regarding materials in contact

  with food should be taken into account and

  generally they set the upper limit of the quality of antioxidant that can be added to one or

  the other component and to the finished polymer blend.

  The process for manufacturing a polyethylene fine modified polyethylene terephthalate sheet comprises the steps of (1) melt-blending a suitable thermal stabilizer with a polyolefin derived from monoolefins having from 1 to

  4 carbon atoms to form a polyolafine sta-

  biliated; (2) heat the polyethylene terephthalate!

  having a vi: intrinsic viscosity of 0.65 to 1.2, above

  above its glass transition temperature in a dry atmosphere of air or nitrogen by maintaining it in this state until this rate of sufficient humidity = branch low to reduce hydrolytic degradation during the later stages of the process is reached; (3) if necessary conduct the stabilized fine polyol and the dried polyethylene terephthalate resin in appropriate proportions to an extruder or the

  two components are mixed in the molten state to form

  sea a homogeneous melted mixture; (4) form a sheet from the homogeneous molten mixture and (5) cool

  quickly the sheet to form an essen-

partially amorphous.

  The molten mixture of the thermal stabilizer

  mique can be performed in the postpolymerization stage

  polyolefin production or may be

  effected by using a conventional mixing extruder

  as for thermoplastic material which appropriately disperses the antioxidant in the polyethylene which has been

  melted in the body of the extruder The operative stage

  re in which the polyethylene terephthalate resin is heated in an anhydrous nitrogen atmosphere or

  air is required to maintain the viscosity

  resin resin. Any humidity, now

  with a sufficiently high intrinsic viscosity during

  in the remaining stages of the process is

  appropriate. It is advantageous to maintain the rate of

  the lowest possible humidity. Generally2 rates

  less than 0.02% are required. We prefer by-

  especially humidity levels below 0.005%

  for PET with high intrinsic viscosity.

  As the containers made in the invention should

  wind have good impact resistance and good

  dimensional stability, it is essential to handle-

  Carefully remove the PET to keep it vis-

* high intrinsic cosity. The mixture of polyole-

  fine containing antioxidant with dried PET can

  be carried out using a peel extrusion technique

  conventional known molecule in which the polyolefin and the PET are heated above their glass transition point and sheared by the molten material to form a homogeneous mixture of

  two different plastics. It seems that polyole-

  fine is dispersed throughout PET but con-

  serve his identity in a separate phase. The forming of the sheet can be carried out according to any conventional technique of forming a film. The sheets used in the following examples are produced with a Prodex film extruder in which the melted sheet is extruded on a cooled and immediately cooled casting roll.

  to minimize the growth of the crystal-

  linearity. Table 1 shows the sheet extrusion conditions used to produce the sheet

  amorphous used to prepare the tanks in the examples

ples of the description.

TABLE 1

CONDITIONS OF EXTRUSION OF SHEETS

  Size of the Prodex extruder of 4.45 cm (1.75 ") Extruder areas 288 C Neck cooling yes Screw cooling no Extruder speed 94 rpm Extruder pressure 19 MPa Intensity of the extruder 10.5 A Temperature of the polymer 296 C Zones of the ring 277 C Zones 1, 2 and 3 of the head all at 288 C Casting roller 1 75 C Casting roller 2 63QC Winding speed 1.2 mm / min Sheet dimensions 0.76 mm x 0.4 m

Material 97% PET / 3% LLDPE.

  The manufacture of wall-mounted thermosets

  thin from the leaf derived from the sta-

  polyolefin / PET binder can be produced by any known method of hot forming including

  vacuum forming, tire pre-stretching-

  matic, forming with pre-stretch on a punch or press forming. The mold should be preheated to

  a temperature sufficient to ensure the desired degree

  re of crystallinity. The choice of the optimum temperature

  male of the mold depends on the type of device

  hot mage, configuration and thickness

  walls of the articles to be molded and other factors.

  The practical range of mold temperatures is between 150 and 215 C. The preferred range is between

170 and 190 C.

  Thermosetting is a term for the process of thermal partial crystallization

  of a polyester article without proper orientation

  precarious happen. In the practice of the invention,

  thermosetting is obtained by maintaining a

  intimate touch between the film or the sheet and the surface

  face of the mold heated for a sufficient time to

  obtain a level of crystallinity conferring properties

  physical tees appropriate to the finished item. We have cons-

  It is believed that the desirable levels of crystallinity should be from about 10 to about 35%. For containers

  intended for use in food applications

  silencing at high temperatures, it has been found that crystallinity rates greater than 15% are necessary to ensure appropriate dimensional stability

  during demolding and during heating in the oven.

  The thermoset article can be separated from the

  mold cavity according to a known demolding process.

  In a process, the release with compressed air, we

  breaks the vacuum established between the mold and the sheet

  mée by introduction of compressed air. As soon as the thermoset article has been removed from the mold, the portion of the sheet remaining in the original plane state is removed to leave the tray finished. As most of the commercial hot forming molds have several cavities to produce several trays from a single sheet, the cutting of the trays leaves a flat matrix made up of the original sheet in which the outline of the trays is cut. 10 to 60% of

  the original sheet in the matrix that must be recycled

  key so that the hot forming operation is safe

  economically satisfactory. This recycling of the matrix implies that a very large amount

  thermal history is incorporated into the sheet. When 40% of the leaf is recycled, it is estimated that certain portions

of the polyolefin / PET mixture are

  subject to five complete recycling cycles. These cy-

  Recycling keys include: (1) grinding; (2)

  heating in a dry atmosphere; (3) the mix

  ge in the molten state with virgin material entering the system; (4) forming into a sheet; (5)

  rapid cooling; (6) the subsequent reheating

  laugh before introduction into the hot forming mold; (7) drawing and thermosetting in the hot forming machine; (8) cooling

  subsequent of the article; and (9) separation of the ar-

  ticle. All of these stages are repeated five times. So the resin is subjected to the very high temperatures of sheet making and hot forming for

  a time much higher than that which appears in the first

  first. This severe exposure to high temperatures affects the intrinsic viscosity of PET and the

  stability of the polyolefin component and, before!

  We were unaware that the method of protecting the

  the PET / polyolefin mixture was critical, particularly in operations where the recycling rate is close to

  %. In the following examples, a poly-

  ethylene terephthalate having intrinsic viscosity & -

  either from 1204 either separately or with linear low density polyethylene (LLDPE) supplied by Dow Chemical

  under the trade name Dowlex 2045 We are

  che and extrude the PET and LLDPE under the conditions of Table 1, then hot forming sheets of

  0.76 mm with a Comet Lab- hot forming machine

  master to obtain bins 13 cm x 13 cm deep 2.5 cm. All the percentages are weight percentages relative to the total weight of the composition,

polymer sheet or tray.

Unstabilized food containers

Examples 1-2

  A sheet of polyterephta- is formed in tubs

  ethylene latex having an intrinsic viscosity of 10O4.

  The intrinsic viscosity is determined after completion of the hot sealing of the tanks, then these tanks are aged at 200 ° C. in an air circulation oven for

  1 hour. The intrinsic viscosity is again determined

  that, the results appear in Table II on the line corresponding to Example 1. In Example 22

  using a sheet of 97% PET / 3% LLDPE without addi-

  antioxidant. The results which appear in Table II clearly show that PET alone or

  PET blended with a polyolefin, such as a polyethylene

  linear low density lene, show a decrease

  important of the intrinsic viscosity during the old-

  smoothing at high temperature when not

  not protected by an antioxidant or a stabilizing system

  health. This drop in intrinsic viscosity would be totally unacceptable in the food containers of Example 3 which are characteristic of articles produced without incorporation of antioxidant according to the

US Patent 4,463,121.

TABLE II

  Cm0) l'sitio .. i la, cuill- AO added Ade of addition of AO Effects of aging%%% Mixture PET in Traces of viscosity Color Example PET LIDPE AO PET IIEPE master the reactor with the intrinsic fingers LIDPE Initial 1 h at 200 C 1 100 OO mc 0 Nn - - - No 0.870 0.60 Stable 2 97 3 O - - - Cui 0.810 0.69 Stable 3 97 3 0.1 CQ ri - Yes - Yes 0.881 0.874 alteration of shade 4 97 3 0.19 (> to 9i Yes Yes - No 0, 888 ND change in shade 97 3 0O, 009 No yes - - Yes Yes 0.926 0, 929 Stable 6 97 3 0.0215 Nn Ocu - Yes very light 0.921 0.957 Stable 7 973 0.024 N- - Yes No 0.937 0.945 Stable * All aging is carried out for 1 hour at 200 C,

ND not available.

Comparative results

Examples 3-7

  All samples in this group of examples

  are prepared from PET / LLDPE sheets

  with varying concentrations of the antioxidant

  particularly preferred polyphole type, 1,3,3-

  trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, supplied by Ethel Corporation under the brand name Ethanox 330. The abbreviation "% AO" appearing in Table II under the composition of the leaf is the percentage of antioxidant relative to the weight of the total composition of the leaf. The aim of this series of experiments is to evaluate the effect of thermal aging at 200 C on three important properties of the tanks usable in microwave ovens and conventional ovens. These characteristics are: (1) the formation of fingerprints - this term designating a phenomenon which manifests itself in the form of alterations in

  the shade, irregular and widely spaced, on a swatch

  tillon of aged tank. Color change typically occurs on surfaces of the bin that have been touched by human hands. This formation of isolated spots is indicated in Table II by yes or no in the category "formation of traces

  of fingers "of the effects of aging. It is understood

  that if the indication is "yes" fingerprints appear after aging. If the indication is "no", the container retains its original uniform appearance; (2) color - the term color indicates the conservation or lack of conservation of the original color of the

  tray after one hour of aging at 200 C. The device

  rition of a change in color is manifested by

  a uniform change in the color of the tank. If the indi-

  cation in the "color" column is "stable" this in-

  indicates that the color has not changed after aging-

  is lying. If the indication is "color change" this-

  indicates that thermal aging has caused

  a significant degree of tint alteration; (3) visco-

  intrinsic sity - intrinsic viscosity tends to decrease

  nuer when the PET is subjected to a high temperature.

  The original intrinsic viscosity is determined and compared with the intrinsic viscosity after one hour at 2000 C. The variables of Examples 3 to 7 include the concentration of AO, the component to which 1 A 0 is added and the method of adding the AOo

Example 3

  In Example 3, 0.1% AO is added to the PET

  in the melting phase during the production of poly-

  mother polyethylene terephthalate. The intrinsic viscosity

  sèque maintains itself satisfactorily, but the

  relatively high concentration of AO in PET

  tribute to the alteration of the color of the PET polymer used

  read in the mixture. This change in hue

  usually consists of yellowing to a browning

  normally milky white shade of the resi-

  do virgin PET. It seems that the high temperatures during the production of PET and the prolonged maintenance of a high temperature during the stay in the state

  solid of the base resin having an intrinsic viscosity

  high dryness (1.04) contribute to the overall alteration of the shade. This color change is very undesirable in applications such as tubs

  food. In addition, aged samples pre-

  feel fingerprints that are also unhealthy

satisfying.

Example 4

  Example 4 corresponds to a mixture identical to the composition of polymers of Example 3 but with the addition of 0.19% of antioxidant. The antioxidant is

  added to both the PET in the reactor and the poly-

  linear low density ethylene in the masterbatch.

  The column "masterbatch" sub-header "mode of ad-

  dition of AO "indicates a procedure comprising an initial stage of preparation of a masterbatch in which PET and LLDPE are mechanically mixed in a ratio of 77/23 in the form of particles in

  pastilles to form a mixture-maltre.

  Next, we conduct this PET malt mix

  and linear low density polyethylene in a former

  Prodex film extruder, along with a re-

  sine PET, in a ratio of 13 to 87% by weight to finally obtain a percentage of LLDPE of 3 and a

  percentage of PET of 97. This process using a

  the masterbatch ensures an improvement in the dispersion of the polyethylene in the PET in the case where the feed hoppers of the film extruder are not

  precisely calibrated to ensure percentages

  resin ages as low as 3%. The viscosity in-

  is maintained and there is no tra-

  these of fingers, however, a deterioration of the tint-

  te bins occurs with this higher concentration of the antioxidant. The antioxidant has a tendency

  clear to yellowing when added

  relatively high ratios to the PET / polyole-

fine.

Examples 5-7

  Film sheets are prepared by em-

  use of a mixture in a ratio of percentages

  97/3 PET / LLDPE targets with various percentages

  antioxidant. This series uses the process of in-

  vention in which the antioxidant is added to the poly-

  linear low density ethylene before any incorporation

  tion with PET. No antioxidant is added to PET and this method corresponds to the column "directly to

  LLDPE "under the header" mode of addition of AO "from Ta-

  bleau II. In this process, the antioxidant is added to

  polyolefin by partially recasting the polyolefin

  cules and homogeneous mixture of the desired amount of an-

  antioxidant to the polyolefin then transformation of the

  resin melted into particles of desired shape such as

  as pellets, granules formed by agglo-

  meration or other desirable forms. This mixture

  is carried out in a Sterling Transfer- extruder

  mix whose body temperature is kept at-

  about 195 C and that of the head at 175 C. The screw turns-

  do at 84 rpm. Then we mix precisely

  low density linear polyolefin with PET

  at the entrance to the neck of the film extruder.

  The film extruder homogeneously mixes PET with stabilized low density linear polyolefin to form a uniform molten mixture. Results regarding aging properties

  tubs made of stabilized poly-based blends

  olefin which appear in Table II show that, even for extremely low concentrations of the antioxidant, the intrinsic viscosity is maintained and the color of the tank is stable over one hour

  of aging at 200 C. In Example 5, where we use

  reads 0.009% by weight of antioxidant, fingerprints appear, while in Example 6, where a slightly higher concentration of

  antioxidant, only barely visible fingerprints

  sibles appear. In Example 7, which uses 0.024

  % by weight of AO, there are no fingerprints.

  This is in sharp contrast to Example 3 in which

  almost eight times the concentration of the year

  antioxidant is necessary to eliminate the formation of fingerprints and where the resin has a color

  unwanted yellow after aging.

  Recycling tests Examples 8-22 When making containers by hot forming from a flat sheet, a typical hot forming process produces around 40% of

  sheets after each forming and cutting cycle.

  The leaf must be shredded and mixed with the material.

  re first virgin made of PET / polyolefin for

  be reused. This recycling gives the polymer mixture

  re a considerable thermal history leading to degradation problems, such as weathering

  hue, the formation of fingerprints,

  decrease in intrinsic viscosity and changes

  tions of crystallinity. To produce food trays

  acceptable hot formed, all pro-

  properties and all previous faults must be

  stabilized or eliminated in a commercial process

  reading notable percentages of crushed waste.

  A typical hot forming process produces up to

  % of shredded waste. The simulation of the operation

  ment in regular regime of such a forming system at

  hot implies that in the ground waste the same re-

  sine is subjected to operations approximately five times

  taken between the preparation of the sheet and the therm

  moforming of the tanks. Therefore, the pattern of experience

  Next, which simulates the reuse of 40% of shredded waste, has a five-cycle system for

  evaluation of thermal stability. The resin used

  is made up of 97% PET (intrinsic viscosity

  dry 1.04), 3% of linear low density polyethylene Dowlex 2045 supplied by Dow Chemical Company and 0.015% of Ethanox 330 supplied by Ethel Corporation. The antioxidant is mixed in the molten state with LLDPE using a Sterling Transfermix extruder then it is transformed into granules which are then mixed in an extruder

  45 mm (1.75 inch) Prodex wrap with PET.

  The operating stages are as follows: (1) the resin / ground waste mixtures are dried

  for 4 hours at 170 C in a dehumidifier hopper

  Conair fication having a dry nitrogen atmosphere, (2) after drying, each sample is placed in a vacuum oven at 100 C to dry it and equilibrate it at the temperature of 1000C, (3) the resin is placed 1000C in the extruder hopper and mixed with stabilized LLDPE

  with an antioxidant to obtain the percentage of

  correct lange, (4) the mixed material is extruded into an amorphous sheet according to the indications previously indicated in table 1, (5) the test trays are hot formed in a Comet Labmaster hot forming machine under the following conditions : preheating time in the oven 12 seconds, oven temperatures 315 C at the top, 225cC at the bottom, molding time 0 seconds,

molding temperature 160 C.

  The excess and unformed portions of the sheet are separated by cutting from the thermoformed trays to obtain a matrix intended to be treated again by recycling, (6) the matrix consisting of the remaining unformed sheet is crystallized at 150 ° C., it is cooled and ground by passing it through a 0.6 mm sieve and mixed with a free PET / LLDPE 97/3 resin in a new resin / shredded waste ratio of 60/40. This mixture of resin and waste is dried

  crushed according to stage 1 and the experimental stages are repeated

  1 to 6 for five cycles. The following properties of the tanks are determined for each of the five cycles: (1) intrinsic viscosity; (2) value "B" with Hunter colorimeter; and (3) percentage of crystallinity calculated from the densities of the tanks. All

  results are shown in Table III.

TABLE III

  Viscosity Value of the Exenple Intrinsic color identification * Density% of crystallinity

  8 shredding of sheet waste 0.877 - 5.5 1.325 -

  9 un aged bin 0.868 - 4.1 1.349 21.3 aged bin 0.859 - 1.4 1.360 31.0

  1st crushing of sheet waste 0.890 - 5.2 1.321 -

  12 un aged bin 0.884 - 4.2 1.341 12.7 13 aged bin 0.868 -2.1 1.361 35.4

  14 3 & me shredding of sheet waste 0.894 - 4.0 1.318 -

  un aged bin 0.886 - 4.0 1.352 30.1 16 aged bin 0.852 - 1.4 1.357 34.5

  17 4th shredding of sheet waste 0.902 - 4.1 1.320 -

  18 unriped bin 0.920 - 4.4 1.350 26.6 19 aged bin 0.880 - 1.7 1, 359 34.5

  5th donut crushing leaf waste 0.886 - 4.8 1.319 -

  21 non-aged tank 0.853 - 4.0 1.352 29.2 22 aged tank 0.885 - 2.0 1, 362 38.1

  "b" value determined with a Hunter Lab Color Tester.

  The values shown in Table III show that the tubs made from film

  whose antioxidant has been added to the polyole-

  finish has excellent retention of intrinsic viscosity, good retention of

  color and excellent crystal regulation

  nity during five waste shredding cycles.

  This degree of stability indicates that the material used

  sant this polyolefin stabilization process

  before the addition of PETt can be recycled by name-

  times without altering the resistance properties

  mechanical and appearance of finished tanks. This apti-

  recycling study is crucial in operations

  commercial hot forming in which the waste

matrix can exceed 40%.

Claims (20)

  1. Method for manufacturing a sheet of polyethylene terephthalate modified with a polyolefin   and recyclable, characterized by the stages which consis-   tent a: (a) mix an effective amount in the melt   a thermal stabilizer with a polyolefin derivative   of olefinic monomers containing from 2 to 6 carbon atoms to form a stabilized polyolefin; (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 C in a dry atmosphere for one   sufficient time to reduce the moisture content of the poly-   ethylene terephthalate below 0.02% by weight to form a dry polyethylene terephthalate; (c) simultaneously conduct the polyterephthalate   dry ethylene and the polyolefin stabilized to a dispo-   molten mixing sitf; (d) mixing a small amount of the stabilized polyolefin with a major amount of dry ethylene terephthalate to form a mixture; (e) mixing the mixture in the molten state to form a homogeneous molten mixture; (f) forming a sheet from the homogeneous molten mixture;   (g) cooling said sheet to form a sheet   the essentially amorphous; (h) placing the amorphous sheet on a mold; (i) hot forming said sheet in a heated mold for a time sufficient to obtain partial crystallization of the amorphous sheet; (j) demolding the partially crystalline sheet from the heated mold; (k) remove the portion of the leaf that has been   contact with the mold surface to leave a   trice; and (1) grinding the matrix to form ground waste and heating the ground waste according to stage (b) and mixing the ground waste with the mixture formed in stage (d) and repeating stages (e) to (1) at least once more.   2. Method according to claim 1, charac-   terized in that the polyolefin is polyethylene.   3. Method according to claim -1 charac-   terized in that the polyathyne is polyethylen! linear low density.   4. The method of claim 1, caraco terized in that the polyethylene is a linear low density polyethylene and the thermal stabilizer is a polyphenol selected from the group consisting of 1,3,5 trimethyl'2- 4,6-tris (3 , 5-di-tert-but-yl-4hydro =   xybenzyl) benzlne and tetrakis (3- (3,5-di-tert-butyl-   Niethylene 4-hydroxyphenyl) ropionate) methaneo o Process according to claim 1, characterized in that the effective amount of the stabilizer   thermal is less than 0.05% by weight.   6. Method according to claim 1, charac-   terized in that the effective amount of the thermal stabilizer is from about 0.005 to about 0.03% by weight.   7. Method according to claim 1, charac-   téri in that said thermal stabilizer is the   1,3,5-t imethyl-2,4,6-tris (3,5-di = tert-butyl-4-hydro- xybenzyl) -benzene;   8. Method for manufacturing an absorbed sheet   thermostable plaice of modified ethylene polyterephthalate   bound by a polyolefin characterized by the stages which consist in: (a) mixing in the molten state an effective amount   a thermal stabilizer with a polyolefin derivative   of olefinic monomers containing 2 to 6 carbon atoms to form a stabilized polyolefin, (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 C in a dry atmosphere for a time sufficient to reduce the moisture content of the polyethylene terephthalate below 0.02% by weight to form a dry polyethylene terephthalate, (c) mixing a small amount of the polyolefin   stabilized with a major amount of polyterephthala-   te of dry ethylene to form a homogeneous molten mixture, (d) form a sheet from the homogeneous molten mixture, and   (e) cooling said sheet to form a sheet the essentially amorphous.   9. Method according to claim 8, character-   laughed in that the polyolefin is polyethylene.   10. The method of claim 8, character-   laughed at in that the polyethylene is linear polyethylene low density area.   11. The method of claim 8, character-   that the polyethylene is linear polyethylene   low density area and the thermal stabilizer is a   polyphenol selected from the group consisting of 1,3,5-   trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl)   benzene and tetrakis (3- (3,5-di-tert-butyl-4-hydroxy-   methylene phenyl) -propionate) methane.   12. Method according to claim 8, character-   laughed at that the effective amount of stabilizer ther-   mique is less than 0.05% by weight.   13. The method of claim 8, character-   laughed at that the effective amount of stabilizer ther-   mique is from about 0.005 to about 0.03% by weight.   14. The method of claim 8, character-   laughed at in that said thermal stabilizer is 1,3,5-   trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene.   15. Method of manufacturing a thermal article   mostable partially crystalline thermoset and undirected, characterized by the stages which consist in: (a) mixing in the molten state an effective quantity of a thermal stabilizer with a derived polyolefin   olefinic monomers containing 2 to 6 carbon atoms   bone to form a stabilized polyolefin, (b) heating a polyethylene terephthalate having an intrinsic viscosity of about 0.65 to about 1.2 to at least 150 C in a dry atmosphere for a time sufficient to reduce the rate of humidity of polyethylene terephthalate below 0.02% by weight to form a dry polyethylene terephthalate, (c) simultaneously conducting said polyterephthalate   dry ethylene and polyolefin stabilized at a dis-   positive melt blend, (d) blend a small amount of the polyolefin   stabilized with a major amount of polyterhephta-   dry ethylene late to form a homogeneous molten mixture uncomfortable,   (e) forming a sheet from said dark mixture   homogeneous, (f) placing said amorphous sheet on a mold, (g) hot forming said sheet to form a   article in a mold heated for a sufficient time   health to obtain a crystallinity between 15 and 35%, (h) removing the article from said heated mold, and   (i) cutting the article from said sheet.   16. The method of claim 15, charac-   terized in that the polyolefin is polyethylene.   17. The method of claim 15, charac-   terized in that the polyethylene is a polyethylene linear low density.   18. The method of claim 15, charac-   terized in that the polyethylene is a linear low density polyethylene and the thermal stabilizer is a polyphenol chosen from the group consisting of   1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydro-   xybenzyl) benzene and tetrakis (3- (3,5-di-tert-butyl-   Methylene 4-hydroxyphenyl) -propionate) methane.   19. The method of claim 15, charac-   terized in that the effective amount of the stabilizer   thermal is less than 0.05% by weight.   20. The method of claim 15, ca-   characterized in that the effective amount of stabilizer   thermal health is about 0.005 to about 0.03% in weight.   21. The method of claim 15, ca-   characterized in that said thermal stabilizer is   1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4- hydroxybenzyl) benzene.