GB2124236A

GB2124236A - Polyester moulding compositions and ovenware therefrom

Info

Publication number: GB2124236A
Application number: GB08318051A
Authority: GB
Inventors: Joseph John Duska; Arnold Baron Finestone; John Bernard Maher
Original assignee: Dart Industries Inc
Current assignee: Dart Industries Inc
Priority date: 1982-07-26
Filing date: 1983-07-04
Publication date: 1984-02-15
Also published as: DE3326733C2; GB8318051D0; IE831046L; SE8304131L; IT1173669B; IT8322179A0; PT77078A; IT8322179A1; KR840005473A; NO832187L; DK338983A; PT77078B; FI831780A0; PH19608A; FR2537149B1; ES8602884A1; AU561068B2; SE8304131D0; AU1449683A; CH663141A5

Abstract

Permanent ovenware capable of repeated use in both conventional thermal and microwave ovens fabricated from wholly aromatic polyester compositions and, more particularly, from oxybenzoyl polyester compositions containing from 1% to 60% by weight of talc containing a minimum content of materials decomposable at elevated temperatures.

Description

SPECIFICATION Polyester moulding compositions and ovenware therefrom Certain plastics materials have found application in the ovenware field. For example, polymethylpentene has been used for injection molded trays which can be used in the preparation of foods.

Polysulfone has also been employed in food handling applications. However, no satisfactory material has been found possessing utiiity over the wide ranges of conditions and of demands which are encountered in the provision of cook-in containers, or ovenware, which can be used in either thermal ovens or microwave ovens.

In addition to the obvious necessity for a material which can withstand the temperatures met in the heat source used for cooking, a material must provide a unique combination of a number of other characteristics before ovenware fabricated from the material can be successfully employed in the preparation of food. The material must have good electrical properties It must be able to undergo severe thermal shocks in that ovenware prepared from it must be capable of going from conditions of extreme cold to high temperatures in relatively brief periods of time. The material must have good hardness and impact strength and possess high tensile and flexural strength. It must also be resistant to boiling water, food acids and fats and to adverse effects from immersion in detergents.

In the area of food related properties the material must impart to the ovenware fabricated from it resistance to staining by a wide variety of foodstuffs. It must provide a surface affording good antistick properties, ready releasability for the food which it contains. it must not emit or give off any volatile matter and it must not have any extractable constituent. And in addition to meeting all of the foregoing requiremenfs, articles prepared from it must present a pleasing and generally uniform appearance in order to be marketable.

The present invention provides an aromatic polyester moulding composition suitable for use in the fabrication of ovenware. The aromatic polyester moulding composition of the invention comprises at least 35% by weight of aromatic polyester and from 1% to 60% by weight of a talc containing a minimum content of materials decomposable at elevated temperatures.

Ovenware meeting the stringent demands of the cook-in container market is provided by fabricating ovenware articles from the moulding composition of the invention.

The wholly aromatic polyesters employed in accordance with the present invention preferably are oxybenzoyl polyesters, and more preferably contain one or more recurrent moiety selected from groups of the following formulae:

where X is a direct bond, 0, S,

NH, or SO2 and n is O or 1 and the total of the integers p+q+r+s+t+u in the moieties present is from 3 to 800.

Combinations of the above units include union of the carbonyl group of Formulae I, II, IV and V with the oxy group of Formulae I, III, IV and VI. In the most general combination units of all the above formulae can be present in a single copolymer. The simplest embodiment would be homopoiymers consisting of units I or IV. Other combinations include mixtures of units II and III, II and VI, Ill and V, V and Vl, and í and IV.

The functional groups attached to benzene rings are preferably in the para (1, 4) positions, but can be located in ortho (1, 2) positions. With respect to the groups containing naphthalene rings, the most desirable locations of the functional groups are 1,4; 1,5 and 2,6, but the groups can also be in the ortho positions.

The symbols p, q, r, s, t and u are 0 or integers and indicate the number of moieties present in the polymer. The total (p+q+r+s+t+u) can vary from 3 to 800 and, when present, the ratio of q/r, c/u, t/r, t/u, q+t/r, q+t/r+u and t/r+u can vary from about 10/11 to about 11/1 0 with the most preferable ratio being 10/10.

Exemplary of materials from which the groups of Formula I may be obtained are p-hydroxybenzoic acid and esters such as phenyl p-hydroxybenzoate, p-acetoxybenzoic acid and isobutyl pacetoxybenzoate. Monomers from which groups of Formula II are derivable include terephthalic acid, isophthalic acid, diphenyl terephthalate, diethyl isophthalate, methylethyl terephthalate and the isobutyl half ester of terephthalic acid. Among the compounds from which the groups of Formula Ill result are p,p'-biphenol; 4,4'-dihydroxybenzophenone; resorcinol and hydroquinone.

Examples of monomers which yield groups represented by Formula IV are 2-hydroxy-6-naphthoic acid; 6-hydroxy-1 -naphthoic acid; 5-acetoxy-1 -naphthoic acid and phenyl 5-hydroxy-1 -naphthoate.

Monomers which yield groups represented by Formula V include 1 ,4-naphthalenedicarboxylic acid; 1 ,5-naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid. The diphenyl esters or dicarbonyl chlorides of these acids can also be used. Examples of monomers which yield groups of Formula VI are 1 ,4-dihydroxynaphthalene; 2,6-diacetoxynaphthalene and 1 ,5-dihydroxynaphthalene.

Particularly preferred for use in the practice of the present invention are monomers which yield oxybenzoyl polyesters.

A preferred class of oxybenzoyl polyesters are copolyesters having recurring units of each of Formulae VII, VIII and IX:

wherein x is --OO- or m isO or 1; n isO or 1; q:r=1 0:15 to 15:10; p:q=1 :100 to 100:1; p+q+r=3 to 600, preferably 20 to 200; the carbonyl groups of the moiety of Formula VII or VIII are linked to the oxy groups of the moiety of Formula VII or IX; and the oxy groups of the moiety of Formula VII or IX are linked to the carbonyl groups of the moiety of Formula Vil or VI II.

Another group of aromatic polyesters which can be employed are the aromatic polyesters containing recurring units of the 2,6-dicarboxynapitthalene moiety and/or the p-oxybenzoyl moiety and symmetrical dioxy aryl moiety, and variations thereof. Such polyesters are disclosed in U.S. Patents Nos. 4,067,852; 4,083,829; 4,130,545; 4,161,470; 4,184,996; 4,219,461; 4,224,433; 4,238,598; 4,238,599; 4,256,624; 4,265,802; 4,279,803; 4,318,841 and 4,318,842.

The preferred copolyesters are those containing recurring units of Formula X:

The synthesis of these polyesters is described in detail in U.S. Pat. No. 3,637,595, entitled "P Oxybenzoyl Copolyesters".

The polyesters useful in the present invention can also be chemically modified by various means such as by inclusion in the polyester of monofunctional reactants such as benzoic acid or tri or higher functional reactants such as trimesic acid. The benzene rings in these polyesters are preferably unsubstituted but can be substituted with non-interfering substituents.

The oxybenzoyl polyesters useful in the present invention can be employed with various fillers of types and in amounts which either promote or at a minimum do not materially affect the desired properties. Examples of suitable fillers include among others glass fibers, milled glass, polytetrafluoroethylene and pigments and mixtures thereof.

While ovenware prepared from compositions comprising the oxybenzoyl polyesters and the various fillers recited above meet most of the general requirements recited earlier, they do not have the uniform, pleasing appearance necessary for a commercially marketable product. In addition, it has been observed that many of the fillers create excess bubbling in the ovenware products at elevated temperatures.

It has been found in accordance with the present invention that a uniform and pleasing appearance can be imparted to the ovenware articles and the undesirable bubbling suppressed or minimized by the inclusion in the oxybenzoyl compositions from which they are molded of talc which contains a minimum amount of materials decomposable at elevated temperatures, e.g. up to 8000 C, such as magnesium carbonate. Among such talcs are talcs which are of high purity, are selectively refined from various ores or have been calcined or subjected to acid treatment.

These talcs which are employed according to the present invention are characterized by a low weight loss of ignition, a low iron content analyzed as iron oxide and a closely controlled particle size.

The weight loss on ignition of the suitable tabs is not more than 6% at 9500C and is 2% or less at 8O00C. The iron content analyzed as iron oxide (Fe203) will be not more than about 1% and that of the particularly preferred talcs will be not more than 0.6% and may be less.

Experiments and tests carried out have demonstrated quite conclusiveiy that it is essential to use such talc in orderto realize the objectives of the present invention. The use of otherforms of talc do not provide satisfactory properties in the finished molded product. However, such other forms of talc can be employed in conjunction with the specified talcs in amounts of from 0.05% to 20% of the required forms of talc.

The talcs containing the minimum amount of decomposable material will be present in amounts of from 1% to 60% based on the total composition weight with the preferred range being from 35% to 55%.

Rutile titanium dioxide can also be employed in conjunction with the talc material, including mixtures of highly refined talcs and other talc. The rutile titanium dioxide when present is suitably used in an amount of from 2% to 20%, preferably 5% to 15%;based on the weight of the total composition.

In the molding composition of the present invention, the resin will generally comprise from 35% to 85% and the total inerts from 65% to 15%, by weight of the composition. For optimum results, the inerts will comprise from 40% to 55% of the molding composition. The inerts suitably comprise up to 55% of highly refined talc and from 0 to 10% of titanium dioxide, by weight of the composition.

While all of the resins hereinbefore described are suitable for use in the present invention, it is preferred to employ an aromatic polyester resin in which units derived from a dibasic acid, hydroxy aromatic acid and aromatic diol are present in the molar proportions of about 1:2:1. Other molar proportions can be employed and resins have been used in which the molar proportions of, illustratively, terephthalic acid, p-hydroxybenzoic acid and biphenol are 1:3:1, 1:5:1, 1:7:1 and 1:3.5:1.

Physical blends of resins in which various proportions of reactants have been employed are also suitable for use.

The compositions of the present invention can be prepared by extrusion in accordance with generally known practice. For example, a twin screw extruder can be employed with addition of the polymer, selected talc and titanium dioxide at the feed throat and with addition of the glass roving at both the vent and feed throat.

The compositions so prepared can then be injection molded according to general practice using techniques familiar to the injection molding field.

The invention will be further described by reference to the following Examples in which all parts and percentages are by weight unless otherwise indicated. Examples 1 to 8 illustrate the synthesis of a copolyester useful in the present invention, while Examples 9 to 18 illustrate molding compositions of the invention.

Example 1 The following quantities of the following ingredients are combined as indicated:- Quantity Item Ingredient Grams Moles A P-hydroxybenzoic acid 138 1 B Phenyl acetate 170 1.25 C Therminol 77 500 D Diphenyl terephthalate 318 1 E Hydrogen chloride ~~~~ F Hydroquinone 111 1.01 G Therminol 77 500 Items A-D are charged to a four-necked, round bottom flask fitted with a thermometer, a stirrer, a combined nitrogen and HCI inlet and an outlet connected to a condenser. Nitrogen is passed slowiy through the inlet. The flask and its contents are heated to 1 800C whereupon HCl is bubbled through the reaction mixture.The outlet head temperature is kept at 1 100--1200C by external heating during the p-hydroxybenzoic acid, phenyl acetate ester exchange reaction.

The flask and its contents are stirred at 1 800C for 6 hours whereupon the HCI is shut off, the outlet head temperature raised for 180-1 900C and the mixture stirred at 22O0C for 3.5 hours. Up to this point, 1 59 grams of distillate are collected in the condenser. Item F is then added and the temperature gradually increased from 2200C to 3200C over a period of 10 hours(lOOC/hr). Stirring is continued at 3200C for 1 6 hours and then for three additional hours at 3400C to form a slurry. The total amount of distillate, consisting of phenol, acetic acid and phenyl acetate, amounts to 384 g.Item G is added and the reaction mixture permitted to cool to 700 C. Acetone (750 ml) is added and the slurry filtered, the solids are extracted in a Soxhlet with acetone to remove items C and G. The solids are dried in vacuo at 11 00C overnight whereupon the resultant copolyester (320 g, 89.2% of theory) is recovered as a granular powder.

Example 2 518 parts of isophthalic acid, 1,557 parts of terephthalic acid, 5,1 75 parts of para-hydroxybenzoic acid, 6,885 parts of acetic anhydride and 2,325 parts of p,p'-bisphenol are mixed together and refluxed for 1 7 hours, at a temperature of about 180"C, after which the reflux condenser is replaced with a distilling head and the temperature is raised to 3450C over a period of 1.25 hours. The reaction mixture is stirred throughout the heating period, being particularly actively mixed during the period in which the temperature is being raised to 3450 C. The yield of polymer is 8,020 parts and 8,010 parts of distillate are recovered. The contents of the reaction vessei are removed, cooled and ground to particle sizes in the 20 to 1 60 mesh range, U.S. Standard Sieve Series.The resin made is of a molecular weight in the 5,000--20,000 range, with an average weight in about the middle of such range. The product is estimated to be about 50% crystalline.

The resin particles are held under vacuum illustratively at an elevated temperature at an absolute pressure of about 100 mm of mercury (13 kPa) for eight hours and recovered as a granular powder.

Example 3 The following quantities of the following ingredients are combined as indicated.

Quantity Item Ingredient Grams Moles A Terephthalicacid 291 1.75 B P-Hydroxybenzoic acid 483 3.50 C p,p'-biphenol 325 1.75 D Acetic anhydride 755 7.40 Items A-D are heated to 1 450C and refluxed overnight. The reflux condenser is removed and a distilling head put in place. The mixture is heated with stirring at a rate of 200 C/hour to 3000C and the contents of the reactor removed. At this point, about 9294% of the theoretical acetic acid is collected. The prepolymer is ground up and advanced as in Example 2, employing a temperature of about250--3750C.

Example 4 Quantity Item Ingredient Grams Moles A P-Hydroxybenzoic acid 276.0 (2.00) B Terephthaloyl chloride 203 1.0 C Trimesic acid 8.4 0.040 D Therminol 66 1274 E p,p'-biphenol 186 1.0 F Acetic anhydride 224.6 2.2 Items A-D are heated to 1 300C and held one hour. The reaction is exothermic and care is taken to maintain temperature at 1 300C. The contents are then heated at 1 550C for one hour and 180"C for 4 hours. The mixture is then cooled to 1 500C and item E added whereby the temperature is further reduced to 1400 C. Item F is then added. This mixture is then refluxed one hour at 1 550C and the reflux condenser replaced by a distillation column.While distilling the acetic acid formed, the contents of the reactor are heated to 330 C and held 3 hours. The suspended polymer is cooled to 2500C and the mixture passed through a filter. The solid material is worked with trichloroethylene to remove the heat transfer fluid. The dried powder is advanced further in vacuum as in Example 2.

Examples 5,6 and 7 The procedure of Example 3 is repeated employing the quantities of the ingredients indicated.

Quantity in moles Item Ingredient Ex. 5 Ex. 6 Ex. 7 A Terephthalic acid 1 1 1 B p-Hydroxybenzoic acid 3 4 5 C p,p'-biphenol 1 1 1 D Acetic anhydride Example 8 268 parts of biphenoi, 396 parts of para-hydroxybenzoic acid, 693.40 parts of acetic anhydride and 238 parts of terephthalic acid are mixed and heated to a temperature of 31 50C over a period of 5 hours at a 300C per hour rate of rise for the temperature. The reaction mixture is stirred throughout the heating period. When the temperature of 31 50C is reached, the polymer contents are removed from the reaction vessel and ground to a particle size in the 20 to 200 mesh range, U.S. Standard Sieve Series.The resin particles are incrementally advanced in an oven to a temperature of 3540C over a period of 1 6 hours and recovered as a granular powder.

Example 9 A molding composition was prepared from the polymer of Example 8 by extruding a mixture of 257.5 parts of the polymer of Example 8, 30 parts of rutile titanium dioxide and 212.5 parts of a high purity talc having the platy structure of natural talc, a loss on ignition of 2% weight percent, an iron content analyzed as Fe2O3 of 0.5% and a particle size distribution in which over 95% of the particles are less than 40 micrometers.

The resulting blend was injection molded to provide molded bowls of a uniform, pleasing appearance which showed no cracking or blistering at minimum temperatures of about 260"C.

Certain of the molded articles were subjected to a stain test in which a dollop of barbecue sauce was placed on the bottom of the molded container. The container was then placed in a 1 77CC (350"F) preheated oven for one hour. At this time the sauce was thick, dark and crusty. After cooling the container was washed with soap and water using a Scrunge pad. The container was examined for stain and the color difference between stain and unstained areas noted. The difference observed was very slight.

Certain other specimens were subjected to a drop test in which five specimens were dropped on their top outside perimeter from continually increasing heights in order to determine their ability to withstand the drop impact without appreciabie damage. The average for these specimens was 100 cm (40 inches).

The results of these tests all indicate the suitability of the molded articles for use as cook-in containers for food.

Example 10 A molding composition was prepared from a polymer produced in accordance with Example 8 by extruding a mixture of 271 parts of polymer and 10 parts of the talc employed in Example 9.

The resuiting blend was injection molded at a screw speed of 100 rpm, an injection pressure of 14 MPa (2000 psi) and at temperature settings of 3550C in Zone 1, 3600C in Zone 2 and 3450C in Zones 3 and 4.

Molded articles of generally pleasing appearance were obtained.

Examples 11-18 In these Examples, 257.5 parts of the resin products of Examples 1-8 were mixed with 202.5 parts of the talc employed in Example 9 and 40 parts of the rutile titanium dioxide by passage through a twin-screw extruder. The reinforced resinous compositions obtained were shaped by injection molding. The molded articles obtained were satisfactory in appearance and in resistance to cracking and blistering at elevated temperatures.

Claims

1. An aromatic polyester moulding composition comprising at least 35% by weight of aromatic polyester and from 1% to 60% by weight of a talc containing a minimum content of materials decomposable at elevated temperatures.

2. A composition according to claim 1 containing from 2% to 20% by weight of rutile titanium dioxide.

3. A composition according to claim 2 wherein the amount of rutile titanium dioxide is from 5% by weight to 1 5% by weight.

4. A composition according to claim 1,2 or 3 wherein the talc has a weight loss on ignition of not more than 6% by weight at 95O0C, and an iron content analyzed as iron oxide of not more than 1% by weight.

5. A composition according to any one of the preceding claims wherein the amount of talc is from 35% by weight to 55% by weight.

6. A composition according to any one of the preceding claims wherein the talc is selected from high purity talc, highly refined talc, calcined talc and acid-treated talc.

7. A composition according to any one of the preceding claims wherein the aromatic polyester is an oxybenzoyl polyester.

8. A composition according to claim 7 wherein the oxybenzoyl polyester contains one or more recurrent moiety selected from groups of the following formulae:

where X is a direct bond, 0, S,

9. A composition according to claim 8 in which the ratios of c/r, q/u, t/r, t/u, q+t/r+u and t/t+u, when present, are from about 10/10 to about 11/10.

10. A composition according to claim 9 in which the ratios are 10/10.

11. A composition according to claim 8, 9 or 10 wherein p+q+r=20 to 200.

12. A composition according to claim 7 wherein the oxybenzoyl polyester has recurring units of each Formulae VII, VIII and IX:

wherein x isOorS 2; m is O or 1; n is O or 1; q:r=10:15 to 15:10; p:q=1 :100 to 100:1; p+q+r=3 to 600; the carbonyl groups of the moiety of Formula VII or VIII are linked to the oxy groups of the moiety of Formula VII or iX; and the oxy groups of the moiety of Formula VII or IX are linked to the carbonyl groups of the moiety of Formula VII or VIII.

1 3. A composition according to claim 7 wherein the oxybenzoyl polyester has recurring units of the formula:

14. A composition according to claim 1 substantially as described with reference to any one of Examples 9 to 18.

1 5. Ovenware comprising a moulded articie of an aromatic polyester moulding composition as claimed in any one of the preceding claims.

1 6. A process of preparing food in a permanent cook-in container capable of repeated usage which comprises placing the food in ovenware-as claimed in claim 15 and heating the food to serving temperature.

1 7. A process according to claim 1 6 wherein the heat source is thermal.

1 8. A process according to claim 1 6 wherein the heat source is microwave.