Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Reexamination Certificate
2001-11-15
2004-11-16
Eashoo, Mark (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
C264S177190, C264S211000, C264S212000
Reexamination Certificate
active
06818160
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to films of poly(trimethylene terephthalate). This invention specifically relates to methods to produce cast films of poly(trimethylene terephthalate) which reduce brittleness of the film on thermal aging, among other benefits.
BACKGROUND OF THE INVENTION
Poly(trimethylene terephthalate), herein abbreviated 3GT, also referred to as polypropylene terephthalate, may be useful in many materials and products in which polyesters are currently used, for example films, carpet fibers, textile fibers, miscellaneous industrial fibers, containers and packaging.
British Patent 578,097 disclosed the synthesis of poly(trimethylene terephthalate) in 1941. The polymer itself is currently commercially available from Shell.
Poly(trimethylene terephthalate) has been contemplated for use in films. Japanese Patent Application JP 08104763 A2 discloses polyester films composed of polypropylene terephthalate, wherein the number of carboxyl end groups in the polyester film is no more than 40 eq/t. To date, the drawbacks of films made from 3GT include loss of tensile properties on aging, e.g., a decrease of more than 50% in elongation at break. Aging is related to ‘organization’ in the glassy regions of the polymer. It is not related to crystallization, which occurs in crystalline regions. Loss in elongation at break is widely used as evidence of aging because elongation is so easy to measure, but other mechanical properties, such as toughness, also decrease. Properties such as heat-sealability, which are related to performance in amorphous regions, are also affected by aging. Aging is accelerated by heating, but will eventually occur even in the absence of heat.
A need still exists for improved cast films of poly(trimethylene terephthalate), and copolymers thereof, which retain tensile properties upon aging.
SUMMARY OF THE INVENTION
The invention herein provides a method to improve the retention of tensile properties upon aging in 3GT cast film comprising the steps of:
(a) prior to film formation, nucleating 3GT resin by adding the mono-sodium salt of a dicarboxylic acid selected from the group consisting of monosodium terephthalate, monosodium napthalene dicarboxylate and monosodium isophthalate as a nucleating agent during the synthesis of the 3GT resin;
(b) casting the nucleated 3GT resin into a film; and
(c) controlling the quench temperature during casting of the film to a temperature in the range of about 10° C. below the Tg of the nucleated 3GT resin to about 15° C. above the Tg of the nucleated 3GT resin.
The invention herein also provides a method to improve the retention of tensile properties upon aging in 3GT cast film comprising the steps of:
(a) prior to film formation, nucleating 3GT resin in situ by adding an appropriate sodium containing species to a polymerization reaction mixture comprising a dicarboxylic acid;
(b) casting the nucleated 3GT resin into a film; and
(c) controlling the quench temperature of the film during casting to a temperature in the range of about 10° C. below the Tg of the nucleated 3GT resin to about 15° C. above the Tg of the nucleated 3GT resin.
Preferably, the quench temperature ranges from about 30° C. to about 70° C., more preferably from about 40° C. to about 65° C. and most preferably from about 50° C. to about 65° C.
DETAILED DESCRIPTION
Definitions
In this disclosure, the word “copolymer” means a polymer polymerized from two or more monomers, and includes terpolymers, or more precisely, a polymer containing two or more repeat units.
The word “homopolymer” means a polymer containing one repeat unit.
A 3GT homopolymer is intended to mean a polymer substantially derived from the polymerization of 1,3-propane diol with terephthalic acid, or alternatively, derived from the ester-forming equivalents thereof (e.g., any reactants which can be polymerized to ultimately provide a polymer of poly(trimethylene terephthalate).
A 3GT copolymer is intended to mean any polymer comprising (or derived from) at least about 80 mole percent trimethylene terephthalate and the remainder of the polymer being derived from monomers other than terephthalic acid and 1,3-propane diol (or their ester forming equivalents)
Tg means the glass transition temperature of a polymer. Typically this is measured by using a differential scanning calorimeter (DSC) per ASTM D-3417 at a heating rate of 10° C./min for heating and cooling, and the mid-point of inflection is reported.
Description
The invention herein provides a method for improving the tensile properties in 3GT film upon aging. Applicants have found that by nucleating 3GT polymer, or copolymers thereof, and controlling the quench temperature during casting of the film to within a certain range, the resulting cast films have improved retention of tensile properties upon aging, generally improved stability of mechanical properties and specifically improved retention of elongation at break. Additionally, the resulting films are optically clear, making them especially useful in packaging applications. Most recent work shows that films prepared in this way (nucleated, controlled quench temperature) may also be tougher, i.e., have higher burst strength.
Poly(trimethylene terephthalate, herein referred to as 3GT, also referred to as poly(propylene terephthalate) or PPT, is a polyester prepared by the condensation polymerization of 1,3-propane diol and terephthalic acid. Poly(trimethylene terephthalate) may also be prepared from 1,3-propane diol and dimethylterephthalate (DMT) in a two-vessel process using tetraisopropyl titanate catalyst, Tyzor® TPT (a registered trademark of E. I. du Pont de Nemours and Company). Molten DMT is added to 1,3-propane diol and catalyst at about 185° C. in a transesterification vessel, and the temperature is increased to 210° C. while methanol is removed. The resulting intermediate is transferred to a polycondensation vessel where the pressure is reduced to one millibar (10.2 kg/cm
2
) and the temperature is increased to 255° C. When the desired melt viscosity is reached, the pressure is increased and the polymer may be extruded, cooled and cut into pellets.
The 3GT resin of the invention herein may be a 3GT homopolymer or a copolymer that preferably contains 80% or more of poly(trimethylene terephthalate) or poly(trimethylene naphthalate) in mole percentage, or blends thereof. These may be modified with up to 20 mol percent of polyesters made from other diols or diacids. The most preferred resin is poly(trimethylene terephthalate) homopolymer. Also preferred are blends and copolymers of poly(trimethylene terephthalate).
Other diacids that are useful to polymerize 3GT resin include isophthalic acid, 1,4-cyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, 1,12-dodecane dioic acid, and the derivatives thereof such as the dimethyl, diethyl, or dipropyl esters of these dicarboxylic acids.
Other diols include ethylene glycol, 1,4-butane diol, 1,2-propane diol, diethylene glycol, triethylene glycol, 1,3-butane diol, 1,5-pentane diol, 1,6-hexane diol, 1,2-, 1,3- and 1,4-cyclohexane dimethanol, and the longer chain diols and polyols made by the reaction product of diols or polyols with alkylene oxides.
The object of the invention, i.e., improved retention of tensile properties upon aging in 3GT cast film, is achieved due to two processing steps: (1) nucleating the 3GT resin, and (2) controlling the quench temperature upon casting, e.g., the temperature of the chill roll.
The 3GT resin may be nucleated by the addition of a nucleating agent, e.g., monosodium terephthalate, or the nucleating agent may be generated in situ by the addition of an appropriate sodium-containing species to a polymerization reaction mixture comprising terephthalic acid. These methods of nucleation are described in co-pending, commonly-assigned, U.S. patent application Ser. No. 09/273,288, filed on Mar. 19, 1999, and issued as U.S. Pat. No. 6,245,844 B1 on Jun. 12, 2001, incorporated by reference herein. Mono-sodium terephthalate
E. I. du Pont de Nemours and Company
Eashoo Mark
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