Polyethylene terephtalate molding resins

Molding compositions based on polyethylene terephthalate and a filler containing a sodium or potassium salt of a carboxylated polymer and an ester of aliphatic carboxylic acid.

The present invention relates to polyethylene terephthalate resins useful in molding applications. More particularly, it relates to polyethylene terephthalate resins containing an inorganic filler or reinforcing material.

It is advantageous to increase the mechanical strength of molded articles formed from a polyethylene terephthalate resin by using a reinforcing material, such as glass fibers, asbestos fibers or other materials

Ί0 fibrous minerals with a coupling agent, in the resin.

In addition, it is sometimes sufficient to simply increase the modulus by using a filler, such as beads or a mineral material with a low aspect ratio, in the resin. However, until now, it has been necessary to use very high mold temperatures, of the order of 130 1300, to obtain articles molded from such reinforced or filled resins having a shiny surface and no not having a rough texture. If these high mold temperatures were not used, the molded articles had a rough surface with poor gloss. It is believed that the rate of crystallization of polyethylene terephthalate is too small below about 150 ° C to give a molded article having good surface characteristics.

Although surface characteristic bohns can be obtained at molding temperatures of 130 ° C or higher, the use of such temperatures is inconvenient in the field of molding, since most molds are heated with l and reach temperatures of only around 85-110 ° 0.

A small number of molding devices use heating means such as oil to reach temperatures higher than 85-110 ° C, but these devices are generally inconvenient to use and moreover, or they generally do not reach no such temperatures or they reach them irregularly due to insufficient coring. Due to these heating problems, it has been found industrially unattractive to use these high temperature molding devices with reinforced or charged polyethylene terephthalate resins.

It is desirable to obtain a reinforced or filled polyethylene terephthalate resin capable of being molded at mold temperatures below about 110 ° C to give a molded article having a smooth and shiny surface.

The polyethylene terephthalate resins reinforced or loaded according to the present invention make it possible to achieve this result by incorporating 1) a sodium or potassium salt of a selected organic polymer containing pendant carboxyl groups and 2) an ester organic of low molecular weight chosen.

More particularly, the resins according to the present invention are compositions essentially comprising;

A) a polyethylene terephthalate having an inherent viscosity of at least about 0.4;

B) between approximately 10% and approximately 60% by weight of a filler or reinforcing material; characterized in that they further comprise:

C) a sodium or potassium salt of an organic polymer which contains pendant carboxyl groups, this material being present in an amount sufficient to give an HH ratio of less than 0.25 to a mixture of the constituents A, B and 0;

D) a compound present in an amount sufficient to give a temperature Tpk at least 4 ° C lower than the temperature Tpk of a mixture of constituents A, B and C, this compound being an organic ester chosen from the product of an aliphatic carboxylic acid of 1 to 20 carbon atoms containing 1 to 3 carboxyl groups and an alcohol of the formula

H0 £ R09 R 'where R is a hydrocarbon radical of 2 to 15 carbon atoms (preferably from 2 to 8 carbon atoms),

R 'is -H or a hydrocarbon radical of 2 to 20 carbon atoms (preferably 2 to 12 carbon atoms), and when R' is H, y is a cardinal number between 2 and 15 (preferably between 2 and 8) and, when R 'is a hydrocarbon radical, there is a cardinal number between 1 and 15 (preferably between 2 and 8).

The polyethylene terephthalate used herein is a polyethylene terephthalate which has an inherent viscosity of at least 0.4. Polyethylene terephthalate preferably has an inherent upper viscosity limit of about 1.2.

The inherent viscosity is measured on a solution of 0.5 g of

P ------- d terephthalate;

lelanf ns volume ratio of 51% t of methylene autoride and: of article and trifluoroacetic methyl chloride at 50 ° C. Polyethylene terephthalate may contain minor amounts of other comonomers such as diethylene glycol or glutaric acid.

The filler or reinforcing material used here includes glass fibers, glass beads, aluminum silicate, asbestos, mica, etc., or combinations of these materials, such as for example a mixture of mica and fiberglass.

The materials present in sufficient quantity for the compositions according to the invention to have a ΖΧτ / Δη ratio of less than 0.25 (component C defined above) include the sodium or potassium salts of organic polymers containing carboxyl groups, such as copolymers of olefins and acrylic or methacrylic acid, or copolymers of aromatic olefins and maleic anhydride. Preferably, these materials are the sodium or potassium salt of ethylene / methacrylic acid copolymers (including the salts both completely and partially neutralized, for example at least 50% neutralized), the sodium salt of styrene / anhydride copolymers maleic (including both fully and partially neutralized salts, e.g. at least about 50% neutralized).

In the copolymers listed above, the olefin or aromatic olefin portion usually constitutes from 50 to 98% by weight of the copolymer and preferably from 80 to 98%. An especially preferred material is the sodium salt of an ethylene / methacrylic acid copolymer. The copolymers can be prepared by conventional high pressure polymerization techniques.

Preferred organic esters of component D specified above are those in which the aliphatic carboxylic acids are hydrocarbon acids containing from 1 to 5 carboxyl groups, preferably 1 or 2 carboxyl groups, and having from 4 to 10 carbon atoms, and alcohols are aliphatic. In other words, the R groups in the alcohols are alkyl or alkylene groups depending on the particular R group. Preferably also when the carboxylic acids contain two or more carboxyl groups, the carboxyl groups have reacted to form ester bonds (000), that is to say that there are no more free carboxyl groups present in ester. Preferably, all of the hydroxyl groups in the alcohols will also have reacted to form ester bonds (C00), that is to say that there are no more free hydroxyl groups present in the ester.

Specific compounds meeting these definitions are listed below [the number in parentheses after each compound is the number of ° C whose temperature

Tpk is lowered by 1% by weight of the compound present (relative to polyethylene terephthalate) in reinforced or charged polyethylene terephthalate]: butyl carbitol adipate (2.9), triethylene glycol caprylate caprylate (2.7 ).

Components (C) and (D) in the compositions according to the present invention help to obtain molded articles with a large surface luster at molding temperatures below 110 ° C by increasing the rate of crystallization of polyethylene terephthalate. Component (C) is believed to primarily aid in increasing the rate of crystallization while component (D) is believed to primarily increase the mobility of polyethylene terephthalate in its supercooled state by reducing the viscosity in this state. Both are necessary to achieve the high sheen observed on articles molded from the composition.

The amount of component (0) present in the compositions according to the present invention is an amount which will give a ratio Λη ^ / ΖΙΗ of the composition less than 0.25 · To determine the ratio Zfeg./ZÙH_VS, the polyethylene terephthalate is molded at 70 ° C. into bars 1.6 mm thick. The bars are heated and between 95 ° G and 120 ° 0 a heat release (called ΔΗ ^) is recorded on a differential scanning calorimeter cell (DSC) mounted on a differential thermal analysis device (ATD) from the Pont 900. The bar is heated to 290 ° 0 (which is above its melting point) and the molten sample is cooled to 10 ° C / minute. Another release of heat between 200 and 220 ° C approximately (called ΔΗ) is the release of heat recorded during the freezing of the sample, a

We / found that the ratio Δϋ_ο is a convenient method for measuring the degree of crystallization.

The temperature Tpk of the composition according to the present invention is the temperature at which heat is released very quickly during the heating cycle specified in the preceding paragraph. As specified above, the amount of component (D) present in the composition according to the present invention is an amount which lowers the temperature Tpk of the composition by at least 4 ° C. compared to that of an identical composition which does not contain no constituent (D).

The upper limits of the quantities of the constituents

C and D are not critical. However, physical properties may be adversely affected as the quantities increase. In general, the upper limit of the amount used for any component will usually be about 12% by weight based on the weight of polyethylene terephthalate, while the lower limit will be about 1%. For the preferred constituent (C), namely salts of ethylene / methacrylic acid copolymer, the upper limit concerning the amount present will be approximately 12% by weight relative to the weight of polyethylene terephthalate while the lower limit will be about 0.5%, but preferably use an amount between 2 and 7%.

In addition to the constituents specified above, the compositions according to the present invention may contain additives commonly used with polyester resins, such as dyes, release agents, antioxidants, ultraviolet stabilizers, flame retardants , etc. Additives which improve properties r

physical, such as tensile strength and elongation, can also be used; such additives are for example epoxy compounds (for example an epoxy compound formed from bisphenol-A and epichlorohydrin) present in proportions of 0.1 to 1.5% by weight relative to the weight of the composition.

The compositions according to the present invention are prepared by mixing the components together by any convenient means. Neither temperature nor pressure is of critical importance. For example, the polyethylene terephthalate can be dry blended in any suitable mixer or barrel with the components B, 0 and D and the mixture is extruded in the molten state. The extruded product can be cut and mixed with a reinforcing agent and then this mixture is extruded in the molten state. More conveniently, all of the components can be dry blended in any suitable mixer or barrel and the mixture is then extruded in the molten state.

The following nonlimiting example describes the best mode of implementing the invention. The AEi ^ / Ah ratio and the temperature TpK are determined as described above, while the brightness of a molded sample is measured with a Gardner apparatus (model GG-9095) adjusted at a chosen angle in degrees specified in l 'example.

EXAMPLE

Dry polyethylene terephthalate (TPE) with an inherent viscosity of about 0.6 is manually mixed with 25% (based on total weight) of OOP 277 B glass fiber, 5.7% (based on the weight of TPE) an ethylene / methacrylic acid copolymer (85/15 ⁱⁿ by weight) which has been neutralized to 60% with sodium (which is component C defined here), and with 5? 7% (relative to the weight of TPE) of caprate-triethylene glycol caprylate (which is component D defined here), 0.6% (based on total weight) of the product of bisphenol A and epichlorohydrin, and 0.3% (based on total weight) of a phenolic antioxidant. Component 0 gives a -Αΐΐ ^ / ΑΗθ ratio of 0.16 and component D gives a Tpk of 15.4 ° C lower than the Tpk of a mixture of the other ingredients.

The resulting mixture is then extruded through a two-stage 5.08 cm single screw extruder at a melt temperature of 285 ° C and under a vacuum of 71.1 cm. The extruded strand is cut and the resulting resin pellets are dried at 110 ° C in a vacuum oven for about 16 hours. The resin pellets are then molded into cups having 9.2 cm in height, 7.5 cm in diameter at the top, 5.5 cm in diameter at the bottom and having a wall thickness of 0.19 cm. The temperature of the melt in the molding machine is 295 ° C., while the surface temperature of the mold is 85 ° C. at a cycle time of 10/20,

The brightness is measured at an angle of 60 ° by the Gardner instrument (model GG-9095) several times for each sample. The sheen is measured around the circumference of the goblet at a third of the height from the top. The highest value is 64 and the lowest value is 50 °

In a comparative test, the same constituents were used except that the caprate-caprylate was omitted. The highest brightness value obtained was 20, while the lowest value was 15, Also the molding cycle had to be increased to 10/30 seconds ^ (injection / residence time) to be able to remove the parts from the mold. Thus, it can be seen that component D is necessary to obtain substantially higher brightness values.