GB2039510A

GB2039510A - Modified polyester compositions

Info

Publication number: GB2039510A
Application number: GB8001034A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1979-01-15
Filing date: 1980-01-11
Publication date: 1980-08-13
Also published as: BR8000287A; FR2446303B1; AU539226B2; GB2039510B; DE3000855A1; FR2446303A1; MX151831A; NL8000237A; JPS55112258A; AU5459280A

Abstract

Modified thermoplastic polyester compositions are provided which comprise (a) a poly(1,4-butylene terephthalate) resin in combination with a poly(ethylene terephthalate) resin, (b) an impact modifier comprising a segmented thermoplastic copolyester, and (c) glass filler and/or reinforcing agent, optionally also including a flame retardant. These compositions are moldable to shaped articles having improved surface appearance substantially without losses in strength, resistance to impact fracture and resistance to heat distortion.

Description

SPECIFICATION Modified polyester compositions This invention relates to modified thermoplastic polyester compositions which are moldable to shaped articles having improved surface appearance. More particularly, the invention pertains to compositions of a poly(1 ,4-butylene terephthalate) resin which include a glass filler and/or reinforcement and a segmented copolyester impact improver, which are further modified with a poly(ethylene terephthalate) resin to reduce the tendency of the molded compositions toward surface blemishing. Optionally, the compositions also include a flame retardant.

High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al, U.S. 2,465,319 and in Pengilly, U.S. 3,047,539, incorporated herein by reference. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.

Poly(l,4-butylene terephthalate) in particular, because of its very rapid crystallization from the melt, has enjoyed increasing use as a component in injection moldable compositions. Workpieces molded from this material, alone or combined with reinforcements, in comparison with otherthermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.

It has been proposed to increase the impact strength of poly(1 ,4-butylene terephthalate) by adding a segmented copolyester in combination with an aromatic polycarbonate; see copending Application 7914500. These combinations are useable as such or in further combination with glass reinforcing agents and/or fillers. The compositions are moldable to a variety of shaped articles suitable for commercial and household purposes.

These compositions provide good overall properties but are nevertheless not entirely satisfactory because of a tendency to form unattractive blemishes on the surface after molding, possibly attributable to the presence of the glass reinforcement/filler material.

It has now been discovered that by including an effective amount of a poly(ethylene teraphthalate) resin in the compositions, this surface blemish problem is overcome and the resulting molded articles have a smooth, attractive surface appearance. Moreover, this result is achieved without detracting from the physical properties normally obtained with the compositions before addition of the poly(ethylene terephthalate) modifier.

It is known that stable polyblends of poly(l,4-butylene terephthalate) and poly(ethylene terephthalate) can be molded into useful reinforced and unreinforced articles, see, e.g., Fox and Wambach, U.S. 3,953,394. It has not been previously recognized, however, that compositions of poly (1 ,4-butylene terephthalate) which are impact modified essentially with a segmented copolyester only and reinforced essentially with glass only and which are susceptible to the described surface blemish problem, can be effectively modified as stated to avoid this problem.

According to this invention, there are provided thermoplastic compositions which are useful for molding, e.g., injection molding, compression molding, transfer molding, and the like, the compositions comprising: (a) a polyester composition comprising a blend of a poly(i 4-butylene terephthalate) resin and a poly(ethylene terephthalate) resin; (b) an impact modifier therefor comprising a segmented thermoplastic copolyester; and (c) an effective amount of a glass filler and/or reinforcing agent.

The polyester resins (a) of the compositions of this invention are available commercially or can be prepared by known techniques, such as by the alcoholysis of esters of terephthalic acid with the corresponding glycol, e.g., ethylene glycol or 1 ,4-butanediol, with the free acids or with halide derivatives thereof, and similar processes. These are described in U.S. 2,465,319 and U.S. 3,047,539, and elsewhere.

Illustratively, the high molecular weight polyesters have an intrinsic viscosity of at least about 0.4 deciliters per gram (dung), and preferably, at least 0.6 deciliters per gram as measured in solution in a 60:40 phenol/tetrachloroethane mixture at 300C.

Especially useful when high melt strength is important are branched high melt viscosity poly(1,4-butylene terephthalate) resins, which include a small amount of e.g., up to 5 mole percent based on the terephthalate units, of a branching component containing at least three ester forming groups. The branching component can be one which provides branching in the acid unit portion of the polyester, or in the glycol unit portion, or it can be a hybrid. Illustrative of such branching components are tri- or tetracarboxylic acids, such as trimesic acid, pyromellitic acid, and lower alkyl esters thereof, and the like, or preferably, polyols, and especially preferably, tetrols, such as pentaerythritol, triols, such as trimethylolpropane; or dihydroxy carboxylic acids and hydroxydicarboxylic acids and derivatives, such as dimethyl hydroxyterephthalate, and the like.

The branched poly(1,4-butylene terephthalate) resins and their preparation are described in Borman, U.S.

3,953,404, the disclosure of which is incorporated herein by reference.

Impact modifier (b) compprises, in general, a thermoplastic copolyester which is elastomeric. Preferably, the copolyester is selected from among materials consisting essentially of a multiplicity of recurring intralinear long chain and short chain ester units connected head-to-tail through ester linkages, said long chain ester units being represented bythefollbwing structure:

and said shortchain ester units being represented by the following structure:

wherein: G is a divalent radical remaining after removal of terminal hydroxyl groups from poly(alkylene oxide) glycols having a carbon to oxygen ratio of about 2.5-4,3, a molecular weight above about 400 and a melting point below about 60 C.:: R is a diva lent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300; and D is a divalent radical remaining after removal of hydroxyl groups from a low molecular weight diol having a molecular weight less than about 250; with the provisos that the short chain ester units constitute about 48-65% by weight of the copolyester, at least about 80% of the R groups must be 1 ,4-phenylene radicals, at least about 80% of the D groups must be 1 ,4-butylene radicals, and the sum of the percentages of the R groups which are not 1,4-phenylene radicals and of the D groups which are not 1,4-butylene radicals cannot exceed about 20%.

Within component, (a), it has been found that even small amounts of the poly(ethylene terephthalate) resin are effective to reduce the tendency toward surface blemishing and improve the surface appearance of articles molded from the compositions. In general, amounts of at least about 5 parts by weight of the poly(ethylene terephthalate) resin, based on 100 parts of (a), (b) and (c), are effective. Usually, amounts of from about 15 to about 40 parts by weight of poly(ethylene terephthalate) are employed. These amounts are subject to variation dependent upon particular requirements.

Usually, within the copolyesters specifically referred to above substantially all of the dicarboxylic acid reactant is terephthalic acid or a mixture of terephthalic acid and isophthalic or phthalic acid. Frequently, substantially all of the diol having a molecular weight less than 250 is 1 ,4-butane-diol, and the poly(alkylene oxide) glycol is poly(tetramethylene oxide) glycol having a molecular weight of about 600-2,000.

Such materials and methods of their preparation are described in the patent literature, e.g., U.S. 3,766,146, incorporated herein by reference, and are available commercially from E.l. DuPont deNemours and Company underthetrade name HYTREL resins.

The amount of the impact modifier (b) can vary widely, but usually this material is present in amounts of at least about 1.0 parts by weight, and preferably from about 5 to about 50 parts by weight of (a) and (b) together.

The filler and/or reinforcing agent (c) comprises glass, especially fibrous or filamentous glass.

The amount of the fibrous glass can vary within a broad range depending on the formulation and needs of the particular composition. Preferably, however, the glass is present in amounts of from about 1 to 90 parts by weight, and more preferably from about 2 to about 40 parts by weight of (a), (b) and (c) combined. In the most preferred embodiments, the glass comprises less than about 35 parts by weight of the combination.

The impact modified polyesters in combination with a filler/reinforcing agent can be rendered flame retardant, using an effective amount of a conventional flame retardant agent (d). As is well known, flame retardants can be based on elementary red phosphorus, phosphorus compounds, halogen and nitrogen compounds alone or preferably in further combination with synergists, such as antimony compounds.

Especially useful and polymeric and oligomeric flame retardant agents comprising tetrabromobisphenol-A carbonate units; see, for example Wambach, U.S. 3,833,685, which is incorporated herein by reference.

Other ingredients, such as dyes, pigments, drip retardants, stabilizers, and the like can be added for their conventionally employed purpose.

The compositions of this invention can be prepared by a number of procedures. In one way, the modifier and glass, especially fibrous glass filler(s)/reinforcing agent(s), as well as fire retardants if present, are put into an extrusion compounder with the resinous components to produce molding pellets. The modifier and fifllerireinforcing agent are dispersed in a matrix of the resin in the process. In another procedure, the modifier and glass filler reinforcing agent are mixed with the resins by dry blending, then either fluxed on a mill and comminuted, or they are extruded and chopped. The modifier and glass filler/reinforcing agent can also be mixed with the resins and directly molded, e.g., by injection or transfer molding techniques.

It is always important to thoroughly free all of the ingredients; resin, modifier, glass fifller/reinforcing agent, and any optional conventional additives from as much water as possible.

In addition, compounding should be carried out to ensure that the residence time in the machine is short; that the temperature is carefully controlled; that the friction heat is utilized; and that an intimate blend between the resin, the modifier and the filler/reinforcing agent is obtained.

Although it is not essential, best results are obtained if the ingredients are pre-compounded, pelletized and then molded. Pre-compounding can be carried out in conventional equipment. For example, after carefully pre-drying the polyester and modifier and the glass filler/reinforcing agent, e.g., a single screw vacuum vented extruder is fed with a dry blend of the ingredients, the screw employed having a long transition section to ensure proper melting. On the pther hand, a twin screw extrusion machine, e.g., a 53 mm Werner Pfleiderer machine, can be fed with resin and additives at the feed port and the filler/reinforcing agent can be fed down stream. In either case, a generally suitable machine temperature will be about 450 to 5600F.

The pre-compounded composition can be extruded and cut up into molding compounds such as conventional granules, pellets, etc., by standard techniques.

The composition can be molded in any equipment conventionally used for glass-filled thermoplastic compositions, e.g., a Newbury type injection molding machine with conventional cylinder temperatures, e.g., 450-535"F. and conventional mold temperatures, e.g., 130-2000F.

Description of the preferred embodiments.

The following examples illustrate the invention. They are set forth as a further description but are not to be construed as limiting the invention. All parts are by weight.

Example 1 A dry blend of poly(1,4-butylene terephthalate) resin (PBT), poly(ethylene terephthalate) resin (PET), segmented copolyester, glass reinforcement/filler and stabilizers is compounded and extruded at 500 F. in an extruder. The extrudate is pelletized and injection molded at 480 F. (mold temperature 150 F.) For purposes of comparison, the corresponding composition without the poly(ethylene terephthalate) resin is also prepared and molded under the same conditions. The formulations and physical properties are shown in Table 1.

TABLE 1 Compositions Comprising Polyesters, Segmented Copolyester and Glass EXAMPLE 1 lA* Ingredients, parts by weight Poly(l,4-butylene terephthalate(a) 24.8 49.8 Poly(ethylene terephthalate) 25 - Segmented copolyesterb 20 20 Glass fibers 30 30 Stabilizers 0.2 0.2 Properties Distortion temp. under load,"F.

at 66 psi 396 394 at 264 psi 298 334 Notched Izod impact, ft. Ibs./in. 3.7 3.7 Unnotched Izod impact, ft.lbs./in; 17.4 17.6 Flexural strength, psi 17,860 17,384 Flexural modulus, psi 716,077 644,469 Tensile strength, psi 10,797 11,223 Gardner impact (bottom), in.-lbs. 16 22 Gardner impact (top), in.-lbs. 56 58 Gardner impact dislodge, in.-lbs. 126 128 Melt Viscosity, poise 4,531 11,182 * comparison experiment a Valox 300, General Electric Co., melt viscosity 2,300-3,800 poise b Hytrel 4056, E.l. DuPont deNemours The article molded from the composition according to the invention, comprising poly(1 ,4-butylene terephthalate) and poly(ethylene terephthalate), is observed to possess a smooth, blemish-free and attractive surface appearance.In contrast, the article molded from the comparison composition, not containing poly(ethylene terephthalate), has a number of unattractive blemishes on the surface which appear to be due to the glass in the composite showing through.

As is shown, the use of the poly(ethylene terephthalate) resin to replace part of the poly(1,4-butylene terephthalate) resin does not detract from the other properties measured.

TABLE 2 Compositions Comprising Polyester Resins, Segmented Copolyester and Glass EXAMPLE 2 3 4 5 6 7 Ingredients, parts by weight Poly(l,4-butyleneterephthalate)a 39.8 29.8 19.8 39.8 29.8 19.8 Poly(ethyleneterephthalate) 10.0 20.0 30.0 25.0 25.0 25.0 Segmented copolyesterb 20.0 20.0 20.0 20.0 15.0 20.0 Glass fibers 30.0 30.0 30.0 15.0 30.0 3.0 Stabilizers 0.2 0.2 0.2 0.2 0.2 0.2 Properties Distortion temp. under load, F. at 264 psi 348 316 298 274 354 267 Notched Izod impact, ft.lbs./in. 3.4 3.3 3.3 1.9 2.6 4.5 Unnotched Izod impact, ft.lbs./in 14.0 14.7 15.3 12.4 13.3 16.9 Flexural strength, psi 17.400 17,600 17,300 14,800 19,300 15,000 Flexural modulus, pisi 640,000 650,000 640,000 440,000 730,000 505,000 Tensile strength, pisi 11,600 11.700 11,500 10,050 12,850 10,200 Gardner impact, dislodge, in.lbs. 116 112 116 106 98 120 a Valox300 b Hytrel 4056 The molded composition has a smooth, blemish-free surface appearance.

Claims

1. A thermoplastic composition comprising: (a) a polyester composition comprising a blend of a poly(1,4-butylene terephthalate) resin and a poly(ethylene terephthalate) resin; (b) an impact modifiertherefor comprising a segmented thermoplastic copolyester; and (c) an effective amount of a glass filler and/or reinforcing agent.

2. A composition as claimed in Claim 1 wherein the impact modifier (b) is present in an amount of at least about 1.0 parts by weight per 100 parts by weight of (a) and (b) together.

3. A composition as claimed in Claim 1 or 2 wherein the impact modifier (b) is present in an amount of from about5to about 50 parts by weight per 100 parts by weight of (a) and (b)together.

4. A composition as claimed in any preceding claim, wherein the impact modifier (b) consists essentially of a multiplicity of recurring long chain ester units and short chain ester units joined head-to-tail through ester linkages, said long chain ester units being represented by the formula

and said short chain units being represented by the formula

where G is a divalent radical remaining after the removal of terminal hydroxyl groups from a poly(alkylene oxide) glycol having a melting point of less than about 60"C., a molecular weight of about 400-4000 and a carbon to oxygen ratio of about 2.5-4.3;R is a divalent radical remaining after removal of carboxyl groups from a dicarboxylic acid having a molecular weight less than about 300 and D is a divalent radical remaining after removal of hydroxyl groups from a diol having a molecular weight less than about 250; provided (a) said short chain ester units amount to about 48-65% by weight of said copolyester, (b) at least about 80% of the R groups in Formulae (I) and (II) are 1,4-phenylene radicals and at least about 80% of the D groups in Formula (Il) are 1,4butylene radicals, and (c) the sum of the percentages of R groups which are not 1,4-phenylene radicals and of D groups which are not 1 4-butylene radicals does not exceed about 20.

5. A composition as claimed in any preceding claim, wherein each said polyester in component (a) has an intrinsic viscosity of at least about 0.4 deciliters per gram when measured in solution in a 60:40 mixture of phenol and tetrachloroethane at 30"C.

6. A composition as claimed in Claim 5 wherein each said polyester in component (a) has an intrinsic viscosity of about 0.6 deciliter per gram when measured in solution in a 60:40 mixture of phenol and tetrachloroethane at 30"C.

7. A composition as claimed in any preceding claim, wherein in component (a), said poly(1,4-butylene terephthalate) resin is linear or branched.

8. A composition as claimed in Claim 7 wherein said branched polyester is a high melt viscosity poly(1,4-butylene terephthalate) resin which includes a small amount of a branching component containing at least three ester forming groups.

9. A composition as claimed in any preceding claim, wherein the mineral filler and/or reinforcing agent (c) comprises fibrous glass.

10. A composition as claimed in any preceding claim, wherein the mineral filler and/or reinforcing agent (c) is present in an amount of from about 1 to about 90 parts by weight per 100 parts by weight of (a) and (b).

11. A composition as claimed in any preceding claim, which also includes (d) a flame retardant amount of a flame retarding agent.

12. Molded articles produced from a composition claimed in any of the preceding claims.