GB2118956A - Resin composition - Google Patents

Abstract

A resin composition is improved in respect of impact strength and tensile elongation and consists essentially of 1 to 95 wt.% of a polyester polyether block copolymer (I) and 99 to 5 wt.% of polytetramethylene terephthalate (II). The polyester polyether block copolymer (I) is obtained from a dicarboxylic acid component comprising 50 to 100 mole% of terephthalic acid and up to 50 mole% of isophthalic acid, a diol component comprising 5 to 95 mole% of a glycol having the formula (1) as given below and 95 to 5 mole% of tetramethylene glycol and a polyalkylene ether glycol, the number-average molecular weight of which is from 500 to 3,000 and the content of said polyalkylene ether glycol in said polyester polyether block copolymer (I) being from 5 to 50 wt.% expressed as phthalate. The formula (1) of the glycol is: <IMAGE> in which R1 and R2 are each hydrogen or an alkyl having 1 to 4 carbon atoms, provided that R1 and R2 are not hydrogen at the same time.

Description

SPECIFICATION Resin composition This invention relates to a resin composition.

More specifically, this invention deals with a resin composition obtained from polytetramethylene terephthalate and a polyester polyether block copolymer and with a resin composition with superior properties such as mechanical properties, electrical properties, chemical resistance, surface gloss, low temperature resistance, impact resistance, thermal deformation properties, and mouldability.

Polytetramethylene terephthalate resin (henceforth referred to as the PBT resin) is a thermoplastic polyester resin with a high crystallinity with affinities for various fillers and additives. Due to this property, reinforced PBT resin to which glass fibres, mica, talc, and flame-retarding agents have been added exhibit excellent properties, and the resin is widely used in various industrial applications such as electrical appliances, electronic parts, and automobile parts. That is to say, the PBT resin has a high mechanical strength, superior durability, weather resistance, chemical resistance, heat resistance, and dimensional stabiiity, as weli as superior electrical properties.The PBT resin has a higher degree of crystallinity compared with polyethylene terephthalate resins, and the speed of crystallization is faster and the cooling-solidification rate is faster. Since the fluid property of the PBT resin is also excellent, the PBT resin has a good mouldability. Thus, the PBT resin is an excellent engineering plastics material with a balance between the electrical and mechanical properties and processing properties.

In spite of all the outstanding properties, the PBT resin also has the following disadvantages.

(1) The PBT resin naturally lacks dimensional precision, compared with noncrystalline and slightly crystalline plastics, and it is particularly affected by the metal mould temperature distribution. The mould shrinkage rate of the PBT resin is greatly dependent on the thickness of the resin, and the moulded product has a tendency to deform and warp with an uneven cooling rate. These undesirable properties extend to shrinkage anisotropy with the orientation of the fibres in the reinforced PBT resins containing glass fibres. This makes the moulded product easy to deform, and warping becomes more common.

(2) PBT resin which is not reinforced has poor flexibility and is very sensitive to notching.

In order to improve upon these disadvantages, terephthalic acid had been partially replaced with an aliphatic dicarboxylic acid, or other resins had been blended to reduce the crystallinity and to minimize the deformation from shrinkage during moulding. The disadvantages were also somewhat alleviated by the use of a filler such as glass beads, talc, and mica, which is less prone to anisotropy than glass fibres. However, none of the methods yielded a material which satisfactorily met the users' demands.

The inventors of the present invention have worked diligently to diminish the disadvantages and have discovered that the impact strength was significantly improved by adding to the PBT resin a polyester polyether block copolymer containing a glycol component with an alkyl group on the side chain. This invention was compieted based on this discovery.

Specifically, this invention deals with a resin composition which basically consists of a polyester polyether block copolymer (I) and polytetramethylene terephthalate (II) in a mixture proportion of 1-95 wt.% of (I) and 99-5 wt.% of (II) in which the polyester polyether block copolymer is made from 50-100 mole% of a dicarboxylic acid mixture containing 50-100 mole% of terephthalic acid and 50-0 mole% of isophthalic acid, a diol mixture containing 5-95 mole% of a glycol indicated by the general formula (1) shown below and 95-5 mole% of tetramethylene glycol, and a polyalkylene ether glycol whose number-average molecular weight is 500-3,000 and in which the said polyalkylene ether glycol component in the block polyether polyester copolymer is present in an amount of 5-50 wt.% based on the total amount of the copolymer and expressed as phthalate. The general formula (1 ) for the glycol is:

(in which R1 and R2 are hydrogen or an alkyl group with 1-4 carbon atoms and R, and R2 are not both hydrogen).

The reason why a polyester resin composition with such an excellent impact resistance is obtained by this invention is not clearly understood, but the following theory has been advanced as a possible explanation.

The thermoplastic polyester polyether elastomers have molecular chains composed of linear polyester units and linear polyether units. Basically, the linear polyester units form the hard segment and the linear polyether units form the soft segment.

In the prior art, a condensation polymer prepared from a dicarboxylic acid which was mainly terephthalic acid and an alkylene glycol, such as ethylene glycol and tetramethylene glycol, which does not have a side chain, has been used as the hard segment in the thermoplastic polyester polyether elastomer. At the same time, a polyalkylene ether glycol such as polytetramethylene ether glycol has been used as the soft segment.

In contrast to the prior art, the inventors used the polyester polyether block copolymer (I) described earlier, which contains 1 ,3-propanediol having an alkyl group as a side chain, as the glycol component in the hard segment. This modification resulted in a soft elastomer with excellent characteristics.

Furthermore, the polyester polyether block copolymer (I) rich in softness also contains a PBT segment in the structure. This gives the elastomer more affinity toward the PBT (II) resin and has a positive effect in improving the impact strength of the PBT resin.

The polytetramethylene terephthalate (II) is a polyester synthesized from terephthalic acid and tetramethylene glycol as starting materials. It is also possible to use other components, including aromatic, aliphatic, and alicyclic dicarboxylic acids such as isophthalic acid, ortho-phthalic acid, naphthalene dicarboxylic acid, adipic acid, sebacic acid, dodecanedicarboxylic acid, and 1,4cyclohexanedicarboxylic acid, or aromatic, aliphatic, and alicyclic diols such as ethylene glycol, propylene glycol, pentamethylene glycol, hexamethylene glycol, decamethylene glycol, neopentyl glycol, 2-methyl-l ,3-propanediol, cyclopentanediol, cyclohexane diol, cyclohexanedimethanol, cyclohexanediethanol, 1 ,4-benzenedimethanol, and 1 ,4-benzenediethanol as the diol component in suitable amounts, depending upon the desired objective.It is also acceptable to use oxy acids such as hydroxybenzoic acid and hydroxyethoxybenzoic acid in this invention.

In synthesizing polytetramethylene terephthalate, the method of the prior art to prepare polyesters can be used without any further change. Specifically, polytetramethylene terephthalate can be prepared by either the direct method, in which the dicarboxylic acid and the diol are allowed to undergo a direct polycondensation reaction, or by the ester interchange method, in which a low-moiecular-weight ester compound of a dicarboxylic acid and a diol are allowed to react and an ester interchange reaction follows.

The method by which a polymer of terephthalic acid and tetramethylene glycol is prepared is described here as an example. One mole of dimethyl phthalate and an excess or a total of 1.1-2.0 molar excess of tetramethylene glycol are allowed to undergo an ester interchange reaction using a standard esterification catalyst under a stream of nitrogen at a normal pressure and at a temperature of ca. 150--2400C. The methanol formed is distilled, and an additional catalyst and discolouration inhibitor are added as needed.The pressure is reduced to less than 5 mm Hg, and the polycondensation is allowed to proceed at ca. 20O2800 C. The catalyst mentioned above can be a wide variety of compounds, but titanium compounds such as tetramethoxytitanium, tetraethoxytitanium, tetra-npropoxytitanium, tetraisopropoxytitanium, and tetrabutoxytitanium, tin compounds such as di-nbutyltin dilaurata, di-n-butyltin oxide, and dibutyltin diacetate, and a combination of an acetate salt of magnesium, calcium, or zinc with antimony oxide or one of the titanium compounds listed above are some of the examples.

It is desirable to use these catalysts in the range of 0.002-0.8 wt.% based on the total amount of the polymer formed. As far as the discolouration inhibitors are concerned, phosphorus containing compounds such as phosphorus acid, phosphoric acid, dimethyl phosphite, tridecyi phosphite, triphenyl phosphite, teimethyl phosphate, tridecyl phosphate, and triphenyl phosphate are effective, and they should be used in the range of 0.0010.3 wt.% base on the total amount of the polymer formed.

The molecular chain of the polyester polyether block copolymer used in this invention is basically composed of polyester units and polyether units, with the polyester units forming the hard segment and the polyether units forming the soft segment.

The polyester hard segment of the polyester polyether block copolymer used in this invention consists of a dicarboxylic acid mixture containing 50-100 mole% of terephthalic acid and 50-0 mole% of isophthalic acid and a mixed diol component containing 5-95 mole% of propanediol with an alkyl group on the side chain and 95-5 mole% of tetramethylene glycol.

The isophthalic acid in the mixed dicarboxylic acid component used in the polyester polyether block copolymer should be used in an amount of up to 50 mole%, preferably up to 30 mole%, depending upon the applications of the resin composition of this invention.

In other words, the addition of isophthalic acid increases the relative concentration of the propylene isophthalate and polytetramethylene isophthalate with alkyl groups on the side chain which comprise the hard segment and which are basically noncrystalline or difficult to crystallize. This increase in the hard segment improves the softness of the composition, but the heat resistance is too drastically reduced when the isophthalic acid concentration exceeds 50 mol%, making the composition unsuitable for practical applications.

The examples of 1 ,3-propanediols with alkyl groups on the side chains indicated by the formula (1), comprising the mixed diol component for the polyester polyether block copolymer, are 2-ethyl-2butyl- 1 ,3-propanediol, 2,2-diethyl- 1 ,3-propanediol, 2-methyl-2-propyl- 1 ,3-propanediol, 2-ethyl- 1,3propanediol, and 2-methyl-1,3-propanediol. Of these examples, 2-methyl-l ,3-propanediol is particularly preferred.

These 1 ,3-propanediols with alkyl groups on the side chains have the alkyl groups in the 2 position and make the structure of the polyester polymers obtained by the condensation polymerization with terephthalic acid irregular. This makes the polymer more pliable and noncrystalline.

On the other hand, tetramethylene glycol undergoes a condensation polymerization with terephthalic acid and yields a hard and highly crystalline polyester with a high melting point, namely, polybutylene terephthalate.

The polyester polyether block copolymer (I) used in this invention has improved softness and mechanical strength attained by a careful combination of the properties of two types of diols.

The concentrations of the 1 ,3-propanediol/tetramethylene glycol components (wherein the propanediol has alkyl groups as side chains) used as a mixture should be in a ratio of 5-95 mole /O/95- 5 mole%, or more preferably 10-70 moleo/o/90-30 mole% respectively. When the concentration of the 1,3-propanediol with alkyl groups as a side chain is less than 5 mole%, the effects imparted by the said diol described earlier are not realized sufficiently, and when the same concentration exceeds 95 mole%, the thermal and mechanical properties of the resin are too adversely affected.

In addition to the mixed dicarboxylic acid component and mixed diol component, polycarboxylic acids and polyols with more than 3 functions can be added to increase the melt viscosity and to increase the polymerization rate of the polyester polyether block copolymer (I). The amount of the polycarboxylic acids and polyols added to the copolymerization should be small. Examples of the said polycarboxylic acids are trimellitic acid, trimesitic acid, pyromellitic acid, and their anhydrides and esters, Examples of the said polyols are trimethylol propane, glycerin and pentaerythritol.

The polyester polyether block copolymer (I) used in this invention can also contain suitable amount of other copolymer compoiients such as polyaliphatic carboxylic acids such as adipic acid, azelaic acid, and sebacic acid, polyaromatic carboxylic acids such as isophthalic acid and 2,6naphthalene dicarboxylic acid, and polyols such as ethylene glycol, propylene glycol, 1 ,6-hexanediol, and 1 ,4-cyclohexanedioi.

The soft segment of the polyester polyether block copolymer used in this invention is formed from a polyalkylene glycol whose number-average molecular weight is 500-3,000. The proportion of the said polyalkylene glycol should be in the range of 5-50 wt.% or more, preferably in the range of 10 40 wt.% based on the total amount of the copolymer. When the concentration of the polyalkylene glycol is less than 5 wt.%, the softness is unsatisfactory, and when the same concentration exceeds 50 wt.%, the product becomes too soft.

Examples of the aforementioned polyalkylene ether glycol are polyethylene glycol, poly(1 ,2- and 1,3-propylene oxide) glycol, poly(tetramethylene oxide) glycol, poly(hexamethylene oxide) glycol, and their copolymers or mixtures thereof. The number-average molecular weight of the polyalkylene ether glycol should be in the range of 500-3,000, or more preferably in the range of 800-2,000. When the number-average molecular weight of the said glycol is less than 500, the heat resistance of the final polymer is too low, and when the same molecular weight exceeds 3,000, the mutual solubility of the final polymer with the hard segment becomes too low.

The polyester polyether block copolymer (I) used in this invention comprises at least the dicarboxylic acid component described above, the diol component, and the polyalkylene ether glycol component, but it can be prepared by any of the standard methods for the preparation of the copolymer polyesters. For example, the polyester polyether block copolymer (i) can be prepared by the direct method, in which the dicarboxylic acid and the glycol are allowed to react with each other, or by the ester interchange method, in which a low-molecular-weight alkyl ester of the dicarboxylic acid and the glycol are allowed to undergo an ester interchange reaction.As an example of the latter method, one mole of a mixture containing dimethyl terephthalate and dimethyl isophthalate or dimethyl terephthalate alone was allowed to react with an excess of 1.1-2.0-fold molar excess of 2-methyl-1,3propanediol and tetramethylene glycol in the presence of a standard esterification catalyst under a stream of nitrogen at a normal pressure at a temperature of about 150--240"C. The methanol produced by the ester interchange reaction was distilled, and the pressure of the reaction mixture was reduced to less than 5 mm Hg. The polycondensation reaction was allowed to proceed under this reduced pressure at about 200--2800C. The polyalkylene ether glycol may be added prior to the ester interchange reaction.

Examples of the suitable catalysts used in such reactions are titanium compounds such as tetramethoxytitaniu m, tetraethoxytitaniu m, tetra-n-propoxytitanium, tetraisopropoxytitani u m- and -tetrabutoxytitanium, tin compounds such as di-n-butyltin dilaurate, di-n-butyltin oxide, and dibutyltin di acetate, and combinations of the diacetate salts of magnesium, calcium, and zinc with antimony oxide or one of the titanium compounds listed above. Of these, the more preferred catalysts are organotitanium compounds. It is preferable to use these catalysts in the range of 0.002-0.8 wt% based on the total amount of the copolymer formed.

In the composition of this invention, these two types of polymers are mixed in the proportions of 1-95 wt.% of the polyester polyether block copolymer (I) and 99-5 wt.% of the polytetramethylene terephthalate (II).

When the proportion of the polyester polyether block copolymer used in this invention is less than 1 wt.%, no improvement is observed in the impact resistance of the composition. At the same time, when the amount of the polyester polyether block copolymer used in this invention exceeds 95 wt.%, the thermal deformation temperature is drastically lovvered, and it becomes impossible to attain the characteristics of this invention.

The mixing of the two polymer components to prepare the composition of this invention can be carried out at a temperature above the melting point of the polymer, preferably at 1000C to 3000C.

More specifically, the method of blending may be by a chemical method, in which the components are dissolved in a solvent prior to mixing, or by a mechanical method, in which the two components are mixed with rollers, Banbury mixers, extruders, or moulding machines. In either case, the standard method and equipment can be used.

In carrying out this invention, it is acceptable to formulate other additives to the composition of this invention, depending upon the various properties and effects desired. More specifically, the additives included in inorganic and organic fillers and reinforcing materials such as carbon black, titanium oxide, pigment alumina, silica oxide, small glass spheres, glass fibres and carbon fibres, lubricants such as organic acid amides and wax, crystallization nuclei, oxidation inhibitors, ultraviolet ray absorption agents, static electricity inhibitors, and flame-retarding agents can be added when needed.

In the following paragraphs, this invention will be explained in more detail using examples, but it is not limited to these examples. In the examples, the term "part" refers to weight parts and the properties were determined by the methods described in the following paragraphs.

(1) Intrinsic Viscosity For polytetramethylene terephthalate, this measurement was made at 250C in o-chlorophenol.

For the polyester polyether block copolymer, this measurement was made by 250C in 0.5 g/dl solution of the copolymer in a mixture of 60 weight parts of phenol and 40 weight parts of 1,1,2,2tetrachloroethane.

(2) 100% Modulus Using the Toyo Baldwin Co. Tensilon UTM-lll-500 universal tester, this measurement was made according to the method described in ASTM D-638.

(3) Vicat Softening Temperature The Yasuda Seki Seisakusho No. 148 HDR Automatic Heat Distortion Tester was used with a steel needle whose diameter was 1 mm under a 1 -kg load. The temperature was raised at a rate of 50 C/hr, and the temperature at which the needle penetrated 1 mm vertically was measured.

(4) Flexural Elasticity This measurement was made according to the method described in ASTM D-790.

(5) Tensile Fracture Elongation The Toyo Baldwin Tensilon UTM-IlI-500 universal tester was used.

(6) Izod Impact Test The Toyo Seiki Seisakusho Izod Impact Tester was used according to the method described in ASTM D-256.

Synthesis 1 A mixture of 600 parts of dimethyl terephthalate, 390 parts of tetramethylene glycol and 0.12 part of titanium tetrabutoxide as a catalyst was placed in a reactor equipped with double helical ribbontype agitator wings. The reaction was allowed to proceed for three hours at 1 600C under normal pressure and in a stream of nitrogen. Next, 0.36 part of additional titanium tetrabutoxide was added and the temperature of the reaction mixture was raised to 2500C over 1.5 hours. The methanol formed was distilled to collect 94% of the theoretical amount formed. Next, 0.02 part of tridecyl phosphite was added to the reaction mixture, and the pressure in the reaction system was reduced to 0.2 mm Hg over the next 1 hour. The polymerization was allowed to proceed under these conditions for 2.5 hours.

The melting point of the polytetramethylene terephthalate was 2230C and the intrinsic viscosity was 0.69.

Synthesis 2 A mixture of 145.5 parts of dimethyl terephthalate 0.6 part of trimellitic acid, 99.9 parts of tetramethylene glycol, 45.9 parts of poly(tetramethylene oxide) glycol whose number-average molecular weight is 1020, and 0.1 7 part of titanium tetrabutoxide catalyst was placed in a reactor equipped with double helical ribbon-type agitator wings. The reaction was allowed to proceed for one hour at 1 800C and 2.5 hours at 2300C under a stream of nitrogen. The methanol formed was distilled and 92% of the theoretical amount formed was collected. Next, the temperature of the reaction mixture was raised to 2500C and the pressure of the reaction system was reduced to 0.3 mm Hg over 40 minutes. The polymerization was allowed to proceed for 3.5 hours under these conditions.The elastomer obtained was examined and the properties of the elastomer are shown in Table 1.

Syntheses 3-6 The starting materials listed in Table 1 were used in the proportions indicated in the same table according to the method of polymerization described in Synthesis 2. The properties of the polymers obtained are also tabulated in Table 1.

TABLE 1

synthesis unit 2 | 3 | 4 | 5 | 6 dimethyl terephthalate parts 145.5 145.5 116.4 93.1 145.5 dimethyl isophthalate ,, 0 0 0 23.3 0 Va) 2-methyl-1,3-propanediol ., 0 35.1 40.5 40.5 99.9 Co tetramethylene glycol ,, 99.9 64.8 40.5 40.5 0 Co poly(tetramethylene oxide) " 45.9 45.9 40.8 40.8 45.9 E glycol (number-average molecular weight 1020) trimellitic acid " 0.6 0.6 1.1 1.1 0.6 titaniumtetrabutoxide " 0.17 0.20 0.17 0.17 0.17 intrinsic viscosity dl/g 1.50 1.58 1.52 1.63 1.41 100% modulus kg/cm2 120 81 62 52 33 vicat softening temperature 0C 117 105 79 53 35 EXAMPLES 14and and Comparative Examples 1-2 The polytetramethylene terephthalate obtained in Synthesis 1 and the polyester polyether block copolymers obtained in Syntheses 2-6 were mixed in the proportion indicated in Table 2.Q.2 wt.% of tridecyl phosphite, based on the total amount of the polymer mixture, was added to this mixture. This final mixture was blended and extruded with an extruder (Osada Seiki 40from extruder) at 2400 C. The blended composition obtained was dried for eight hours at 80"C and moulded into test pieces at 2300C using a moulding machine (Nissei Injection Moulding machine TS--100 model). The mechanical strength of the test pieces obtained was summarized in Table 2. The mechanical strengths of the PBT resin obtained in Synthesis 1 and the polyester polyether block copolymer obtained from a glycol component with no side chain obtained in Synthesis 2 are also shown in the Table as Reference 1 and Reference 2.

TABLE 2

comparative reference example example unit 1 2 1 2 3 4 1 2 = synthesis 1 parts 100 ~ 80 resin) x E " 2 " 2 130 - - - - - 20 3 " 3 " - ~ 20 40 - - - = Co - - - - 20 - - = 4.

o ò " 5 " ~ ~ ~ ~ 20 ~ ~ O s , 5 rr 20 ~ .

flexural elasticity kg/cm2 26000 490 16000 11000 13000 1000Q V o elongation % 80 830 310 520 550 380 o 270 9 impact resistance no V (notched) kg.cm/cm 27 í racture 19 36 31 32 11 The purpose of-the invention is an improvement of a blend composition of a polyester polyether block copolymer and polytetramethylene terephthalate. This is attained by incorporation of the branched glycol having the formula (1) in the glycol component of the polyester polyether block copolymer. The resin composition is improved with respect to balanced properties between impact resistance and tensil fracture elongation, compared with a resin composition consisting of a polyester polyether block copolymer in which the glycol component does not contain a branched glycol and polytetramethylene terephthalate. It will be understood from comparison between the examples 1 to 4 and the comparative example 2 that the invention is unexpectedly improved with regard to the tensile fracture elongation and the impact resistance.

Claims (5)

1. A resin composition which comprises 1 to 95 wt.% of a polyester polyether block copolymer (I) and 99 to 5 wt% of polytetramethylene terephthalate (it), the polyester polyether block copolymer (I) being obtained from at least a dicarboxylic acid component comprising 50 to 100 mole% of terephthalic acid or an ester thereof and up to 50 mole% of isophthalic acid or an ester thereof, a diol component comprising 5 to 95 mole% of a glycol having the formula (1) as given below and 95 to 5 mole% of tetramethylene glycol and a polyalkylene ether glycol, the number-average molecular weight of which is from 500 to 3,000 and the content of said polyalkylene ether glycol in said polyester polyether block copolymer (I) being from 5 to 50 wt.% expressed as phthalate, the formula (1) of the glycol being:

in which R1 and R2 are each hydrogen or an alkyl group having 1 to 4 carbon atoms, provided that R1 and R2 are not hydrogen at the same time.

2. A resin composition as claimed in claim 1, in which said glycol having the formula (1) is 2 methyl-i 3-propylene glycol.

3. A resin composition as claimed in claim 1 or 2, in which the polyester polyether block copolymer (I) is obtained from the dicarboxylic acid component, the diol component, the polyalkylene ether glycol and at least one other copolymer component selected from polycarboxylic acids and polyols with more than 3 functions.

4. A resin composition as claimed in claim 1,2 or 3, in which the polyester polyether block copolymer (I) is obtained from the dicarboxylic acid component, the diol component, the polyalkylene ether glycol and at least one other copolymer component selected from polyaliphatic carboxylic acids, polyaromatic carboxylic acids and polyols (other than said diol component).

5. A resin composition as claimed in claim 1, and substantially as hereinbefore described with reference to the Syntheses and Examples.