Patent Description:
Polyester resins are generally excellent in transparency, mechanical strength, processability, solvent resistance, and the like. Therefore, polyester resins are widely used for fibers, films, sheets, and the like and are also utilized in recycling.

However, polyester resins are susceptible to hydrolysis due to degradation over time, and therefore, a carbodiimide compound is sometimes added thereto as a polyester resin modifier for the purpose of suppressing hydrolysis and improving hydrolysis resistance.

For example, PLT <NUM> and PTL <NUM> indicate that a certain urea-modified carbodiimide has good compatibility with polyester resins and is capable of improving hydrolysis resistance of polyester resins. Specifically, as a working example, a urea-modified carbodiimide to which urea bonds are introduced by di-n-butylamine (boiling point at <NUM> atm: <NUM>) and which has the number of carbodiimide groups (degree of polymerization of carbodiimide groups) of <NUM> or <NUM> is disclosed. In addition, a urea-modified carbodiimide to which urea bonds are introduced by n-butylamine (boiling point at <NUM> atm: <NUM>) and which has the number of carbodiimide groups (degree of polymerization of carbodiimide groups) of <NUM> is disclosed.

As described above, the urea-modified carbodiimide disclosed in PLT <NUM> and PLT <NUM> is a urea-modified carbodiimide to which urea bonds are introduced by using an amine compound having a boiling point of as high as <NUM> or higher, or a urea-modified carbodiimide having a degree of polymerization of carbodiimide groups of <NUM> when an amine compound having a boiling point lower than <NUM> is used.

However, when an amine compound having a high boiling point is used as raw material, the unreacted amine compound is likely to remain in the obtained urea-modified carbodiimide without being distilled away. In addition, urea bonds are sometimes cleaved by heating during melt kneading with polyester resins, causing the amine compound to be liberated, and the amine compound may remain in a polyester resin composition including the urea-modified carbodiimide without vaporizing. Such a residual amine may adversely affect performance of polyester resins to which the urea-modified carbodiimide is added.

In addition, even in the case where n-butylamine, which has a boiling point lower than that of di-n-butylamine, is used as an amine compound, the urea-modified carbodiimide having a degree of polymerization of carbodiimide groups of <NUM> increases the melt viscosity of a polyester resin composition including the urea-modified carbodiimide and worsens processability.

Therefore, the polycarbodiimide compound to be added to polyester resins is required to have an amount of residual amine as low as possible and to have good processability in kneading, molding, without deteriorating hydrolysis resistance imparted to the polyester resins through addition of the polycarbodiimide compound.

The present invention has been made so as to solve the above problems and aims at providing a polycarbodiimide compound which has a small amount of residual amine and has good processability when the polycarbodiimide compound is added to polyester resin while keeping hydrolysis resistance of polyester resin imparted thereto through addition of the polycarbodiimide compound and at providing a polyester resin composition and polyester resin modifier using the polycarbodiimide compound.

The present invention is based on the following finding: a polycarbodiimide compound in which terminal isocyanate groups are capped by an amine compound having a predetermined boiling point and which has a predetermined degree of polymerization of carbodiimide groups is excellent as a polyester resin modifier in terms of hydrolysis resistance and processability.

That is, the present invention provides the following [<NUM>] to [<NUM>], as defined in the appended claims.

The polycarbodiimide compound of the present invention has a small amount of residual amine derived from raw material and can be obtained with high quality. In addition, by virtue of adding the polycarbodiimide compound to polyester resins, good processability in kneading, molding is provided without deteriorating hydrolysis resistance imparted to the polyester resins.

Accordingly, a polyester resin composition using the polycarbodiimide compound has good hydrolysis resistance and is excellent in processability.

Further, according to the present invention, a polyester resin modifier capable of successfully imparting hydrolysis resistance to polyester resins is provided by using the polycarbodiimide compound.

Hereinafter, a polycarbodiimide compound, and a polyester resin composition and polyester resin modifier using the polycarbodiimide compound according to the present invention will be described in detail.

The polycarbodiimide compound of the present invention is represented by the following general formula (<NUM>):.

RmNH<NUM>-m-CO-NH-Z-(N=C=N-Z)n-NH-CO-NH<NUM>-mRm     (<NUM>).

The amine compound constitutes both terminals of the polycarbodiimide compound represented by formula (<NUM>) above, caps terminal isocyanate groups, and introduces urea bonds. The amine compound is represented by RmNH<NUM>-m, and m is <NUM> or <NUM>. That is, the amine compound is a primary amine (RNH<NUM>) or a secondary amine (R<NUM>NH). R is a hydrocarbon group, and two Rs in the secondary amine may be the same or different from each other. In addition, Rs at both terminals represented in formula (<NUM>) above may be the same or different from each other.

The amine compound is a compound having a boiling point at <NUM> atm (hereinafter simply referred to as a "boiling point") of <NUM> or lower, preferably having a boiling point of <NUM> to <NUM>, and more preferably having a boiling point of <NUM> to <NUM>.

When an amine compound having a high boiling point exceeding <NUM> is used as raw material for synthesizing the polycarbodiimide compound, the unreacted amine compound is likely to remain in the polycarbodiimide compound without being distilled away. A polycarbodiimide compound with a large amount of residual amine may adversely affect performance of polyester resins to which the polycarbodiimide compound is added.

In addition, urea bonds in the polycarbodiimide compound are likely to be cleaved at about <NUM> to <NUM>, the urea bonds are also likely to be cleaved by, for example, heating during melt kneading with polyester resins, causing the amine compound to be liberated, and the liberated amine compound may remain without vaporizing.

In contrast, an amine compound with a boiling point of <NUM> or lower is likely to vaporize, and when such an amine compound is used as raw material for synthesizing the polycarbodiimide compound, the amine compound is less likely to remain in the polycarbodiimide compound, and a high quality polycarbodiimide compound with a small amount of residual amine is obtained. In addition, a boiling point of <NUM> or higher is preferable for obtaining sufficient reactivity in reaction for capping the terminal isocyanate groups at the time of synthesizing the polycarbodiimide compound.

Examples of the amine compound includes an aliphatic amine having a boiling point of <NUM> or lower. Specific examples thereof include primary amines such as n-propylamine (boiling point: <NUM>), n-butylamine (boiling point: <NUM>), isobutylamine (boiling point: <NUM>), sec-butylamine (boiling point: <NUM>), tert-butylamine (boiling point: <NUM>), and cyclohexylamine (boiling point: <NUM>); and secondary amines such as diethylamine (boiling point: <NUM>) and diisopropylamine (boiling point: <NUM>). One of them may be used alone, or two or more thereof may be used in combination. Among these, from the viewpoint of, for example, ease of uniform mixing at the time of adding the polycarbodiimide compound to polyester resins, the amine compound is one or more selected from cyclohexylamine and diisopropylamine, and cyclohexylamine is preferable.

Z in formula (<NUM>) above is a residue obtained by removing two isocyanate groups from an aliphatic diisocyanate compound. A diisocyanate compound is a compound having two isocyanate groups.

The term "aliphatic diisocyanate compound" used herein means a diisocyanate compound which is not a compound in which carbon atoms directly bonded to isocyanate groups constitute an aromatic ring. That is, the hydrocarbon group bonded to isocyanate groups may be linear or cyclic and also includes a hydrocarbon group in which a carbon atom not directly bonded to an isocyanate group constitutes an aromatic group.

When Z described above is a compound in which carbon atoms directly bonded to isocyanate groups constitute an aromatic ring, that is, a compound derived from an aromatic isocyanate compound, the polycarbodiimide compound is less likely to impart sufficient hydrolysis resistance to polyester resins, polyester resins to which the polycarbodiimide compound is added has high viscosity, and processability in kneading, molding becomes poor.

Examples of the aliphatic diisocyanate compound include tetramethylene diisocyanate, hexamethylene diisocyanate, <NUM>,<NUM>-cyclohexane diisocyanate, dicyclohexylmethane-<NUM>,<NUM>'-diisocyanate, methylcyclohexane diisocyanate, <NUM>,<NUM>-bis(isocyanatomethyl)cyclohexane, <NUM>-isocyanatomethyl-<NUM>,<NUM>,<NUM>-trimethylcyclohexyl isocyanate (another name: isophorone diisocyanate), xylylene diisocyanate, and <NUM>,<NUM>-bis(<NUM>-isocyanato-<NUM>-propyl)benzene (another name: tetramethylxylylene diisocyanate). One of them may be used alone, or two or more thereof may be included. Among these, dicyclohexylmethane-<NUM>,<NUM>'-diisocyanate, isophorone diisocyanate, and tetramethylxylylene diisocyanate are preferable from the viewpoint of safety, the effect of improving hydrolysis resistance of polyester resin.

The symbol n in formula (<NUM>) above represents the number of carbodiimide groups contained in the polycarbodiimide compound and is herein referred to as "degree of polymerization of carbodiimide groups".

The above symbol n is any integer of <NUM> to <NUM>, preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>.

The polycarbodiimide compound added to polyester resins can impart hydrolysis resistance by virtue of its carbodiimide groups. When the above n is less than <NUM>, sufficient hydrolysis resistance cannot be provided. In addition, when the above n is <NUM> or less, the polycarbodiimide compound is enabled to have adequate viscosity at a heating temperature in melt kneading with polyester resin, compatibility becomes good, and a uniform mixture with polyester resin is likely to be obtained. Accordingly, such a polycarbodiimide compound has good processability in kneading, molding.

A method for producing the polycarbodiimide compound is not particularly limited and the polycarbodiimide compound can be produced by a known production method. For example, the polycarbodiimide compound can be produced by a production method comprising the step of subjecting the aliphatic diisocyanate compound to carbodiimidization reaction using a carbodiimidizing catalyst to obtain an isocyanate-terminated polycarbodiimide, and the step of performing reaction for capping a terminal isocyanate group of the isocyanate-terminated polycarbodiimide using the amine compound to obtain the polycarbodiimide compound. The method shown in Examples below is exemplified as a specific production method.

The carbodiimidizing catalyst has an action of promoting decarboxylation condensation reaction of the aliphatic diisocyanate compound. Examples thereof include an organic phosphorous compound such as a phospholene compound and a phosphoric ester compound; and an organometallic compound such as a metal alkoxide, a metal carbonyl complex, and a metal acetylacetonato complex. Phospholene oxides are preferable as the organic phosphorous compound from the viewpoint of catalytic activity. In addition, alkoxides of titanium, hafnium, zirconium are preferable as the organometallic compound.

Phospholene oxides are more preferable, and specific examples thereof include <NUM>-methyl-<NUM>-phenyl-<NUM>-phospholene-<NUM>-oxide, <NUM>-methyl-<NUM>-ethyl-<NUM>-phospholene-<NUM>-oxide, <NUM>-phenyl-<NUM>-phospholene-<NUM>-oxide, <NUM>-ethyl-<NUM>-phospholene-<NUM>-oxide, <NUM>-methyl-<NUM>-phospholene-<NUM>-oxide, and <NUM>-phospholene isomers thereof. Among these, <NUM>-methyl-<NUM>-phenyl-<NUM>-phospholene-<NUM>-oxide is more preferable from the viewpoint of catalytic activity, availability.

An amount of the carbodiimidizing catalyst to be used for the carbodiimidization reaction may be a catalyst amount usually required to promote carbodiimidization reaction and is appropriately set according to the type of the diisocyanate compound, which is reaction raw material, the temperature and time for carbodiimidization reaction, the degree of polymerization of carbodiimide groups in a polycarbodiimide compound to be obtained. Usually, such an amount is <NUM> to <NUM> parts by mass, preferably <NUM> to <NUM> parts by mass, and more preferably <NUM> to <NUM> parts by mass with respect to <NUM> parts by mass of the aliphatic diisocyanate compound.

A reaction temperature for the carbodiimidization reaction is appropriately set according to adequate promotion of the reaction, the degree of polymerization of carbodiimide groups in a polycarbodiimide compound to be obtained. Usually, the reaction temperature is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably <NUM> to <NUM>.

A reaction time for the carbodiimidization reaction is appropriately set according to reaction temperature, the degree of polymerization of carbodiimide groups in a polycarbodiimide compound to be obtained. Usually, the reaction time is preferably <NUM> to <NUM> hours, more preferably <NUM> to <NUM> hours, and still more preferably <NUM> to <NUM> hours.

A reaction temperature for reaction for capping a terminal isocyanate group of the isocyanate-terminated polycarbodiimide is appropriately set, according to the type of the amine compound used for capping within a range capable of promoting the reaction without causing side reaction. Usually, the reaction temperature is preferably <NUM> to <NUM>, more preferably <NUM> to <NUM>, and still more preferably <NUM> to <NUM>.

A reaction time for reaction for capping a terminal isocyanate group of the isocyanate-terminated polycarbodiimide is appropriately set according to reaction temperature, the type of the amine compound. Usually, the reaction time is preferably <NUM> to <NUM> hours, more preferably <NUM> to <NUM> hours, and still more preferably <NUM> to <NUM> hours.

The polyester resin composition of the present invention comprises the above-described polycarbodiimide compound and polyester resin.

From the viewpoint of performance required for its application, the polyester resin composition may comprises a known additive applied to polyester resins such as an antioxidant, a flame retardant, an ultraviolet absorber, and a colorant, for example, to the extent not impairing the effect of the present invention as needed.

The polyester resins are resins having, as a basic constitution, a polycondensate of a polycarboxylic acid and a polyhydric alcohol, a polycondensate of a hydroxy acid, and well-known polyester resins can be used.

Examples of the polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), polybutylene adipate terephthalate (PBAT), a polyhydroxyalkanoic acid (PHA) such as polylactic acid (PLA) and polyhydroxy butyric acid (PHB), polycaprolactone (PCL), polyethylene naphthalate, polyarylate, and an ethylene terephthalate-isophthalate copolymer. One of them may be used alone, or two or more thereof may be used in combination. Among these, PET, PBT, PBS, PBSA, PLA, and PHB are preferably used from the viewpoint of industrial availability and recyclability. From the viewpoint of biomass plastic, PLA, PHB are preferable, for example.

In the polyester resin composition, a content of the polycarbodiimide compound is preferably <NUM> to <NUM> parts by mass, more preferably <NUM> to <NUM> parts by mass, and still more preferably <NUM> to <NUM> parts by mass with respect to <NUM> parts by mass of the polyester resin.

When the content is <NUM> parts by mass or more, sufficient hydrolysis resistance can be imparted to the polyester resin. In addition, when the content is <NUM> parts by mass or less, deterioration in processability in kneading and molding caused by excessive addition of the polycarbodiimide compound can be prevented, and reduction in strength of a molded article formed from the polyester resin composition can be suppressed.

The polyester resin composition can be obtained by melting and kneading the polycarbodiimide compound and the polyester resin, for example. At this time, a mixture obtained by mixing the polycarbodiimide compound and the polyester resin in advance may be melted and kneaded, or the polycarbodiimide compound may be added to the polyester resin having been melted followed by kneading. Furthermore, a resin compound such as a masterbatch is once prepared, and the resin compound and polyester resin may be melted and kneaded by any of the above methods. It should be noted that the above-described additives may be added besides the polycarbodiimide compound to the extent not impairing the effect of the present invention.

Melting and kneading means is not particularly limited, and a known kneader can be used. Examples of the kneader include a single-screw extruder, a twin-screw extruder, and a rolling mixer.

Production of a polyester resin product using the polyester resin composition can be carried out by molding using a known method such as an injection molding method, a film molding method, a blow molding method, and a foam molding method. The polyester resin composition can be molded into various forms such as a film form, a sheet form, and a block form at a temperature equal to or higher than the melting point of the polyester resin used.

A polyester resin modifier of the present invention includes the above-described polycarbodiimide compound.

As described above, the polycarbodiimide compound of the present invention is capable of successfully imparting hydrolysis resistance by adding the polycarbodiimide compound to polyester resins and therefore can be preferably used as a polyester resin modifier.

The polyester resin modifier includes a compatibilizer having a function of improving compatibility of polyester resins. At least one of resins to which the compatibilizer is added is polyester resins. The compatibilizer can successfully compatibilize different types of polyester resins with each other or successfully compatibilize polyester resins and polyamide resins.

A polyester resin composition with good compatibility can be obtained, also in a case where the polyester resin modifier is such a compatibilizer, by the same operation as melt kneading for obtaining the above-described polyester resin composition using different types of polyester resins or using polyester resins and polyamide resins.

Polyester resins to which the compatibilizer is added may be selected from the polyester resins listed in the description for the polyester resin composition.

In a case where a polyester resin composition is prepared by using different type of polyester resin in combination, compatibility is usually poor when a difference between solubility parameters (SP values) of polyester resin (A) and polyester resin (B), which are different from each other, obtained by Fedors' method is <NUM> (cal/cm<NUM>)<NUM>/<NUM> or more. For example, PLA (<NUM>) and PBS (<NUM>), PLA (<NUM>) and PBSA (<NUM> to <NUM>), PET (<NUM>) and PLA (<NUM>), PLA (<NUM>) and PCL (<NUM>) are exemplified (the numerical values in the parentheses are SP values [(cal/cm<NUM>)<NUM>/<NUM>]).

While the compatibilizer can be applied to any type of polyester resin, the compatibilizer is especially effective in improving compatibility between different type of polyester resin with the difference between SP values thereof is as large as <NUM> (cal/cm<NUM>)<NUM>/<NUM> or more.

In addition, while examples of the polyamide resins are not particularly limited, examples thereof include nylon <NUM> and nylon <NUM> which are general-purpose resin. Even in a case where a polyester resin and a polyamide resin are used in combination to prepare a polyester resin composition, the compatibilizer can effectively improve compatibility therebetween.

Whether compatibility between different types of resins used in combination for a polyester resin composition to which the compatibilizer is added is good or poor can be determined using, as an index, a haze of a sheet-shaped molding (specimen) of the polyester resin composition. The haze can be measured by, in particular, the method described in Examples described later using a value measured by a method according to JIS K <NUM>:<NUM>, that is, out of transmitted light passing through a specimen, a percentage of transmitted light that deviates from the incident light by <NUM>° or more due to forward scattering. With a decrease in the value of the haze, the scattering of light becomes smaller, and the transmittance of the specimen becomes better. As such, compatibility between different types of resins used in combination for the polyester resin composition is considered to be good when the transmittance is good.

In a case where the polyester resin modifier is the compatibilizer, the polycarbodiimide compound in a polyester resin composition may also exert good compatibility at the same content as described above.

The polyester resin modifier may preliminarily include, in addition to the polycarbodiimide compound, the same additives described in the description for the polyester resin composition as appropriate according to application thereof to the extent not impairing the effect of the present invention. When such a polyester resin modifier is used in producing the polyester resin composition described above, effort for separately adding the additives can be saved, and work efficiency can be enhanced.

It should be noted that while characteristics of the modifier are not particularly limited, the modifier is preferably in solid form, especially, in powder or pellet form from the viewpoint of ease of handling.

Details of the raw material compounds used for synthesizing polycarbodiimide compounds in Examples and Comparative Examples described below are shown below.

Analyses and measurement in synthesizing polycarbodiimide compounds were conducted by the apparatuses or methods shown below.

Apparatus used: Fourier transform infrared spectrophotometer "FTIR-8200PC" (manufactured by SHIMADZU CORPORATION).

Apparatus used: automatic titrator "COM-<NUM>" (manufactured by HIRANUMA Co.

A toluene solution of DBA with a known concentration was mixed with an isocyanate-terminated polycarbodiimide obtained through polycarbodiimidization reaction, the terminal isocyanate group and DBA were reacted, the remaining DBA was subjected to neutralization titration with a hydrochloric acid standard solution, and the amount of remaining isocyanate groups (terminal NCO amount [mass%]) was calculated by a potentiometric titration method. The degree of polymerization n of carbodiimide groups was obtained from this terminal NCO amount.

To a reaction container equipped with a reflux condenser and a stirrer, <NUM> parts by mass of HMDI and <NUM> parts by mass of <NUM>-methyl-<NUM>-phenyl-<NUM>-phospholene-<NUM>-oxide as a carbodiimidizing catalyst were added followed by stirring and mixing at <NUM> for <NUM> hours under nitrogen stream to conduct carbodiimidization reaction to obtain an isocyanate-terminated polycarbodiimide.

With respect to the obtained isocyanate-terminated polycarbodiimide, an absorption peak around the wavelength of <NUM>-<NUM> derived from the carbodiimide groups was observed by IR spectrum measurement. In addition, the terminal NCO amount was <NUM>% by mass, and the degree of polymerization of carbodiimide groups was <NUM>.

Thereafter, under nitrogen stream, <NUM> parts by mass (an amount equivalent to the amount of terminal isocyanate groups in the isocyanate-terminated polycarbodiimide in terms of mole) of CHA was added to the isocyanate-terminated polycarbodiimide at <NUM> followed by stirring and mixing for <NUM> hours to conduct capping reaction for terminal isocyanate groups.

After the absorption peak at the wavelength of <NUM> to <NUM>-<NUM> derived from the isocyanate groups was confirmed to have disappeared by IR spectrum measurement, the reaction product was taken out of the reaction container and cooled to room temperature to obtain a light yellow transparent solid polycarbodiimide compound.

Each polycarbodiimide compound having the predetermined degree of polymerization n shown in Table <NUM> below was synthesized in the same manner as in Example <NUM> except that the diisocyanate compound, amine compound, and reaction conditions (temperature and time) of carbodiimidization reaction were respectively changed as shown in Table <NUM> below in Example <NUM>.

To a reaction container equipped with a reflux condenser and a stirrer, <NUM> parts by mass of MDI and <NUM> parts by mass of CHA were added followed by stirring and mixing at room temperature (<NUM>) for <NUM> hours under nitrogen stream to conduct capping reaction for terminal isocyanate groups of MDI. Thereafter, <NUM> parts by mass of <NUM>-methyl-<NUM>-phenyl-<NUM>-phospholene-<NUM>-oxide was added as a carbodiimidizing catalyst followed by stirring and mixing at <NUM> for <NUM> hours to conduct carbodiimidization reaction, and a light yellow transparent solid polycarbodiimide compound was obtained.

Each polyester resin composition was prepared using the polycarbodiimide compound synthesized in each of Examples and Comparative Examples described above and polyester resins (and a polyamide resin) shown below.

Ny6: nylon <NUM>; "UNITIKA nylon <NUM> A1030BRL," manufactured by UNITIKA LTD.

After <NUM> parts by mass of PBSA was melted at <NUM> using a laboratory mixer ("segment mixer KF70V," manufactured by Toyo Seiki Seisaku-sho, Ltd. , LABO PLASTOMILL (R); the same applies hereinafter), <NUM> parts by mass of the polycarbodiimide compound was added thereto followed by kneading for three minutes to prepare polyester resin composition (<NUM>).

After <NUM> parts by mass of PLA and <NUM> parts by mass of PBSA were melted at <NUM> using a laboratory mixer, <NUM> parts by mass of the polycarbodiimide compound was added thereto followed by kneading for three minutes to prepare polyester resin composition (<NUM>) (PET/PBSA).

After <NUM> parts by mass of PLA and <NUM> parts by mass of PBS were melted at <NUM> using a laboratory mixer, <NUM> parts by mass of the polycarbodiimide compound was added thereto followed by kneading for three minutes to prepare polyester resin composition (<NUM>) (PET/PBS).

After <NUM> parts by mass of PET and <NUM> parts by mass of Ny6 were melted at <NUM> using a laboratory mixer, <NUM> parts by mass of the polycarbodiimide compound was added thereto followed by kneading for three minutes to prepare polyester resin composition (<NUM>) (PET/Ny6).

Each of the polycarbodiimide compounds and polyester resin compositions obtained above was evaluated in terms of the following items. Evaluation results thereof are summarized and shown in Table <NUM> below.

The polycarbodiimide compound was dissolved in tetrahydrofuran and subsequently mixed with acetonitrile to precipitate the polycarbodiimide compound followed by filtration. The quantity of the unreacted amine compound remaining in the filtrate was determined by high performance liquid chromatography (HPLC). Measurement conditions of HPLC are as follows.

In Table <NUM> below, evaluation results in which the case where the amount of residual amine is less than <NUM> ppm is designated as "A", and the case where the amount of residual amine is <NUM> ppm or more is designated as "B" are shown.

The polyester resin composition (<NUM>) was molded into a sheet form with a thickness of about <NUM> by hot pressing at <NUM>, and a strip-shaped specimen with a width of <NUM> and a length of <NUM> was subsequently prepared.

A tensile test was conducted immediately after the preparation (early stage) and after damp heat treatment. The damp heat treatment was carried out by exposing the specimen to a temperature of <NUM> and relative humidity of <NUM>% for <NUM> hours using a damp heat tester.

The tensile test was carried out by measuring tensile elongation at breakage of the specimen under conditions of a gauge length of <NUM> and tensile speed of <NUM>/min using a tensile tester ("<NUM>" manufactured by Instron Corporation). The relative ratio of the tensile elongation after damp heat treatment was calculated based on the tensile elongation at the early stage as <NUM>.

With an increase in the relative ratio of tensile elongation, the degree of decrease in tensile elongation before and after damp heat treatment becomes smaller, and hydrolysis resistance can be said to be excellent.

In Table <NUM> below, evaluation results in which the case where the relative ratio of tensile elongation is <NUM> or more is designated as "A", the case where the relative ratio of tensile elongation is <NUM> or more and less than <NUM> is designated as "B", and the case where the relative ratio of tensile elongation is less than <NUM> is designated as "C" are shown. Incidentally, as a comparative reference, the same tensile test as described above was also conducted on the case where no polycarbodiimide compound was added, and the evaluation result thereof was "C".

The melt viscosity of polyester resin composition (<NUM>) was measured at <NUM> by a capillary rheometer ("flow tester CFT-500D," manufactured by SHIMADZU CORPORATION) using an orifice with a diameter of <NUM> × <NUM>.

It can be said that with a decrease in the melt viscosity, the processability in uniformly mixing polyester resin composition (<NUM>) becomes better, and molding is easier, and processability is excellent.

In Table <NUM> below, evaluation results in which the case where the melt viscosity is less than <NUM>,<NUM> Pa·s is designated as "A", the case where the melt viscosity is <NUM>,<NUM> Pa·s or more and less than <NUM>,<NUM> Pa·s is designated as "B", and the case where the melt viscosity is <NUM>,<NUM> Pa·s or more is designated as "C" are shown.

Each of obtained polyester resin compositions (<NUM>) to (<NUM>) was molded into a sheet form with a thickness of <NUM> to <NUM> by hot pressing to prepare a specimen (<NUM> × <NUM>). The hot pressing temperature was set to <NUM> for polyester resin compositions (<NUM>) and (<NUM>) and to <NUM> for polyester resin composition (<NUM>).

In addition, each blank specimen was prepared in the same manner as the above-described specimen using each polyester resin composition obtained by conducting the same operation except that the polycarbodiimide compound was not added in preparing polyester resin compositions (<NUM>) to (<NUM>).

The haze of each of the specimens and blank specimens was measured by a method according to JIS K <NUM>:<NUM> using a haze meter ("NDH5000," manufactured by NIPPON DENSHOKU INDUSTRIES CO.

As a value of the haze decreases, light scattering becomes smaller, and transmittance of the specimen becomes better. When compatibility between two types of resins among polyester resin compositions (<NUM>) to (<NUM>) is good, transmittivity of the specimen is good, and the haze value decreases. Therefore, the haze value was used as an index of compatibility.

It can be said that with an increase in the difference (ΔH) obtained by subtracting the haze value of the specimen from the haze value (reference value) of the blank specimen, the effect of the added polycarbodiimide compound as a compatibilizer is superior.

In Table <NUM> below, evaluation results in which the case where the ΔH is <NUM>% or more is designated as "A", the case where the ΔH is <NUM>% or more and less than <NUM>% is designated as "B", and the case where the ΔH is less than <NUM>% is designated as "C" are shown. Examples <NUM> and <NUM> are reference examples.

As seen from the evaluation results in Table <NUM>, it can be said that the obtained polycarbodiimide compound according to the present invention has a small amount of residual amine derived from raw material, and the quality thereof is high.

In addition, the result of hydrolysis resistance for polyester resin composition (<NUM>) obtained by using the polycarbodiimide compound is also good, processability thereof is also excellent, and it has been confirmed that the polycarbodiimide compound provides a good effect as a polyester resin modifier.

Claim 1:
A polycarbodiimide compound represented by the following general formula (<NUM>):

        RmNH<NUM>-m-CO-NH-Z-(N=C=N-Z)n-NH-CO-NH<NUM>-mRm     (<NUM>)

wherein Rm is a hydrocarbon residue of an amine compound which is represented by RmNH<NUM>-m and m is <NUM> or <NUM>, and the amine compound being one or more selected from cyclohexylamine and diisopropylamine;
Z is a residue obtained by removing two isocyanate groups from an aliphatic diisocyanate compound; and
n is any integer of <NUM> to <NUM>, and n being determined according to the method specified in the specification.