PRODUCTION METHOD FOR CHLORINATED VINYL CHLORIDE RESIN

Abstract

The present invention provides a method for producing a chlorinated polyvinyl chloride which is excellent in thermal stability (initial discoloration resistance, heat-resistant stability) and is capable of providing a transparent article. The present invention relates to a method for producing a chlorinated polyvinyl chloride through thermal chlorination of a reaction solution including a vinyl chloride aqueous suspension that contains a vinyl chloride resin in a hermetically sealable reaction vessel, the method including: step 1 of initiating thermal chlorination by heating the reaction solution to 55 C. to 70 C. and then introducing chlorine into the reaction vessel; step 2 of raising the temperature of the reaction solution while maintaining the temperature inside the reaction vessel not higher than the glass transition temperature of a partially chlorinated polyvinyl chloride; and step 3 of carrying out the thermal chlorination at a predetermined temperature of 85 C. or higher but lower than 115 C. after the chlorine content of the partially chlorinated polyvinyl chloride reaches 58% by weight or more, the steps 1 to 3 being performed under stirring at a net stirring power (Pv) inside the reaction vessel of 0.2 to 2.5 kw/m.sup.3 per 1 m.sup.3 of the reaction solution.

Claims

1. A method for producing a chlorinated polyvinyl chloride through thermal chlorination of a reaction solution including a vinyl chloride aqueous suspension that contains a vinyl chloride resin in a hermetically sealable reaction vessel, the method comprising: step 1 of initiating thermal chlorination by heating the reaction solution to 55 C. to 70 C. and then introducing chlorine into the reaction vessel; step 2 of raising the temperature of the reaction solution while maintaining the temperature inside the reaction vessel not higher than the glass transition temperature of a partially chlorinated polyvinyl chloride; and step 3 of carrying out the thermal chlorination at a predetermined temperature of 85 C. or higher but lower than 115 C. after the chlorine content of the partially chlorinated polyvinyl chloride reaches 58% by weight or more, the steps 1 to 3 being performed under stirring at a net stirring power (Pv) inside the reaction vessel of 0.2 to 2.5 kw/m.sup.3 per 1 m.sup.3 of the reaction solution.

2. The method for producing a chlorinated polyvinyl chloride according to claim 1, wherein the thermal chlorination is carried out at a predetermined temperature of 85 C. or higher but lower than 95 C. after the chlorine content of the partially chlorinated polyvinyl chloride reaches 58% by weight or higher but lower than 60% by weight in the step 3.

3. The method for producing a chlorinated polyvinyl chloride according to claim 1, wherein the thermal chlorination is carried out at a predetermined temperature of 95 C. or higher but lower than 105 C. after the chlorine content of the partially chlorinated polyvinyl chloride reaches 60% by weight or higher but lower than 62% by weight in the step 3.

4. The method for producing a chlorinated polyvinyl chloride according to claim 1, wherein the thermal chlorination is carried out at a predetermined temperature of 105 C. or higher but lower than 115 C. after the chlorine content of the partially chlorinated polyvinyl chloride reaches 62% by weight or higher in the step 3.

5. A chlorinated polyvinyl chloride article comprising a chlorinated polyvinyl chloride produced by the method for producing a chlorinated polyvinyl chloride according to claim 1.

6. The chlorinated polyvinyl chloride article according to claim 5, which contains 80 to 95% by weight of the chlorinated polyvinyl chloride and has a transparency of 1 to 10 in a shape of a 5-mm-thick plate.

Description

DESCRIPTION OF EMBODIMENTS

[0068] Embodiments of the present invention are more specifically described in the following with reference to, but not limited to, examples.

EXAMPLE 1

[0069] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0070] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.).

[0071] Then, the temperature of the aqueous suspension was raised to 90 C. over 1.1 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0072] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0073] Thermal chlorination was continued for 9.8 hours from introduction of chlorine (temperature at this time is referred to as a thermal chlorination temperature), while the temperature of the aqueous suspension was maintained at 90 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 58.2% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 0.6 kw/m.sup.3.

[0074] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0075] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 58.2% by weight was 91.1 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained not higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 90 C.

[0076] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.9% by weight.

[0077] The obtained chlorinated polyvinyl chloride was blended with a butyl tin maleate stabilizer, butyl stearate, a methyl methacrylate-butadiene-styrene (MBS) resin, and an acrylic processing aid (polymethyl methacrylate) to prepare a chlorinated polyvinyl chloride composition in which the chlorinated polyvinyl chloride content was 92.5% by weight, the butyl tin maleate stabilizer content was 1.9% by weight, butyl stearate content was 0.5% by weight, the MBS resin content was 4.6% by weight, and the acrylic processing aid content was 0.5% by weight.

[0078] The obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 185 C., thereby providing a chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate.

EXAMPLE 2

[0079] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0080] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.).

[0081] Then, the temperature of the aqueous suspension was raised to 95 C. over 1.4 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0082] Thermal chlorination was continued for 8.2 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 95 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 60.7% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 0.5 kw/m.sup.3.

[0083] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0084] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 60.7% by weight was 105.8 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained not higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 95 C.

[0085] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 65.0% by weight.

[0086] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

EXAMPLE 3

[0087] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0088] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.)

[0089] Then, the temperature of the aqueous suspension was heated to 100 C. over 2.0 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0090] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0091] Thermal chlorination was continued for 6.5 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 100 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 61% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 1.2 kw/m.sup.3.

[0092] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0093] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 61% by weight was 108.0 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained not higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 100 C.

[0094] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.8% by weight.

[0095] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

EXAMPLE 4

[0096] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0097] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.)

[0098] Then, the temperature of the aqueous suspension was raised to 110 C. over 2.6 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0099] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0100] Thermal chlorination was continued for 4.2 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 110 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 62.5% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 1.8 kw/m.sup.3.

[0101] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0102] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 62.5% by weight was 118.6 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained not higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 110 C.

[0103] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 65.0% by weight.

[0104] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

EXAMPLE 5

[0105] The chlorinated polyvinyl chloride obtained in Example 1 was blended with a butyl tin maleate stabilizer, butyl stearate, a MBS resin, an acrylic processing aid to prepare a chlorinated polyvinyl chloride composition in which the chlorinated polyvinyl chloride content was 88.4% by weight, the butyl tin maleate stabilizer content was 2.6% by weight, the butyl stearate content was 0.5% by weight, the MBS resin content was 7.5% by weight, and the acrylic processing aid content was 1.0% by weight.

[0106] The obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 185 C., thereby providing a chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate.

EXAMPLE 6

[0107] The chlorinated polyvinyl chloride obtained in Example 1 was blended with polyvinyl chloride, a butyl tin maleate stabilizer, butyl stearate, a MBS resin, and an acrylic processing aid to prepare a chlorinated polyvinyl chloride composition in which the chlorinated polyvinyl chloride content was 82.5% by weight, the vinyl chloride resin content was 2.8% by weight, the butyl tin maleate stabilizer content was 1.9% by weight, the butyl stearate content was 0.5% by weight, the MBS resin content was 4.6% by weight, and the acrylic processing aid content was 1.5% by weight.

[0108] The obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 185 C., thereby providing a chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate.

EXAMPLE 7

[0109] The chlorinated polyvinyl chloride obtained in Example 1 was blended with polyvinyl chloride, a butyl tin maleate stabilizer, butyl stearate, a MBS resin, and an acrylic processing aid to prepare a chlorinated polyvinyl chloride composition in which the chlorinated polyvinyl chloride content was 78.5% by weight, the vinyl chloride resin content was 14.0% by weight, the butyl tin maleate stabilizer content was 1.9% by weight, the butyl stearate content was 0.5% by weight, the MBS resin content was 4. 6% by weight, and the acrylic processing aid content was 0.5% by weight.

[0110] The obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 185 C., thereby providing a chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate.

EXAMPLE 8

[0111] The chlorinated polyvinyl chloride obtained in Example 1 was blended with a butyl tin maleate stabilizer, butyl stearate, a MBS resin, and an acrylic processing aid to prepare a chlorinated polyvinyl chloride composition in which the chlorinated polyvinyl chloride content was 95.2% by weight, the butyl tin maleate stabilizer content was 0.8% by weight, the butyl stearate content was 0.5% by weight, the MBS resin content was 3.0% by weight, and the acrylic processing aid content was 0.5% by weight.

[0112] The obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 185 C., thereby providing a chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate.

COMPARATIVE EXAMPLE 1

[0113] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0114] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.).

[0115] Then, the temperature of the aqueous suspension was raised to 95 C. over 0.5 hours. At this time, the temperature inside the reaction vessel exceeded the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0116] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0117] Thermal chlorination was continued for 7.9 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 95 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 58.0% by weight. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 0.1 kw/m.sup.3.

[0118] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0119] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 58.0% by weight was 86.6 C. That is, the temperature of the aqueous suspension in the reaction vessel exceeded the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 95 C.

[0120] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.8% by weight.

[0121] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

COMPARATIVE EXAMPLE 2

[0122] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0123] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.)

[0124] Then, the temperature of the aqueous suspension was raised to 100 C. over 0.7 hours. At this time, the temperature inside the reaction vessel exceeded the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0125] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0126] Thermal chlorination was continued for 6.1 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 100 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 58.9% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 2.8 kw/m.sup.3.

[0127] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0128] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 58.9% by weight was 93.0 C. That is, the temperature of the aqueous suspension in the reaction vessel exceeded the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 100 C.

[0129] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.9% by weight.

[0130] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

COMPARATIVE EXAMPLE 3

[0131] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0132] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.)

[0133] Then, the temperature of the aqueous suspension was raised to 110 C. over 1.0 hour. At this time, the temperature inside the reaction vessel exceeded the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0134] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0135] Thermal chlorination was continued for 3.8 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 110 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 59.4% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 3.0 kw/m.sup.3.

[0136] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0137] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 59.4% by weight was 96.5 C. That is, the temperature of the aqueous suspension in the reaction vessel exceeded the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 110 C.

[0138] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.0% by weight.

[0139] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

COMPARATIVE EXAMPLE 4

[0140] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 80 C.

[0141] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 80 C.).

[0142] Then, the temperature of the aqueous suspension was raised to 90 C. over 1.1 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0143] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0144] Thermal chlorination was continued for 9.1 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 90 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 58.3% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 0.6 kw/m.sup.3.

[0145] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0146] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 58.3% by weight was 91.5 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained hot higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 90 C.

[0147] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.9% by weight.

[0148] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

COMPARATIVE EXAMPLE 5

[0149] A 300-L glass-lined reaction vessel was charged with 200 kg of deionized water and 56 kg of a vinyl chloride resin having an average degree of polymerization of 600. The contents were stirred to give an aqueous suspension in which the vinyl chloride resin was dispersed in the water. Then, the inside of the reaction vessel was heated to raise the temperature of the aqueous suspension to 70 C.

[0150] Next, the reaction vessel was decompressed for removal of oxygen (oxygen amount: 100 ppm), and chlorine (oxygen content: 50 ppm) was introduced thereinto in such a manner that the partial pressure of chlorine was set to 0.4 MPa to initiate thermal chlorination (chlorination onset temperature: 70 C.)

[0151] Then, the temperature of the aqueous suspension was raised to 90 C. over 1.1 hours such that the temperature did not exceed the glass transition temperature of a partially chlorinated polyvinyl chloride.

[0152] The glass transition temperature of the partially chlorinated polyvinyl chloride was obtained by differential scanning calorimetry (DSC) in conformity with JIS K7121.

[0153] Thermal chlorination was continued for 10.3 hours from introduction of chlorine, while the temperature of the aqueous suspension was maintained at 90 C. and the partial pressure of chlorine was maintained at 0.4 MPa after the chlorine content of the partially chlorinated polyvinyl chloride reached 55.8% by weight. Then, supply of chlorine gas was stopped to terminate thermal chlorination. The net stirring power (Pv) from the start to the end of thermal chlorination in the reaction vessel was 0.6 kw/m.sup.3.

[0154] In the thermal chlorination step, a hydrogen peroxide solution (200 ppm) was added at a rate of 15 ppm/Hr of hydrogen peroxide relative to the vinyl chloride resin after the chlorine content reached 61% by weight until the end of the chlorination reaction.

[0155] The glass transition temperature when the chlorine content of the partially chlorinated polyvinyl chloride reached 55.8% by weight was 91.3 C. That is, the temperature of the aqueous suspension in the reaction vessel was maintained not higher than the glass transition temperature of the partially chlorinated polyvinyl chloride in the reaction vessel during a period from the start of thermal chlorination until the temperature was raised to 90 C.

[0156] Next, nitrogen gas was fed thereinto for removal of unreacted chlorine. The obtained chlorinated polyvinyl chloride slurry was neutralized with sodium hydroxide, washed with water, dehydrated, and dried to give a chlorinated polyvinyl chloride in the powder form. The obtained chlorinated polyvinyl chloride had a chlorine content of 64.8% by weight.

[0157] A chlorinated polyvinyl chloride composition and a chlorinated polyvinyl chloride article were obtained in the same manner as in Example 1, except that the above chlorinated polyvinyl chloride was used.

<Evaluation>

[0158] The chlorinated polyvinyl chloride compositions and the chlorinated polyvinyl chloride articles obtained in the examples and the comparative examples were evaluated for the following parameters. Table 1 shows the results.

(1) Degree of Yellowness

[0159] The degree of yellowness of each obtained chlorinated polyvinyl chloride article in the shape of a 2-mm-thick plate as a test sample was measured with a colorimeter produced by Nippon Denshoku Industries Co., Ltd.

(2) Thermal Stability

[0160] Each obtained chlorinated polyvinyl chloride composition was wound around a roll at 190 C. and roll-kneaded for a minute to be formed into a sheet. The sheet was heated in a gear oven at 200 C. The time (minutes) required for blackening of the sheet was measured.

(3) Transparency

[0161] Each obtained chlorinated polyvinyl chloride composition was wound around a roll at 165 C. and roll-kneaded for a minute, and pre-heated for three minutes and then pressurized for four minutes in a press machine at 165 C., thereby providing a test sample in the shape of a 5-mm-thick plate. The transparency of the obtained test sample was measured with a HAZE METER produced by Nippon Denshoku Industries Co., Ltd.

TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Step Thermal chlorination onset temperature ( C.) 70 70 70 70 70 70 70 Heat-up time (hours) 1.1 1.4 2 2.6 1.1 1.1 1.1 Thermal chlorination temperature ( C.) 90 95 100 110 90 90 90 Glass transision temperature at thermal chlorination 91.1 105.8 108 118.6 91.1 91.1 91.1 temperature ( C.) Chlorine content at thermal chlorination temperature 58.2 60.7 61 62.5 58.2 58.2 58.2 (wt %) Net stirring power (kw/m.sup.3) 0.6 0.5 1.2 1.8 0.6 0.6 0.6 Composition Chlorinated vinyl chloride 92.5 92.5 92.5 92.5 88.4 82.5 78.5 (wt %) Vinyl chloride 2.8 14.0 Butyl tin maleate stabilizer 1.9 1.9 1.9 1.9 2.6 1.9 1.9 Butyl stearate 0.5 0.5 0.5 0.5 0.5 0.5 0.5 MBS resin 4.6 4.6 4.6 4.6 7.5 4.6 4.6 Acrylic processing aid 0.5 0.5 0.5 0.5 1.0 1.5 0.5 Evaluation Chlorine content of chlorinated vinyl chloride 64.9 65.0 64.8 65.0 64.9 64.9 64.9 resin (wt %) Degree of yellowness 26 24 22 24 24 23 25 Thermal stability (minutes) 70 70 80 80 90 70 70 Transparency 3.4 4.1 3.8 3.5 4.7 5.8 35.1 Comparative Comparative Comparative Comparative Comparative Example 8 Example 1 Example 2 Example 3 Example 4 Example 5 Step Thermal chlorination onset temperature ( C.) 70 70 70 70 80 70 Heat-up time (hours) 1.1 0.5 0.7 1.0 1.1 1.1 Thermal chlorination temperature ( C.) 90 95 100 110 90 90 Glass transision temperature at thermal chlorination 91.1 86.6 93 96.5 91.5 91.3 temperature ( C.) Chlorine content at thermal chlorination temperature 58.2 58 58.9 59.4 58.3 55.8 (wt %) Net stirring power (kw/m.sup.3) 0.6 0.1 2.8 3.0 0.6 0.6 Composition Chlorinated vinyl chloride 95.2 92.5 92.5 92.5 92.5 92.5 (wt %) Vinyl chloride Butyl tin maleate stabilizer 0.8 1.9 1.9 1.9 1.9 1.9 Butyl stearate 0.5 0.5 0.5 0.5 0.5 0.5 MBS resin 3.0 4.6 4.6 4.6 4.6 4.6 Acrylic processing aid 0.5 0.5 0.5 0.5 0.5 0.5 Evaluation Chlorine content of chlorinated vinyl chloride 64.9 64.8 64.9 64.0 64.9 64.8 resin (wt %) Degree of yellowness 30 31 30 30 36 38 Thermal stability (minutes) 50 50 60 50 50 40 Transparency 23.5 35.0 32.2 38.3 43.4 39.1

INDUSTRIAL APPLICABILITY

[0162] The present invention can provide a method for producing a chlorinated polyvinyl chloride that has high initial discoloration resistance and heat-resistant stability to be excellent in thermal stability and is capable of providing a transparent article.