JPH0225923B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a vinyl chloride polymer (hereinafter simply referred to as PVC), and in particular to a method for obtaining PVC that has excellent processability and mechanical strength. In general, the molding process of PVC is strongly dependent on the particle morphology, state, and molecular structure because it uses a semi-molten powder processing method. Increasing the bulk specific gravity of PVC powder reduces the volume of the container required for storage, makes it easier to drop and fill from the hopper into the processing machine, and improves the penetration of the resin inside the processing machine. This is an essential condition for improving workability. However, when the bulk specific gravity increases, the gelation rate slows down, and the molded product is more likely to have cracks or cracks. Therefore, in order to increase the bulk specific gravity of PVC obtained by the suspension polymerization method, efforts have been made to change the type of dispersant, the amount added, the stirring speed, the shape of the stirring blade, etc. There is a limit. In addition, in the suspension polymerization method, a method of lowering the polymerization temperature is adopted as a way to increase the average degree of polymerization of PVC.
Lowering the polymerization temperature lowers the bulk specific gravity of PVC.
As the average degree of polymerization of PVC increases, the mechanical strength of the molded product should improve, but gelling properties deteriorate, so methods of increasing the molding temperature and adding large amounts of processing aids were adopted. However, it is difficult to obtain a uniform gelled state, and it is extremely difficult to improve mechanical strength. Furthermore,
When the bulk specific gravity of PVC with a high average degree of polymerization is increased,
The gelling property becomes worse. In addition, as a method to increase the bulk density of PVC,
Macromolecular Science, Volume A11, 1223~
Page 1234, 1977 describes a method in which vinyl chloride monomer is added before and after a pressure drop occurs in aqueous suspension polymerization of vinyl chloride monomer, but the gelling property It is also stated that there is a significant decrease in Further, U.S. Pat. No. 3,945,985 and U.S. Pat. No. 3,956,251 disclose suspension polymerization of PVC, in which PVC is first produced at a temperature of 15 to 50°C with a polymerization yield of 1 to 60%.
A polymerization method has been provided in which after polymerizing PVC, the polymerization temperature is raised to 60 to 80°C to polymerize PVC with a lower degree of polymerization. However, in these methods, there is a very low possibility that high molecular weight PVC and low molecular weight PVC will be mixed in the form of secondary or tertiary particles. That is, the suspension polymerized PVC particles are tertiary particles with an average particle size of about 100 microns, in which secondary particles with an average particle size of about 0.5 to 1.5 microns are aggregated with appropriate voids. The secondary particles are said to be composed of fibrils in which PVC molecular chains aggregate. In these methods, PVC with different molecular weights are mixed inside the secondary particles, so not only do they exhibit gelling properties that are lower than those between the two PVCs, but also the bulk specific gravity hardly increases, so there is no improvement in processability. Less is. Furthermore, when high molecular weight PVC and low molecular weight PVC are blended, they are mixed in the form of tertiary particles, but the bulk specific gravity does not increase. Therefore, the present invention provides a method for producing PVC which not only has a large bulk specific gravity and excellent gelling properties, but also has excellent mechanical strength of processed molded products. That is, the present invention performs the first stage polymerization of vinyl chloride monomer or a mixture of vinyl chloride monomer and other copolymerizable monomer in an aqueous medium, and the polymerization degree is greater than 600. A high molecular weight vinyl chloride polymer is obtained, and a mixture with a vinyl chloride monomer or another monomer copolymerizable with the vinyl chloride monomer and a dispersant are added to an aqueous medium containing the high molecular weight vinyl chloride polymer. production of a vinyl chloride polymer, characterized in that the monomer is subjected to a second stage polymerization such that the degree of polymerization is lower than that of the high molecular weight vinyl chloride polymer obtained in the first stage polymerization. It's a method. Other monomers that can be copolymerized with the vinyl chloride monomer that can be used in the present invention are not particularly limited, and known monomers can be used. In general, those having ethylenically unsaturated groups, such as olefin compounds such as ethylene and propylene; vinyl esters such as vinyl acetate and vinyl propionate; unsaturated monocarboxylic acids and their alkyl esters such as acrylic acid and α-alkyl acrylic acid. acrylic acid, methacrylic acid, ethyl acrylate, methyl methacrylate, acrylic acid amide,
Methacrylamide; unsaturated nitriles such as acrylonitrile; unsaturated dicarboxylic acids such as maleic acid and fumaric acid; alkyl esters thereof;
and its anhydrides; vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether;
Various other known copolymerizable monomers are preferably used. Further, the dispersant used in the present invention may be a known dispersant, for example, partially saponified polyvinyl alcohol, vinyl acetate-maleic anhydride copolymer, polyvinylpyrrolidone, gelatin, starch, methyl cellulose, hydroxypropyl cellulose, etc. are preferably used. used. The amount of these dispersants added is not necessarily limited and varies depending on the type of dispersant, stirring efficiency, polymerization temperature, type and composition of other copolymerizable monomers, particle size of PVC, etc. It is generally used in an amount of 0.02 to 2.0%, preferably 0.05 to 1%, based on the vinyl chloride monomer. The amount of dispersant added when polymerizing the second-stage monomer in the present invention affects the processing characteristics of the resulting PVC; for example, if the amount of dispersant is too small, processability will decrease. It is best to determine the amount to be added in advance. A known polymerization initiator is used in the polymerization of the monomers in the present invention, and commonly used polymerization initiators include, for example, lauroyl peroxide, tert-butyl peroxypivalate,
Benzoyl peroxide, isopropyldioxycarbonate, azobisisobutyronitrile,
Known oil-soluble polymerization initiators such as α,α'-azobis-4-methoxy2,4-dimethylvaleronitrile are preferably used. In the present invention, the polymerization rate of the monomer polymerized in the first stage is preferably 50% or more, preferably 70% or more. If the polymerization rate is lower than 50%, secondary particles and free monomers may coexist within the PVC tertiary particles surrounded by the dispersant.
Then, in the second stage of polymerization, when the dispersant, monomer, and if necessary a polymerization initiator are added and the monomer is polymerized, there is a possibility that PVC will be mixed in the secondary particles. There may also be cases where the effect is not fully demonstrated. On the other hand, when the polymerization rate is 50% or more, preferably 70% or more, there is almost no free monomer.
Since the pressure in the polymerization reactor begins to decrease, at this point, a dispersant, a monomer, and, if necessary, a polymerization initiator are newly added and the second stage polymerization is performed to fully exhibit the effects of the present invention. The polymerization conditions for the first stage of the present invention are not particularly limited, and may be selected from known polymerization conditions that result in a degree of polymerization greater than 600. For example, add the necessary dispersant, monomer, and polymerization initiator to an aqueous medium, and
By polymerizing the monomers at a temperature of 70℃,
PVC with a degree of polymerization greater than 600 can be obtained. In the second stage polymerization in the present invention, new vinyl chloride monomer or chloride is added to the aqueous medium, ie, the polymerization system, containing high molecular weight PVC with a polymerization degree higher than 600 obtained in the first stage polymerization. A mixture of the vinyl monomer and other monomers that can be copolymerized, a dispersant, and a polymerization initiator if necessary are added so that the degree of polymerization is lower than that of the high molecular weight PVC obtained in the first stage. It is an important requirement to polymerize the above monomers. For example, even if the degree of polymerization is the same, even if dried high molecular weight PVC is added to an aqueous medium and only the above-mentioned second stage polymerization is carried out, the molded product will have fish eyes and spots. The product will be different from the intended product. Therefore, in the present invention, the first
One of the requirements is to carry out the second stage polymerization subsequent to the stage polymerization, ie without drying the first stage polymer. However, it is possible to prepare the polymerization system by separating the first stage polymer from the aqueous medium and adding the necessary aqueous medium and additives for polymerization again without drying the polymer. Furthermore, as described above, one of the important requirements is to add new monomers and dispersants during the second stage polymerization that is carried out subsequent to the first stage polymerization. This is because if monomers are not added prior to the second stage polymerization, there will be almost no increase in the bulk specific gravity as described above, and the processability of the resulting PVC will not be improved, and similarly, the addition of dispersants can be obtained without
It is not possible to improve the workability of PVC. In the second stage polymerization of the present invention, the means for polymerizing the monomers so that the degree of polymerization is lower than the degree of polymerization of the high molecular weight PVC obtained in the first stage polymerization is not particularly limited, and any known means can be used. , the method can be employed as is or with modification. Generally, the second stage polymerization temperature is 60 to 85°C, preferably 5 to 20°C higher than the first stage polymerization temperature, or
Means such as adding a chain transfer agent during stage polymerization are preferably employed. The chain transfer agent may be appropriately selected from known ones, but generally includes saturated hydrocarbons such as pentane and heptane; chlorinated hydrocarbons such as carbon tetrachloride and trichlorethylene; propionaldehyde and butyl. Aldehydes such as aldehydes; organic mercaptans such as dodecyl mercaptan and 2-mercaptoethanol are preferably used. In particular, organic mercaptans have a large chain transfer effect, so that low molecular weight PVC can be efficiently polymerized. Examples of organic mercaptans include alkyl mercaptans such as octyl mercaptan and dodecyl mercaptan; mercaptoalkanols such as 2-mercaptoethanol and α-thioglycerol; alkyl dithiols such as ethanedithiol and propanedithiol; thioglycolic acid, thiolactic acid, etc. Thiocarboxylic acids; thioglycolic acid alkyl esters such as thioglycolic acid n-butyl ester and thioglycolic acid n-hexyl ester are generally preferably used.
The amount of chain transfer agent to be used is not necessarily limited as it varies depending on the polymerization temperature and type of chain transfer agent, but generally it is 0.001 to vinyl chloride monomer.
It may be in the range of ~10% by weight, preferably 0.01~5% by weight. In the present invention, the high molecular weight PVC obtained in the first stage polymerization and the low molecular weight PVC obtained in the second stage polymerization are
The difference in the degree of polymerization of PVC is not necessarily limited and can be selected depending on the degree of improvement in workability required, but if a sufficient improvement in workability is required, the difference in degree of polymerization should be 200 or more. and preferable. Generally, low molecular weight polymers and high molecular weight polymers are treated as compatible blends. The mechanical properties of blended polymers are organized by parallel models of the mechanical properties of low molecular weight polymers and high molecular weight polymers. Therefore, the mechanical properties of the blended polymer are average values determined by the composition ratio of each component. However, according to the present invention, (a) the mixing ratio of low molecular weight PVC and high molecular weight PVC increases at least on the particle order of secondary particles or higher, and the bulk specific gravity of the PVC particles increases and the gelation rate is accelerated. thing,
(b) A chemical reaction between high molecular weight PVC and low molecular weight PVC, such as a graft reaction, occurs during the polymerization process; (c)
Since the morphology of PVC particles is expected to exhibit specificity that is not possible with conventional known methods, processability and mechanical properties will be improved above average values. That is, PVC produced by the method of the present invention
The mechanical properties of high molecular weight PVC and low molecular weight PVC
It exhibits properties that are far superior to those calculated from the composition ratio. As the degree of polymerization of PVC decreases, the gelation rate increases, but the mechanical strength decreases. In the present invention, the degree of polymerization of high molecular weight PVC is P ¹ _W ,
When the amount of polymerization is W ₁ , the degree of polymerization of low molecular weight PVC is P ² _W , and the amount of polymerization is W ₂ , when P ¹ _W −P ² _W >400,
It is preferable that 0.02≦W ₂ /W ₁ +W ₂ <0.25. When W ₂ /W ₁ +W ₂ ≧0.25, the amount of low molecular weight PVC with reduced mechanical strength may increase compared to high molecular weight PVC.
The mechanical strength of PVC may be reduced. Also
In the range of W ₂ /W ₁ +W ₂ <0.02, improvements in workability and mechanical strength may be small. Furthermore,
When 0<P ¹ _W −P ² _W ≦400, it is preferable that the range is 0.05≦W ₂ /W ₁ +W ₂ <0.50. P ¹ _W −
When the value of P ² _W is small, it is desirable to have a large amount of low molecular weight PVC polymerized from the viewpoint of improving processability.
When W ₂ /W ₁ +W ₂ ≧0.50, sufficient improvement in mechanical strength may not be expected. Furthermore, when W ₂ /W ₁ +W ₂ <0.05, the improvement in workability may be very small. Therefore, it is most preferable to set P ¹ _W −P ² _W ≧200. Furthermore, in the present invention, P ¹ _W −
It is preferable to select a production method in which high molecular weight PVC with P ² _W >400 and low molecular weight PVC are polymerized because the amount of polymerized low molecular weight PVC is small and the effects of the present invention can be easily exhibited. In addition, in the present invention, the low molecular weight obtained in the second stage polymerization, which exhibits the effects of the present invention most, is
The degree of polymerization of PVC is the degree of polymerization of the high molecular weight PVC,
Since it varies somewhat depending on the amount of polymerization, etc., it may be determined in advance, but it is generally suitable to select from the range of 200 to 600. As described above, the PVC obtained by the present invention has significantly improved physical properties when compared to a simple blend of high molecular weight PVC and low molecular weight PVC. The cause of this is not always clear, but
Not only are high molecular weight PVC and low molecular weight PVC mixed in the form of secondary particles or higher, but also high molecular weight
Low molecular weight PVC is wrapped around the surface of PVC, which has a particle structure similar to a two-phase structure, and high molecular weight
It is presumed that this is due to the graft polymerization of a portion of low molecular weight PVC to PVC. EXAMPLES In order to explain the present invention more specifically, Examples and Comparative Examples will be described below, but the present invention is not limited to these Examples. In addition, the abbreviation P– _W in Examples and Comparative Examples indicates the weight average degree of polymerization. Furthermore, the measured values shown in Examples and Comparative Examples were based on the following measuring method. (1) Weight average degree of polymerization and bulk specific gravity Determined according to the method of JIS K-6721. (2) Tensile test Preheat the formed sheet at 175℃ for 10 minutes.
After punching a 1 mm thick sheet pressed at 40 kg/cm ² for 10 minutes into a No. 2 test piece, JIS K-7113
The measurement was carried out at a temperature of 23°C and a tensile speed of 10 mm/min according to the method of . (3) Gelation time A mixed sample prepared by cold blending the stabilizer and PVC using a Henschel mixer was measured using a Brabender plasticorder. Example 1 8 g of partially saponified polyvinyl alcohol and 3 g of methylcellulose were placed in a 30-inch autoclave with a stirrer.
Pour 10 g of tertiary butyl peroxypivalate into 12 Kg of ion-exchanged water dissolved in it, and after degassing the autoclave, add 8 Kg of vinyl chloride monomer.
C. for 5 hours to obtain high molecular weight PVC with the degree of polymerization shown in Table 1. Next, 2 kg of ion-exchanged water in which vinyl chloride monomer, dodecyl mercaptan, tertiary butyl peroxypivalate, and partially saponified polyvinyl alcohol were dissolved in the proportions shown in Table 1 was pressurized into an autoclave under nitrogen pressure, and the mixture was heated at 57°C. 4
Low molecular weight PVC with a degree of polymerization shown in Table 1 after polymerization over time
I got it. The characteristic values (degree of polymerization, bulk specific gravity) of the obtained PVC are shown in Table 1. The thus obtained PVC
The compositions were formulated according to Table A and blended using a Henschel mixer. Gelation time was measured for this mixed sample.

[Table] Next, mix the mixed sample at 170°C using a mixing roll.
The mixture was kneaded at ℃ for 5 minutes to form a sheet with a thickness of 1 mm. This sheet was press-molded and subjected to a tensile test. The results are shown in Table 1. Table 1 shows that under the conditions shown in Example 1, dispersants, chain transfer agents,
The same procedure as in Example 1 was carried out except that one or all of the vinyl chloride monomers were omitted, and the results are shown in Table 1 Nos. 5 to 11 as comparative examples.

[Table] Example 2 12 kg of ion-exchanged water in which 10 g of partially saponified polyvinyl alcohol and 4 g of methyl cellulose were dissolved in a stainless steel autoclave equipped with a 30 mm stirrer was charged with 12 g of tertiary butyl peroxypivalate, and after degassing the autoclave, vinyl chloride was dissolved. Charge 8 kg of polymer and polymerize at 50℃ for 6 hours to obtain high molecular weight.
PVC (degree of polymerization 1550) was obtained. Next, 2 kg of ion exchange water in which 3 g of partially saponified polyvinyl alcohol and 1 g of methyl cellulose were dissolved, and 1 kg of vinyl chloride monomer were added.
Kg, 2.5 g of 2-mercaptoethanol, and 2 g of lauroyl peroxide were introduced into the autoclave under nitrogen pressure, and polymerization was carried out at 60° C. for 4 hours to obtain low molecular weight PVC (degree of polymerization: 350). The bulk specific gravity of the obtained PVC was 0.58. A stabilizer was added to the thus obtained PVC in the same manner as in Example 1, and the gelation time and tensile strength were measured. Gelation time is 7.3 minutes,
The tensile strength was 570Kg/ ^cm2 . As a comparative example, bulk specific gravity of high molecular weight PVC (degree of polymerization 1550) obtained by polymerization at 50° C. for 6 hours was 0.49. Example 3 After charging 1 kg of ion-exchanged water in which 1.5 g of partially saponified polyvinyl alcohol and 0.6 g of methyl cellulose, 0.5 g of tertiary butyl peroxypivalate, and 10 g of vinyl acetate were charged into a stainless steel autoclave equipped with a stirrer, the autoclave was removed. After heating, add 350g of vinyl chloride monomer and heat at 57°C.
Polymerization was performed for a period of time to obtain high molecular weight PVC (degree of polymerization 1000).
Next, after purging the remaining monomer, 50 c.c. of ion exchange water in which 0.5 g of polyvinylpyrrolidone was dissolved,
0.15 g of azobisisobutyronitrile, 2 g of dodecyl mercaptan and 80 g of vinyl chloride monomer were charged, and polymerization was carried out at 70° C. for 4 hours to obtain low molecular weight PVC (degree of polymerization 240). The bulk specific gravity of the obtained PVC is 0.44
It was hot. The gelation time of a sample prepared by mixing 100 parts by weight of the PVC thus obtained with 2 parts by weight of dibutyltin maleate and 1 part by weight of dibutyltin laurate was 3.1 minutes. The tensile strength of the sheet produced by roll kneading was 520 Kg/cm ² . As a comparative example, high molecular weight PVC (degree of polymerization 1000) polymerized in the same manner as in Example 3 had a bulk specific gravity of 0.38. Also, the gelation time is 5.2 minutes, and the tensile strength is 500
It was Kg/ ^cm2 . Example 4 1 kg of ion-exchanged water in which 1.5 g of partially saponified polyvinyl alcohol and 0.6 g of methylcellulose were dissolved and 0.5 g of tertiary butyl peroxypivalate were placed in a two-stainless steel autoclave equipped with a stirrer, and after degassing the autoclave, vinyl chloride was removed. Add 350g of monomer and polymerize at 57℃ for 5 hours to achieve high molecular weight.
Got PVC. Next, 100 g of ion exchange water in which 0.6 g of partially saponified polyvinyl alcohol and 0.2 g of methylcellulose were dissolved, 0.2 g of tertiary butyl peroxypivalate, and 2-mercaptoethanol were added.
0.2 g, vinyl chloride monomer 80 g, and other monomers that can be copolymerized shown in Table 2 were pressurized into an autoclave using nitrogen pressure, and the low molecular weight
Polymerized PVC. Table 2 shows the characteristic values of the obtained PVC and the gelation time and tensile strength of a sample mixed with a stabilizer in the same manner as in Example 1. Furthermore, Table 2 No.
Example 4 is a comparative example in which the same procedure as in Example 4 was carried out except that a dispersant of partially saponified polyvinyl alcohol and methyl cellulose was not added in the second stage polymerization.

[Table] Example 5 After charging 1 kg of ion exchange water in which 1.5 g of partially saponified polyvinyl alcohol and 0.6 g of methyl cellulose and 0.5 g of tertiary butyl peroxypivalate were charged into a stainless steel autoclave equipped with a stirrer, the autoclave was degassed. After adding 350g of vinyl chloride monomer, polymerize at 57℃ for 5 hours to obtain high molecular weight.
PVC (degree of polymerization 1000) was obtained. Next, 0.3 g of partially saponified polyvinyl alcohol and 0.1 g of methylcellulose.
50 g of ion-exchanged water in which PVC was dissolved, 0.15 g of tertiary butyl peroxypivalate, 0.2 g of 2-mercaptoethanol, and 90 g of vinyl chloride monomer were charged and polymerized at 57°C for 3 hours to obtain low molecular weight PVC (polymerization degree
450). The bulk specific gravity of the obtained PVC was 0.44. Also, for comparison, the high molecular weight of the first stage of the present invention
Separately polymerize PVC and second stage low molecular weight PVC,
The bulk specific gravity of PVC blended with the monomer composition ratio charged in the first stage polymerization and second stage polymerization of the present invention was measured. As a result, the bulk specific gravity of the blended PVC is 0.40
It was hot. Example 6 1 kg of ion-exchanged water in which 1.5 g of partially saponified polyvinyl alcohol and 0.6 g of methylcellulose were dissolved was placed in a stainless steel autoclave equipped with a stirrer.
and tertiary butyl peroxypivalate 0.5g
I prepared it. After degassing the autoclave, 350 g of vinyl chloride monomer was charged and polymerized at 57°C for 5 hours to obtain high molecular weight PVC (degree of polymerization 1010). Next, 100 g of ion exchange water in which 1.0 g of partially saponified polyvinyl alcohol and 0.4 g of methylcellulose were dissolved, 0.15 g of lauroyl peroxide, and vinyl chloride monomer
80 g was charged and polymerized at 79°C for 2 hours to obtain low molecular weight PVC (degree of polymerization 440). The bulk specific gravity of the obtained PVC was 0.45. Furthermore, the gelation time and tensile strength of the PVC thus obtained were measured in the same manner as in Example 1. As a result, the gelation time was 5.9 minutes, and the tensile strength was 560 Kg/cm ² cm ² . Also, for comparison, the sample obtained only by the first stage polymerization of Example 6
As a result of measuring the physical properties of PVC, the bulk specific gravity was 0.37 and the tensile strength was 525 Kg/cm ² .

Claims (1)

[Claims] 1. A first stage polymerization of vinyl chloride monomer or a mixture of vinyl chloride monomer and other copolymerizable monomer is carried out in an aqueous medium, and the degree of polymerization is less than 600. A high molecular weight vinyl chloride polymer is obtained, and then an aqueous medium containing the high molecular weight vinyl chloride polymer is added with a new vinyl chloride monomer or another monomer copolymerizable with the vinyl chloride monomer. and a dispersant, and carry out a second stage polymerization of the monomers so that the degree of polymerization is lower than that of the high molecular weight vinyl chloride polymer obtained in the first stage polymerization. Method for producing vinyl polymer. 2 Let the degree of polymerization of the high molecular weight vinyl chloride polymer obtained in the first stage be P ¹ _W and the amount of polymerization W ₁ , and the degree of polymerization of the polymer obtained in the second stage be P ² _W and the amount of polymerization W ₂ . When P ¹ _W −P ² _W ＞400, 0.02≦W ₂ /W ₁ +W ₂ <0.25, and when O＜P ¹ _W −P ² _W ≦400, 0.05≦W ₂ /W Claim 1: Polymerization under conditions such that ₁ +W ₂ <0.50
Manufacturing method described. 3 The degree of polymerization of the polymer obtained in the second stage polymerization is
200 to 600. The manufacturing method according to claim 1. 4. The production method according to claim 1, wherein the second stage polymerization is carried out in the presence of a chain transfer agent. 5. The manufacturing method according to claim 4, wherein the chain transfer agent is an organic mercaptan. 6. The method according to claim 1, wherein the polymerization rate of the high molecular weight vinyl chloride polymer obtained in the first stage is 70% or more.