JPH06199911A - Production of vinyl chloride-based polymer - Google Patents

Abstract

PURPOSE:To obtain the subject polymer suitable as a medical packing material, etc., effectively preventing yellowing by irradiation with gamma rays, sterilizable by irradiation with gamma rays, by adding a specific antioxidant to a polymerization system at a specific point of time in subjecting vinyl chloride to suspension polymerization. CONSTITUTION:First, vinyl chloride or a monomer mixture containing vinyl chloride and an oil-soluble polymerization initiator (preferably di-isopropyl peroxydicarbonate) are suspended in an aqueous medium and suspension polymerization is started by using the aqueous suspended dispersion. Then at a stage when the polymerization ratio reaches 15-70%, a benzene ring-containing phosphite-based antioxidant (e.g. diphenyl monodecyl phosphite) is added to the polymerization system to give the objective polymer. The phosphite-based antioxidant is preferably dissolved in a solvent or suspended in water, pumped up and fed to the polymerization system. The suspension polymerization is preferably carried out at 40-70 deg.C usually.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a vinyl chloride polymer, and more particularly to a method for producing a vinyl chloride polymer in which yellowing due to irradiation is effectively suppressed.

[0002]

2. Description of the Related Art Conventionally, when a vinyl chloride polymer is used in medical devices such as pharmaceutical packaging, it is sterilized with ethylene oxide gas according to the Japanese Pharmacopoeia (hereinafter referred to as EOG sterilization).
Is usually done. However, it was not always a good sterilization method because of environmental problems near the sterilization room when performing EOG sterilization, and the problems of ethylene oxide gas adhesion and permeation to medical devices that had undergone EOG sterilization.

Instead, there is a method of sterilization by irradiating with gamma rays from a radiation source containing a radioactive isotope. Gamma-ray sterilization usually uses a radiation source containing ⁶⁰ Co or ¹³⁷ Cs, and sterilizes by adjusting the total irradiation dose depending on the material, property, or contamination of the material to be sterilized. The maximum equipment is 5 Mrad. Polyvinyl chloride-based polymers are also used for packaging materials such as food packaging containers, films, sheets, etc. For example, gamma rays are irradiated for the purpose of sterilizing these packaging materials or foods containing contents. Sometimes.

[0004]

However, when gamma-ray sterilization is carried out, the vinyl chloride polymer becomes yellow,
Strength or elongation tends to decrease. In order to solve these drawbacks, it is necessary to improve the composition of the vinyl chloride polymer molded article by blending, for example, blending higher fatty acid zinc salt and higher fatty acid calcium salt (Japanese Patent Publication No. 60-236).
No. 22), a plasticizer, an epoxy stabilizer, a higher fatty acid zinc / calcium salt, and a metal silicate or hydrotalcites (JP-A-63-110241).
Japanese Unexamined Patent Publication (Kokai) No. 64-38461, etc.) has been proposed, but its effect of preventing yellowing is still insufficient. Therefore, an object of the present invention is to provide a method for producing a vinyl chloride-based polymer, which can stably maintain physical properties against gamma-ray irradiation and can effectively prevent disadvantages such as yellowing.

[0005]

According to the present invention, suspension polymerization is carried out using an aqueous suspension dispersion in which vinyl chloride or a monomer mixture containing at least vinyl chloride is suspended and dispersed together with an oil-soluble polymerization initiator. In the method for producing a vinyl chloride polymer by carrying out the method, the polymerization rate is 15% to 70%.
In the stage between the above, there is provided a method for producing a vinyl chloride polymer, which comprises adding a phosphite antioxidant having at least one benzene ring in the molecule to the polymerization system.

That is, the present invention has succeeded in solving the above problems by adding a specific antioxidant to the polymerization system at a fixed timing after the initiation of polymerization. For example, the phosphite-based antioxidant used in the present invention is required to have at least one benzene ring in the molecule, and a phosphite-based antioxidant not containing a benzene ring has a γ-ray It cannot effectively prevent yellowing against irradiation. That is, it is considered that high molecular radicals and chlorine atoms are generated in the vinyl chloride polymer by γ-ray irradiation, and conjugated double bonds due to the hydrogen abstraction reaction are chained to cause yellowing. The benzene ring is considered to have an action of terminating the chain of this conjugated double bond, and it is presumed that this effectively prevents yellowing due to γ-ray irradiation. In the present invention, typical examples of the benzene ring-containing phosphite-based antioxidant include the following general formula (1):

[0007]

[Chemical 2]

[Wherein, R ^{1 to} R ³ are each a monovalent hydrocarbon group, and at least ^one of R ^{1 to} R ³ has a benzene ring] The phosphite compounds represented may be mentioned. The monovalent hydrocarbon group R ^{1 to} R ³ preferably has 5 to 20 carbon atoms, and specific examples thereof include an alkyl group, an aryl group and an aralkyl group. And any one of R ^{1 to} R ³ is an aryl group or an aralkyl group and is not included when all of them are alkyl groups. That is, of R ^{1 to} R ³ ,
Either of them contains at least one benzene ring. The suitable examples of the phosphite compound used in the present invention are shown below.

Tris (2,4-di-t-butylfephosphite, 2,2-methylenebis (4,6-di-t-butylphenyl) octylphosphite, triphenylphosphite, tris (nonylphenyl) phosphite Fight,
Diphenylmono (2-ethylhexyl) phosphite,
Diphenyl monodecyl phosphite, diphenyl monodecyl phosphite, diphenyl monotridecyl phosphite, etc.

These phosphite compounds are used alone or in combination of two or more, and the addition amount thereof is preferably in the range of 0.01 to 5 parts by weight per 100 parts by weight of the monomer. .

Further, in the present invention, when the above phosphite compound is added to the polymerization system, the polymerization rate is 15% to
It must be between 70% of the time. For example, if it is added at a time when the polymerization rate is less than 15%, the particle size of the obtained polymer becomes coarse and scale is attached to the inside of the polymerization vessel, which is not preferable. Further, when the phosphite compound is added at a point of time when the polymerization rate exceeds 70%, it becomes difficult to uniformly disperse the phosphite compound in the polymer, and as a result, the γ
The linearity is not sufficiently exhibited, and the yellowing prevention effect of the vinyl chloride polymer against γ-ray irradiation is reduced. As for the polymerization rate during suspension polymerization, the time-dependent change of the polymerization rate from the start of polymerization (start of temperature increase) can be measured in advance for each constant charging raw material. You can set the timing. The means for adding the phosphite compound to the polymerization system is arbitrary, but generally, a solution or dispersion prepared by dissolving in a suitable solvent or suspending in water is pumped up. It is preferable to charge it.

According to the present invention, except that the specific phosphite compound is added to the polymerization system at a specific timing as described above, a suspension polymerization known per se can be carried out to obtain the desired poly (polyvinyl alcohol) compound. A vinyl chloride polymer can be obtained. For example, in a polymerization vessel, an aqueous suspension dispersion containing a monomer and an oil-soluble polymerization initiator is prepared by using a dispersion stabilizer, and polymerization is started by heating the dispersion.
After the polymerization is completed, the unreacted monomer is recovered, and the obtained polymer slurry is dried to obtain the desired polymer.

As the monomer to be used for the polymerization, in addition to vinyl chloride alone, a mixture of vinyl chloride, which is mainly vinyl chloride and is copolymerizable with vinyl chloride (usually 50% by weight or more of vinyl chloride), is also available. Can be used. Comonomers copolymerized with vinyl chloride include ethylene, propylene, and 1.
Α-olefins such as butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene; acrylic acid Acrylic acid such as methyl acrylate and ethyl acrylate, or an ester thereof; methacrylic acid such as methacrylic acid or methyl methacrylate or an ester thereof; maleic acid or an ester thereof; vinyl ester such as vinyl acetate or vinyl propionate; lauryl vinyl ether, Examples thereof include vinyl ethers such as isobutyl vinyl ether; maleic anhydride; acrylonitrile; styrene; vinylidene chloride; and other monomers copolymerizable with vinyl chloride. These can be used alone or in combination of two or more.

Examples of the oil-soluble polymerization initiator include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate and diethoxyethyl peroxydicarbonate; t-butyl peroxyneodecanate. t-butylperoxypivalate, t-hexylperoxypivalate, α-cumylperoxyneodecanate, 2,4
A perester compound such as 4-trimethylpentyl-2-peroxy-2-neodecanate; acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate,
Peroxides such as 3,5,5-trimethylhexanoyl peroxide and lauroyl peroxide; azobis-2,
Azo compounds such as 4-dimethylvaleronitrile and azobis (4-methoxy-2,4-dimethylvaleronitrile) can be used alone or in combination of two or more. Further, as these oil-soluble polymerization initiators, a water-soluble catalyst such as potassium persulfate, ammonium persulfate, hydrogen peroxide, cumene hydroperoxide, etc. may be used alone or in combination with 2
It is also possible to use a combination of two or more species.

Further, examples of the dispersion stabilizer used for suspending and dispersing the above-mentioned monomer in an aqueous medium together with a polymerization initiator include water-soluble or oil-soluble partially saponified polyvinyl alcohol, polyacrylic acid, acetic acid. Suspending agents such as copolymers of vinyl and maleic anhydride, cellulose derivatives such as hydroxypropylmethyl cellulose, natural or synthetic polymer compounds such as gelatin; solid dispersants such as calcium phosphate, hydroxyapatite; sorbitan monolaurate, sorbitan trio. Nonionic emulsifiers such as rate and polyoxyethylene alkyl ether; sodium alkyl benzene sulfonate such as sodium lauryl sulfate and sodium dodecyl benzene sulfonate, and anionic emulsifiers such as sodium dioctyl sulfosuccinate, alone or in combination It can be used in combination of the above.

In addition, an aqueous medium, a monomer, a polymerization initiator,
The method of charging the dispersion stabilizer and the like in the polymerization vessel and the charging ratio may be performed in the same manner as in the conventional method.For example, after the polymerization is started, a part of the polymerization initiator or the dispersion stabilizer may be added later at a certain stage. it can. Further, the polymerization temperature is 40 to 7 as in the conventional case.
It may be set in the range of 0 ° C. Further, in this polymerization system, a polymerization regulator, a chain transfer agent, a pH regulator, a gelation improving agent, an antistatic agent, a cross-linking agent, a filler, a buffer, which are appropriately used for vinyl chloride-based polymerization, as needed. It is also optional to add agents, scale inhibitors and the like.

EXAMPLE 1 900 kg of deionized water, 480 g of partially saponified polyvinyl alcohol (dispersant), t-butyl peroxyneodecanate (polymerization initiator) were placed in a stainless steel autoclave equipped with a stirrer and a jacket having an internal volume of 2000 liters. ) 480 g was charged, the inside of the polymerization vessel was degassed to 50 mmHg, and then 600 kg of vinyl chloride monomer was charged. While stirring the inside of the vessel, hot water was passed through the jacket to raise the temperature to 50 ° C. to initiate polymerization. When the polymerization rate reached 30%, 600 g of 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite was dispersed in water and the mixture was pressed under a pump.

When the pressure in the polymerization vessel dropped to 6.0 kg / cm ² G, the unreacted monomer was recovered, the slurry containing the polymer was taken out of the vessel, dehydrated and dried to obtain a vinyl chloride resin. .

Example 2 In Example 1, instead of 2,2-methylenebis (4,6-di-t-butylphenyl) octylphosphite, the same amount of tris (2,4-di-t-butylphenyl) was used. )
A vinyl chloride resin was produced in the same manner as in Example 1 except that phosphite was added.

Example 3 In Example 1, except that 2,2-methylenebis (4,6-di-t-butylphenyl) octylphosphite was replaced by the same amount of diphenylmonotridecylphosphite. A vinyl chloride resin was produced in the same manner as in Example 1.

Example 4 The same as Example 1 except that the 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite was added at a polymerization rate of 60%. Vinyl chloride resin was manufactured.

Comparative Example 1 A vinyl chloride resin was produced in the same manner as in Example 1 except that 2,2-methylenebis (4,6-di-t-butylphenyl) octylphosphite was not added.

Comparative Example 2 The same as Example 1 except that the addition time of 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite was 5% in the polymerization rate. Vinyl chloride resin was manufactured.

Comparative Example 3 The same as Example 1 except that the addition time of 2,2-methylenebis (4,6-di-t-butylphenyl) octyl phosphite was set to 75% of the polymerization rate. Vinyl chloride resin was manufactured. Table 1 shows the particle size distribution of this resin and the state of scale generation in the polymerization vessel.

55 parts by weight of dioctyl phthalate (DOP), 5 parts by weight of epoxidized soybean oil, and 0.2 parts of zinc stearate per 100 parts by weight of the powdery polymer thus obtained.
By weight, 0.2 parts by weight of calcium stearate and 0.1 parts by weight of stearic acid were added to obtain a blend. Rolled this blend at 150 ℃, thickness 2mm, 10cm × 10cm
The sheet was press-molded and irradiated with 2.5 Mrad γ-rays to compare the colorability before and after irradiation. The results are shown in Table 1.
The criteria for evaluation of colorability are as follows.

Evaluation of colorability: ○ Little coloring △ Little coloring × Strong coloring

[0027]

[Table 1]

[0028]

EFFECTS OF THE INVENTION According to the present invention, it is possible to produce a vinyl chloride polymer in which yellowing due to γ-ray irradiation is effectively avoided. Therefore, this vinyl chloride-based polymer has a γ
It is extremely useful as a packaging material for medical treatment and the like, which is sterilized by irradiation with rays.

Claims (2)

[Claims] 1. A vinyl chloride polymer is obtained by carrying out suspension polymerization using an aqueous suspension dispersion in which vinyl chloride or a monomer mixture containing at least vinyl chloride is suspended and dispersed together with an oil-soluble polymerization initiator. In the method for producing, a vinyl chloride-based compound characterized in that a phosphite-based antioxidant having at least one benzene ring in the molecule is added to the polymerization system at a stage where the polymerization rate is between 15% and 70%. Method for producing polymer. 2. The phosphite-based antioxidant is represented by the following general formula (1): [Wherein, R ^{1 to} R ³ are each a monovalent hydrocarbon group, and at least ^one of R ^{1 to} R ³ has a benzene ring] The production method according to claim 1, which is a phosphite compound.