JP3246995B2 - Method for producing acrylic polymer - Google Patents

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 an acrylic polymer by subjecting an acrylic monomer to radical addition polymerization in a screw extruder.

[0002]

2. Description of the Related Art When polymerizing an acrylic monomer, generally, a solution polymerization method using water or an organic solvent, a suspension polymerization method, an emulsion polymerization method, and the like have been mainly used. This is because in a so-called bulk polymerization method in which such a medium is not used at all or very little, the viscosity of the system increases so that mechanical stirring is almost impossible due to the progress of the polymerization reaction. This was because heat could not be properly removed and the state became uncontrollable, and as a result, an acrylic polymer having satisfactory performance could not be obtained.

[0003] A so-called polymerization reaction extrusion technique in which a monomer is directly introduced into a screw extruder to continuously polymerize the monomer while thermally decomposing a polymerization initiator in the extruder is a known technique (for example, And JP-B-37-6744), which is an advantageous technique.

[0004] Because screw extruders usually have a sufficient heat capacity, they can be heated and cooled, and can be stirred and kneaded even if the obtained polymer is quite viscous, and the polymerization reaction is difficult. This is because it has heat exchange performance sufficient to control the progress of the heat transfer. In addition, if a molding die is connected to the exit of the screw extruder, the resulting polymer can be molded into a product of a desired shape, and the process can be centralized.
This is because it has the advantage of continuous operation.

[0005]

However, in order to achieve the polymerization reaction extrusion, it is necessary to substantially complete the polymerization reaction within the residence time of the monomer in the extruder. Regarding the radical addition polymerization reaction of the acrylic monomer, when using a normal extruder, it is necessary to secure a sufficient residence time by making the flow rate extremely small or making the extruder extremely long. Otherwise, the conversion of the polymerization reaction will be low, and a satisfactory acrylic polymer cannot be obtained.

Generally, in the polymerization reaction of an acrylic monomer, if oxygen is present in the reaction system, oxygen molecules and free radicals react with each other. Therefore, the polymerization reaction substantially takes place until oxygen in the system is almost consumed. Does not progress. That is, the polymerization reaction is delayed. In addition, as a result of this polymerization inhibition reaction, unnecessary acrylic oligomers of about 2 to 10 mer of acrylic monomers are generated in large amounts.

As a fundamental solution to these problems, a method is known in which oxygen existing in the reaction system is replaced with nitrogen in advance, but this method is not completely applicable to polymerization reactive extrusion. It is very complicated. Because the extruder is a continuous transfer machine having an inlet and an outlet unlike a normally sealed reaction vessel, it is technically difficult to reduce the oxygen concentration to a level sufficient for the need. The resulting acrylic polymer has a low polymerization conversion and contains oligomers.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned conventional problems, and it is intended that an acrylic monomer is subjected to radical addition polymerization in an extruder, and that the polymerization conversion rate is high. Another object of the present invention is to provide a method for producing an acrylic polymer having a small amount of oligomers and high heat resistance.

[0009]

The present invention relates to an acrylic monomer having a dissolved oxygen concentration of 1 ppm or less, and 0.1 to 2 parts by weight of the following formula (1) based on 100 parts by weight of the acrylic monomer. )
A stannous compound represented by the formula (R {COO}) ₂ Sn: Formula (1) [In the formula (1), R represents an alkyl group having 5 to 14 carbon atoms] and a polymerization initiator Acrylic monomer that is supplied to an extruder, radically polymerizes the acrylic monomer by free radicals generated by thermal decomposition of the polymerization initiator in the screw extruder, and continuously discharges the polymer from the outlet of the screw extruder This is a method for producing a polymer.

In the present invention, the acrylic monomer is
Esters of acrylic acid or methacrylic acid having an alkyl group having about 1 to 14 carbon atoms, and at least one or more selected from acrylic acid, methacrylic acid, acrylonitrile, methacrylonitrile, acrylamide, N-substituted acrylamide, and hydroxyacrylate Refers to a compound.

Particularly preferred acrylic monomers include, for example, acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, methacryl Acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, octyl methacrylate, stearyl methacrylate,
Glycidyl methacrylate and the like can be mentioned.

If necessary, a small amount of one or more vinyl compounds copolymerizable with the acrylic monomer may be used. Examples of such a vinyl compound include maleic anhydride, N-vinylpyrrolidone,
Vinyl acetate, styrene and derivatives thereof (eg, alkylenestyrene such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, ethylstyrene, dimethylstyrene, butylstyrene, etc., chlorostyrene) and the like. .

The acrylic monomer supplied to the screw extruder is required to have a dissolved oxygen concentration of 1 ppm or less. For the above reasons, it is most preferable that oxygen is not present in the reaction system in any case, but if the concentration of dissolved oxygen in the acrylic monomer is 1 ppm or less due to the action of the stannous compound described below. The effect of the present invention can be obtained even if oxygen enters in the polymerization reaction extrusion step. However, when it exceeds 1 ppm, the polymerization reaction is not completed in the screw extruder, and problems such as generation of oligomers occur.

Incidentally, the measurement of the dissolved oxygen concentration is carried out, for example, by
It can be directly measured by a polaro-type dissolved oxygen meter using platinum / silver as an electrode.

In the present invention, the stannous compound represented by the formula (1) [where R represents an alkyl group having 5 to 14 carbon atoms] includes, for example, stannous octylate, decyl Stannous acid, stannous dodecylate, and the like can be mentioned. In particular, stannous octylate, which is widely used as a catalyst for urethane foam production, is easily available, and is particularly preferably used.

When this stannous compound is dissolved in an acrylic monomer, a good polymerization reaction without delay of polymerization due to oxygen inhibition reaction or oligomer formation can be achieved without strict nitrogen replacement as is usually performed. Becomes possible. In other words, the introduction of the stannous compound has the same effect as the apparent replacement with nitrogen. This is a great advantage when using a non-sealed screw extruder as the reactor.

The reason for this is not necessarily clear, but it is probably due to the fact that the stannous compound consumes oxygen by directly reacting with the dissolved oxygen in the acrylic monomer and lowers the absolute oxygen concentration of the system. Can be

Moreover, the stannous compound has a strong reducing effect, and has a dual effect of effectively acting as a heat stabilizer on the acrylic polymer. This is because the allyl-based polymer obtained by bulk polymerization has a strong thermal history as compared with those obtained by other polymerization methods, and thus is susceptible to thermal deterioration due to oxidation.

The amount of the stannous compound must be 0.1 to 2 parts by weight, preferably 0.3 to 1.5 parts by weight, based on 100 parts by weight of the acrylic monomer. The amount added is 0.
If the amount is less than 1 part by weight, a sufficient effect cannot be obtained. Conversely, if the amount exceeds 2 parts by weight, the thermal properties of the acrylic polymer are significantly impaired, and the concentration of tin increases to increase skin (human body). The risk of irritation also increases.

The polymerization initiator used in the present invention may be a general one which can be used for solution polymerization of an ordinary acrylic polymer, but is soluble in an acrylic monomer and has a half-life of 1 hour. Those having a temperature of about 60 to 150 ° C are preferred.

If the one-hour half-life temperature of less than 60 ° C. is used, the polymerization reaction rate is so high that there is a danger of a runaway reaction, and the temperature of the reaction system is controlled until control becomes possible. When the temperature is lowered, the viscosity increases due to the effect of the polymer already existing in the system, and the reaction is easily stopped.
When the temperature exceeds 50 ° C., the polymerization reaction rate becomes too slow, and the polymerization reaction is no longer completed in the extruder.
Therefore, if the temperature of the reaction system is increased, new problems such as volatilization and decomposition of the acrylic monomer and decomposition of the obtained acrylic polymer tend to occur.

The half-life temperature of one hour means a temperature at which the half-life of a substance dissolved in benzene or toluene is one hour. The half-life of the polymerization initiator can be determined, for example, by using diphenyl {1-picrylhydrazyl (DPPH), a kind of polymerization inhibitor, and measuring the disappearance rate by an ultraviolet absorption spectrum.

Examples of such a polymerization initiator include, for example,
Benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, p-chlorobenzoyl peroxide, o-methylbenzoyl peroxide, bis-3,
Diacyl peroxides such as 5,5-trimethylhexanol peroxide and bis-3,5,5-trimethylhexanol peroxide, dicumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5
{(T-butylperoxy)} hexane, t-butylcumyl peroxide, di-t-butylperoxide,
1,3-bis (t-butylperoxyisopropyl)
Organic diperoxides such as dibenzenes such as benzene, peroxyketals such as 1,1-di-t-butylperoxycyclohexane, alkyl peresters such as t-butylperoxybenzoate, and percarbonates such as diisopropyl peroxycarbonate. Oxide, 2,
2'-azobis (2,4-dimethylvaleronitrile),
Examples include azonitrile compounds such as 2,2′─azobisisobutyronitrile and 2,2′─azobiscyclohexylnitrile.

The amount of the polymerization initiator to be added is preferably 0.02 to 2 parts by weight based on 100 parts by weight of the acrylic monomer. If the addition amount is less than 0.02, the polymerization reaction is difficult to complete in the extruder. Conversely, if the addition amount exceeds 2 parts by weight, the polymerization reaction speed tends to be too high, and the risk of runaway reaction tends to increase. There is.

In the present invention, in order to impart appropriate properties to the obtained acrylic polymer, the acrylic monomer as a raw material may be, for example, the above-mentioned acrylic monomer, if necessary. Acrylic polymers polymerized as, other polymers, organic solvents, plasticizers, glass fibers, mica,
A compounding agent such as an inorganic filler such as talc may be added. The amount of these additives is 10
It is preferably 30 parts by weight or less based on 0 parts by weight.

In the present invention, the acrylic monomer, the stannous compound, the polymerization initiator, and the compounding agent to be added as required are all or some of them mixed in advance, or are independently supplied to the screw extruder. Supplied. In this case, it is particularly preferable that the acrylic monomer and the stannous compound are sufficiently dissolved and mixed in advance and then supplied to the extruder, but this is not always necessary.

In the present invention, the screw extruder comprises:
A screw screw extruder, a twin screw extruder, and a multi-screw extruder having three or more screws are used.

As the single screw extruder, one having a general full-flight type screw, one having a discontinuous flight type screw, a pin barrel, a mixing head, and the like are used. As the twin screw extruder, any of a meshing co-rotating type, a meshing different direction rotating type, and a non-meshing different direction rotating type can be used.

Among the above screw extruders, a meshing (self-wiping) co-rotating twin-screw extruder having a partially kneading element is particularly preferably used. Regardless of which screw extruder is selected, it is desirable that the screw extruder barrel has at least one vent port for vacuum degassing in at least one place.

The barrel temperature of the screw extruder is appropriately set, but its profile varies depending on the type of acrylic monomer and polymerization initiator used, and the average residence time. However, in essence, in the front part of the screw extruder, the acrylic monomer component is transferred while raising the temperature within a range that does not cause a boiling or runaway reaction, and the polymerization reaction proceeds sufficiently in the center part, Further, it is preferable that an appropriate temperature is set for each section so that a polymer viscosity at which screw pumping can be performed in the subsequent stage is obtained.

At this time, the average residence time can be obtained by the following equation (2). Average residence time = (Internal volume of screw extractor / Discharge flow rate) × Filling rate formula (2)

However, it is technically difficult to measure the filling rate in the equation (2). Therefore, for example, a certain amount of powder that is insoluble and infusible in a fluid, such as aluminum flakes having an average particle size of about 1 mm, is charged all at once from the material supply port, and the time required for them to be extruded from the discharge port is determined by the frequency. Measured as a distribution,
The average residence time can be obtained directly from the probability distribution function based on this.

The desired average residence time can be ensured by appropriately designing the barrel diameter and length of the extrusion cavity, the shape and rotation speed of the screw, and the shapes of the breaker, die head, die and the like provided at the extruder outlet. Or by selection.

If the resulting acrylic polymer contains volatile substances due to residual unreacted acrylic monomers, generation of decomposition products, or the use of solvents or plasticizers, it may be necessary to prepare They can be removed through the vacuum vent of the screw extruder. Also, the second directly connected
May be supplied to the extruder, and the devolatilization under reduced pressure may be repeated.

The acrylic polymer obtained in the present invention preferably has an average molecular weight of 10,000 to 900,000, more preferably 10,000 to 600,000.

It is preferable that the acrylic polymer discharged from the extruder is subjected to a post-treatment such as shaping into a desired shape through a molding die and cooling. Typically, after molding into a plurality of rods and exposing to cooling water, an acrylic polymer is continuously formed on a molding material pellet cut into an appropriate length, or on a support formed simultaneously (or separately). A laminated body or the like that has been applied is considered.

[0037]

According to the method for producing an acrylic polymer of the present invention, an acrylic monomer having a dissolved oxygen concentration of 1 ppm or less and a formula (0.1 to 2 parts by weight based on 100 parts by weight of the acrylic monomer) are used. The stannous compound shown in 1) and a polymerization initiator are supplied to a screw extruder, and the acrylic monomer is subjected to radical addition polymerization by free radicals generated by thermally decomposing the polymerization initiator in the screw extruder. By extruding the polymer continuously from the outlet of the screw extruder, the screw extruder enables fine temperature control during the polymerization reaction due to the excellent convective heat transfer and interface renewal effect given to the contents. Therefore, there is no runaway reaction or decrease in reaction conversion caused by the thickening accompanying rapid polymerization reaction, which is seen in general radical bulk polymerization in a reaction tank. Place Without performing, without causing a reduction in polymerization conversion rate due to oxygen inhibition reaction, low production of oligomer, and can be obtained thermal stability superior acrylic polymer continuously.

[0038]

The present invention will be described below with reference to examples. Example 1 39 mm in diameter consisting of a self-wiping double-screw element and a kneading disc element, L
/ D42 screw type co-rotating with screw
A 90 mmφ nozzle-shaped die was attached to the tip of a shaft screw extruder (trade name “BT # 40” manufactured by Plastics Engineering Laboratory Co., Ltd.).

Then, the preset temperature is set in advance at the inlet portion (first to second
90 ° C in the barrel section), central part (2nd to 6th barrel section)
150 ° C at outlet, 18 at outlet (7th barrel and die section)
The temperature was set to 0 ° C., and the screw rotation speed was set to 90 rotations / minute.

Next, 80 kg of methyl methacrylate was placed in a 100 liter tank, and the methyl methacrylate 1
Stannous octoate (Johoku Chemical Co., Ltd.
1.0 part by weight of trade name "KCS-405-T") and 0.1 part by weight of benzoyl peroxide were blended and dissolved to obtain a raw material solution.

Subsequently, the temperature of the raw material solution was raised to 25 ° C.
The nitrogen gas (purity: 99.9%) was blown in at a flow rate of 10 liters / min while maintaining the pressure at less than 10% to perform nitrogen substitution of dissolved oxygen. At this time, the oxygen concentration of the raw material solution in the tank was measured using a dissolved oxygen meter (trade name “UC-12-S, manufactured by Central Chemical Co., Ltd.).
(OL type), and when the oxygen concentration reached 0.5 ppm, the nitrogen substitution was stopped.

This was converted to 70 g / g by a chemical gear pump.
At a flow rate of 1 minute, the mixture was continuously supplied to a meshing type co-rotating twin screw extruder to perform bulk polymerization. Then, the bend port provided in the barrel near the outlet of the extruder was depressurized, and devolatilization of volatile components contained in the melt was performed simultaneously.

After continuous operation for 20 minutes from the start of the supply of the raw material solution, a part of the methyl methacrylate polymer discharged from the die was sampled and used as a polymer sample for analytical evaluation. Immediately thereafter, the average residence time was measured using aluminum flakes having an average particle size of 500 μm.

Example 2 A polymerization reaction extrusion was carried out in the same manner as in Example 1 except that stannous octylate to be added to the raw material solution was 0.5 part by weight based on 100 parts by weight of methyl methacrylate. The combined sample was collected and the average residence time was measured.

Example 3 The same set-type co-rotating twin screw extruder as in Example 1 was set at a temperature of 120.degree. C. at the inlet and 16 at the center.
0 ° C, 110 ° C at outlet, screw speed 13
It was set to 0 / min. Next, 80 kg of butyl acrylate is placed in a 100-liter tank, and stannous octylate (trade name "KCS-405-T" manufactured by Johoku Chemical Co., Ltd.) is added in an amount of 0.5 weight per 100 parts by weight of the butyl acrylate. And 0.2 parts by weight of azoisobutyronitrile were mixed and dissolved to obtain a raw material solution. Thereafter, in the same manner as in Example 1, nitrogen replacement and supply to an extruder (however, the flow rate was set to 100 g / min) were carried out to carry out polymerization reaction extrusion, to collect a polymer sample, and to measure the average residence time. Was.

Comparative Example 1 Polymerization reaction extrusion was carried out in the same manner as in Example 1 except that stannous octylate was not used, and a polymer sample was collected and the average residence time was measured.

Comparative Example 2 Polymerization extrusion was carried out in the same manner as in Example 2 except that the nitrogen substitution was stopped when the dissolved oxygen reached 2.0 ppm, and a polymer sample was collected and the average residence time was measured. Was.

Comparative Example 3 Polymerization extrusion was carried out in the same manner as in Example 3 except that stannous octylate was not used at all, and a polymer sample was collected and the average residence time was measured.

Comparative Example 4 In the same manner as in Example 3 except that di {n} octyltin laurate (trade name “OT # 1”, manufactured by Asahi Denka Kogyo KK) was used instead of stannous octylate. The polymerization reaction extrusion was performed, and a polymerization sample was collected and the average residence time was measured.

With respect to the polymer samples obtained in Examples 1 to 3 and Comparative Examples 1 to 4, the amount of the residual monomer was measured by gas chromatography to determine the conversion of the polymerization reaction, and the gel-per chromatography ( GPC) to determine the weight average molecular weight and the yield of the oligomer. The results are shown in Table 1.

[0051]

[Table 1]

As is clear from Table 1, in each of Examples 1 to 3 of the present invention, the reaction conversion of the obtained acrylic polymer was high, exceeding 95%, and the oligomers which were problematic The amount produced was very small and the average molecular weight was high. On the other hand, in the case of Comparative Examples 1 to 4, the reaction conversion of the obtained acrylic polymer was low, oligomers were formed in large amounts, and the average molecular weight was low.

[0053]

The method for producing an acrylic polymer of the present invention has the above-mentioned structure, so that the polymerization conversion by the oxygen inhibition reaction does not decrease, the production of oligomers is low, and the heat stability is low. An acrylic polymer having excellent properties can be continuously obtained.

Claims (1)

(57) [Claims] 1. An acrylic monomer having a dissolved oxygen concentration of 1 ppm or less, and a stannous compound (R 次) represented by the following formula in an amount of 0.1 to 2 parts by weight based on 100 parts by weight of the acrylic monomer. COO─) ₂ Sn (wherein R represents an alkyl group having 5 to 14 carbon atoms);
The polymerization initiator and the screw extruder are supplied to the screw extruder, and the acrylic monomer is subjected to radical addition polymerization by free radicals generated by thermally decomposing the polymerization initiator in the screw extruder, and the polymer is continuously discharged from the screw extruder outlet. A method for producing an acrylic polymer, comprising: