JPH11322814A - Production of low-molecular weight emulsion resin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a low-molecular weight emulsion resin capable of forming a coating film manifesting performances excellent in chemical and efflorescence resistance, glossiness and surface smoothness including water resistance without using a chain transfer agent. SOLUTION: A redox-based emulsion polymerization of (B) an ethylenically unsaturated monomer is carried out with (C) a water-soluble organic peroxide- based initiator having >=1% solubility in water and (D) a reducing agent by using (A) a copolymerizable surfactant. The molar ratio of the component D to the component C is preferably 0.01-1.

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 low molecular weight emulsion resin which gives a film having excellent water resistance, substrate adhesion, chemical resistance, efflorescence resistance, gloss and surface smoothness. Specifically, for example, it is possible to create products useful as paints, coating agents, and sealing agents that require various coatings for building interior / exterior, steel, industrial products, etc., and particularly require water resistance, gloss, and substrate adhesion. The present invention relates to a method for producing a low molecular weight emulsion resin.

[0002]

2. Description of the Related Art In a conventional emulsion resin, when a surfactant, which is an essential component, oozes (bleeds) onto the surface of a coating film or when a water-soluble inorganic polymerization initiator is used, the inorganic roots of the emulsion resin remain in the coating film. , There is a disadvantage that the water resistance is inferior to that of the solvent-based resin.

Some proposals have been made as a countermeasure such as a method for producing an emulsion resin using a copolymerizable surfactant. However, a coating having water resistance comparable to that of a solvent-based resin is not always provided. Absent.

The weight-average molecular weight of an emulsion resin obtained by radical addition polymerization by thermal dissociation using a water-soluble inorganic polymerization initiator is usually 200,000 to several million. Easy to cause poor adhesion, substrate adhesion, chemical resistance, efflorescence resistance,
Deterioration of gloss and surface smoothness becomes a problem.

[0005] Therefore, when the molecular weight is reduced by increasing the amount of the water-soluble inorganic polymerization initiator in order to improve this, it is impractical because the water resistance is deteriorated as described above. In addition, when a chain transfer agent is used, the odor of the mercaptan type becomes a problem, and the item of “low odor” required for the emulsion resin in recent years cannot be satisfied. Therefore, it is not always effective in reducing the molecular weight.

Further, the above-mentioned emulsion resin has a disadvantage that the gloss and surface smoothness of the film are inferior to those of the solvent-based resin.

To improve this, a method of increasing the amount of emulsifier to reduce the particle size has been proposed, but this method causes a problem that the water resistance is deteriorated because the amount of emulsifier is increased.

That is, in the prior art, a low molecular weight and a low inorganic substance content, a fine particle and a low emulsifier content are used without using a chain transfer agent, and excellent water resistance, substrate adhesion, chemical resistance, efflorescence resistance and gloss are obtained. There is no method for producing an emulsion resin having properties and surface smoothness.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above problems and provides a film having excellent water resistance, substrate adhesion, chemical resistance, efflorescence resistance, gloss and surface smoothness. It is an object of the present invention to provide a method for producing a low molecular weight emulsion resin to be provided.

[0010]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that a specific copolymerizable surfactant is used and a specific initiator system is used. Low-molecular weight, low inorganic matter content, fine particles and low emulsifier content without using a chain transfer agent to form a coating film with good film-forming property, that is, good particle fusion property, excellent water resistance, and excellent substrate adhesion A method for producing an emulsion resin having chemical resistance, chemical resistance, efflorescence resistance, gloss and surface smoothness was found, and the present invention was completed.

That is, the present invention uses a copolymerizable surfactant (A) having a polymerizable double bond in a molecule and converts an ethylenically unsaturated monomer (B) into a water-soluble polymer having a water solubility of 1% or more. A method for producing a low-molecular-weight emulsion resin, comprising performing redox-based emulsion polymerization of a water-soluble organic peroxide-based initiator (C) and a reducing agent (D).

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The component (A) of the present invention and the copolymerizable surfactant having a polymerizable double bond in the molecule include, for example, Aqualon HS-05, HS-10 and HS-2.
0, HS-1025, BC-05, BC-10, BC-
20, BC-0515, BC-1025, BC-202
0 (all manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Adecaria Soap SE-5N, SE-10N, SE-20N, SE-10
25N, NE-10, NE-20, NE-30, NE-
40 (manufactured by Asahi Denka Kogyo KK), Antox-MS
-60 (manufactured by Nippon Emulsifier Co., Ltd.), Eleminor JS-2
(Manufactured by Sanyo Chemical Co., Ltd.), Latemul S-180, S-18
0A (all manufactured by Kao Corporation) and the like, but an anionic copolymerizable surfactant and a nonionic copolymerizable surfactant having both a polymerizable double bond and a polyoxyethylene chain in the molecule. And the like are preferable in terms of polymerization stability.

Examples of the polymerizable double bond group of the copolymerizable surfactant include a propenyl group, an allyl group, a vinyl group, a maleic acid group, an acryloyl group, and a methacryloyl group. , Allyl group,
It is a vinyl group. The maleic acid group, acryloyl group, methacryloyl group, etc. have an ester bond at the bond with the main structure of the emulsifier, and cause hydrolysis during and after manufacture, so that the emulsifier component is released from the resin skeleton and copolymerized. As in the case of an emulsion resin using a general emulsifier having no property, it is in a state of only being adsorbed on the particle surface. For this reason, the water resistance of the coating decreases.

The amount of the copolymerizable surfactant to be used is 0.02 to 20%, preferably 0.1 to 10%, based on the weight of all monomers. If it is less than 0.02%, the stability during the polymerization is deteriorated, and a large amount of grit is generated, so that industrialization becomes difficult. If it exceeds 20%, the water resistance of the coating decreases.

As the copolymerizable surfactant, either anionic or nonionic one may be used alone,
Both types may be used in combination. As for the type of the polymerizable double bond group, one type may be used alone, or two or more types may be used in combination.

The type of the component (B) of the present invention and the ethylenically unsaturated monomer are not particularly limited. Generally, alkyl (meth) acrylate monomers, vinyl ester monomers, various vinyl compounds Can be used. Specific examples thereof include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate,
Alkyl (meth) acrylate monomers such as ethylhexyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate;
(Meth) acrylic acids such as acrylic acid and methacrylic acid; amides of (meth) acrylic acid such as acrylamide, methacrylamide, N-methylolacrylamide and diethylaminopropylacrylamide; dimethylaminoethyl (meth) acrylate and diethylaminoethyl (meth) ) Amino acids of (meth) acrylic acid such as acrylate and aminoethyl vinyl ether; styrene, α-
Aromatic hydrocarbon-based vinyl monomers such as methylstyrene, chlorostyrene, vinyltoluene; nitrile group-containing vinyl monomers such as (meth) acrylonitrile; vinyl ester monomers such as vinyl acetate and vinyl propionate;
Epoxy-containing vinyl monomers such as glycidyl (meth) acrylate; hydroxyl-containing vinyl monomers such as 2-hydroxyethyl (meth) acrylate and hydroxyl-modified vinyl-modified hydroxyalkyl vinyl monomers; trifluoro (meth) acrylate; Fluorine-containing vinyl monomers such as pentafluoro (meth) acrylate;
Vinyl group-containing monomers such as polyethylene glycol monomethacrylate and polypropylene glycol monomethacrylate; and copolymerizable ultraviolet absorbers and copolymerizable light stabilizers. These monomers are used according to the intended use and purpose. May be used alone or in combination of two or more. In particular, acrylic acid and methacrylic acid are preferable in terms of good copolymerizability and particle stability, and when two or more kinds are used in combination, it is preferable to combine acrylic acid and methacrylic acid.

Specific examples of the component (C) of the present invention and the water-soluble organic peroxide initiator having a water solubility of 1% or more include tertiary butyl hydroperoxide and cumene hydroperoxide. From the viewpoint of water solubility, it is preferable to use tertiary butyl hydroperoxide.

Component (C) is used in an amount of 0.02 to 20%, preferably 0.1 to 20% by weight based on the weight of all monomers.
10%. If it is less than 0.02%, the molecular weight is increased and the particle fusing property is reduced, so that the chemical resistance and the efflorescence resistance are deteriorated. In addition, the degree of polymerization is reduced, and the unreacted monomer is largely left. On the other hand, if it exceeds 20%, the molecular weight becomes too low, the minimum required film strength as a coating agent cannot be obtained, and the peroxide odor of undecomposed tert-butyl hydroperoxide and the tertiary butanol odor of decomposition by-products are obtained. Odor problems occur.

The component (D) of the present invention is used for redox emulsion polymerization, and is a reducing agent used in combination with the component (C). Examples of the reducing agent include sodium thiosulfate, sodium hydrogen sulfite, ascorbic acid, and sodium pyrophosphate. Rongalite is used, but Rongalite is preferably used from the viewpoints of reduction of inorganic components, polymerization stability, prevention of corrosion of the metal reaction vessel and prevention of coloring of the emulsion resin.

The molar ratio of the reducing agent as the component (D) to the water-soluble organic peroxide-based initiator having a water solubility of 1% or more as the component (C) is preferably 0.01 to 1, and more preferably 0.01 to 1. Preferably it is 0.05-0.5. If it is less than 0.01, it is insufficient to decompose all the initiators, and the emulsion polymerization itself cannot be carried out smoothly. On the other hand, if it is 1 or more, all the initiators are decomposed before the polymerization is completed, and a large amount of unreacted monomer remains, which is not suitable.

The above molar ratio is generally set to 0.8 to 1 (equimolar) as a conventional known technique.
The present inventor added the component (C) initially or added it together with the component (B), and separately added the component (D) as a reducing agent separately from the component (B). The present inventors have found a method for synthesizing a low-molecular-weight emulsion resin having an extremely small amount of unreacted monomers by smoothly completing polymerization with an agent (inorganic component).

The method for synthesizing the emulsion resin in the present invention can be carried out by a usual emulsion polymerization method, except that the radical generation mechanism is a redox system. However, it is noted that it is a redox system polymerization. It needs to be synthesized. The initial charge to the reactor can be water alone,
The component (A) may be added. The addition of the component (B) may be performed alone, or a mixture of water and the component (A) and emulsified in advance may be added. The component (C) may be initially charged together with water, or may be added together with the component (B). However, if the component (D) is mixed with a previously emulsified component (B), polymerization may start in the system and must be avoided. Further, when the component (D) is initially charged, it is decomposed and deactivated by heat, so that the polymerization is not carried out smoothly. For this reason, it is necessary to add together and separately from the component (B). Further, since the present invention is a redox polymerization utilizing oxidation and reduction reactions, mixing of the components (C) and (D) outside the reaction system must be absolutely avoided.

The weight average molecular weight of the emulsion resin in the present invention is from 0.2 to 200,000, preferably from 1 to 10
It is ten thousand. If it is less than 20000, the minimum required mechanical strength as a coating film cannot be obtained, and if it exceeds 200,000, the film-forming property is reduced and the desired performance cannot be obtained.

The average particle size of the emulsion resin in the present invention is from 0.01 to 0.5 μm, preferably from 0.0 to 0.5 μm.
5 to 0.2 μm. If it is less than 0.01 μm, the polymerization stability and the product stability deteriorate. If it exceeds 0.5 μm, the film-forming properties are reduced, and the desired performance cannot be obtained.

It should be noted that introducing a crosslinking mechanism between particles into the emulsion resin in the present invention does not hinder the purpose of the present invention. For example, if a cross-linking mechanism that is stable in water, such as the cross-linking of an active carbonyl group and a hydrazide group, which is a known technique, and the cross-linking proceeds simultaneously with the evaporation of water, not only improves the film strength but also improves the water resistance. The properties, chemical resistance and efflorescence resistance are also improved.

It is also possible to blend the emulsion resin of the present invention with other commercially available emulsion resins and aqueous resins. In this case, the emulsion resin of the present invention is provided with excellent performance, and is effective in improving the film properties.

In utilizing the present invention, various known additives such as pigments, dispersing agents, wetting agents, color separation preventing agents, defoaming agents, solvents, etc. are added to the obtained low molecular weight emulsion resin.
Film-forming aid, plasticizer, antifreeze, thickener, viscosity modifier,
pH adjusters, preservatives, and the like can be added according to applications and purposes.

[0028]

The most important feature of the present invention resides in a method for producing a low molecular weight emulsion resin. That is, a copolymerizable surfactant (A) having a polymerizable double bond in the molecule is used, and the ethylenically unsaturated monomer (B) is dissolved in water at a solubility of 1%.
Redox emulsion polymerization of the water-soluble organic peroxide initiator (C) and the reducing agent (D) described above is performed. The water-soluble organic peroxide-based initiator is basically lipophilic and has a very good affinity for the ethylenically unsaturated monomer.
In the case of emulsion polymerization using a completely water-soluble inorganic initiator, the penetration of initiator radicals into the emulsifier micelles is stochastically small, and thus a high molecular weight polymer is produced. Is easy to enter the emulsifier micelle as described above, and in the presence of a large amount of initiator radical,
It is considered that a low molecular weight emulsion resin can be obtained because polymerization proceeds under a reaction mechanism corresponding to so-called “microsuspension polymerization”. Further, when a persulfate-based initiator is used, the initial pH in the system becomes considerably low due to the effect of sulfate, which is a decomposition product thereof. For this reason, the activity of the emulsifier is reduced, and an emulsion having a relatively large particle size is obtained because the number of micelles of the emulsifier is reduced.
In the case of the present invention, since the initial pH is near neutrality, the activity of the emulsifier is high and the number of micelles of the emulsifier is also large, so that a fine particle emulsion can be obtained.

That is, the feature of the present invention is that, by using a specific copolymerizable surfactant and a specific initiator system, a low molecular weight and a low inorganic substance, a fine particle and a low molecular weight can be obtained without using a chain transfer agent. Emulsifier with the amount of emulsifier, forming a coating film with good film-forming property, that is, particle fusion property, and having excellent water resistance, substrate adhesion, chemical resistance, efflorescence resistance, gloss and surface smoothness A method for producing a resin is provided.

[0030]

EXAMPLES Examples of the present invention will be described below together with comparative examples, but the present invention is not limited thereto. Parts and% in examples are parts by weight and% by weight unless otherwise specified.

<Examples 1 to 5 and Comparative Example 1> A reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, a nitrogen gas inlet tube, a dropping funnel and a dropping funnel for simultaneous injection was prepared as shown in Table 1 as an initial charge. The ion-exchanged water and tertiary butyl hydroperoxide described (comparative example 1 described in Table 2) were charged.

Next, after the temperature was raised to 60 ° C. while introducing nitrogen gas, the monomer mixture shown in Table 1 (Comparative Example 1 was described in Table 2) was stirred and mixed with an emulsifier and ion-exchanged water. Was added dropwise over 4 hours. A solution prepared by dissolving Rongalite described in Table 1 (comparative example 1 described in Table 2) in ion-exchanged water at the same time as the dropping of the monomer emulsion was started was added.
The mixture was dropped over time.

After the co-injection of the Rongalit aqueous solution was completed, the mixture was further maintained at 60 ° C. for 1 hour, and then cooled to adjust the pH to 8.5.
To obtain an emulsion resin having a solid content of 44%.

<Comparative Examples 2 to 5> Ion-exchanged water and persulfate initiator shown in Table 2 were initially charged into a reactor equipped with a stirrer, thermometer, reflux condenser, nitrogen gas inlet, and dropping funnel. Was charged.

Next, after the temperature was raised to 70 ° C. while introducing nitrogen gas, a monomer emulsion obtained by stirring and mixing the monomer mixture shown in Table 2 with an emulsifier and ion-exchanged water was added dropwise over 4 hours.

After completion of the dropping of the monomer emulsion, the temperature was raised to 80 ° C. over 30 minutes and maintained for 2 hours, then cooled to adjust the pH to 8.5, and an emulsion resin having a solid content of 44% was obtained. .

[0037]

[Table 1]

[0038]

[Table 2]

<Reference Examples 1 to 5 and Comparative Reference Examples 1 to 5>
To evaluate the clear film performance of the polymer emulsion resin, 3 parts of Texanol was added as a film-forming aid to 100 parts of the emulsion resin shown in Tables 1 and 2 so that the MFT would be 0 ° C. or less. It was adjusted.

Next, this resin liquid was applied to a galvanized sheet with a film applicator at a wet thickness of 150 μm, and dried at room temperature for 7 days to obtain a test piece.

The test pieces were evaluated for water resistance, gloss, adhesion, and alkali resistance. The results are shown in Tables 3 and 4.

[0042]

[Table 3]

[0043]

[Table 4]

The methods for evaluating the properties are as follows.

Water resistance: After the test piece was immersed in water for 7 days, the whitening state immediately after being taken out and the coated surface state after drying were visually measured, and judged according to the following evaluation criteria. ：: No abnormality △: Medium whitening, gloss finish ×: Complete whitening, complete gloss finish

Gloss: The test piece was measured for 60 ° specular gloss.

Adhesion: 2 m on the test piece with a cutter knife
An incision having a width of m was formed to make 25 goban eyes, and a peeling test using a cellophane tape was performed to display the remaining number of gobang eyes.

Alkali resistance: A glass watch glass having a diameter of 50 mm was filled with a 10% sodium hydroxide solution, adhered so as to cover the painted surface of the test piece, and left standing for 7 days to visually measure the state of the coating film. And the following evaluation criteria. ：: No abnormality △: Swelling or peeling is partially observed ×: Swelling or peeling is observed over the entire surface

Claims (3)

[Claims] 1. A water-soluble organic peroxide having a water solubility of 1% or more by using a copolymerizable surfactant (A) having a polymerizable double bond in a molecule and using an ethylenically unsaturated monomer (B). A method for producing a low-molecular-weight emulsion resin, comprising performing a redox emulsion polymerization of a product initiator (C) and a reducing agent (D). 2. The molar ratio of the reducing agent as the component (D) to the water-soluble organic peroxide-based initiator having a water solubility of 1% or more as the component (C) is 0.01 to 1. The method for producing an emulsion resin according to claim 1. 3. The method for producing an emulsion resin according to claim 1, wherein the weight average molecular weight of the emulsion resin is 0.2 to 200,000.