JPH0656916A - Water-base emulsion and its production - Google Patents

Abstract

PURPOSE:To obtain a water-base emulsion which does not contain a low- molecular emulsifier, is excellent in resistance to water and solvents, and can form a transparent film. CONSTITUTION:A water-base emulsion is obtd. by subjecting a radical- polymerizable unsatd. monomer to emulsion polymn. in water in the presence of a water-sol. cellulose acetate. The cellulose acetate may be one having a low degree of substitution, e.g. of about 0.1-1.0%, and is used in an amt. of 5-50-wt.% of the sum of it and the monomer. The emulsion, excellent in transparency, is useful as a coating binder, a coating material, or an adhesive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called soap-free aqueous emulsion containing no low molecular weight emulsifier and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Aqueous emulsions are usually obtained by emulsion polymerization of radically polymerizable unsaturated monomers using a low molecular weight surfactant or the like as an emulsifier. However, since the emulsifier is water-soluble and has a low molecular weight, the water resistance of the coating film formed by the aqueous emulsion is significantly reduced.

Therefore, there has been proposed a soap-free emulsion which does not contain a low-molecular weight emulsifier, has excellent coating properties and is useful as a binder for paints and the like. For example, Japanese Patent Publication No. 61-44901 discloses a method of polymerizing a radically polymerizable unsaturated monomer in the presence of a grafted cellulose derivative. However, this method requires a step for obtaining a grafted cellulose derivative which is a high molecular weight emulsifier. Therefore, the manufacturing process for obtaining the aqueous emulsion is complicated, which is industrially disadvantageous.

Further, JP-A-51-28188 and JP-A-2-151601 disclose a method of polymerizing a radically polymerizable unsaturated monomer in the presence of cellulose nitrate or ligninsulfonic acid and its salt. It is disclosed. But,
The aqueous emulsions obtained by these methods are colored and the coating is opaque. Therefore, the use of the aqueous emulsion is limited.

On the other hand, water-soluble cellulose acetate, which is a semi-synthetic polymer, is used as a coating agent for pharmaceuticals, a binder for tablets, an aqueous paste and the like. This water-soluble cellulose acetate is obtained by subjecting cellulose acetate, which is a cellulose derivative, to a deacetylation reaction in the presence of an acidic catalyst to reduce the degree of substitution (for example, US Pat. No. 21,290,52). However, it is not known to use such water-soluble cellulose acetate as a polymeric emulsifier in emulsion polymerization.

[0006]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an aqueous emulsion which does not contain a low molecular weight emulsifier and has excellent water resistance and solvent resistance and which can form a transparent film.

Another object of the present invention is a binder for paints,
It is to provide an aqueous emulsion useful as a coating agent and the like.

Still another object of the present invention is to provide a method for producing an aqueous emulsion which can industrially advantageously produce an emulsion having the above-mentioned excellent properties.

[0009]

The present inventors have conducted extensive studies to achieve the above object, and as a result, emulsion polymerization using water-soluble cellulose acetate produces an aqueous emulsion having excellent stability and extremely high transparency. Find what you get,
The present invention has been completed.

That is, the present invention is an emulsion obtained by emulsion-polymerizing a radical-polymerizable unsaturated monomer using water as a dispersion medium in the presence of an emulsifier, which is an aqueous emulsion containing water-soluble cellulose acetate as an emulsifier. provide.

In the above aqueous emulsion, the amount of water-soluble cellulose acetate is 50% by weight of the radically polymerizable unsaturated monomer.
It is preferably 5 to 50% by weight with respect to 95% by weight.

The present invention also provides a method for producing an aqueous emulsion in which water is used as a dispersion medium to polymerize a radically polymerizable unsaturated monomer in the presence of water-soluble cellulose acetate.

In the present specification, the term "aqueous emulsion" is used to include an aqueous dispersion sometimes called a latex.

The water-soluble cellulose acetate may be any water-soluble cellulose acetate having a dispersibility for polymer particles. Such water-soluble cellulose acetate is usually composed of low-substituted cellulose acetate, and its substitution degree is, for example, 0.3 to 1.0, preferably 0.4 to
It is about 0.9. The degree of substitution of acetic acid can be adjusted by deacetylating cellulose acetate in the presence of an acidic catalyst.

The degree of polymerization of the water-soluble cellulose acetate may be within a range that does not impair the water resistance, the operability of polymerization, etc., and is, for example, 20 to 1600, preferably 50 to 1000, and more preferably 100 to 800. . The viscosity of the water-soluble cellulose acetate aqueous solution is not particularly limited, and may be, for example, a 6 wt% aqueous solution viscosity of about 10 to 1500 cps.

The water-soluble cellulose acetate has a feature that it stabilizes the polymer particles in the aqueous emulsion by emulsion polymerization of the radical-polymerizable unsaturated monomer and forms a highly transparent film.

As the radically polymerizable unsaturated monomer, various α, β-ethylenically unsaturated compounds, for example, compounds having an acryloyl group, a methacryloyl group, a vinyl group and the like can be used. More specifically, the monomer includes
The following monomers are included. In addition, unless otherwise specified, the term “(meth) acrylate” is used below to mean acrylate and methacrylate.

(A) (Meth) acrylate Examples of (meth) acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl. (Meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, hexyl (meth)
Acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) Examples thereof include acrylate, methoxyethyl (meth) acrylate and ethoxyethyl (meth) acrylate.

Preferred (meth) acrylates are methyl methacrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth).
An alkyl (meth) acrylate having an alkyl group having about 1 to 12 carbon atoms such as acrylate is included.

(B) Aromatic Vinyl Compound The aromatic vinyl compound includes, for example, styrene, α-methylstyrene, vinyltoluene and the like. Styrene is often used as the aromatic vinyl compound.

(C) Monomer Having Functional Group Such a monomer has a hydroxyl group such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate and allyl alcohol. α, β-ethylenically unsaturated compounds; α, β-ethylenically unsaturated compounds having amino groups such as dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate; (meth) acrylamide, diacetone (meth) acrylamide Α, β-ethylenically unsaturated compounds having amide groups such as; α, β-ethylenically unsaturated compounds having glycidyl groups such as glycidyl (meth) acrylate and allyl glycidyl ether; N-methylol (meth) acrylamide, N -Methoxymethyl (meth) acrylamide, - alpha having a N- methylol group or N- alkoxymethyl groups such as ethoxymethyl (meth) acrylamide, and β- ethylenically unsaturated compound.

(D) Acidic monomer Examples of the acid monomer include α, β-, such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, itaconic acid half ester, maleic acid, and maleic acid half ester.
Ethylenically unsaturated carboxylic acids; α, β-ethylenically unsaturated sulfonic acids such as sodium styrenesulfonate and sodium vinylsulfonate. Preferred acidic monomers include α, β-ethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid.

(E) Vinyl Ester Vinyl ester includes vinyl acetate, vinyl caproate,
Ve such as vinyl propionate and vinyl versatate
Included is a vinyl ester called oVa.

(F) Other monomers Olefin such as ethylene, butadiene, isoprene and chloroprene; (meth) acrylonitrile; vinyl halide such as vinyl chloride and vinylidene chloride; allyl ester such as allyl acetate; methyl vinyl ketone and the like. Examples thereof include vinyl ketones; vinyl ethers such as methyl vinyl ether; crotonaldehyde; fumaric acid esters such as diethyl fumarate, dipropyl fumarate, dibutyl fumarate, di (2-ethylhexyl) fumarate and maleic acid esters corresponding thereto.

These radically polymerizable unsaturated monomers may be used alone or in combination of two or more. When forming a film with an aqueous emulsion, the preferable radically polymerizable unsaturated monomer has a glass transition temperature (Tg) of 10 ° C. or higher as a whole, preferably 15 to 75 ° C., more preferably 20 to
It is selected to constitute a polymer at around 50 ° C. When the aqueous emulsion is used as a pressure-sensitive adhesive or the like, the radically polymerizable unsaturated monomer has a glass transition temperature (Tg) of 10 ° C. or less as a whole, preferably −100.
It is selected so as to constitute a polymer at about 0 ° C to 0 ° C.

When the acrylic aqueous emulsion is constituted, the radical-polymerizable unsaturated monomer may have a glass transition temperature of 50 ° C. or higher, preferably 70 ° C. to 130 ° C.
In many cases, a hard monomer forming a hard polymer and a soft monomer forming a soft polymer having a glass transition temperature of 20 ° C. or lower, preferably about −100 ° C. to 0 ° C. are used in combination. Typical hard monomers include, for example, methyl methacrylate, t-butyl methacrylate, styrene, acrylonitrile, and the like, and typical soft monomers include, for example, ethyl acrylate, butyl acrylate, acrylate-2. -Ethylhexyl and the like can be mentioned. The ratio of the hard monomer and the soft monomer can be selected in a wide range according to the kind of the monomer and the glass transition temperature of the desired polymer particles,
For example, hard monomer / soft monomer = 10 to 90
/ 90 to 10 (weight ratio), preferably 25 to 75/75
It is about 25 (weight ratio).

The polymer particles of the aqueous emulsion are
(1) Acrylic polymer or styrene-acrylic polymer capable of easily adjusting the glass transition temperature of polymer particles, (2) Vinyl ester polymer containing vinyl ester such as vinyl acetate as a constituent unit, (3) Styrene as a constituent unit It is often formed from a styrene-based polymer containing as.

The glass transition temperature means a value calculated by the following Tobolsky calculation formula.

1 / Tg = Wa / Tga + Wb / Tgb + ... [wherein Tg is the glass transition temperature (° K) of the copolymer, T
ga is the glass transition temperature (° K) of the homopolymer of monomer a, Tgb is the glass transition temperature (° K) of the homopolymer of monomer b, Wa is the weight fraction of monomer a, and Wb is the weight fraction of monomer b. Shown] Further preferred radically polymerizable unsaturated monomers contain acidic monomers, especially α, β-ethylenically unsaturated carboxylic acids, in order to enhance the stability of the aqueous emulsion. Further, the stability of the aqueous emulsion can be further enhanced by neutralizing the carboxyl group of the α, β-ethylenically unsaturated carboxylic acid with a basic substance such as ammonia or amines. The amount of the α, β-ethylenically unsaturated carboxylic acid used is 0.1 to 15% by weight, preferably 0.1% by weight based on the total amount of the radically polymerizable unsaturated monomer.
It is about 5 to 10% by weight.

Further, in order to further improve the adhesion, water resistance and flexibility of the coating film, a radical polymerizable unsaturated monomer having a crosslinkable functional group such as glycidyl group, N-methylol group or N-alkoxymethyl group. It is effective to use a polymer. The monomer having a glycidyl group is often used in combination with a monomer having an active hydrogen atom such as a carboxyl group. The amount of the monomer having a crosslinkable functional group is 0.1 to 2 in the total amount of the radically polymerizable unsaturated monomer.
It is 0% by weight, preferably about 0.5 to 15% by weight.

The ratio of the water-soluble cellulose acetate to the radically polymerizable unsaturated monomer can be selected within a wide range in consideration of the operability of emulsion polymerization and the stability of the aqueous emulsion, but usually the water-soluble cellulose acetate is used. / Radical polymerizable unsaturated monomer = 5 to 50/95 to 50 (wt%), preferably 10 to 40/90 to 60 (wt%), more preferably 15 to 35/85 to 65 (wt%) It is a degree. If the amount of the water-soluble cellulose acetate used is less than 5% by weight, the stability of the aqueous emulsion tends to decrease, and if it exceeds 50% by weight, the viscosity is usually high although it depends on the solid content of the aqueous emulsion, and the polymerization operability is high. Is easy to decrease.

The structure of the polymer particles in the aqueous emulsion is not limited to a homogeneous structure, and may be any of a heterophase structure such as a microdomain structure or a core / shell structure. Also,
The shape of the polymer particles is not limited to the spherical shape, and may be an irregular shape. The average particle size of the polymer particles can be appropriately set from the viewpoints of dispersion stability, viscosity, coating properties, etc., and is, for example, 10 nm to 100 μm, preferably 50 nm to 50 nm.
It is about μm.

The solid content concentration of the aqueous emulsion cannot be unconditionally determined because it varies depending on the application.
It is about 10 to 60% by weight.

In the method of the present invention, the radical-polymerizable unsaturated monomer is emulsion-polymerized in the presence of water-soluble cellulose acetate using water as a dispersion medium. The emulsion polymerization method is not particularly limited, and, for example, (1) a method of mixing an aqueous solution of water-soluble cellulose acetate and a radical-polymerizable unsaturated monomer in the presence of a water-soluble radical polymerization initiator, and polymerizing the mixture. (2) A method in which a radical-polymerizable unsaturated monomer is added dropwise to an aqueous solution of water-soluble cellulose acetate in the presence of a water-soluble radical polymerization initiator in a stepwise or continuous manner to perform polymerization, (3) water-soluble radical polymerization In the presence of an initiator, to an aqueous solution of water-soluble cellulose acetate,
A multi-stage polymerization method in which radical-polymerizable unsaturated monomers having different compositions are dropped and polymerized stepwise or continuously is exemplified.

Examples of the water-soluble polymerization initiator include conventional compounds such as hydrogen peroxide, potassium persulfate, ammonium persulfate, 2,2-azobis (2-aminopropane) hydrochloride and redox type polymerization initiator. it can. The amount of the water-soluble polymerization initiator used is usually about 0.01 to 5% by weight based on the radically polymerizable unsaturated monomer.

The emulsion polymerization temperature can be selected according to the type of the polymerization initiator and the like, and is usually about 0 to 120 ° C. In addition,
Emulsion polymerization may be performed under pressure depending on the type of radically polymerizable monomer.

When emulsion polymerization is carried out in the presence of water-soluble cellulose acetate, it seems that a graft polymerization reaction also occurs between the water-soluble cellulose acetate and the radically polymerizable unsaturated monomer.
Therefore, when the obtained aqueous emulsion is used, it is possible to form a tough and transparent film while being excellent in water resistance and solvent resistance.

In emulsion polymerization, if necessary,
Conventional ingredients such as buffers, chain transfer agents and the like may be used. In addition to water-soluble cellulose acetate, anionic surfactants, as long as the characteristics of the coating such as water resistance are not impaired,
Emulsion polymerization is performed by using a nonionic surfactant, a cationic surfactant, a surfactant such as an amphoteric surfactant, and at least one emulsifier selected from protective colloids such as water-soluble polymers and water-soluble oligomers. Good. Moreover, you may add an emulsifier to the aqueous emulsion obtained by emulsion polymerization as needed. As the surfactant, anionic surfactants and nonionic surfactants are often used alone or in combination.

An organic solvent may be added to the aqueous emulsion thus obtained. As an organic solvent,
For example, aromatic solvents such as benzene, toluene, xylene; alicyclic solvents such as cyclohexane; aliphatic solvents such as hexane; alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol; ethyl acetate, butyl acetate, etc. And the like; ketones such as acetone and methyl ethyl ketone; and mixed solvents thereof.

A film-forming aid, for example, a polyhydric alcohol such as ethylene glycol or acetylene glycol; a cellosolve such as methyl cellosolve, ethyl cellosolve or butyl cellosolve; carbitol or butyl carbitol acetate may be added to the aqueous emulsion. Good.

In the aqueous emulsion, if necessary, conventional additives such as a plasticizer, a rust preventive, a dispersant, and
A defoaming agent, a thickener, a neutralizing agent, an antiseptic, an antifreezing agent, an antistatic agent, waxes, a crosslinking agent and the like may be added.

The aqueous emulsion of the present invention can be used as a binder for paints and printing inks, cellophane for plastic films, a coating agent for packaging materials such as paper, and an adhesive. Since the aqueous emulsion forms a transparent film, it can be used as a clear paint or coating agent as it is, and can be used as a paint or a printing ink composition by adding a coloring agent such as a dye or a pigment. The pigment may be added after being dispersed in advance with a dispersant.

The aqueous emulsion of the present invention can be applied to various base materials such as metal, ceramics, concrete, plastic, wood, paper and cloth. When used as a paint, it can be used not only as an overcoating agent but also as an undercoating agent. In this case, a conventional paint such as an acrylic paint, a urethane paint, an epoxy paint, an alkyd resin paint, etc. may be applied on the undercoat film.

[0044]

Since the aqueous emulsion of the present invention contains water-soluble cellulose acetate as a polymeric emulsifier,
It has excellent solvent resistance and can form a transparent film. for that reason,
Aqueous emulsions are useful as binders for paints, coating agents, adhesives, pastes and the like.

Further, according to the method of the present invention, it is possible to obtain an aqueous emulsion having the above-mentioned excellent properties by using water-soluble cellulose acetate which is industrially easily available.

[0046]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 A flask equipped with a stirrer, a reflux condenser and a thermometer was charged with 8 parts of water.
84 g and water-soluble cellulose acetate (degree of substitution 0.88) 86
and g and dissolve while stirring while flowing nitrogen gas,
Heated to 85 ° C. In an aqueous solution of water-soluble cellulose acetate,
Methyl methacrylate 38g, butyl acrylate 132g
And a monomer mixture of 9 g of acrylic acid and an initiator solution prepared by dissolving 0.6 g of potassium persulfate in 50 g of water were added dropwise over 3 hours, respectively, and then the mixture was stirred at 85 ° C. for 4 hours for polymerization, and room temperature was obtained. Cooled down.

Then, the pH is adjusted to 7.5 by adding aqueous ammonia, the solid content concentration is 21.3% by weight, and the viscosity is 7
A stable aqueous emulsion of 6.4 cps (30 ° C) was obtained.

When the obtained aqueous emulsion was applied to a glass plate and formed into a film at room temperature, an extremely highly transparent film was formed. Further, when the coating was rubbed with gauze containing gasoline and the state of the coating was observed and the gasoline resistance was examined, the coating did not whiten at all.

Example 2 A flask equipped with a stirrer, a reflux condenser and a thermometer was charged with 8 parts of water.
21 g and water-soluble cellulose acetate (degree of substitution 0.88) 86
g and were charged, and the contents were dissolved by stirring while flowing nitrogen gas. After dropping 3 g of methyl methacrylate, 9 g of butyl acrylate, and 1 g of acrylic acid into the aqueous solution of water-soluble cellulose acetate, the mixture was heated, and at 80 ° C., 0.04 g of potassium persulfate was added to 2.5 g of water. The dissolved initiator solution was added and heated to 85 ° C.

Then, a monomer mixture of 49 g of methyl methacrylate, 169 g of butyl acrylate and 11 g of acrylic acid and an initiator solution prepared by dissolving 0.8 g of potassium persulfate in 48 g of water were added dropwise over 3 hours. After 8
The mixture was stirred at 5 ° C. for 4 hours for polymerization, and cooled to room temperature.

Next, the pH is adjusted to 7.5 by adding aqueous ammonia, the solid content concentration is 26.4% by weight and the viscosity is 9%.
A stable aqueous emulsion of 3.6 cps (30 ° C.) was obtained.

When the obtained aqueous emulsion was applied to a glass plate and a film was formed at room temperature, an extremely highly transparent film was formed. Further, when the coating was rubbed with gauze containing gasoline and the state of the coating was observed and the gasoline resistance was examined, the coating did not whiten at all.

Claims (3)

[Claims] 1. An emulsion obtained by emulsion-polymerizing a radically polymerizable unsaturated monomer using water as a dispersion medium in the presence of an emulsifier, the aqueous emulsion containing water-soluble cellulose acetate as an emulsifier. 2. The amount of water-soluble cellulose acetate is 5 to 50 relative to 50 to 95% by weight of the radical-polymerizable unsaturated monomer.
The aqueous emulsion according to claim 1, which is a weight percent. 3. A method for producing an aqueous emulsion, which comprises polymerizing a radically polymerizable unsaturated monomer using water as a dispersion medium in the presence of water-soluble cellulose acetate.