JP2006152051A5 - Method for producing acrylic aqueous pressure-sensitive adhesive composition - Google Patents

Description

The present invention relates to a method for producing an acrylic water - based pressure-sensitive adhesive composition having excellent adhesive strength and holding power, excellent water whitening resistance , and good productivity .

Accordingly, an object of the present invention is to provide a method for producing an acrylic water-based pressure-sensitive adhesive composition which is excellent in both adhesive force and holding force and excellent in water whitening resistance.

That is, the present invention is a method in which a polymerizable monomer component containing (meth) acrylates is charged all at once into a closed pressure reaction vessel in which an aqueous medium is present, and the pressure in the closed pressure reaction vessel at the start of the reaction is reduced. obtained by emulsion polymerization to control the force in the range of 0.1 to 1.5 MPa, 100% modulus we measured at a tensile test at a temperature of 25 ° C. 0.02 to 0.2 MPa, elongation rate is 2,000 to 7,000%, and method for producing acrylic aqueous pressure-sensitive adhesive composition characterized in that water extractable material contains form available-water-dispersible acrylic resin dry film is not more than 2 wt% I will provide a.

Method for producing an aqueous acrylic pressure-sensitive adhesive composition of the present invention has excellent holding power and adhesive strength both and an acrylic aqueous pressure-sensitive adhesive composition excellent in water whitening resistance, high production efficiency, and, more safely Adhesive products that can be manufactured and are composed of an acrylic water-based pressure-sensitive adhesive composition and a substrate are excellent in adhesive strength, holding power, and water whitening resistance, and are suitable as adhesive labels, adhesive tapes, special adhesive sheets, etc. is there.

Moreover, it is preferable that the dry film formed from the acrylic aqueous pressure-sensitive adhesive composition of the present invention has a glass transition temperature (hereinafter referred to as Tg) of −25 ° C. or lower. Tg is preferably as low as possible, but is particularly preferably −25 to −60 ° C. When the Tg is in such a range, the physical properties as a pressure-sensitive adhesive, that is, the balance of physical properties such as adhesive force and holding force is excellent. Tg in the present invention is based on the numerical values obtained by the measuring methods described in the examples below.

Furthermore, the acrylic aqueous pressure-sensitive adhesive composition of the present invention contains, for example, a polymer obtained by emulsion polymerization of a polymerizable monomer component described later.

When the polymerizable monomer component is specifically exemplified, the main component of the aqueous pressure-sensitive adhesive is:
(A) Carboxyl group-containing ethylenically unsaturated monomer, 0.5 to 10% by weight
(B) a copolymer comprising 100% by weight of a polymerizable monomer component, the essential component being an alkyl (meth) acrylate having an alkyl group having 4 to 12 carbon atoms and 45 to 99.5% by weight. It is.

Furthermore, specifically, the polymerizable monomer component containing (meth) acrylates is charged all at once into a closed pressure reaction vessel in which an aqueous medium exists, and the inside of the closed pressure reaction vessel at the start of the reaction. This is a method for producing an acrylic aqueous pressure-sensitive adhesive composition obtained by emulsion polymerization while controlling the pressure within a range of 0.1 to 1.5 MPa.

At this time, within 180 minutes from the start of the reaction, the polymerization conversion of the polymerizable monomer component to proceed to 95% or more, efficiently preferable because it can produce an aqueous acrylic pressure-sensitive adhesive composition. That is, it is preferable that the time the polymerization conversion rate of the polymerizable monomer component is required to be 95% or more to set the reaction conditions such that within 180 minutes. Examples of means for setting the reaction conditions so as to be within 180 minutes include adjusting the polymerizable monomer component, the temperature at the start of polymerization, and the like. Further, as the time the polymerization conversion rate of the polymerizable monomer component is required to be 95% or more, further be carried out in the range of 10 to 120 minutes, safety, particularly preferred from the viewpoint of productivity.

The polymerization conversion of the polymerizable monomer component in the production method of the acrylic aqueous pressure-sensitive adhesive composition of the present invention, the total charge amount of the polymerizable monomer component (i.e., if all monomers have been converted to polymer ) And the weight of solid content in the water-dispersed acrylic polymer, and is obtained by the following formula.

The polymerization conversion ratio (%) = 100 × ([solids concentration of water-dispersed acrylic polymer] - [solid content concentration of the raw material other than the polymerizable monomer component]) / [total charge of the polymerizable monomer component Concentration relative to raw material]
However, each component in the formula represents the following value.
Solid content concentration of water-dispersed acrylic polymer: Actual measurement (%)
Solid content concentration of raw materials other than polymerizable monomer components: Calculated value (%)
Concentration of polymerizable monomer component to all charged raw materials: Calculated value (%)

The sealed pressure reaction vessel used in the method for producing the acrylic water-based pressure-sensitive adhesive composition refers to a pressure-resistant sealed reaction vessel such as an autoclave, and is equipped with a stirrer, a pressure increasing / decreasing device, and an inert gas inlet. It is preferable. Further, when the material of the inner surface of the sealed pressure reactor is made of glass-lined, the amount of aggregates decreases generated during the emulsion polymerization of the polymerizable monomer component, or, aggregates are hardly adhered to the container Or when the aggregates adhere to the container, the aggregates can be easily removed, the maintenance in the container is facilitated, and when the water-dispersed acrylic polymer is continuously produced in the same sealed pressure reaction container. It is preferable because productivity (a time required for maintenance can be shortened) is improved.

In the production method, the polymerizable monomer component is subjected to emulsion polymerization by controlling the pressure in the sealed pressure reaction vessel at the start of the reaction to a range of 0.1 to 1.5 MPa using a sealed pressure reaction vessel. However, in this case, it is preferable to carry out the reaction while maintaining the pressure in the closed pressure reaction vessel so as to exceed the vapor pressure of the mixture of the aqueous medium and the polymerizable monomer component. In this case, an inert gas may be pressurized and filled into the sealed pressure reaction vessel.

The pressure in the reaction system is not particularly limited as long as the pressure in the sealed pressure reaction vessel at the start of the reaction is controlled within the range of 0.1 to 1.5 MPa, but the pressure in the reaction vessel is not limited. Maintaining the reaction vessel liquid (a mixture of an aqueous medium and a polymerizable monomer component) at a pressure equal to or higher than the vapor pressure can suppress boiling of the reaction vessel liquid, resulting in the formation of aggregates. It is preferable because it can be prevented. The degree of pressurization depends on the composition and concentration of the mixture of the aqueous medium and the polymerizable monomer component, but is in the range of 0.1 to 1.5 MPa. In addition, a pressure does not mean an absolute pressure, but means the differential pressure | voltage which made normal pressure 0 MPa.

In the above production method, since the polymerizable monomer component is subjected to emulsion polymerization in a closed pressure reaction vessel, the temperature in the vessel at the time of emulsion polymerization is not particularly limited, for example, a condition that exceeds the boiling point of water as a medium. It is possible to perform emulsion polymerization safely even underneath. In the case of a reaction vessel attached to a condenser, which is used when producing an ordinary acrylic polymer by emulsion polymerization, if the reaction vessel boils, the content may blow out from the reaction vessel, or the reaction vessel will boil. However, since a closed pressure reaction vessel is used in the present invention, it is possible to control the contents so that they do not boil as necessary. Can be avoided. In particular, when emulsion polymerization is performed at a high temperature (a temperature equal to or higher than the boiling point of the mixture of the aqueous medium and the polymerizable monomer component), when the inside of the reaction vessel is pressurized with an inert gas, boiling in the reaction vessel can be suppressed, As a result, it is preferable because the generation of aggregates can be reduced.

Moreover, the time the polymerization conversion rate of the polymerizable monomer component is required to reach 95%, after a polymerization initiator added to the reaction vessel, a starting point when the polymerization exotherm was observed, successively the reaction vessel The polymerization conversion rate is obtained from the above-mentioned formula by sampling the contents of the above, and indicates the time required for the polymerization conversion rate to reach 95%.

The aqueous medium at the time of emulsion polymerization of a polymerizable monomer component, is not particularly limited, and water may be used alone, or by using a mixed solution of water and a water-soluble solvent Also good. Examples of the water-soluble solvent used here include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, and butyl cellosolve, and polar solvents such as N-methylpyrrolidone. A mixture of two or more can be used.

The monomers used in the above method, the (a), (b), is a available (c), when using the monomers, the polymerization conversion of the polymerizable monomer component Since it is preferable that the time required for the rate to reach 95% is substantially within 180 minutes, a highly reactive polymerizable monomer component that does not significantly reduce the polymerization rate during emulsion polymerization is used in combination. It is preferable to do.

Moreover, in the said manufacturing method, when the aqueous medium in which the polymer particle [A] whose average particle diameter is 10-300 nm is used as an aqueous medium, the quantity of the aggregate which generate | occur | produces at the time of emulsion polymerization is suppressed very little. Furthermore, it is preferable because the particle diameter of the obtained water-dispersed acrylic polymer can be easily controlled within a practical range (50 to 1000 nm). Water-dispersed acrylic polymers generally increase in viscosity when the particle size decreases, so to obtain water-dispersed acrylic polymers with a high solid content, the particle size should be controlled to a certain size. is required.

The type of the polymer particle [A] is not particularly limited. For example, a polymer (hereinafter referred to as ethylene) by radical polymerization of an ethylenically unsaturated monomer such as an acrylic polymer or a butadiene polymer. And a polyurethane resin and a polyester resin containing a polymer having a urea bond and a urethane bond. In addition, a mixture of these various polymers, for example, an acrylic polymer / polyurethane resin mixture, a grafted (blocked) product of various polymers, for example, an unsaturated polyester polymer or an alkyd resin, Examples include grafted products. In particular, the polymer particle [A] is preferably an ethylenic polymer from the viewpoint that the adjustment of the particle diameter and the polymer design are easy and the polymer particle [A] can be easily produced by the method described later. In particular, when the polymer particle [A] is an acrylic polymer obtained by emulsion polymerization of a polymerizable monomer component mainly composed of (meth) acrylate in an aqueous medium, in emulsion polymerization (meth) compatibility and the polymerizable monomer component mainly composed of acrylate, good compatibility with the polymer produced by polymerization of a polymerizable monomer component, further, dispersion stability This is preferable because a good water-dispersible acrylic polymer is easily obtained.

When the polymer particle [A] is an acrylic polymer, the production method of the polymer particle [A] includes (1) water, polymerizable monomer component, polymerization initiator, (if necessary, emulsifier and dispersion Stabilizer) and other raw materials are charged in a batch and polymerized, (2) so-called pre-emulsion method in which water, a polymerizable monomer component and an emulsifier are mixed in advance, or (3) monomer dropping method, etc. It can manufacture by the method of. Among these, the method of batch charging and polymerizing the raw materials of (1) is particularly preferable because the polymer particles [A] can be efficiently produced in a short time. Moreover, what was illustrated as an above-mentioned polymerizable monomer component can be used as (meth) acrylate used in the case of polymerization, and another monomer.

Furthermore, when producing the polymer particles [A] composed of an acrylic polymer, an emulsifier or other dispersion stabilizer may be used, or a polymerization initiator or a chain transfer agent may be used. it can. These examples can be used the same ones used during the emulsion polymerization of the polymerizable monomer component to be described later.

The ratio of the polymerizable monomer component mainly composed of the polymer particle [A] and (meth) acrylate is not particularly limited, but the polymer particle [A] (solid content) is on a weight basis. If the range of the weight) / polymerizable monomer component = 5/95 to 40/60, maintaining high productivity in the emulsion polymerization of the polymerizable monomer component, and suppresses the generation of aggregates It is preferable because a water-dispersed acrylic polymer can be produced stably.

Next, in the above production method, when the polymerizable monomer component is emulsion-polymerized in an aqueous medium, it can be polymerized using an emulsifier or other dispersion stabilizer. Further, as described above, when the polymerizable monomer component is emulsion-polymerized in the presence of the polymer particles [A], the emulsion polymerization can be stably performed without using an emulsifier and other dispersion stabilizers. It is possible, and when the obtained water-dispersed acrylic polymer is formed into a film, it is preferable because various physical properties such as water resistance of the film are improved.

Examples of other dispersion stabilizers other than the emulsifier that can be used in the production method include, for example, polyvinyl alcohol, fiber ether, starch, maleated polybutadiene, maleated alkyd resin, polyacrylic acid (salt), poly Synthetic or natural water-soluble polymer materials such as acrylamide, water-based acrylic resin, water-based polyester resin, water-based polyamide resin, water-based polyurethane resin and the like can be mentioned, and one or a mixture of two or more of these can be used .
In the production method described above, the polymerizable monomer component is emulsion-polymerized using a sealed pressure reaction vessel, under the condition that the dissolved oxygen concentration in the liquid in the sealed pressure reaction vessel is 3 ppm or less. Emulsion polymerization is preferable because inhibition of radical polymerization due to oxygen can be avoided, and emulsion polymerization can proceed smoothly to produce a water-dispersed acrylic polymer efficiently. As a method for lowering the dissolved oxygen concentration in the liquid in the sealed reaction vessel, the aqueous medium, the polymerizable monomer component, and the polymerization initiator are lowered in different vessels, and then these are mixed. Examples include a method, a method of lowering dissolved oxygen after charging an aqueous medium, a polymerizable monomer component, and a polymerization initiator into a closed pressure reaction vessel, and the method can be appropriately selected according to the apparatus to be used. However, in any method, it is preferable that the dissolved oxygen concentration in the liquid in the closed pressure reaction vessel at the start of emulsion polymerization is 3 ppm or less . The method in a liquid (aqueous medium, or in some cases a mixture of a solution or the like of polymer particles [A] and an emulsifier aqueous medium containing, and a polymerizable monomer component, and polymerization initiator) to lower the dissolved oxygen concentration in the Specifically, (1) While stirring in the container, an inert gas was continuously blown or bubbled from one mouth of the container, and dissolved while blowing inert gas and oxygen from the other mouth. A method of reducing the oxygen concentration, (2) A method of lowering the dissolved oxygen concentration by boiling the liquid in the container once under stirring and cooling in an inert gas atmosphere, (3) Inside the container And a method of reducing the dissolved oxygen concentration by lowering the partial pressure of oxygen in the container by lowering the pressure in the container after the inert gas is pressurized and filled in the container. Among these, in order to reduce the dissolved oxygen in the liquid in the container, (3) the method of repeating the operation of lowering the pressure in the container after pressurizing and filling with an inert gas is efficient. Since dissolved oxygen can be reduced, it is preferable. The step of lowering the pressure in the container after pressurizing and filling with the inert gas is preferably repeated 2 to 10 times. The greater the number of repetitions of this step, the lower the dissolved oxygen concentration. Since the oxygen concentration is difficult to decrease, the efficiency is deteriorated.

When the inert gas is pressure-filled into the sealed pressure reaction vessel, for example, the pressure is filled at 0.1 to 2.0 MPa, preferably 0.2 to 1.5 MPa. When the pressure is lower than this range, the number of repetitions may be increased to make the dissolved oxygen concentration 3 ppm or less, or it may not be possible to make it 3 ppm or less. Moreover, when lowering the pressure in the reaction vessel, for example, the pressure is reduced to -0.04 to -0.09 MPa. If the degree of vacuum is lower than this range, the number of repetitions may be increased to make the dissolved oxygen concentration 3 ppm or less, or the existing oxygen concentration may not be made 3 ppm or less. Furthermore, the pressure of the emulsion during polymerization of the reaction vessel of the polymerizable monomer component, depending on the reaction temperature during the emulsion polymerization to be described below, at normal pressure, or performing the pressurized emulsion polymerization in an inert gas Can do. The pressure here does not mean an absolute pressure but a differential pressure obtained by setting the normal pressure to 0 MPa. Moreover, as inert gas, noble gases, such as nitrogen gas, helium, and argon, can be mentioned, You may use these 1 type or in mixture of 2 or more types. As the type of inert gas, nitrogen gas is particularly preferable from the viewpoints of economy and versatility. The purity of the inert gas is usually 95% or more, preferably 98% or more.

In the above production method, since the polymerizable monomer component is subjected to emulsion polymerization in a closed pressure reaction vessel, the temperature in the vessel at the time of emulsion polymerization is not particularly limited, for example, a condition that exceeds the boiling point of water as a medium. It is possible to perform emulsion polymerization safely even underneath. In the case of a reaction vessel attached to a condenser, which is used when producing an ordinary acrylic polymer by emulsion polymerization, if the reaction vessel boils, the content may blow out from the reaction vessel, or the reaction vessel will boil. However, since a closed pressure reaction vessel is used in the present invention, these problems can be avoided. In particular, when emulsion polymerization is performed at a high temperature (a temperature equal to or higher than the boiling point of the mixture of the aqueous medium and the polymerizable monomer component), when the inside of the reaction vessel is pressurized with an inert gas, boiling in the reaction vessel can be suppressed, As a result, it is preferable from the viewpoint that the generation of aggregates can be prevented. The pressure at the time of pressurizing with an inert gas in order to suppress boiling in the reaction vessel is the liquid in the reaction vessel (the aqueous medium and the polymerizable monomer component) at the highest temperature reached in the reaction vessel during emulsion polymerization. It is preferable that the pressure be equal to or higher than the vapor pressure of the mixture). If the pressure equal to or higher than the vapor pressure is maintained, boiling in the reaction vessel can be completely suppressed.

In the emulsion polymerization of the polymerizable monomer component, it can be obtained by radical polymerization using only these peroxides, or by a redox polymerization initiator in which a reducing agent is used in combination with the peroxide.

These polymerization initiators may be used in amounts that allow the polymerization to proceed smoothly. However, if water resistance is required for the obtained water-dispersed acrylic polymer film or the like, the amount used is minimized. The amount used is preferably 0.3% by weight or less based on the weight of the polymerizable monomer component (in the case of a redox polymerization initiator used in combination with a reducing agent, the total amount of an oxidizing agent and a reducing agent). ) Is preferable. In the present invention, if it is necessary to adjust the molecular weight of the water-dispersed acrylic polymer, a compound having a chain transfer ability of the polymerizable monomer component as a molecular weight modifier during the emulsion polymerization, for example, lauryl mercaptan, octyl Mercaptans such as mercaptan, dodecyl mercaptan, 2-mercaptoethanol, octyl thioglycolate, 3-mercaptopropionic acid and thioglycerin, or α-methylstyrene dimer may be added.

Polymerization conversion rate (%) = 100 × ([Solid content concentration of sample] − [Solid content concentration of raw material other than polymerizable monomer component]) / [Concentration of polymerizable monomer component to all charged raw materials]
However, each component in the formula represents the following value.
Sample solid content concentration: Actual measurement (%)
Solid content concentration of raw materials other than polymerizable monomer components: Calculated value (%)
Concentration of polymerizable monomer component to all charged raw materials: Calculated value (%)

Comparative Example 2
An acrylic aqueous pressure-sensitive adhesive composition was obtained in the same manner as in Comparative Example 1 except that the monomer mixture shown in Table 1 was used. The average particle diameter (50% median diameter), solid content concentration, and viscosity of the polymer particles contained in the acrylic aqueous pressure-sensitive adhesive composition were as described in Table 1. Elongation rate, glass transition temperature (measured Tg), gel fraction (toluene insoluble fraction) of the coating film obtained using this acrylic aqueous pressure-sensitive adhesive composition, and adhesive strength and holding power of the pressure-sensitive adhesive sheet The evaluation results of the tack are shown in Table 2.

Claims (3)

The polymerizable monomer component containing (meth) acrylates is charged all at once into a closed pressure reaction vessel in which an aqueous medium exists, and the pressure in the closed pressure reaction vessel at the start of the reaction is 0.1 to 1. was controlled in the range of .5 MPa obtained by emulsion polymerization, 0.02 to 0.2 MPa 100% modulus measured at tensile test at a temperature of 25 ° C., the elongation 2000-7 000 %, and production method of the acrylic aqueous pressure-sensitive adhesive composition characterized in that water extractable material contains 2 wt% or less is dry coating capable of forming a water-dispersed acrylic Le resin. The method for producing an acrylic aqueous pressure-sensitive adhesive composition according to claim 1, wherein the dry coating has a gel fraction of 10 to 50% by weight . The glass transition temperature of the dry film is at -25 ° C. or less, the polymerizable monomer component, wherein the total weight of the heavy polymerizable monomer component, (a) a carboxyl group-containing ethylenically unsaturated monomer The acrylic water according to claim 1, comprising 0.5 to 10% by weight of a monomer and (b) 45 to 99.5% by weight of an alkyl ( meth) acrylate having an alkyl group having 4 to 12 carbon atoms. For producing a pressure-sensitive adhesive composition.