JP2002241730A - Method for drying water-dispersed PSA composition, method for producing water-dispersed PSA sheets, and water-dispersed PSA sheets - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a water dispersion type adhesive sheet in which the formation of bubbles are controlled and which has good appearance, and to provide the water dispersion type adhesive sheet. SOLUTION: The method for producing the water dispersion type adhesive sheet, comprising coating a support with a water dispersion type adhesive composition and then blowing hot air on the support in a drying section to dry the coated adhesive composition, thereby forming the adhesive layer on the support, is characterized in that the temperature of the hot air in the first half of a falling drying rate period is set to a lower temperature within +50 deg.C than the temperature of a wet bulb.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for drying a water-dispersed pressure-sensitive adhesive composition which suppresses the generation of bubbles and a method for producing water-dispersed pressure-sensitive adhesive sheets (sheets, tapes, films, etc.) having good appearance. And water-dispersible pressure-sensitive adhesive sheets produced by this production method.

[0002]

2. Description of the Related Art Conventionally, a solvent type adhesive has been mainly used as an adhesive. However, since these solvent-based pressure-sensitive adhesives are synthesized or dissolved in an organic solvent, volatilization of the solvent at the time of coating is environmentally problematic, and water in which pressure-sensitive adhesive particles are dispersed or emulsified in an aqueous medium is used. Conversion to a dispersion-type adhesive is being pursued.

[0003] However, the water-dispersed pressure-sensitive adhesive has a problem that it is necessary to evaporate water having a large latent heat of evaporation in a drying step, and the drying time is longer than that of a solvent-type pressure-sensitive adhesive. Therefore,
When the drying temperature was set high to increase the productivity, bubbles were generated in the pressure-sensitive adhesive layer, which had an adverse effect on the appearance.

That is, as shown in FIG. 1, air bubbles generated in the pressure-sensitive adhesive layer remain as bubbles inside the pressure-sensitive adhesive layer, or a part of the air bubbles protrudes to the outside and a convex portion is formed on the surface of the pressure-sensitive adhesive layer. Or rupture to form a recess on the surface of the pressure-sensitive adhesive layer. As a result, the pressure-sensitive adhesive layer becomes non-uniform and the transparency is reduced, and the surface of the pressure-sensitive adhesive layer becomes poor in smoothness.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the conventional problems, and provides a method for drying a water-dispersed pressure-sensitive adhesive composition which suppresses generation of bubbles in a pressure-sensitive adhesive layer. The purpose is to do. Furthermore, a method for producing water-dispersible pressure-sensitive adhesive sheets (sheets, tapes, etc.) having good appearance, including the above-mentioned drying method, and a water-dispersible pressure-sensitive adhesive having a pressure-sensitive adhesive layer having a bubble size of 150 μm or less produced by this method. The purpose is to provide sheets.

[0006]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the bubbles found in the pressure-sensitive adhesive layer are generated during the drying step. It was presumed that the water content of the pressure-sensitive adhesive composition was rapidly vaporized and left as bubbles due to the rapid rise in the temperature of the pressure-sensitive adhesive that occurred immediately after the critical moisture content, that is, in the first half of the reduced-rate drying period.

That is, generally, the drying process of the pressure-sensitive adhesive sheet can be divided into a material preheating period, a constant rate drying period, and a reduced rate drying period as shown in FIG.

[0008] Here, the material preheating period refers to a period during which the surface temperature of the pressure-sensitive adhesive composition layer rises and is maintained at a constant temperature. Here, it is a period during which the temperature of the pressure-sensitive adhesive composition layer rises due to the hot air supplied into the drying zone, and most of the heat of the hot air is spent on the temperature rise of the pressure-sensitive adhesive composition layer, and almost all of the drying time is consumed. It is not done.

The constant rate drying period refers to a period from a state in which the temperature of the pressure-sensitive adhesive composition layer is kept substantially constant to a time when the water content in the pressure-sensitive adhesive layer reaches a limit water content. In the constant rate drying period,
Although the surface temperature of the pressure-sensitive adhesive composition layer keeps a substantially constant temperature (the surface temperature at this time is called wet bulb temperature), water evaporates from the surface of the pressure-sensitive adhesive composition layer, and the water evaporates from the surface. Moisture inside the pressure-sensitive adhesive composition layer moves toward the surface so as to follow. Therefore, during the constant rate drying period, the pressure-sensitive adhesive composition layer is dried at a substantially constant drying rate until the moisture content in the pressure-sensitive adhesive composition layer reaches the limit moisture content. Generally, the higher the temperature of the pressure-sensitive adhesive layer, the more water moves from the inside of the pressure-sensitive adhesive layer to the surface.

The reduced drying period refers to a drying period until the moisture content in the pressure-sensitive adhesive composition layer reaches the equilibrium moisture content from the limit moisture content. In the rate-decreasing drying period, the moisture evaporating from the surface of the pressure-sensitive adhesive composition layer becomes larger than the water moving from the inside to the surface, and the drying rate decreases with a decrease in the water remaining in the pressure-sensitive adhesive composition layer. . During the reduced-rate drying period, the temperature of the pressure-sensitive adhesive composition layer rises, and the drying of the pressure-sensitive adhesive layer ends when the moisture content in the pressure-sensitive adhesive composition layer reaches the equilibrium moisture content.

That is, in the drying step of the pressure-sensitive adhesive composition, during the constant-rate drying period, the amount of heat supplied by the hot air is mainly used for drying moisture, and the temperature of the pressure-sensitive adhesive composition is a constant value called wet bulb temperature. It is dried while maintaining the temperature,
When the moisture content reaches the limit moisture content, the amount of heat consumed by drying decreases, and the temperature of the pressure-sensitive adhesive composition rises rapidly.
At this time, it is estimated that the moisture inside the pressure-sensitive adhesive layer is vaporized and remains as bubbles.

Therefore, in the present invention, in a drying step of applying a water-dispersed pressure-sensitive adhesive to a support and then blowing the support with hot air to dry the support, the temperature of the hot air in at least the first half of the reduced-rate drying period is reduced to the wet-bulb temperature. By taking into account and controlling,
By suppressing a sharp rise in the temperature of the pressure-sensitive adhesive composition and slowly drying the pressure-sensitive adhesive layer when the pressure-sensitive adhesive layer has a low viscosity, bubbles generated by vaporization of water in the pressure-sensitive adhesive layer are reduced.

That is, the present invention provides a method for drying a water-dispersed pressure-sensitive adhesive composition in which the water-dispersed pressure-sensitive adhesive composition on a support is dried with hot air while passing through a drying section. A method for drying a water-dispersed pressure-sensitive adhesive composition (Claim 1), wherein the pressure is set within + 50 ° C. from the wet-bulb temperature. Preliminary drying is performed by setting the hot air temperature and air velocity in the drying section so that the adhesive is dried, and the surface temperature and moisture content of the pressure-sensitive adhesive composition in the drying section during the preliminary drying are measured, and the wet-bulb temperature and the reduced-rate drying are determined from these. Ask for a period,
A method for drying a water-dispersed pressure-sensitive adhesive composition, wherein the hot air temperature in the first half of the reduced-rate drying period is set within + 50 ° C. of the wet-bulb temperature in accordance with the obtained wet-bulb temperature (claim 2).
In particular, the present invention relates to a method for drying a water-dispersed pressure-sensitive adhesive composition in which the hot air velocity is preferably 15 m / sec or less (claim 3).

The present invention also provides a coating step of coating at least a water-dispersed PSA composition on a support.
Forming a pressure-sensitive adhesive layer on a support by the method for drying a water-dispersible pressure-sensitive adhesive composition according to (4), wherein the pressure-sensitive adhesive sheet is a water-dispersible pressure-sensitive adhesive sheet; The present invention relates to water-dispersed pressure-sensitive adhesive sheets (claim 5), which have a bubble size in the pressure-sensitive adhesive layer of 150 μm or less, which is produced by a method for producing the pressure-sensitive adhesive layer.

Therefore, according to the first aspect of the present invention, the temperature of the hot air in the first half of the reduced-rate drying period is set within + 50 ° C. from the wet bulb temperature, so that the temperature of the pressure-sensitive adhesive composition rises sharply. And the growth of bubbles generated by rapid vaporization of water can be suppressed. And by slowly drying the adhesive layer when the viscosity is low,
This is to reduce bubbles generated when water evaporates in the pressure-sensitive adhesive layer.

According to the second aspect of the present invention, the pre-drying is performed by setting the conveying speed of the support, setting the hot air temperature and the air speed in the drying section so that the adhesive composition dries at the conveying speed. Perform, measure the surface temperature and moisture content of the pressure-sensitive adhesive composition in the drying section at the time of preliminary drying, determine the wet-bulb temperature and the reduced-rate drying period from these, according to the determined wet-bulb temperature, the first half of the reduced-rate drying period Hot air temperature + 50 ° C from wet bulb temperature
Because it is set within, the wet bulb temperature and the lapse rate drying period can be easily obtained, and particularly, the rapid temperature rise of the pressure-sensitive adhesive composition can be controlled, and water evaporates in the pressure-sensitive adhesive layer. This is to reduce the air bubbles generated by the operation.

According to the third aspect of the present invention, since the wind speed of the hot air is 15 m / sec or less, the generation of bubbles can be more effectively suppressed.

According to the fourth aspect of the present invention, a water-dispersed pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer having small bubbles can be manufactured.

According to the fifth aspect of the present invention, it is possible to reduce the bubble size in the pressure-sensitive adhesive layer to 150 μm or less, and to improve the transparency and surface smoothness of the pressure-sensitive adhesive layer. it can. The water-dispersed pressure-sensitive adhesive sheets produced in this way can be used for various applications, but because of their good appearance, they can be suitably used for packaging and surface protection.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 is a longitudinal sectional view showing a schematic configuration of the entire apparatus for manufacturing a pressure-sensitive adhesive sheet according to an embodiment of the present invention.
FIG. 4 is a longitudinal sectional view illustrating a schematic configuration of a drying unit illustrated in FIG. 3.

The apparatus for manufacturing a pressure-sensitive adhesive sheet according to the present embodiment
As shown in FIG. 3, roughly divided into a support supply roll 2 on which a support 1 such as a sheet, a tape, or a film is wound, and a support 1 from the support supply roll 2. A coating unit 3 for coating (applying) the pressure-sensitive adhesive composition to a desired thickness, and heating the pressure-sensitive adhesive composition applied to the support 1 to remove the solvent from the pressure-sensitive adhesive composition The drying unit 4 includes an adhesive layer, and a winding unit 5 that winds the support 1 heated and dried in the drying unit 4. Hereinafter, the configuration of each unit will be described in detail.

The support supply roll 2 has a support 1 wound in the form of a sheet, tape, or film.

In the present invention, the support 1 is not particularly restricted but includes, for example, papers (Japanese paper, kraft paper, etc.), cloths (cotton, cloth, synthetic fiber, non-woven fabric, etc.) and plastics (cellophane, cellophane, etc.). Polypropylene, ethylene / propylene copolymer, polyester, polyethylene, polyvinyl chloride, acetate, polystyrene, polyacrylonitrile, etc.), metal foil, or a plastic laminate of these can be used. Its thickness is usually 10 ~
Although it is about 300 μm,
It can be determined appropriately according to the purpose. Further, the support may be one which has been subjected to a known treatment such as an undercoating treatment, a sealing treatment, a corona treatment, and a back surface treatment.

The coating unit 3 applies the pressure-sensitive adhesive composition to the support 1 from the support supply roll 2 so as to have a desired width and a desired thickness in the width direction of the support 1. It is for. The coating unit 3 adheres, for example, a liquid supply layer 31 for supplying the pressure-sensitive adhesive composition to the surface of the pressure-sensitive adhesive composition supplied from the liquid supply layer 31 according to a desired width of the support 1. A coating roll 32 for controlling the thickness of the pressure-sensitive adhesive composition attached to the coating roll 32 together with the coating roll 32, and the support 1 in close contact with the coating roll 32. And a backup roll 34 for transporting the paper. In this way, the pressure-sensitive adhesive composition is applied to the support 1 so that the support 1 has a desired width and a desired thickness.

The configuration of the coating unit 3 is not limited to the reverse coater described above, but may be another coating system such as a comma coater, a roll coater, or a gravure coater. The method of adjusting the thickness of the pressure-sensitive adhesive composition can also be appropriately changed and implemented in accordance with each coating method.

The drying unit 4 is heated by blowing hot air onto the support when the support 1 coated with the pressure-sensitive adhesive composition is transported from the coating unit 3 and passes through the drying unit 4. A solvent and an unreacted monomer are removed from the pressure-sensitive adhesive composition to form a pressure-sensitive adhesive layer. The drying unit 4 used in the present invention is divided into drying zones 41 which can be dried by directly blowing hot air onto the support and which can independently control the temperature of the hot air. At least three or more drying zones 41 are provided. It is necessary. It is preferable that the number of the drying zones 41 is large because more precise control of the drying conditions can be performed. The drying apparatus is not particularly limited as long as it satisfies these conditions, but a floating method in which hot air is blown from above and below the support has a high drying ability and is preferably used.

FIG. 4 shows a drying unit 4 of a floating type.
FIG. 4 is a cross-sectional view showing a specific example of the drying zone 41, and hot air outlets 42 are provided above and below the drying zone 41, respectively. The shape, number, mounting position, and the like of the hot air outlets 42 are not particularly limited, and those conventionally known can be used.

In the present invention, the drying zone 41 has a structure shown in FIG.
As shown in the figure, a thermometer 43 and a moisture meter 44 for measuring the surface temperature and the moisture content of the pressure-sensitive adhesive composition layer are provided.
The thermometer 43 and the moisture meter 44 are not particularly limited as long as they can measure the surface temperature and the moisture content of the pressure-sensitive adhesive composition at any time. Is preferably used.

The winding section 5 includes a guide roller 51 for guiding the support 1 dried in the drying section 4 in a predetermined direction, and a dried support 1 guided by the guide roller 51. And a support take-up roll 52 for take-up.

Next, the manufacturing process for manufacturing the pressure-sensitive adhesive sheet by the embodiment apparatus configured as described above will be described below.

The adhesive sheet is pre-dried in order to determine the constant rate drying period, the reduced rate drying period, and the wet bulb temperature at the first set support speed. First, the pressure-sensitive adhesive composition is applied to the support 1 supplied from the support supply roll 2 by the coating unit 3 so as to have a desired width and a desired thickness of the support 1.

The support 1 coated with the pressure-sensitive adhesive composition as described above is conveyed to the drying section 4. At this time, the drying temperature conditions in all the zones are set to be the same, and the conditions are determined so that the pressure-sensitive adhesive composition is dried. The drying temperature is determined according to the transport speed, but is usually in the range of about 70 to 140 ° C. At this time, the speed of the hot air is desirably 15 m / sec or less, preferably 10 sec or less. If the speed of the hot air is higher than 15 m / sec, bubbles may be generated regardless of the subsequent temperature adjustment. In addition, the wind speed here means the wind speed at the time when the hot air is jetted from the nozzle.

It is confirmed that the surface temperature of the pressure-sensitive adhesive composition in the final zone is equal to the temperature of the hot air (normal temperature difference is within 2 ° C.).
It is confirmed that it becomes. When drying is confirmed under arbitrary conditions, the surface temperature and the moisture content of the pressure-sensitive adhesive composition layer are measured for each zone by a thermometer and a moisture meter installed for each zone. From this, the relationship between the surface temperature and the moisture content with respect to the drying time is determined.

The constant temperature at the beginning of drying is defined as the wet bulb temperature, and the portion where the surface temperature rises is defined as the boundary between the constant-rate drying period and the reduced-rate drying period. That is, the zone after the surface temperature rises is defined as the reduced drying period, and the zone before that is defined as the constant drying period. The reduced-rate drying period determined in this way is divided into a first half and a second half.

In the present invention, the ratio between the first half of the reduced-rate drying period and the second half of the reduced-rate drying period is not particularly limited.
In order to efficiently dry the water-dispersed pressure-sensitive adhesive and suppress foaming, it is desirable that the first half of the reduced-rate drying period is set to １ ／, preferably １ ／, of the zone corresponding to the entire reduced-rate drying period. For example, when the drying zones corresponding to the reduced-rate drying period are five zones, the first half of the reduced-rate drying period is set to two zones, preferably three zones, and the remaining zones are set to the latter half of the reduced-rate drying period.

In the present invention, the hot air temperature in the first half of the reduced-rate drying period is within + 50 ° C. of the wet bulb temperature, preferably within + 40 ° C. of the wet bulb temperature, and more preferably + 3 ° C. in the wet bulb temperature.
Adjust so as to be within the range of 0 ° C. (usually the wet bulb temperature or higher). Hot air temperature 50% lower than wet bulb temperature
If the pressure is higher than the above, the temperature of the pressure-sensitive adhesive layer increases when the pressure-sensitive adhesive layer has a low viscosity, and the drying speed is extremely lowered at a hot air temperature lower than the wet bulb temperature. It is necessary to.

The hot air temperature in the latter half of the reduced-rate drying period may be the same as the initially set temperature, or may be higher than the set temperature. It is preferable to set a slightly higher hot air temperature and / or hot air speed.

Under the drying conditions determined by the above preliminary drying, the adhesive composition applied to the support 1 is dried by heating, and the solvent and unreacted monomer are removed from the adhesive composition to form an adhesive layer. I do. At this time, since the hot air temperature in the first half of the rate-decreasing drying period is reduced, it is possible to suppress a sharp rise in the temperature of the pressure-sensitive adhesive composition, and to reduce bubbles generated by water vaporizing in the pressure-sensitive adhesive layer. be able to.

In the winding step, the support 1 dried in the drying section 4 is wound in the winding section 5. Thus, an adhesive sheet is manufactured.

By the above method, a water-dispersed pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer comprising the water-dispersed pressure-sensitive adhesive composition according to the present invention provided on a support can be produced. As the water-dispersed pressure-sensitive adhesive composition used in the present invention, an acrylic, natural rubber-based, synthetic rubber-based, or a mixture of these pressure-sensitive adhesives is used by dispersing in water using an emulsifier or a dispersant. be able to.

The acrylic pressure-sensitive adhesive is used for the purpose of improving the adhesion of the pressure-sensitive adhesive layer to the support and the initial adhesion to the adherend to the (meth) acrylic acid ester which is the main monomer. It is also possible to use a polymer obtained by using a functional group-containing vinyl monomer in combination with an appropriate emulsifier or dispersant and using an appropriate polymerization initiator or the like.

As the (meth) acrylate, a wide variety of monomers or monomer mixtures can be used. For example, methyl (meth) acrylate, ethyl (meth) acrylate, (meth) acryl Propyl acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, pentyl (meth) acrylate, ( Neopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate , Isodecyl (meth) acrylate, lauryl (meth) acrylate, bornyl (meth) acrylate Isobornyl (meth) acrylate, (meth) acrylate, myristyl (meth) acrylate, pentadecyl and stearyl (meth) acrylate.

These (meth) acrylates are:
It is preferred to use from 60 to 99% by weight of the total monomer mixture. If it is less than 60% by weight, the adhesive properties may be impaired.

The amount of the functional group-containing vinyl monomer can be appropriately selected according to the type of each monomer within a range of 40% by weight or less of the total monomer mixture, but good pressure-sensitive adhesiveness is exhibited. In order to achieve this, it is desirable to determine the amount to be used so that the glass transition point of the obtained polymer is usually −20 ° C. or lower.

Examples of the functional group-containing vinyl monomer copolymerizable with the (meth) acrylic acid ester include acrylic acid, methacrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, (meth) Hydroxyalkyl acrylate, glycerin dimethacrylate, glycidyl (meth) acrylate, methyl glycidyl methacrylate, aminoethyl (meth) acrylate, 2-
Functional monomers such as methacryloyloxyethyl isocyanate, triethylene glycol diacrylate,
Polyfunctional monomers such as ethylene glycol dimethacrylate and trimethylolpropane tri (meth) acrylate, vinyl acetate, styrene, (meth) acrylonitrile, N-vinylpyrrolidone, (meth) acryloylmorpholine, cyclohexylmaleimide, isopropylmaleimide, (meth) Acrylamide and the like can be mentioned.

As the emulsifier used in the present invention, generally used anionic or nonionic emulsifiers can be used. Examples of the anionic type include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkylphenyl ether sulfate, sodium polyoxyethylene alkyl sulfosuccinate, and the like. Further, for example, a radical polymerizable emulsifier into which a propenyl group or the like is introduced may be used.

Examples of the nonionic emulsifier include polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene fatty acid ester, and polyoxyethylene polyoxypropylene block polymer. These anionic or nonionic emulsifiers Depending on the type of monomer, one or more kinds can be used.

In the present invention, the emulsifier is used in an amount of 0.1 to 5 parts by weight, preferably 0.4 to 3 parts by weight, based on 100 parts by weight of the monomer mixture.
By limiting the amount of the emulsifier to the above value or less, a water-dispersed pressure-sensitive adhesive excellent in water resistance and adhesive properties can be obtained.

The polymer particle size of the water-based pressure-sensitive adhesive produced by emulsion polymerization using the above emulsifier may be 0.1 to 3 μm as long as it has good mechanical stability and coatability.
m, preferably 0.2 to 1 μm. Here, when the particle size is smaller than 0.1 μm, the viscosity of the water-dispersed pressure-sensitive adhesive increases, and when the particle size is larger than 3 μm, the fusion property between the particles may decrease and the cohesive force may decrease.

Examples of the polymerization initiator used in the present invention include azo-based, persulfate- and peroxide-based polymerization initiators, and redox initiators obtained by combining persulfates, peroxides and reducing agents. For example, 2,2'-azobis (2-methylpropionamidine) disulfate, 2,2'-azobis (2-amidinopropane) dihydrochloride, potassium persulfate, ammonium persulfate, benzoyl peroxide, t-butyl hydroperoxide Oxides, hydrogen peroxide, a combination of sulfate and sodium bisulfite, a combination of peroxide and sodium ascorbate, and the like can be mentioned, and one or more of these initiators can be used.

In the present invention, the polymerization initiator is used in an amount of 0.02 to 0.5 part by weight, preferably 0.08 to 0.3 part by weight, based on 100 parts by weight of the monomer mixture. If the amount is less than 0.02 parts by weight, it is difficult to obtain the effect as a polymerization initiator.

In the present invention, a chain transfer agent may be used to adjust the molecular weight of the acrylic polymer. The chain transfer agent is not particularly limited, and examples thereof include 1-dodecanethiol, mercaptoacetic acid, 2-mercaptoethanol, 2-ethylhexyl thioglycolate, and 2,3-dimethylcapto-1-propanol. One or two or more are used depending on the purpose and application.

The natural rubber-based and synthetic rubber-based pressure-sensitive adhesives used in the present invention include natural rubber latex, styrene-butadiene latex, and polyisobutylene latex. These rubber-based pressure-sensitive adhesives can be used by being dissolved in various solvents or emulsified in water with the above-mentioned emulsifier by an appropriate method.

The pressure-sensitive adhesive composition of the present invention may contain various additives as required, for example, a crosslinking agent, a release regulator, a tackifier, a plasticizer, a softener, a filler, a pigment, a dye, an aging agent. Inhibitors and the like can be added.

The solid content of the pressure-sensitive adhesive composition of the present invention is not particularly limited, but is desirably 50% by weight or more in order to shorten the drying time after coating. Also, when the viscosity of the pressure-sensitive adhesive composition is high, when coating on a support using the above-described reverse coater, a rib is easily generated on the coated surface, and a pickup roll such as a gravure coater is used. When transferring the pressure-sensitive adhesive to the coating roll by using the same, there is a possibility that a problem that the pressure-sensitive adhesive cannot be picked up may occur, and the viscosity of the pressure-sensitive adhesive composition is 0.4 Pa ·
s or less, preferably 0.3 Pa · s or less, more preferably 0.02 to 0.2 Pa.s. It is preferably s.

The thickness of the pressure-sensitive adhesive composition after drying is not particularly limited, and may be a thickness exceeding 1 mm, but is generally 500 μm or less, preferably 3 to 300 μm, particularly preferably about 5 to 200 μm. Thus, the effect of the present invention appears remarkably.

The pressure-sensitive adhesive sheets provided with the water-dispersed pressure-sensitive adhesive composition layer on a support as described above can be used for water vaporization caused by a rapid temperature rise of the pressure-sensitive adhesive composition applied to the support. Since the growth of bubbles generated by the reaction can be suppressed, pressure-sensitive adhesive sheets having a bubble size of 150 μm or less, preferably 100 μm or less can be manufactured.
When the bubble size is 150 μm or less, the effect on the transparency and smoothness of the pressure-sensitive adhesive layer is small, and a pressure-sensitive adhesive sheet having excellent appearance can be obtained.

[0058]

As described above, the present invention relates to a method for drying a water-dispersed pressure-sensitive adhesive composition, wherein the water-dispersed pressure-sensitive adhesive composition on a support is dried with hot air while passing through a drying section. A method for drying a water-dispersed PSA composition, wherein the hot air temperature in the first half is set within + 50 ° C. from the wet bulb temperature (Claim 1). Preliminary drying is performed by setting the hot air temperature and air velocity in the drying section so that the pressure-sensitive adhesive composition dries, and the surface temperature and moisture content of the pressure-sensitive adhesive composition in the drying section during predrying are measured. The water dispersion type according to claim 1, wherein the temperature and the reduced-rate drying period are obtained, and the hot air temperature in the first half of the reduced-rate drying period is set within + 50 ° C from the wet-bulb temperature according to the obtained wet-bulb temperature. In the method for drying the pressure-sensitive adhesive composition (Claim 2) In particular, the method according to the present invention relates to a method for drying a water-dispersed pressure-sensitive adhesive composition in which the hot air velocity is preferably 15 m / sec or less (claim 3). It is possible to suppress the growth of bubbles generated by vaporization of water caused by a rapid rise in temperature of the composition. According to the method for producing a water-dispersed pressure-sensitive adhesive sheet of the present invention (Claim 4) due to this excellent effect, it is possible to reduce the size of bubbles in the pressure-sensitive adhesive layer, and to improve the transparency and the like of the pressure-sensitive adhesive layer. Surface smoothness can be improved. Water-dispersed pressure-sensitive adhesive sheets having a bubble size of 150 μm or less produced in this way (Claim 5)
Can be used for various applications, but because of its good appearance, it can be suitably used for packaging and surface protection.

[0059]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples. In the following, all parts are parts by weight.

Reference Example 1 (Adhesive Composition) In a reactor equipped with a thermometer, an anchor-type stirring blade (blade width 100 mm), a nitrogen inlet tube and a reflux cooling tube, ion-exchanged water 4 was added.
0 parts were added, and the atmosphere was replaced with nitrogen for 1 hour while stirring. 0.1 parts of potassium persulfate was added as an initiator, and the temperature was increased to 70 ° C.
And then 97 parts of butyl acrylate and 3 parts of acrylic acid
Part, sodium polyoxyethylene alkyl sulfosuccinate (“Newcol 293” manufactured by Nippon Emulsifier Co.) 0.5
Was emulsified with 35 parts of water over 3 hours, and the resulting mixture was subjected to emulsion polymerization treatment. After the reaction, the mixture was neutralized with 10% aqueous ammonia to obtain a water-dispersible acrylic adhesive having a solid content of 54% by weight and an average particle diameter of 400 nm. Agent was obtained.

Reference Example 2 (Preparation of Adhesive Tape) The water-dispersed acrylic pressure-sensitive adhesive obtained in Reference Example 1 was applied to a polyester support having a thickness of 40 μm with a comma coater so that the thickness after drying became 130 μm. The adhesive sheet was obtained by drying under the conditions of each example and comparative example using a floating-type dryer that was divided into six zones and that could independently control the drying conditions. The drying conditions were determined according to Reference Example 3.

Reference Example 3 The pressure-sensitive adhesive sheet was preliminarily dried to determine the constant rate drying period, the decreasing rate drying period, and the wet bulb temperature. As an initial condition,
Support speed 6m / min, hot air temperature 110 ° C, wind speed 10m /
Drying was performed in seconds, and it was confirmed that the pressure-sensitive adhesive layer was formed. In this state, when the surface temperature and the moisture content of the pressure-sensitive adhesive composition were measured for each zone, the results are shown in Table 1. From this result, the temperature of the first zone, 50.5 ° C.
Is defined as the wet bulb temperature, and the second and subsequent zones where the temperature rise has started are defined as the reduced-rate drying period.

Comparative Example 1 The size of the bubbles in the pressure-sensitive adhesive layer prepared under the conditions of Reference Example 3 was 160 μm.

Example 1 In the first zone during the constant-rate drying period, the hot air temperature was 110 ° C.
Second and third wind speeds of 10 m / sec and the first half of the drying period
In the zone, the hot air temperature is 100 ° C., the wind speed is 10 m / sec, the fourth zone, the fifth zone, and the sixth zone in the latter half of the reduced rate drying period are hot air temperature of 110 ° C. and the wind speed are 10 m / sec to form an adhesive layer. Was.

Example 2 In the first zone during the constant-rate drying period, the hot air temperature was 110 ° C.
The wind speed is 10 m / sec, the hot air temperature is 70 ° C. and the wind speed is 10 m /
Second zone, the fifth zone in the second half of the reduced rate drying period,
In the sixth zone, the hot air temperature was set to 110 ° C. and the air speed was set to 10 m / sec to evaporate the water in the pressure-sensitive adhesive layer to form a pressure-sensitive adhesive layer.

Example 3 In the first zone during the constant-rate drying period, the hot air temperature was 110 ° C.
The second zone, the third zone, and the fourth zone in which the wind speed is 10 m / sec and the first half of the reduced-rate drying period is the hot air temperature of 90 ° C., the wind speed is 10 m / second, and the fifth and sixth zones in the second half of the reduced-rate drying period. In this method, water in the pressure-sensitive adhesive layer was evaporated by setting the hot air temperature to 110 ° C. and the wind speed to 10 m / sec to form the pressure-sensitive adhesive layer.

(Evaluation Method) The size of the main air bubbles was measured by observing the pressure-sensitive adhesive sheet obtained as described above under a microscope. The results are shown in Table 1.

[0068]

[Table 1]

As is clear from the results of the examples in Table 1,
By setting the temperature of hot air heating at + 50 ° C. or less with respect to the wet bulb temperature in the first half of the lapse rate drying period, bubbles in the pressure-sensitive adhesive layer are small, the appearance is good, and the surface of the pressure-sensitive adhesive tape has excellent smoothness. You can see that it is.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of pressure-sensitive adhesive tapes in which bubbles are generated.

FIG. 2 is an explanatory diagram showing a relationship between a material temperature and a moisture content in a drying step of pressure-sensitive adhesive sheets.

FIG. 3 is a longitudinal sectional view showing a schematic configuration of an entire apparatus for manufacturing a pressure-sensitive adhesive sheet according to an embodiment of the present invention.

4 is a vertical sectional view showing a schematic configuration of a drying unit of the manufacturing apparatus shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support 2 Support supply roll 3 Coating part 4 Drying part 5 Support take-up part 41 Dry zone 42 Hot-air outlet 43 Thermometer 44 Moisture meter

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D075 BB24Z BB33Z BB93Z BB95Z CA12 CA13 CA48 DA04 DB01 DB18 DB20 DB33 DB36 DB37 DB38 DB40 DB43 DB48 DC40 EA06 EA10 EA35 EB10 EB12 EB14 EB19 EB22 EB24 CA05 AA04 A0504 CA06 CA08 CB01 CB02 CC02 CC03 GA01 4J040 CA001 CA011 DF041 DF051 JA03 PA23 QA04 QA09

Claims (5)

[Claims] 1. A method for drying a water-dispersed pressure-sensitive adhesive composition, wherein the water-dispersed pressure-sensitive adhesive composition on a support is hot-air-dried while passing through a drying section, wherein the hot-air temperature in the first half of the reduced-rate drying period is a wet-bulb temperature. A method for drying a water-dispersed PSA composition, wherein the temperature is set within + 50 ° C. 2. Preliminary drying is performed by setting the conveying speed of the support, setting the hot air temperature and the air speed in the drying unit so that the adhesive composition dries at this conveying speed, and performing the pre-drying. The surface temperature and moisture content of the agent composition are measured, and the wet-bulb temperature and the reduced-rate drying period are determined from these, and the hot air temperature in the first half of the reduced-rate drying period is within + 50 ° C. of the wet-bulb temperature according to the determined wet-bulb temperature Characterized in that it is set to
A method for drying the water-dispersed PSA composition according to claim 1. 3. The method for drying a water-dispersed PSA composition according to claim 1, wherein the velocity of the hot air is 15 m / sec or less. 4. A pressure-sensitive adhesive on a support by a coating step of applying at least a water-dispersible pressure-sensitive adhesive composition on a support, and a method for drying the water-dispersible pressure-sensitive adhesive composition according to claim 1 or 2. A method for producing a water-dispersed pressure-sensitive adhesive sheet, comprising a step of forming a layer. 5. A water-dispersed pressure-sensitive adhesive sheet produced by the method for producing a water-dispersed pressure-sensitive adhesive sheet according to claim 4, wherein the size of bubbles in the pressure-sensitive adhesive layer is 150 μm or less.