JP5046152B2 - Manufacturing method for environmentally friendly adhesives - Google Patents

Description

The present invention relates to a method for producing an environmentally friendly pressure-sensitive adhesive capable of reducing the concentration of volatile organic compounds (VOC).

  Acrylic pressure-sensitive adhesives are used in a very wide range of fields such as adhesion of interior materials for buildings, adhesion of automobile interiors, and adhesion of electronic components. As described above, acrylic pressure-sensitive adhesives are widely used because they have very excellent adhesiveness, but there is a problem of odor as a problem that acrylic pressure-sensitive adhesives always have.

  The odor of such an acrylic pressure-sensitive adhesive is generally considered to be due to residual monomers contained in the pressure-sensitive adhesive, and various methods have been proposed to reduce the odor of such an acrylic pressure-sensitive adhesive.

  For example, Japanese Patent Application Laid-Open No. 2002-69411 (Patent Document 1) specifies a solution polymerization in order to produce a high-purity acrylic polymer having a small amount of volatile components such as a residual initiator or an unreacted monomer. A method is disclosed in which an amount of an azo-based initiator is used, and solution polymerization is completed at a specific reaction temperature in the main reaction before polymerization and in the ripening reaction in the latter half of polymerization. It is disclosed that ethyl acetate is used as a reaction solvent for this reaction.

Japanese Patent Laid-Open No. 2003-306650 (Patent Document 2) discloses an acrylic pressure-sensitive adhesive layer in which the amount of volatile components released when a pressure-sensitive adhesive tape is heated at 90 ° C. for 30 minutes for 6 minutes or more is 150 ppm or less. An adhesive tape having the following is disclosed. In this case, ethyl acetate is used as a reaction solvent.

Further, JP-A-2004-315767 (Patent Document 3) discloses a pressure-sensitive adhesive used in applications where odor is a problem, such as closed spaces and electronic components, and is non-volatile when heated at 90 ° C. for 30 minutes. An acrylic pressure-sensitive adhesive having a partial concentration of 500 ppm or less is disclosed. Specifically, a monomer is charged in an ethyl acetate solvent, and lauroyl peroxide having a 10-hour half-life temperature of 62 ° C. is added in several portions so that unreacted acrylic monomer does not easily remain. In order to reduce the odor of the adhesive.

  For example, as disclosed in Patent Documents 1 to 3 above, one of the causes of the odor of the acrylic pressure-sensitive adhesive is a residual monomer. By reducing the residual amount of such a monomer, the acrylic pressure-sensitive adhesive The peculiar odor which has is reduced.

However, the odor of the acrylic adhesive is not only due to the residual monomer odor as described above, but also due to the concentration of volatile organic compounds (VOC) generated from the acrylic adhesive. Even if it is increased to reduce the amount of residual monomer, the odor of the acrylic pressure-sensitive adhesive is not reduced by itself.

The pressure-sensitive adhesive as described above is generally obtained by reacting an acrylic monomer dissolved in ethyl acetate as a reaction solvent as shown below.
For example, in Example 1 of JP-A-8-245805 (Patent Document 4), ethyl acetate is used as a reaction solvent, ethyl methacrylate and methoxyethyl acrylate are used, and 2,2-azobis (2 , 4-dimethylvaleronitrile) is disclosed.

Moreover, as an adhesive sheet used when processing the electronic component of JP 2000-234079 A (Patent Document 5), for example, as shown in Synthesis Example 2, ethyl acetate and another solvent (heptane) are used as a reaction solvent. It is also disclosed that a pressure-sensitive adhesive for processing electronic parts is used.

  The pressure-sensitive adhesive is used by applying an ethyl acetate solution of the pressure-sensitive adhesive obtained as described above, and removing the ethyl acetate as a solvent. Accordingly, the obtained acrylic pressure-sensitive adhesive necessarily contains ethyl acetate which is an organic solvent.

By the way, the guidelines for indoor air pollution established by the Ministry of Health, Labor and Welfare include formaldehyde, toluene, xylene, parachlorobenzene, ethylbenzene, styrene, chlorpyrifos, di-2-ethylhexyl phthalate, diazinon, acetaldehyde, and fenocarb. It has been pointed out that these individual concentrations in the air and total volatile organic compounds (TVOC) containing these compounds are considered indoor air pollution sources, which cause sick house disease. Yes.

In the acrylic pressure-sensitive adhesive, the above compound is not used directly, but when an organic substance generated from the acrylic pressure-sensitive adhesive is analyzed, aldehydes are detected. In the production process of acrylic pressure-sensitive adhesives, aldehydes are generally not used. Therefore, careful consideration was given to the origin of such aldehydes, but it was also derived from ethyl acetate used as a reaction solvent. I understood that. That is, ethyl acetate is (1) produced by dimerization reaction of acetaldehyde, (2) produced directly by dissolving ethylene in acetic acid, and (3) obtained by esterification reaction of acetic acid and ethanol. Industrially, most of them are (1) dimerization reaction of acetaldehyde and (2) acetic acid and ethylene. However, the ethyl acetate obtained by the above method (1) contains a considerable amount of acetaldehyde and ethanol.

Ethanol contained in the ethyl acetate is oxidized to acetaldehyde. Since such an oxidation reaction easily proceeds during the storage and transportation of ethyl acetate and the process of producing the acrylic adhesive, the ethyl acetate used as a reaction solvent is used to reduce the odor of the acrylic adhesive. It is necessary to remove acetaldehyde and ethanol contained as impurities therein, and at the same time, it is necessary to increase the reaction rate and reduce the amount of residual monomer as much as possible.
JP 2002-69411 A Japanese Patent Laid-Open No. 2003-306650 JP 2004-315767 A JP-A-8-245805 JP 2000-234079

  The present invention is to reduce the odor of the acrylic pressure-sensitive adhesive in the prior art as described above, and the present invention aims to provide a method for producing an environmentally-friendly pressure-sensitive adhesive with less volatile organic substances. It is said.

In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, at least a part of an acrylic monomer is dissolved in an organic solvent containing ethyl acetate, and the acrylic monomer is polymerized in the presence of a polymerization initiator. A method for producing an environmentally friendly adhesive,
As the reaction solvent for the polymerization reaction, ethyl acetate having an aldehyde compound content of 10 ppm or less and an alcohol component content of 100 ppm or less contained in ethyl acetate is used,
As a polymerization initiator, the molecular weight of the polymerization initiator is in the range of 200 to 250, the number of carbons in the radical side chain of the polymerization initiator is in the range of 4 to 9, and the polymerization initiator has a half-hour of 10 hours. It is characterized by using a polymerization initiator having an initial temperature in a range of 45 to 55 ° C.

In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, ethyl acetate having a small amount of aldehyde compound and aldehyde component of ethyl acetate is used as a reaction solvent, and a reaction initiator within a specific range is used as a polymerization initiator. Because it is used, the amount of total VOC generated from the adhesive is small.

  According to the present invention, it is possible to easily produce an environmentally friendly pressure-sensitive adhesive that generates a small amount of aldehyde compound, residual monomer, and volatile residual initiator.

Next, the production method of the environmentally friendly pressure-sensitive adhesive of the present invention will be specifically described.
In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, at least a part of an acrylic monomer is dissolved in an organic solvent containing ethyl acetate, and the acrylic monomer is polymerized in the presence of a polymerization initiator. is there.

  In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, (meth) acrylic acid alkyl ester having an alkyl group having an alkyl group usually having 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms, is exemplified as an acrylic monomer. be able to. Such (meth) acrylic acid alkyl esters can be used alone or in combination. Such (meth) acrylic acid alkyl ester is usually used in an amount in the range of 20 to 100 parts by weight, preferably 60 to 99.5 parts by weight, based on 100 parts by weight of the whole acrylic monomer to be used. . In the present invention, a linear alkyl acrylate having 4 or more carbon atoms such as butyl (meth) acrylate (BA) and a branch having 4 or more carbon atoms having a branch such as 2-ethylhexyl (meth) acrylate are used. It is preferable to use it in combination with the alkyl acrylate it has.

Furthermore, in the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, an acrylic monomer having a functional group can be used as the acrylic monomer.
Examples of acrylic monomers having a functional group that can be used in the present invention include carboxyl group-containing acrylic monomers such as (meth) acrylic acid and crotonic acid, and hydroxyl group-containing acrylic monomers such as 2-hydroxyethyl (meth) acrylate. Examples thereof include monomers and epoxy group-containing monomers such as allyl glycidyl ether. Acrylic monomers having such functional groups can be used alone or in combination. Such a functional group-containing acrylic monomer is usually used in an amount in the range of 0.001 to 20 parts by weight, preferably 0.1 to 10 parts by weight, in 100 parts by weight of the whole acrylic monomer to be used. The

  In the present invention, other monomers copolymerizable with the acrylic monomers as described above can be used. Examples of such other monomers include vinyl compounds such as styrene. Such other monomers can be used alone or in combination. Such other monomers can be used in an amount usually in the range of 0 to 30 parts by weight, preferably 0 to 10 parts by weight, in 100 parts by weight of the whole acrylic monomer to be used.

In producing the environmentally friendly pressure-sensitive adhesive of the present invention, at least a part of the acrylic monomer as described above is dissolved and reacted in a reaction solvent containing ethyl acetate.
In the present invention, ethyl acetate is used as a reaction solvent. Ethyl acetate used as a reaction solvent in the present invention can be produced by an ester reaction between acetic acid and ethanol. Industrially, ethyl acetate is produced directly by dissolving ethylene in acetic acid without passing through ethanol, There is ethyl acetate produced by the dimerization reaction of acetaldehyde. Such ethyl acetate contains other components such as formaldehyde, acetaldehyde, and ethanol due to the production method. Such components are generally removed by distillation after producing ethyl acetate. By such distillation, aldehydes such as formaldehyde and acetaldehyde are removed, but alcohol components are aldehydes. Not as much removed. Alcohols are oxidized to aldehydes, and alcohols contained in distilled ethyl acetate are sticky from acrylic monomers during storage, transportation, and use in the production of adhesives. In the method for producing an environmentally friendly pressure-sensitive adhesive according to the present invention, the aldehydes contained in ethyl acetate are 10 ppm or less, and the content of alcohol components. It is preferable to use ethyl acetate having a content of 100 ppm or less, further using ethyl acetate having a content of aldehydes of 5 ppm or less and an alcohol content of 50 ppm or less.

Specifically, for example, distilled ethyl acetate obtained by distilling the crude ethyl acetate produced by each method is repeatedly distilled until the aldehydes in the ethyl acetate at the time of producing the adhesive are 10 ppm or less and the alcohol component is 50 ppm or less. In addition, there is a method of removing not only aldehydes contained in distilled ethyl acetate but also alcohol components.
Depending on the production method, acetic acid may be contained in ethyl acetate.
In the present invention, it is advantageous to use ethyl acetate obtained by the method of directly producing ethyl acetate from acetic acid and ethylene among the methods for producing ethyl acetate, because residual aldehydes and alcohol components are reduced. It is desirable to use the aldehydes, acetic acid, alcohol components and the like contained in the ethyl acetate after removing them.

By removing not only aldehydes but also alcohol components, aldehydes are not generated during the polymerization of acrylic monomers, and the concentration of total VOC (total volatile organic compounds) obtained in the adhesive Can be reduced.

The ethyl acetate as described above is usually used in an amount in the range of 20 to 200 parts by weight, preferably 70 to 100 parts by weight, based on 100 parts by weight of the acrylic monomer.
By using ethyl acetate in such an amount, at least part of the acrylic monomer, preferably all of the acrylic monomer is dissolved in ethyl acetate.

In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, a specific polymerization initiator is used when (co) polymerizing an acrylic monomer in ethyl acetate.
The molecular weights of the polymerization initiators used in the present invention are both in the range of 200 to 250, the number of carbons in the radical side chain of the polymerization initiator is in the range of 4 to 9, and the polymerization initiator A polymerization initiator having a 10-hour half-life temperature in the range of 45 to 55 ° C is used.

Such a polymerization initiator has a high reaction rate during the polymerization reaction and has good radical dispersibility, so that the residual monomer can be reduced. Further, since the residual initiator is difficult to volatilize, it is derived from the initiator. Odor can also be reduced. Examples of such polymerization initiators include t-butyl peroxydecate (BPND, molecular weight: 244 ° C., number of carbons in radical side chain: 4,9, 10 hours half-temperature: 47 ° C. ), T-hexyl peroxypivalate (HPP, molecular weight: 202 ° C., carbon number of radical side chain: 4,6, 10 hour half-temperature: 53 ° C.).

In the present invention, the polymerization initiator has a molecular weight in the above range, the number of carbons in the radical side chain is in the above range, and a 10-hour half-life temperature in the above range includes two types of polymerization initiators. It is preferable to use the above to perform (co) polymerization of acrylic monomers. By using two or more kinds of polymerization initiators, acrylic monomers dissolved or dispersed in the reaction solvent ethyl acetate can be (co) polymerized at a very high reaction rate, and the residual amount of acrylic monomers can be reduced. Remarkably reduced. For this reason, in the pressure-sensitive adhesive obtained by the method of the present invention, the VOC concentration caused by the unreacted monomer and the polymerization initiator can be kept very low.

  When using a plurality of different types of polymerization initiators as described above, all of the plurality of initiators can be collectively added to the reaction solution, but added separately into the reaction solution. Is preferred.

  When the polymerization initiator is divided and added to the reaction solution in this way, the order of addition of the polymerization initiator is not particularly limited, but for example, it is preferable to sequentially add from the polymerization initiator having a low 10-hour half-life temperature. Thus, by adding a polymerization initiator having a low 10-hour half-life temperature first, and sequentially adding a polymerization initiator having a high 10-hour half-life temperature, the acrylic monomer can be efficiently polymerized. Since the residual ratio of acrylic monomers in the obtained adhesive is extremely low, the total VOC of the obtained adhesive shows a low value.

In addition, by adding a plurality of polymerization initiators as described above, there is no significant increase in aldehydes in the reaction solution.
The total amount of the polymerization initiators as described above is usually 0.05 to 1 part by weight, preferably 0.001 part by weight with respect to 100 parts by weight of the acrylic monomer dissolved or dispersed in ethyl acetate as the reaction solvent. Used in an amount in the range of 4 to 0.7 parts by weight. When two types of polymerization initiators are used, the amount of each polymerization initiator used is, for example, a value obtained by internally dividing the total amount of polymerization initiators at a ratio in the range of 1:10 to 10: 1. Can do.

  In the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, a reaction liquid in which an acrylic monomer is dissolved or dispersed in ethyl acetate as a reaction solvent as described above is heated with stirring, and a polymerization initiator is added to the reaction liquid. Is added to initiate the reaction. The heating temperature at this time is set within the range of this boiling point ± 10 ° C. because the boiling point of ethyl acetate as the reaction solvent is 76.8 ° C.

Although the above reaction can be carried out in air, it is preferably carried out in an inert gas atmosphere such as nitrogen gas or helium gas. By carrying out the reaction in such an inert gas atmosphere, the generation of aldehydes due to oxidation can be suppressed, and the total VOC of the resulting pressure-sensitive adhesive can be kept low.

  Thus, the polymerization reaction can be terminated by adding ethyl acetate as described above or lowering the temperature of the reaction solution 3 to 12 hours after the addition of the first polymerization initiator.

  In this way, an ethyl acetate solution of an environmentally friendly pressure-sensitive adhesive can be obtained. This ethyl acetate solution is environmentally friendly as it is by adjusting the amount of ethyl acetate to adjust the solid content to a range of usually 10 to 70% by weight, preferably 30 to 60% by weight. It can be set as the coating liquid of an adhesive.

The environmentally friendly pressure-sensitive adhesive thus obtained usually has a weight average molecular weight measured by GPC of 3
The acrylic pressure-sensitive adhesive is in the range of 100,000 to 1,000,000, and the glass transition temperature obtained by the Fox equation for this acrylic pressure-sensitive adhesive is usually in the range of −70 to 0 ° C.

When the amount of the acrylic monomer remaining in the environmentally friendly pressure-sensitive adhesive (ethyl acetate solution) thus obtained was measured using gas chromatography, the residual amount of each acrylic monomer used was usually 40 ppm or less. 30 ppm or less. In general, an acrylic pressure-sensitive adhesive is produced by a solution polymerization method using commercially available ethyl acetate without using a specific polymerization initiator as used in the present invention as a polymerization initiator. It is known that the used acrylic monomer remains in an amount of about 50 to 1000 ppm, and the amount of the acrylic monomer remaining in the pressure-sensitive adhesive obtained by the method of the present invention is extremely low.

In addition, using a pressure-sensitive adhesive (test piece, thickness: 70 μm (dry)) obtained by applying the pressure-sensitive adhesive (ethyl acetate solution) obtained by the production method of the present invention at 65 ° C. by a sampling back method. When the VOC in steam when heated for 2 hours is determined, the VOC of formaldehyde is usually 0.1
μg / test piece or less, preferably 0.08 μg / test piece or less, VOC of acetaldehyde is usually 0.2 μg / test piece or less, preferably 0.1 μg / test piece or less, and total volatile organic compound (TVOC) is Usually 500 μg / test piece or less, preferably 3
00 μg / test piece or less.

Here, the test piece used for the measurement of VOC in the present invention is 80 mm × 700 mm ×
The thickness is 70 μm (dry). Also, the sampling back method performed using this test piece is, after pasting a test piece of a certain size as described above to the SUS mesh,
Put in a standardized bag (for example, Tedlar Bag, AA-10 manufactured by GS Science), replace the air in this with high-purity nitrogen gas (purity 99.999%), and then test piece in the bag filled with this nitrogen gas And heated at 65 ° C. for 2 hours. The volatile component is released from the pressure-sensitive adhesive by heating into the bag, and thus the volatile component released into the bag is collected. The total VOC was measured by analyzing the collected components with GC-MS. The aldehyde compound is analyzed by dissolving the collected components in a predetermined solvent and then analyzing the solution using high performance liquid chromatography. These are methods for analyzing volatile components contained in the pressure-sensitive adhesive layer, and are general methods for measuring VOCs. In the present invention, Agilent technology gas chromatograph 6890N and mass detector 5973N were used as GC-MS as an analytical device. Also, as high performance liquid chromatography, Alltance manufactured by Nippon Waters Co., Ltd. was used and used column. Used ODS-80A, 75 × 4.6 mm, 3 μm manufactured by GL Science Co., Ltd., and UV having a wavelength of 360 nm was used as a detector.

As described above, the environmentally friendly pressure-sensitive adhesive obtained by the production method of the present invention shows low values of VOC of individual components and also low values of TVOC. In particular, this pressure-sensitive adhesive has a characteristic that the content of aldehydes is low. Furthermore, the amount of residual monomer is remarkably reduced by the production by the method of the present invention. Therefore, the environmentally friendly pressure-sensitive adhesive produced by the method of the present invention is unlikely to become a pollution source of indoor air pollution (sick house). In addition, the environmentally friendly pressure-sensitive adhesive produced by the method of the present invention is less likely to cause contamination of electronic components due to VOC even when used for bonding electronic components, for example, and can stably bond electronic components. .

  In the production of the environmentally friendly pressure-sensitive adhesive produced by the method of the present invention, in addition to the above components, a chain transfer agent such as dodecyl mercaptan may be blended to perform (co) polymerization of acrylic monomers. .

Moreover, when using the obtained ethyl acetate solution as an adhesive, crosslinking agents, such as an epoxy compound and an isocyanate compound, can also be mix | blended.
Furthermore, when using the obtained ethyl acetate solution as an adhesive, a filler such as an inorganic filler, an organic filler, and a composite filler can be blended, and a colorant can be blended. Furthermore, it can add and use the component generally mix | blended with an adhesive.

Next, the acrylic pressure-sensitive adhesive of the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
[Production example]
<Synthesis of ethyl acetate by Tischtchenko method>
A reactor equipped with a stirrer was charged with 170 kg of aluminum chips and 2240 kg of ethyl acetate, heated to 70 ° C., 815 kg of 98-99% ethanol was added over 6 hours, and chlorine gas was introduced into the reactor as a promoter. As the reaction proceeded in this way, about 22 m ³ of hydrogen gas was generated. When the generation of hydrogen gas is completed, the reaction solution is transferred to an aging can, 30 kg of zinc oxide is added to the aging can, and the temperature of the reaction solution is maintained at 30 to 40 ° C. for the first day. From the second day to the fifth day, aluminum alkoxide, which is a catalyst for synthesizing ethyl acetate, was prepared by maintaining the temperature at 25 ° C. to 30 ° C. and further aging.

  10 parts by weight of acetaldehyde was charged into a reaction kettle with respect to 1 part by weight of the aluminum alcoholate obtained as described above, and ethyl acetate (1) was synthesized by a dimerization reaction of acetaldehyde at a temperature of 12 to 14 ° C. .

Since the crude ethyl acetate (1) thus obtained contained various impurities, the crude ethyl acetate was distilled and purified to obtain distilled ethyl acetate (1-1). In this distilled ethyl acetate (1-1), acetaldehyde derived from the raw material was mixed in an amount exceeding 10 ppm, and ethanol derived from the catalyst raw material was mixed in an amount exceeding 200 ppm.

Subsequently, this distilled ethyl acetate (1-1) was further distilled once to obtain purified ethyl acetate (1-2). When the components were analyzed by gas chromatography, the amounts of acetaldehyde and alcohol components contained in the purified ethyl acetate (1-2) were as follows.
Ethyl acetate content: 99.5% by weight
Acetaldehyde ... 10ppm
Alcohol: 150ppm.
<Synthesis of ethyl acetate by direct synthesis of acetic acid and ethylene>
In a 200 ml autoclave equipped with a magnetic stirrer, 70% potassium cation exchange, 350 ° C., dried for 5 hours to completely remove adhering water or crystal water, 3.0 g of dodecadungstosilicate, After charging 60.5 g of 99.5% acetic acid (manufactured by Kokusan Kagaku Co., Ltd.), the mixture was heated while slowly absorbing 0.69 mol of 99.5% ethylene in acetic acid and reacted at 180 ° C. for 5 hours. To give ethyl acetate (2).

The reaction product thus obtained (ethyl acetate (2)) had an acetic acid conversion of 22.1% and an ethyl acetate yield of 21.8%.
The crude ethyl acetate (2) was distilled to obtain distilled ethyl acetate (2-1). The result of gas chromatographic analysis of this distilled ethyl acetate (2-1) is as follows.
Ethyl acetate content: 99.9%
Acetaldehyde: 1 ppm or less Alcohol: 50 ppm
The alcohol content in distilled ethyl acetate (2-1) immediately after the production was low.

The distilled ethyl acetate (2-1) was further distilled once to obtain purified ethyl acetate (2-2).
When the components were analyzed by gas chromatography, the amounts of acetaldehyde and alcohol components contained in the purified ethyl acetate (2-2) were as follows.
Ethyl acetate content: 99.9%
Acetaldehyde: 1 ppm or less Alcohol: 5 ppm.
<Synthesis of ethyl acetate by esterification reaction of acetic acid and ethanol>
Ethyl acetate (3) was obtained by performing a conventional ether reaction using commercially available acetic acid and commercially available ethanol.

This ethyl acetate (3) was distilled to obtain distilled ethyl acetate (3-1). The components of this distilled ethyl acetate are as follows.
Ethyl acetate content: 99.8%
Acetaldehyde: 1 ppm or less Alcohol: 400 ppm.

The distilled ethyl acetate (3-1) obtained as described above was further distilled once to obtain purified ethyl acetate (3-2). The components contained in this purified ethyl acetate (3-2) are as follows.
Ethyl acetate content: 99.9%
Acetaldehyde: 1 ppm or less Alcohol: 50 ppm.
[Example 1]
In a reaction vessel equipped with a nitrogen introduction tube, a stirring means, a thermometer and a reflux device, 57.7 parts by weight of butyl acrylate (BA), 40 parts by weight of 2-ethylhexyl acrylate (2EHA), 2 parts by weight of acrylic acid (AA), 2-hydroxyethyl acrylate (2HEA) 0.30 part by weight, n-dodecyl mercaptan 0.03 part by weight, and purified ethyl acetate (2-2) 90 obtained by further once-distilling the ethyl acetate produced from ethylene and acetic acid Part by weight was added, and t-butylperoxyneodecanoate (BPND, Mw = 2) which is the first polymerization initiator as an initial polymerization initiator.
44, carbon number of radical side chain = 4,9, 10 hour half-life temperature = 47 ° C.) After adding 0.006 parts by weight, the air in the reaction vessel was replaced with nitrogen gas, and the temperature in the reaction vessel was The reaction was started by heating to 80 ° C.

While maintaining the reaction temperature at 80 ° C., 0.033 parts by weight of the above-described polymerization initiator, BPND; was added in several portions and reacted for 2 hours.
Thereafter, the reaction temperature was raised to 81 ° C., and the second polymerization initiator t-hexyl peroxypivalate (HPP, Mw = 202, carbon number of radical side chain = 4,6, 10 hours half-life temperature = 53 ° C
) After adding 0.6 parts by weight of a solution prepared by dissolving 7 parts by weight of ethyl acetate (2-2) in several portions, the reaction temperature was maintained at 81-82 ° C. for another 3.5 hours. Reacted.

After 3.5 hours, a large amount of the ethyl acetate (2-2) was placed in the reaction vessel to dilute the reaction solution to stop the reaction (solid content = 43%). The weight average molecular weight measured by GPC of the obtained acrylic pressure-sensitive adhesive was 500,000, and the glass transition temperature (Tg) was −59 ° C.

  The acrylic adhesive thus obtained was applied to the peeled substrate surface to produce a 70 μm (dry) adhesive sheet, and the acrylic monomer contained in the adhesive sheet was gas chromatographed. In this acrylic pressure-sensitive adhesive, it was found that BA was 30 ppm, AA was 30 ppm, and 2EHA was 20 ppm.

A test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. The result was 0.06 μg / test piece or less, and acetaldehyde The VOC was measured to be 0.07 μg / test piece, and the VOC of this test piece was measured to be 300 μg / test piece.
[Comparative Example 1]
In Example 1, instead of purified ethyl acetate (2-2) used as a reaction solvent, purified ethyl acetate (1-2) obtained by further distilling ethyl acetate (1) distilled by Tischtchenko method was used. The weight average molecular weight was 500,000, and the glass transition temperature (Tg) was −59.
An acrylic pressure-sensitive adhesive at 0 ° C. was produced.

  Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. The acrylic adhesive contained 35 ppm BA, 30 ppm AA, and 15 ppm 2EHA.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. As a result, 0.1 μg / test piece was obtained. When VOC was measured, it was 0.3 μg / test piece, and when TVOC of this test piece was measured, it was 1700 μg / test piece.
[Example 2]
In Example 1, instead of purified ethyl acetate (2-2) used as a reaction solvent, distilled ethyl acetate (2-1) obtained by distilling ethyl acetate (2) produced from ethylene and acetic acid was used. Thus, an acrylic pressure-sensitive adhesive having a weight average molecular weight of 500,000 and a glass transition temperature (Tg) of −59 ° C. was produced.

Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. In the acrylic adhesive, BA is 30 ppm, AA is 3
0 ppm and 2EHA were contained in an amount of 20 ppm.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. The VOC of 0.1 μg / test piece was measured, and the TVOC of this test piece was measured to be 500 μg / test piece.
[Comparative Example 2]
In Example 2, instead of purified ethyl acetate (2-2) used as a reaction solvent, distilled ethyl acetate (3-1) obtained by distillation of ethyl acetate (3) obtained for the ester reaction of acetic acid and ethanol was obtained. An acrylic pressure-sensitive adhesive having a weight average molecular weight of 500,000 and a glass transition temperature (Tg) of −59 ° C. was produced in the same manner except that was used.

Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. In the acrylic pressure-sensitive adhesive, BA was contained in an amount of 30 ppm, hereinafter, AA was 20 ppm or less, and 2HEA was contained in an amount of 30 ppm or less.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. As a result, 0.1 μg / test piece was obtained. When VOC was measured, it was 0.3 μg / test piece, and when TVOC of this test piece was measured, it was 2500 μg / test piece.
Example 3
In Example 1, instead of purified ethyl acetate (2-2) used as a reaction solvent, distilled ethyl acetate (3-1) obtained by distillation of ethyl acetate (3) obtained by ester reaction of acetic acid and ethanol was used. Further, an acrylic pressure-sensitive adhesive having a weight average molecular weight of 500,000 was produced in the same manner except that purified ethyl acetate (3-2) subjected to precision distillation was used.

  Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. The acrylic adhesive contained 30 ppm BA, 30 ppm AA, and 20 ppm 2EHA.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. As a result, 0.1 μg / test piece was obtained. When VOC was measured, it was 0.3 μg / test piece, and when TVOC of this test piece was measured, it was 2000 μg / test piece.
[Comparative Example 3]
In Example 1, the same amount of lauroyl peroxide (Mw: 398, carbon number 11,11, 10 ° C half-life temperature 61.6 ° C) was used in place of BPND as the first polymerization initiator, and the second polymerization was started. An acrylic pressure-sensitive adhesive having a weight average molecular weight of 500,000 and a glass transition temperature (Tg) of −59 ° C. was produced in the same manner except that the same amount of lauroyl peroxide was used instead of HPP as the agent.

Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. In the acrylic adhesive, BA is 650 ppm, AA is
40 ppm, 2EHA was contained in an amount of 680 ppm.

A test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. As a result, it was 0.06 μg / test piece. The VOC of 0.08 μg / test piece was measured, and the TVOC of this test piece was measured to be 4200 μg / test piece.
[Comparative Example 4]
In Example 1, t-butylperoxy-2-ethylhexanoate (perbutyl O, Mw: 216, carbon number of radical side chain = 4, 7, 10 ° C. half-life temperature: 72 hours as the first polymerization initiator ), And the same amount of t-butylperoxy-2-ethylhexanoate was used in place of HPP as the second polymerization initiator, and the weight average molecular weight was 500,000, and the glass transition temperature (Tg) was the same. : An acrylic pressure-sensitive adhesive at −59 ° C. was produced.

Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. In the acrylic adhesive, BA is 720 ppm, AA is 4
0 ppm and 2EHA were contained in an amount of 700 ppm.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. The VOC of 0.08 μg / test piece was measured, and the TVOC of this test piece was measured to be 6600 μg / test piece.
[Comparative Example 5]
In Example 1, instead of BPND as the first polymerization initiator, 2,2′-azobisisobuteronitrile (AIBN) [AIBN, Mw = 164, carbon number of radical side chain = 3, 3, 10 (Time half-life temperature = 65 ° C.)] in the same amount and the second polymerization initiator HPP was used as it was, and the weight average molecular weight was 500,000 and the glass transition temperature (Tg) was −59 ° C. An acrylic adhesive was produced.

Using the acrylic pressure-sensitive adhesive thus obtained, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1, and the acrylic monomer contained in this pressure-sensitive adhesive sheet was analyzed using gas chromatography. In the acrylic adhesive, BA is 300 ppm, AA is 5
0 ppm and 2EHA were contained in an amount of 400 ppm.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet, and the VOC for formaldehyde was measured by the sampling back method. As a result, 0.8 μg / test piece was obtained. The VOC of 0.1 μg / test piece was measured, and the TVOC of this test piece was measured to be 2500 μg / test piece.

  According to the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, the amount of aldehydes in the acrylic pressure-sensitive adhesive that causes odor, or the amount of alcohol that is oxidized with time to become aldehydes is small. The residual amount of unreacted acrylic monomer and the amount of volatile residual initiator are also reduced. Therefore, the odor is reduced in the pressure-sensitive adhesive produced by the method of the present invention.

  For this reason, the acrylic pressure-sensitive adhesive produced by the method of the present invention is less irritating even when used in a closed space such as an interior of a building or an interior of an automobile. In addition, since the amount of volatile components generated is small, deterioration of electronic components due to erosion of volatile components hardly occurs even when used for bonding electronic components.

Claims (4)

A method of producing an environmentally friendly pressure-sensitive adhesive by dissolving at least a part of an acrylic monomer in an organic solvent containing ethyl acetate and polymerizing the acrylic monomer in the presence of a polymerization initiator,
As the reaction solvent for the polymerization reaction, ethyl acetate having an amount of aldehyde compound contained in ethyl acetate of 10 ppm or less and an alcohol component of 100 ppm or less is used,
As a polymerization initiator, the molecular weight of the polymerization initiator is in the range of 200 to 250, the number of carbons in the radical side chain of the polymerization initiator is in the range of 4 to 9, and the polymerization initiator has a half-hour of 10 hours. A method for producing an environmentally friendly pressure-sensitive adhesive, comprising using a polymerization initiator having an initial temperature in a range of 45 to 55 ° C.   2. The method for producing an environmentally friendly pressure-sensitive adhesive according to claim 1, wherein the amount of the acetaldehyde compound in the ethyl acetate is 5 ppm or less and the content of the alcohol component is 50 ppm or less. 3. The method for producing an environmentally friendly pressure-sensitive adhesive according to claim 1, wherein the ethyl acetate is produced by direct synthesis from acetic acid and ethylene. The ethyl acetate is distilled ethyl acetate obtained by synthesizing crude ethyl acetate by heating while absorbing ethylene in the acetic acid and then distilling the resulting crude ethyl acetate. The method for producing an environmentally friendly pressure-sensitive adhesive according to any one of items 1 to 3.