JP5046151B2 - Manufacturing method for environmentally friendly adhesives - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive generating little volatile organic compounds and having excellent environmental suitability. <P>SOLUTION: The eco-friendly adhesive is produced by dissolving at least a part of an acrylic monomer in a reaction solvent and polymerizing the acrylic monomer in the presence of a polymerization initiator. At least two kinds of the polymerization initiators having different structures each having a molecular weight of 200-250, a carbon number of the alkyl group on the radical side chain of the initiator of 4-9 and a 10 hr half-life temperature of 45-55&deg;C are added in multiple stages and the polymerization reaction is carried out at a temperature higher than the 10 hr half-life temperature of the initiator by &ge;15&deg;C. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to an environmentally friendly pressure-sensitive adhesive having less unreacted monomer and further 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, a method of reducing the residual monomer by multistage polymerization by changing the polymerization conditions of the acrylic monomer is employed. Moreover, when performing multistage polymerization, the content rate of an unreacted monomer is also changed by changing the polymerization initiator to be used. For example, as an adhesive sheet used when processing an electronic component disclosed in Japanese Patent Application Laid-Open No. 2000-234079 (Patent Document 1), for example, as shown in Synthesis Example 2, ethyl acetate and heptane are used as a reaction solvent. To 2-ethylhexyl acrylate and 2-hydroxyethyl acrylate, the reaction initiator Trigonox 23-C70 (manufactured by Kayaku Akzo Co., Ltd.) was added and stirred at 55 ° C. for 30 minutes. It is shown that ester HP-70 ( polymerization initiator) was added and reacted for another 2 hours to obtain a polymer having a weight average molecular weight of 600,000.

  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. Therefore, the obtained acrylic pressure-sensitive adhesive necessarily contains ethyl acetate and heptane, which are volatile organic solvents. Furthermore, Trigonox 23-C70 and Kayaester HP-700 used here are polymerization initiators, but the polymerization temperature after adding Trigonox 23-C70 at the initial stage of polymerization is as low as 55 ° C., Volatile low molecular weight substances derived from the initiator added at the initial stage of polymerization remain in the system, and an odor derived from the initiator is observed.

In the examples of JP-A-2002-306650 (Patent Document 2 ), a mixture of n-butyl acrylate, 2-ethylhexyl acrylate, acrylic acid, and 2-hydroxyethyl methacrylate is dissolved in ethyl acetate. At the reflux point, lauroyl peroxide (10 hour half-life temperature: 62 ° C.) was added as a polymerization initiator for reaction, and after 4 hours, a polymerization initiator in half the amount of lauroyl peroxide used first was added. Furthermore, it is described that polymerization is continued to produce an acrylic polymer solution.

However, in the method described in Patent Document 2 , the polymerization initiator added in two portions is the same polymerization initiator, and the polymerization initiator added first, the polymerization initiator added later, There is no technical idea for using the characteristics of the respective polymerization initiators by using different ones. Patent Document 2 discloses an adhesive tape having an acrylic adhesive layer in which the amount of volatile components released when it is desired to heat the adhesive tape at 90 ° C. for 30 minutes for 6 minutes or more is 150 ppm or less. . This Patent Document 2 describes that peroxide polymerization initiators and azo polymerization initiators can be used when polymerizing acrylic monomers, and these polymerization initiators include at least two types. It is described that they can be used in combination. In this case, when the polymerization initiator becomes a radical, the molecular weight of the polymerization initiator is 30 to 60 or more, or 150 to 300 or more, and the 10-hour half-life is It is desirable to use a polymerization initiator at 90 ° C. or lower, and it is further described that a compound having no aromatic ring in the molecule is desirable for reducing the amount of unreacted monomer. .

In Patent Document 2 , as a specific method for setting the amount of volatile components contained in the acrylic pressure-sensitive adhesive to 150 ppm or less, a method of separating / removing residual monomers in the reflux solvent from the polymerization odor, acrylic monomers, A low boiling point scavenger monomer that reacts with the modified vinyl monomer but is easy to volatilize and remove is added to the polymerization equipment to suppress odor, and the resulting acrylic polymer is put into a poor solvent to leave the residual monomer in the poor solvent. And a method for removing it by dissolving it in an aqueous solution.

For example, as disclosed in the above Patent Documents 1 and 2 , one of the causes of odor of acrylic pressure-sensitive adhesive is residual monomer, and acrylic pressure-sensitive adhesive is obtained by reducing the residual amount of such monomer. Although the odor peculiar to the acrylic monomer which is possessed is reduced to some extent, there is no description about reducing the residual initiator and the volatile low molecular weight substance derived from the initiator.

In addition, the odor of acrylic adhesives is not only the odor due to the residual monomers and initiators described above, but also the total volatile organic compounds (VOC) generated from acrylic adhesives. Even if the polymerization rate 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.
Here, in producing such an acrylic polymer, impurities contained in ethyl acetate used as a reaction raw material are often brought into the reaction apparatus. Examples of such impurities include aldehydes, Examples of alcohols and acetic acid. For example, ethyl acetate, which is widely used as a reaction solvent, may contain a considerable amount of aldehydes and alcohols depending on the production method. When these components are brought into the reaction system, the resulting acrylic system It often remains in the polymer and becomes a source of odor.

Since organic substances that cause such odors can also cause sick house disease, the guidelines for indoor air pollution established by the Ministry of Health, Labor and Welfare regarding these volatile organic substances include formaldehyde, toluene, xylene, There are parachlorobenzene, ethylbenzene, styrene, chlorpyrifos, di-2-ethylhexyl phthalate, diazinon, acetaldehyde, fenocarb, their individual concentrations in air, and the total volatile organic compounds containing these compounds (TVOC = Total Volatile Organic Compounds) is considered a source of indoor air pollution. And it has been pointed out that such volatile organic compounds cause sick house disease.

  Therefore, when producing an acrylic polymer, naturally it is necessary to keep the residual amount of unreacted residual monomers and low molecular weight substances derived from the initiator as low as possible during the polymerization reaction process. Careful attention is also required with respect to components introduced into the reaction system as impurities contained therein.

For example, in an 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 adhesives, aldehydes are generally not used, so careful examination of the origin of such aldehydes is surprisingly derived from ethyl acetate used as a reaction solvent. I found out. 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, (1) it is mostly due to the dimerization reaction of acetaldehyde. However, a large amount of acetaldehyde and ethanol are mixed in the ethyl acetate obtained by the method (1), and a large amount of acetic acid is contained in the ethyl acetate obtained by the method (2). .

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, 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 2000-234079 JP 2002-306650 A

  This invention reduces the odor of the acrylic adhesive in the above prior arts, and this invention aims at providing the environment-responsive adhesive with few volatile organic substances.

The environmentally friendly pressure-sensitive adhesive of the present invention is an environmentally friendly pressure-sensitive adhesive obtained by dissolving at least a part of an acrylic monomer in a reaction solvent and polymerizing the acrylic monomer in the presence of a polymerization initiator. And
As the polymerization initiator, both the molecular weights of the polymerization initiators are in the range of 200 to 250, the carbon number of the alkyl group in the radical side chain of the polymerization initiator is in the range of 4 to 9, and the polymerization At least two kinds of polymerization initiators having different structures in which the 10-hour half-life temperature of the initiator is both in the range of 45 to 55 ° C. are added in multiple stages, and the polymerization initiator using the polymerization reaction temperature It is characterized by reacting at a temperature higher by 15 ° C. or more than the 10-hour half-life temperature.

The environmentally friendly pressure-sensitive adhesive of the present invention uses a specific polymerization initiator as a polymerization initiator, adds the polymerization initiator in multiple stages, and further reduces the 10-hour ratio of the polymerization initiator using the reaction temperature. By setting the temperature 15 ° C. or more higher than the initial temperature, the monomer used can be reacted efficiently, the residual ratio of the monomer can be remarkably lowered, and the odor derived from the initiator can be significantly reduced. In such an acrylic pressure-sensitive adhesive, the monomer remaining in the pressure-sensitive adhesive without being polymerized is detected as a volatile organic substance (VOC), but is detected as this VOC in the pressure-sensitive adhesive of the present invention. There is almost no odor peculiar to acrylic adhesives because the content of the residual monomer and the low molecular weight substance derived from the initiator is extremely low.

  Further, the use of the acrylic pressure-sensitive adhesive of the present invention using ethyl acetate having a low concentration of acetaldehyde and alcohol necessarily contained as impurities in the reaction solvent reduces the total VOC from the pressure-sensitive adhesive.

  The environmentally friendly pressure-sensitive adhesive of the present invention has a low residual rate of the low molecular weight substance derived from the used acrylic monomer and initiator, and therefore has a low odor peculiar to the acrylic pressure-sensitive adhesive. Furthermore, the environmentally friendly pressure-sensitive adhesive of the present invention can reduce the content of volatile organic substances (VOC).

Next, the environmentally friendly pressure-sensitive adhesive of the present invention will be specifically described.
The environmentally friendly pressure-sensitive adhesive of the present invention is an acrylic pressure-sensitive adhesive in which an acrylic monomer is (co) polymerized in a reaction solvent, and at least two different types of polymerization initiators are used during (co) polymerization. Then, it is obtained by conducting the reaction in multiple stages.

  As an example of the acrylic monomer constituting the environmentally friendly pressure-sensitive adhesive of the present invention, a (meth) acrylic acid alkyl ester having an alkyl group in which the alkyl group usually has 1 to 18 carbon atoms, preferably 4 to 12 carbon atoms. Can be mentioned. 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, the environment-responsive pressure-sensitive adhesive of the present invention may be copolymerized with an acrylic monomer component having a functional group as an acrylic monomer component.
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 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the whole acrylic monomer to be used. The

  In this invention, you may copolymerize with the other monomer component which can be copolymerized with the above acrylic monomers further. Examples of such other monomers include vinyl compounds such as styrene. Such other monomers can be used alone or in combination. Such other monomers are usually copolymerized in an amount within 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.

The environmentally friendly pressure-sensitive adhesive of the present invention can be obtained by (co) polymerization by dissolving or dispersing the above acrylic monomer in an organic solvent.
The organic solvent used as a reaction solvent in the present invention is ethyl acetate. Ethyl acetate used as a reaction solvent when producing the environmentally friendly pressure-sensitive adhesive of the present invention can be produced by an esterification reaction between acetic acid and ethanol. Industrially, ethylene is dissolved in acetic acid. There is ethyl acetate directly produced without passing through ethanol, or ethyl acetate produced by dimerization reaction of acetaldehyde. Such ethyl acetate contains other components such as acetaldehyde and ethanol due to the production method. Such components are generally removed by distillation after producing ethyl acetate, but aldehydes such as acetaldehyde are removed by such distillation, but alcohol components remain. Alcohols eventually become aldehydes when oxidized, and alcohols contained in distilled ethyl acetate are stored, transported and used as acrylic monomers until used in the production of adhesives. In the process of producing a pressure-sensitive adhesive, it is oxidized to aldehydes. Therefore, in the method for producing an environmentally friendly pressure-sensitive adhesive of the present invention, not only the content of aldehydes contained in ethyl acetate is reduced as much as possible. Furthermore, the alcohol content is kept as low as possible.

In particular, in the present invention, not only the content of aldehydes contained in ethyl acetate used as a reaction solvent is usually 10 ppm or less, but also ethyl acetate having an alcohol component content of 100 ppm or less is used. Is aldehyde: 5 ppm or less, alcohol 5
Use ethyl acetate that is below 0 ppm.

Specifically, for example, distilled ethyl acetate obtained by distilling the crude ethyl acetate produced by each method is distilled, and the aldehyde compound in the ethyl acetate at the time of producing the adhesive is 10 ppm or less, and the alcohol component is 100 ppm or less. There is a method in which not only aldehydes contained in distilled ethyl acetate but also alcohol components are removed by repeated distillation until the reaction is completed.

  In the present invention, it is advantageous to use ethyl acetate obtained by directly producing ethyl acetate from acetic acid and ethylene among the methods for producing ethyl acetate, because there are few remaining aldehydes and alcohol components. The aldehydes, alcohols, acetic acid and the like contained in the ethyl acetate are preferably used after removal.

In this way, by removing not only aldehydes but also alcohol components, aldehydes are not generated in the process of polymerizing acrylic monomers, and the concentration of total VOC (total volatile organic compounds) in the resulting adhesive is reduced. 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, with respect to 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 environment-friendly pressure-sensitive adhesive of the present invention, different types of specific polymerization initiators are used when (co) polymerizing acrylic monomers 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 A polymerization initiator having a different structure with a 10 hour half-life temperature in the range of 45-55 ° C is used.

Such a polymerization initiator has high reactivity at the time of polymerization reaction and good dispersibility of radicals, so that it is possible to reduce the residual monomer efficiently, and by limiting the reaction temperature, It is possible to reduce the amount of initiator to be generated, and to reduce the production of volatile low molecular weight substances.

  As an example of such a polymerization initiator, the peroxide type | system | group initiator represented by following formula (1) can be mentioned.

However, in the above formula (1), R ^1, R ^2, together with each independently represent an alkyl group having 4-9 carbon atoms, the molecular weight of the compound represented by the formula (1) is 200 to 250.
Examples of such polymerization initiators, t- butyl peroxy deca ethylhexanoate (BPND, molecular weight: 24 4, carbon atoms in the alkyl group of the radical side chains: 4, 9, 10 hours half-life temperature: 47 ° C.), t- Peroxide initiators such as hexyl peroxypivalate (HPP, molecular weight: 202, carbon number of alkyl group in radical side chain: 6, 4 and 10 hours half-temperature: 53 ° C), 2,2'-azobis ( Examples include azo initiators such as 2,4-dimethylvaleronitrile (molecular weight: 248, carbon number of alkyl group in radical side chain: 6, 6, 10 hours half-life temperature: 51 ° C). In view of reactivity, ease of remaining of the low molecular weight substance derived from the initiator, and odor, it is preferable to use a peroxide-based initiator.In the present invention, the above polymerization initiators are used in combination.

  Further, in the present invention, the polymerization initiator has a molecular weight within the above range, the carbon number of the alkyl group of the radical side chain is within the above range, and a 10-hour half-life temperature is within the above range. Use two or more types. By using two or more kinds of polymerizable initiators, acrylic monomers dissolved or dispersed in the reaction solvent ethyl acetate can be (co) polymerized at a very high reaction rate. Acrylic monomers and initiators The residual amount of the derived low molecular weight substance is 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 initiator can be kept very low.

  When an initiator having a low molecular weight is used as the polymerization initiator, the polymerization rate of the monomer is good because the radical dispersibility during the polymerization is high, and the amount of unreacted residual monomer can be reduced. Further, the low molecular weight substance derived from the initiator generated during the polymerization is also less likely to be distilled off during the reaction and remain in the pressure-sensitive adhesive because of its low molecular weight. However, when it remains in the pressure-sensitive adhesive, the molecular weight is small and it is volatile, which tends to cause the odor of the pressure-sensitive adhesive. In addition, when the molecular weight of the polymerization initiator is large, the radical dispersibility is low during the polymerization, and the amount of residual monomer increases in the initial stage. By making both of the molecular weights in the range of 200 to 250, it is possible to obtain a pressure-sensitive adhesive that hardly causes the disadvantages described above and has less odor.

  In the present invention, when a plurality of different types of polymerization initiators are used, all of the plurality of initiators can be collectively added to the reaction solution, but dividedly added to the reaction solution. Is preferred.

When adding to the reaction liquid in such a divided manner, the order of addition of the polymerization initiator is not particularly limited, but for example when using an initiator having a structure of R ¹ -OO-CO-R ² , It is preferable to use a compound having a small number of carbon atoms in the radical side chain represented by R ¹ . In this way, by setting the blending order in the polymerization initiator and blending the polymerization initiator accordingly, the acrylic monomer can be efficiently polymerized, and the acrylic monomer and start causing odor in the resulting pressure-sensitive adhesive Since the residual ratio of the volatile low molecular weight substance derived from the agent becomes 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.
As described above, as the polymerization initiator used in the present invention, a polymerization initiator having a specific molecular weight, a carbon number of a specific radical side chain alkyl group, and a specific 10-hour half-life temperature is used. By using such a polymerization initiator, the dispersion of radicals during polymerization can be improved, the residual monomer can be reduced, and the compound derived from the polymerization initiator that remains slightly after polymerization is also low in volatility. Therefore, the odor derived from the polymerization initiator can be reduced. In addition, by keeping the polymerization temperature high from the polymerization process to the final stage, the residual initiator and the low-molecular weight volatile initiator-derived component are removed from the reaction system during the polymerization and remain in the resulting adhesive. You can avoid it.

  The polymerization initiators as described above are generally 0.05 to 1 part by weight, preferably 0 with respect to 100 parts by weight of the acrylic monomer dissolved or dispersed in ethyl acetate as the reaction solvent in total. 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. Is preferred.

  In the present invention, the reaction is started by heating a reaction solution in which an acrylic monomer is dissolved or dispersed in ethyl acetate as a reaction solvent as described above, and adding a polymerization initiator to the reaction solution. Is done. 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.

  Furthermore, the reaction temperature is set to a temperature that is 15 ° C. or more higher than the 10-hour half-life temperature of the polymerization initiator used. By carrying out the reaction at such a temperature, an adhesive with less odor can be obtained.

  If the reaction temperature is low outside the above range, initiator-derived volatile components generated during polymerization may not be removed, and these components may remain in the adhesive and cause odor. There is. If the reaction temperature is high outside the above range, it is difficult to effectively control this reaction.

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 thus obtained environmentally friendly pressure-sensitive adhesive (ethyl acetate solution) of the present invention was measured using gas chromatography, the residual amount of each acrylic monomer used was usually 60 ppm or less, In many cases, it is 50 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 2000 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 the adhesive (test piece, thickness: 70 μm (dry)) obtained by applying the environmentally friendly adhesive (ethyl acetate solution) of the present invention, heating at 65 ° C. for 2 hours by the sampling back method When the VOC in the steam after the determination is obtained, the VOC of formaldehyde is usually 0.06 μg / test piece or less, preferably 0.03 μg / test piece or less, and the VOC of acetaldehyde is usually 0.07 μg / test piece or less, preferably Is 0.04 μg / test piece or less, and the total volatile organic compound (TVOC) is usually 300 μg / test piece or less, preferably 200 μg / test piece or less.

Here, the test piece used for the measurement of VOC in the present invention is 80 mm × 100 mm ×
It has a thickness of 70 μm (dry) and is a widely used sample size in VOC measurement. Moreover, the sampling back method performed using this test piece is a standardized bag (after the test piece of a certain size as described above is attached to the SUS mesh.
For example, put it in a Tedlar bag, AA-10 made by GS Science, and replace the air in it with high-purity nitrogen gas (purity 99.999%), then put a test piece in the bag filled with this nitrogen gas and put it at 65 ° C. Heat for 2 hours, release the volatile components from the adhesive into the bag by heating,
Thus, the volatile components released into the bag are collected. The total VOC is measured by analyzing the collected components with GC-MS. In addition, aldehyde compounds are analyzed by dissolving the collected components in a predetermined solvent and then analyzing this solution using high performance liquid chromatography. These are methods for analyzing volatile components contained in the adhesive layer. It is a general method for measuring VOCs.

In the present invention, a gas chromatograph 6890N and a mass detector 5973N manufactured by Agilent Technology were used as GC-MS as an analyzer.
In addition, Alltance manufactured by Nippon Waters Co., Ltd. is used as a high performance liquid chromatography which is an analytical device, and ODS-80A, 75 × 4.6 mm, 3 μm manufactured by GL Science Co., Ltd. is used as a detector. Used UV having a wavelength of 360 nm.

As described above, the environmentally friendly pressure-sensitive adhesive of the present invention shows a low value of VOC for each component and a low value of TVOC. In particular, this pressure-sensitive adhesive has a characteristic that the content of aldehydes is low. Furthermore, the amount of the low molecular weight product derived from the residual monomer and the initiator 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 a pressure-sensitive adhesive, a filler such as an inorganic filler, an organic filler, or a composite filler can be blended, or a coloring material 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.
[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), First, 0.31 part by weight of 2-hydroxyethyl acrylate (2HEA), 0.03 part by weight of n-dodecyl mercaptan, and 90 parts by weight of purified ethyl acetate (2-2) were added. Add the initiator t-butylperoxyneodecanoate (BPND, Mw = 244, carbon number of radical side chain = 4,9, 10 hour half-life temperature = 47 ° C.) 0.006 part by weight After the air inside was replaced with nitrogen gas, the reaction was started by heating so that the temperature in the reaction vessel reached 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-hexylperoxypivalate (HPP, Mw = 202, carbon number of radical side chain = 6 and 4, 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 to 82 ° C. Reacted for hours.

After 3.5 hours, a large amount of 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, BA was contained in an amount of 30 ppm, hereinafter, AA was 30 ppm or less, and 2EHA was contained in an amount of 20 ppm or less.

The purified ethyl acetate (2-2) used in Example 1 was obtained by distilling crude ethyl acetate produced by directly introducing ethylene into acetic acid, and then re-distilling precisely again. Its composition is as follows.
Ethyl acetate content: 99.9%
Acetaldehyde: 1 ppm or less Formaldehyde: 1 ppm
Alcohol: 5ppm.

In addition, a test piece [80 × 100 mm × thickness 70 μm (dry)] was cut out from the above-mentioned pressure-sensitive adhesive sheet and measured for VOC with respect to formaldehyde by the sampling back method. As a result, it was 0.06 μg / test piece or less, and acetaldehyde The VOC was measured to be 0.07 μg / test piece, and the TVOC of this test piece was measured to be 300 μg / test piece.
[Example 2]
In Example 1, the same weight average molecular weight was used except that the same amount of HPP was used in place of BPND as the first polymerization initiator, and the same amount of BPND was used in place of HPP as the second polymerization initiator. 50
An acrylic pressure-sensitive adhesive having 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 50 ppm, AA is 4
0 ppm and 2EHA were contained in an amount of 50 ppm.

Since the number of carbons in the radical side chain of the first polymerization initiator, HPP, is larger than the number of carbons in the radical side chain of the second polymerization initiator, BPND, the amount of residual monomer increased slightly. .
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, it was 0.07 μg / test piece. The VOC was measured to be 0.07 μg / test piece, and the TVOC of this test piece was measured to be 500 μg / test piece. Both VOC and TVOC showed slightly higher values than Example 1. It was.
[Comparative Example 1]
In Example 1, BPND as the first polymerization initiator was used as it was, and the same amount of BPND was used instead of HPP as the second polymerization initiator. Temperature (Tg): An acrylic adhesive having a temperature 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 390 ppm, AA is
40 ppm, 2EHA was contained in an amount of 380 ppm.

In this comparative example, since the first polymerization initiator and the second polymerization initiator were BPND, the amount of residual monomer in the obtained acrylic pressure-sensitive adhesive was large.
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 was measured to be 0.07 μg / test piece, and the TVOC of this test piece was measured to be 2500 μg / test piece. Both VOC and TVOC showed high values.
[Comparative Example 2]
In Example 1, the same amount of HPP was used instead of BPND as the first polymerization initiator, and HPP as the second polymerization initiator was used as it was. Temperature (Tg): An acrylic adhesive having a temperature 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 400 ppm, AA is
40 ppm, 2EHA was contained in an amount of 410 ppm.

In this comparative example, since the first polymerization initiator and the second polymerization initiator were HPP, the amount of residual monomer in the obtained acrylic pressure-sensitive adhesive was large.
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, it was 0.07 μg / test piece. The VOC was measured to be 0.07 μg / test piece, and the TVOC of this test piece was measured to be 2600 μg / test piece. Both VOC and TVOC showed high values.
[Comparative Example 3]
In Example 1, the same amount of lauroyl peroxide (LPO, Mw = 398, carbon number of radical side chain = 11,11, 10-hour half-life temperature = 62 ° C.) was used instead of BPND as the first polymerization initiator. 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 above LPO was used as it was as the second polymerization initiator. .

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
40ppm, 2HEA was contained in an amount of 680ppm, and the amount of residual monomer was large.

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 was measured to be 0.07 μg / test piece, and the TVOC of this test piece was measured to be 2900 μg / test piece. Both VOC and TVOC showed high values.

Since the environment-responsive pressure-sensitive adhesive of the present invention uses a plurality of specific polymerization initiators having different structures, the content of unreacted monomer in the resulting pressure-sensitive adhesive is remarkably reduced, which is unique to acrylic pressure-sensitive adhesives. The odor is significantly reduced. In addition, the pressure-sensitive adhesive of the present invention has a low content of volatile organic substances and low VOC and TVOC values, and is suitable for the adhesion of sealed rooms, cars, electronic parts, and the like. The pressure-sensitive adhesive of the present invention has a small amount of aldehydes in the acrylic pressure-sensitive adhesive that causes odors, or a small amount of alcohol that is oxidized with time to become aldehydes, and the remaining unreacted acrylic monomer remains. The amount and amount of volatile residual initiator is also low. Therefore, the acrylic pressure-sensitive adhesive 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. Accordingly, the pressure-sensitive adhesive of the present invention reduces odor and is unlikely to cause sick house disease. 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 (7)

A method for producing an environmentally friendly pressure-sensitive adhesive comprising dissolving at least a part of an acrylic monomer in a reaction solvent and polymerizing the acrylic monomer in the presence of a polymerization initiator,
As the polymerization initiator, both of the molecular weights of the polymerization initiator are in the range of 200 to 250, the number of carbons of the radical side chain of the polymerization initiator is in the range of 4 to 9, and the polymerization initiator At least two kinds of polymerization initiators having different structures each having a 10-hour half-life temperature in the range of 45 to 55 ° C. are added in multiple stages, and the polymerization initiator using the polymerization reaction temperature is reduced to 10 hours and a half. A method for producing an environmentally friendly pressure-sensitive adhesive, characterized in that the reaction is carried out at a temperature higher than the initial temperature by 15 ° C. or more. 2. The method for producing an environmentally friendly pressure-sensitive adhesive according to claim 1, wherein the polymerization reaction is performed at a temperature within a range of 76.8 ± 10 ° C. The method for producing an environmentally friendly pressure-sensitive adhesive according to claim 1 or 2 , wherein the polymerization initiator is a peroxide-based initiator represented by the following formula (1):

(However, in said formula (1), R < ¹ >, R < ² > represents a C4-C9 alkyl group each independently.). Method for producing environmentally friendly type pressure-sensitive adhesive of claim 3 wherein, characterized in that added to the above said polymerization initiator from the carbon number less polymerization initiator R ^1. The method for producing an environmentally friendly pressure-sensitive adhesive according to any one of claims 1 to 4 , wherein a residual monomer concentration in the environmentally friendly pressure-sensitive adhesive is 150 ppm or less. 6. The reaction solvent according to claim 1, wherein the reaction solvent is ethyl acetate, the amount of the acetaldehyde compound in the ethyl acetate is 10 ppm or less, and the content of the alcohol component is 100 ppm or less . The manufacturing method of the environmentally friendly adhesive as described in one term . The total amount of volatile organic substances (TVOC) measured by the sampling back method with respect to the environmentally friendly pressure-sensitive adhesive is 500 μg / test piece or less, any one of claims 1 to 6 The manufacturing method of the environmentally friendly adhesive as described in one term .