JP7014419B2 - UV curable hot melt adhesive - Google Patents

Description

The present invention relates to an ultraviolet curable hot melt adhesive.

Acrylic adhesives are used in adhesive tapes, product labels, and the like. Further, since the acrylic adhesive is excellent in transparency, heat resistance and weather resistance, it is also used in optical displays of electronic devices such as personal computers, smartphones, televisions and digital cameras.

From the viewpoint of improving the usage environment, it is recommended to make the adhesive solvent-free, and the acrylic adhesive is also becoming hot melt. Since the hot melt adhesive does not require a drying process for removing the solvent in the coating process on the support, it does not require equipment for the drying process and greatly contributes to energy saving.

Particularly in recent years, an ultraviolet curable hot melt adhesive containing a (meth) acrylic polymer having an ultraviolet reactive group has been developed. After applying the ultraviolet curable hot melt adhesive to the support in a heated and melted state, the ultraviolet curable hot melt adhesive is irradiated with ultraviolet rays to impart a crosslinked structure between the (meth) acrylic polymers. To develop stickiness. According to such an ultraviolet curable hot melt adhesive, good adhesiveness that cannot be achieved by a conventional thermoplastic acrylic adhesive can be obtained.

For example, Patent Document 1 describes an ultraviolet curable hot melt adhesive containing a vinyl-based copolymer (A) having a glass transition temperature of −5 ° C. or lower and a weight average molecular weight of 50,000 to 350,000. Disclosed is an ultraviolet curable hot melt adhesive obtained by polymerizing the vinyl-based copolymer (A) with a specific monomer component as a constituent component.

Japanese Unexamined Patent Publication No. 2006-299017

On the other hand, it has been reported that the ultraviolet curable hot melt adhesive produces decomposition products when irradiated with ultraviolet rays. There is a problem that this decomposition product causes an odor to be generated in the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays. It is considered that the decomposition products that cause the generation of odor are generated by the decomposition of the side chains of the (meth) acrylic polymer and the monomers remaining without contributing to the polymerization reaction of the (meth) acrylic polymer. Be done.

Therefore, Patent Document 1 discloses that the content of the monomer component that can cause an odor in the vinyl-based copolymer (A) is reduced as a measure for improving the odor. However, it is not possible to sufficiently reduce the odor of the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays only by adjusting the content of the monomer component, and further improvement is desired.

On the other hand, in order to reduce the odor caused by the decomposition products, it is conceivable to add an adsorbent to the ultraviolet curable hot melt adhesive. The adsorbent can adsorb the decomposition products and reduce the odor of the UV curable hot melt adhesive.

However, according to the studies by the present inventors, it has been found that when the adsorbent is simply added to the ultraviolet curable hot melt adhesive, the thermal stability of the ultraviolet curable hot melt adhesive is significantly reduced when it is heated and melted. Since the ultraviolet curable hot melt adhesive is applied to the support in a state of being heated and melted, it is in a state of being heated and melted for a long time before the application. Ultraviolet curable hot melt adhesives with low thermal stability cause gelation and coloring during heat melting.

Therefore, an object of the present invention is to provide an ultraviolet curable hot melt adhesive in which the generation of odor after irradiation with ultraviolet rays is reduced by an adsorbent and the thermal stability at the time of heating and melting is also excellent. ..

The ultraviolet curable hot melt adhesive of the present invention is a (meth) acrylic polymer (A) having an ultraviolet reactive group, an adsorbent (B), and a hindered phenol-based antioxidant containing no nitrogen atom in the molecule ( It is characterized by containing C) and a phosphorus-based antioxidant (D).

[(Meta) Acrylic Polymer (A)]
The ultraviolet curable hot melt adhesive of the present invention contains a (meth) acrylic polymer (A) having an ultraviolet reactive group. The (meth) acrylic polymer which becomes the main chain in the (meth) acrylic polymer (A) having an ultraviolet reactive group is a polymer or a copolymer of a (meth) acrylic monomer. In addition, (meth) acrylic means acrylic or methacrylic.

The (meth) acrylic polymer (A) preferably contains a (meth) acrylic monomer unit having no ultraviolet reactive group and a carboxy group in the molecule, and a monomer unit having an ultraviolet reactive group in the molecule. .. It is preferable that none of the monomer units has an aromatic ring in the molecule that absorbs light rays in the ultraviolet region.

An ultraviolet reactive group is a functional group that is excited by irradiation with ultraviolet rays to generate radicals, and the radicals cause a hydrogen abstraction reaction to form a crosslinked structure between the molecules of the (meth) acrylic polymer (A). say.

Examples of the ultraviolet reactive group include a functional group having a benzophenone skeleton, a functional group having a benzoin skeleton, and a functional group having a thioxanthone skeleton.

The (meth) acrylic monomer having no ultraviolet reactive group and carboxy group in the molecule is not particularly limited, and is, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n. -Butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, n-hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate , N-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, alkyl (meth) acrylate such as lauryl (meth) methacrylate, and alkyl having 1 to 8 carbon atoms in the alkyl group. It preferably contains (meth) acrylate. As the alkyl (meth) acrylate having 1 to 8 carbon atoms of the alkyl group, 2-ethylhexyl (meth) acrylate and butyl (meth) acrylate are preferable, and 2-ethylhexyl acrylate and butyl acrylate are more preferable. The (meth) acrylic monomer having no ultraviolet reactive group and carboxy group in the molecule may be used alone or in combination of two or more. The (meth) acrylate means acrylate or methacrylate.

In the (meth) acrylic polymer (A), the content of the (meth) acrylic monomer unit having no ultraviolet reactive group and carboxy group in the molecule is preferably 89.65 to 99.75% by mass, and 91. 5 to 97% by mass is more preferable, and 92.5 to 95% by mass is particularly preferable. In order to achieve excellent coatability and tackiness of the UV curable hot melt adhesive, the content of the (meth) acrylic monomer unit having no UV reactive group and carboxy group in the molecule is within the above range. It is desirable to do. However, the (meth) acrylic monomer that does not have an ultraviolet reactive group or a carboxy group in the molecule is oxidatively decomposed when the ultraviolet curable hot melt adhesive is irradiated with ultraviolet rays, and the decomposition product that causes the generation of odor is produced. Especially easy to occur. Therefore, the effect according to the present invention is particularly effective when the (meth) acrylic polymer (A) contains a (meth) acrylic monomer unit having no ultraviolet reactive group and a carboxy group in the molecule at the above-mentioned high content. Can be demonstrated. Even in such a case, the adsorbent (B) can adsorb the decomposition product and greatly reduce the generation of odor of the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays.

In particular, among the (meth) acrylic monomers having no ultraviolet reactive group and carboxy group in the molecule, butyl (meth) acrylate is oxidatively decomposed when the ultraviolet curable hot melt adhesive is irradiated with ultraviolet rays, and n-. Prone to produce decomposition products such as butanol, n-butanol, and n-butyl formate. These decomposition products are particularly prone to odor. Therefore, the effect according to the present invention can be particularly exhibited when the (meth) acrylic monomer having no ultraviolet reactive group and carboxy group in the molecule contains butyl (meth) acrylate.

The content of the butyl (meth) acrylate unit in the (meth) acrylic monomer unit having no ultraviolet reactive group and carboxy group in the molecule is preferably 70% by mass or more, preferably 70 to 99.65% by mass. , 70-85% by mass is more preferable. According to the present invention, even when the content of the butyl (meth) acrylate unit is high as described above, the adsorbent (B) greatly reduces the generation of odor of the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays. be able to.

The monomer having an ultraviolet reactive group in the molecule is not particularly limited as long as it can be polymerized with a (meth) acrylic monomer having no ultraviolet reactive group and a carboxy group in the molecule. Since the ultraviolet reactive group is the same as above, the description thereof will be omitted.

Examples of the monomer having an ultraviolet reactive group in the molecule include a (meth) acrylic monomer having no ultraviolet reactive group and a carboxy group in the molecule, and a monomer having a carboxy group and a radically polymerizable unsaturated double bond. It is preferably copolymerizable.

The UV-reactive group contained in the monomer having a UV-reactive group in the molecule is not particularly limited, but includes a functional group having a benzophenone skeleton, a functional group having a benzoin skeleton, and a functional group having a thioxanthone skeleton. Can be mentioned. Of these, a functional group having a benzophenone skeleton is preferable. A functional group having a benzophenone skeleton can independently cause a hydrogen abstraction reaction by irradiation with ultraviolet rays, which makes it possible to efficiently form a crosslinked structure between the molecules of the (meth) acrylic polymer (A). Become. The ultraviolet reactive group may be contained alone or in combination of two or more in the molecule.

As the monomer having an ultraviolet reactive group in the molecule, a (meth) acrylic monomer having an ultraviolet reactive group in the molecule is preferable, a (meth) acrylate having an ultraviolet reactive group in the molecule is more preferable, and a benzophenone skeleton. A (meth) acrylate having a functional group having a functional group in the molecule is particularly preferable. The monomer having an ultraviolet reactive group in the molecule may be used alone or in combination of two or more.

The monomer having an ultraviolet reactive group in the molecule is not particularly limited, and for example, 4-acryloyloxybenzophenone, 4-acryloyloxyethoxybenzophenone, 4-acryloyloxy-4'-methoxybenzophenone, 4-acryloyloxyethoxy- 4'-Methoxybenzophenone, 4-acryloyloxy-4'-bromobenzophenone, 4-acryloyloxyethoxy-4'-bromobenzophenone, 4-methacryloyloxybenzophenone, 4-methacryloyloxyethoxybenzophenone, 4-methacryloyloxy-4'- Examples thereof include methoxybenzophenone, 4-methacryloyloxyethoxy-4'-methoxybenzophenone, 4-methacryloyloxy-4'-bromobenzophenone, 4-methacryloyloxyethoxy-4'-bromobenzophenone, and 4-acryloyloxybenzophenone is preferable. The monomer having an ultraviolet reactive group in the molecule may be used alone or in combination of two or more.

In the (meth) acrylic polymer (A), the content of the monomer unit having an ultraviolet reactive group in the molecule is preferably 0.15 to 0.5% by mass, more preferably 0.17 to 0.4% by mass. It is preferable, and 0.2 to 0.35% by mass is particularly preferable. When the content of the monomer unit having an ultraviolet reactive group in the molecule is 0.15 to 0.5% by mass, the ultraviolet curable hot melt adhesive exhibits excellent adhesiveness.

The (meth) acrylic polymer (A) preferably further contains a monomer unit having a carboxy group and a radically polymerizable unsaturated double bond. That is, the (meth) acrylic polymer (A) has a (meth) acrylic monomer unit having no ultraviolet reactive group and a carboxy group in the molecule, a monomer unit having an ultraviolet reactive group in the molecule, and a carboxy group. And a monomer unit having a radically polymerizable unsaturated double bond.

As the monomer having a carboxy group and a radically polymerizable unsaturated double bond, it is copolymerized with a (meth) acrylate having no ultraviolet reactive group and a carboxy group in the molecule and a monomer having an ultraviolet reactive group in the molecule. If possible, there is no particular limitation. Further, it is preferable that the monomer having a carboxy group and a radically polymerizable unsaturated double bond does not have an ultraviolet reactive group in the molecule.

Examples of the monomer having a carboxy group and a radically polymerizable unsaturated double bond include monocarboxylic acids such as acrylic acid, methacrylic acid and β-carboxyethyl acrylate, and dicarboxylic acids such as fumaric acid and maleic acid. Of these, acrylic acid and methacrylic acid are preferable, and acrylic acid is more preferable. The monomer having a carboxy group and a radically polymerizable unsaturated double bond may be used alone or in combination of two or more.

In the (meth) acrylic polymer (A), the content of the monomer unit having a carboxy group and a radically polymerizable unsaturated double bond is preferably 0.1 to 10% by mass, more preferably 3 to 9% by mass. When the content of the monomer unit having a carboxy group and a radically polymerizable unsaturated double bond is 0.1 to 10% by mass, it is an ultraviolet curable type having excellent thermal stability, coatability and adhesiveness at the time of heat melting. A hot melt adhesive can be provided.

The (meth) acrylic polymer (A) may contain a monomer unit other than the above-mentioned monomer unit. Examples of other monomers include styrene and its derivatives, (meth) acrylamide-based monomers, vinyl ester-based monomers, and vinylamide-based monomers.

The weight average molecular weight (Mw) of the (meth) acrylic polymer (A) is preferably 10,000 to 500,000, more preferably 80,000 to 300,000, and particularly preferably 100,000 to 250,000. The UV-curable hot-melt adhesive may have reduced coatability during heating and melting due to the addition of the adsorbent (B). However, by using the (meth) acrylic polymer (A) having a weight average molecular weight within the above range, the decrease in coatability of the ultraviolet curable hot melt adhesive due to the adsorbent (B) during heating and melting is reduced. can do.

The weight average molecular weight of the (meth) acrylic polymer (A) is a polystyrene-equivalent value measured by a GPC (gel permeation chromatography) method. Specifically, 6 to 7 mg of the (meth) acrylic polymer (A) was collected, the collected (meth) acrylic polymer (A) was supplied to a test tube, and then THF (tetrahydrofuran) was added to the test tube. The (meth) acrylic polymer (A) is diluted 500-fold and filtered to prepare a measurement sample.

The weight average molecular weight of the (meth) acrylic polymer (A) can be measured by the GPC method using this measurement sample.

The weight average molecular weight Mw of the (meth) acrylic polymer (A) can be measured, for example, with the following measuring device and measuring conditions.
Measuring device Waters ACQUITY APC system Measuring conditions Column: Waters HSPgel (TM) HR MB-M
Mobile phase: Tetrahydrofuran used 0.5 mL / min
Detector: RI detector
Standard material: polystyrene
SEC temperature: 40 ° C

The method for producing (polymerizing) the (meth) acrylic polymer (A) is not particularly limited, and examples thereof include solution polymerization, bulk polymerization, suspension polymerization, and emulsion polymerization. Further, when polymerizing using a solvent in solution polymerization or the like, it is necessary to detreat the solvent by a predetermined method.

[Adsorbent (B)]
The ultraviolet curable hot melt adhesive of the present invention contains an adsorbent (B). The adsorbent (B) can selectively adsorb a specific component from substances such as gas and liquid that are in contact with the surface of the adsorbent (B). The adsorbent (B) can adsorb the decomposition products generated by irradiating the ultraviolet curable hot melt adhesive with ultraviolet rays, thereby greatly reducing the generation of odor in the ultraviolet curable hot melt adhesive. Can be done.

Examples of the adsorbent (B) include a chemical adsorbent and a physical adsorbent. Examples of the physical adsorbent include activated carbon, activated alumina, silica gel, mesoporous silica, diatomaceous earth, high silica zeolite, and polymer adsorbents.

As the adsorbent (B), a physical adsorbent is preferable, activated carbon and high silica zeolite are preferable, and high silica zeolite is particularly preferable. These adsorbents (B) have excellent affinity with the (meth) acrylic polymer (A), and can greatly reduce the generation of odor of the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays.

In the high silica zeolite, the molar ratio (SiO ₂ / Al ₂ O ₃ ) of silica (SiO ₂ ) to alumina (Al ₂ O ₃ ) is preferably 5 or more. The high silica zeolite having a molar ratio (SiO ₂ / Al ₂ O ₃ ) of 5 or more can greatly reduce the generation of odor of the ultraviolet curable hot melt adhesive after ultraviolet irradiation.

The molar ratio of silica (SiO ₂ ) to alumina (Al ₂ O ₃ ) in high silica zeolite (SiO ₂ / Al ₂ O ₃ ) is determined by, for example, inductively coupled plasma emission spectroscopic analysis (ICP-AES). It can be calculated from the analysis. Inductively coupled plasma emission spectroscopic analysis can be performed using, for example, the device name "OPTIMA5300DV" manufactured by PerkinElmer.

The high silica zeolite preferably has a composition represented by the following formula (I).
M _{2 / n} O ・ Al ₂ O ₃・ xSiO ₂・ yH ₂ O (I)
(In the formula (I), M represents a metal ion, n is the valence of the metal ion M, x is a number of 5 or more, and y is a number of 0 or more.)

Examples of the metal ion M in the formula (I) include alkali metal ions and alkaline earth metal ions. Specific examples thereof include calcium ion, barium ion, potassium ion, and sodium ion. Of these, sodium ions are particularly preferable because they can highly reduce the generation of odors in the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays.

In the formula (I), x is the molar ratio (SiO ₂ / Al ₂ O ₃ ) of silica (SiO ₂ ) to alumina (Al ₂ O ₃ ), which is a number of 5 or more. By setting x to 5 or more in the formula (I), it is possible to highly reduce the generation of odor of the ultraviolet curable hot melt adhesive after irradiation with ultraviolet rays.

The composition of the high silica zeolite can be calculated, for example, from quantitative analysis of elements by inductively coupled plasma atomic emission spectroscopic analysis (ICP-AES).

The BET specific surface area of the physical adsorbent is preferably 100 to 4000 m ² / g, more preferably 100 to 2000 m ² / g, and particularly preferably 100 to 1000 m ² / g. By using a physical adsorbent having a BET specific surface area within the above range, the odor of the ultraviolet curable hot melt adhesive can be highly reduced.

The BET specific surface area of the physical adsorbent can be calculated by the BET method based on the amount of nitrogen gas adsorbed.

The content of the adsorbent (B) in the ultraviolet curable hot melt adhesive is preferably 0.1 to 15 parts by mass, preferably 0.2 to 10 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer (A). Parts are more preferable, and 2 to 8 parts by mass are particularly preferable. By setting the content of the adsorbent (B) to 0.1 parts by mass or more, it is possible to provide an ultraviolet curable hot melt adhesive having a high and reduced generation of odor after irradiation with ultraviolet rays. By setting the content of the adsorbent (B) to 15 parts by mass or less, it is possible to reduce the decrease in thermal stability of the ultraviolet curable hot melt adhesive at the time of heating and melting due to the addition of the adsorbent (B).

[Hindered phenolic antioxidant (C)]
The ultraviolet curable hot melt adhesive of the present invention contains a hindered phenolic antioxidant (C). In the ultraviolet curable hot melt adhesive of the present invention, by using the above-mentioned adsorbent (B), the odor derived from the (meth) acrylic polymer (A) and the decomposition products of the residual monomer is highly reduced after ultraviolet irradiation. Has been done. However, according to the studies by the present inventors, it has been found that the addition of only the adsorbent (B) may reduce the thermal stability of the ultraviolet curable hot melt adhesive during heating and melting. It is considered that such a decrease in thermal stability is partly due to oxygen in the air adsorbed by the adsorbent (B). The adsorbent (B) adsorbs oxygen in the air and easily incorporates it into the ultraviolet curable hot melt adhesive. It is considered that this oxygen promotes the decomposition of the (meth) acrylic polymer (A), and the thermal stability of the ultraviolet curable hot melt adhesive at the time of heating and melting tends to decrease. Therefore, in the ultraviolet curable hot melt adhesive of the present invention, a hindered phenol-based antioxidant (C) and a phosphorus-based antioxidant (D) are used in combination. As a result, the decomposition of the (meth) acrylic polymer (A) due to the oxygen adsorbed by the adsorbent (B) can be reduced, and the excellent thermal stability of the ultraviolet curable hot melt adhesive during heat melting can be ensured. It becomes possible to do.

The hindered phenolic antioxidant (C) does not contain a nitrogen atom in the molecule. As a result, the decomposition of the (meth) acrylic polymer (A) can be greatly reduced, and the decrease in the thermal stability of the ultraviolet curable hot melt adhesive at the time of heating and melting due to the addition of the adsorbent (B) can be reduced. can.

Examples of the hindered phenolic antioxidant (C) include pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] and octadecyl-3- (3,5-di-tert). -Butyl-4-hydroxyphenyl) propionate, 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and the like can be mentioned. Of these, pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate] is preferable. The hindered phenolic antioxidant (C) may be used alone or in combination of two or more.

As the hindered phenolic antioxidant (C), a commercially available product can also be used. For example, BASF's product names "Irganox 1010", "Irganox 1076", "Irganox 259" and the like can be mentioned.

In the ultraviolet curable hot melt adhesive, the mass ratio of the hindered phenol-based antioxidant (C) to the adsorbent (B) [hindered phenol-based antioxidant (C) / adsorbent (B)] is 0. 01 to 5 is preferable, 0.1 to 4 is more preferable, and 0.125 to 0.5 is particularly preferable. By setting the mass ratio within the above range, it is possible to provide an ultraviolet curable hot melt adhesive having excellent thermal stability at the time of heating and melting and having a high and reduced generation of odor after irradiation with ultraviolet rays.

The content of the hindered phenol-based antioxidant (C) in the ultraviolet-curable hot-melt adhesive is preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer (A), and is 0. .1 to 3 parts by mass is more preferable, and 0.8 to 1.2 parts by mass is particularly preferable. By keeping the content of the hindered phenolic antioxidant (C) within the above range, the decrease in thermal stability of the ultraviolet curable hot melt adhesive during heating and melting due to the addition of the adsorbent (B) is reduced. be able to.

[Phosphorus-based antioxidant (D)]
The ultraviolet curable hot melt adhesive of the present invention contains a phosphorus-based antioxidant (D). As described above, by using a phosphorus-based antioxidant (D) in combination with a hindered phenol-based antioxidant (C), an ultraviolet curable hot-melt adhesive can be obtained by heating and melting by adding an adsorbent (B). It is possible to reduce the decrease in thermal stability.

Examples of the phosphorus-based antioxidant (D) include tris (2,4-di-tert-butylphenyl) phosphite, triphenylphosphine, triisodecylphosphite, trisnonylphenylphosphite, and tris (2,4-). Di-tert-butylphenyl) phosphite, and 3,9-bis (2,6-di-t-butyl-4-methylphenoxy) -2,4,8,10-tetraoxa-3,9-diphosphaspiro [5] .5] Undecan and the like. The phosphorus-based antioxidant (D) may be used alone or in combination of two or more.

As the phosphorus-based antioxidant (D), a commercially available product can also be used. For example, BASF's product name "IRGAFOS 168", ADEKA Corporation's product name "Adekastab TPP", "Adekastab 3010", "Adekastab 1178", "Adekastab TPP", "Adekastab 2112", and "Adekastab PEP-36". "And so on.

In the ultraviolet curable hot melt adhesive, the mass ratio of the phosphorus-based antioxidant (D) to the adsorbent (B) [phosphorus-based antioxidant (D) / adsorbent (B)] is 0.01 to 5. Preferably, 0.1 to 4 is more preferable, and 0.125 to 0.5 is particularly preferable. By setting the mass ratio within the above range, it is possible to provide an ultraviolet curable hot melt adhesive having excellent thermal stability at the time of heating and melting and having a high and reduced generation of odor after irradiation with ultraviolet rays.

The content of the phosphorus-based antioxidant (D) in the ultraviolet-curable hot-melt adhesive is preferably 0.1 to 5 parts by mass, preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer (A). Up to 3 parts by mass is more preferable, and 0.8 to 1.2 parts by mass is particularly preferable. By setting the content of the phosphorus-based antioxidant (D) within the above range, it is possible to reduce the decrease in thermal stability of the ultraviolet curable hot-melt adhesive during heating and melting due to the addition of the adsorbent (B). can.

The ultraviolet curable hot melt adhesive of the present invention has other additives such as a tackifier, a plasticizer, a reactive diluent, a polymerization initiator, a flame retardant, and an antistatic agent as long as the physical properties are not impaired. May further be included.

The method for producing the ultraviolet curable hot melt adhesive is not particularly limited, and is, for example, a (meth) acrylic polymer (A), an adsorbent (B), a hindered phenol-based antioxidant (C), and a phosphorus-based polymer. Examples thereof include a method of producing an ultraviolet curable hot melt adhesive by supplying an antioxidant (D) and, if necessary, other additives to a general-purpose kneading device, stirring and kneading while heating.

The ultraviolet curable hot melt adhesive is heated, melted, and then applied to the adherend. Therefore, the UV curable hot melt adhesive is usually supplied to a coating machine and heated and melted.

The UV curable hot melt adhesive contains a hindered phenolic antioxidant (C) and a phosphorus-based antioxidant (D). As a result, in the heating and melting steps for coating, the oxidative deterioration of the (meth) acrylic polymer (A) caused by the adsorbent (B) is highly reduced. Therefore, gelation and coloring of the ultraviolet curable hot melt adhesive are substantially prevented, the pot life is long, and the handleability is excellent.

Then, the ultraviolet curable hot melt adhesive that has been heated and melted is applied to the adherend and then irradiated with ultraviolet rays to form a crosslinked structure between the (meth) acrylic polymers (A). Will be done. As a result, the (meth) acrylic polymer (A) develops the desired adhesiveness. Since the ultraviolet curable hot melt adhesive contains an adsorbent (B), the generation of odor due to the decomposition products of the (meth) acrylic polymer (A) and the residual monomer after irradiation with ultraviolet rays is highly reduced.

Further, the ultraviolet curable hot melt adhesive is suitably used for applications of adhesive sheets such as labels. The adhesive sheet has an adhesive layer laminated and integrated on the support. The pressure-sensitive adhesive layer is formed by applying an ultraviolet-curable hot-melt adhesive onto a support and then irradiating the ultraviolet-curable hot-melt adhesive with ultraviolet rays to cure the pressure-sensitive adhesive layer.

In the ultraviolet curable hot melt adhesive of the present invention, the generation of odor due to the decomposition products of the (meth) acrylic polymer (A) and the residual monomer after irradiation with ultraviolet rays is highly reduced by the adsorbent (B). Further, by using the hindered phenolic antioxidant (C) and the phosphorus-based antioxidant (D), the thermal stability of the ultraviolet curable hot melt adhesive at the time of heating and melting by the addition of the adsorbent (B) can be obtained. The drop can be reduced to a high degree. As a result, the ultraviolet curable hot melt adhesive can exhibit excellent thermal stability when it is heated and melted in the coating process.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

(Synthesis Example 1: Synthesis of (meth) acrylic polymer (A))
Table 1 shows butyl acrylate, 2-ethylhexyl acrylate, acrylic acid, 4-acryloyloxybenzophenone, lauryl mercaptan and ethyl acetate in a 2 L separable flask equipped with a stirrer, a cooling tube, a thermometer and a nitrogen gas inlet. The reaction solution contained in the mixed amount was supplied and stirred at a rotation speed of 100 rpm.

After replacing the inside of the separable flask with nitrogen gas, the reaction solution was refluxed using a water bath. Next, a radical polymerization reaction was started by partially adding t-hexyl peroxypivalate (trade name "Perhexyl PV" manufactured by NOF CORPORATION) as a polymerization initiator into the separable flask. From the start of the reaction to 5 hours, t-hexyl peroxypivalate was added in a plurality of times, and the mixture was further polymerized for 1 hour. Table 1 shows the total amount of t-hexyl peroxypivalate added. Then, the polymerized reaction product was dried under normal pressure and reduced pressure at 130 ° C. to obtain a (meth) acrylic polymer (A). The weight average molecular weight of the (meth) acrylic polymer (A) was 187,000.

In Synthesis Example 1, all the monomers containing butyl acrylate, 2-ethylhexyl acrylate, acrylic acid, and 4-acryloyloxybenzophenone were used in the above polymerization reaction. Therefore, the odor (adsorption rate) of the ultraviolet curable hot melt adhesive, which will be described later, was not evaluated for the residual monomer.

Next, the details of each component used in Examples and Comparative Examples described later are described below.
(Adsorbent (B))
-Adsorbent (B1) [High silica zeolite, molar ratio of silica (SiO ₂ ) to alumina (Al ₂ O ₃ ) 5 or more (SiO ₂ / Al ₂ O ₃ ), and has a composition represented by the above formula (I). In the above formula (I), M is a sodium ion, n is 1 and x is 5 or more, sodium aluminosilicate, having a BET specific surface area of 350 to 900 m ² / g, Union Showa Co., Ltd. Product name "Silica-3000"]
-Adsorbent (B2) [Activated carbon powder, BET specific surface area within the range of 800 to 2000 m ² / g, manufactured by Kuraray Chemical Co., Ltd. Product name "Kuraraycol PK-W5A"]

(Hindered phenolic antioxidant (C))
-Hindered phenolic antioxidant (C1) [pentaerythritol tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], a product manufactured by BASF that does not contain nitrogen atoms in the molecule. Name "Irganox 1010"]
Hindered phenolic antioxidant (C2) [2,4-bis (n-octylthio) -6- (4-hydroxy 3', 5'-di-t-butylanilino) -1,3,5-triazine, BASF's trade name "Irganox 565", which contains a nitrogen atom in the molecule]

(Phosphorus-based antioxidant (D))
-Phosphorus-based antioxidant (D1) [Tris (2,4-di-tert-butylphenyl) phosphite, manufactured by BASF, trade name "IRGAFOS 168"]
(Sulfur-based antioxidant)
-Sulfur-based antioxidant [Product name "ADEKA STAB AO-412S" manufactured by ADEKA Corporation]

(Examples 1 to 9, Comparative Example A and Comparative Examples 1 to 4)
The (meth) acrylic polymer (A), the adsorbent (B1), the adsorbent (B2), the hindered phenolic antioxidant (C1), the hindered phenolic antioxidant (C2), obtained in Synthesis Example 1, After adding the phosphorus-based antioxidant (D1) and the sulfur-based antioxidant in the amounts shown in Table 2 into a stirring and kneader equipped with a heating device, the mixture is heated at 130 ° C. for 1 hour. By kneading while kneading, an ultraviolet curable hot melt adhesive was obtained.

[evaluation]
The ultraviolet curable hot melt adhesives obtained in Examples and Comparative Examples were evaluated for odor and thermal stability according to the following procedure. The results are shown in Table 2.

[Odor]
The ultraviolet curable hot melt adhesive was heated to 130 ° C. to melt it, and then coated on a polyethylene terephthalate film so as to have a thickness of 20 μm. After that, the ultraviolet curable hot melt adhesive coated on the polyethylene terephthalate film is irradiated with ultraviolet rays (UV-C) at an irradiation intensity of 50 mW / cm ² and an integrated light amount of 100 mJ / cm ² , and the ultraviolet curable hot melt is applied. The adhesive was cured to form an adhesive layer. As a result, a pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer was laminated and integrated on a polyethylene terephthalate film was manufactured.

(Odor: sensory evaluation)
By smelling the adhesive sheet produced above, the degree of odor of the adhesive sheets of Examples 1 to 9 and Comparative Examples 1 to 4 with respect to the adhesive sheet of Comparative Example A was evaluated according to the following evaluation criteria.
Inferior: I felt the same odor as the adhesive sheet of Comparative Example A.
Good: I felt that the odor was improved to some extent compared to the adhesive sheet of Comparative Example A.
Yu: I felt that the odor was clearly improved compared to the adhesive sheet of Comparative Example A.

(Odor: adsorption rate)
0.4 g of the pressure-sensitive adhesive layer was peeled off from the pressure-sensitive adhesive sheet prepared above, the pressure-sensitive adhesive layer was put into a sealable vial, and the pressure-sensitive adhesive layer was immediately sealed. Next, the vial was stored in a 40 ° C. environment for 30 minutes to extract the gas component released from the pressure-sensitive adhesive layer. The extracted gas components were qualitatively and quantified using gas chromatography-mass spectrometry (GC-MS). The measuring device and measuring conditions are described below.
<Measuring device>
GC: Thermo Scientific TRACE1310
MS: Thermo Scientific ISQ-LT
Column: TG-5MS manufactured by Thermo Scientific
<Measurement conditions>
Agitator temperature: 40 ° C
Incubation time: 30 minutes Syringe temperature: 40 ° C
Inlet temperature: 250 ° C
Oven temperature: After heating at 40 ° C for 2 minutes, it takes 26 minutes from 40 ° C to 300 ° C.
The temperature is raised at 10 ° C./min, and then heated at 300 ° C. for 3 minutes.
Gas injection amount: 1.0 mL

The gas components were identified from the obtained gas chromatography chart. As a result, n-butanol, n-butanol and n-butyl formate were detected as gas components derived from butyl acrylate. It is considered that odor is generated by these gas components.

The peak area of each detected gas component was obtained from the chart. For n-butanol, the peak area detected from the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet of Comparative Example A is defined as X, and the peak area detected from the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheets of Examples 1 to 9 and Comparative Examples 1 to 4 is defined as X. As Y, the adsorption rate was calculated by the following formula. When the value of the adsorption rate became 0 or less due to an error or the like, the adsorption rate was set to 0%. The adsorption rates of n-butanol and n-butyl formate were calculated in the same manner as above except that n-butanol and n-butyl formate were used instead of n-butanol.
Adsorption rate (%) = [100 × (XY)] / X

It is shown that the higher the adsorption rate calculated by the above formula, the more each gas component is adsorbed by the adsorbent (B), and the odor derived from the gas component is reduced.

[Thermal stability]
20 g of an ultraviolet curable hot melt adhesive was placed in a 70 mL glass bottle and heated in an oven at 130 ° C. for 168 hours. The UV-curable hot-melt adhesive after heating was evaluated for gel generation and coloring according to the following procedure.

(Thermal stability: gel generation)
The UV-curable hot-melt adhesive after heating was mixed with a spatula, and the presence or absence of gel generation was visually confirmed and evaluated according to the following evaluation criteria.
Inferior: Gel occurred.
Yu: No gel was generated.

(Thermal stability: coloring)
The UV-curable hot-melt adhesive after heating was visually observed and evaluated according to the following evaluation criteria.
Inferior: Obvious discoloration is observed, which is a problem.
Ryo: Some discoloration was observed, but this is not a problem.
Yu: No discoloration was observed.

According to the present invention, it is possible to provide an ultraviolet curable hot melt adhesive having excellent thermal stability and high and reduced generation of odor after irradiation with ultraviolet rays.

Claims (6)

A (meth) acrylic polymer (A) having an ultraviolet reactive group, an adsorbent (B), a hindered phenolic antioxidant (C) containing no nitrogen atom in the molecule, and a phosphorus-based antioxidant (D). A UV curable hot melt adhesive characterized by containing. The ultraviolet curable hot melt adhesive according to claim 1, wherein the ultraviolet reactive group of the (meth) acrylic polymer (A) is a functional group having a benzophenone skeleton. The ultraviolet curable hot melt adhesive according to claim 1 or 2, wherein the adsorbent (B) contains a physical adsorbent. The ultraviolet curable hot melt adhesive according to any one of claims 1 to 3, wherein the adsorbent (B) contains high silica zeolite. The mass ratio of the hindered phenolic antioxidant (C) to the adsorbent (B) [hindered phenolic antioxidant (C) / adsorbent (B)] is 0.01 to 5. The ultraviolet curable hot melt adhesive according to any one of claims 1 to 4. Claim 1 is characterized in that the mass ratio of the phosphorus-based antioxidant (D) to the adsorbent (B) [phosphorus-based antioxidant (D) / adsorbent (B)] is 0.01 to 5. The ultraviolet curable hot melt adhesive according to any one of 5 to 5.