JPS5933148B2 - pressure sensitive adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure sensitive adhesive composition with excellent cohesive strength, tackiness and durability.

Conventional pressure-sensitive adhesives include so-called rubber-based pressure-sensitive adhesives made mainly of natural rubber, SBR, and IR, combined with tackifying resins, softeners, fillers, etc., and acrylic acid with acrylic acid ester as the main monomer. Acrylic pressure-sensitive adhesives copolymerized with representative polar monomers are currently used for packaging,
Widely used for stationery, medical and other industrial applications.

Among these, rubber-based pressure-sensitive adhesives have the convenience of being able to adhere to a relatively large number of adherends, but they also have durability (weather resistance, heat resistance) due to the double bond in the diene part of the main component. It has the disadvantage that it cannot be used in the field of permanent or semi-permanent adhesives because of its poor properties. On the other hand, acrylic pressure-sensitive adhesives have been used in an increasing number of applications in recent years due to their excellent weather resistance. However, in the case of acrylic pressure-sensitive adhesives, the molecular weight is limited due to problems with conventional polymerization technology and solution coating technology, and at most the weight average molecular weight (
There was a need to reduce Mw) to 100 or less. Thus, although it is possible to obtain an acrylic pressure-sensitive adhesive with excellent tackiness and adhesive strength, only a very poor holding force value, ie, cohesive force, can be obtained in the adhesive tape test. Conventionally, one way to increase this cohesive force was to
The lack of cohesive strength has been compensated for by sacrificing adhesion and tackiness to some extent and intermolecular crosslinking. As a crosslinking method, a method is known in which a monomer having a functional group is copolymerized into a base polymer, and the copolymer is coated with a suitable crosslinking agent to form a covalent bond or an ionic bond. For example,
Cross-linking using acrylic acid as a functional group and an isocyanate compound as a cross-linking agent, as in Patent Publication No. 147,
There are those using acrylic acid and an epoxy compound as in Japanese Patent Publication No. 0-34578, and those using acrylic acid and an alkali metal as in Japanese Patent Publication No. 52-26765.

However, in the conventionally used acrylic copolymers, the cohesive force is very low before crosslinking, so in order to obtain the desired cohesive force, it is necessary to crosslink to a fairly high degree and reliably. It was extremely difficult to find a balance with adhesiveness, and strict conditions had to be adopted during crosslinking. The inventors of the present invention have made intensive studies to eliminate the drawbacks of conventional rubber-based and acrylic-based pressure-sensitive adhesives, and as a result, have discovered the following new pressure-sensitive adhesive composition.

The details of the invention will be described below.

The gist of the present invention is that the general formula (A-B-A)n or (A-B
) n {where A is a vinyl polymer block with a glass transition temperature of 20°C or higher, B is an acrylic ester or general formula represented by the general formula CH2-CHCOORl (wherein R1 is an alkyl group having 4 or more carbon atoms) A polymer or copolymer block containing a methacrylic acid ester represented by the formula CH2-CCOOR2 (in the formula, R2 is an alkyl group having 8 or more carbon atoms) as a constituent unit, and the content of B block is 60 to 98
% by weight of a block copolymer.

General formula (A-B-A)n or (A-B) used in the present invention
A in the block copolymer represented by n is a vinyl polymer block having a glass transition temperature (Tg) of 20°C or higher,
A vinyl polymer block having a glass transition temperature (Tg) of 50° C. or higher is more suitable.

Vinyl compounds forming this block include styrene, methyl methacrylate, α-methylstyrene, O-methylstyrene, P-methylstyrene, ethyl methacrylate, n-propyl methacrylate, acrylonitrile, vinyl acetate, etc. Styrene or methacrylate is particularly preferred for its adhesive properties and cohesive strength of the block copolymer.

A block copolymer in which the glass transition temperature (Tg) of the A block portion is less than 20°C cannot exhibit the excellent cohesive force and adhesiveness that are the characteristics of the present invention. Next B
The polymer or copolymer forming the block component is an acrylic ester having an alkyl group having 4 or more carbon atoms, such as n-butyl acrylate, IsO-butyl acrylate, Ter-butyl acrylate, isoamyl acrylate, 2-ethylhexyl acrylate, n-butyl acrylate, Octyl acrylate, lauryl acrylate, or methacrylic ester having an alkyl group having 8 or more carbon atoms,
For example, it is a polymer or copolymer block containing one or more monomers selected from the group of n-octyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate as a constituent unit. Acrylic acid,
Polar monomers such as methacrylic acid, maleic anhydride, itaconic acid, acrylamide, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate may be copolymerized.

The permissible content of (A-B-A)n or (A-B)n block copolymer in this B floc is 60 to
98% by weight, preferably 70-95% by weight
is within the range of If the B block content is less than 60% by weight, that is, if the A block content is 40% by weight or more, it is almost impossible to exhibit tackiness as a whole, and the gist of the present invention is not fulfilled.

On the other hand, when the B block component exceeds 98% by weight, that is, when the A component accounts for less than 2% by weight, the cohesive force is so low that the characteristics of the present invention cannot be exhibited.

As a method for synthesizing the block copolymer of the composition of the present invention, the following methods can be employed. A functional group at the end, such as a hydroxyl group, a carboxyl group, an isocyanate group, a thiol group,
After synthesizing a polymer having an amino group, a block copolymer can be obtained by a condensation reaction with an appropriate terminal functional group.

More specifically, when a vinyl monomer is polymerized using a polymerization initiator having a functional group, such as hydrogen peroxide or 4,4'-azobis(4-cyano-1-pentanol), a polymer having a terminal hydroxyl group, 4,4'- When a vinyl monomer is polymerized using azobis (4-cyanopentanoic acid), a polymer having a terminal carboxyl group can be obtained.
Furthermore, vinyl polymerization using mercaptoethanol as a chain transfer agent can yield a polymer having a terminal hydroxyl group, trichloroacetyl chloride to yield a terminal acid chloride group, and trichloroacetic acid to yield a polymer having a terminal carboxyl group. In addition, a polymer having the aforementioned terminal functional group, ie, a hydroxyl group, a carboxyl group, or an acid chloride group, and an excess diisocyanate compound such as 2,4-tolylene diisocyanate (TDI), methylene bisphenyl isocyanate (M
DI), etc., a polymer having terminal isocyanate groups can be obtained.

Similarly, terminal acid chlorol)F? Polymers having terminal amino groups can be synthesized by reacting the polymer with an excess of diamine, such as ethylenediamine.

A block copolymer can be obtained by reacting the terminal groups of the thus obtained polymers having terminal functional groups in an appropriate combination.

Examples of appropriate combinations include a terminal hydroxyl group and a terminal isocyanate group, a terminal carboxyl group and a terminal isocyanate group, and a terminal amino group and a terminal acid chloride group. Here, the molecular weight of each block can be controlled by polymerization conditions (amount of polymerization initiator, amount of chain transfer agent, polymerization temperature) of the terminal functional group polymer. Alternatively, m-diisopropyl benzene monoperoxide is used as a polymerization initiator, the monomer composition forming one block is vinyl-polymerized, the terminal isopropyl group is oxidized with oxygen to form a hydroperoxide, and this is used as an initiator; There is a method of obtaining a block copolymer by polymerizing monomers that form a block.

Alternatively, the block copolymer of the present invention can also be obtained by reacting a terminal carboxyl group, a terminal isocyanate group, and t-butyl hydroperoxide to form a perester, and polymerizing a second block-forming monomer with this terminal initiator. be able to.

Characterization of the obtained terminally functional prepolymer or block copolymer can be carried out by a conventionally known method.

The molecular weight and molecular weight distribution can be measured using an osmotic pressure measuring device, a vapor pressure osmometer, a light scattering measuring device, a gel permeation chromatograph (GPC), or the like. Further, the composition can be identified using an infrared absorption spectrometer, a near-infrared absorption spectrometer, an ultraviolet absorption spectrometer, a nuclear magnetic resonance spectrometer, or the like.

Furthermore, in the block copolymer synthesis method cited as an example, the yield of block polymer may not reach 100% and a block A composition polymer and a block composition (co)polymer B may exist individually. It can be separated by the following method.

That is, by first extracting the obtained copolymer with an appropriate solvent that is a good solvent for the A-block composition copolymer and a non-solvent for the B-block composition (co)polymer, a simple substance of the A-block composition polymer is extracted. , and then add B block (
By extracting with a suitable solvent that is a good solvent for the co)polymer and a non-solvent for the A-block composition polymer, the simple substance of the B-block composition (co)polymer can be removed, and the block copolymer can be isolated. be able to. Alternatively, each block composition polymer and block copolymer can be separated using a chromatograph, such as a thin layer chromatograph, using a suitable combination of developing solvent and carrier.

Furthermore, many researchers have already confirmed that it is possible to distinguish between block copolymers and random copolymers using the above method. It was possible to distinguish it from coalescence.

In the composition of the present invention, it is not necessary for the block copolymer to be 100%; the purpose of the present invention can be satisfied even if A block and B block alone are present; however, the block copolymer is entirely (co) It is preferable that the content of the polymer be 20% or more in order to fully exhibit the characteristics of the present invention.

Further, in the present invention, the pressure-sensitive adhesive composition can be prepared by using the block copolymer alone, but if necessary, a tackifier resin and a softener may be added.

Although this composition shows sufficient cohesive strength without crosslinking, it may be slightly crosslinked depending on the purpose of use. Conventionally known crosslinking techniques (chemical crosslinking, electron beam crosslinking), etc. can be used. Of course.

Pressure-sensitive adhesive tapes using this composition are prepared in the same manner as before, in the form of a solution in an appropriate solvent such as ethyl acetate, toluene, cyclohexane, methyl ethyl ketone, etc., applied to a base material such as polyester or silicone-treated release paper, and then dried with hot air. It is made by evaporating the solvent.
Furthermore, it is possible to achieve a good balance between heat-melting properties and adhesive physical properties, and an excellent adhesive tape can be obtained even when applied by a hot-metal process.
Since the pressure-sensitive adhesive composition of the present invention is constructed as described above, it has excellent cohesive force, adhesiveness, and durability.

This will be explained below using examples.

Example 1 Styrene monomer 100 was placed in a 11-separable flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen introduction tube.
V1 toluene 4007, as a polymerization initiator, 4,4'-
Azobis(4-cyano-1pentanol) (hereinafter ACP)
)2y, 0.5f7 of dodecyl mercaptan was added as a chain transfer agent, and polymerization was carried out at 80° C. for 16 hours under a nitrogen stream to obtain polystyrene with terminal hydroxyl groups.

The thus obtained toluene solution of polystyrene was added dropwise to a large amount of n-hexane while stirring to cause precipitation. After washing twice with fresh n-hexane, dry in a vacuum dryer for 6 minutes.
It was dried at 0°C for 24 hours. The molecular weight of this polymer is M
w=22000, Mw/Mn=2.51 (GPC measurement)
, the glass transition temperature was 100°C. Next, 5y of 2,4-tolylene diisocyanate (TDI) was added to 50% of toluene.
1f dissolved in 7 and equipped with a stirring device! The mixture was placed in a separable flask, heated to 40°C, and the toluene solution of the hydroxyl-terminated polystyrene obtained earlier was added dropwise through the attached dropping funnel over a period of 3 hours.

After reacting for another 4 hours after the dropwise addition, this solution was
It was dropped into hexane to collect the precipitate. It was washed twice with fresh n-hexane and dried in a vacuum dryer at 40°C for 24 hours.
Meanwhile, 2 ethylhexyl acrylate (2EHA), 65y butyl acrylate (BA
) 30t, ethyl acrylate (EA) 5f1, ethyl acetate 400f1, and ACPO. 5y was charged, and polymerization was carried out at 79° C. for 12 hours under a nitrogen stream. After the polymerization was completed, the polymer was dropped into a large amount of methanol with stirring to recover the polymer, washed with methanol, and dried in a vacuum dryer at 60° C. for 24 hours. The molecular weight of the obtained polymer was Mw=260000, . Mw/Mw-3.
It was 11. Next, this terminal hydroxyl group (2EHA-BA-
EA) Copolymer 100y was dissolved in toluene 4007, charged into a 11 separable flask, and after adding 0.57 of dibutyltin dilaurate, the temperature was raised to 60°C.

Further, a toluene solution (polymer concentration: 40% by weight) 507 of terminal isocyanate polystyrene prepared earlier was added dropwise over 1 hour.

After the dropwise addition was completed, the flask was kept at 60° C. and the reaction was further carried out for 4 hours to obtain a block copolymer. This block copolymer solution was applied to a polyester film subjected to anchor treatment using a knife coater, and then dried with hot air at 90° C. for 10 minutes to prepare an adhesive tape.

When the adhesive physical properties of this adhesive tape were measured, the SP adhesive strength was 9507/15, the holding power was 2000 minutes, and the ball tack was 11, which were very excellent. Furthermore, S
P adhesion strength was determined by lightly pasting a 15 cTn wide tape on a stainless steel plate, pressing it with a 2 kg roller 5 times and leaving it for 20 minutes.
! /Mi! This is the force when peeling off at a speed of l.

In addition, the holding force was expressed as the time required for the tape to slip off when the tape was pressure-bonded to a stainless steel plate with an area of 25 m 1 L x 25 mm and a load of 1 kg was applied to the bottom end of the tape (at 20° C.).

Also, the ball tack is J. This is based on the DOw method.

Examples 2, 3, and 4 In the same manner as in Example 1, styrene, toluene, and ACPl dodecyl mercaptan in the predetermined amounts shown in Table 1 were charged into a reactor and polymerized at 80° C. for 16 hours to synthesize polystyrene with terminal hydroxyl groups.

After polymerization, the product was repeatedly purified by reprecipitation and washing, and then reacted with 2,4-tolylene diisocyanate (TDI) to obtain terminal isocyanate polystyrene. Meanwhile, in the reactor, predetermined amounts of 2EHA, BA. EA monomer and a polymerization initiator ACPI ethyl acetate were charged and polymerization was carried out at 75° C. for 25 hours to synthesize a terminal hydroxyl group copolymer.

After repeated purification by reprecipitation washing, this terminal hydroxyl group copolymer 100y was redissolved in toluene and reacted with terminal isocyanate polystyrene 20y in the same manner as in Example 1 to obtain a block copolymer solution.

An adhesive tape was prepared by coating an anchor-treated polyester film to a film thickness of 50 μm and drying, and its adhesive properties were measured. Compositions and results are shown in Tables 1, 2, and 3. Example 5 A poly(methyl methacrylate-acrylic acid ester) block copolymer was synthesized by carrying out the same procedure as in Example 4 except that methyl methacrylate 1007 was used instead of styrene 1007.

The SP adhesive strength of the adhesive tape made using this adhesive is 8
70y/15m77! The adhesive properties were very good, with a holding power of 100 minutes and a ball tack of 12. Examples 6 and 7 Styrene monomer 1007 and diisopropylbenzene hydroperoxide 2 as a polymerization initiator were placed in a 11-separable flask equipped with a stirrer, a thermometer, and a nitrogen inlet tube.
Toluene 300f7 was charged as a solvent, and the reactor was heated to 90°C.

Flow nitrogen gas into the reactor and expel it to the air in the system.
Polymerization was carried out for 15 hours at °C. Next, the reaction solution was precipitated and recovered in a large amount of methanol, and then purified using toluene as a solvent and methanol as a precipitant by repeating 5 redissolutions and reprecipitations, followed by vacuum drying at 60° C. for 12 hours. Next, a 5% by weight cumene solution of this polymer was prepared and charged into a reactor.8
The temperature was raised to 0° C., and oxygen gas was bubbled into the reaction solution for 8 hours.

After the reaction was completed, the mixture was dropped into a large amount of methanol and precipitated, and purified by repeating redissolution and reprecipitation in a toluene (solvent)-methanol (precipitant) system.

Through this operation, the terminal isopropyl group, which is an initiator fragment, was converted to hydroperoxide with oxygen to obtain terminal peroxide polystyrene.

Next, a block copolymer was synthesized by polymerizing specified monomers using the terminal hydroperoxide of this polystyrene as an initiator.

That is, the above-mentioned terminal hydroperoxide polystyrene, 2-ethylhexyl acrylate, butyl acrylate, acrylic acid, and ethyl acrylate monomers and a predetermined amount of ethyl acetate as a solvent were charged into a four-separable flask, and polymerization was carried out at 60° C. for 24 hours under a nitrogen stream. I went to

This reaction solution was then dropped dropwise into a large amount of methanol to precipitate it, and was further purified by repeating redissolution and reprecipitation three times in an ethyl acetate (solvent)-methanol (precipitant) system. The thus obtained block copolymer was separated and identified using thin layer chromatography and was found to be a poly(styrene-acrylic acid ester) block copolymer.

Next, a 40% by weight solution of ethyl acetate as a sample was prepared and applied onto a polyester film in the same manner as in Examples 1 to 4 to produce an adhesive tape, and the adhesive properties were measured.

The results are summarized in Table 4.

Claims (1)

[Claims] 1 General formula (A-B-A)_n or (A-B)_n {where A is a vinyl polymer block with a glass transition temperature of 20°C or higher, B is the general formula CH_2=CHCOOR_1( In the formula R
_1 is an alkyl group with a carbon number of 4 or more) or methacrylic acid ester represented by the general formula ▲ Numerical formula, chemical formula, table, etc. are available ▼ (in the formula, R_2 is an alkyl group with a carbon number of 8 or more) 1. A pressure-sensitive adhesive composition comprising a block copolymer represented by a polymer or copolymer block containing an acid ester as a constituent unit} and having a B block content of 60 to 98% by weight. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the vinyl polymer block of A is polystyrene. 3. The pressure-sensitive adhesive composition according to claim 1, wherein the vinyl polymer block of A is polymethyl methacrylate. 4. The pressure-sensitive adhesive composition according to claim 1, 2, or 3, wherein the B block is a copolymer containing 2-ethylhexyl acrylate and butyl acrylate as constituent units.