JPS5931547B2 - pressure sensitive adhesive composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure-sensitive adhesive composition that has excellent cohesive strength at high temperatures as well as adhesive strength at room and low temperatures.

In general, pressure-sensitive adhesives are sensitive to the effects of temperature: as the temperature rises, the adhesive strength increases, but the cohesive strength decreases, and conversely, as the temperature decreases, the cohesive strength increases, but the adhesive strength decreases. It has the property of being accepted.

Therefore, considering the temperature difference in the workplace, it can be said that the most required performance for a pressure-sensitive adhesive is high cohesiveness in the hot summer months and high tackiness in the low temperature winter months. However, cohesiveness and adhesiveness have contradictory properties, and it is not easy to exhibit both properties at the same time. For example, for rubber-based pressure-sensitive adhesives, methods include post-crosslinking using a rubber with a large molecular weight using an appropriate crosslinking method in order to increase the cohesive force at high temperatures, and methods using highly aromatic resins as tackifiers. is adopted, but although the above purpose is achieved, on the other hand,
A major drawback is that the adhesive strength decreases. Note that the cohesive force here is referred to as holding power and is evaluated based on creep resistance, and the adhesive force is evaluated based on peel stress from an adherend.

Styrene polymer blocks (abbreviated as S) and isoprene polymers (abbreviated as I) that have appeared in recent years -
A block copolymer containing 5-1-5- as a constituent unit is known, for example, from Japanese Patent Publication No. 17037/1983, and has excellent properties as a thermoplastic rubber, and is also useful as a pressure-sensitive adhesive. However, it is very interesting. However, although this type of block copolymer has a high level of cohesive strength at high temperatures, its adhesive strength at room temperature or below room temperature is not necessarily satisfactory. In other words -5-1-5
- a block copolymer having a constituent factor of, for example, 5
-1-5, 5-1-5-1 or 1-5-1-5-1
Although it has excellent properties as a thermoplastic rubber, it has disadvantages as a pressure-sensitive adhesive. In other words, among these copolymers, those that are sufficiently flexible and have high adhesive strength at room temperature and below will have a low cohesive strength at high temperatures, and conversely, those that have high cohesive strength at high temperatures will have a low cohesive strength at room temperature and below. Does not exhibit sufficient adhesion. The block copolymer (1-S-1) used in the present invention has stronger and more elastic properties in the polymer state than block copolymers containing -S-1-S- as a constituent unit. It has been generally considered unsuitable as a polymer for pressure-sensitive adhesives because of its markedly inferior properties.

However, the present inventors limited the block copolymer known as I-S-1 to a specific one and combined it with a specific tackifier resin. It was possible to obtain a pressure-sensitive adhesive composition with high adhesive strength and little change in performance due to temperature. That is, the present invention provides (4) -S-1 (herein, I is an isoprene polymer block, S is a vinyl aromatic hydrocarbon polymer block, the molecular weight of the block copolymer is 30,000 to 400.0001 (the ratio of S block to the total molecules is 7 to 60% by weight), 013) aliphatic hydrocarbon resin, This is a pressure-sensitive adhesive composition containing 10 to 250 parts by weight of a tackifier consisting of one or more of aliphatic hydrocarbon resins, terpene resins, and rosin resins.

The block copolymer 1-S-1, which is one of the important components constituting the pressure-sensitive adhesive composition of the present invention, is composed of three components: an isoprene polymer, a vinyl aromatic hydrocarbon polymer, a block, and an isoprene polymer. A block copolymer consisting of the following elements.

Here, the vinyl aromatic hydrocarbon polymer block can be industrially inexpensive as long as it has a glass transition point of 35°C or higher.
Polystyrene is most preferred because it is also easily available. Examples of vinyl aromatic hydrocarbons that can be used include α-methylstyrene, vinyltoluene, and vinylnaphthalene. Note that the isoprene polymer block is limited to isoprene polymers. With polymers other than isoprene, pressure-sensitive adhesives having sufficient adhesive strength and cohesive strength as in the present invention cannot be obtained. Further, the molecular weight of the block copolymer is 30,000 to 400,00.
0, particularly preferably 60,000 to 250,000. If the molecular weight is too low, cohesive force and instantaneous adhesion (tack) will decrease, which is undesirable. Furthermore, if the molecular weight is too high, the adhesive strength will decrease and the viscosity will become too high, causing problems in performance as an adhesive as well as problems in terms of workability. The molecular weight here refers to the number average molecular weight, and is measured by conventional methods such as osmotic pressure method and gel permeation chromatography method. The ratio of the vinyl aromatic hydrocarbon polymer (S) in the 1-S-1 block copolymer to the total molecule, ie, the content of S, is preferably in the range of 7 to 60% by weight, particularly 12 to 35% by weight.

If the S content is too high, the adhesive strength will be greatly reduced, especially at room temperature or below, and the adhesive will no longer be satisfactory as a pressure-sensitive adhesive. On the other hand, if the S content is too low, the cohesive force will drop significantly and the adhesive will not exhibit sufficient properties as a pressure-sensitive adhesive. The I-S-1 block copolymer used in the present invention is produced by a known method of polymerizing each monomer in a suitable solvent in the presence of a catalyst such as metallic lithium or organic lithium.

Most preferred solvents are inert hydrocarbons. Examples of organic lithium include methyllithium, ethyllithium, propyllithium, α-naphthyllithium, methyldilithium, trimethyldilithium, dibutadienyldilithium, and disterenyllithium. Typical examples of methods for producing block copolymers include the following method.

(1) Method of first polymerizing isoprene monomer, then adding and polymerizing vinyl aromatic hydrocarbon monomer, and finally adding and polymerizing isoprene monomer (2) Coexistence of isoprene monomer and vinyl aromatic hydrocarbon monomer (3) A method in which isoprene is polymerized using a dilithium-based catalyst, and then a vinyl aromatic hydrocarbon is added and polymerized (4) Isoprene monomer and vinyl aromatic carbonization In method (2), in which the hydrogen monomers are separately polymerized and the blocks are bonded using a suitable coupling agent, both monomers coexist, but due to their copolymerization properties, the isoprene monomer is substantially not polymerized. As a result, a block copolymer which meets the purpose of the present invention can be obtained.

Note that the molecular weights of the isoprene polymers at both ends of the block copolymer do not necessarily have to be equal. Another important component of the pressure sensitive adhesive composition of the present invention is the tackifying resin.

In other words, the 1-S-1 block copolymer alone or the tackifier resin alone does not exhibit performance as a pressure-sensitive adhesive, but the superior performance is only achieved when the two are used in combination. It is important to combine a tackifier based on a specific tackifier with the I-S-1 block copolymer. Examples of the tackifying resin used in the present invention include aliphatic hydrocarbon resins, alicyclic hydrocarbon resins, rosin resins, and terpene resins.
When a chroman-indene resin, a phenolic resin, and an aromatic hydrocarbon resin are used in combination with the I-S-1 block copolymer, the excellent pressure-sensitive adhesive performance characteristic of the present invention is not exhibited. Examples of aliphatic and alicyclic hydrocarbon resins include olefin polymers, diolefin polymers, isoprene, piperylene polymers, and hydrogenated petroleum resins (Polymer Processing Special Issue 11, 1975, No. 114). Page, Polymer Processing Special Issue 8, 1971, page 105). Examples of rosin-based resins include pentaerythronyl esterified rosin, glycerin esterified rosin, and hydrogenated products thereof (Kobunshi Kako Separate Issue 8, page 105). An example of terpene resin is α
- Pinene polymers, β-pinene polymers, α,β monomixed pinene polymers, etc. (Polymer processing ditto). These resins may be used alone or in combination of two or more. The amount of these resins used is preferably 10 to 250 parts by weight per 100 parts by weight of the I-S-1 block copolymer. More preferably, it is 30 to 150 parts by weight. In addition, if the main component is aliphatic hydrocarbon resin, alicyclic hydrocarbon resin, rosin resin, or terpene resin,
Resins other than these may be mixed. However, in this case, in order to obtain excellent performance, it is necessary to keep the mixing ratio below 50% by weight. Appropriate amounts of anti-aging agents, fillers, plasticizers, softeners, etc. may be added to the pressure-sensitive adhesive composition of the present invention, if necessary.

These additives can be dissolved in the solvent of the pressure-sensitive adhesive and mixed in solution form, or they can be mixed in a kneader or internal mixer in the presence or absence of a solvent and with or without heating. mixed. They may also be mixed in an aqueous dispersion system. Furthermore, other different types of polymers such as ethylene-propylene copolymers,
Polyethylene, polypropylene, polyisoprene, acrylic ester copolymer, styrene-butadiene copolymer, styrene-isoprene-styrene copolymer, ethylene monovinyl acetate copolymer, polyvinyl acetate, or the like may be mixed. Examples of the substrate for the pressure-sensitive adhesive of the present invention include cellophane paper, kraft paper, high-quality paper, coated paper, Japanese paper, cloth, polyvinyl chloride, polypropylene, polyester, and aluminum foil.

Examples of pressure sensitive adhesives include adhesive tapes and adhesive labels, and the pressure sensitive adhesive compositions of the present invention are particularly suitable for adhesive labels at or below room temperature. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Using a 51 pressure reactor, n-
Isoprene was first polymerized at 50° C. for 3 hours in the presence of a butyllithium catalyst, and then a predetermined amount of styrene monomer was added and polymerized while stirring at 50° C. for 3 hours.

Next, the same amount of isoprene as the initially added isoprene monomer was added, and the polymerization was continued for an additional 3 hours. The solution after polymerization is dropped into a large amount of methanol to precipitate the copolymer,
It was taken out and dried. The obtained I-S-1 block copolymer is shown in Table 1. Note that samples with different styrene contents were adjusted by changing the amounts of styrene monomer and isoprene monomer added, and samples with different molecular weights were adjusted by changing the amount of catalyst. 1) Evaluation by infrared absorption spectroscopy 2) Evaluation by gel permeation chromatography Using the above ISI, a toluene solution of a pressure-sensitive adhesive composition was prepared according to the formulation shown in Table 2.

ISI-1 to 4 were completely dissolved in 150 parts by weight of toluene over a day and night, but ISI-5, which has a high molecular weight, dissolved in 150 parts by weight of toluene.
00 parts by weight of toluene and two days and nights were required for complete dissolution. The toluene solution thus obtained was coated on cellophane to a thickness of about 30 microns and dried to produce cellophane-based pressure-sensitive adhesives A1-5. 1) YSPxll5O manufactured by Yasushi Oil Co., Ltd. 2) 2,2-methylenepis(4-methyl-6-t-butylphenol) The cohesive force and adhesive force of this pressure-sensitive adhesive were evaluated using the following method, and the results are shown in Table 3. .

(1) Cohesive strength (creep resistance performance): Cellophane base pressure sensitive adhesive 20m/m vertically, 20mm horizontally
The adhesive surfaces were pressed together using m/m sized surfaces, the upper end of one cellophane adhesive was fixed, and a load of 1 kg was suspended from the lower end of the other cellophane adhesive in an atmosphere of 40°C. A creep test was conducted and the time taken to fall was measured.

The longer this time, the greater the cohesive force. (2) Adhesive strength: Based on the 180 degree constant speed peel test specified in JIS.

Width 10m/m, length 180mm from cellophane base pressure sensitive adhesive
Cut out a test piece of m/m, and the length of the test piece is 110 m.
/m part was crimped with a roller to a 1m/m thick polyethylene plate (crimping speed 300m/m/min, 1 reciprocation), then the loose part was folded back 180 degrees and the tip was subjected to an Instron tensile test. The polyethylene plate is gripped at the top of the machine and the polyethylene plate is gripped at the bottom of the machine, and the peeling stress when peeled off at a speed of 300 m/m/min is defined as the adhesive strength. Note that the temperature during the test is 22°C. A cellophane-based pressure sensitive adhesive using ISI-2 with a molecular weight of 131,000 and a styrene content of 20.4% has both excellent cohesive strength at high temperatures and excellent adhesive strength at room temperature. However, those with too high styrene content (ISI-3) or those with too high molecular weight (ISI-5) do not have a satisfactory level of adhesive strength, and those with too low styrene content (SI-1)
, or one whose molecular weight is too low (ISI-4) also has extremely low cohesive force.

Example 2 An I-S-1 block copolymer (ISI-6) having a styrene content of 24.9% and a molecular weight of 102,0000 was obtained in the same manner as in Example 1.

On the other hand, the solvent, catalyst, etc. were the same as in Example 1, but a predetermined amount of styrene monomer was first added and polymerized, then isoprene monomer was added and polymerized, and finally, styrene monomer was added again at the beginning of the polymerization. The same amount was added and polymerized. The copolymer obtained by these methods was
It is shown in Table 4 together with I-6. The copolymer thus obtained was made into a pressure-sensitive adhesive composition according to the formulation shown in Table 5, dissolved in toluene, coated on high-quality paper, and then dried to form a pressure-sensitive adhesive composition (A) based on high-quality paper. -6 to 8) were produced. 1) YSPxlOOO2) 2,5-di-t-butylhydroquinone Table 6 shows the results of evaluating the performance of these adhesives.

Pressure-sensitive adhesives using ISI-6 have both excellent high-temperature cohesive strength and excellent adhesive strength, while those using SIS-1 have excellent high-temperature cohesive strength but insufficient adhesive strength. It has several points. Regarding SIS-2, an attempt was made to improve the adhesive strength by lowering the styrene content, but although the rate of improvement was small, the high-temperature cohesive strength decreased significantly. Using the pressure-resistant reactor of Example 351, using cyclohexane as a solvent and n-butyllithium as a catalyst, the polymerization temperature was 60.
The following three types of block copolymers were prepared at .degree.

In the first step, the same amount of styrene monomer and isoprene monomer were added simultaneously and polymerized for 2 hours, then in the second step, the same amount of isoprene monomer as in the first step was added and polymerized, and I-S- A 1-bution copolymer (ISI-7) was obtained.

On the other hand, in the first step, the same amount of styrene monomer and isoprene monomer are added and polymerized simultaneously, and then in the second step, the same amount of styrene monomer and isoprene monomer as in the first step is simultaneously added and polymerized. A 1-S-1-S block copolymer (ISIS-1) was obtained. Further ISI
Perform the first and second stage polymerization operations in the same manner as S-1,
Subsequently, in the third step, the same amounts of styrene monomer and isoprene monomer as in the first and second steps were added and polymerized to obtain a block copolymer (SISIS-1). The molecular weight of each block copolymer is approximately 80,000 and the styrene content is approximately 30%. A toluene solution containing the pressure-sensitive adhesive shown in Table 7 was prepared, and the solution was coated on high-quality paper and dried.
-9 to 11) were produced.

1) YSP×1150 2) Pressure-sensitive adhesive using Mitsui Petrochemical's Hiretsu T-100ISI-7 has excellent high-temperature cohesive strength and adhesive strength, but The performance of adhesives using block copolymers containing constituent factors is unsatisfactory (Table 8).

Example 4 An isoprene-styrene-isoprene block copolymer (ISI-8) was produced by the same polymerization method as in Example 1 except for the method of adding monomers.

That is, first, isoprene monomer was added and polymerized, then styrene monomer was added and polymerized, and finally, isoprene monomer equivalent to half the amount of the isoprene monomer initially added was added and polymerized. The molecular weight of ISI-8 is 112,0
00 and its styrene content is. It was 25.2%. A toluene solution of a pressure-sensitive adhesive composition was prepared using the block copolymer according to the formulation shown in Table 9. The toluene solution was coated on cellophane and dried to obtain a cellophane-based pressure-sensitive adhesive.

The performance of these pressure sensitive adhesives was evaluated according to the method of Example 1.
The measured results are shown in Table 10. A-12-15, which contains the tackifier resin selected in the present invention, has both excellent cohesive strength at high temperatures and adhesive strength at room temperature, but the resin component is aromatic hydrocarbon resin or phenolic resin. Cellophane-based pressure-sensitive adhesives, which are mainly composed of , have low adhesive strength.

Example 5 Table 11 using ISI-6 and SIS-1 of Example 2
The pressure-sensitive adhesive formulations (A-18, 19) shown in (A-18, 19) were prepared by heating and dissolving them at 160° C. in a nitrogen stream in a dissolving tank equipped with a stirrer.

The heated melt was coated on a polyester film and cooled to obtain a pressure-sensitive adhesive having a polyester film base.

Regarding A-18 and 19, the cohesive force at high temperature was measured by the same method as shown in Example 1, and the adhesive force was measured at a low temperature of 5°C.

A-18 using ISI-6 has excellent low-temperature adhesion and high-temperature cohesion, but A-18 using SIS-1
-19 has high high-temperature cohesive strength but very low low-temperature adhesive strength.

Claims (1)

[Scope of Claims] 1 (A) I-S-I (herein, I is an isoprene polymer) based on 100 parts by weight of a block copolymer composed of isoprene and vinyl aromatic carbon hydrogen and whose general formula is represented by the following formula. The combined block, S is a vinyl aromatic hydrocarbon polymer block, the molecular weight of the block copolymer is 30,000 to 400,000, the proportion of the S block to the entire molecule is 7 to 60% by weight), (B) A pressure-sensitive adhesive composition containing 10 to 250 parts by weight of a tackifier made of one or more of aliphatic hydrocarbon resin, alicyclic hydrocarbon resin, terpene resin, and rosin resin. thing.