JPH11263957A - Pressure-sensitive adhesive composition and adhesive sheets coated with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive composition which can be prepared in a high solid content concentration in a low viscosity and has excellent adhesive characteristics satisfying an adhesive force and a cohesive force. SOLUTION: This pressure-sensitive adhesive composition comprises as the main component a polymer of monomers containing an acrylic monomer of the formula: CH2 =C(R<1> )COOR<2> (R<1> is H or methyl group; R<2> is a 2-14C alkyl group) in an amount of >=50 wt.%, and having a number-average molecular weight of >=60,000, a weight-average molecular weight of >=100,000 and a functional group introduction rate of >=50% to the molecular chain ends of the polymer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-sensitive adhesive composition which can be adjusted to a high solid content, and to tape- or sheet-like adhesive sheets using the same.

[0002]

2. Description of the Related Art A pressure-sensitive adhesive is prepared by mixing a tackifying resin or a crosslinking agent with a polymer solution, and then applying the resulting mixture on a support and drying it to form a tape or sheet. Adhesive sheets such as shapes. In recent years, it has been demanded to reduce the amount of solvent used as much as possible from the viewpoint of drying efficiency, energy saving, and work environment.

[0003] In response to this demand, if the polymer solution is made to have a high solid content, the viscosity of the polymer solution increases, which causes a problem in workability when applying the solution on a support and a roughened surface to be applied. Causes inconvenience. Attempts have been made to lower the molecular weight of the polymer to lower the viscosity and increase the solids concentration.However, in this case, the cohesive strength after cross-linking is insufficient. There are problems such as shortage.

[0004]

SUMMARY OF THE INVENTION In view of such circumstances, the present invention can be adjusted to a low viscosity and a high solid content.
In addition, it is an object of the present invention to obtain a pressure-sensitive adhesive composition having excellent adhesive properties, particularly satisfying adhesive strength and cohesive strength, and adhesive sheets thereof.

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above-mentioned object, and as a result, when a configuration was introduced in which a predetermined amount of a functional group was introduced into the molecular chain terminal of the polymer, Even when a polymer solution having a low viscosity and a high solid content is reduced by reducing the molecular weight of the polymer, if this is cross-linked with a cross-linking agent or the like, a cross-linked polymer having a long molecular chain length can be generated, thereby immediately improving the adhesive properties. The present inventors have found that a pressure-sensitive adhesive composition and an adhesive sheet satisfying adhesive force and cohesive force can be obtained, and have completed the present invention.

That is, the present invention provides a compound represented by the general formula: CH ₂ ＝ C
(R ¹ ) a monomer containing 50% by weight or more of an acrylic monomer represented by COOR ² (wherein R ¹ is hydrogen or a methyl group, and R ² is an alkyl group having 2 to 14 carbon atoms) A pressure-sensitive adhesive characterized in that the polymer has a number average molecular weight of 60,000 or more, a weight average molecular weight of 100,000 or more, and a functional group introduction rate of a molecular chain terminal of 50% or more. The composition (Claim 1), in particular, the pressure-sensitive adhesive composition having the composition described above containing 0.05 to 7 parts by weight of a crosslinking agent per 100 parts by weight of the polymer as the main agent (Claim 2) is there. The present invention also relates to an adhesive sheet having a pressure-sensitive adhesive composition having the above-mentioned composition on a support, and an adhesive layer obtained by crosslinking the adhesive composition.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The acrylic monomer in the present invention has the general formula: CH ₂ ＣC (R ¹ ) COOR ² (R ¹ is a hydrogen or methyl group, R ² is an alkyl group having 2 to 14 carbon atoms) Which is a monomer represented by the formula: butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, isononyl acrylate, etc.
Acrylic esters having two alkyl groups are preferably used. Along with this acrylic monomer, a modifying monomer copolymerizable therewith may be used in combination.
In order to obtain good adhesive properties, the acrylic monomer is 50% by weight or more, preferably 70% by weight of the whole monomer.
As described above, the content is more preferably 80% by weight or more. Further, it is desirable to select the monomer composition so that the glass transition point of the polymer is 250K or less.

The above-mentioned modifying monomers include vinyl acetate, vinyl propionate, styrene, (meth) acrylamide, mono- or diesters of maleic acid, N-methylol (meth) acrylamide, glycidyl (meth) acryle -N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth)
Examples include acrylamide, 2-hydroxypropyl (meth) acrylate, (meth) acrylic acid, oligoester (meth) acrylate, and ε-caprolactone (meth) acrylate.

In the present invention, a monomer containing 50% by weight or more of such an acrylic monomer has a number average molecular weight of 60,000 or more, a weight average molecular weight of 100,000 or more, A polymer having a group introduction ratio of 50% or more is produced. Here, the “number average molecular weight” and “weight average molecular weight” are measured by a gel permeation chromatography (GPC method). The term “functional group introduction rate at the molecular chain end” means that the amount of the polymer having a functional group introduced at the molecular chain end is 50% or more based on the whole polymer, and the GPC method. Is calculated from the number average molecular weight according to the above formula and the amount of functional group at the end of the molecular chain in nuclear magnetic resonance spectrum (NMR).

The functional group introduction rate at the end of the molecular chain is 5
According to a polymer of 0% or more (usually up to 90%), the molecular weight of the polymer is reduced as described above, and even when a polymer solution having a low viscosity and a high solid content is subjected to a crosslinking treatment, Pressure-sensitive adhesive composition that has a high degree of establishment of a reaction between molecular chain ends and produces a crosslinked polymer having a long molecular chain length, and as a result, has excellent adhesive properties, and particularly satisfies adhesive strength and cohesive strength Is obtained. On the other hand, in the case of a polymer having a functional group introduction rate of less than 50% at a molecular chain terminal, it is difficult to form a crosslinked polymer having a long molecular chain as described above by the crosslinking treatment, and the pressure-sensitive polymer has good adhesive properties. It becomes difficult to obtain an adhesive composition.

The functional group introduction rate at the terminal of the molecular chain is 50%.
Even with the above, if the molecular weight of this polymer is too low, it is still difficult to produce the above-mentioned crosslinked polymer.
For this reason, as described above, the polymer having a functional group introduction rate at the molecular chain terminal of 50% or more used in the present invention may have a number average molecular weight of 60,000 or more and a weight average molecular weight of 100,000 or more. Needed. As the upper limit of the molecular weight, the molecular weight can be set as high as possible as long as a high solid content can be obtained at a low viscosity that does not hinder the coatability, and is appropriately determined according to the composition of the polymer or the type of the solvent. . Usually, the number average molecular weight is 150,000 or less and the weight average molecular weight is 40
It is better to be less than 10,000.

In the present invention, the polymer having the specified functional group introduction rate and molecular weight at the molecular chain end is, for example, a monomer containing 50% by weight or more of the acrylic monomer described above. By performing solution polymerization in the presence of a chain transfer agent having the above, and at that time, considering the solubility of the above chain transfer agent, the chain transfer constant, the consumption rate, etc., select appropriate polymerization conditions, especially the polymerization system The chain transfer agent can be produced by adding the chain transfer agent by a dropping method with the progress of polymerization so as to make the concentration of the chain transfer agent substantially constant from the beginning to the end of the polymerization.

The above-mentioned chain transfer agent having a functional group is for introducing a functional group into a molecular chain terminal of a polymer, and is, for example, 2-mercaptoethanol, 1-mercapto-2-propanol. , 3-mercapto-1-propanol, chain transfer agents having a hydroxyl group such as p-mercaptophenol, carboxyls such as mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid and 2-mercaptonicotinic acid A chain transfer agent having a group is used. These vary depending on solubility and chain transfer constant, but generally, per 100 parts by weight of the monomer,
It is used in a ratio of 0.01 to 5 parts by weight. If too much,
In some cases, the molecular weight may be too low, or an unreacted chain transfer agent may remain as an impurity to inhibit the crosslinking reaction. If the molecular weight is too low, problems such as incompatibility of adhesive strength and cohesive strength may easily occur.

The pressure-sensitive adhesive composition of the present invention comprises, as a main component, a polymer whose functional group introduction rate and molecular weight at the above-mentioned molecular chain are respectively specified, and usually has a solid content of 40% by weight or more, preferably 50% by weight or more, more preferably 60% by weight
It is handled as a polymer solution having a high solid content of not less than 70% by weight (usually up to 70% by weight). Further, the solution viscosity at this time is 500 poise or less at room temperature, preferably 300 poise or less, more preferably 200 poise or less (usually 5 poise) without impairing coatability and other handling properties.
It should be adjusted to 0 poise).

Such a pressure-sensitive adhesive composition may contain various additives, such as tackifier resins, fillers, and pigments, which are blended with the general pressure-sensitive adhesive composition, if necessary. Can be. In particular, as the tackifying resin, if the tackifying resin having a functional group of the same type as the functional group introduced into the molecular chain terminal of the polymer is included, since the effect of increasing the reaction rate of the terminal functional group is obtained, preferable.

The pressure-sensitive adhesive composition of the present invention is finally subjected to a crosslinking treatment so as to exhibit excellent adhesive properties satisfying adhesive strength and cohesive strength. The cross-linking treatment increases the molecular chain length of the polymer and appropriately forms a cross-linked structure due to the reactivity of the functional group introduced at the terminal of the molecular chain.To achieve this purpose, usually, When preparing the pressure-sensitive adhesive composition, a polyfunctional compound that reacts with a functional group at the molecular chain end of the polymer is preferably contained in advance as a crosslinking agent. In this case, a tin compound or the like may be contained as a catalyst together with the above-mentioned crosslinking agent.

When the functional group of the polymer is a hydroxyl group, tolylene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate,
Polyisocyanate compounds such as hexamethylene diisocyanate, 1,5-naphthalenediisocyanate, and adducts of polyvalent alcohol and diisocyanate are used. When the functional group of the polymer is a carboxyl group, aziridine compounds, diamine compounds, alicyclic polyisocyanate compounds such as hexamethylene diisocyanate and isophorone diisocyanate are used. The amount of these crosslinking agents used is determined according to the amount of the functional group of the polymer, but is usually 0.05 to 100 parts by weight of the polymer.
It is preferable to use 7 parts by weight. If too much, the adhesive strength will decrease,
If the amount is too small, the cohesive strength becomes insufficient, and both are not preferred.

In the pressure-sensitive adhesive composition of the present invention, if the functional groups introduced at the molecular chain terminals of the polymer react by themselves upon activation of heat or water, etc. It is not necessary to intentionally include a crosslinking agent such as
Even in a system without this cross-linking agent, by activation of heat or water,
By cross-linking the functional groups, a cross-linked polymer having a long molecular chain and exhibiting the same effect as described above can be produced.

In the present invention, such a pressure-sensitive adhesive composition is coated on a support, dried and subjected to the above-mentioned crosslinking treatment, so that one side or both sides of the support have a thickness of one side. Adhesive sheets such as tapes and sheets having a cross-linked adhesive layer usually having a thickness of 10 to 200 μm are obtained. As the above-mentioned support, various plastic films, papers, laminated papers, non-woven fabrics, metal foils, foam sheets and the like are used.

[0020]

Next, an embodiment of the present invention will be described in more detail. Hereinafter, “parts” means “parts by weight”.

Example 1 A reaction vessel equipped with a cooling pipe, a nitrogen introduction pipe, a thermometer and a stirrer was charged with 66 parts of ethyl acetate as a solvent, 45 parts of 2-ethylhexyl acrylate, 50 parts of butyl acrylate, and 5 parts of acrylic acid. , 2,2'-azobisisobutyronitrile 0.1.
1 part and 0.03 part of 2-mercaptoethanol were added, and after purging with nitrogen, the temperature was raised to carry out a polymerization reaction. Sampled during the polymerization, the consumption of 2-mercaptoethanol was measured by gas chromatography, and the remaining monomer was dropped by the dropping method so that 2-mercaptoethanol had the same concentration as in the initial stage of polymerization. It was additionally polymerized to make the total amount of 2-mercaptoethanol used 0.1 part. The polymerization temperature was kept at 60 ° C. for 4 hours from the start and then at 70 ° C. for 2 hours.

In this way, when the weight average molecular weight is 15
A polymer having a number average molecular weight of 70,000 (in terms of polystyrene by the GPC method) and an introduction ratio of hydroxyl groups at molecular chain terminals of 60% is produced, and a solution containing this polymer at 60% by weight (viscosity at room temperature: 100 poise). To 100 parts of the solid content of the polymer solution, 3.2 parts of a trimethylolpropane tolylene diisocyanate adduct and 0.032 part of dibutyltin laurate were added, and a pressure-sensitive adhesive composition was added. did. This was applied on a polyester film having a thickness of 25 μm so that the thickness after drying became 50 μm, and heat-treated at 120 ° C. for 3 minutes to prepare an adhesive tape.

Example 2 80 parts of 2-ethylhexyl acrylate and 15 parts of ethyl acrylate were used as a solvent with 33 parts of toluene and 33 parts of ethyl acetate as a solvent.
Part, acrylamide 5 parts, 2,2'-azobisisobutyronitrile 0.1 part, 2-mercaptoethanol 0.0
Using 9 parts (total amount), a polymer having a weight average molecular weight of 240,000, a number average molecular weight of 120,000, and a hydroxyl group introduction ratio of molecular chain terminal of 56% was produced in the same manner as in Example 1. A solution (viscosity at room temperature: 130 poise) containing 60% by weight of the union was obtained. 2.6 parts of hexamethylene diisocyanate adduct of trimethylolpropane, 0.026 parts of dibutyltin laurate and 15 parts of terpene-modified phenol were added to 100 parts of the solid content of the polymer solution. Thus, a pressure-sensitive adhesive composition was obtained. Using this, an adhesive tape was produced in the same manner as in Example 1.

Example 3 Using 66 parts of ethyl acetate as a solvent, isononyl acrylate 9
Using 0 part, acryloylmorpholine 10 parts, 2,2'-azobisisobutyronitrile 0.1 part, and thioglycolic acid 0.05 part (total amount), the weight average molecular weight was A polymer having a molecular weight of 220,000, a number average molecular weight of 100,000, and a carboxyl group introduction ratio at a molecular chain terminal of 55% was produced, and a solution containing this polymer at 60% by weight (viscosity at room temperature: 120 poise) was obtained. Was. To this polymer solution was added 0.05 part of tetraglycidyl meta-xylene diamine per 100 parts of the solid content to obtain a pressure-sensitive adhesive composition. Using this, an adhesive tape was produced in the same manner as in Example 1.

Example 4 Tolylene diisocyanate of trimethylolpropane was added to 100 parts of the solid content of the polymer solution obtained in Example 1.
Then, 3.2 parts of an adduct, 15 parts of a polymerized rosin, and 0.032 part of dibutyltin laurate were added to obtain a pressure-sensitive adhesive composition. Using this, an adhesive tape was formed in the same manner as in Example 1.
Was prepared.

Comparative Example 1 In a reaction vessel equipped with a cooling pipe, a nitrogen inlet pipe, a thermometer and a stirrer, using 66 parts of ethyl acetate as a solvent, 45 parts of 2-ethylhexyl acrylate, 50 parts of butyl acrylate, and 5 parts of acrylic acid , 2,2'-azobisisobutyronitrile 0.1.
1 part, 0.035 part of 2-mercaptoethanol (total amount)
, And after purging with nitrogen, the temperature was raised to carry out a polymerization reaction. At that time, the whole amount of the chain transfer agent was charged from the beginning of the polymerization. The polymerization temperature was kept at 60 ° C. for 4 hours from the start and then at 70 ° C. for 2 hours.

Thus, the weight average molecular weight is 24
A polymer having a number average molecular weight of 120,000 and a hydroxyl group introduction ratio at a molecular chain terminal of 25% was produced, and a solution containing this polymer at 60% by weight (viscosity at room temperature: 130 poise) was obtained. To 100 parts of the solid content of the polymer solution, 3.2 parts of a trimethylolpropane tolylene diisocyanate adduct and 0.032 part of dibutyltin laurate were added, and a pressure-sensitive adhesive composition was added. did. Using this, an adhesive tape was produced in the same manner as in Example 1.

Comparative Example 2 Using 66 parts of ethyl acetate as a solvent, 45 parts of 2-ethylhexyl acrylate, 50 parts of butyl acrylate, 5 parts of acrylic acid, and 0.1 parts of 2,2'-azobisisobutyronitrile.
Part, lauryl mercaptan 0.233 part (total amount), the polymerization average molecular weight was 240,000 in the same manner as in Example 1.
The number average molecular weight is 120,000, and the introduction ratio of hydroxyl groups at molecular chain terminals is 0.
% Of the polymer was obtained, and a solution containing this polymer at 60% by weight (viscosity at room temperature: 130 poise) was obtained. To 100 parts of the solid content of this polymer solution, tolylene diisocyanate adduct of trimethylolpropane was added.
And 0.032 parts of dibutyltin laurate to give a pressure-sensitive adhesive composition. Using this, an adhesive tape was produced in the same manner as in Example 1.

Comparative Example 3 Using 66 parts of ethyl acetate as a solvent, 45 parts of 2-ethylhexyl acrylate, 50 parts of butyl acrylate, 5 parts of acrylic acid, 2,2'-azobisisobutyronitrile 0.1
And 0.235 parts (total) of 2-mercaptoethanol in the same manner as in Example 1 to obtain a weight-average molecular weight of 6
A polymer having a number average molecular weight of 30,000 and a hydroxyl group introduction rate of 77% was produced, and a solution containing this polymer at 60% by weight (viscosity at room temperature: 40 poise) was obtained. To 100 parts of the solid content of the polymer solution, 3.2 parts of a trimethylolpropane tolylene diisocyanate adduct and 0.032 part of dibutyltin laurate were added, and a pressure-sensitive adhesive composition was added. did. Using this, as in Example 1,
An adhesive tape was prepared.

With respect to the adhesive tapes prepared in Examples 1 to 4 and Comparative Examples 1 to 3, the peeling adhesive force and the holding force were measured by the following methods. These measurement results
The results were as shown in Table 1 below.

<Peeling Adhesive Strength> An adhesive tape of 20 mm × 100 mm was pressure-bonded to a stainless steel plate sanded with a # 280 sandpaper as an adherend in such a manner that a 2 kg roller was reciprocated once. After 20 minutes at 23 ° C, 23 ° C,
The force required for 180-degree peeling was measured under an atmosphere of 65% RH and a pulling speed of 300 mm / min.

<Holding force> An adhesive tape was adhered to a phenol resin plate with an adhesive area of 10 mm × 20 mm, and after 20 minutes,
It was left at 80 ° C. for 20 minutes. Next, the phenol resin plate was hung down, a uniform load of 500 g was applied to the free end of the adhesive tape, and the time (minute) until the adhesive tape dropped at 80 ° C. was measured.

[0033]

As is evident from the results shown in Table 1 above, Examples 1 to 4 of the present invention reduce the molecular weight of the polymer to obtain a polymer solution having a high solid content (60% by weight) and a low viscosity. It can be seen from the pressure-sensitive adhesive composition prepared and used as a base, an adhesive tape having excellent adhesive properties, which satisfies the peeling adhesive strength and the holding power, was obtained. On the other hand, in Comparative Examples 1 to 3, it was found that an adhesive tape having good adhesive properties as described above was not obtained, and the effect of improving the holding power was particularly poor.

[0035]

As described above, the present invention makes it possible to easily produce a polymer solution having a low viscosity and a high solid content concentration by using a polymer having a specified functional group introduction rate and molecular weight at the molecular chain terminal as a main component. A pressure-sensitive adhesive composition having excellent adhesive properties, which can produce a crosslinked polymer having a long molecular chain length by cross-linking the same, thereby satisfying adhesive strength and cohesive strength, and its adhesion Sheets can be obtained.

 ──────────────────────────────────────────────────の Continuation of front page (72) Inventor Hiroshi Morishiki 1-2-1, Shimohozumi, Ibaraki-shi, Osaka Nitto Denko Corporation

Claims (3)

[Claims] 1. General formula; CH ₂ ＣC (R ¹ ) COOR ²
(Wherein, R ¹ is hydrogen or a methyl group, and R ² is C ² -C 2
A polymer containing 50% by weight or more of an acrylic monomer represented by the formula (1), having a number average molecular weight of 60,000 or more and a weight average molecular weight of 1
A pressure-sensitive adhesive composition characterized by having a molecular chain terminal functional group introduction ratio of 50,000 or more and a molecular chain terminal functional group introduction ratio of 50,000 or more. 2. The pressure-sensitive adhesive composition according to claim 1, wherein the crosslinking agent is contained in an amount of 0.05 to 7 parts by weight based on 100 parts by weight of the polymer as a main agent. 3. An adhesive sheet comprising a support and an adhesive layer obtained by crosslinking the pressure-sensitive adhesive composition according to claim 1 or 2.