JPH08269420A - Delayed tack pressure-sensitive adhesive composition - Google Patents

Abstract

PURPOSE: To obtain an emulsion-type delayed tack pressure-sensitive adhesive composition which does not posesses pressure-sensitive adhesiveness at ordinary temperature, can develop pressure-sensitive adhesiveness when heated to a specified temperature or higher and is excellent in handleability. CONSTITUTION: A delayed tack pressure-sensitive adhesive composition comprising a solution (A) containing a resin of a glass transition temperature of 20 deg.C or above, which is prepared by copolymerizing 3-60wt.% unsaturated carboxylic monomer with 40-97wt.% hydrophobic monomer and 0-50wt.% other monomers and at least 5wt.% of which is solubilized and aqueous acrylic resin emulsion (B) comprising a resin of a glass transition temperature of -30 deg.C or below, wherein the ratio A/B is 15/85 to 50/50 by weight (wherein A is the amount of the nonvolatiles of component A, and B is that of component B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an emulsion-type pressure-sensitive adhesive composition, which does not exhibit tackiness at room temperature, but exhibits tackiness when heated above a certain temperature. The invention relates to a delayed tack type pressure-sensitive adhesive composition having excellent properties.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
The pressure-sensitive adhesive composition is applied to a sheet and then dried to obtain a sheet-shaped pressure-sensitive adhesive, and the sheet coated with the pressure-sensitive adhesive is often stored in a roll shape. At the present time, the release paper is used for the purpose of not adhering the back surface of the base material to the adhesive coated surface during storage,
The use of release paper has a problem that the work is complicated and the release paper that is unnecessary after using the adhesive is expensive, etc., and the back surface of the base material and the adhesive coated surface do not have to be used as much as possible. Various measures have been taken to prevent adhesion.

For example, a delayed-tack type pressure-sensitive adhesive composition comprising a thermoplastic resin and a tackifying resin is blended with a crystalline plasticizer for the purpose of suppressing the tackiness at room temperature, so that the crystals melted only when heated. There is a method in which the plasticizer softens the thermoplastic resin so that the tackiness is developed. However, since the crystalline plasticizer gradually diffuses into the pressure-sensitive adhesive and softens the thermoplastic resin even below its melting point, tackiness occurs over time, and the back surface of the base material and the pressure-sensitive adhesive coated surface are still stored during storage. There was still the problem of causing adhesion with.

On the other hand, in order to solve the above problems, a method of adding a wax instead of the crystalline plasticizer has been attempted, but not only is it insufficient to suppress the development of tackiness caused by aging, There was a problem that the tackiness was lost after the final heating. In addition, any of the delayed tack type pressure-sensitive adhesives currently used or proposed develops tackiness at a relatively low temperature, so it is necessary to lower the drying temperature when drying the pressure-sensitive adhesive after coating it on a substrate. However, the production efficiency was extremely low.

[0005]

As a result of various studies to solve the above problems, the present inventors have found that the object of the present invention can be achieved by adopting the following constitution, and the present invention completed. That is, the delayed tack-type pressure-sensitive adhesive composition of the present invention comprises (A) 3 to 60% by weight of a carboxyl group-containing unsaturated monomer (a), 40 to 97% by weight of a hydrophobic monomer (b), and others. Monomer (c) 0
A resin-containing solution containing a resin having a glass transition temperature of 20 ° C. or higher, which is obtained by copolymerizing 50% by weight to 50% by weight, and 5% by weight or more of the resin is solubilized, and
(B) An acrylic resin aqueous emulsion made of a resin having a glass transition temperature of −30 ° C. or less, and the weight ratio (A) / (B) of the non-volatile components of the above components is 15/85 to 50 /
50 of the delayed tack type pressure-sensitive adhesive composition.

The resin that constitutes the resin-containing solution (A) that constitutes the delayed tack type pressure-sensitive adhesive composition of the present invention comprises 3 to 60% by weight of the unsaturated monomer (a) having a carboxyl group and a hydrophobic monomer. It is a resin obtained by copolymerizing 40 to 97% by weight of the body (b) and 0 to 50% by weight of the other monomer (c).

Examples of the unsaturated monomer (a) having a carboxyl group include acrylic acid (105 ° C.), methacrylic acid (130 ° C.) and itaconic acid (160 ° C.) (the values in parentheses are The glass transition temperature of the homopolymer, and the same shall apply hereinafter). The component (a) is used so as to account for 3 to 60% by weight, preferably 5 to 50% by weight of the resin constituting the resin-containing solution (A) in the present invention. When it is less than 3% by weight, it is difficult to sufficiently solubilize the obtained resin in water, and as a result, there is a problem that the miscibility with the acrylic resin aqueous emulsion of the component (B) described later is lowered, On the other hand, if it exceeds 60% by weight, there arises a problem that the viscosity of the resin-containing solution increases with time.

Examples of the hydrophobic monomer (b) include methyl methacrylate (105 ° C), ethyl acrylate (-22 ° C), butyl acrylate (-54 ° C), 2
-Vinyl aromatic compounds such as ethylhexyl acrylate (-85 ° C) and styrene (100 ° C), vinyl chloride (8
Vinyl halides such as vinylidene chloride (-20 ° C), vinyl acetate (30 ° C), vinyl propionate (1
0 ° C) vinyl ester, ethylene (-125 ° C),
Examples thereof include olefinic monomers such as butadiene (-109 ° C) and acrylonitrile (130 ° C).

The component (b) is used so as to occupy 40 to 97% by weight, preferably 50 to 95% by weight, of the resin constituting the resin-containing solution (A) in the present invention. Four
When the content is less than 0% by weight, the affinity between the resin of the resin-containing solution (A) and the resin of the acrylic resin aqueous emulsion (B) cannot be secured, the viscosity tends to increase during storage, and sufficient adhesiveness after heating is obtained. On the contrary, when the characteristics are not obtained, and when it exceeds 97% by weight, the ratio of the component (a) is relatively decreased, which causes aggregation and precipitation of the resin in the resin-containing solution (A). Becomes

The term "hydrophobic" as used herein means that the solubility in water at 20 ° C. is 8 g / 100 ml or less. Specific examples of the other monomer (c) include acrylamide (153 ° C.), 2-hydroxyethyl acrylate (-15 ° C.), diacetone acrylamide (65 ° C.) and the like.

The component (c) is used in an amount of 0 to 50% by weight, preferably 0 to 50% by weight, of the resin constituting the resin-containing solution (A) in the present invention in order to secure the water solubility of the resin or to adjust the glass transition temperature described later. Is used so as to occupy 0 to 40% by weight. When it exceeds 50% by weight, the proportion of the component (a) and / or the component (b) is relatively decreased, the miscibility with the aqueous emulsion (B) is decreased, and the viscosity is increased with time. The problem arises.

The resin-containing solution (A) is a component for suppressing the development of tackiness when the pressure-sensitive adhesive composition is applied / dried and when the coated sheet is stored in a roll form. Therefore, the glass transition temperature of the resin is 20 ° C. or higher, preferably 30 ° C. to 130, so that the resin does not exhibit tackiness at room temperature.
Must be ℃. If the glass transition temperature is lower than 20 ° C., there is a problem that the tackiness is already expressed during coating and drying of the pressure-sensitive adhesive composition, and if the glass transition temperature is too high, the tackiness is expressed. Therefore, the heating temperature becomes high, which leads to high energy consumption.

The component (A) of the present invention is 5% by weight.
As described above, it is necessary to use a resin-containing solution containing a resin in which 10% by weight is preferably solubilized. In the present invention, the solubilization rate means that the resin-containing solution obtained by polymerization by the polymerization method described below is diluted with water so that the nonvolatile content becomes 15% by weight, and then the diluted solution is subjected to centrifugal acceleration of 1.8 ×.
Centrifuging at 10 ⁵ g for 60 minutes, the non-volatile content in the obtained supernatant was measured to be w parts by weight, and the non-volatile content in the diluent used for centrifugation was measured to be W parts by weight. Is the solubilization rate represented by the following formula.

Solubilization rate = w / W × 100 (% by weight)

Therefore, for example, in the case where an alkali and / or an organic solvent is added to the polymerization system before or during the polymerization for producing a resin-containing solution to carry out the copolymerization, When the solubilization rate of the obtained polymerization product containing the produced copolymer resin is already 5% by weight or more, the alkali and / or organic solvent for the solubilization treatment is added again. You don't have to.

The alkali used for the solubilization treatment is an inorganic water-soluble alkali, such as sodium hydroxide or potassium hydroxide; or an inorganic salt which shows alkalinity when dissolved in water, such as sodium hydrogen carbonate or pyrophosphate. Sodium and the like; other examples include aqueous ammonia and organic amines. Addition of alkali is as described above.
It is not always necessary to carry out after the polymerization of the resin-containing solution, and in some cases, copolymerization may be carried out after neutralizing the monomer before the polymerization by adding an alkali. The amount of the alkali used may be an amount that completely neutralizes the carboxyl group in the copolymer resin, or may be an amount that partially neutralizes the carboxyl group.

The organic solvent used for the solubilization treatment may be supplementarily added when it cannot be sufficiently solubilized in water only by adding an alkali, or may be solubilized by adding only an organic solvent. The organic solvent to be used is not particularly limited, but texanol, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether and their acetates, benzyl alcohol, butyl carbitol acetate, 2,2,4-trimethyl-1,3,3
-Pentanediol and the like.

Furthermore, the weight average molecular weight (Mw) of the resin constituting the resin-containing solution of the component (A) is 3000.
It is desirable that it is ˜30,000 because it is excellent in miscibility with the acrylic aqueous emulsion (B) and is excellent in tackiness when heated. If the Mw is 3000 or less, tackiness is likely to occur even when dried at a low temperature, and the tackiness tends to increase with time. Further, when the Mw is 30,000 or more, the stability when mixed with the resin aqueous emulsion of the component (B) decreases, the adhesiveness upon heating decreases, and it takes a long time to develop the adhesiveness. is there.

As a method for producing the resin-containing solution which is the above-mentioned component (A), for example, each constituent monomer mixture is prepared by a conventional method in an organic solvent and a polymerization initiator such as benzoyl peroxide or t-butyl hydroperoxide is used. Examples of the method include solution polymerization using an organic peroxide such as oxide or an azo initiator such as azobisisobutyronitrile. At this time, it is also possible to use a chain transfer agent such as an organic halide or an alkyl mercaptan as a molecular weight regulator. After distilling off the solvent from the resin solution thus obtained under reduced pressure, water is added and, if necessary, an alkali and / or a solvent is further added to obtain a resin-containing solution (A) of the resin having the above-mentioned solubilization rate. To do.

As another method for producing the resin-containing solution which is the component (A), emulsion polymerization of a conventional method is carried out, that is, the monomer mixture constituting the copolymerization is emulsified and copolymerized by using an emulsifier. There is also a method of adding an alkali to solubilize water, but in this method, it is essential to use a chain transfer agent for controlling the molecular weight. The alkali used herein may be ammonia, an organic amine such as triethylamine or ethanolamine, or an inorganic alkali such as sodium hydroxide, but it is most preferable to use ammonia.

The emulsifiers used are sodium dialkyl sulfosuccinate, alkali salts of alkyl sulfonic acids, alkali metal salts of oxyalkylated alcohols or alkyl phenols, alkali salts of fatty acids such as anionic surfactants, nonionic surfactants. Various kinds of surfactants can be used alone or in combination. The amount used is usually 0.1 to 10% by weight with respect to the resin content. In addition, depending on the purpose, a cationic surfactant may be used alone or in combination with a nonionic surfactant.

The polymerization initiator used in the emulsion polymerization is preferably an inorganic peroxide such as potassium persulfate, sodium persulfate, ammonium persulfate or hydrogen peroxide, but other than azobisisobutyronitrile or azobisvaleronitrile. Azo initiators; organic peroxide initiators such as benzoyl peroxide, lauroyl peroxide and t-butyl peroxide can also be used. Further, a reducing agent such as Rongalit, L-ascorbic acid, an organic amine, or a metal salt may be used in combination with these initiators and used as a redox initiator.

The resin constituting the acrylic resin aqueous emulsion (B) constituting the delayed tack type pressure-sensitive adhesive composition of the present invention has a glass transition temperature of -30 ° C or lower, preferably -40 ° C or lower. is necessary.
This component (B) is for developing tackiness.

Aqueous acrylic resin emulsions composed of resins having a glass transition temperature of -30 ° C or lower include, for example, butyl acrylate (-54 ° C), 2-ethylhexyl acrylate (-85 ° C) and lauryl acrylate (-65).
(.Degree. C.) and the like, which are mainly composed of monomers having a low glass transition temperature of a homopolymer. Further, in order to adjust the glass transition temperature, ethylene (-125 ° C) or butadiene (-10
It is also possible to copolymerize (9 ° C.).

As the method for producing the resin aqueous emulsion (B), a method of emulsion copolymerizing a monomer mixture which constitutes a copolymerization by an ordinary method of emulsion polymerization, that is, (A) is used. The same as the emulsion polymerization method at the time of production). In the present invention, instead of using an ordinary emulsifier, a so-called protective colloid in which a monomer mixture constituting a resin is copolymerized or polymerized by using various protective colloid agents in the resin-containing solution (A) component of the present invention. A polymerization method can also be adopted.

Examples of the protective colloid agent include hydroxyethyl cellulose, polyethylene oxide propylene oxide block polymer, and an alkali-soluble unsaturated carboxylic acid copolymer. The weight ratio (A) / (B) of the non-volatile components of each component is 15/85 to 50/50,
It is preferably 20/80 to 50/50. If the ratio of the component (A) is less than 15, it will exhibit tackiness at room temperature, and cannot be a delayed tack type pressure-sensitive adhesive.
When the ratio of the component (A) exceeds 50, it does not become tacky even when heated.

When the glass transition temperature of the resin constituting the component (A) is 20 to 60 ° C., the weight ratio (A) / (B) of the nonvolatile components is 25/75 to 50.
/ 50 is preferable, and when the glass transition temperature of the resin constituting the component (A) is 60 to 110 ° C,
The non-volatile weight ratio (A) / (B) of each component is 15 /
It is preferably 85 to 25/75.

The delayed tack-type pressure-sensitive adhesive composition of the present invention is added with a tackifying resin such as a rosin derivative, a terpene resin, a petroleum resin or the like, or the pressure-sensitive adhesive property is impaired, in order to improve the adhesive strength. It is also possible to add waxes such as paraffin and long-chain fatty acids and amides thereof, and inorganic fillers such as titanium oxide and talc to the extent that they are not present.

The delayed tack-type pressure-sensitive adhesive composition is applied to a support such as paper and dried, and the pressure-sensitive adhesiveness is developed by heating at the time of adhesion to be used for sealing labels, tapes, packages, etc. .

The drying temperature after the application of the present delayed tack type pressure-sensitive adhesive composition to a substrate and the heating temperature for developing the adhesiveness are the glass transition temperature of the resin constituting the resin-containing solution of the component (A) of the present invention. Strongly depends on. That is, the drying temperature is preferably + 30 ° C. or lower than the glass transition temperature of the resin in the component (A), and if it exceeds that temperature, it tends to have tackiness at the time of drying. Further, the heating temperature for developing the tackiness needs to be a temperature equal to or higher than the drying temperature, and preferably + 30 ° C. or higher of the glass transition temperature of the resin in the component (A).

[0031]

EXAMPLES Next, the present invention will be described in detail with reference to Examples and Comparative Examples. Parts and% in the examples are parts by weight and% by weight, unless otherwise specified. Production Example 1 150 parts of methyl cellosolve was charged into a reactor equipped with a temperature controller, a stirrer, a reflux condenser, a supply container and a nitrogen introducing tube, and the atmosphere was replaced with nitrogen. After heating the reactor to 80 ° C., a mixture of 100 parts of the monomer mixed solution shown in Table 1 and 0.1 part of t-dodecyl mercaptan was supplied from a supply container I, and 2 parts of azobisisobutyronitrile was added to 50 parts of methyl cellosolve. What was melt | dissolved in was added uniformly over 4 hours each from the supply container II.

After completion of the addition, the reactor was kept at 80 ° C. and aged for 2 hours to obtain a uniform polymer solution. Then, by using a rotary evaporator under reduced pressure, methyl cellosolve was almost completely distilled off, and then deionized water was added,
Ammonia is further added to neutralize the solution, and the pH is 8 and the nonvolatile content is 25.
% Resin containing solution was obtained.

The solubilization ratio of the resin in the resin-containing solution was 100%, and the weight average molecular weight was about 5,000 as measured by gel permeation chromatography (GPC).

[0034]

[Table 1]

Production Examples 2-8 Using the same equipment as in Production Example 1, the monomer composition, solvent, initiator, etc. were changed as shown in Table 1 to obtain uniform polymer solutions, and then the solvent was added. A resin-containing solution as shown in Table 1 was obtained by distillative water replacement and neutralization. Production Example 9 Using the same apparatus as in Production Example 1, 40 parts of water and 0.06 part of sodium persulfate were charged into the reactor. Separately, the following was prepared as the feed I.

[0036] Separately, as a feed II, an initiator solution was prepared by dissolving 0.7 part of sodium persulfate in 10 parts of water.

After the inside of the reactor charged with the above-mentioned initiator solution was replaced with nitrogen gas, 1 part of the feed I was fed into the reactor.
0% was added and the mixture was heated to 90 ° C. Then
After 10% of the feed II was charged into the reactor, the rest of the feed I and the feed II were uniformly fed to the reactor over 3 to 3.5 hours. 1.5 hours after the end of supply 9
It was kept at 0 ° C. and emulsion-polymerized to obtain a resin aqueous emulsion. The nonvolatile content of this resin aqueous emulsion is about 52%
Met.

Table 2 shows the composition of the monomers, the non-volatile content of the produced emulsion and the glass transition temperature (calculated value) of the resin.

[0039]

[Table 2]

Production Examples 10 and 11 A resin aqueous emulsion was obtained according to Production Example 9 except that the same apparatus as in Production Example 9 was used and the monomer composition was changed as shown in Table 2. The results are shown in Table 2.

Production Example 12 Using the same apparatus as in Production Example 9, 100 parts of the resin-containing solution produced in Production Example 1 was charged into the reactor. Separately, the following was prepared as the feed I.

Feed I Butyl Acrylate 90 parts Methyl Methacrylate 9.5 parts Itaconic Acid 0.5 parts Separately, as Feed II, 20 parts of water, 0.6 parts of sodium persulfate and 0.15 of sodium hydroxide. An initiator solution with parts dissolved was prepared.

After replacing the inside of the reaction vessel with nitrogen gas,
In the same reaction vessel was added 10% of each of the above feeds I and II and the mixture was heated to 90 ° C. Then feed I
And the rest of II were uniformly supplied to the same reaction vessel over 3 hours. After the end of the supply, the mixture was kept at 90 ° C. for 1.5 hours for emulsion polymerization to obtain a resin aqueous emulsion. The nonvolatile content of this resin aqueous emulsion was about 45%. The results are shown in Table 2.

Examples 1 to 7 and Comparative Examples 1 to 7 The resin-containing solutions prepared in the above Production Examples and the resin aqueous emulsion were mixed at the ratios shown in Tables 3 and 4, and stirred to produce a delayed tack type pressure-sensitive adhesive composition. The thing was prepared. The obtained composition was applied onto the surface of a polyester film using an applicator so that the dry coating film would be 25 ± 1 g / m ^2, and dried at 50 ° C. for 10 minutes to prepare a test piece A. Separately from this, apply under similar application conditions,
A test piece B was prepared by drying at 80 ° C. for 5 minutes.

The test pieces A and B were evaluated according to the following test methods and evaluation criteria, and the results are shown in Tables 3 and 4. In Comparative Example 3, the mixing stability was poor and the mixture was separated into two layers, an aqueous layer and an emulsion layer, after standing for one day. Further, in Comparative Example 6, it was difficult to mix uniformly, and the dry coating film was non-uniform.

Adhesion test: the above test piece (2.5 × 10
(cm) is heated at 140 ° C. for 30 seconds and then adhered to a stainless steel plate (SUS) whose surface has been polished, and a tensile strength of 180 ° (pulling speed: 300 mm / min) using a tensile tester (manufactured by Instron). Was measured and evaluated according to the following criteria.

∘: more than 1000 g / 25 mm ∘: 750 to 1000 g / 25 mm Δ: 500 to 750 g / 25 mm x: less than 500 g / 25 mm

Holding power test: the above test piece (2.0 × 2.
(0 cm) is heated at 140 ° C. for 30 seconds and then adhered to a surface-polished stainless steel plate (SUS), a load of 1 kg is applied, and a holding force (time until peeling) is obtained at 20 ° C. and a humidity of 65%. It was measured and evaluated according to the following criteria.

◎ ・ ・ ・ More than 60 minutes ○ ・ ・ ・ 30 to 60 minutes △ ・ ・ ・ 10 to 30 minutes × ・ ・ Less than 10 minutes

Blocking test; test pieces A and B described above
The pressure-sensitive adhesive composition coating surface is overlaid, and 0.5 kg /
The state of peeling after leaving at 40 ° C. for 1 day under a load of cm ² was evaluated according to the following criteria.

◎ ・ ・ ・ Peeling without any resistance ○ ・ ・ ・ Peeling with strength less than 10 g / 25 mm △ ・ ・ ・ Peeling with strength 10-20 g / 25 mm × ・ ・ ・ 20 g / 25 mm or more Peeling strength is required

[0052]

[Table 3]

[0053]

[Table 4]

[0054]

EFFECTS OF THE INVENTION The delayed tack type pressure-sensitive adhesive composition of the present invention does not exhibit tackiness at room temperature and exhibits tackiness when heated to a certain temperature or higher, so that it is easy to handle.
Further, the adhesive property after heating, that is, the adhesive force and the holding power are excellent, and the sheet coated with the present adhesive composition is also excellent in blocking resistance, so that it is useful as a delayed tack type adhesive, and peels off. It is possible to provide an adhesive sheet that does not require paper. The need for release paper is extremely beneficial in terms of resource saving.

Claims (6)

[Claims] 1. An unsaturated monomer (a) having 3 to 60% by weight of a carboxyl group (A) and a hydrophobic monomer (b) 40 to 40% by weight.
97% by weight and other monomer (c) 0 to 50% by weight
A resin-containing solution containing a resin having a glass transition temperature of 20 ° C. or higher obtained by copolymerization of 5% by weight or more and having 5% by weight or more thereof solubilized, and (B) a glass transition temperature of − A delayed tack type pressure-sensitive adhesive composition comprising an acrylic resin aqueous emulsion comprising a resin at 30 ° C. or lower and having a non-volatile weight ratio (A) / (B) of each component of 15/85 to 50/50. 2. The weight ratio (A) / nonvolatile content of each component
The delayed tack type pressure-sensitive adhesive composition according to claim 1, wherein (B) is 20/80 to 50/50. 3. The glass transition temperature of the resin constituting the component (A) is 20 to 60 ° C., and the weight ratio (A) / (B) of the non-volatile components of each component is 25/75 to. 50 /
The delayed tack type pressure-sensitive adhesive composition according to claim 1, which is 50. 4. The glass transition temperature of the resin constituting the component (A) is 60 ° C. or higher, and the weight ratio (A) / (B) of the nonvolatile components is 15/85 to 25. / 7
The delayed tack type pressure-sensitive adhesive composition according to claim 1, which is 5. 5. The delayed tack type pressure-sensitive adhesive composition according to claim 1, wherein the resin constituting the component (A) has a weight average molecular weight (Mw) of 3,000 to 30,000. 6. The delayed tack type pressure-sensitive adhesive composition according to claim 1, wherein the emulsion of the component (B) is obtained by emulsion polymerization in the presence of the resin-containing solution of the component (A). .