JP2605118B2 - Resin composition for pressure-sensitive adhesive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a tacky / adhesive force and an adhesive force to a non-polar adherend.
The present invention relates to a resin composition for a pressure-sensitive adhesive excellent in cohesive force balance, low-temperature tackiness, and the like. More specifically, the present invention relates to a resin composition for a pressure-sensitive adhesive suitable for uses such as paper labels, packing tapes, cellophane tapes, masking tapes, and various slips.

[Conventional technology]

Conventionally, solvent-type acrylic resins, styrene-butadiene rubber, natural rubber, and the like have been used in combination with a tackifier as necessary as a resin for a pressure-sensitive adhesive used for paper labels, packing tapes, and the like. Was.

However, since a solvent is used, the use of a solvent-type base resin is decreasing year by year in view of pollution control, fire and explosion risks, safety and health problems, and the like, and the use of an aqueous dispersion-type base resin is shifting.

As such an aqueous dispersion type base resin, an aqueous dispersion of an acrylic copolymer resin containing an acrylate ester as a main component is used for a wide range of applications. Adhesive strength (tack) and cohesive strength (holding power) are difficult to balance, and those with high low-temperature tack have low holding power at high temperatures, Conversely, increasing the holding power at high temperatures has the disadvantage of lowering low temperature tack.

One of the drawbacks is that the price is relatively high.

In terms of price, it is advantageous to use an aqueous dispersion of a styrene-butadiene copolymer as the base resin for the pressure-sensitive adhesive. JP-A-55-48270 discloses a pressure-sensitive adhesive comprising an aqueous emulsion of a carboxylated styrene-butadiene rubber polymer and an aqueous emulsion of a tackifying resin.

In this case, the styrene-butadiene rubber copolymer rubber alone has insufficient tackiness, and in order to improve this drawback, it is essential to incorporate a large amount of a tackifier.
Although the adhesive strength is improved by this, the molecular weight of the tackifier is low, so that when used in a large amount, it causes a decrease in cohesive strength.

Furthermore, in order to produce the aqueous dispersion of the pressure-sensitive adhesive, apart from the production of the aqueous dispersion of the base resin, a complicated step of emulsifying a solid tackifier at room temperature generally to obtain an aqueous dispersion is required. It is necessary and disadvantageous in terms of price.

In this step, a large amount of a surfactant is required to stabilize the emulsion as an aqueous dispersion of the tackifier, which often causes a decrease in viscosity / adhesive strength and a decrease in water resistance.

In some cases, a method in which a tackifier dissolved in a solvent is emulsified using a surfactant is used, but since the solvent is mixed in the pressure-sensitive adhesive, there is a problem in terms of pollution, safety and health. Becomes

Due to the above-mentioned disadvantages, the use of aqueous dispersions of styrene-butadiene copolymer rubber is limited in practice.

On the other hand, JP-A-57-57707 and JP-A-56-145,909 disclose a pressure-sensitive adhesive having a base resin made of an aqueous dispersion of a synthetic rubber without using a tackifier.

These methods are characterized in that acrylates, especially butyl acrylate and 2-ethylhexyl acrylate are copolymerized in a specific composition range in addition to styrene and butadiene as a base resin.

[Problems to be solved by the invention]

The above method has an advantage that the price is lower than that of a pressure-sensitive adhesive using an aqueous dispersion of an acrylic resin as a base resin, but does not sufficiently improve the balance between adhesion and cohesion.

Further, there is a problem of workability after application to labels, tapes and the like.

That is, the pressure-sensitive adhesive containing the aqueous dispersion of the synthetic rubber as a base resin does not contain a tackifier (generally a resin having a high softening point at 70 to 130 ° C.) and contains a soft rubber component as a main component. The so-called "glue" is bad. When applying to labels, tapes, etc., after drying and processing in punching, die cutting, slitting, etc., pressure sensitive adhesive often adheres to the processing blade or cut surface, It causes problems such as contamination, and the label cannot be peeled off as usual.

The object of the present invention is to solve the above-mentioned problems, and to greatly reduce or not require the compounding amount of the tackifier, to have a high viscosity / adhesive force to a nonpolar adherend, and to increase the adhesive force and cohesive force. An object of the present invention is to provide an inexpensive resin composition for a pressure-sensitive adhesive which is excellent in balance, excellent in low-temperature tackiness, good in workability after coating, and inexpensive.

[Means for solving the problem]

The present inventors have conducted intensive research to solve the above-mentioned problems. As a result, a pressure-sensitive adhesive resin composition having excellent tackiness can be obtained by using a mixture of a butadiene-based copolymer having a low styrene content and a butadiene-based copolymer having a high styrene content. Surprisingly, the present inventors have found that the workability after coating is also improved in this mixed system, and completed the present invention.

That is, the present invention relates to (A) a low styrene-containing copolymer obtained by copolymerizing styrene of less than 10% by weight, butadiene 40 to 90% by weight, butyl acrylate and / or 2-ethylhexyl acrylate 5 to 55% by weight as main components. An aqueous dispersion of a polymer and (B) a copolymer obtained by copolymerizing as a main component 31 to 65% by weight of styrene, 5 to 39% by weight of butadiene, and 5 to 30% by weight of butyl acrylate and / or 2-ethylhexyl acrylate. A resin composition for a pressure-sensitive adhesive obtained by mixing an aqueous dispersion of a styrene-containing copolymer with a solid content weight ratio of (A) / (B) = 95/5 to 5/95.

 Hereinafter, the present invention will be described in more detail.

The low styrene-containing copolymer used in the present invention is a component for imparting tackiness / adhesion to a non-polar adherend and low-temperature viscosity, and has a styrene content of less than 10% by weight. However, from the viewpoint of compatibility with the high styrene-containing copolymer, the content is preferably 5% by weight or more. If it is 10% by weight or more, the tackiness and adhesion to non-polar adherends are reduced, and the low-temperature tackiness is also reduced.

The butadiene content is 40 to 90% by weight, preferably 50 to 90%.
80% by weight. If it is less than 40% by weight, low-temperature tackiness may not be sufficiently exhibited when mixed with a high styrene-containing copolymer, and if it is more than 90% by weight, the cohesive strength, particularly the holding power at high temperatures, is greatly reduced. The content of butyl acrylate and / or 2-ethylhexyl acrylate is 5 to 5.
55% by weight, preferably 15-45% by weight. If it is less than 5% by weight, sufficient adhesive strength cannot be obtained, and if it exceeds 55% by weight, it is disadvantageous in terms of price.

On the other hand, the high styrene-containing copolymer used in the present invention is a component that imparts high cohesive strength and appropriate viscosity / adhesiveness, and has a styrene content of 31 to 65% by weight, preferably 35 to 60% by weight.
It is.

If the amount is less than 31% by weight, sufficient cohesion may not be obtained when mixed with the low styrene-containing copolymer, and if it exceeds 65% by weight, the viscosity / adhesive strength may be significantly reduced.

The content of butadiene is 5 to 39% by weight, the content of butyl acrylate and / or 2-ethylhexyl acrylate is 5 to 30% by weight, and when both components are less than 5% by weight,
When mixed with a low styrene-containing copolymer, compatibility may not be sufficient. When butadiene exceeds 39% by weight, sufficient cohesive strength cannot be obtained, and when butyl acrylate and / or 2-ethylhexyl acrylate exceeds 30% by weight, sufficient cohesive strength cannot be obtained.

The mixing ratio of the aqueous dispersion (A) of the low styrene-containing copolymer and the aqueous dispersion (B) of the high styrene-containing copolymer is (A) / (B) = 95/5 to 5 in terms of solids weight ratio. / 95, preferably 90
/ 10 to 10/90. If the mixing ratio is more than 95/5, the cohesive strength is not sufficient, and the holding power at high temperatures is particularly low. If it is less than 5/95, the adhesive strength is not sufficient, and the adhesiveness at low temperatures is particularly poor.

Examples of other monomers copolymerizable with styrene, butadiene, butyl acrylate or 2-ethylhexyl acrylate include: ethylenically unsaturated carboxylic acids such as (meth) acrylic acid and itaconic acid; (meth) acrylic acid Hydroxyl-containing monomers such as 2-hydroxyethyl; unsaturated carboxylic amides such as (meth) acrylamide and N-methylol (meth) acrylamide and N-
Substituted compounds; functional group-containing monomers usually used for emulsion polymerization such as glycidyl (meth) acrylate-containing monomers such as glycidyl (meth) acrylate; and nitrile group-containing monomers such as (meth) acrylonitrile; Aromatic vinyl compounds such as methylstyrene and divinylbenzene; vinyl esters such as vinyl acetate and vinyl propionate; and (meth) acrylates other than butyl acrylate and 2-ethylhexyl acrylate.

The production of the aqueous dispersion (A) of the low styrene-containing copolymer and the aqueous dispersion (B) of the high styrene-containing copolymer used in the present invention may be in accordance with a known emulsion polymerization method, and is not particularly limited.

Examples of surfactants used for emulsion polymerization include alkyl sulfates, alkyl benzene sulfonates,
Anionic surfactants such as dialkyl sulfosuccinates and alkyl diphenyl ether disulfonates, and nonionic surfactants such as polyoxyethylene alkyl esters, alkyl ethers and alkyl phenyl ethers are used alone or in combination of two or more. Can be

Examples of the polymerization initiator include a water-soluble initiator such as potassium persulfate and ammonium persulfate, or a redox initiator combined with a reducing agent such as a sulfite.

Known chain transfer agents such as mercaptans and organic halogen compounds such as carbon tetrachloride can be used as the molecular weight regulator.

When used as a pressure-sensitive adhesive, the resin composition for a pressure-sensitive adhesive of the present invention is generally used in a pressure-sensitive adhesive composition such as a thickener, an antifoaming agent, a wetting agent, an antioxidant, and a filler. Various additives used can be blended, and if necessary, a tackifier, a plasticizer and the like can be blended.

As the tackifier, rosin-based, rosin derivative-based, terpene resin-based, petroleum resin-based, phenolic resin-based, and the like, and are usually added as an aqueous dispersion, the amount of which is added according to the gist of the present invention. , Relatively small.

Specifically, the amount of the aqueous dispersion of the tackifier is preferably not more than 40 parts based on 100 parts of the resin composition for a pressure-sensitive adhesive of the present invention in terms of the solid content weight ratio.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

 All parts and percentages in the examples are on a weight basis.

製造 Production example of aqueous dispersion of low styrene-containing copolymer (1)
~ (3)｝ 350 parts of water, 0.3 parts of sodium dodecylbenzenesulfonate and 6.0 parts of potassium persulfate were charged into an autoclave, and the inside of the autoclave was purged with nitrogen. With stirring, the temperature was raised to 60 ° C., and 10% of the mixed monomer emulsion shown in Table 1 was charged and polymerized for 1.5 hours. Next, the remaining mixed monomer emulsion was added in about 10 hours, and after polymerization for about 15 hours, the mixture was cooled and 2.7 parts of diethylhydroxyamine was added.

製造 Production example of aqueous dispersion of copolymer of comparative example (a)-
(B)｝ A method similar to that of Production Examples (1) to (3) of the aqueous dispersion of the low styrene-containing copolymer, except that the composition of the mixed monomer was changed to the composition shown in Tables 1 (a) to (b). Manufactured.

製造 Production example of aqueous dispersion of high styrene-containing copolymer (a)
~ (C)｝ In an autoclave are charged 365 parts of water, 0.8 parts of sodium dodecylbenzenesulfonate, 6.0 parts of itaconic acid, 30 parts of styrene and 5.0 parts of potassium sulfate, and the inside of the autoclave is purged with nitrogen. Under stirring, the temperature was raised to 70 ° C., and the polymerization was carried out for 1 hour.

Next, an emulsion of the mixed monomer shown in Table 1 was added in about 6 hours, and after polymerization for about 10 hours, the mixture was cooled and 2.7 parts of diethylhydroxyamine was added.

<< Production Example of Aqueous Dispersion of Copolymer of Comparative Example (C) >> Production Example of Aqueous Dispersion of High Styrene-Containing Copolymer (a) except that the composition shown in Table 1 (C) was used as the mixed monomer composition. ) To (c) in the same manner.

(Examples 1-2) The aqueous dispersions of Production Examples (2) and (c) were mixed at a solid content weight ratio of 80/20 and 70/30. After adjusting the pH to 8.5 with 8% aqueous ammonia, unreacted monomers were removed by steam stripping, and the solid content was reduced to 50% by an evaporator.
%. Next, Primal ASE-60 as a thickener
(Alkali-soluble emulsion: manufactured by Nippon Acrylic Co., Ltd.) was added in a small amount to adjust the viscosity to about 5,000 centipoise. Apply this to release paper (applying amount of about 60 g / m ² )
After drying for 3 minutes, high-quality paper was pressed against the coated surface, and the pressure-sensitive adhesive was transferred to the high-quality paper to prepare a sample piece. The following physical properties were measured for this sample piece.

 Table 2 shows the results.

(The physical properties were measured by the following methods.) 1. Adhesive strength: A 2.5 cm wide test piece was placed on a polyethylene plate (length 10 c).
m, width 4 cm, thickness 2 mm), and affixed under a constant pressure (two passes through a roll with a load of 2 kg).

The tensile strength at the time of 180 ° peeling was measured in an atmosphere at 20 ° C.

Pulling speed: 300mm / min 2. Adhesive strength (tack): Inclined ball tack (J.DOW method)
The maximum diameter of the stainless steel ball stopped on the pressure-sensitive adhesive layer was indicated by 1 point every 1/32 inch. (For example, 2/32 inch is 2,
10/32 inch is indicated as 10. The measurement was performed in an atmosphere of 20 ° C. and 0 ° C.

3. Cohesive force (holding force): A test piece having a width of 2.5 cm was brought into contact with a surface-polished stainless steel plate in an area of 2.5 cm x 2.5 cm, and was adhered under a constant pressure (two passes through a roll having a load of 2 kg).

This was suspended vertically and a load of 1 kg was applied to the lower end, and allowed to stand still in an atmosphere at 20 ° C. and 60 ° C., and the time until the load dropped was measured and indicated in minutes.

4. Processability: Adhesion of test pieces when 20 pieces of 5cm width test pieces are stacked and cut with a push-cut cutter while the pressure-sensitive adhesive layer is sandwiched between high quality paper and release paper. Alternatively, the state of contamination of the blade with the pressure-sensitive adhesive was visually determined.

◎: very good, ：: good Δ: slightly poor, ×: poor (Comparative Examples 1 and 2) Examples 1 to 1 were used except that the aqueous dispersions of Production Examples (2) and (c) were used alone. A pressure-sensitive adhesive test piece was prepared and tested in the same manner as in the method shown in FIG. Table 2 shows the results.

(Comparative Example 3) Except that the aqueous dispersions of Production Example (2) and Comparative Production Example (C) were mixed at a solid content weight ratio of 70/30, the sensitization was carried out in the same manner as in Examples 1 and 2. Create a pressure-adhesive test specimen,
The test was performed.

 Table 2 shows the results.

(Examples 3 to 5) Example 1 was repeated except that the aqueous dispersions of Production Examples (1) and (b) were mixed at a solid content weight ratio of 40/60, 50/50, 60/40.
Test pieces were prepared by preparing pressure-sensitive adhesive test pieces in the same manner as in the methods shown in FIGS. Table 2 shows the results.

(Examples 6 to 8) Example 1 except that the aqueous dispersions of Production Examples (3) and (b) were mixed at a solid content weight ratio of 50/50, 60/40, 70/30.
A pressure-sensitive adhesive test piece was prepared and tested in the same manner as the methods shown in FIGS.

 Table 2 shows the results.

(Comparative Examples 4 to 6) Pressure-sensitive adhesion was performed in the same manner as in Examples 1 and 2, except that the aqueous dispersions of Production Examples (1), (3) and (b) were used alone. A test piece was prepared and tested.

 Table 2 shows the results.

(Comparative Examples 7 to 8) The aqueous dispersion of Comparative Production Example (a) or (b) and the aqueous dispersion of Production Example (b) were mixed at a solid content weight ratio of 60/40 or 5
Except for mixing at 0/50, pressure-sensitive adhesive test pieces were prepared and tested in the same manner as in Examples 1 and 2.

 Table 2 shows the results.

Examples 9 to 11 The aqueous dispersions of Production Examples (2) and (a) were mixed at a solid content weight ratio of 10/90, 20/80, 30/70. Each with 20% KOH
After adjusting to H8, unreacted monomers were removed by steam stripping, and concentrated to a solid content of 50% by an evaporator. D-101 (aqueous dispersion of hydrogenated rosin glycerin ester: 50% solid content,
Resin softening point 71-78 ° C: manufactured by Rika Hercules) was blended at a solids weight ratio of 100/20. Other than this, Example 1
A pressure-sensitive adhesive test piece was prepared and tested in the same manner as the methods shown in FIGS.

 Table 2 shows the results.

(Comparative Examples 9 to 10) Except that the aqueous dispersions of Production Examples (2) and (a) were used alone, pressure-sensitive adhesive test pieces were prepared in the same manner as in Examples 9 to 11. And tested.

 Table 2 shows the results.

[Effect of the Invention] As is clear from the examples and comparative examples, the aqueous dispersion (A) of the low styrene-containing copolymer and the aqueous dispersion (B) of the high styrene-containing copolymer of the present invention are mixed. The resin composition for a pressure-sensitive adhesive is used when an aqueous dispersion of the copolymer (A) or (B) is used alone, and when an aqueous dispersion of a copolymer outside the composition range of the present invention is mixed. It is evident that the composition achieves an excellent balance of adhesion and cohesion, which cannot be obtained by the above method, and has a high adhesion to non-polar adherends.

Since the pressure-sensitive adhesive composition using the resin composition for a pressure-sensitive adhesive of the present invention has good workability after application and drying, and is relatively inexpensive, the significance of the present invention is great.

Claims (1)

(57) [Claims] 1. A low styrene-containing copolymer obtained by copolymerizing (A) less than 10% by weight of styrene, 40 to 90% by weight of butadiene, and 5 to 55% by weight of butyl acrylate and / or 2-ethylhexyl acrylate. An aqueous dispersion of a polymer and (B) a copolymer obtained by copolymerizing as a main component 31 to 65% by weight of styrene, 5 to 39% by weight of butadiene, and 5 to 30% by weight of butyl acrylate and / or 2-ethylhexyl acrylate. A resin composition for a pressure-sensitive adhesive obtained by mixing an aqueous dispersion of a styrene-containing copolymer with a solid content weight ratio of (A) / (B) = 95/5 to 5/95.