JPH0739568B2 - Synthetic latex for adhesives - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synthetic latex for a pressure-sensitive adhesive obtained by copolymerizing a lipophilic mixed monomer in the presence of a hydrophilic polymer latex.

Adhesives are widely used for applications such as cellophane tapes, various packaging tapes, masking tapes, and other tapes, various labels, and seals.

It is necessary for the pressure-sensitive adhesive to attract a slight amount of force to the adherend, to exert a surprisingly large adhesive force, and to keep the adhesive force without being impaired in a wide temperature range.

That is, the basically important properties of the pressure-sensitive adhesive are tack (adhesive force), adhesive force and cohesive force, and it is necessary that these three physical properties are balanced.

And, depending on the application, it is necessary to further have performances other than these basic physical properties.For example, in high-grade label applications, heat resistance and light resistance (adhesive performance changes even when exposed to sunlight during adhesive label storage). No) is an important performance requirement.

Natural rubber and synthetic rubber have been widely recommended and used as elastic materials for adhesives, but since there is almost no tack of the polymer itself, the polymer is dissolved in a solvent and rosin, rosin acid ester, terpene resin, aliphatic carbonization is used. It is used as a so-called solvent-type pressure-sensitive adhesive to which a tackifying resin such as hydrogen resin and styrene resin, a plasticizer, a filler and an antioxidant are added.

Disadvantages of this method are that air pollution caused by the use of a solvent, fire, occupational safety and health problems, and poor heat resistance and light resistance peculiar to diene-based adhesives.

On the other hand, latex-type pressure-sensitive adhesives are also manufactured in contrast to solvent-type pressure-sensitive adhesives.

Some of the latex-type adhesives are mainly composed of acrylic-based latex, natural rubber-based latex and synthetic rubber-based latex.

Acrylic latex adhesive is a copolymer whose main component is an acrylate ester having 4 to 10 carbon atoms in the alkyl group, but at the local point, it is expensive and has low cohesive strength. The point is a drawback. Although it is possible to improve the cohesive force by copolymerizing with a monomer having a reactive functional group, this method brings about tack and a decrease in adhesive force.

Since the natural rubber-based latex adhesive has almost no tack of the natural rubber polymer itself, it is necessary to use it in combination with the tackifying resin emulsion or, if necessary, a plasticizer or the like.

Disadvantages of natural rubber-based latex adhesives are that the tackifying resin must be dispersed by a costly process and that heat resistance and light resistance are poor.

Therefore, the present inventors, as a pressure-sensitive adhesive, is a latex-based system that has less problems in terms of pollution and safety and hygiene in comparison with solvent-based systems, maintains excellent tack, adhesive strength and cohesive strength, and has a heat deterioration characteristic of a diene system. We thought that it would be industrially significant if a new pressure-sensitive adhesive with improved ultraviolet absorption deterioration could be obtained, and conducted extensive studies.

As a result, surprisingly, by copolymerizing a lipophilic mixed monomer containing a conjugated diene in the presence of a hydrophilic polymer latex, as a synthetic latex particle for adhesives, its structure was completely different from the conventional one. The present invention was found by finding out that a polymer is produced, which has excellent heat resistance and light resistance, and also has good adhesive performance.

That is, the present invention provides a synthetic latex for a pressure-sensitive adhesive obtained by copolymerizing a lipophilic mixed monomer containing a conjugated diene in the presence of a hydrophilic polymer.

And, the synthetic latex for pressure-sensitive adhesive of the present invention is considered to have a heterogeneous double structure of a hydrophilic polymer layer and a lipophilic polymer layer, and the lipophilic polymer layer inside the particle has a hydrophilic polymer layer inside the particle. It is considered that many latex particles selectively located on the surface of each particle are included, and a two-step polymerization method is used for production.

That is, the hydrophilic polymer latex obtained in the first step is used as a seed to polymerize the lipophilic mixed monomer in the second step.

Specifically, the hydrophilic polymer latex is (meth)
It is obtained by polymerizing a monomer consisting of an acrylic ester and, if necessary, a vinyl ester, together with an α, β-unsaturated carboxylic acid for the purpose of imparting hydrophilicity. The hydrophilic polymer latex preferably has a pH of 2 to 6 and a solid content concentration of 20 to 40%.

Typical examples of the acrylic acid ester (first-first component) include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, and hexyl (meth) acrylate. Examples include ethyl acrylate, isobutyl acrylate, butyl acrylate, 2
Monomers having a low glass transition temperature (Tg) of its homopolymer such as ethylhexyl acrylate and lauryl methacrylate are preferred because they can be effectively used. Examples of the vinyl ester (component 1-2) include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl-2-ethylhexoate and vinyl benzoate. Further, as the α, β-unsaturated carboxylic acid (first to third components) used for the purpose of imparting hydrophilicity to the monomer, acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid, crotonic acid, halo Acrylic acid (2-chloroacrylic acid, 2-bromoacrylic acid, 3-chloroacrylic acid, 2,3-dichloroacrylic acid, 3,3-dichloroacrylic acid, etc.), 2-phenylacrylic acid, 3-phenyl Acrylic acid, etc. Further, in addition to the above monomers, if necessary, a monomer copolymerizable with the above monomers, such as acrylonitrile, N-methylolacrylamide,
There is no problem even if glycidyl acrylate, 2-hydroxyethyl acrylate or the like is used.

The amount of the (meth) acrylic acid ester in the hydrophilic polymer is in the range of 20 to 98% by weight, preferably 40 to 80% by weight, based on the total amount of the monomers in the hydrophilic polymer.
The amount of vinyl ester is preferably 0 to 80% by weight, and particularly preferably 0 to 30% by weight. The amount of α, β-unsaturated carboxylic acid, which is a reactive hydrophilic monomer that further enhances the hydrophilicity of the obtained polymer latex, is preferably 10% by weight or less based on the total amount of monomers. The Tg of the hydrophilic polymer thus obtained must be -20 ° C or lower. If it exceeds -20 ° C, the tack of the final latex obtained by polymerizing the lipophilic monomer will be insufficient.

The hydrophilic seed latex obtained as described above is used at a solid content of 5 to 50% by weight in the second stage polymerization, that is, the lipophilic mixed monomer is copolymerized.

And the monomers used in the second stage of polymerization are 1,
Conjugated dienes (component 2-1) such as 3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene and other substituted dienes such as 2-chloro-1,3-butadiene, preferably Is butadiene and an aromatic vinyl monomer (component 2-2) such as styrene and a styrene derivative,
Preferably styrene and methyl (meth) acrylate,
Ethyl (meth) acrylate, butyl (meth) acrylate, butyl (meth) acrylate, 2-ethyl (meth) acrylate, hexyl (meth) acrylate and other (meth) acrylic acid esters (second component), preferably 2 -Ethylfoxyl acrylate and butyl acrylate, and α, β-unsaturated carboxylic acid (component 2-4) copolymerizable therewith. Examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, fumaric acid, itaconic acid, maleic acid, crotonic acid and the like.

In addition to the above monomers, acrylonitrile, N-
A copolymerizable monomer such as methylol acrylamide or 2-hydroxyethyl acrylate can also be used in combination.

The amount of conjugated diene in the lipophilic mixed monomer is preferably 5 to 80% by weight, and the amount of aromatic vinyl monomer is preferably 0 to 70% by weight, based on the total amount of monomers used in the second-stage polymerization. Further, the amount of (meth) acrylic acid ester is 0 to
50% by weight is preferable, and it is preferable to use 10% by weight or less of α, β-unsaturated carboxylic acid.

The synthetic latex for pressure-sensitive adhesives of the present invention can be obtained by two-step polymerization, but the polymerization method and the polymerization conditions in each step are in accordance with known emulsion polymerization and do not require special methods or conditions.

The synthetic latex for pressure-sensitive adhesives is obtained by polymerizing a lipophilic mixed monomer containing a conjugated diene in the presence of a hydrophilic polymer latex, wherein the hydrophilic polymer layer is on the surface of the particle and the lipophilic polymer layer is It is considered that the latex contains a large number of latex particles selectively located inside the particle, and the latex has a manufacturing method and a structure which is completely different from the conventional one.

The thus-obtained synthetic latex for pressure-sensitive adhesive has excellent adhesive performance and, as a diene-based latex, excellent heat resistance and light resistance.

Further, the synthetic latex for pressure-sensitive adhesives of the present invention can be used alone by thickening it, but it can also be used by blending with a tackifying resin in order to obtain higher adhesive strength. Examples of the tackifying resin include rosin, rosin acid ester, and terpene resin. Further, if necessary, various plasticizers and softeners, fillers such as zinc white, titanium oxide and calcium carbonate, antioxidants, ultraviolet absorbers, stabilizers and the like can be appropriately added.

A pressure-sensitive adhesive containing the synthetic latex for pressure-sensitive adhesive of the present invention,
It is suitable for a wide range of adhesive applications such as various tapes, labels and seals.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

Examples 1 to 9 Emulsion polymerization compounding compositions shown in Table 1 were added to a monomer in an autoclave under a nitrogen atmosphere at a temperature of 80 ° C. for 8 hours for polymerization to polymerize the hydrophilic seed latex A, B, C, D, E was obtained, and then, in the presence of the above hydrophilic seed latex, the monomer composition shown in Table 2 was used at a temperature of 60 to 70 ° C. under a nitrogen atmosphere using the emulsifier, catalyst and the like shown in Table 2. It was polymerized for 20 hours. After completion of the polymerization, the pH of the latex was adjusted to 7 with caustic soda, and steam stripping was performed to remove the residual monomers to synthesize the synthetic latex F, G, H, I, J, K, L for adhesives of the present invention.
I got M and N. Next, a small amount of partially saponified poval was added to the above synthetic latex for pressure-sensitive adhesive to adjust the viscosity to about 10,000 centipoise, and this was applied to release paper (applied amount about 30 g / m ² ).
And dried at 120 ° C. for 2 minutes. Next, an adhesive was transferred to a high-quality paper by a transfer method to obtain an adhesive raw paper sample, and the following physical properties were measured.

Tack: Measured with a tilting ball tack. Inclined plate angle 30
Degree, run distance 10 cm. Ball diameter is displayed as x / 32 inch.

Cohesion: Adhesive base paper sample is attached to a stainless steel plate (2 cm x 2 cm area), a load of 1 kg is applied to one lower end of the vertically suspended adhesive base paper sample, and the load is dropped by leaving it in an atmosphere at 60 ° C. The retention time (minutes) before the measurement was measured.

Adhesive strength: A sticky base paper sample was stuck on a stainless steel plate with a constant pressure (2 kg roller) (2.5 cm width), and the tensile strength was measured when 180-degree angle peeling was performed. Tensile speed
300 mm / min.

Light resistance: The adhesive base paper sample was irradiated with ultraviolet rays for 60 hours with a fade meter, and then the above adhesive strength was measured to obtain the adhesive strength retention rate. (Retention rate = adhesive strength after UV irradiation / adhesive strength before UV irradiation) Heat resistance: Adhesive base paper sample at 110 ° C
After leaving it in the atmosphere for 60 hours, measure the above adhesive strength,
The retention rate of adhesive strength was determined. (Retention rate = Adhesive force after heat treatment) Table 3 shows the measurement results of these physical properties.

Comparative Example Synthetic latexes O and P for adhesives having compositions outside the scope of the present invention shown in Table 2 were obtained in the same manner as in the examples. Various physical properties of these synthetic latexes for pressure-sensitive adhesives were measured in the same manner as in Examples, and the results are shown in Table 3.
Various physical properties of the commercially available acrylic latex adhesive and the commercially available rubber solvent type adhesive were also measured, and the results are shown in Table 3.

From these results, it is clear that the synthetic latex for pressure-sensitive adhesives of the present invention has excellent adhesive performance and aging resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Sugiyama 1-3-1 Yokou, Kawasaki-ku, Kawasaki-shi, Kanagawa Asahi Dow Co., Ltd. (56) Reference JP-A-56-34777 (JP, A)

Claims (3)

[Claims] 1. A synthetic latex for pressure-sensitive adhesive obtained by emulsion copolymerization of 50 to 95 parts by weight of a lipophilic mixed monomer in the presence of 5 to 50 parts by weight of a hydrophilic polymer latex. 2. A hydrophilic polymer latex comprising (meth) acrylic acid ester containing 4 to 10 carbon atoms in 20 to 98 parts by weight of alcohol component and 0 to 10 parts by weight of α, β-unsaturation. A polymer latex obtained by copolymerizing a carboxylic acid and 0 to 80 parts by weight of a vinyl ester or other copolymerizable monomer, and the glass transition point (Tg) of the copolymer is -20 ° C or lower. The synthetic latex for pressure-sensitive adhesives according to claim (1). 3. A lipophilic mixed monomer comprising 5 to 80 parts by weight of a conjugated diene, 0 to 70 parts by weight of an aromatic vinyl monomer, 0 to 10 parts by weight of an α, β-unsaturated carboxylic acid, and 0 to 50. A mixed monomer comprising a (meth) acrylic acid ester or another copolymerizable monomer containing 4 to 10 carbon atoms in parts by weight of an alcohol component, and the mixed monomer according to claim (1). Synthetic latex for adhesives.