JPH01297480A - Pressure-sensitive adhesive of emulsion type - Google Patents

Abstract

PURPOSE:To obtain the subject adhesive for pressure-sensitive adhering tape, etc., having excellent tack strength, adhesive force and cohesive force with good balance, showing good adhesion even to polyolefin, containing aromatic methylene resin in copolymer emulsion in specific ratio. CONSTITUTION:(A) 100 pts.wt. (as solid) copolymer composed of 60-99.9wt.% one monomer of (meth)acrylic ester having 4-12C linear alkyl group, 0.1-5wt.% at least one monomer of unsaturated monocarboxylic acid and dicarboxylic acid is subjected to emulsion polymerization with (B) 5-40 pts.wt. aromatic methylene resin containing no oxygen atom to afford the aimed adhesive showing good adhesion even to adherend having poor tackiness and adhesion.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an emulsion-type pressure-sensitive adhesive made of an acrylic copolymer, and more specifically, it has high adhesive strength, adhesion strength, and cohesive strength, and The present invention relates to an acrylic copolymer emulsion type pressure sensitive adhesive that has excellent adhesive strength even to adherends with poor adhesiveness.

(Prior Art) Conventionally, natural rubber-based, silicone-based, and acrylic polymer-based pressure-sensitive adhesives are known, and pressure-sensitive adhesives such as adhesive tapes,
Widely used in adhesive sheets and various other applications. Among these pressure-sensitive adhesives, acrylic polymer-based adhesives have superior weather resistance and aging resistance compared to natural rubber-based adhesives, so there is less decline in adhesive strength and cohesive strength due to oxidation and deterioration over time. In addition, it has the advantage that it has superior properties such as adhesive strength, adhesion strength, and cohesive strength, and is lower in cost than silicone-based materials.

Therefore, pressure-sensitive adhesives based on acrylic polymers are used in a wide range of applications, and in addition to their usefulness, there is a need for products with a higher level of balance in terms of adhesion and adhesion. . There are two types of acrylic polymer pressure-sensitive adhesives: solvent-based and emulsion-based. Solvent-based adhesives have better performance than emulsion-based adhesives, but a solvent recovery process is required in the production of adhesive tapes and sheets. become.

Therefore, the emulsion type, which does not require a solvent recovery process and is superior in terms of pollution, productivity, and cost, has recently attracted attention compared to the solvent type, and has improved performance such as adhesive strength, adhesive strength, and cohesive force. There is now a need for superior acrylic polymer emulsion type pressure sensitive adhesives.

However, pressure-sensitive adhesives based on acrylic polymers have a problem in that they lack adhesive strength to adherends such as polyolefins, which have poor adhesive properties.

Therefore, it was necessary to develop an acrylic polymer-based emulsion-type pressure-sensitive adhesive that has high levels of adhesive strength, adhesion strength, and cohesive strength, and also exhibits good adhesion to adherends such as polyolefin. desired.

(Problem to be solved by the invention) Adhesive force and cohesive force in pressure-sensitive adhesives have an inverse relationship; increasing the adhesive force lowers the cohesive force, while increasing cohesive force lowers the adhesive force. Therefore, it is extremely difficult to increase both properties, but as a result of extensive research, we have found that emulsion-type pressure-sensitive adhesives based on acrylic polymers containing aromatic methylene resin have improved adhesive strength, adhesion strength, and cohesion. The present invention was achieved by discovering that the adhesive has a high level of adhesive strength and exhibits good adhesive strength even to adherends such as polyolefin.

(Means for Solving the Problem) As a solution to the above-mentioned problem, the composition of the monomer is at least one selected from acrylic esters and methacrylic esters having a chain alkyl group having 4 to 12 carbon atoms. 60 to 99.8% by weight of monomer, 0.1 to 5% by weight of at least one monomer selected from unsaturated monocarboxylic acids and dicarboxylic acids, and 0 to 38% of other copolymerizable monomers. An emulsion type consisting of 100 parts by weight (solid content) of a copolymer (A) obtained by copolymerizing .9% by weight and 5 to 40 parts by weight of an aromatic methylene resin (B) that does not substantially contain oxygen atoms. A pressure sensitive adhesive is provided.

The present invention will be explained in detail below.

Emulsion type pressure sensitive of the present invention! The copolymer emulsion contained in the adhesive Ii contains (1) an acrylic ester or methacrylic ester having a chain alkyl group having 4 to 12 carbon atoms, (2) an unsaturated monocarboxylic acid, a dicarboxylic acid, ( 3) Obtained by copolymerizing a monomer mixture consisting of other copolymerizable monomers.

The above (1) acrylic ester and methacrylic ester monomers having a chain alkyl group having 4 to 12 carbon atoms include 2-ethylhexyl acrylate, butyl acrylate, isononyl acrylate, octyl acrylate, and 2-methacrylic acid. -Ethylhexyl, butyl methacrylate, isonocyl methacrylate, octyl methacrylate, and the like. Among these, 2-ethylhexyl acrylate and butyl acrylate are particularly preferred, and these acrylic ester and methacrylic ester monomers can be used alone or in combination of two or more.

The amount of the acrylic ester or methacrylic ester monomer having a chain alkyl group having 4 to 12 carbon atoms is 60 to 38.9% by weight, preferably 70 to 9% by weight in the monomer mixture.
It is 5% by weight. If it is less than 60% by weight, the adhesive force and adhesion will be insufficient, while if it exceeds 99.9% by weight, the cohesive force will decrease.

In the above (2) unsaturated monocarboxylic acid or dicarboxylic acid? As for the body, acrylic acid and methacrylic acid.

Examples include itaconic acid, crotonic acid, and maleic acid. These monomers can be used alone or in a mixture of two or more. The amount of unsaturated monocarboxylic acid and dicarboxylic acid monomers used is 0.1 to 5% by weight, preferably 0.5 to 4% by weight in the monomer mixture. If it is less than 0.1% by weight, sufficient cohesive force cannot be obtained;
If it exceeds this, the adhesive strength will decrease.

(3) Other copolymerizable monomers include amides such as acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide; nitriles such as acrylonitrile and ethyl methacrylate; methyl acrylate , methyl methacrylate, ethyl acrylate, ethyl methacrylate, vinyl acetate, allyl phthalate, allyl acrylate, allyl methacrylate, etc., other than the above-mentioned acrylic esters and methacrylic ester monomers having a chain alkyl group having 4 to 12 carbon atoms. and aromatic vinyl compounds such as styrene. These monomers can be used alone or in combination of two or more.

The amount of other copolymerizable monomers used is 0 to 39.8% by weight, preferably 5 to 35% by weight in the monomer mixture. If the amount exceeds 9% by weight, the adhesive strength will be impaired.

As the emulsifier used in preparing the above copolymer emulsion, any known and commonly used emulsifier can be used, but representative examples include sodium alkyl diphenyl ether disulfonate, alkyl diphenyl ether disulfonate, and anionic surfactant. Sodium sulfate, sodium lauryl alcohol sulfate, sodium dodecylbenzene sulfonate, etc. Nonionic surfactants include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyethylene glycol sorbitan monolaurate, etc. The activators can be used alone or in combination of two or more.

In addition, as a polymerization initiator used in copolymerizing the above copolymer emulsion, hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate, t-
Known and commonly used initiators such as butyl hydroperoxide can be used, and redox initiators formed by combining such polymerization initiators with known reducing substances such as 7-scorbic acid or sulfites can also be used.

In the present invention, the aromatic methylene resin containing substantially no oxygen atoms contained in the emulsion-type pressure-sensitive adhesive of the present invention is defined as having a chemical structure in which aromatic compounds are bonded by methylene groups, and having an oxygen atom. It is a resin that contains virtually no . "Contains virtually no"
means aromatic methylene resin obtained by the following method,
This refers to the extent to which oxygen cannot be detected even by an oxygen detection device.

Aromatic methylene resin is obtained by polymerizing an aromatic compound and formaldehyde in the presence of a specific catalyst, and by using a strongly acidic cation exchange Ml resin as the catalyst, oxygen is substantially removed. This yields an aromatic methylene resin containing no carbon. Examples of the aromatic compound include benzene derivatives such as benzene, toluene, xylene, methylbenzene and trimethylbenzene, polycyclic aromatic compounds such as naphthalene and anthracene, and derivatives thereof. These may be used alone or in combination of two or more. In addition to formaldehyde, the formaldehyde may also be one that generates monomeric formaldehyde during the reaction, and is preferably trioxane (formaldehyde trimer). It is manufactured by the method described in No. 81-213216.

The aromatic methylene resin preferably has a softening point of 80 to 130°C. If it is less than 80°C, the cohesive force tends to be poor, while if it exceeds 130°C, the adhesive strength tends to be poor.

The above aromatic methylene resins can be used alone or in combination of two or more. The amount of aromatic methylene resin used is 5 to 40 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the solid copolymer emulsion. If it is less than 5 parts by weight, the adhesive strength will be insufficient;
If it exceeds parts by weight, the cohesive force will decrease.

By incorporating this aromatic methylene resin into the above-mentioned copolymer emulsion, the adhesive strength, adhesion strength, and cohesive strength of the emulsion-type pressure-sensitive adhesive can be further improved, and it can be applied to adherends with poor adhesiveness. This has the unexpected effect of increasing adhesive strength.

The following method may be mentioned as a method for incorporating an aromatic methylene resin into a copolymer emulsion.

(1) A method of adding and mixing an aromatic methylene resin to a comonomer emulsion. In this case, the dispersibility of the aromatic methylene resin is improved if it is emulsified in advance.

(2) A method of incorporating an aromatic methylene resin into a copolymer emulsion by dissolving the aromatic methylene resin in advance in a monomer mixture used for polymerization of the copolymer emulsion and emulsion polymerizing the same.

(3) A method of combining methods (1) and (2) above.

A preferred method is the method (2) above, which provides a much better adhesive force and is more suitable for the purpose of the present invention.

In addition to the above ingredients, the emulsion type pressure-sensitive adhesive of the present invention may contain fillers, pigments, thickeners, antifoaming agents, anti-aging agents, crosslinking agents, wetting agents, plasticizers, and tackifiers. Additives such as can be used in combination.

(Example) Hereinafter, the present invention will be explained in more detail with reference to Examples.

Note that parts and % mean parts by weight and % by weight, respectively.

Examples 1-1 to 1-9, Comparative Examples 1-1 to 1-7 Preparation of copolymer emulsion> 1.0 part of sodium lauryl sulfate (anionic surfactant) and polyoxyethylene in 60 parts of ion-exchanged water 3.0 parts of nonylphenyl ether (nonionic surfactant) was added to prepare an emulsifier aqueous solution, and Example 1
-1 to 1-9, Comparative Examples 1-1 to 1-7 (Table 1), and 0.02 part of N-dodecylmercaptan was added as a degree of modification regulator and emulsified.

Next, 40 parts of ion-exchanged water and 0.3 parts of sodium persulfate were charged into a 1-liter four-bottle flask equipped with a stirrer, thermometer, reflux condenser, and dropping funnel, and the temperature was raised to 70°C while purging with nitrogen. Then, when the liquid temperature reached 70°C, the above-mentioned seven-spot emulsion was added dropwise over 3 hours. After the completion of the 0 dropwise addition, stirring was continued at 80°C for 2 hours to complete the emulsion polymerization.

Dispersion of resin into copolymer emulsion> Example 1-1
~1-9, Comparative Examples 1-1 to 1-7 (Table-1) Resin 10
0 part was dissolved in 100 parts of toluene, the solution was added to a 3% sodium alkylbenzene sulfonate solution, and dispersed with a homomixer. After dispersion, toluene was recovered by vacuum distillation to obtain an aqueous dispersion of each resin. .

Aqueous dispersions of these resins were added to the copolymer emulsion. Note that the parts of each resin shown in Table 1 are parts by weight as solid content.

Using each of the emulsion-type pressure-sensitive adhesives thus obtained, pressure-sensitive adhesive sheets were prepared according to the methods described below, and tests on adhesive strength, adhesion strength, and cohesive strength were conducted. The results are shown in Table 1. Table 1 also shows the overall evaluation results of the balance of each gender.

(Preparation of adhesive sheet) Apply each emulsion-type pressure-sensitive adhesive to high-quality paper (64 g/layer 2 tsubo) so that the dry weight is 25 g/m2, dry, and layer release paper on the adhesive-coated surface. They were joined to create an adhesive sheet.

(Adhesive force test) J, A sample with a length of 10 cm is pasted on a slope with an inclination angle of 30' in an atmosphere of 23°C x 6.5% RH according to the Dow method, and a diameter of X/32 is measured from a position 10 cm above the slope. An inch-sized steel pole was rolled, and the size of the pole with the largest diameter that stopped on the sample was indicated by X.

The larger the value of X, the higher the adhesive strength.

(Adhesion test) A high-density polyethylene plate with a thickness of 2 layers, a width of 5011 layers, and a length of 125 m or a stainless steel plate of 5US304 was
Polished by the method of l5-z-0137, and then [25■
Otori, 250mm long adhesive sheet at 23℃ x 60%RH
It was applied in a room with a 3kg roller 5 times back and forth, and after 2 hours it was peeled off at an angle of 180° at a tensile test a (S-500 manufactured by Shimadzu Corporation) at a tensile speed of 300 + * + * / min. Adhesive strength was measured. The larger the number, the higher the adhesive strength.

(Cohesive force test) 5US3 with a thickness of 3 m layer, width of 50 am, and length of 80 m5+
04 stainless steel plate was polished by the method specified in J l5-z-0237, and the ball mating part was 25 mm x 25 mm.
Place the adhesive sheet so that the distance is 1 mm, and apply it by making 5 reciprocations with a 3 kg roller.Hang a 1 kg weight on the bottom edge of the adhesive sheet and measure the length of deviation after 60 minutes in an O atmosphere of 40 mm.
m layers) or the time (minutes) for shedding. The smaller the length of the deviation, the higher the cohesive force.

(Evaluation of adhesion balance) The results of the 2 adhesion tests, adhesive strength tests, and cohesive strength tests were comprehensively evaluated and indicated as O: excellent, Δ: good, and ×: poor.

As is clear from Table 1, Examples 1-1 to 1-9, which are adhesives of the present invention, all have excellent adhesive strength, adhesive strength,
Figure 2 shows the cohesive force and tk balance.

Comparative Example 1-1 is a case in which no resin is added, and the adhesive strength to polyethylene is poor.

Comparative Example 1-2 is a case where the content of aromatic methylene resin is higher than the range of the present invention, and the adhesive force and cohesive force are inferior.

Comparative Examples 1-3.1-4 are cases where a resin other than aromatic methylene resin was used, and the cohesive force was poor.

Comparative Examples 1-5 are cases in which unsaturated monocarboxylic acid and dicarboxylic acid are not used, and the cohesive force is poor.

Comparative Examples 1-6 are cases where the amount of unsaturated monocarboxylic acid and dicarboxylic acid used is larger than the range of the present invention, and the adhesive strength is inferior.

Comparative Examples 1-7 are cases in which the amount of other copolymerized 0-weight materials used is greater than the range of the present invention, and the adhesive strength to polyethylene is poor.

Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-6 Example 1
-1 to 1-9 - Preparation of co-hair coalescent emulsions>, a heptamer mixture (Example 2) was used instead of the monomer mixture.
Compositions of -1 to 2-9 and Comparative Examples 2-1 to 2-6 (Table-2)
) to resin (Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-
Emulsion polymerization was carried out in the same manner as in Example 1, except that a solution obtained by mixing and dissolving the composition of Example 6 (Table 2)) was used. In addition, each part of resin shown in Table 2 is 1 part of beads as a solid content.

Using each emulsion type pressure sensitive adhesive obtained in this way,
An adhesive sheet was prepared in the same manner as in Example 1, and the adhesive strength and
Adhesion and cohesion tests were conducted. The results are shown in Table 2, and the overall evaluation results of the balance of each of the above performances are also shown in Table 2.
Shown below.

As is clear from Table 2, Examples 2-1 to 2-9, which are adhesives of the present invention, all have excellent adhesive strength, adhesive strength,
Examples 1-1 to 1-9 showing the balance of cohesive force
The adhesive strength of this example tends to be better than that of the present example.

Comparative Example 2-1 is a case in which the content of aromatic methylene resin is higher than the range of the present invention, and the adhesive force and cohesive force are inferior.

Comparative Examples 2-2 and 2-3 are cases in which a resin other than aromatic methylene resin is used, and the cohesive force is poor.

Comparative Example 2-4 is a case where unsaturated monocarboxylic acid and dicarboxylic acid are not used, and the cohesive force is poor.

Comparative Example 2-5 uses more unsaturated monocarboxylic acids and dicarboxylic acids than the range of the present invention, and has poor adhesive strength.

Comparative Example 2-6 is the use of other copolymerizable monomers I
This is a case where the amount of IC is larger than the range of the present invention, and the adhesive strength to polyethylene is poor.

(Effect of the invention) The emulsion-type pressure-sensitive adhesive of the present invention has excellent adhesion, adhesion, and cohesion in a well-balanced manner, and exhibits good adhesion, especially to adherends with poor adhesive properties such as polyolefins. Therefore, the emulsion-type pressure-sensitive adhesive of the present invention can be effectively used in various applications such as pressure-sensitive adhesive tapes and sheets.

Claims (2)

[Claims] (1) At least one monomer selected from acrylic esters and methacrylic esters having a chain alkyl group having 4 to 12 carbon atoms, with a monomer composition of 60 to 99.9
% by weight, 0.1 to 5% by weight of at least one monomer selected from unsaturated monocarboxylic acids and dicarboxylic acids, and 0 to 39.9% by weight of other copolymerizable monomers. An emulsion-type pressure-sensitive adhesive comprising 100 parts by weight (solid content) of a copolymer (A) consisting of the following: and 5 to 40 parts by weight of an aromatic methylene resin (B) substantially free of oxygen atoms. (2) The emulsion-type pressure-sensitive adhesive according to claim 1, wherein the copolymer (A) is emulsion polymerized in the presence of part or all of the aromatic methylene resin (B).