JPH0249347B2 - SUKURIININSATSUTOKOSEINOYOIMIZUBUNSANGATAKANATSUSETSUCHAKUZAI - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an acrylic water-dispersed pressure-sensitive adhesive having good screen printing coating properties, and particularly to an acrylic emulsion-based water-dispersed pressure-sensitive adhesive. In recent years, acrylic pressure-sensitive adhesives have become widely used in place of conventional natural rubber-based and synthetic comb-based pressure-sensitive adhesives due to their excellent adhesive properties, durability, and weather resistance. Also, among these acrylic pressure-sensitive adhesives,
Recently, water-dispersed products that do not use organic solvents have been intensively developed from the viewpoints of resource saving, environmental pollution prevention, and fire prevention. Such acrylic water-dispersed pressure-sensitive adhesives generally contain acrylic esters, copolymerizable monomers such as methacrylic esters, vinyl acetate, styrene, vinylidene chloride, etc., carboxyl group-containing monomers such as acrylic acid, Hydroxyl group-containing monomers such as 2-hydroxyethyl methacrylate, amide group-containing monomers such as acrylamide,
It is produced by emulsion polymerization in an aqueous medium together with crosslinking monomers such as diallyl phthalate and ethylene glycol dimethacrylate, other modifying monomers, chain transfer agents, plasticizers, etc. Usually, antifoaming agents, thickeners, PH regulators, pigments, fungicides, etc. are added to this, and knife co.
Film is coated with a suitable coating machine such as a roll coater.
It is widely used to make adhesive sheets, labels, films, stickers, etc. by directly applying it to the base material of paper or sheets or by transferring it from release paper. On the other hand, when conventionally printing parts printed on various plastics, films, plates, or metal plates, especially screen-printed parts, are to be attached to an adherend as a nameplate, etc., a double-sided adhesive tape is applied to the back side of the printed part, and It was necessary to punch out the required pattern and attach it to the adherend, resulting in extremely poor workability. In view of such conventional technology, the present inventors devised a method of applying a pressure-sensitive adhesive directly to the back surface of a nameplate, etc. using a screen printing coating method, and found a pressure-sensitive adhesive suitable for this purpose. . That is, the present invention provides a water-dispersed pressure-sensitive adhesive comprising an aqueous dispersion of a polymer that is sticky at room temperature and is obtained by polymerizing a monomer mixture mainly composed of acrylic esters and/or methacrylic esters in an aqueous medium. and the viscosity measured at a rotor rotation speed of 6 rpm using a B-type viscometer for water-dispersed pressure-sensitive adhesives.
(The rotation speed of the same rotor as the above rotor is 60 r.p.
It is a water-dispersed pressure-sensitive adhesive with good screen printing application properties, and is characterized by a thixotropic index (viscosity measured in m.m.) in the range of 2.5 to 5.5. In the case of screen printing, the pressure-sensitive adhesive to be applied preferably has good fluidity and drainage properties. Ordinary water-based and solvent-based pressure-sensitive adhesives have good fluidity, but they have poor liquid drainage and continue to drip, making workability poor.On the other hand, ordinary emulsion-based water-dispersed pressure-sensitive adhesives It is essentially thixotropic, and there is a big difference in the fluidity of the liquid from aqueous and solvent-based pressure-sensitive adhesives.When applying screen printing, the liquid drains well, but it is difficult to use a squeegee to transfer the liquid to a screen cloth. Due to the poor fluidity of the liquid when it is mixed, it is difficult to obtain a uniform coating. However, when the thixotropic properties of acrylic emulsion-based water-dispersed pressure-sensitive adhesives are within a certain range, both the fluidity and drainage properties of the liquid when squeezed with a squeegee are not suitable for screen printing coating. It will become. That is, when the viscosity of an acrylic emulsion water-dispersed pressure-sensitive adhesive is measured using a B-type viscometer (viscosity measured at a rotor rotational speed of 6rpm)/(rotational speed of the same rotor as the above rotor 60rpm). A material whose viscosity is adjusted to have a thixotropic index (hereinafter referred to as "TI value") in the range of 2.5 to 5.5 (viscosity measured in pm) is suitable for screen printing coating. The viscosity and TI value as used in the present invention refer to values determined under the following conditions. Viscometer: B-type viscometer (BM type) Rotor used: #4 Rotor rotation speed: 60r.pm (60r.pm and 6r.pm when measuring TI value) Measurement temperature: 25℃ Measurement method: Under the above conditions Rotate the rotor placed in the specified position in the object to be measured, read the indicated value 90 seconds after the start of rotation,
Convert to viscosity using the conversion table. Screen printing using printing ink is generally widely practiced, and the pressure sensitive adhesive according to the present invention can be applied instead of ink using this screen printing technique. For example, a screen made of silk, nylon, polyester, stainless steel, etc. with minute holes is stretched over a frame, and paper (stencil) is used to cut out the lines or patterns to be painted on the screen. , place it on the object to be coated (base material), apply pressure-sensitive adhesive from the back of the screen, and squeeze with a squeegee.
Pressure-sensitive adhesive is transferred to the surface of the object to be coated (substrate) through a screen, along the cut-out lines or patterns, and then applied to the paper along the cut-out lines or patterns. It is. Compared to other plate-type coating methods such as gravure coating, which can similarly draw drawing lines and patterns, this coating method has simple plate-making and coating processes, and can be applied thickly.
It has many features and merits, such as the ability to choose from a wide range of types and shapes of objects to be coated (substrate), so it is widely used for displays, nameplates, and other applications. The pressure-sensitive adhesive of the present invention is suitable for use in such displays, nameplates, etc., and is particularly preferably used for nameplates. This means, for example, that the front side of the nameplate is screen printed with ink, and then the same screen is used to apply pressure-sensitive adhesive to the back side, creating a nameplate with pressure-sensitive adhesive in the required areas with the minimum amount of application. This is because the method can be used. The method for producing the acrylic pressure-sensitive adhesive used in the present invention will be described below. The following monomers are polymerized in an aqueous medium in the presence of a known anionic emulsifier, nonionic emulsifier, amphoteric emulsifier, or cationic emulsifier. (1) The main monomer is an ester of acrylic acid and/or methacrylic acid and an aliphatic primary alcohol having 8 or less carbon atoms (hereinafter referred to as "(meth)acrylic acid ester"), and this is used as the main monomer. 50% by weight
(hereinafter simply referred to as "%") or more, preferably
More than 60%. 50% (meth)acrylic acid ester
If it is less than 10%, the resulting pressure-sensitive adhesive tends to have poor tackiness, which is not preferable. Further, as the (meth)acrylic ester, 2-ethylhexyl acrylate (hereinafter referred to as "HA") and butyl acrylate (hereinafter referred to as "BA") are preferable. (2) Less than 10% of the total monomers, preferably 1 to 5 unsaturated monomers having polar groups such as carboxyl, hydroxyl, amide, or glycidyl groups and one carbon-carbon double bond. %. These are added to improve cohesive strength, but because of their high glass transition temperatures, adding more than 10% tends to impair the tackiness of the resulting pressure-sensitive adhesive. (3) Ethylenically unsaturated monomers having one carbon-carbon double bond that can be copolymerized with the main monomer of (1), such as styrene, vinyl acetate, vinylidene chloride,
Cyclohexyl acrylate, stearyl methacrylate should not exceed 50% of the total monomers, preferably
30% or less. These are blended to improve cohesive strength, but if it exceeds 50%, the adhesive strength of the resulting pressure-sensitive adhesive tends to decrease. (4) Furthermore, if necessary, carbon-carbon compounds such as ethylene glycol dimethacrylate and diallyl phthalate
Unsaturated monomers with two or more carbon double bonds account for 5% or less of the total monomers. These monomers are optionally treated with a chain transfer agent,
A plasticizer and the like are added and radical copolymerization is performed to produce an aqueous dispersion of a polymer whose main monomer is (meth)acrylic acid ester, which is sticky at room temperature. In order for this polymer to have tackiness at room temperature, the glass transition temperature of the resulting polymer must be between -60°C and -
Preferably, the temperature is in the range of 30°C. Then, the TI value of the aqueous dispersion of this polymer is 2.5.
Adjust so that it is within the range of ~5.5. In order to provide screen printing, it is necessary that the TI value be within this range, and it is particularly preferred that the TI value be within the range of 3 to 5. When the TI value is less than 2.5, when used for screen printing, the fluidity of the liquid is good, but the liquid drainage is extremely poor, and the liquid drips forever, resulting in poor workability. On the other hand, if it exceeds 5.5,
Although the liquid drainability is good, when the liquid is squeezed with a squeegee, the fluidity is poor (the thixotropic property becomes too large) and a uniform film thickness cannot be obtained. The TI value of the aqueous dispersion of the polymer obtained by emulsion polymerization in the present invention may be a certain value even without using a viscosity modifier, but it is better to adjust it using a viscosity modifier. preferable. The viscosity modifier used in the present invention includes known agents that have a thickening effect without impairing the stability of the emulsion, such as polyacrylic acid and its salts, polyvinyl alcohol, and cellulose derivatives such as carboxylated methylcellulose. ,
The TI value of the present invention can be obtained by using polyethylene glycol fatty acid esters with an HLB of 15 or higher alone or in appropriate combinations; Particularly preferred is the combined use of viscosity modifiers having a TI value of 2 or less, such as polyvinyl alcohol, cellulose derivatives, and polyethylene glycol fatty acid esters with an HLB of 15 or more. Further, when adjusting the TI value, if an alkali thickening type viscosity modifier is used, it is necessary to adjust the pH of the system to 6 or higher. In addition, antifoaming agents, pigments, anti-skinning agents, etc. can also be added as necessary. The preferred viscosity varies depending on the coating thickness, but if the thickness after drying is about 15 to 30μ, 3000
~10000cP. If the viscosity is lower than 3000cP, flickering is likely to occur during printing, or
If it is higher than 10000cP, liquidity tends to be poor. When the pressure-sensitive adhesive of the present invention is applied using the screen printing coating method, 1) Since the pressure-sensitive adhesive can be applied in a free pattern using screen printing, it is possible to apply the pressure-sensitive adhesive in a free pattern. This eliminates the need to attach double-sided adhesive tape to the back of nameplates, etc., improving work efficiency. 2) Adhesive strength can be freely adjusted by selecting the screen mesh of the printing plate and the thickness of the film surface. 3) Since it is acrylic, it has good light resistance and weather resistance. 4) Because it is a water-based type that essentially does not contain solvents, you can work with peace of mind without worrying about fire or toxicity. 5) When punching items coated with pressure-sensitive adhesive, less adhesive adheres to the blade of the punching machine than when pasting conventional double-sided adhesive tape. It can be expected to have excellent features such as polycarbonate, polyester, and other plastics, paper,
It uses metal as the base material and can demonstrate sufficient performance for manufacturing nameplates, stickers, and labels. Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples, and various modifications can be made without departing from the technical idea of the present invention. Furthermore, in the Examples, parts mean parts by weight, and percentages mean percent by weight, and the adhesive strength, holding power, and tack were measured by the following methods. <Adhesive strength> The thickness of the 50μ thick polyester film after drying is
Directly apply pressure sensitive adhesive to 25μ, 100μ
Dry for 2 minutes at ℃ to create an adhesive film. Regarding this, 180 degree peeling strength was measured according to JISZ-0237. <Holding power> An adhesive film similar to the adhesive strength test was made, pasted on a stainless steel plate 25 x 25 mm, and held at 40℃ for 1 kg.
A load was applied and the time until it peeled off was measured. <Tatsu> Make an adhesive film similar to the adhesive strength test,
Ball tack was measured in accordance with the J.Dow method of JISZ-0237. The angle of the inclined plate is 30 degrees. Example 1 47.0 parts of water was charged into a 54-necked flask equipped with a stirrer, thermometer, cooling tube, and dropping funnel, and the temperature was raised to 80°C. Next, 70 parts of HA, 30 parts of BA, 3.5 parts of methacrylic acid (hereinafter referred to as "MAA"), 0.3 parts of N-methylolacrylamide (hereinafter referred to as [N-MAM]), and 0.1 part of dodecyl mercaptan (hereinafter referred to as "DM"). A mixture of 8 parts of polyoxyethylene nonyl phenyl ether sulfate,
It was emulsified with 21.5 parts of water and continuously dropwise polymerized with 1 part of 5% ammonium persulfate aqueous solution for 4 hours. During this time, the polymerization temperature was maintained at 80 ± 2°C, and after the addition was completed, the temperature was maintained for another 1 hour, and then cooled to room temperature to obtain a base polymer emulsion with a viscosity of 350 cP, a solid content of 54.5%, and a pH of 1.9. Ta. 100 parts of this base polymer emulsion was adjusted to pH 7.8 with aqueous ammonia, and a highly polymerized polycarboxylic acid type emulsion (Toagosei Chemical Industry Co., Ltd. trade name: Aron AS-7022 (PH=
2.5, solid content 35%)) and 0.5 part of a 5% aqueous solution of HLB20 polyoxyethylene distearate (melting point 80°C), pH 6.8, solid content 54.0%, TI value 3.3.
A pressure sensitive adhesive was obtained. This pressure-sensitive adhesive was applied 300 times to a 100μ thick polyester film using a 100-mesh silk screen, and a uniform pattern with good fluidity and dripping was obtained. Separately, the results of measuring the adhesive properties of this pressure-sensitive adhesive are shown in Table 1.

[Table] Example 2 60 parts of HA, 40 parts of BA, 10 parts of methyl acrylate (hereinafter referred to as "MA"), 3 parts of MAA, N-
Emulsion polymerization was carried out in the same manner as in Example 1 using a composition of 0.1 part of MAM and 0.1 part of DM, and the result was a pH of 2.1, a viscosity of 450 cP, and a solid content of
A 56.5% base polymer emulsion was obtained. This base polymer emulsion 100
The pH was adjusted to 7.2 with aqueous ammonia, and high molecular weight polycarboxylic acid emulsion (Toagosei Chemical Co., Ltd. trade name Aron AS-7050 (PH) was added as a viscosity modifier.
= 2.3, solid content = 35%)) diluted to 20% with water, 5.0 parts, cellulose thickener (Fuji Chemical Co., Ltd.)
Added 4.0 parts of a 3% aqueous solution of hydroxyethylcellulose A-5000 (trade name), viscosity 880cP, TI value 4.2.
A pressure sensitive adhesive was obtained. Example 1 with this pressure sensitive adhesive
The same process was repeated 300 times, and the workability was good. The adhesive properties of this pressure sensitive adhesive were as shown in Table 2.

[Table] Example 3 75 parts of HA, 10 parts of cyclohexyl acrylate,
9 parts MA, 6 parts vinyl acetate, 4 parts MAA, N-
Emulsion polymerization was carried out in the same manner as in Example 1 using a composition of 0.5 parts of MAM and 0.08 parts of DM, with a pH of 1.8, a viscosity of 180 cP, and a solid content of
A 53% base polymer emulsion was obtained. To this base polymer emulsion, 1.3 parts of sodium polyacrylate (trade name Aron A-20L, manufactured by Toagosei Kagaku Kogyo Co., Ltd.) and polyvinyl alcohol (trade name Poval 420, manufactured by Kuraray Co., Ltd.) are added as viscosity modifiers.
Added 0.5 part of 5% aqueous solution of, viscosity 4300cP, TI
A pressure sensitive adhesive with a value of 4.8 was obtained. 300 as in Example 1
As a result of repeated screen coating, the fluidity and drainability of the liquid when squeezed with a squeegee were both good, but some foaming occurred. However, when an antifoaming agent was used in combination, no foaming occurred and extremely good screen printability was exhibited. Table 3 shows the adhesive properties of this material.
Shown below.

[Table] Examples 4 to 6, Comparative Examples 1 to 2 Screen printing coatings using the same base polyemulsion as in Example 1 and adjusting various TI values with the same viscosity modifier as in Example 2. Table 4 shows the results of the workability investigation.

【table】

Claims (1)

[Claims] 1. A water-dispersed pressure-sensitive adhesive consisting of an aqueous dispersion of a polymer that is sticky at room temperature and is obtained by polymerizing a monomer mixture mainly composed of acrylic esters and/or methacrylic esters in an aqueous medium. , the thixotropy of water-dispersed pressure-sensitive adhesives measured with a B-type viscometer as (viscosity measured at a rotor rotational speed of 6rpm)/(viscosity measured at a rotational speed of the same rotor as the above rotor at 60rpm). A water-dispersible pressure-sensitive adhesive with good screen printing application properties, characterized by a tropic index in the range of 2.5 to 5.5.