JPS6032869A - Water dispersion type pressure-sensitive adhesive having improved coating performance of screen printing - Google Patents

Abstract

PURPOSE:An adhesive having a specific viscosity and liquid fluidity and liquid break during drawing with a squeeze which are suitable for screen printing coating, obtained by polymerizing a monomer mixture consisting essentially of (meth) acrylate in a water medium. CONSTITUTION:The desired adhesive comprising a water dispersion of a polymer having adhesivity at room temperature obtained by polymerizing a monomer mixture consisting essentially of (meth)acrylate (preferably >=60wt% based on total monomer) in a water medium, having 2.5-5.5 thixotropic index shown by a Brookfield viscometer (viscosity measured at 6r.p.m. revolution speed of rotor)/ (viscosity measured at 60r.p.m. revolution speed of the same rotor).

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 rubber-based pressure-sensitive adhesives due to their excellent adhesive properties, durability, and weather resistance.

Among these acrylic pressure-sensitive adhesives, recently, water-dispersible adhesives 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-human tetraxyethyl methacrylate, amide group-containing monomers such as acrylamide, crosslinking monomers such as diallyl phthalate and ethylene glycol dimethacrylate, other modifying monomers, chain transfer agents, plasticizers, etc. in an aqueous medium. It is made by emulsion polymerization in Then, usually, antifoaming agents, thickeners, heat regulators, pigments, antifungal agents, etc. are added to this, and a suitable coating machine such as a knife coater or roll coater is used to coat the substrate of film, paper, or sheet. It is widely used in the production of adhesive sheets, labels, films, stickers, etc. by direct coating or transfer coating from release paper.

On the other hand, when pasting printed matter printed on various plastics, films, plates, or metal plates, especially screen printed matter, to an adherend as a nameplate, etc., it is necessary to apply double-sided adhesive tape to the back side of the printed material, and It was necessary to punch out a 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. According to a B-type viscometer for water-dispersed pressure-sensitive adhesives (rotor rotational speed 6 r, p,
The chicken tropic index expressed as: (viscosity measured at m,)/(viscosity measured at the rotation speed of the same rotor as the above rotor, p, m,) is 2.5 to 5.5.
This is a water-dispersible pressure-sensitive adhesive with good screen printing application properties.

When applying by screen printing, it is preferable that the applied pressure-sensitive adhesive 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, resulting in poor workability.On the other hand, ordinary emulsion-based water-dispersed pressure-sensitive adhesives It is essentially thixotropic and has a large difference in fluidity from aqueous and solvent-based pressure sensitive adhesives.
When coating by screen printing, the liquid drains well, but it is difficult to obtain a uniform coating because of the poor fluidity of the liquid when squeezed onto the screen cloth with a squeegee.

However, when the thixotropic property of an acrylic emulsion-based water-dispersed pressure-sensitive adhesive is within a certain range, both the fluidity and draining 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-based water-dispersed pressure-sensitive adhesive is measured using a B-type viscometer (rotation speed of the rotor is 6 r, p,
The chicken tropic index (hereinafter referred to as "rTI value") expressed as viscosity measured at m, / (viscosity measured at rotation speed of the same rotor as the rotor 6 Or, p, m) is 2.5 to 5. A coating whose viscosity is adjusted to within the range of .5 is suitable for screen printing coating.

The viscosity and 1゛■ value referred to by Kinei Yuj refer to values found under the following conditions.

Viscosity meter 2B type viscometer (BM type) Rotor used:
#4 Rotation speed of 0-tor: 60 r, p, In, (T I
When measuring the value, use 00 r*p, In 6 r+p, m,
) Measuring temperature: 25°C Measuring method 2. Under the above conditions, rotate the four-couple placed in the specified position in the object to be measured, read the indicated value 90 seconds after the start of rotation, and convert it 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 areas to be painted on the screen. , place it on the object to be coated (substrate), apply pressure-sensitive adhesive from the back of the screen, and squeeze with a squeegee to apply the pressure-sensitive adhesive through the screen and through the cut-out drawing line or artist. Transfer the pressure-sensitive adhesive to the surface of the object to be coated (substrate), and apply pressure-sensitive adhesive along the lines cut out on the paper or according to the artist's pattern.'1
-.゛Compared to other plate-type coating methods such as gravure coating, which can similarly draw stroke lines and painters, this coating method has the following advantages: the plate-making and coating process is simple, thick coating is possible, and the coating material (base) is easy to coat. It has many features and benefits, such as a wide range of materials and shapes to choose from, so it is widely used for displays, nameplates, etc.

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, a nonionic emulsifier, an amphoteric emulsifier, and a cationic emulsifier.

(1) Acrylic acid and/or methacrylic acid and carbon 98
The following esters with aliphatic primary alcohols (hereinafter referred to as "(meth)acrylic acid esters") are the main monomers, and this constitutes 50% by weight of the total monomers (hereinafter simply referred to as "%").
or more, preferably 60% or more. If the (meth)acrylic acid ester is less than 50%, the resulting pressure-sensitive adhesive tends to have poor tackiness, which is undesirable. - HA J) and butyl acrylate (referred to as
(hereinafter referred to as 1BAj) is preferred.

(2) Unsaturated monomers having polar groups such as carboxyl groups, hydroxyl groups, amide groups, glycidyl groups and one carbon-carbon double bond account for 10% or less of the total monomers, preferably 1
~5%. These are blended to improve the cohesive direction, but since they have a high glass transition temperature, if they are added in an amount exceeding 10%, the tackiness of the resulting pressure-sensitive adhesive tends to deteriorate.

(3) Ethylenically unsaturated monomers having one carbon-carbon double bond that can be copolymerized with the filQ main monomer, for example,
Styrene, vinyl acetate, vinylidene chloride, cyclohexyl acrylate, and stearyl methacrylate account for 50% or less of the total monomers, preferably 30% or less. These are added to improve the cohesive direction, but if the amount exceeds 50%, the adhesive strength of the resulting pressure-sensitive adhesive tends to decrease.

(4) Furthermore, if necessary, unsaturated monomers having two or more carbon-carbon double bonds, such as ethylene glycol dimethacrylate and diallyl phthalate, may be contained in an amount of 5% or less of the total monomers.

A chain transfer agent, a plasticizer, etc. are added to these monomers as necessary to perform radical copolymerization. Produce an aqueous dispersion.

In order for this polymer to have tackiness at room temperature, the glass transition temperature of the resulting polymer is preferably in the range of 160°C to -30°C.

Then, the TI value of the aqueous dispersion of this polymer was 2.5-rc.
4) In order to provide screen printability, the TI value must be within this range,
Particularly preferred is a TI value in the range 6-5. If the TI value is less than 2.5, when subjected to 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, the liquid drainability is good, but when the liquid is squeezed with a squeegee at °C, the fluidity is poor (the thixotropic property becomes too large), and a uniform film thickness cannot be obtained. TI of the aqueous dispersion of polymer obtained by emulsion polymerization in the present invention
Although a predetermined value may be obtained without using a viscosity modifier, it is preferable to adjust the value using a viscosity modifier.

The viscosity modifier used in the present invention includes known agents that have a thickening effect without impairing emulsion stability, such as cellulose inducers such as polyacrylic acid and its salts, polyvinyl alcohol, and carboxylated methyl cellulose. The TI value of the present invention can be obtained by using polyethylene glyco-subfatty esters with an HLB of 15 or higher alone or in appropriate combinations, but when polyacrylic acid and its salts have a TI value of 6.
It is particularly preferred to use the above viscosity modifier in combination with a viscosity modifier that itself has 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.

need to be adjusted.

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 30 μm, the viscosity is 5000 to 10 μm.
It is about 000cP. If the viscosity is lower than 3DOOcP, flickering is likely to occur during printing (or 100UDc
If it is higher than p, the fluidity 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. There is no need to attach double-sided adhesive tape to the back of nameplates, etc., which improves 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.

5) 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, there is no need to worry about fire or damage (you can work with confidence).

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.

You can expect excellent features such as polycarbonate,
Using various plastics such as polyester, paper, and metal as base materials, it can demonstrate sufficient performance for manufacturing nameplates, stickers, and labels.

Hereinafter, the present invention will be explained in more detail with reference to Examples.
However, the present invention is not limited to these, and various modifications can be made without departing from the technical idea of the present invention. Furthermore, in the examples, parts mean M, and % means MR%, and the adhesive strength, holding power, and tack were measured by the following methods.

Adhesive strength> 50μ thick polyester film with a dry thickness of 25μ
Apply pressure sensitive adhesive directly to the surface and dry for 2 minutes at 100°C to create an adhesive film. This is awesome JISZ-
0237, the 180 degree peeling strength was measured.

Holding power> An adhesive film was made in the same manner as in the adhesive strength test, and was attached to a stainless steel plate at 25X and 25 m@1, and the time until it peeled off was measured at 40° C. by applying a 1-y load.

KuTack〉 Make an adhesive film similar to the adhesive strength test and JISZ-
Ball tack was measured according to the J-Daw method of 0237. The angle of the inclined plate is 30 degrees.

Example 1 5I equipped with stirrer, thermometer, cooling tube, and dropping funnel!
On the 4th day, 47.0 parts of water was charged into the flask, and the temperature was raised to 80°C. Next, 70 parts of HA, 50 parts of 13A, methacrylic acid (
(hereinafter referred to as rMAAJ) 6.5 parts, N-methylol acrylamide (hereinafter referred to as rN-MAM) o, 3
Part, dodecyl mercaptan (hereinafter referred to as "DM") 0
．． One part of the mixture was emulsified with 8 parts of polyoxyethylene nonylphenyl ether sodium sulfate and 21.5 parts of water, and continuously dropwise polymerized with 1 part of a 5% ammonium persulfate aqueous solution over 4 hours. During this period, the polymerization temperature was maintained at 80±2° C., and after the completion of the dropwise addition, the temperature was maintained for an additional 1 hour.

100 parts of this base polymer emulsion was prepared with aqueous ammonia to pH 7.8 km, and as a viscosity modifier, a highly polymerized polycarboxylic acid type emulsion (Toagosei Chemical Co., Ltd. trade name: Aro/AS-7022 (pH=2. 5,
Solid content 65%)
．． Added 5 parts, pl-is, 8, solids content 54.0%
, a pressure sensitive adhesive having a TI value of 3.6 was obtained.

This pressure-sensitive adhesive was coated 600 times on a 100 μm thick polyester film using a 100-mesh silk screen, and a uniform pattern with good fluidity and dripping could be obtained.

Separately, the results of measuring the adhesive properties of this pressure-sensitive adhesive are shown in Table 1.

Table 1 Example 2 60 parts Bi, 12 parts Bi, methyl acrylate (hereinafter "M
Aj) 10 parts, MAA 3 parts, N-MAMo, 1
Emulsion polymerization was carried out in the same manner as in Example 1 with a composition of 1 part DMo and 1 part DMo, pH 2.1 and viscosity 420 cP.

A base polymer emulsion with a solids content of 56.5% was obtained. This base polymer emulsion 100
The pH was adjusted to Z2 with aqueous ammonia, and a high molecular weight polycarboxylic acid emulsion (Toagosei Chemical Industry Co., Ltd. trade name: Aron AS-7050 (pH = 2.3) was added as a viscosity modifier.
, solid content = 65%) diluted with water to 20%5.
0 parts, 3% aqueous solution of cellulose thickener (Fuji Chemical ■ trade name hydroxyethyl cellulose A-5000) 4
．． A pressure sensitive adhesive having a viscosity of 8800 cP and a TI value of 42 was obtained. With this pressure-sensitive adhesive, 60
Although the coating was applied 0 times in a row, the workability was good. The adhesive properties of this pressure sensitive adhesive were as shown in Table 2.

Table 2 Example 6 Bi 75 parts, cyclohexyl acrylate 109, MA9
part, vinyl acetate/L/6 parts, M A A 4 parts, N-MA
Emulsion polymerization was carried out in the same manner as in Example 1 using a composition of 5 parts of Mo and 0.8 parts of DMD to obtain a base polymer emulsion having a pH of 1.8, a viscosity of 180 cP, and a solid content of 56%. This base polymer emulsion contains 1.3 parts of sodium polyacrylate (Toagosei Chemical Industry Co., Ltd., trade name: Aron A-2OL) as a viscosity modifier, and 0.0 parts of a 5% aqueous solution of polyvinyl alcohol (Kuraray, trade name: Poval 420).
A pressure sensitive adhesive having a viscosity of 4300 cP and a TI value of 4.8 was obtained. As a result of repeating screen coating 300 times in the same manner as in Example 1, 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 6 shows the adhesive properties of this product.

Table 3 Examples 4 to 6, Comparative Examples 1 to 2 Using the same Sibase polymer emulsion as in Example 1,
Table 4 shows the results of examining the screen printing applicability of various TI values prepared using the same viscosity modifier as in Example 2.

Table 4 Continued from page 1 0 Inventor Masao Kurihara Laboratory, Funami-cho, Minato-ku, Nagoya ■-1 Laboratory of Toagosei Chemical Industry Co., Ltd.

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. According to the B-type viscosity ratio of the water-dispersed pressure-sensitive adhesive (viscosity measured at a rotor rotational speed of 6 r, p, m)/(rotational speed of the same rotor as the above rotor 60 r, p, m, A water-dispersible pressure-sensitive adhesive having good screen printing coatability, characterized in that the chicken tropic index expressed by the viscosity (viscosity measured in ) is in the range of 2.5 to 5.5.