WO2002092715A1

WO2002092715A1 - Aqueous acrylic adhesives, preparing method thereof and explosion-proof tapes using such adhesives for fixing braun tubes

Info

Publication number: WO2002092715A1
Application number: PCT/KR2002/000235
Authority: WO
Inventors: Yong-In Lee
Original assignee: Shinwha Intertek Corp.
Priority date: 2001-05-11
Filing date: 2002-02-15
Publication date: 2002-11-21
Also published as: KR20020086141A; CN1507482A; KR100388796B1

Abstract

The present invention relates to an aqueous acrylic adhesive containing one or more polyester resins, and to a preparation method thereof. The present invention also relates to a high quality explosion-proof adhesive tape for fixing a Braun tube, which comprises a tape substrate made of PET, PP or Nylon film and an adhesive layer made of the aqueous acrylic adhesive containing one or more polyester resins according to the present invention, and which can improve the reassembly process of the Braun tube.

Description

AQUEOUS ACRYLIC ADHESIVES. PREPARING METHOD THEREOF AND EXPLOSION-PROOF TAPES USING SUCH ADHESIVES FOR FIXING BRAUN TUBES

TECHNICAL FIELD

The present invention relates to aqueous acrylic adhesives, a preparing method thereof and to explosion-proof tapes using such adhesive for fixing a

Braun tube. The adhesive tape using an aqueous acrylic adhesive of the present invention can be used to attach and affix a band-type steel bracket to a Braun tube that is used for an imaging equipment such as a television set.

BACKGROUND ART

In general, Braun tubes can be damaged easily by an exterior force applied thereto because they are made of glass and a vacuum is maintained inside. Braun tubes, therefore, cannot be directly fixed in a casing or housing. Instead, an explosion-proof band made of metal is attached to the circumference of the Braun tube, and then this explosion-proof band is fixed in the casing or housing. If the explosion-proof band is fixed onto the Braun tube with the aid of a buffering adhesive tape, it is possible to prevent damage to the Braun tube and minimize the scattering area of fragments in case of an implosion caused by an exterior force or accident.

The market size of Braun tubes grows increasingly because the rapidly growing information technology market requires better display media. Especially, Braun tubes for conventional television sets are getting larger in size and higher in quality, and expensive color Braun tubes with high-resolution and flat-panel displays are also currently being developed to be used in next generation computer monitors, large screen color television sets, high definition televisions (HDTV) and the like. Braun tubes go through many assembly steps and strict testing steps before being distributed as final products. During the final tests after completion of assembly, inferior products, which have defects in parts or which resulted from errors in the assembly process and which cannot provide satisfactory performance, are culled. In this case, because the final products are expensive, they have to be disassembled to fix the problems and then reassembled to be put on the market. During the disassembly, the adhesive tape fixed on the Braun tube for explosion-proofing has to be removed. However, it is very difficult to remove because the tape is usually adhered firmly to the Braun tube, because

the adhesive layer is produced by a thermal treatment above 200°C for 30 - 40

minutes in the assembly process for the Braun tube. In the disassembly process, up to now, the adhesive layer has been removed by dissolving with an organic solvent or by physical force. However, these methods take a long time and may also cause other problems such as environmental pollution and damage to the circumference of the Braun tube. Such problems are especially more serious when the adhesive tape is prepared with an oil-soluble adhesive.

Explosion-proof tape for fixing the Braun tube comprises an adhesive and a tape substrate. An oil-soluble acrylic adhesive, which has been widely used as an adhesive, is inexpensive and has advantages of excellent adhesion and a simple production process. However, the use of the oil-soluble acrylic adhesive is regulated in developed countries because there is a danger of fire or producing harmful volatile vapors, as well as environmental pollution, during the production and reproduction process. Therefore, studies for developing aqueous adhesives to replace the oil-soluble adhesives, and to have good properties and reasonable prices compared to the oil-soluble adhesives have been made intensively.

Aqueous adhesives are classified into three types such as a heterogeneous type using water as a suspension medium, a homogeneous type dissolved in water and an alcoholic solution type that can be diluted with water. The heterogeneous type can be classified further into an emulsion polymerization type, a suspension polymerization type and a forced emulsification type, depending on the polymerization method. Among them, an emulsion adhesive generally refers to the emulsion polymerization type adhesive, and most of the aqueous adhesives belong to this type. The emulsion adhesives are classified into acrylic, rubber and ethylene vinyl adhesives depending on the main ingredient. Synthetic rubber adhesives are used to a degree in manufacturing the adhesive tapes due to their rubber-like characteristic, but they have a problem in the mechanical stability of the emulsion. The ethylene vinyl acetate adhesives are made by increasing the ethylene content compared to glues or by co-polymerizing with acrylic components having a low glass transition temperature (T_g), to provide adhesion. However, their demand and use are limited compared to the aqueous acrylic type yet.

Currently, the aqueous acrylic adhesives have been most widely used as alternatives to the oil-soluble adhesive products. The reasons are as follows. They are generally superior in adhesion to a wide variety of materials, in their anti-weathering and low-temperature characteristics. Furthermore, because they are emulsion type adhesives having cross-linking ability, they have compatibility with other polymeric emulsions, good adjustability and operating efficiency resulting from their wide range of viscosity, and the content of solid substances can be made high.

However, the conventional aqueous acrylic adhesives have a low efficiency in production due to their slow drying speed, a lower adhesion and a higher price, compared to the oil-soluble adhesives (Korean Patent Publication No. 96-7184). In order to solve the above problems, the content of the solid substances may be increased, and special raw materials may be used, to increase the production speed and adhesion. However, these efforts are economically inefficient because the cost of the raw materials increase and also cause other problems in reassembly process resulted from excessive residual substances after the high temperature production process (U.S. Patent No. 4,839,413 and U.S. Patent No. 4,954,558).

In addition, the conventional emulsion type adhesives are also slightly inferior in their adhesive performance properties such as adhesion, cohesive force, shearing force and heat resistance even if they contain the same polymer components as the solvent type adhesives. One of the reasons for this results from the differences in the mechanisms for forming the adhesive film. In the case of the solvent type adhesive, a continuous film is formed while the organic solvent evaporates from the homogeneous solution. However, in the case of the emulsion type, the film is formed while the water dries out from the discontinuous system of the emulsion particles. In addition, it is because the emulsion type adhesive contains low molecular weight substances such as surfactants or defoaming agents and viscosity modulating agents (generally viscosity- enhancing agents), etc, which are not helpful to their adhesive performance. Although it depends on the methods and processes for forming the film, such phenomena cause lowering of the moisture- and water-resistant properties, tackiness and other adhesive properties of the emulsion type adhesive compared to the solvent type adhesive.

Regarding the tape substrate, a polyethylene(PE) film has been widely used. However, it has only a limited use in the fabrication process for the Braun

tubes which is carried out at a high temperature above 200°C because of its low

melting point, it is impossible to dry quickly, the preparation process takes a long time, and its adhesive state may be changed by melting the adhesive again easily.

SUMMARY OF INVENTION

It is therefore an object of the present invention to provide improved aqueous acrylic adhesives and a preparation method thereof.

It is another object of the present invention to provide high quality explosion-proof tapes for fixing a Braun tube which comprise the aqueous acrylic adhesives of the present invention, which have excellent adhesive properties and which especially can improve the reassembly process of the Braun tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic drawing of the cross-section of an aqueous acrylic explosion-proof tape for fixing a Braun tube in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is achieved as a result of efforts made by the present inventors to produce high quality aqueous acrylic adhesive tapes economically which have excellent adhesive properties and which especially can improve the production process of the Braun tube greatly.

The adhesive according to the present invention essentially comprises aqueous acrylic adhesive components and polyester resins. The adhesive of the present invention may optionally comprise other components such as surfactants, rubber latex resins and/or other necessary components in order to improve the adhesive properties. The aqueous acrylic adhesive components, which are main adhesive components in the present invention, are produced by the polymerization of acrylic monomers. The polyester resins are added with the acrylic monomers together in the polymerization process.

The glass transition temperature (T_g) of an adhesive to maintain adhesion

substantially is generally below 0°C, preferably -10°C to - 50°C. The monomers

used as raw materials for the present invention are not limited on condition that they are acrylic compounds satisfying the above condition in the final adhesive and having at least one double bond to be able to polymerize. Typical examples of acrylic monomers useful in preparing aqueous acrylic adhesives may include acrylic acid (hereinafter referred to as "AA"), metacrylic acid (hereinafter referred to as "MA"), itaconic acid (hereinafter referred to as "IA"), ethyl acrylate (hereinafter referred to as "EA"), butyl acrylate (hereinafter referred to as "BA"), ethylhexyl acrylate (hereinafter referred to as "EHA"), hydroxyethyl acrylate (hereinafter referred to as "HEA"), isodecyl acrylate (hereinafter referred to as "IDA") and the like. In the present invention, BA and EHA are used as essential ingredients in order to achieve the adhesive properties of the adhesive. And the amount of BA and EHA used is at least 60% and more preferably at least 85% by weight of the total acrylic monomers.

As minor ingredients, a small amount of vinyl compounds such as

styrene (ST), α-methylstyrene (α-MS), hydroxyethyl metacrylate (HEMA), methyl

metacrylate (MMA), glycidyl metacrylate (GMA), vinyl acetate (VAc), acrylonitrile (AN), acrylamide (AM), anhydrous maleic acid or mixtures thereof may be added as a monomer for co-polymerization. In order to improve the adhesion, a small amount of polyfunctional monomers such as N-methanolacrylamide or tetraethylene glycol diacrylate (TEGDA) may also be added during the emulsion polymerization.

In preparation of the adhesive of the present invention, an appropriate amount of polyester resins are added during the polymerization process of acrylic monomers. In this case, the adhesive properties of the adhesive tape provided by the present invention will be better because PET film is used for a tape substrate in the present invention. It is preferable to use the polyester resins in an amount below 20% by weight of the total adhesive. And it is preferable that the above polyester resins are aqueous polyester resins.

In preparation of the adhesive, polymerization is usually carried out in the ambient atmosphere. For the polymerization method, a monomer addition method, an emulsion addition method or a seed polymerization method may be applied. Among them, the suitable method can be selected according to the monomers, but it is necessary to consider the mean particle size, particle size distribution and particle structure of the required emulsion. However, it does not matter which one of the above emulsion polymerization methods is used as long as it agrees with the object of the present invention. Typically used initiators for the emulsion polymerization reaction are ammonium persulfate (APS), sodium persulfate (SPS), potassium persulfate (KPS) and the like. The above initiators may be used alone or in combination with a reducing agent such as sodium hydrogen sulfite to make an oxidation-reduction catalyst system. The initiation

temperature is typically 70°C - 90°C, and the amount of the initiator used is

0.01% - 10% and preferably 0.1% - 1% by weight of the total monomers.

One method to solve the prior problems of the emulsion adhesives such as the low moisture- and water-resistant properties and the inferiority in tackiness and other adhesive properties is to add surfactants, and in this case, the kinds and the amount of the surfactants are important. Examples of the above method include that anionic and non-ionic surfactants are added together, or reactive surfactants and oligomeric or polymeric emulsifiers are added. Generally, it is preferable that any surfactants be added in the least amount necessary so as to minimize the problems of the emulsion adhesives and have a good effect on the physical properties of the adhesives. When a micronization of an emulsion is applied, or an emulsion having a cross-liking ability in combination with suitable surfactants is used, it may help to obtain a better result. Especially, if anionic and non-ionic surfactants are used together, particles do not aggregate during the polymerization process, and the stability upon storage of the emulsion increases. Generally used examples of anionic surfactants include alkali metal alkyl sulfates such as sodium lauryl sulfate, carboxylic acids, sulfonic acids, phosphoric acid esters and the like. Generally used examples of non-ionic surfactants include ethyleneoxide derivatives of alkylphenols such as octylphenoxy- polyethoxyethanol and nonylphenoxypolyethoxyethanol, linear or branched alcohol ethers of C₆ - C₁₅, and polyalkylene glycols, such as polypropylene glycol, having a mean molecular weight of 800 - 2000. More particular examples of the above anionic and non-ionic surfactant are Emulon S133D and Monopol NP 1018 (Dongnam Synthetic Co., Korea). And recently, a variety of reactive anionic and non-ionic surfactants such as SE-10N or NE-10 (Asahi Denka Kogyo K.K., Japan) have been developed and used. The amount of the surfactants used in the present invention is 0.1% - 5 % and preferably 0.2% - 2 % by weight of the total adhesive. The amount of the anionic surfactants used is 5% - 50% and preferably 10% - 40% by weight of the non-ionic surfactants.

It is acceptable to add buffer solutions such as sodium bicarbonate or disodium phosphate solution to stabilize the emulsion during the polymerization process. It is also acceptable to carry out the polymerization process by adding support resins containing BA and/or EHA and AA, or alkali soluble resins. In this case, the molecular weight of the resins is typically in the range of 1000 - 15000 and especially preferably in the range of 2000 - 3000.

The adhesive properties and salvage properties can be increased when other emulsions such as natural rubber latex, SBR latex, neophrene latex or chlorophrene latex are added to the aqueous acrylic adhesive prepared by adding polyester resins.

Before coating onto a tape substrate, in order to increase the shear strength, a small amount of cross-linking agents such as 1 ,6-hexanediol diglycidyl ether, hardening agents containing zinc ions and acting at a high temperature, such as ammonia water-treated zinc oxide or zinc resinate, zinc duodeconoate, or butyl zimate, poly-functional aziridines or zirconium, melamine and isocyanate compounds may be added. After the adhesive is obtained as described above, silane coupling agents such as γ-aminopropyltriethoxysilane may be added at the final step. To improve the tackiness, tackifiers may be added to the adhesives prepared as described above. The tackifiers that may be used in the present invention are the hydrocarbon petroleum resins such as Wingtack 10 (Goodyear), Escorex 5320 (Exxon Chemical Co.) and Regalrez 1018 (Hercules Chemical Co.), or the rosin esters such as Aquatac 6085 (Arizona Chemical Co.) and Pentalyn H (Hercules Chemical Co.).

When the emulsion should be stored for a long time, it is preferable to add antioxidants such as hindered phenols, aromatic amines or phosphite compounds including Iganox1010 (Ciba-Geigy Co.), Wingstay L (Goodyear), BNX-1000 (Mayzo), Ethanox 330 (Ethyl Co.), lonol (Shell Chemical), Polygard HR, Naugard 445 (Uniroyal Co.), Borg-Warner 626 (Chemical Additive Div., GE Co.) and the like.

Additionally, wetting agents such as dioctyl sulfosuccinate, pH regulating agents such as ammonia water, anti-foaming agents (approximately 0.005 - 0.1%), dyes, fillers, pigments, preservatives, leveling agents, aromatics and the like can be supplementally added.

To adjust the viscosity of the adhesive, a small amount of a viscosity- enhencing compound such as ethylcellulose (EC), carboxymethylcellulose (CMC), soda acrylate (CARBOPOL) and/or polyether polyol (Rheolate, Rheox Inc.), etc. is used. The viscosity of the adhesive is adjusted to 1500cps - 9000cps and more preferably to 3000 - 5000cps by adding the above-exemplified viscosity-enhancing agents. If the ratio of solid substances is high, the product can be dried quickly, and accordingly the production efficiency can be increased. Therefore, the ratio of solid substances in the present invention is preferably 50% - 70% and more preferably 55% - 65% by weight of the total adhesive.

One embodiment of the preparation method for the adhesive according to the present invention is as follows. At first, a pre-emulsion solution is prepared by mixing a monomer mixture of BA and EHA, a monomer selected from the group consisting of EA, HEA, AA, IA, AM and mixtures thereof, surfactants and de- ionized water. A portion of the obtained pre-emulsion solution, deionized water and polyester resin are added to a polymerization reactor and the mixture is stirred well. The remainder of the above pre-emulsion solution, deionized water and initiator solution are slowly added to the above polymerization reactor for polymerization. After all of the reactants are added, the temperature of the reaction mixture is raised, and then the reaction is continued until there are no un-reacted monomers in the reaction mixture. After completion of the reaction, the vessel is cooled, the pH of the polymerization product is adjusted, and then the viscosity is adjusted by adding a viscosity-enhancing agent to obtain the adhesive according to the present invention. Another embodiment of the preparation method for the adhesive according to the present invention is as follows. An anti-foaming agent is slowly added to the adhesive obtained according to the above procedure while stirring vigorously to prevent aggregation, the pH of the mixture is adjusted, and then rubber latex resins and antioxidants are further added to the mixture. The mixture is then stirred while maintained under vacuum to prevent foaming.

The adhesive tape of the present invention is prepared by the following process using PET, PP (including CPP and OPP) or Nylon film as a tape substrate. The aqueous acrylic adhesive prepared according to the present invention is coated onto one side of a PET, PP (including CPP and OPP) or Nylon film, and then the film is dried. The adhesive side of the film is then attached to one side of a support made of a glass wool mesh cloth. The adhesive is coated again onto the other side of the glass wool mesh cloth, and then the film is dried to obtain an adhesive tape.

More particularly, the aqueous adhesive is coated onto one side of the PET, PP (including CPP and OPP) or Nylon film. The volatile solvent in the adhesive is removed in a drying chamber to generate the adhesive layer. Glass wool mesh cloth is attached onto the adhesive layer generated on the above film as shown in Figure 1. Onto the glass wool mesh cloth attached onto the film, the aqueous adhesive is coated again to generate another adhesive layer. The release agent layer on the film surface can be formed by coating the release agent onto the above film or can be formed at the final step of the preparation process of the tape. Figure 1 is a schematic drawing of the cross-section of an aqueous acrylic explosion-proof tape for fixing a Braun tube in accordance with the present invention, wherein the reference numericals designate the following components: 1 : glass wool mesh cloth;

2, 2' : aqueous acrylic adhesive layers;

3 : PET film, PP film or Nylon film layer; and

4 : release agent layer

EXAMPLES

The present invention will be further illustrated by way of the following Examples, but is by no means limited thereto.

In the following examples, the term "part" represents weight part. The adhesion tests of the adhesive tapes prepared in the following Examples were carried out as follows. The adhesive tape was cut to a width of 26mm to make a sample, the sample was attached to a test plate using pressing equipment and

then 30 min later the adhesion was measured by pulling the attached tape at 90°

with a tension tester. The salvage values were measured as follows. A sample adhesive tape was attached to a Braun tube, and then a steel explosion-proof

band was covered onto the adhesive tape. After a firing process at 30 - 260°C for

2.5 hours, the explosion-proof band was cut, and the sample tape was detached. The amount of the remaining adhesive on the sample tape was measured and expressed in % by weight as the salvage value. The adhesion and salvage values represent the physical properties of the tape. In general, higher adhesion and lower salvage values indicate a higher quality of the tape.

Example 1

A pre-emulsion solution comprising 28 parts of BA, 22 parts of EHA, 1.5 parts of AA, 1.0 part of HEA, 0.5 parts of AM, 0.6 parts of Monopol NP 1018, 0.2 parts of SE-10N and 20 parts of deionized water was prepared in a glass or stainless steel reactor. In a polymerization reactor installed with a reflux

condenser, a thermometer and a stirrer, 10% of the prepared pre-emulsion

solution, 5 parts of deionized water and 5 parts of polyester resin AQ 1045

(Eastman Chemical Co.) were added. The resulting mixture was then stirred

thoroughly at 75°C. To this mixture, the remaining 90% of the above pre-

emulsion solution and an initiator solution comprising 15.85 parts of deinonized

water, 0.3 parts of ammonium persulfate and 0.05 parts of sodium phosphate

were slowly added for 5 hours for polymerization. After the reactants were added

completely, the temperature was raised to 80°C, and then the reaction mixture

was reacted for 1 more hour. After being cooled, the pH of the mixture was

adjusted to 5.5 - 6.0 using 8% zinc ammonium bicarbonate (ZAB) solution

prepared with ammonia water, zinc oxide and ammonium bicarbonate, and then

the viscosity of the mixture was adjusted to 3500cps with a viscosity-enhancing

agent, to obtain an aqueous acrylic adhesive.

The aqueous acrylic adhesive as obtained above was coated onto one

side of a PET film, and then the volatile substances in the adhesive were removed in a drying chamber to generate an adhesive layer. The adhesive tape was prepared by attaching a glass wool mesh cloth onto the adhesive layer and

coating the aqueous adhesive again onto the glass wool mesh cloth attached onto the adhesive layer to form another adhesive layer as shown in Figure 1. The adhesion and salvage values of the prepared tape were 790gf/26mm and 3.0%, respectively.

Example 2 An aqueous acrylic adhesive was prepared by the same procedure as in

Example 1 except that EW-370 (SK Chemical) was used as a polyester resin instead of AQ 1045, and then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 750gf/26mm and 5.0%, respectively. Example 3

An aqueous acrylic adhesive was prepared by the same procedure as in

Example 1 except that 3 parts of AQ 1350 and 2 parts of AQ 1950 were used as polyester resins instead of 5 parts of AQ 1045. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 770gf/26mm and 4.0%, respectively.

Comparative Example 1

An aqueous acrylic adhesive was prepared by the same procedure as in

Example 1 except that 30 parts of BA and 25 parts of EHA were used without using 5 parts of polyester resin AQ 1045, and then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 790gf/26mm and 25.0%, respectively.

Example 4

An aqueous acrylic adhesive was prepared by the same procedure as in Example 1 except that 3 parts of AQ 1045 and 2 parts of support resin having a number-averaged molecular weight of about 2500 prepared with BA/AA were used instead of 5 parts of polyester resin AQ 1045. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 820gf/26mm and 5.0%, respectively. Example 5

An aqueous acrylic adhesive was prepared by the same procedure as in Example 1 except that 1 part of AQ 14000 and 4 parts of a support resin having a number-averaged molecular weight of about 2500 prepared with BA/AA were used instead of 5 parts of polyester resin AQ 1045. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 840gf/26mm and 8.0%, respectively.

Example 6

An aqueous acrylic adhesive was prepared by the same procedure as in

Example 1 except that 0.1 parts of Emulon S133D and 0.1 part of SE-10N were used instead of 0.2 parts of SE-10N. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 780gf/26mm and 3.0%, respectively.

Comparative Example 2

An aqueous acrylic adhesive was prepared by the same procedure as in Example 1 except that 30 parts of BA, 25 parts of EHA and 0.2 parts of Emulon S133D were used without using 5 parts of polyester resin AQ 1045 and 0.2 parts of SE-10N. And then an adhesive tape was prepared with the obtained adhesive. During the coating process in preparation of an adhesive tape, foaming and aggregation were observed. The adhesion and salvage values of the adhesive tape were 740gf/26mm and 30.0%, respectively.

Example 7

An aqueous acrylic adhesive was prepared by the same procedure as in Example 1 except that 0.3 parts of potassium persulfate and 0.05 parts of sodium bicarbonate were used instead of 0.3 parts of ammonium persulfate and 0.05 parts of sodium phosphate. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 780gf/26mm and 3.0%, respectively.

Example 8 An aqueous acrylic adhesive was prepared by the same procedure as in

Example 1 except that 1.0 part of AA and 0.5 parts of IA were used instead of 1.5 parts of AA. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 800gf/26mm and 5.0%, respectively. Example 9

An aqueous acrylic adhesive was prepared by the same procedure as in Example 1 except that 30 parts of BA, 20 parts of EHA, 2.0 parts of AA and 1.0 part of HEA were used instead of 28 parts of BA, 22 parts of EHA, 1.5 parts of AA, 1.0 part of HEA and 0.5 parts of AM. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 760gf/26mm and 5.0%, respectively.

Example 10

While stirring at a high speed to prevent aggregation, ammonia water was added to a mixture of 90 parts of the adhesive prepared in Example 1 and 0.05 parts of anti-foaming agent, in order to adjust the pH of the mixture to 7.0. To the resulting mixture, 9.7 parts of natural rubber latex NC-405, 0.2 parts of SE-10N and 0.05 parts of antioxidant were added. The mixture was then stirred for 30 minutes under a vacuum to prevent foaming, to prepare an aqueous acrylic adhesive. And then an adhesive tape was prepared with the obtained adhesive. The adhesion and salvage values of the adhesive tape were 780gf/26mm and 4.0%, respectively.

EFFECT OF THE INVENTION The adhesive tapes comprising the aqueous acrylic adhesive according to the present invention as an adhesive layer have an excellent adhesion and

can also be removed easily by treating with warm water at 70°C - 90°C for 2 - 3

minutes in the reassembly process of the Braun tube. In this case, the amount of remaining adhesive on the Braun tube or its circumference (salvage value) is so small that it does not exceed 5%.

Because the melting points and thermal deformation temperatures of the PET, PP and Nylon film are high enough, there is no limitation in the use of these films in the assembly process for the Braun tube which is carried out at a relatively high temperature. Therefore, it is possible to dry the adhesive according to the present invention at a high temperature, the processing time can be shortened by more than 30%, and accordingly production efficiency can be improved. Furthermore, because the adhesive tape of the present invention adheres well on the glass, it adheres firmly to the glass wool mesh cloth or a Braun tube. As a result, the adhesive tape of the present invention has an advantage of being able to fix the Braun tube firmly even at a high temperature due to its stability at a high temperature.

Claims

1. An aqueous acrylic adhesive comprising:

(1) 30wt% - 80wt% of acrylic adhesive components, which are obtained by polymerizing at least 60wt% of a monomer mixture of butyl acrylate and ethylhexyl acrylate to the total weight of acrylic monomers with a monomer selected from the group consisting of ethyl acrylate, hydroxyethyl acrylate, acrylic acid, itaconic acid, acrylamide and mixtures thereof, to the total weight of adhesive; and

(2) no more than 20wt% of one or more polyester resins to the total weight of adhesive.

2. The aqueous acrylic adhesive according to claim 1 , wherein the polyester resins are aqueous polyester resins.

3. The aqueous acrylic adhesive according to claim 1 , wherein the aqueous acrylic adhesive further comprises one or more rubber latex resins.

4. The aqueous acrylic adhesive according to claim 3, wherein the rubber latex resins are natural rubber latex resins.

5. The aqueous acrylic adhesive according to claim 1 , wherein the aqueous acrylic adhesive further comprises 0.1 wt% - 5wt% of reactive anionic and non- ionic surfactants to the total weight of adhesive.

6. The aqueous acrylic adhesive according to any one of claims 1 to 5, wherein the amount of the monomer mixture of butyl acrylate and ethylhexyl acrylate is no less than 85wt% to the total weight of the acrylic monomers.

7. A preparation method of the aqueous acrylic adhesive according to claim 1 , comprising the steps of

(1) preparing a pre-emulsion solution by mixing a monomer mixture of butyl acrylate and ethylhexyl acrylate, a monomer selected from the group consisting of ethyl acrylate, hydroxyethyl acrylate, acrylic acid, itaconic acid, acryl amide and mixtures thereof, surfactants and deionized water;

(2) adding a portion of the above pre-emulsion solution, deionized water and one or more polyester resins to a polymerization reactor while stirring;

(3) polymerizing by adding slowly the rest of the pre-emulsion solution, deionized water and an initiator solution to the mixture prepared in step (2); and (4) reacting until there are no unreacted monomers and then cooling the reaction mixture.

8. An explosion-proof adhesive tape for fixing a Braun tube, comprising a tape substrate and an adhesive layer, wherein the adhesive layer comprises the aqueous acrylic adhesive according to any one of claims 1 to 6.

9. The explosion-proof adhesive tape for fixing a Braun tube according to claim 8, wherein the tape substrate comprises PP including CPP and OPP, PET or Nylon film.