CN114106234A

CN114106234A - Preparation method and application of ultraviolet-curable acrylic copolymer

Info

Publication number: CN114106234A
Application number: CN202111435810.6A
Authority: CN
Inventors: 卢新亚
Original assignee: Shenzhen Lihe Bohui Photosensitive Material Co ltd
Current assignee: Shenzhen Lihe Bohui Photosensitive Material Co ltd
Priority date: 2021-11-29
Filing date: 2021-11-29
Publication date: 2022-03-01

Abstract

The invention discloses a preparation method of an ultraviolet-curable acrylic copolymer, which comprises the following steps: s1, polymerizing the acrylate monomer mixture in a solvent to form a copolymer solution; s2, adding benzophenone and/or benzophenone derivatives into the copolymer solution; s3 heating the whole solution to evaporate the solvent and produce a solvent-free UV-curable acrylic copolymer. The invention not only simplifies the production process of the UV curing pressure-sensitive adhesive, but also effectively improves the pressure-sensitive adhesive performance and the thermal stability of the product in the hot melting production process while maintaining the advantages of the existing UV curing technology, and simultaneously introduces the benzophenone or the derivative thereof, thereby improving the product quality of the acrylate copolymer.

Description

Preparation method and application of ultraviolet-curable acrylic copolymer

Technical Field

The invention relates to the technical field of pressure-sensitive adhesives, in particular to a preparation method and application of an ultraviolet-curable acrylic copolymer.

Background

(meth) acrylic copolymers are widely used in a variety of industrial and consumer products, and in particular (meth) acrylic pressure sensitive adhesives have many desirable properties and technical advantages, such as ease of use, excellent durability, optical properties, and removability after long-term use. At present, solvent-type acrylic pressure-sensitive adhesives are mainly used in the adhesive tape industry to produce high-performance pressure-sensitive adhesive products, but the solvent-type pressure-sensitive adhesives generally contain 45-60% of organic solvents, so that great pressure is brought to energy conservation and environmental protection. The UV curing hot melt pressure sensitive adhesive is more and more important along with increasingly strict environmental regulations and continuously rising solvent cost in recent years.

Patent nos. CN 106566424A and CN109651974B disclose two UV pressure sensitive adhesives, which mainly consist of (meth) acrylate copolymers, photoresponsive monomers, photopolymerizable monomers, and photoinitiators. However, in the actual production process of the UV pressure-sensitive adhesive which is coated and photocured to form the final product (such as a tape or a label), the UV illumination time is only a few seconds to a few minutes, and the small molecular monomers contained in the pressure-sensitive adhesive can not be completely photopolymerized, so that the final product contains higher residual monomers and odor. The VOC content is far greater than the application requirements of most products. The higher residual monomer content of the final product is the biggest obstacle to commercialization of this technical route.

Patent numbers CN106459302B and US9475968 disclose the preparation method and application of two (meth) acrylate polymers containing grafted acrylic monomers, respectively. UV curable pressure sensitive adhesives can be prepared by adding an appropriate amount of a small molecule light sensitizer to such (meth) acrylate polymers. The technical route overcomes the defect of high residual monomer content of the UV pressure-sensitive adhesive, but the prepared UV pressure-sensitive adhesive still has some important defects and needs to be further improved. For example, the unsaturated double bonds of the grafted acrylic monomer have poor thermal stability and are easily thermally crosslinked at high temperature, resulting in a sharp rise in melt viscosity, and thus cannot be hot-melt processed and coated. In addition, the micromolecules decomposed by the added light guiding agent not only cause higher VOC, but also have strong smell and mobility, and certain health hidden troubles exist in the product. Because of the poor thermal stability of the acrylic monomer, the grafting reaction temperature cannot be too high, often a catalyst needs to be added to promote the reaction degree, and at the same time a thermal stabilizer needs to be added to prevent possible thermal cross-linking of the acrylic monomer during the reaction. However, these additives not only contribute to high VOC of the product, but also reduce the uv curing efficiency.

US patent US 4144157, US 7745505, US 10526425 and the like disclose different types of specific benzophenone-containing monomers and the use of copolymerization processes to prepare benzophenone-containing (meth) acrylate PSAs. However, all these methods still suffer from certain drawbacks, such as that the specific monomer co-containing benzophenone must be synthesized by a separate, complex, and costly step, and therefore is much more expensive than conventional photoinitiators. In addition, the synthesis pollution of the production process is large, the wastewater is difficult to treat, the commercial production of the raw materials is severely restricted, and the market still cannot buy suitable products without commercialization at present.

Disclosure of Invention

In order to overcome the defects of the prior art route, the invention provides a preparation method and application of an ultraviolet curable (methyl) acrylic copolymer, which not only simplifies the production process of the UV curable pressure-sensitive adhesive, but also effectively improves the performance of the pressure-sensitive adhesive and the thermal stability of a product in the hot melting production process while maintaining the advantages of the existing UV light curing technology, and simultaneously introduces benzophenone or derivatives thereof, thereby improving the product quality of the acrylate copolymer.

To achieve the above object, the present invention provides a method for preparing an ultraviolet curable acrylic copolymer, comprising the steps of:

s1, polymerizing the acrylate monomer mixture in a solvent to form a copolymer solution;

s2, adding benzophenone and/or benzophenone derivatives into the copolymer solution;

s3 heating the whole solution to evaporate the solvent and produce a solvent-free UV-curable acrylic copolymer.

Preferably, the monomer mixture includes a monomer of formula CH₂Acrylic or methacrylic ester monomer of-CH (R1) (C00R2) wherein R1 is H or CH₃R2 is an alkyl group containing l-20 carbons.

Preferably, the monomer mixture is a (meth) acrylic or vinyl functional monomer, and the functional group of the functional monomer includes one or more of a carboxyl group, a hydroxyl group, an acid anhydride group, an amine group, an amide group, an epoxy group, or an isocyanate group.

Preferably, the benzophenone derivative contains one or more reactive groups including carboxyl, hydroxyl, acid anhydride, amine, epoxy, acid chloride or isocyanate groups.

Preferably, the acrylic copolymer has a glass transition temperature of less than 20 ℃ and the weight average molecular weight of the acrylate copolymer is greater than 50000 g/mol.

Preferably, the acrylic copolymer has a glass transition temperature of 0 ℃ or lower, and the weight average molecular weight of the acrylic copolymer is more than 10⁵g/mol。

Preferably, in step S3, the heating temperature is 160-180 ℃.

The invention also discloses application of the ultraviolet cured acrylic copolymer, and the ultraviolet cured acrylic copolymer obtained by the preparation method is used for producing the UV cured pressure sensitive adhesive.

Preferably, the UV-curable pressure-sensitive adhesive is produced under the irradiation of an ultraviolet lamp at 200-500 nm.

Preferably, the UV-curable pressure-sensitive adhesive is a hot-melt coated pressure-sensitive adhesive or a liquid adhesive;

the invention has the beneficial effects that: compared with the prior art, the preparation method of the ultraviolet-curable acrylic copolymer provided by the invention is added with the benzophenone, does not add any photoinitiator, and can effectively realize the UV curing under the irradiation of an ultraviolet lamp, so that the pressure-sensitive adhesive for the adhesive tape can be produced; under the premise of not needing an initiator or a light curing agent, the benzophenone generates hydrogen abstraction light curing reaction under the irradiation of UV light, so that more free radicals can be generated, the reaction rate is accelerated, and the light curing efficiency is higher.

Drawings

FIG. 1 is a flow chart of the steps of the present invention.

Detailed Description

The technical solutions in the embodiments of the present application will be described clearly and completely with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments, not all embodiments, of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Also, this application uses specific language to describe embodiments of the application. Reference throughout this specification to "one embodiment," "an embodiment," and/or "some embodiments" means that a particular feature, structure, or characteristic described in connection with at least one embodiment of the present application is included in at least one embodiment of the present application. Therefore, it is emphasized and should be appreciated that two or more references to "an embodiment" or "one embodiment" or "an alternative embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, some features, structures, or characteristics of one or more embodiments of the present application may be combined as appropriate.

Referring to fig. 1, the present application discloses a method for preparing a uv-curable acrylic copolymer, comprising the steps of: s1, polymerizing the acrylate monomer mixture in a solvent to form a copolymer solution; s2, adding benzophenone and/or benzophenone derivatives into the copolymer solution; s3 heating the whole solution to evaporate the solvent and produce a solvent-free UV-curable acrylic copolymer.

The monomer mixture comprises: 70-95 parts by weight of molecular formula CH₂Acrylic or methacrylic ester monomer of-CH (R1) (C00R2) wherein R1 is H or CH₃And R2 is an alkyl group having 1 to 20 carbons. The monomer mixture may also be 0.1 to 30 parts by weight of a (meth) acrylic or vinyl functional monomer having a functional group including a carboxyl group,one or more of hydroxyl groups, acid anhydride groups, amine groups, amide groups, epoxy groups, or isocyanate groups.

The benzophenone derivative contains one or more of a carboxyl group, a hydroxyl group, an acid anhydride group, an amine group, an epoxy group, an acid chloride group or an isocyanate group.

The acrylic copolymer has a glass transition temperature of less than 20 deg.C, preferably less than 0 deg.C, and the weight average molecular weight of the acrylic copolymer is greater than 50000g/mol, preferably 10⁵g/mol。

In step S3, the heating temperature is 160-180 ℃, at which the solvent can be evaporated and the branching reaction can be promoted, thereby forming the solvent-free UV-curable acrylic copolymer.

The invention also discloses an application of the ultraviolet cured acrylic copolymer for producing the UV cured pressure sensitive adhesive; the UV curing pressure sensitive adhesive is generated under the irradiation of an ultraviolet lamp with the wavelength of 200-500 nm; the UV curing pressure sensitive adhesive is hot melt coating pressure sensitive adhesive or liquid adhesive. In a specific implementation process, one or more additives can be added into the whole reaction system to further improve the performance, such as tackifying resin, antioxidant, light stabilizer, adhesion promoter and the like; one or more additional fillers may be added to enhance properties, such as fibers, carbon black, zinc oxide, titanium dioxide, solid or hollow glass microspheres, microspheres of other materials, silica, silicates, and the like.

The application is illustrated below by means of specific examples:

example 1

The ingredients were weighed according to the following table

Components	Weight (gram)
		Acrylic acid 2-ethylhexyl ester	100
Acrylic acid methyl ester	10
		Acrylic acid	70
Vinyl acetate (VAA)	30
		2-Hydroxyethyl acrylate	10
Acrylic acid n-butyl ester	780
		AIBN initiator	4

500 g of the monomer mixture and 500 g of ethyl acetate solvent were transferred to a 3 l jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 15 minutes, the remaining monomer mixture and 300 g of ethyl acetate solvent were added to the reactor via a dropping funnel over a period of 3 hours. After the addition was complete, the reaction was continued at reflux temperature for 4 hours to ensure that all residual AIBN was reacted. At this point, 3 grams of 4-aminobenzophenone was added to the reactor and slowly heated to about 160 ℃ to devolatilize most of the solvent and other organic volatiles. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final copolymer sample was measured to have a melt viscosity of about 41000cps at 140 ℃.

Example two:

the materials were weighed as in example one and 500 grams of the monomer mixture and 500 grams of ethyl acetate solvent were transferred to a 3 liter jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 15 minutes, the remaining monomer mixture and 300 g of ethyl acetate solvent were added to the reactor via a dropping funnel over a period of 3 hours. After the addition was complete, the reaction was continued at reflux temperature for 4 hours to ensure that all residual AIBN was reacted. And slowly heated to about 160 c to devolatilize most of the solvent and other organic volatiles. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final measured melt viscosity of the copolymer sample at 140 ℃ was about 39100cps

To further evaluate the performance of the copolymers prepared in examples one and two for use in UV-curable hot melt pressure sensitive adhesives. The copolymers prepared in examples 1 and 2 were uniformly coated on a 50-micron thick polyester film by means of slot-die hot-melt coating, the coating thickness being controlled to about 50 microns. UV curing was then carried out in a desk-top UV curing machine (medium pressure mercury column, H lamp, 120W/cm) with a total UVC curing radiation dose controlled at 0.06J/cm. The 1800 peel force of the UV-irradiated film samples on stainless steel plates was measured according to the PSTC-101 method (Pressure Sensitive Tape Council Pressure Sensitive Tape Commission Standard), and the room temperature adhesion retention was evaluated according to the PSTC-107 test method. The application time on the stainless steel plate was controlled to 30 minutes and 24 hours, respectively. The following table lists the test conditions and results for the peel force and room temperature bond retention of sample 1800:

	example 1	Example 2
			Adhesive holding force (2 kg/in)²) Minute of	>10000	10
180 ℃ stainless Steel peel force (30 min bond), N/in	17.7	28.5 (a large amount of glue residues on the steel plate)
			180 degree stainless steel peel force (24 hour bond), N/in	20.3	27.1 (a large amount of glue residues on the steel plate)

From the table, we can clearly find that the pressure sensitive adhesive with benzophenone is obviously superior to the pressure sensitive adhesive without the conventional pressure sensitive adhesive in both the adhesive force and the peeling force, so that the effect of the application is obviously superior to the prior art.

The benzophenone and the derivatives thereof added in the application can also be benzophenone containing epoxy, namely 4- (2, 3-epoxypropoxy) benzophenone, and the synthesis process is as follows: 4-hydroxybenzophenone (19.82 g, 0.1mol) was dissolved in 100ml of petroleum ether to form a homogeneous solution. After the solution was cooled to 0 ℃ and boron trifluoride etherate (0.2g) was added dropwise to the solution. Then, epichlorohydrin (37.0g, 0.4mol) was slowly added dropwise to the solution. Finally, the reaction temperature was raised to 70 ℃ and the reaction was continued at this temperature for 3 hours. After the reaction was completed, unreacted epichlorohydrin and petroleum ether were removed by distillation under reduced pressure, 100mL of ethanol was added to redissolve the product, and then potassium hydroxide (5.62g, 0.1m01) was added and stirring was continued for 2 hours. After removing the formed salt by filtration and removing the ethanol by distillation under reduced pressure, the product is dissolved in dichloromethane again, the residual salt is washed off by distilled water and the dichloromethane is removed by evaporation under reduced pressure, and finally the product is white solid, namely 4- (2, 3-epoxypropoxy) benzophenone.

Example three:

components	Weight (gram)
		Acrylic acid 2-ethylhexyl ester	190
Acrylic acid methyl ester	10
		Acrylic acid	80
Vinyl acetate (VAA)	20
		Acrylic acid n-butyl ester	700
AIBN initiator	3.8

The amounts of the materials in the above table were weighed and then 500 g of the monomer mixture and 450 g of ethyl acetate solvent were transferred to a 3 l jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 30 minutes, the remaining monomer mixture of table 1 and 350 grams of ethyl acetate solvent were added to the reactor via a dropping funnel over a 2.5 hour period. After the addition was complete, the reaction was continued at reflux temperature for 4.5 hours to ensure that all the residual AIBN had reacted. At this point, 3.3 grams of 4- (2, 3-epoxypropoxy) benzophenone was added to the reactor and heated slowly to about 180 ℃ to devolatilize most of the solvent and other organic volatiles. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final copolymer sample was determined to have a melt viscosity of about 37700cps at 140 ℃.

Example four:

the amounts in the tables of the examples were weighed and then 500 g of the monomer mixture and 450 g of ethyl acetate solvent were transferred to a 3 l jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 30 minutes, the remaining monomer mixture of table 1 and 350 grams of ethyl acetate solvent were added to the reactor via a dropping funnel over a 2.5 hour period. After the addition was complete, the reaction was continued at reflux temperature for 4.5 hours to ensure that all the residual AIBN had reacted. At this point, and slowly heated to about 180 ℃, most of the solvent and other organic volatiles are devolatilized. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final copolymer sample was determined to have a melt viscosity of about 38100cps at 140 ℃.

In order to further evaluate the performance of the copolymers prepared in examples three and four for UV-curable hot-melt pressure-sensitive adhesives, the copolymers prepared in examples three and four were uniformly coated on a 50-micron thick polyester film by means of slit hot-melt coating, and the coating thickness was controlled to be about 60 microns. UV curing was then carried out in a desk-top UV curing machine (medium pressure mercury column, H lamp, 120W/cm) with a total UVC curing radiation dose controlled at 0.08 joules/cm.

The 1800 peel force of the UV-irradiated film samples on stainless steel plates was measured according to the PSTC-101 method (Pressure Sensitive Tape Council Pressure Sensitive Tape Commission Standard), and the room temperature adhesion retention was evaluated according to the PSTC-107 test method. The application time on the stainless steel plate was controlled to 30 minutes and 24 hours, respectively. The following table lists the test conditions and results for the peel force and room temperature bond retention of sample 1800.

The test result shows that the copolymer prepared in the third embodiment of the invention has excellent UV curing performance and can form effective high-degree photocuring under UV irradiation. The pressure-sensitive adhesive film formed after UV irradiation not only has good bonding stripping force, but also has very good bonding retention, and is suitable for preparing high-performance low-VOC pressure-sensitive adhesive tapes. On the other hand, the test results show that the copolymer prepared in example four has no photo-curing to any extent under the UV irradiation condition, the adhesive film strength or the bonding retention after the UV irradiation is very low, and when the copolymer is peeled from a steel plate, the colloid is seriously damaged, and a large amount of residual glue is left on the steel plate.

For the benzophenone and its derivatives added in the present application, it may also be benzophenone of an isocyanate group. 111.1 g of isophorone diisocyanate (IPDI), 100 g of ethyl acetate, 0.04 g of dibutyltin dilaurate (DBTDL) were introduced into a 500 ml flask. After the contents of the flask were heated to 40 ℃ under nitrogen with stirring, 122 g of 4- (2-hydroxyepoxy) benzophenone was slowly added to the flask over a period of 90 minutes to allow selective attachment of the hydroxyl groups to the more reactive isocyanate groups of IPDI. The reaction mixture was stirred continuously for 30 minutes, then the temperature was slowly raised to 50 ℃ and the reaction was continued for 60 minutes. The final product was NMR confirmed that 4- (2-hydroxyepoxy) benzophenone had reacted completely with IPDI to form benzophenone containing isocyanate groups (IPDI-BP).

Example five:

components	Weight (gram)
		Acrylic acid 2-ethylhexyl ester	700
Acrylic acid n-butyl ester	220
		2-Hydroxyethyl acrylate	80
AIBN initiator	4.4

The amounts of the materials in the above table were weighed and then 500 g of the monomer mixture and 450 g of ethyl acetate solvent were transferred to a 3 l jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 30 minutes, the remaining monomer mixture of table 1 and 350 grams of ethyl acetate solvent were added to the reactor via a dropping funnel over a 2.5 hour period. After the addition was complete, the reaction was continued at reflux temperature for 4.5 hours to ensure that all the residual AIBN had reacted. At this point, 11.0 grams of benzophenone containing isocyanate groups (IPDI-BP) was added to the reactor and heated slowly to about 130 deg.C to devolatilize most of the solvent and other organic volatiles. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final copolymer sample was measured to have a melt viscosity of about 21700cps at 130 ℃.

Example six:

the amounts of the materials in the table of example five were weighed and then 500 g of the monomer mixture and 450 g of ethyl acetate solvent were transferred to a 3 l jacketed reactor. The contents of the reactor were heated to reflux temperature (about 80 ℃) under nitrogen with stirring. After maintaining reflux for about 30 minutes, the remaining monomer mixture of table 1 and 350 grams of ethyl acetate solvent were added to the reactor via a dropping funnel over a 2.5 hour period. After the addition was complete, the reaction was continued at reflux temperature for 4.5 hours to ensure that all the residual AIBN had reacted. And slowly heated to about 170 c to devolatilize most of the solvent and other organic volatiles. The reactor was then evacuated at this temperature and the residual volatiles were further devolatilized until the residual volatiles content in the copolymer sample was less than 0.5%. The final copolymer sample was found to have a melt viscosity of about 20900cps at 130 ℃.

To further evaluate the performance of the copolymers prepared in examples five and six for use in UV-curable hot melt pressure sensitive adhesives. The copolymers prepared in examples 1 and 2 were uniformly coated on a 50 μm thick polyester film by slot hot melt coating, and the coating thickness was controlled to about 20 μm. UV curing was then carried out in a desk-top UV curing machine (medium pressure mercury column, H lamp, 120W/cm) with a total UVC curing radiation dose controlled at 0.04 joules/cm. The 1800 peel force of the UV-irradiated film samples on stainless steel plates was measured according to the PSTC-101 method (Pressure Sensitive Tape Council Pressure Sensitive Tape Commission Standard), and the room temperature adhesion retention was evaluated according to the PSTC-107 test method. The application time on the stainless steel plate was controlled to 30 minutes and one week, respectively. The following table lists the test conditions and results for the peel force and room temperature bond retention of sample 1800.

The test result shows that the copolymer prepared in the fifth embodiment of the invention has excellent UV curing performance and can form effective high-degree photocuring under UV irradiation. The pressure-sensitive adhesive film formed after UV irradiation has very high adhesion retention and very stable adhesion stripping force, the stripping force is increased by about 10 percent after the pressure-sensitive adhesive film is attached for one week, the adhesive film can be easily and cleanly stripped from a steel plate, and the pressure-sensitive adhesive film is particularly suitable for preparing a strippable adhesive tape or a label. On the other hand, it is shown that the copolymer prepared in example six is not substantially photo-cured to any extent under the same UV irradiation conditions, leaving a large amount of residual glue on the steel plate when peeled therefrom, and cannot be used for preparing a peelable tape or label.

In addition, for the third example, the glycidyl methacrylate (epoxy group-containing monomer) and the epoxy group-containing benzophenone were added during the preparation of the acrylate polymer, and the other polymer compositions, polymerization processes, and sample preparation methods were completely the same as those of the third example. But the melt viscosity of the sample rises to 158100cps at 140 ℃, which is increased by 320% compared with the melt viscosity of the sample in the third example, but the obtained hot melt sample contains a large amount of gel particles, and the hot melt coating cannot be carried out to produce pressure-sensitive adhesive products, which shows that the high temperature stability of the polymer containing acrylic double bonds is poor, the high temperature self-crosslinking of the contained acrylic double bonds can occur, and the high temperature hot melt processing and coating process is difficult to be suitable.

The above disclosure is only for a few specific embodiments of the present invention, but the present invention is not limited thereto, and any variations that can be made by those skilled in the art are intended to fall within the scope of the present invention.

Claims

1. A method for preparing an ultraviolet-curable acrylic copolymer, comprising the steps of:

2. Preparation of the UV-curable acrylic copolymer according to claim 1A method, characterized in that the monomer mixture comprises: molecular formula is CH₂Acrylic or methacrylic ester monomer of-CH (R1) (C00R2) wherein R1 is H or CH₃R2 is an alkyl group containing l-20 carbons.

3. The method of claim 1, wherein the monomer mixture is a (meth) acrylic or vinyl functional monomer, and the functional group of the functional monomer includes one or more of a carboxyl group, a hydroxyl group, an acid anhydride group, an amine group, an amide group, an epoxy group, and an isocyanate group.

4. The method of claim 1, wherein the benzophenone derivative comprises one or more reactive groups selected from the group consisting of carboxyl, hydroxyl, acid anhydride, amine, epoxy, acid chloride and isocyanate groups.

5. The method of claim 1, wherein the acrylic copolymer has a glass transition temperature of less than 20 ℃ and the weight average molecular weight of the acrylate copolymer is greater than 50000 g/mol.

6. The method for producing an ultraviolet-curable acrylic copolymer according to claim 5, wherein the acrylic copolymer has a glass transition temperature of 0 ℃ or lower, and the weight-average molecular weight of the acrylic copolymer is more than 10⁵g/mol。

7. The method for preparing an ultraviolet-curable acrylic copolymer as set forth in claim 1, wherein the heating temperature is 160-180 ℃ in step S3.

8. Use of a UV-curable acrylic copolymer obtained by the process according to any one of claims 1 to 7 for the production of a UV-curable pressure-sensitive adhesive.

9. The use of the UV-curable acrylic copolymer as claimed in claim 8, wherein the UV-curable pressure-sensitive adhesive is produced under the irradiation of an UV lamp of 200-500 nm.

10. Use of the UV-curable acrylic copolymer according to claim 8, wherein the UV-curable pressure-sensitive adhesive is a hot-melt coated pressure-sensitive adhesive or a liquid adhesive.