CN114517070B

CN114517070B - High-purity acrylate adhesive, preparation method and application thereof, optical transparent film and preparation method

Info

Publication number: CN114517070B
Application number: CN202210182781.5A
Authority: CN
Inventors: 冯娇; 张警
Original assignee: Sichuan Zhongjiu Guofeng Technology Co ltd
Current assignee: Sichuan Zhongjiu Guofeng Technology Co ltd
Priority date: 2022-02-25
Filing date: 2022-02-25
Publication date: 2022-12-09
Anticipated expiration: 2042-02-25
Also published as: CN114517070A

Abstract

The invention discloses a high-purity acrylate adhesive, a preparation method and application thereof, an optical transparent membrane and a preparation method thereof, belonging to the field of high molecular compounds and synthetic adhesives. The optical transparent film prepared by the high-purity acrylate adhesive has the advantages of good breaking strength, elongation at break and cleanliness, high light transmittance and low haze.

Description

High-purity acrylate adhesive, preparation method and application thereof, optical transparent film and preparation method

Technical Field

The invention belongs to the field of high molecular compounds and synthetic adhesives, and particularly relates to a high-purity acrylate adhesive, a method for preparing the high-purity acrylate adhesive, application of the high-purity acrylate adhesive in preparation of an optical transparent membrane, an optical transparent membrane prepared from the high-purity acrylate adhesive, a method for preparing the optical transparent membrane, and application of the optical transparent membrane in optical display bonding.

Background

The existing preparation method of the acrylate adhesive generally comprises three types of solvent polymerization method, emulsion polymerization method and bulk polymerization (solvent-free type) according to the formulation, the bulk polymerization acrylate adhesive can be applied by heating and melting, electron beam or light initiation, and because the bulk polymerization acrylate adhesive does not contain organic solvent and water, the solvent or dispersing agent is not volatilized by heating after the application of glue, and the pressure-sensitive adhesive is formed by natural cooling or is further formed by electron beam irradiation or light curing. Among them, the solvent polymerization method and the emulsion polymerization method have the problems of high energy consumption and serious environmental pollution in the preparation process, still have a large amount of Volatile Organic Compounds (VOC) volatilization in the use process, and the adhesive is difficult to purify to high purity (solvent residue is easy to exist under the condition that the adhesive layer is thick), so the solvent polymerization method and the emulsion polymerization method are difficult to be used in special application environments with extremely high requirements, such as the special optical application field. The polymerization process of the bulk polymerization method has little pollution, and the adhesive has no solvent, so the relative purity is higher, no serious VOC volatilization exists in the use process, and the method is very green and environment-friendly and is the main development direction of the industry.

CN103725245B discloses a solvent-free UV curing glue for an optical transparent adhesive tape, and a preparation method and application thereof. The solvent-free UV curing glue for the optical transparent adhesive tape is prepared by taking aliphatic polyurethane acrylate, hyperbranched polyester acrylate, an acrylate monomer, mercaptan, tackifying resin, a leveling agent and a photoinitiator as raw materials, the flexibility and the light transmittance (91.9% -92.5%) of an OCA colloid are improved through the aliphatic polyurethane acrylate with low functionality, the haze (0.3% -0.5%) is reduced, the crosslinking density and the colloid strength of the colloid are improved through adding the hyperbranched polyester acrylate, the viscosity of the adhesive is adjusted by taking the acrylate monomer as a diluent to improve the workability, the adhesion of the adhesive is improved through adding the mercaptan containing an ether structure, and the dosage of the photoinitiator is 1.06% -5.0%. When no specialty mercaptan was added, the peel force of the OCA product was significantly reduced.

CN110776855A is improved on the basis of CN103725245B technical scheme, and discloses a UV photocuring high-transmittance optical cement and a preparation method thereof. The technology controls the reaction temperature (70-75 ℃) and the stirring speed (80 r/min), and simultaneously adopts the mode of dropwise adding the monomer and the initiator in batches (dropwise adding the dropping funnel at a constant speed), so that the viscosity is slowly increased in the reaction process, and the prepolymer with proper viscosity is obtained; the problem of reaction implosion caused by the rapid temperature rise in bulk polymerization is solved. According to the technology, N atom-containing polar monomers and an active diluent react with acrylate and an auxiliary agent, the light transmittance of an obtained adhesive film is over 99.0%, the haze is reduced to 0.1%, the initial adhesion, the holding adhesion and the peeling force are excellent, however, CN110776855A uses a large amount of azobisisobutyronitrile (the amount of which is 0.18-0.3 wt%), the amount of an initiator is equivalent to that of the initiator during solvent polymerization (for example, CN202010610058.3 adopts a solvent polymerization method to prepare a low-adhesion pressure-sensitive adhesive, the amount of the initiator is 0.05-1%), under the solvent-free bulk polymerization condition, a large amount of the initiator causes reaction to be difficult to control, and the reaction is still easy to form a solid through depolymerization, in addition, a thermal initiator and a photoinitiator are simultaneously used in the patent, and the photoinitiator is easy to remain except for the problem that a large amount of the thermal initiator is easy to cause depolymerization. Meanwhile, the technical scheme relies on a polar monomer containing N atoms and an active diluent to improve the bonding strength, the light transmittance is improved and the haze is reduced by utilizing hydrophilic hydroxyl in hydroxyalkyl acrylate, when the key components are lacked in the technical scheme, the performances of the adhesive film such as the light transmittance, the bonding strength and the like can obviously slide down, and the haze is obviously increased, so that the adhesive film can not meet the requirements of the electronic industry on the adhesive film performance, for example, the UV-cured acrylic pressure-sensitive adhesive disclosed in CN103224757A and the use method thereof.

The bulk polymerization method is mainly divided into bulk photopolymerization and bulk thermal polymerization. All materials of the bulk polymerization are used as reaction monomers, so that the local concentration of the monomers is high, the reaction rate is high, and the viscosity of a polymer system is rapidly increased along with the reaction, so that a remarkable self-acceleration phenomenon can be formed. The self-acceleration phenomenon is also called gel effect, and is a phenomenon in which the polymerization rate significantly increases when the polymerization reaction proceeds to a certain extent. The reaction rate and the reaction molecular weight of photopolymerization can be controlled by the illumination intensity, the initiator concentration, the molecular weight regulator concentration and the material ratio, so that bulk photopolymerization is currently more mature bulk polymerization. However, in the bulk photopolymerization process, the illumination intensity is reduced along with the deeper illumination depth in the system, so that a non-uniform reaction is formed, and the reaction system is easy to generate coacervate after the viscosity is increased to become impurities in the adhesive system, thereby influencing the purity and the optical performance. In addition, the initiator in the system has more residues after the reaction is finished, further decomposition possibly initiates polymerization in the process of storing the adhesive, and the formed free radicals are in a yellowing condition under a trace amount of oxygen in the system, so that the optical performance is influenced.

Since the bulk thermal polymerization is very easy to be controlled and polymerized suddenly, the bulk thermal polymerization is often used for directly curing a liquid into a solid, such as preparing a PMMA (polymethyl methacrylate) plate, and no report that the acrylate monomer is used as a main material to prepare a high-purity adhesive without sudden polymerization and residue through the bulk thermal polymerization is found.

Disclosure of Invention

The invention is an improved bulk thermal polymerization process, which not only overcomes the problems of high energy consumption, environmental pollution and difficult solvent purification of solvent and emulsion polymerization, but also overcomes the problems of gel group impurities and initiator residues which are easy to appear in bulk polymerization, can prepare a high-purity adhesive without the gel group impurities and the initiator residues, is convenient for long-term storage without deterioration and yellowing, and the optical transparent film prepared by the adhesive has better tensile property caused by the defects of better purity, lower haze and lower impurities.

In order to solve the technical problems in the prior art, one embodiment of the invention adopts the following technical scheme:

a preparation method of a high-purity acrylate adhesive comprises the steps of heating acrylic acid (acrylate) monomer raw materials to a specified temperature, adding a thermal initiator for multiple times, wherein the amount of the thermal initiator added for the first time is larger than that of the thermal initiator added for each subsequent time, gradually increasing the viscosity of a reaction system along with the increase of the adding times of the initiator, detecting the viscosity of the reaction system after each time of adding the thermal initiator, stopping adding the thermal initiator until the viscosity reaches 2000-10000cps at 25 ℃, and obtaining an acrylic resin solution, namely the high-purity acrylate adhesive.

As used herein, the term "acrylate based adhesive" has the same meaning as "acrylic resin solution" and is used interchangeably.

The acrylic acid (ester) monomer comprises acrylic acid alkyl ester, acrylic acid aryl ester, acrylic acid hydroxy ester, acrylic acid carboxyl (ester) and partial special acrylic acid monomer.

The alkyl acrylate is selected from the following monomers: 2-ethylhexyl (meth) acrylate, pentyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, n-nonyl (meth) acrylate, isoamyl (meth) acrylate, n-decyl (meth) acrylate, isodecyl (meth) acrylate, dodecyl (meth) acrylate, isobornyl (meth) acrylate, cyclohexyl (meth) acrylate, isostearyl acrylate, 2-methylbutyl (meth) acrylate, bicyclodecane acrylate, cyclohexyl acrylate, 3, 5-trimethylcycloethyl acrylate. When preparing the high-purity acrylate adhesive, one or more of the alkyl acrylates can be used. 2-ethylhexyl (meth) acrylate means 2-ethylhexyl methacrylate or 2-ethylhexyl acrylate, pentyl (meth) acrylate means pentyl methacrylate or pentyl acrylate; n-octyl (meth) acrylate means n-octyl methacrylate or n-octyl acrylate; the same explanation applies to other alkyl acrylate monomers.

The acrylic carboxyl (ester) is selected from acrylic acid, methacrylic acid, cyanoacrylate, ethacrylic acid, n-propylacrylic acid, isobutylacrylic acid, itaconic acid (i.e. methylenesuccinic acid, H) ₂ C＝C(COOH)-CH ₂ -COOH), β -carboxyethyl acrylate, maleic acid, and the like. When the high-purity acrylate adhesive is prepared, the acrylic carboxyl (ester) can be one or more of the acrylic carboxyl (ester).

The acrylic acid hydroxy ester is selected from hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc. When the high-purity acrylate adhesive is prepared, one or more of the acrylate hydroxyl esters can be used. Hydroxyethyl (meth) acrylate means hydroxyethyl methacrylate or hydroxyethyl acrylate, hydroxypropyl (meth) acrylate means hydroxypropyl methacrylate or hydroxypropyl acrylate, hydroxybutyl (meth) acrylate means hydroxybutyl methacrylate or hydroxybutyl acrylate, and other similar expressions are explained in the same way.

Aryl acrylate means phenyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate. When preparing the high-purity acrylate adhesive, the aryl acrylate used may be one or more of the aryl acrylates. Phenyl (meth) acrylate means phenyl methacrylate or phenyl acrylate, and 2-phenoxyethyl (meth) acrylate means 2-phenoxyethyl methacrylate or 2-phenoxyethyl acrylate.

Specific acrylic monomers are selected from the group consisting of ethyl 2-vinyloxyethoxy (meth) acrylate, hydroxyethyl caprolactone (meth) acrylate, tetrahydrofuran ester (meth) acrylate, N-vinylpyrrolidone, N-vinylcaprolactam, N-isobutoxymethacrylamide, N-dimethylacrylamide, N-diethylacrylamide, acetylacetone, acrylamide, acryloylmorpholine, acrylonitrile, styrene, methylstyrene, glycidyl (meth) acrylate, cyclotrimethylolpropane formal acrylate, and the like. When the high-purity acrylate adhesive is prepared, one or more special acrylic monomers can be used. 2-ethyleneoxyethoxy (meth) acrylate means 2-ethyleneoxyethoxy ethyl methacrylate or 2-ethyleneoxyethoxy ethyl acrylate, and hydroxyethyl caprolactone (meth) acrylate means hydroxyethyl caprolactone methacrylate or hydroxyethyl caprolactone acrylate; the tetrahydrofuran (meth) acrylate refers to tetrahydrofuran methacrylate or tetrahydrofuran acrylate; glycidyl (meth) acrylate means glycidyl (meth) acrylate or glycidyl methacrylate.

The starting materials may include, in addition to the acrylate monomer, thermal initiator, a polymerization regulator such as dodecyl mercaptan in an amount of 0.01 to 2wt% based on the acrylate monomer. Preferably, the invention can utilize 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate and acryloyl morpholine according to the mass ratio of (4-6) 1 (2-3) to (1-2) to (0.1-1): (0-1) mixing to form acrylic acid (ester) monomer, also called acrylic acid (ester) monomer mixed solution.

Besides, the invention can be used for preparing 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, isobornyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate and acryloyl morpholine according to the mass ratio of (4-6) 1, (2-3), (1-2), (0.1-1): (0.001-1) to form an acrylic monomer, which may also be referred to as an acrylic monomer mixture.

As used herein, the term "thermal initiator" means that at a certain temperature, the initiator generates a radical or anion, cation, etc. by thermal decomposition to generate a reactive species, and the formed reactive species initiates and polymerizes an acrylic acid (ester) monomer. The thermal initiator includes but is not limited to azo type initiators, peroxy compound initiators. The azo initiator is selected from one or more of Azobisisobutyronitrile (AIBN), azobisisoheptonitrile (ABVN, AIVN), dimethyl Azobisisobutyrate (AIBE), azobisisobutyramidine hydrochloride (AIBA), azobisisobutyrimidazoline hydrochloride (AIBI), and azobisisobutyronitrile formamide (V30). Peroxy compound initiators are compounds of the type which contain peroxy groups (-O-), upon heating, the-O-bond breaks, splitting into two corresponding free radicals, thereby initiating polymerization of the monomer. The peroxy compound initiator is selected from, for example, benzoyl peroxide, benzoyl tert-butyl peroxide, methyl ethyl ketone peroxide, dilauroyl peroxide (LPO), and the like.

When the thermal initiator is a solid material, the thermal initiator can be dissolved, suspended or diluted by using an acrylic acid (ester) monomer at normal temperature, room temperature or below a specified temperature to obtain a thermal initiator solution (or suspension), and then the thermal initiator solution (or suspension) is added into the acrylic acid (ester) monomer heated to the specified temperature to initiate polymerization. Normal temperature, room temperature usually means 20-25 ℃.

The term "active species" refers to a monomer radical or ion formed after the initiator initiates the monomer, and further chain growth is performed by taking the radical or ion as a center to form a polymer chain.

The "prescribed temperature" is a temperature at which the half-life of the thermal initiator to be added is 0.5 to 10min (half-life calculation formula is logt) _1/2 = A/T-B), in the formula, T _1/2 The time required for the initiator to decompose to half the initial concentration; a and B are constants calculated for each initiator, and T is the absolute temperature (Kelvin); if the specified temperature is too high, the reaction is too rapid and difficult to control; if the specified temperature is too low, the reaction time is too long, which affects the efficiency of the operation. The specified temperature is preferably a temperature at which the half-life is 1 to 6min, particularly preferably a temperature at which the half-life is 5 min. The following table shows the A and B values and half-lives at 1h, 10h, and 0.05h for the corresponding initiators.

TABLE 1A, B values and half-lives of the initiators

The method for raising the temperature of the acrylic acid (ester) monomer raw material to a predetermined temperature may be a one-time temperature raising or a temperature raising program, and the method is not limited. The temperature programming is beneficial to reducing the temperature difference of the acrylic acid (ester) monomer raw material and leading the internal temperature and the external temperature to be consistent.

The term "multiple times" in the case of multiple additions of thermal initiator means two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, thirteen, fourteen or fifteen times, or means other times greater than fifteen times, such as twenty, thirty, forty, fifty times, any number above or in between, wherein the first addition of thermal initiator is the first addition of thermal initiator, and the other additions of thermal initiator are classified as subsequent additions of thermal initiator. For example, the thermal initiator is added in 10 portions, and the order of addition of the thermal initiator, except for the first addition of the thermal initiator, is included in the scope of the subsequent addition of the thermal initiator.

Preferably, the amount of the thermal initiator added for the first time is 2-20ppm, such as 2ppm, 3ppm, 4ppm, 5ppm, 6ppm, 7ppm, 8ppm, 9ppm, 10ppm, 11ppm, 12ppm, 13ppm, 14ppm, 15ppm, 16ppm, 17ppm, 18ppm, 19ppm, 20ppm or some amount in between such amounts such as 8.5ppm, 10.5ppm, 14.6ppm, etc. The amount of the first thermal initiator to be added is preferably 8 to 15ppm, and particularly preferably 10 to 12ppm.

The amount of the thermal initiator added for the first time is larger than the amount of the thermal initiator added for each subsequent time, which means that the amount of the thermal initiator added for each subsequent time is smaller than the amount of the thermal initiator added for the first time, and if the thermal initiator is added for 10 times, the amount of the thermal initiator added for each subsequent time is smaller than the amount of the thermal initiator added for the first time when the thermal initiator is added for 9 subsequent times. For example, if the amount of thermal initiator added for the first time is 2ppm, the amount of initiator added for each subsequent time is less than 2ppm; if the amount of the thermal initiator added for the first time is 20ppm, the amount of the thermal initiator added for each subsequent time is less than 20ppm, including the amount of the thermal initiator added for any one or more values between zero and less than 20, and optionally, the amount of the thermal initiator added for each subsequent time is the same or different.

The purpose of adding a large amount of thermal initiator for the first time is to generate free radicals after the thermal initiator is decomposed to overcome factors which are not beneficial to reaction, such as acrylic acid (ester) monomer or acrylic acid (ester) monomer mixed solution, which may not remove clean oxygen, polymerization inhibitor (which may be added due to storage and transportation) possibly contained in raw materials, and the like, so that the reaction is started, the reaction temperature rise is controlled within 5 ℃, the temperature rise rate is controlled within 0.1-2 ℃/min, too much first-time addition amount may cause too fast and uncontrollable temperature rise, and too little addition amount causes too long reaction starting time.

In order to eliminate oxygen in the acrylic acid (ester) monomer or the acrylic acid (ester) monomer mixture, nitrogen or other inert gas is generally introduced into the mixture after the acrylic acid (ester) monomer is mixed to remove oxygen, and optionally, the oxygen removal time is 20min or more to ensure that the oxygen in the mixed solution is removed as much as possible.

As the initiator is added, the polymerization reaction starts, and the polymerization reaction is exothermic, so that the temperature of the reaction system automatically rises. In the polymerization reaction process, the rising condition of the reaction temperature needs to be controlled, namely the reaction temperature is controlled, after a large amount of thermal initiator is added for the first time, the reaction temperature does not exceed 5 ℃, in addition, the temperature rising speed is controlled within 0.1-2 ℃/min, and the temperature rising speed can be controlled through the proportion of the dosage of the acrylic acid (ester) monomer and the initiator or the proportion of the dosage of the acrylic acid (ester) monomer mixed liquid and the initiator.

In the case where the above-mentioned conditions for the addition of the initiator are satisfied, the amount of the thermal initiator to be added subsequently is preferably 0.5 to 3ppm per time, and the amount of the initiator to be added per time may be any one of 0.5ppm, 1ppm, 1.5ppm, 2ppm, 2.5ppm, 3ppm and therebetween, and more preferably 1ppm per time.

The total amount of the thermal initiator added to the acrylic monomer or the mixed solution is 500ppm or less, preferably 100ppm or less, for example, the total amount of the thermal initiator added to the acrylic monomer mixed solution is 90ppm, 80ppm, 70ppm, 60ppm, 50ppm, 45ppm, 40ppm, 35ppm, 30ppm, 25ppm, 20ppm, 15ppm, 10ppm, 5ppm, 4ppm or 3ppm, or a total amount represented by any value of 500ppm or less and 3ppm or more. For example, when the total amount of the thermal initiator is 100ppm, the mass concentration of the thermal initiator in the high-purity acrylate adhesive is one ten thousandth.

After the thermal initiator is added for the first time, the appropriate time needs to be selected for each subsequent addition of the thermal initiator, and the appropriate time is selected as follows: the interval of time for which the initiator is added is not less than the half-life of the initiator, preferably 1.5 to 5 times the half-life of the initiator, particularly preferably 2 to 3 times the half-life of the initiator, and the change state corresponding to the temperature rise during this interval is: the viscosity is correspondingly increased by naturally increasing the temperature to the maximum value after the thermal initiator is added last time and then falling back to the initial set value (for improving the cooling efficiency, the outside of the reactor can adopt known cooling means such as cooling water, cooling oil and cold air). The initial set point is referred to as "specified temperature".

After adding the thermal initiator each time, directly testing the viscosity of the reaction system by using an online viscometer or testing the viscosity of the reaction system by using a rotational viscometer after sampling, judging the viscosity at 25 ℃ according to the detected viscosity, and selecting the time for stopping adding the thermal initiator according to the viscosity requirement of the acrylic resin solution if the viscosity at 25 ℃ reaches the range of 2000-10000cps to obtain the acrylic resin solution, namely the high-purity acrylate adhesive. The viscosity of the acrylic resin solution is preferably controlled to be within 3000-6000cps, and the adhesive can meet the standard that the wide performance can meet the use requirement.

The cross-linking agent, the photoinitiator, the polymerization inhibitor, the thickening agent, the tackifier, the hardening agent, the accelerator, the antistatic agent, the softening agent, the coloring agent, the antioxidant, the thickening agent, the leveling agent, the light-resistant agent, the defoaming agent, the stabilizer, the preservative, the coupling agent, the flame retardant, the lubricant, the catalyst, the filler, the surfactant, the toughening agent and other auxiliary agents are common auxiliary agents in the optical pressure-sensitive adhesive, when the high-purity acrylate adhesive is prepared, the auxiliary agents can be not added or added except for two raw materials of an acrylic acid (ester) monomer and a thermal initiator, the addition type is selected according to the performance requirement of the high-purity acrylate adhesive, and the auxiliary agents are not necessary for preparing the most basic high-purity acrylate adhesive. Or after the high-purity acrylate adhesive is prepared by using two raw materials of an acrylic acid (acrylate) monomer and a thermal initiator, other auxiliary agents are continuously added to further adjust the performance of the high-purity acrylate adhesive. These auxiliaries may be those conventional in the art.

The cross-linking agent can be selected from hexanediol diacrylate (HDDA), ethylene Glycol Dimethacrylate (EGDMA), polyethylene glycol n dimethacrylate (PEGnDMA), ethoxylated (2) bisphenol A dimethacrylate (E2 BADMA), trimethylolpropane trimethacrylate (TMPTMA), diallyl phthalate (DAP), pentaerythritol acrylate (PETA) or trimethylolpropane triacrylate (TMPTA), and other single cross-linking agents known in the industry and mixtures thereof.

The photoinitiator may be selected from known single photoinitiators such as Benzophenone (BP), 4-Methylbenzophenone (MBZ), 4-Phenylbenzophenone (PBZ), benzoin diethyl ether (BDK), benzoin butyl ether, 2-hydroxy-methylphenylpropane-1-one (1173), 1-hydroxycyclohexyl benzophenone (184), 2-methyl-1- (4-methylthiophenyl) -2-morpholino-1-propanone (907), 2,4, 6-trimethylbenzoyldiphenylphosphine oxide (TPO), ethyl 2,4, 6-trimethylbenzoylphenylphosphonate (TPO-L), isopropylthioxanthone (ITX), ethyl 4- (N, N-dimethylamino) benzoate (EDAB), methyl o-benzoylbenzoate (1156), diphenyliodonium salt hexafluorophosphate (810), isooctyl p-N, N-dimethylaminobenzoate, methyl o-benzoylbenzoate (OMBB), and the like, and mixtures thereof.

The solid content of the acrylic resin solution is 10-50wt%, such as 10wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%, or any content between these solid content values, preferably 25-40wt%; the solid content is adjusted by controlling the reaction degree, the reaction molecular weight and the distribution thereof, in order to achieve the purpose of final comprehensive performance of the pressure-sensitive adhesive after easy construction, coating, leveling, defoaming and curing, a proper solid content is usually selected, and if necessary, the solid content can be diluted by adding a monomer into a high-solid-content resin solution, which is also a conventional method in the field.

The invention provides application of a high-purity acrylate adhesive, which can be used for preparing an optical transparent film.

The invention provides an optical transparent film, which has an upper layer structure, a middle layer structure and a lower layer structure, wherein the upper layer structure and the lower layer structure are release films, the middle layer structure is optical transparent adhesive, and the thickness of the middle layer structure is 50-500 mu m to form sandwich adhesive; the middle layer structure adopts the high-purity acrylate adhesive.

The preparation method of the optical transparent film comprises the following steps: adding an auxiliary agent into the acrylic resin solution, coating the acrylic resin solution on a release film, controlling the thickness of a glue layer to be an ideal thickness, and covering another release film to form sandwich adhesive. And irradiating and curing the sandwich adhesive to obtain the optical transparent film.

The "ideal thickness" refers to the designed thickness of the optical transparent film, usually in the range of 50-500 μm, but the thickness can be adjusted within or outside the range according to the application scenario of the optical transparent film. The release film can be a release film conventional in the art, and a PET release film (polyethylene terephthalate film, also called mylar) is one of the most common types; the thickness and the weight of the release film have great influence on the convenience, the yield, the usability and the like of the final application of the optical transparent film, so that when the release film is used, the thickness and the weight of the release film are selected to a certain extent. The radiation curing refers to that the sandwich adhesive is placed in an environment with a UV wave band (such as 365 nm) (light source devices generating UVA wave bands include, but are not limited to, high-pressure mercury lamps, low-pressure mercury lamps, LED lamps and the like) and a certain illumination (such as illumination of 5000 Lux) for a certain time (such as 10 min) to be cured to obtain a final film. The UVA band refers to ultraviolet rays having a wavelength of 320 to 420 nm. The release film usually contains a release agent, such as any one of an organosilicon release agent, a fluorine release agent and a fluorine silicon release agent, and the release agent is used for preventing the formed composite material product, namely the optical transparent adhesive, from being adhered to the polyester film and is convenient for demoulding from the polyester film.

When the optically transparent film is prepared, the additive added to the acrylic resin solution is one or more of cross-linking agent, photoinitiator, polymerization inhibitor, thickener, tackifier, hardener, accelerator, antistatic agent, softener, colorant, antioxidant, thickener, leveling agent, light resistance agent, defoamer, stabilizer, preservative, coupling agent, flame retardant, lubricant, catalyst, filler, surfactant, toughening agent and the like, and the materials can adopt conventional materials in the field.

In the present invention, the term "low-pressure mercury lamp" means a mercury vapor arc lamp having a mercury vapor pressure of 1.3 to 13Pa (0.01 to 0.1 mmHg), a main emission wavelength of 253.7nm (0.01 mmHg) in the ultraviolet region, and an equivalent energy of 471.0kJ/mol (112.5 kcal/mol), which constitutes 70% of the total energy of the lamp.

The optical transparent film is applied to the bonding of the optical display module.

In order to verify the performance of the acrylic resin solution and the related products, the following test methods were used:

1. and (3) viscosity measurement:

viscosity: after the reaction is finished, the final viscosity of the acrylic resin solution is measured by a rotational viscometer according to GB/T2794-2013 single-cylinder rotational viscometer method for measuring viscosity of adhesives.

2. Solid content measurement:

about 1g of sample is taken, 0.5wt% of p-methoxyphenol (polymerization inhibitor) is uniformly mixed, the sample is placed in a vacuum oven at 60 ℃, after vacuum is maintained for 4 hours, the residual solid mass is weighed, the solid content C = M1/M0 is 100%, wherein M1 is the residual solid mass, and M0 is the sum of the initial sample mass and the polymerization inhibitor mass. The process can be implemented by referring to GB/T2793-1995, determination of the content of the non-volatile matters in the adhesive.

3. Accelerated shelf life test:

under the condition of keeping away from light, after a sample is placed at 85 ℃ and 85% humidity for 12 hours, the transparency and the appearance requirement are measured without obvious change, and the method is specifically referred to (GBT 2423.50-2012 environmental test part 2: a test method test Cy constant damp heat is mainly used for the accelerated test of the element).

4. Light transmittance and haze test of optically transparent film

And (3) testing by using a photoelectric haze meter according to GB/T2410-2008 'determination of light transmittance and haze of transparent plastics'.

5. Testing of breaking Strength and elongation at Break of optically transparent film

The tensile testing machine is adopted to implement according to the national standard GB/T30776-2014.

6. 180 degree peel force test

The test was carried out by a peel force tester according to GB/T25256-2010 test methods for optical functional films, release films, 180 ℃ peel force and residual adhesion rate.

7. Holding power test method

The test was carried out in accordance with GB/T4851-2014 test methods for adhesive tape holding power using a constant temperature type adhesive tape holding power tester.

8. Film defect counting

Cutting 6 x 6cm of membrane, removing the light release film, attaching the membrane to a 316 stainless steel frame with the inner frame size of 5 x 5cm, the frame width of 2cm and the frame thickness of 1mm to form a transparent visible area with the area of 5 x 5cm, and then counting the defects (particles or bubbles) of the membrane by visual observation in a bright environment.

9. Initiator residue detection method

And (3) testing the total ion current spectrum of the sample components by adopting a headspace sample injector and a GC-MS combined instrument, and determining the residual condition of the initiator after comparing the total ion current spectrum with the standard spectrum of the American 'EPA/NIH' mass spectrum atlas.

Compared with the prior art, the invention at least obtains the following beneficial effects:

the optical transparent film prepared by the acrylic resin solution is compared with the optical transparent film prepared by the acrylic resin solution of a contrast sample which is prepared by adopting UV bulk polymerization and has basically the same components, basically the same viscosity, basically the same solid content and completely the same coating process, and the result shows that the tensile strength of the optical transparent film prepared by the invention is more than 35 percent greater than that of the contrast sample polymerized by the UV bulk polymerization, the elongation at break is more than 19 percent greater than that of the contrast sample polymerized by the UV bulk polymerization, and the cleanliness of the film is greatly improved (the film has no obvious visual defect).

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.

The thermal initiator Azobisisoheptonitrile (ABVN) used in the embodiment of the invention is dissolved and diluted by adopting corresponding reaction monomers (room temperature), and the solid-to-liquid ratio is 1. The term "thermal initiator added" in the examples is meant to be a thermal initiator after dilution by dissolution.

1. The preparation of the acrylate adhesive (acrylic resin solution) is carried out in a thousand-level clean workshop in the experimental environment.

Comparative example 1UV bulk polymerization

2-ethylhexyl acrylate (55 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (20 g), hydroxyethyl acrylate (10 g), hydroxypropyl acrylate (5 g), benzoin diethyl ether (photoinitiator BDK,0.2 g) and dodecyl mercaptan (0.1 g) were mixed and placed in a 250ml four-necked flask, and oxygen was bubbled through nitrogen for 20min. And opening a low-pressure mercury lamp with the wavelength of UVA wave band and the central wave band of 365nm (the mercury lamp is 40cm away from the central position of the four-neck flask), starting temperature rise after about 30min, and finishing the reaction after about 1h after the temperature rises to 90 ℃. The acrylic resin solution obtained by the reaction was tested for viscosity and solid content, as shown in Table 2.

Example 1

2-ethylhexyl acrylate (55 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (20 g), hydroxyethyl acrylate (10 g), hydroxypropyl acrylate (5 g) and dodecyl mercaptan (0.1 g) were mixed and placed in a 250ml four-necked flask, and oxygen was bubbled with nitrogen gas for 20min. Heating to 90 ℃, adding 10ppm of thermal initiator ABVN for the first time, increasing the temperature of the reaction system after 10min, gradually increasing to the highest point of 95 ℃ and then falling back to 90 ℃; supplementing 2ppm of thermal initiator ABVN again, and after the temperature is gradually increased to 95 ℃, falling back to 90 ℃ again; the time interval of adding the thermal initiator ABVN in two adjacent times is 10min (the change processes of natural temperature rise and temperature drop are completed within 10min, cooling water is arranged outside the reactor, and the temperature drop speed is adjusted); sampling and monitoring the viscosity of the reaction system until the viscosity of reactants (sampled and cooled to 25 ℃ for testing) reaches the preset target 4000cps after 5 times of adding 10ppm (2 ppm each time) of thermal initiator ABVN again, cooling and discharging to obtain the high-purity acrylate adhesive. The acrylic resin solution obtained from the reaction was tested for solid content, as shown in Table 2.

Comparative example 2UV bulk polymerization

2-ethylhexyl acrylate (40 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (25 g), hydroxyethyl acrylate (15 g), hydroxypropyl acrylate (5 g), acryloylmorpholine (5 g), 1-hydroxycyclohexyl phenyl ketone (photoinitiator 184,0.2 g) and dodecyl mercaptan (0.1 g) were mixed and filtered with filter paper, placed in a 250ml four-necked flask, and bubbled with nitrogen to remove oxygen for 20min. Turning on a low-pressure mercury lamp (the mercury lamp is 40cm away from the center of the four-neck flask) with the wavelength of UVA wave band and the central wave band of 365nm, starting temperature rise within about 20 minutes, completing the reaction about 1 hour after the temperature rise to obtain an acrylic resin solution, and testing the viscosity and the solid content of the acrylic resin solution obtained by the reaction, wherein the test is shown in Table 2.

Example 2

2-ethylhexyl acrylate (40 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (25 g), hydroxyethyl acrylate (15 g), hydroxypropyl acrylate (5 g), acryloylmorpholine (5 g) and dodecylmercaptan (0.1 g) were mixed and filtered through filter paper, and then placed in a 250ml four-necked flask, and oxygen was bubbled with nitrogen gas for 20min. Heating to 95 ℃, adding 12ppm of thermal initiator ABVN for the first time, increasing the temperature of the reaction system after 4min, gradually increasing to the highest point of 100 ℃ and then falling back to 95 ℃; supplementing 1.5ppm of thermal initiator ABVN again, gradually increasing the temperature to 100 ℃ and then falling back to 95 ℃ again; the time interval of adding the thermal initiator ABVN in two adjacent times is 10min (the change processes of natural temperature rise and temperature fall are completed within 10min, cooling water is arranged outside the reactor, and the temperature fall speed is adjusted); sampling and monitoring the viscosity of the reaction system until the viscosity of reactants (tested when the sample is cooled to 25 ℃) reaches 5100cps of a preset target after 6 times of adding 9ppm (1.5 ppm each) of thermal initiator ABVN again, and cooling and discharging to obtain the high-purity acrylate adhesive. The acrylic resin solution obtained from the reaction was tested for solids content, as shown in Table 2.

Example 3

2-ethylhexyl acrylate (55 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (20 g), hydroxyethyl acrylate (10 g), hydroxypropyl acrylate (5 g) and dodecyl mercaptan (0.1 g) were mixed, filtered through filter paper, placed in a 250ml four-necked flask, and purged with nitrogen to remove oxygen for 20min. Heating to 110 ℃, adding 20ppm of thermal initiator Azobisisobutyronitrile (AIBN) for the first time, increasing the temperature of the reaction system after 10min, gradually increasing to the highest point of 116 ℃, and then falling back to 110 ℃; supplementing 2.5ppm of thermal initiator AIBN again, gradually increasing the temperature to 116 ℃ and then falling back to 110 ℃ again; the time interval of adding the thermal initiator AIBN in two adjacent times is 10min (the change process of natural temperature rise and temperature fall is completed within 10min, cooling water is arranged outside the reactor, and the speed of temperature fall is adjusted); sampling and monitoring the viscosity of the reaction system until the thermal initiator AIBN with 12.5ppm (2.5 ppm each time) is supplemented for 5 times again, the viscosity of the reactant (tested by cooling to 25 ℃) reaches the preset target 4300cps, and cooling and discharging, namely the high-purity acrylate adhesive. The acrylic resin solution obtained from the reaction was tested for solid content, as shown in Table 2.

Example 4

2-ethylhexyl acrylate (55 g), 2-ethylhexyl methacrylate (10 g), isobornyl acrylate (20 g), hydroxyethyl acrylate (10 g), hydroxypropyl acrylate (5 g) and dodecyl mercaptan (0.02 g) were mixed and filtered through filter paper, and then placed in a 250ml four-necked flask, and oxygen was bubbled with nitrogen gas for 20min. Heating to 105 ℃, adding 14ppm dilauroyl peroxide (thermal initiator LPO) for the first time, increasing the temperature of the reaction system after 7min, gradually increasing to the highest point of 110 ℃, and then falling back to 105 ℃; supplementing 2ppm of thermal initiator LPO again, gradually increasing the temperature to 110 ℃ and then falling back to 105 ℃ again; the time interval between two adjacent thermal initiators LPO is 10min (the change process of natural temperature rise and temperature fall is completed within 10min, cooling water is arranged outside the reactor, and the speed of temperature fall is adjusted); sampling and monitoring the viscosity of the reaction system until the viscosity of reactants (tested by cooling to 25 ℃) reaches 3800cps after 6 times of adding 12ppm (2 ppm each time) of thermal initiator LPO, cooling and discharging, namely the high-purity acrylate adhesive. The acrylic resin solution obtained from the reaction was tested for solids content, as shown in Table 2.

The high purity acrylate adhesives prepared in examples 1-4 and the acrylic resin solutions prepared in comparative examples 1-2 by UV bulk polymerization were subjected to performance tests, and the results are shown in Table 2.

TABLE 2 Properties of Adhesives of examples 1-4 and comparative examples 1-2

As can be seen from Table 1, the viscosity and solid content of the comparative example and the example are not greatly different, the residual initiator is detected in the comparative example, and the residual initiator is not detected in the example. After the double-85 treatment, the adhesive in the comparative example has obvious yellowing and deterioration, and the adhesive in the example is colorless and transparent without any change, so that the adhesive has better preservation performance.

2. The acrylic adhesives (acrylic resin solutions) prepared in examples 1 to 4 and comparative examples 1 to 2 were used to produce optically transparent films (all experimental environments were thousand-level clean rooms).

Comparative examples 3-4 production of optically transparent films Using the acrylic resin solutions of comparative examples 1-2

0.2wt% of cross-linking agent HDDA and 0.2wt% of photoinitiator BDK are respectively added into the acrylic resin solution of the comparative examples 1-2, the acrylic resin solution is coated on a PET release film with the thickness of 75 mu m and the gram weight of release force of 20g, the thickness of a glue layer is 150 mu m, and then another PET release film with the thickness of 50 mu m and the gram weight of release force of 10g is covered to form sandwich glue. And (3) placing the laminated rubber in an environment with 365nm wavelength and 5000Lux illumination for irradiating for 10min to obtain optical transparent membranes I and II, wherein comparative example 1 corresponds to the optical transparent membrane I, and comparative example 2 corresponds to the optical transparent membrane II.

Examples 5 to 8

0.2 percent of cross-linking agent HDDA and 0.2 percent of photoinitiator BDK are respectively added into the high-purity acrylate adhesives of the embodiments 1 to 4, the high-purity acrylate adhesives are coated on a PET release film with the thickness of 75 mu m and the gram weight of release force of 20g, the adhesive layer thickness is 150 mu m, and then another PET release film with the thickness of 50 mu m and the gram weight of release force of 10g is covered to form sandwich adhesive. And placing the laminated adhesive in an environment with a wavelength of 365nm and an illumination intensity of 5000Lux, and irradiating for 10min to obtain optical transparent membranes III, IV, V and VI, wherein the embodiment 1 corresponds to the optical transparent membrane III, the embodiment 2 corresponds to the optical transparent membrane IV, and the like.

The property profiles of the optically transparent films I to VI are shown in Table 3.

TABLE 3 Properties of optically transparent films of comparative examples and examples

As can be seen from Table 3, compared with the optical transparent films I and II, the fracture elongation of the optical transparent films III, IV, V and VI is improved, the tensile strength is obviously improved, the light transmittance is improved, and the haze is reduced, which shows that the optical transparent films prepared by the embodiment of the invention have better performance than the proportion. Comparative example 1 used about 0.2wt% of the photoinitiator BDK when preparing the acrylate-based adhesive, comparative example 2 used about 0.2wt% of the photoinitiator 184 when preparing the acrylate-based adhesive, examples 1 to 4 according to the present invention used about 22 to 35ppm of the thermal initiator when preparing the acrylate-based adhesive, and comparative example 1 used more than 50 times the amount of the photoinitiator as compared with examples 1 to 4, but the optically transparent film obtained in the examples according to the present invention had better properties, such as higher holding power, and no visual defects, indicating higher purity. Meanwhile, the thermal initiator used in the invention is little, but the elongation at break, tensile strength, light transmittance, haze, peeling force and holding power all meet the requirements of the optical transparent film.

Although the invention has been described herein with reference to illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure.

Claims

1. A preparation method of a high-purity acrylate adhesive is characterized in that the adhesive is obtained through bulk thermal polymerization and is prepared from raw materials including an acrylic acid (ester) monomer and a thermal initiator, in the preparation process, the acrylic acid (ester) monomer raw material is heated to a specified temperature, then the thermal initiator is added for multiple times, the quantity of the thermal initiator added for the first time is larger than that of the thermal initiator added for each subsequent time, the viscosity of a reaction system gradually rises along with the increase of the adding times of the initiator, the viscosity of the reaction system is detected after the thermal initiator is added for each time, the viscosity reaches 2000-10000cps until the temperature reaches 25 ℃, and the thermal initiator is stopped being added, so that the high-purity acrylate adhesive is obtained; the specified temperature is the temperature at which the half-life of the added thermal initiator is 0.5-10 min; the amount of the thermal initiator added for the first time is 10-20ppm, and the amount of the thermal initiator added for each subsequent time is 0.5-3ppm; the total amount of the thermal initiator added into the reaction system is 20-32.5ppm; the interval time of adding the thermal initiator each time is 1.5-5 times of the half-life period of the thermal initiator, and in each interval time, the change state of the corresponding temperature rise of the reaction system is that the temperature rises to the maximum value naturally after the thermal initiator is added last time, and then falls back to the specified temperature.

2. The method of claim 1, wherein the thermal initiator is an azo initiator or a peroxide initiator.