A cop multilayer composite film and a preparation method thereof

Abstract

The application provides a COP multilayer composite film and a preparation method thereof. The COP multilayer composite film comprises, from top to bottom, a diffusion coating layer, a core layer, a first adhesive layer, a first PET substrate layer, a second adhesive layer, a prism structure, a second PET substrate layer and a back coating layer. The first adhesive layer is composed of two components of UV adhesives, namely, A adhesive and B adhesive. The A adhesive is composed of the following components: acrylic resin, methyl methacrylate, tripropylene glycol diacrylate, alpha-hydroxy ketone and triethyl phosphonoacetate. The B adhesive is composed of the following components: acrylic resin, diethylene glycol divinyl ether, phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide, dimethyl sulfoxide and resorcinol monobenzoate. The first adhesive layer of the COP multilayer composite film can match the core layer and the first PET substrate layer, and can avoid the occurrence of warping after bonding in the case of surface bonding.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical film for liquid crystal television, in particular to a COP multi-layer composite film and a preparation method thereof. BACKGROUND

[0002] The backlight module of a general liquid crystal television usually comprises a diffuser sheet, a prism sheet, a reflective polarizing film, etc. Among them, the reflective polarizing film passes the light that can be used by the liquid crystal panel in the backlight source, and reflects the other half of the light that cannot be used back to the backlight source for repeated use, thereby greatly improving the overall brightness of the liquid crystal television, so the reflective polarizing film is also commonly called a reflective polarizing brightening film, a double brightening film, or a core layer, etc. The composite film with the prism sheet bonded with the diffuser sheet is commonly referred to as a DOP composite film (Diffuser on Prism), and the composite film with the prism sheet bonded with the reflective polarizing film is commonly referred to as a COP composite film (Core on Prism).

[0003] For example, CN 112946794 A discloses a high-brightness DOP (Diffuser on Prism) composite film, which comprises a diffuser film, a prism film, and an adhesive layer bonding the two into a whole, the prism film is formed with a plurality of parallel prism structures, and the top of at least part of the prism structures is integrally formed with a vertically upward extending long strip-shaped flange. The prior art sets a vertically upward extending flange on the top of the prism structure of the prism film, which can penetrate into the adhesive layer through the flange, avoiding the top of the prism structure entering the adhesive layer, so that the width of the top of the prism structure being damaged can be controlled by the thickness of the flange, thus the DOP composite film of the prior art can obtain a larger central brightness value, and has higher brightness compared with the prior art. In addition, by setting the flange, the bonding area is increased, and a greater bonding strength can be obtained. The composite film of the prior art increases the thickness by adding the adhesive layer compared with the optical film with independent structure. At the same time, due to the difference in surface tension between the adhesive layer and the two side films, a large size shrinkage will occur when curing in a large size bonding range, and warping deformation is easy to occur after bonding.

[0004] To solve the above technical problems, the applicant discloses a DOP composite film with improved structure for a backlight module in its patent application CN 115826111 A, which includes a diffusion film and a prism film. The prism film faces the light source or light guide plate of the backlight module, and the diffusion film faces the liquid crystal display layer. A plurality of parallel prism structures are formed on the prism film. The top of at least part of the prism structures is integrally formed with a vertically upward extending long strip-shaped flange. The flange and the prism structure are integrally formed by photocuring resin. The bottom of the first base material layer of the diffusion film is formed with a corresponding number of grooves for inserting the flanges of the prism film. The diffusion film and the prism film are integrally bonded by the adhesive filled in the grooves and the inserted flanges. This prior art removes the large-area adhesive layer in the prior art, and the inserted flanges are locally bonded by the adhesive, which can avoid warping and deformation, reduce material requirements and save a large amount of material cost, greatly increase the structural strength and the firmness of bonding. The above prior art improves the surface bonding to local line contact, reduces the thickness of the adhesive layer, reduces the amount of local adhesive under the condition of ensuring the firmness of bonding, thereby reducing the stretching amount of the adhesive and avoiding the probability of warping due to bonding.

[0005] However, with the popularization of the light and thin trend of liquid crystal televisions, new films become thinner and thinner. For example, the thickness of the core layer in the COP composite film is usually only about 30 µm, which cannot provide a flange and a groove with sufficient height, and can only be surface-bonded. In order to avoid warping during large-area bonding, it is necessary to use film materials and adhesives with similar expansion rates as much as possible. However, materials with similar expansion rates may not necessarily meet the needs of the corresponding film in terms of optical performance, and it is difficult to find an adhesive with similar expansion rates to the two materials when bonding films with different expansion rates. Therefore, new technologies need to be developed to overcome the above-mentioned defects of the prior art. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a COP multi-layer composite film and a preparation method thereof to reduce or avoid the above-mentioned problems.

[0007] To solve the above technical problems, the application provides a COP multilayer composite film, which comprises, from top to bottom, a diffusion coating layer, a core layer, a first adhesive layer, a first PET substrate layer, a second adhesive layer, a prism structure, a second PET substrate layer and a back coating layer, wherein the first adhesive layer is composed of two components of UV adhesive, namely A adhesive and B adhesive; the A adhesive is composed of 30-40 wt% of acrylic resin, 15-30 wt% of methyl methacrylate, 10-20 wt% of tripropylene glycol diacrylate, 1-3 wt% of α-hydroxy ketone and 5-10 wt% of triethyl phosphonoacetate, and the sum of the above components is 100 wt%; the B adhesive is composed of 35-45 wt% of acrylic resin, 20-40 wt% of diethylene glycol divinyl ether, 2-4 wt% of phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide, 5-10 wt% of dimethyl sulfoxide and 3-8 wt% of resorcinol monobenzoate, and the sum of the above components is 100 wt%.

[0008] Preferably, the A adhesive is coated on the lower surface of the core layer, and the B adhesive is sprayed on the upper surface of the first PET substrate layer.

[0009] Preferably, the weight ratio of the A adhesive to the B adhesive is 10:1.

[0010] Preferably, the total thickness of the adhesive layer obtained after curing of the first adhesive layer is 12-18 µm.

[0011] Preferably, the core layer is a multilayer reflective polarizing film, wherein the side of the core layer facing the first PET substrate layer is a PEN substrate.

[0012] Preferably, the thickness of the core layer is 25-35 µm.

[0013] The application further provides a preparation method of the COP multilayer composite film, which comprises the following steps: firstly, uniformly coating a mixed solution of acrylic resin and PMMA microbeads on the upper surface of the core layer by using micro-embossing roll coating technology to form a core layer with a diffusion coating layer on the upper surface; then, uniformly coating a mixed solution of acrylic resin and PMMA microbeads on the lower surface of the second PET substrate layer by using micro-embossing roll coating technology to form a back coating layer, and simultaneously, forming a prism structure on the upper surface of the second PET substrate layer by using micro-molding technology; thereafter, bonding the first PET substrate layer and the prism structure together by using micro-embossing roll coating and UV curing technology; finally, coating A adhesive on the lower surface of the core layer and spraying B adhesive on the upper surface of the first PET substrate layer by using micro-embossing roll coating technology, and then pressing the adhesive-coated surfaces of the core layer and the first PET substrate layer together and irradiating with ultraviolet light, so that the core layer and the first PET substrate layer are bonded together.

[0014] Preferably, the preparation step of the A adhesive is: adding acrylic resin and methyl methacrylate in a container, stirring for 15 minutes, then adding tripropylene glycol diacrylate and stirring for 15 minutes, finally adding triethyl phosphonoacetate and α-hydroxy ketone and stirring for 15 minutes, standing for 1 hour, dropping the prepared solution onto the glass sheet, observing no flocculation and bubbles, and sealing for storage.

[0015] Preferably, the preparation step of the B adhesive is: adding acrylic resin in a container, stirring for 15 minutes, then adding resorcinol monobenzoate, stirring for 15 minutes, then adding dimethyl sulfoxide and stirring for 15 minutes, finally adding diethylene glycol divinyl ether and phenyl bis (2, 4, 6-trimethylbenzoyl) phosphine oxide and stirring for 15 minutes, standing for 1 hour, dropping the prepared solution onto the glass sheet, observing no flocculation and bubbles, and sealing for storage.

[0016] Preferably, the ultraviolet light irradiation time is 30-60 seconds.

[0017] The first adhesive layer of the COP multilayer composite film of the present application can match the core layer and the first PET substrate layer, and can avoid the occurrence of warping after bonding in the case of face bonding. BRIEF DESCRIPTION OF DRAWINGS

[0018] The following drawings are merely intended to schematically illustrate and explain the present application, and do not limit the scope of the present application.

[0019] Figure 1 A structure diagram of a COP multilayer composite film according to one embodiment of the present application is shown. DETAILED DESCRIPTION

[0020] In order to have a clearer understanding of the technical features, objects and effects of the present application, the specific embodiments of the present application will be described with reference to the drawings. Identical components are denoted by identical reference numerals.

[0021] As shown in Figure 1 The present application proposes a COP multilayer composite film, the lower side of which faces the light source and the upper side of which faces the liquid crystal panel. The COP multilayer composite film of the present application comprises, from top to bottom, a diffusion coating layer 10, a core layer 20, a first adhesive layer 30, a first PET substrate layer 40, a second adhesive layer 50, a prism structure 60, a second PET substrate layer 70, and a back coating layer 80.

[0022] The uppermost diffusion coating layer 10 contains PMMA particles, which are coated on the core layer 20 and have the effect of increasing the haze shielding. The PMMA particles in the diffusion coating layer 10 can disperse light and improve the viewing angle width.

[0023] The core layer 20 can be any kind of reflective polarized film available on the market to increase the overall brightness of the composite film. In a specific embodiment, the core layer 20 of the present application can employ a multi-layer reflective polarized film, wherein the side of the core layer 20 facing the first PET substrate layer 40 is a PEN substrate, the thickness of the core layer 20 is 25-35 pm, preferably a commercially available 33 pm multi-layer optical film (MOF) or diffuse reflective polarized film (DRPF) is employed.

[0024] The first adhesive layer 30 is used to bond the core layer 20 and the underlying first PET substrate layer 40 together.

[0025] The other side of the first PET substrate layer 40 is bonded to the underlying prism structure 60 through the second adhesive layer 50. The prism structure 60 serves to increase brightness.

[0026] The prism structure 60 can be integrally formed on the upper surface of the underlying second PET substrate layer 70 by conventional UV curing.

[0027] The back coating layer 80 located at the lowermost layer contains PMMA microspheres, and the back coating layer 80 is coated on the lower side surface of the second PET substrate layer 70 to improve the anti-scratch and anti-blocking ability of the lower surface through the PMMA microspheres.

[0028] Compared with the conventional DOP composite film, such as the DOP composite film disclosed in CN 115826111 A, the COP multi-layer composite film of the present application has a core layer 20 inserted therein. The prism structure 60 and the first PET substrate layer 40 can be combined by the existing technology of line bonding to reduce the amount and thickness of the second adhesive layer 50, thereby reducing the probability of warping.

[0029] However, as mentioned earlier, due to the thickness constraint of the inserted core layer 20 for optical properties, the thickness cannot be too large (the thickness of the core layer available on the market is generally 25-35 pm), so the core layer 20 can only be face-bonded to the first PET substrate layer 40 through the first adhesive layer 30. Due to the large difference in the expansion rate of the core layer 20 and the first PET substrate layer 40, the composition of the first adhesive layer 30 needs to be selected to balance the difference in the expansion rate of the core layer 20 and the first PET substrate layer 40.

[0030] Based on the above analysis, the present application proposes a first adhesive layer 30 suitable for face bonding, which can match the core layer 20 and the first PET substrate layer 40 to avoid warping after bonding.

[0031] Specifically, the first adhesive layer 30 of the present application is composed of two components of UV adhesives, namely A adhesive and B adhesive, wherein the A adhesive is composed of the following components: acrylic resin 30-40 wt%, methyl methacrylate 15-30 wt%, tripropylene glycol diacrylate 10-20 wt%, alpha-hydroxy ketone 1-3 wt%, triethyl phosphonoacetate 5-10 wt%, the sum of the above components being 100 wt%; the B adhesive is composed of the following components: acrylic resin 35-45 wt%, diethylene glycol divinyl ether 20-40 wt%, phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide 2-4 wt%, dimethyl sulfoxide 5-10 wt%, resorcinol monobenzoate 3-8 wt%, the sum of the above components being 100 wt%. The A adhesive is coated on the lower surface of the core layer 20, and the B adhesive is sprayed on the upper surface of the first PET substrate layer 40, the weight ratio of the A adhesive and the B adhesive being 10:1, and the total thickness of the adhesive layer obtained after curing of the first adhesive layer 30 being 12-18 µm.

[0032] Examples 1-3

[0033] The following table shows the preparation of A adhesive by mass parts: acrylic resin and methyl methacrylate were added to a container, stirred for 15 minutes, then tripropylene glycol diacrylate was added and stirred for 15 minutes, and finally triethyl phosphonoacetate and alpha-hydroxy ketone were added and stirred for 15 minutes, and left to stand for 1 hour. The prepared solution was added dropwise to a glass sheet, and no flocculation and air bubbles were observed. The solution was sealed and stored for later use.

[0034]

[0035] Comparative Examples 1-3

[0036] The following table shows the preparation of A adhesive by mass parts as a comparison.

[0037]

[0038] Examples 4-6

[0039] The following table shows the preparation of B adhesive by mass parts: acrylic resin was added to a container, stirred for 15 minutes, then resorcinol monobenzoate was added and stirred for 15 minutes, then dimethyl sulfoxide was added and stirred for 15 minutes, and finally diethylene glycol divinyl ether and phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide were added and stirred for 15 minutes, and left to stand for 1 hour. The prepared solution was added dropwise to a glass sheet, and no flocculation and air bubbles were observed. The solution was sealed and stored for later use.

[0040]

[0041] Comparative Examples 4-6

[0042] The following table shows the preparation of B adhesive in parts by mass as a comparison.

[0043]

[0044] Comparative Examples 7-9

[0045] The B adhesive was prepared in the same parts by mass as in Examples 4-6, but the order of the preparation steps was different.

[0046] The preparation method of Comparative Example 7 was as follows: the acrylic resin and diethylene glycol divinyl ether were added to a container, stirred for 15 minutes, then the phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide was added and stirred for 15 minutes, after which the dimethyl sulfoxide was added and stirred for 15 minutes, and finally the resorcinol monobenzoate was added, stirred for 15 minutes, and left to stand for 1 hour.

[0047] The preparation method of Comparative Example 8 was as follows: the acrylic resin and diethylene glycol divinyl ether were added to a container, stirred for 15 minutes, then the dimethyl sulfoxide was added and stirred for 15 minutes, after which the phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide was added and stirred for 15 minutes, and finally the resorcinol monobenzoate was added, stirred for 15 minutes, and left to stand for 1 hour.

[0048] The preparation method of Comparative Example 9 was as follows: the acrylic resin and diethylene glycol divinyl ether were added to a container, stirred for 15 minutes, then the dimethyl sulfoxide was added and stirred for 15 minutes, after which the resorcinol monobenzoate was added and stirred for 15 minutes, and finally the phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide was added, stirred for 15 minutes, and left to stand for 1 hour.

[0049] The prepared adhesive solution of Comparative Examples 7-9 was dropped onto a glass sheet, and flocculation was observed, so it could not be used.

[0050] Examples 7-9

[0051] The A adhesive prepared in Examples 1-3 was coated on one side of a 30 µm PEN film (10 cm x 10 cm) by micro-concave roll coating technology, and the B adhesive prepared in Examples 4-6 was sprayed on one side of a 100 µm PET film (10 cm x 10 cm). The PEN film and the PET film were pressed together with the adhesive-coated surfaces opposite each other and irradiated with ultraviolet light for 30-60 seconds, thereby bonding the PEN film and the PET film together. In Example 7, the A adhesive of Example 1 was combined with the B adhesive of Example 4; in Example 8, the A adhesive of Example 2 was combined with the B adhesive of Example 5; and in Example 9, the A adhesive of Example 3 was combined with the B adhesive of Example 6.

[0052] The film layers of Examples 7-9 were observed and measured for the degree of bending after 1 hour, 24 hours, 1 week, 1 month, and 3 months after bonding, respectively. The film layers were placed on a glass flat plate, and the maximum height (mm) of the highest point of the film layer and the surface of the glass flat plate was measured. The maximum height of the film layer of each of Examples 7-9 was less than 0.1 mm, and no obvious warping was observed.

[0053] Comparative Examples 10-12

[0054] The film layers of Comparative Examples 10-12 were obtained using the same method as Examples 7-9. In Example 10, the A adhesive of Comparative Example 1 was combined with the B adhesive of Comparative Example 4. In Example 11, the A adhesive of Comparative Example 2 was combined with the B adhesive of Comparative Example 5. In Example 12, the A adhesive of Comparative Example 3 was combined with the B adhesive of Comparative Example 6.

[0055] The film layers of Comparative Examples 10-12 were observed and measured for the degree of bending after 1 hour, 24 hours, 1 week, 1 month, and 3 months after bonding, respectively. The film layers were placed on a glass flat plate, and the maximum height (mm) of the highest point of the film layer and the surface of the glass flat plate was measured. The maximum height of the film layer of each of Comparative Examples 10-12 is shown in the following table.

[0056]

[0057] The film layers of Comparative Examples 10-12 had obvious warping.

[0058] Comparative Examples 13-15

[0059] The film layers of Comparative Examples 13-15 were obtained using a different method than Examples 7-9. In Comparative Example 13, the A adhesive of Example 1 was combined with the B adhesive of Example 4. In Comparative Example 14, the A adhesive of Example 2 was combined with the B adhesive of Example 5. In Comparative Example 15, the A adhesive of Example 3 was combined with the B adhesive of Example 6. In each of Comparative Examples 13-15, the A adhesive and the B adhesive were each formed on the surface of a PEN film and a PET film by coating.

[0060] The film layers of Comparative Examples 13-15 were observed and measured for the degree of bending after 1 hour, 24 hours, 1 week, 1 month, and 3 months after bonding, respectively. The film layers were placed on a glass flat plate, and the maximum height (mm) of the highest point of the film layer and the surface of the glass flat plate was measured. The maximum height of the film layer of each of Comparative Examples 13-15 is shown in the following table.

[0061]

[0062] The film layers of Comparative Examples 13-15 were initially acceptable, but the warping increased over time.

[0063] The basic parameters of the COP composite film of the present application are shown in the following table.

[0064]

[0065] The preparation method of the COP multilayer composite film of the present application is further described below with reference to the accompanying drawings. As shown in the drawings, the preparation method of the COP multilayer composite film of the present application comprises the following steps:

[0066] First, the mixture of acrylic resin and PMMA microbeads is uniformly coated on the upper surface of the core layer 20 by using the micro-concave roller coating technology to form the core layer 20 with the diffusion coating layer 10 on the upper surface.

[0067] Then, the mixture of acrylic resin and PMMA microbeads is uniformly coated on the lower surface of the 100µm-thick second PET substrate layer 70 by using the micro-concave roller coating technology to form the back coating layer 80 with the functions of scratch resistance, anti-static, and anti-adhesion, and at the same time, the prism structure 60 with a 70µm ridge height is made on the upper surface of the second PET substrate layer 70 by using the micro-molding technology.

[0068] After that, the 100µm-thick first PET substrate layer 40 is bonded with the prism structure 60 by using the micro-concave roller coating and UV curing technology, and the thickness of the second adhesive layer 50 between them is about 5µm.

[0069] Finally, the A adhesive is coated on the lower surface of the core layer 20 and the B adhesive is sprayed on the upper surface of the first PET substrate layer 40 by using the micro-concave roller coating technology, and then the surfaces of the core layer 20 and the first PET substrate layer 40 with the adhesives are pressed together and irradiated with ultraviolet light for 30-60 seconds, so as to bond the core layer 20 and the first PET substrate layer 40 together.

[0070] Those skilled in the art should understand that although the present application is described in the manner of multiple embodiments, not every embodiment contains only one independent technical solution. The description in the specification is only for the sake of clarity, those skilled in the art should understand the specification as a whole and understand the technical solutions involved in each embodiment as a way of combining different embodiments to understand the protection scope of the present application.

[0071] The above is only a specific embodiment of the present application, and is not intended to limit the scope of the present application. Any equivalent changes, modifications and combinations made by those skilled in the art without departing from the concept and principles of the present application shall fall within the scope of protection of the present application.

Claims

1. A COP multilayer composite film, which is sequentially provided from top to bottom with a diffusion coating layer, a core layer, a first adhesive layer, a first PET substrate layer, a second adhesive layer, a prism structure, a second PET substrate layer, and a back coating layer, characterized in that, The first adhesive layer is composed of two components of UV adhesive, A adhesive and B adhesive, wherein the A adhesive is composed of the following components: acrylic resin 30-40 parts by mass, methyl methacrylate 15-30 parts by mass, tripropylene glycol diacrylate 10-20 parts by mass, α-hydroxy ketone 1-3 parts by mass, triethyl phosphonoacetate 5-10 parts by mass; the B adhesive is composed of the following components: acrylic resin 35-45 parts by mass, diethylene glycol divinyl ether 20-40 parts by mass, phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide 2-4 parts by mass, dimethyl sulfoxide 5-10 parts by mass, resorcinol monobenzoate 3-8 parts by mass; the A adhesive is coated on the lower surface of the core layer, and the B adhesive is sprayed on the upper surface of the first PET substrate layer; the core layer is a multilayer reflective polarizing film, wherein the side of the core layer facing the first PET substrate layer is a PEN substrate.

2. The COP multilayer composite film of claim 1, wherein, The weight ratio of the A adhesive and the B adhesive is 10:

1.

3. The COP multilayer composite film of claim 1, wherein, The total thickness of the adhesive layer obtained after curing of the first adhesive layer is 12-18 µm.

4. The COP multilayer composite film of claim 1, wherein, The thickness of the core layer is 25-35 µm.

5. A method of producing a COP multilayer composite film as claimed in any one of claims 1 to 4, characterized by, The method comprises the following steps: first, using micro-concave roller coating technology, the mixed solution of acrylic resin and PMMA microbeads is uniformly coated on the upper surface of the core layer to form a core layer with a diffusion coating on the upper surface for standby; then, using micro-concave roller coating technology, the mixed solution of acrylic resin and PMMA microbeads is uniformly coated on the lower surface of the second PET substrate layer to form a back coating, at the same time, using micro-molding technology, a prism structure is made on the upper surface of the second PET substrate layer; then, through micro-concave roller coating and UV curing technology, the first PET substrate layer and the prism structure are bonded together; finally, through micro-concave roller coating technology, A adhesive is coated on the lower surface of the core layer, and B adhesive is sprayed on the upper surface of the first PET substrate layer, the surfaces of the core layer and the first PET substrate layer coated with adhesive are pressed together and irradiated with ultraviolet light, so that the core layer and the first PET substrate layer are bonded together.

6. The method for preparing the COP multilayer composite film as described in claim 5, characterized in that, The preparation steps of the A adhesive are as follows: acrylic resin and methyl methacrylate are added to a container, stirred for 15 minutes, then tripropylene glycol diacrylate is added and stirred for 15 minutes, finally triethyl phosphonoacetate and α-hydroxy ketone are added and stirred for 15 minutes, and then left for 1 hour, the prepared solution is added dropwise to a glass sheet, no flocculation and bubbles are observed, and the prepared solution is sealed and stored for standby.

7. The method for preparing the COP multilayer composite film as described in claim 5, characterized in that, The preparation steps of the B adhesive are as follows: acrylic resin is added to a container, stirred for 15 minutes, then resorcinol monobenzoate is added and stirred for 15 minutes, then dimethyl sulfoxide is added and stirred for 15 minutes, finally diethylene glycol divinyl ether and phenyl bis(2,4,6-trimethylbenzoyl) phosphine oxide are added and stirred for 15 minutes, and then left for 1 hour, the prepared solution is added dropwise to a glass sheet, no flocculation and bubbles are observed, and the prepared solution is sealed and stored for standby.

8. The method for preparing the COP multilayer composite film as described in claim 5, characterized in that, The ultraviolet light irradiation time is 30-60 seconds.

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