UV structural glue, preparation method thereof and optical film

Abstract

The invention discloses UV structural glue, a preparation method thereof and an optical film, and the UV structural glue comprises the following components in parts by weight: 20-60 parts of an oligomer, 40-80 parts of a monomer, 3-8 parts of a photoinitiator and 3-8 parts of a demolding aid, the monomers comprise a first monomer and a second monomer, the first monomer is tetrahydrofuran methyl ester, the second monomer comprises at least one of 1, 6-hexanediol diacrylate and trimethylolpropane triacrylate, and the shore hardness of the UV structural glue is 30-60D; the oligomer is aliphatic polyurethane acrylate with the functionality of 2 to 3. The UV structural glue provided by the invention is used for being coated on an optical film base material and forming an optical structure through imprinting, and the UV structural glue can ensure enough adhesive force on the premise of ensuring easy demolding, also has excellent low shrinkage, toughness and weather resistance, and needs low curing energy.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical film materials, and in particular relates to a UV structural glue formula suitable for forming a deep structure on a substrate surface, a preparation method thereof, and an optical film. Background Art

[0002] In some optical film products, it is usually necessary to emboss UV optical structures on the substrate surface. However, when forming UV deep structures on the substrate surface through the embossing process, existing UV adhesives have the following problems:

[0003] 1. Insufficient adhesion: When UV deep structure is embossed on the substrate, demoulding is often difficult due to the deep structure and certain specific textures. Therefore, a higher proportion of release agent is added. However, the use of release agent will affect the adhesion of UV glue on the substrate.

[0004] 2. High curing energy: The energy of UV light will be attenuated when it penetrates the substrate, so the curing energy usually needs 500-2000mJ / cm 2 , which affects the improvement of machine speed and thus affects the improvement of production efficiency.

[0005] 3. Large shrinkage: Glue shrinkage will directly affect the adhesion of the glue to the substrate and affect the stability of the structure.

[0006] 4. Poor toughness: Poor toughness can lead to structural breakage or deformation during the winding process.

[0007] 5. Poor weather resistance: If the product is used in car interiors, the temperature inside the car can reach 80°C or above in summer, and existing products cannot meet the needs of high temperature environments.

[0008] Existing patents (such as CN201410763150.8 and CN202010620542.4) improve adhesion by adjusting UV formulations, but fail to address issues such as mold release, poor toughness, low curing energy, and weather resistance during deep structure imprinting. Therefore, there is an urgent need to develop a UV adhesive suitable for deep structure applications that combines high adhesion, low shrinkage, good toughness, low curing energy, excellent weather resistance, and easy demolding. Summary of the Invention

[0009] In order to address the deficiencies of the prior art, the present invention provides a UV structural glue, a preparation method thereof, and an optical film. The UV structural glue provided by the present invention is applied to an optical film substrate layer to form an optical structure. While ensuring easy demolding, it can ensure sufficient adhesion, and also has excellent low shrinkage, toughness, and weather resistance, and requires low curing energy.

[0010] In order to achieve the above-mentioned purpose of the invention, the present invention provides a UV structural glue for coating on an optical film substrate layer to form an optical structure by embossing, which comprises, by weight: 20-60 parts of oligomers, 40-80 parts of monomers, 3-8 parts of photoinitiators, and 3-8 parts of demolding aids.

[0011] The oligomer is a 2-3 functional aliphatic polyurethane acrylate.

[0012] The monomers include a first monomer and a second monomer, wherein the first monomer is tetrahydrofuran methyl ester; the second monomer includes at least one of 1,6-hexanediol diacrylate and trimethylolpropane triacrylate;

[0013] The Shore hardness of the UV structural adhesive is 30-60D.

[0014] Furthermore, the monomer further includes a third monomer, and the third monomer is alkoxylated bisphenol A diacrylate.

[0015] Furthermore, the monomers further include a fourth monomer, and the fourth monomer is isobornyl methacrylate.

[0016] Furthermore, the demoulding aid is polyether-modified silicone.

[0017] Furthermore, the photoinitiator is an α-hydroxyalkanone photoinitiator, an acylphosphine oxide photoinitiator, and a hydrogen abstraction free radical photoinitiator ITX.

[0018] Furthermore, the addition amount of the acylphosphine oxide photoinitiator is 1.5-2%.

[0019] The present invention also provides a method for preparing the above-mentioned UV structural adhesive, comprising:

[0020] According to parts by weight, 20-60 parts of oligomer, 40-80 parts of monomer, 3-8 parts of photoinitiator, and 3-8 parts of auxiliary agent are added to a light-proof reactor and stirred and mixed at a stirring temperature of 40-45° C., a rotation speed of 110-120 r / min, and a stirring time of 90-120 min. The mixture is then allowed to stand and defoam for 0.5-1.5 h to obtain a UV structural adhesive.

[0021] The present invention also provides an optical film, comprising a substrate layer and an optical structure arranged on at least one surface of the substrate layer, wherein the optical structure is made of the above-mentioned UV structural glue.

[0022] The UV structural adhesive provided by this invention utilizes a combination of tetrahydrofuran methyl ester as a first monomer and 1,6-hexanediol diacrylate or trimethylolpropane triacrylate as a second monomer to enhance the curing rate. The addition of a release agent also ensures sufficient adhesion between the UV structural adhesive and the substrate. Furthermore, the UV structural adhesive meets the required toughness, with a hardness range of 30-60D, preventing the structure from breaking or deforming during the winding of optical film products. The addition of a third monomer further adjusts the hardness of the UV structural adhesive to meet the requirements of structural winding. The addition of a fourth monomer and the use of a di- or tri-functional aliphatic polyurethane acrylate as an oligomer enhance the product's weather resistance and low shrinkage. The combination of an α-hydroxyalkanone photoinitiator, an acylphosphine oxide photoinitiator, and a hydrogen-abstraction free radical photoinitiator (ITX) increases the UV structural adhesive's absorptivity to light sources of all wavelengths, enabling the adhesive to cure even at lower energy levels. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments.

[0024] Figure 1 This is a schematic diagram of a common embossing structure by UV structural glue embossing in the present invention;

[0025] Figure 2 This is another common embossing structure schematic diagram of the present invention by UV structural glue embossing;

[0026] Figure 3 This is a schematic diagram of the process of stamping the UV structural adhesive of the present invention onto a substrate through a metal mold;

[0027] Reference numerals:

[0028] 1. Base material; 2. Prism structure; 3. Anti-peeping structure; 4. Metal mold; 5. UV structural glue; 6. Rubber pressure wheel; 7. UV lamp. DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and examples. It will be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention. It should also be noted that, for ease of description, the accompanying drawings only illustrate portions relevant to the present invention, not all structures.

[0030] like Figure 1-Figure 3Shown are two common embossed optical structures in optical films - a prism structure 2 and an anti-peep structure 3. The optical structure is achieved by coating UV structural glue on a substrate 1 and then embossing the desired structure with a metal mold 4. The depth of the embossed optical structure is usually 50-120 μm. Due to the particularity of the structure and the large depth of the structure, it is difficult to demold the UV structural glue from the mold. In order to reduce the difficulty of demolding, a demolding aid needs to be added to the UV structural glue formula, and the proportion of the demolding aid is higher than that in common UV glues. However, the addition of the demolding aid will affect the adhesion between the adhesive layer and the substrate. Moreover, the optical film product with an optical structure embossed on the substrate is prone to breakage or deformation when it is rolled up during the production process.

[0031] The substrate is PET or PC, preferably a PC substrate.

[0032] Therefore, the present invention provides a UV structural adhesive that can improve demolding difficulty, enhance adhesion between the substrate and the UV structural adhesive, and reduce breakage and deformation during product winding. The UV structural adhesive comprises: 20-60 parts oligomer, 40-80 parts monomer, 3-8 parts photoinitiator, and 3-8 parts demolding aid.

[0033] The monomers include a first monomer and a second monomer, wherein the first monomer is tetrahydrofuran methyl ester; and the second monomer is at least one of 1,6-hexanediol diacrylate and trimethylolpropane triacrylate.

[0034] The first monomer has a polar tetrahydrofuran ring, which can significantly improve the adhesion of UV structural adhesive to the substrate. The addition amount of tetrahydrofuran should not be less than 15%, and the addition amount is: 15%-40%. If the tetrahydrofuran addition amount is less than 15%, the UV adhesive will not adhere to the substrate or will fall off after the ring test.

[0035] The second monomer is at least one of 1,6-hexanediol diacrylate and trimethylolpropane triacrylate, wherein 1,6-hexanediol diacrylate is a bifunctional monomer, which can increase the single curing speed of the glue at low cross-linking density, and has strong dilution ability, can significantly reduce the viscosity of the system, has good flexibility, and is also helpful for substrate adhesion. The addition amount should be: 10%-30%.

[0036] Trimethylolpropane triacrylate is a trifunctional monomer that can significantly increase the curing rate of the system, but the film tends to become brittle after curing. Therefore, the addition amount should not exceed 5%, and the addition amount should be: 2%-5%.

[0037] Optical film products need to be rolled up during the production process. At the same time, the structure on the optical film products does not want to be deformed during the rolling process. Therefore, the hardness of the UV structural glue needs to be controlled. If the UV structural glue is too hard, the structure will break during the rolling process. If it is too soft, the structure will deform, affecting the performance of the final product.

[0038] The combined use of the first and second monomers in the UV structural adhesive formula of the present invention can adjust the hardness of the UV structural adhesive so that the final product meets performance requirements. Since the first monomer, tetrahydrofuran methyl ester, is a monofunctional monomer, and the second monomer is a difunctional or trifunctional multifunctional monomer, the addition of the multifunctional second monomer increases the hardness of the adhesive. By mixing the monofunctional and multifunctional monomers, the hardness of the UV structural adhesive can be adjusted. The Shore hardness of the UV structural adhesive is 30 to 60D. A UV structural adhesive with a Shore hardness of 30 to 60D can ensure that the structure of the optical film product will not break during winding and the optical film product will not deform.

[0039] To ensure the Shore hardness of the UV structural adhesive is within the desired range of 30-60D, a third monomer, alkoxylated bisphenol A diacrylate, can be added. Alkoxylated bisphenol A diacrylate contains ethoxy groups, which can lower the Tg value of the UV structural adhesive coating and increase its flexibility, further adjusting the Shore hardness of the cured system. Alkoxylated bisphenol A diacrylate is also low-cost, which helps optimize formulation costs.

[0040] The addition amount of the third monomer is: 0-40%.

[0041] In order to improve the weather resistance of UV structural adhesive, a fourth monomer, isobornyl methacrylate, can be further added. Isobornyl methacrylate has low shrinkage, good water and heat resistance, and also helps to improve adhesion.

[0042] The added amount of the fourth monomer is 0-20%.

[0043] The oligomer is a 2-3 functional aliphatic polyurethane acrylate, and the formed UV structural adhesive has good flexibility and excellent weather resistance.

[0044] Aromatic polyurethane acrylate should be avoided as the oligomer because it contains benzene rings, its chain is rigid and has poor flexibility, and it is easy to break when the structure of UV structural glue is deep.

[0045] The aliphatic polyurethane acrylates include but are not limited to CN965, CN968, CN929, and CN981 from Sartomer; EB264 from Cytec; and 611B-85, 613B-80, and 615-100 from Changxing Chemical.

[0046] The photoinitiator is an α-hydroxyalkanone photoinitiator, an acylphosphine oxide photoinitiator, and a hydrogen abstraction free radical photoinitiator ITX. The α-hydroxyalkanone photoinitiator includes but is not limited to at least one of 184 and 1173; the acylphosphine oxide photoinitiator includes but is not limited to at least one of TPO and 819.

[0047] The added amount of the α-hydroxyalkanone photoinitiator is 3%-4%; the added amount of the acylphosphine oxide photoinitiator is 0.5%-2%. Due to the large depth of the imprinted structure, in order to improve the curing effect of the contact part between the bottom of the imprinted structure and the mold, thereby improving the demolding performance, the content of the long-wavelength acylphosphine oxide photoinitiator can be increased. Therefore, the added amount of the acylphosphine oxide photoinitiator is preferably 1.5-2%.

[0048] The weight ratio of the α-hydroxyalkanone photoinitiator to the acylphosphine oxide photoinitiator is (3-4): (0.5-2).

[0049] like Figure 3 As shown, UV structural glue is transferred to the surface of the substrate 1 by means of embossing with a metal mold 4. Due to the energy attenuation of the UV lamp 7 penetrating the substrate and the need to increase the machine speed in the actual production process to improve production efficiency, the energy required for UV glue curing should be as low as possible.

[0050] Therefore, it is necessary to introduce hydrogen abstraction free radical photoinitiator ITX into the photoinitiator. The absorption wavelength of ITX can reach 430nm, which has entered the visible light absorption region. When combined with α-hydroxyalkane ketone photoinitiator and acylphosphine oxide photoinitiator, the glue system can have a higher absorption rate for light sources of various wavelengths, so that UV structural glue can be cured at lower energy. The required curing energy range is 150-200mj / cm 2 .

[0051] The added amount of the hydrogen abstraction free radical photoinitiator ITX is 0.3%-1%.

[0052] The demoulding aid is a polyether-modified silicone, including but not limited to at least one of BYK-333, BYK-UV3500, BYK-UV3505, TEGO-ZG-400, and TEGO-RAD2200.

[0053] The viscosity of the UV structural glue formed by the above formula is in the range of 200-1500 cps. The UV structural glue meets the requirements of UV structural process molding within this range. UV structural glue with too low or too high viscosity will affect the molding of the UV structure.

[0054] The present invention also provides a method for preparing the above-mentioned UV structural adhesive, comprising:

[0055] According to parts by weight, 20-60 parts of oligomer, 40-80 parts of monomer, 3-8 parts of photoinitiator, and 3-8 parts of auxiliary agent are added to a light-proof reactor and stirred and mixed at a stirring temperature of 40-45° C., a rotation speed of 110-120 r / min, and a stirring time of 90-120 min. The mixture is then allowed to stand and defoam for 0.5-1.5 h to obtain a UV structural adhesive.

[0056] The present invention also provides an optical film, comprising a substrate layer and an optical structure arranged on at least one surface of the substrate layer, wherein the optical structure is made of the above-mentioned UV structural glue.

[0057] The following is further described by specific examples:

[0058] Example 1:

[0059] The mass fractions of each component of the glue are:

[0060] 60 parts of oligomer, which is an aliphatic polyurethane acrylate with an average functionality of 2 and a solid content of 100%;

[0061] The monomers are: 35 parts by weight of tetrahydrofuran methyl ester (THFA), 5 parts by weight of trimethylolpropane triacrylate (TMPTA);

[0062] The photoinitiator was selected as 184 4 parts, TPO 2 parts, and ITX 0.7 parts;

[0063] The amount of the release agent is 4 parts, and the release agent is ZG-400 from TEGO.

[0064] Example 2:

[0065] The mass fractions of each component of the glue are:

[0066] 60 parts of oligomer, which is an aliphatic polyurethane acrylate with an average functionality of 3 and a solid content of 100%;

[0067] The monomers are: 30 parts by weight of tetrahydrofuran methyl ester (THFA), 10 parts by weight of 1,6-hexanediol diacrylate (HDDA);

[0068] The photoinitiator was selected as 184 4 parts, TPO 2 parts, and ITX 0.7 parts;

[0069] The amount of the release agent is 4 parts, and the release agent is ZG-400 from TEGO.

[0070] Example 3:

[0071] The mass fractions of each component of the glue are:

[0072] 38 parts of oligomer, which is an aliphatic polyurethane acrylate with an average functionality of 2 and a solid content of 100%;

[0073] The monomers are: 25 parts by weight of tetrahydrofuran methyl ester (THFA), 2 parts by weight of trimethylolpropane triacrylate (TMPTA), 25 parts by weight of 2 (ethoxy) bisphenol A diacrylate BPA (EO) 2DA and 10 parts by weight of 20 (ethoxy) bisphenol A diacrylate BPA (EO) 20 DA.

[0074] The photoinitiator is selected as 184 3 parts, TPO 2 parts, and ITX 0.5 parts.

[0075] The amount of the release agent is 4 parts, and the release agent is ZG-400 from TEGO.

[0076] Example 4:

[0077] The mass fractions of each component of the glue are:

[0078] 40 parts of oligomer, wherein the average functionality of the oligomer is trifunctional aliphatic polyurethane acrylate, and the solid content is 100%;

[0079] The monomers are: 22 parts by weight of tetrahydrofuran methyl ester (THFA), 3 parts by weight of trimethylolpropane triacrylate (TMPTA), 15 parts by weight of 1,6-hexanediol diacrylate (HDDA), 10 parts by weight of 20 (ethoxy) bisphenol A diacrylate BPA (EO) 20DA and 10 parts by weight of isobornyl methacrylate (IBOA).

[0080] The photoinitiator is selected as 184 3 parts, TPO 2 parts, and ITX 0.5 parts.

[0081] The amount of the release agent is 4 parts, and the release agent is ZG-400 from TEGO.

[0082] Comparative Example 1:

[0083] Compared with Example 3, no ITX was used in the photoinitiator.

[0084] Comparative Example 2:

[0085] Compared with Example 3, the mass fraction of the photoinitiator TPO is 1 part.

[0086] Comparative Example 3:

[0087] Compared with Example 3, the amount of tetrahydrofuran methyl ester (THFA) is 10 parts by weight.

[0088] Comparative Example 4:

[0089] Compared with Example 3, the amount of the release agent is 1 part by weight.

[0090] Comparative Example 5:

[0091] Compared with Example 4, the trifunctional monomer trimethylolpropane triacrylate (TMPTA) is 10 parts by weight.

[0092] Comparative Example 6:

[0093] Compared with Example 4, the functionality of the oligomer is 4.

[0094] Comparative Example 7:

[0095] Compared with Example 4, the oligomer is an aromatic polyurethane acrylate with an average functionality of 3.

[0096] The process of UV structural glue is UV molding machine curing, and the base material uses Toray's PC base material with a thickness of 100μm.

[0097] (1) The mold structure is a privacy film structure with a structural depth of 100 μm;

[0098] (2) The glue temperature is controlled at 50-65℃, and the mold temperature is controlled at 50-65℃;

[0099] (3) The UV wavelength is selected between 260-380 nm, and the UV energy is selected between 200 mJ / cm 2 .

[0100] After the UV structural glue is embossed, the tests and performance evaluations include the following aspects.

[0101] (1) Mold release: Observe during the molding process to see if the glue can be released from the mold and listen for any sound of release. If it can be released from the mold with a slight or no sound, it is OK. Otherwise, it is NG.

[0102] (2) Bending resistance: After forming and rolling, place the film for 72 hours and observe whether there are cracks on the film surface.

[0103] (3) Shore hardness: The glue is solidified and made into an ingot. The hardness is measured with a Shore hardness tester (type D) to obtain the value.

[0104] (4) Structural image: Observe the structure under a microscope to see if there are any defects.

[0105] (5) Adhesion: For the adhesion test at room temperature, a 100-grid test was conducted at room temperature of 25°C using a paint film adhesion tester in accordance with the national standard GB / T 1720-89. The adhesion of the adhesive layer to the substrate was tested using a 100-grid test.

[0106] The adhesion test after environmental testing (aging) is to place the product in an environmental testing (aging) chamber at a temperature of 65°C and a humidity of 95% RH for 500 hours, then take out the sample and place it at a room temperature of 25°C for 2 hours before testing the adhesion again.

[0107]

[0108] By comparing the experimental results of Case 1 and Example 3, it can be seen that the hydrogen abstraction free radical photoinitiator ITX can achieve better curing effect of UV glue when the structure is deeper and the curing energy is lower.

[0109] By comparing the experimental results of Case 2 and Example 3, it can be seen that slightly increasing the content of the long-wavelength acylphosphine oxide photoinitiator can improve the curing effect of the contact part between the bottom of the adhesive layer and the mold, thereby improving the demoulding performance.

[0110] By comparing the experimental results of Case 3 with those of Example 3, it can be seen that tetrahydrofuran methyl ester (THFA) has a significant effect on the adhesion of the glue on the substrate, especially on the adhesion improvement after the aging test.

[0111] Comparing the experimental results of Case 4 with those of Example 3 reveals that a large proportion of silicone additives is essential for the demolding of deeper structures during production. When the final product requires flexural resistance, the hardness of the cured glue cannot be too high, otherwise it will easily break. However, soft glue is more difficult to demold than hard glue, so a large proportion of silicone additives is required to improve demolding. However, the addition of additives can affect the adhesion of the glue to the substrate, so a balance must be struck between demolding and adhesion. The amount of silicone additive added is preferably less than 5%, and the amount of tetrahydrofuran (THFA) added should be no less than 15%.

[0112] By comparing the experimental results of Case 5 and Example 4, it can be seen that adding too much trifunctional monomer will affect the overall toughness of the glue and make it more likely to break.

[0113] By comparing the experimental results of Case 6 and Example 4, it can be seen that the increase in the functionality of the oligomer will affect the overall toughness of the glue, making it more likely to break.

[0114] By comparing the experimental results of Case 7 with those of Example 4, it can be seen that aromatic oligomers affect the overall toughness of the glue, making it more likely to break.

[0115] Based on the experimental results of the three comparative examples 5, 6, and 7, the glue system should maintain a relatively low functionality and reduce the use of aromatic substances to improve the toughness of the product.

[0116] Note that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A UV structural adhesive, characterized in that: The composition comprises, by weight: 20-60 parts of oligomer, 40-80 parts of monomer, 3-8 parts of photoinitiator, and 3-8 parts of release agent; The monomers include a first monomer and a second monomer, wherein the first monomer is tetrahydrofuran methyl ester; the second monomer includes at least one of 1,6-hexanediol diacrylate and trimethylolpropane triacrylate; The Shore hardness of the UV structural adhesive is 30-60D.

2. The UV structural adhesive according to claim 1, characterized in that: The oligomer is an aliphatic polyurethane acrylate with 2-3 functionalities.

3. The UV structural adhesive according to claim 1, characterized in that: The monomer further includes a third monomer, and the third monomer is alkoxylated bisphenol A diacrylate.

4. The UV structural adhesive according to any one of claims 1 to 3, characterized in that: The monomers further include a fourth monomer, and the fourth monomer is isobornyl methacrylate.

5. The UV structural adhesive according to any one of claims 1 to 3, characterized in that: The demoulding aid is polyether-modified silicone.

6. The UV structural adhesive according to any one of claims 1 to 3, characterized in that: The photoinitiator is an α-hydroxyalkanone photoinitiator, an acylphosphine oxide photoinitiator and a hydrogen abstraction free radical photoinitiator ITX.

7. The UV structural adhesive according to claim 6, characterized in that: The added amount of the acylphosphorus oxide photoinitiator is 1.5-2%.

8. A method for preparing UV structural adhesive, for preparing the UV structural adhesive according to any one of claims 1 to 7, characterized in that: According to parts by weight, 20-60 parts of oligomer, 40-80 parts of monomer, 3-8 parts of photoinitiator, and 3-8 parts of auxiliary agent are added to a light-proof reactor and stirred and mixed at a stirring temperature of 40-45° C., a rotation speed of 110-120 r / min, and a stirring time of 90-120 min. The mixture is then allowed to stand and defoam for 0.5-1.5 h to obtain a UV structural adhesive.

9. An optical film, characterized in that: The optical film comprises a substrate layer and an optical structure arranged on at least one surface of the substrate layer, and the optical structure is made of any one of the UV structural adhesives described in claims 1-7.

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