An acrylic foam tape resistant to high temperature and high humidity environments and its preparation method

Abstract

The present invention discloses an acrylic foam tape resistant to high temperature and high humidity environments. Calculated by weight parts, it comprises the following raw materials: 50 - 70 parts of polyacrylate; 5 - 25 parts of modified resin; 0.5 - 2 parts of curing agent; 0.5 - 2 parts of coupling agent; 0.3 - 1 part of antioxidant; 30 - 50 parts of solvent; 0.3 - 3 parts of foaming microspheres; 0.5 - 3 parts of color paste. Among them, the polyacrylate comprises the following raw materials by weight parts: 30 - 50 parts of soft monomer; 5 - 20 parts of hard monomer; 1 - 5 parts of crosslinking monomer; 2 - 5 parts of functional monomer; 40 - 70 parts of solvent; 0.1 - 1 part of free radical initiator. The present invention also discloses a preparation method of the corresponding acrylic foam tape. The acrylic foam tape of the present invention can absorb impact force, is waterproof, has extremely low VOC content, and especially has good adhesion performance and shear resistance in high temperature and high humidity environments.

Description

Technical Field

[0001] The present invention belongs to the technical field of acrylic foam, and particularly relates to an acrylic foam tape resistant to high temperature and high humidity environments and a preparation method thereof. Background Art

[0002] Nowadays, people are increasingly inseparable from electronic products such as computers and mobile phones. These electronic products are prone to falling or colliding during use. Therefore, it is necessary to paste foam on the lower frame of the screen of these electronic products for buffer protection. The commonly used buffer foams at present are PE foam, PU foam, and EVA foam, and adhesives are applied on the foam for bonding.

[0003] The commonly used acrylic foam tapes on the market generally use PE foam and PU foam as the base materials, and then apply acrylic glue on the back. Due to the limitations of the production process of PE foam, large and uneven flat pores are obtained, and the pores are often open pores. In high temperature and high humidity environments, water vapor will enter the foam, and the additives added to the foam often precipitate. Due to the different materials of the foam and the acrylic glue, the foam and the adhesive layer separate at the interface, thus affecting the normal use of the product; due to its own material, PU foam is prone to chipping during die-cutting, and generally an open-cell structure is also obtained, resulting in poor waterproof effect.

[0004] In the prior art, there are also cases where acrylic glue is directly foamed to obtain acrylic foam tapes, but generally, photo-curing or low-temperature thermal curing is used on the market, which will cause the problem of incomplete volatilization of organic small molecules, resulting in a very high VOC content in the foam tape. When used in high temperature and high humidity environments, organic small molecules will precipitate, and water vapor enters the interior of the foam, causing the polymer chains to break, resulting in insufficient internal cohesion of the foam and the foam cracking under stress, which will affect the normal use of electronic products. Summary of the Invention

[0005] In view of one or more of the above deficiencies or improvement requirements in the prior art, the present invention provides an acrylic foam tape resistant to high temperature and high humidity environments and a preparation method thereof. The acrylic foam tape has an extremely low VOC content and still has good adhesiveness in high temperature and high humidity environments.

[0006] To achieve the above object, according to one aspect of the present invention, an acrylic foam tape is provided. Its structure includes two layers of release films and one layer of foam. The VOCs content of the foam is less than 50 g / kg, and further less than 30 g / kg.

[0007] As a further improvement of the present invention, the average diameter of the pores of the foam is 0.02 - 0.07 mm, and the average pore spacing is 0.01 - 0.05 mm. While ensuring buffer performance, the foam can also have good strength.

[0008] As a further improvement of the present invention, the water contact angle of the foam is greater than 100° and less than 150°, and more preferably, the water contact angle of the foam is greater than 110° and less than 140°.

[0009] As a further improvement of the present invention, the aging rate X of the peel strength of the acrylic foam tape does not exceed 15%; the aging rate X of the peel strength = (T1 - T2) / T1, where T1 is the peel strength at room temperature before aging and T2 is the peel strength after aging.

[0010] There is no clear limit on the thickness of the foam. When applied to electronic products, the upper limit is preferably 1 mm, more preferably 0.8 mm, the lower limit is preferably 0.05 mm, and more preferably 0.1 mm.

[0011] As a further improvement of the present invention, the foam comprises the following raw materials in parts by weight: 50 - 70 parts of polyacrylate resin, 5 - 15 parts of modified resin, 0.5 - 2 parts of curing agent, 0.5 - 2 parts of coupling agent, 0.3 - 1 part of antioxidant, 0.3 - 3 parts of foaming microspheres, 0.5 - 3 parts of color paste, and 30 - 50 parts of solvent.

[0012] As a further improvement of the present invention, the polyacrylate resin comprises the following raw materials in parts by weight and is polymerized from the following raw materials:

[0013] 30 - 50 parts of soft monomer, 5 - 20 parts of hard monomer, 1 - 5 parts of crosslinking monomer; 2 - 5 parts of functional monomer; 40 - 60 parts of solvent; 0.1 - 1 part of free radical initiator.

[0014] Preferably, the soft monomer has a Tg lower than -20°C, and the addition amount of the soft monomer is 30 - 50 parts. When it is less than 30 parts, the viscosity of the polymer is low. When it exceeds 50 parts, the cohesive force of the polymer is poor, and the anti-shear performance at high temperature is extremely poor. The soft monomer is further preferably one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and lauryl acrylate.

[0015] Preferably, the hard monomer has a Tg higher than 90°C, and the addition amount of the hard monomer is 5 - 30 parts. When it is less than 5 parts, the cohesive force of the polymer is poor, and the anti-shear performance at high temperature is extremely poor. When it is higher than 30 parts, the viscosity of the polymer is low. The hard monomer is further preferably one or more of styrene, acrylonitrile, and methyl methacrylate.

[0016] Preferably, the addition amount of the crosslinking monomer is 1 - 5 parts. When it is less than 1 part, the later strength of the polymer is low. When the addition amount is higher than 5 parts, it will cause gelation during polymerization. The crosslinking monomer is further preferably one or more of acrylic acid, methacrylic acid, N-methylol acrylamide, and hydroxyethyl acrylate.

[0017] Preferably, the functional monomer is a fluorine-containing monomer in the side chain. On the one hand, due to the strong polarity of fluorine atoms, the interaction between polymer chains is relatively strong, improving the high-temperature resistance of the polymer. On the other hand, the introduction of fluorine atoms reduces the surface energy of the polymer, increases the water contact angle of the polymer, and greatly improves the waterproof performance. The chemical structural formula of the monomer is shown in the following formula (1) or formula (2):

[0018]

[0019] In formula (1) and formula (2), R is an alkyl group containing fluorine atoms, with the number of carbon atoms not exceeding 8 and the number of fluorine atoms being 3 - 12.

[0020] Preferably, the solvent is one or more of ethyl acetate, isopropanol, toluene, and heptane.

[0021] Preferably, the addition amount of the radical initiator is 0.1 - 1 part. When it is less than 0.1 part, monomer polymerization may not occur. When the addition amount is higher than 1 part, the molecular weight of the polymer will decrease, and the strength of the polymer foam in the later stage will be insufficient. The radical initiator is further preferably one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, diisopropyl peroxydicarbonate, and dicumyl peroxide.

[0022] As a further improvement of the present invention, the preparation method of the polyacrylate resin includes the following steps:

[0023] Weigh the corresponding weight parts of the soft monomer and 4 / 5 of the solvent, introduce nitrogen protection, and at 78 - 82 °C, dropwise add 2 / 3 of the radical initiator, 1 / 10 of the solvent, and the corresponding weight parts of the hard monomer and functional monomer, and carry out the dropwise addition reaction for 2 - 2.5 h, then keep the temperature for 1 - 1.5 h;

[0024] Dropwise add the remaining 1 / 3 of the radical initiator and 1 / 10 of the solvent, and then keep the temperature at 76 - 80 °C for 3 - 4 h to obtain the polyacrylate.

[0025] As a further improvement of the present invention, the softening point of the modified resin is 120 - 150 °C. The high softening point resin can improve the heat resistance of the polyacrylate. On the other hand, the molecular weight of the resin is relatively small, which can improve the viscosity of the polymer foam. The addition amount of the modified resin is 5 - 15 parts. When it is less than 5 parts, the viscosity of the polymer is insufficient. When it is higher than 15 parts, the initial viscosity and cohesion of the polymer foam will decrease. The modified resin is preferably one or more of rosin resin, terpene resin, terpene phenol resin, and polyurethane resin.

[0026] As a further improvement of the present invention, the addition amount of the curing agent is 0.5 to 2 parts. When it is less than 0.5 part, the crosslinking degree of the polymer foam is insufficient, resulting in too low strength and easy to break. When it is higher than 2 parts, the viscosity of the polymer decreases, and gelation is likely to occur during production. The curing agent is preferably one or more of isocyanate curing agents, epoxy curing agents, and pyridine-based curing agents.

[0027] As a further improvement of the present invention, the coupling agent is a silane coupling agent, and the addition amount is 0.5 to 2 parts. When it is less than 0.5 part, the crosslinking degree of the polymer foam tape is too low, and the adhesiveness is poor. On the contrary, when it is higher than 2 parts, the adhesion of the foam tape will also decrease.

[0028] As a further improvement of the present invention, the antioxidant is one or more of 1010, 1076, 168, 618, UV928, DLTDP, and 412S, which can effectively improve the oxidation of the product at high temperatures.

[0029] As a further improvement of the present invention, the solvent is one or more of ethyl acetate, isopropyl alcohol, toluene, and heptane.

[0030] As a further improvement of the present invention, the foaming microspheres are unexpanded foaming microspheres, with an initial foaming temperature of 130 - 150 °C, a maximum foaming temperature of 150 - 170 °C, a rupture temperature of 170 - 220 °C, and the foaming temperature range not exceeding 50 °C. The initial foaming temperature is higher than the highest temperature of the drying temperature range, otherwise, partial foaming during the drying process will not reach the expected foaming effect. The addition amount of the foaming microspheres is 0.3 to 3 parts. When it is less than 0.3 part, the foaming ratio of the polymer foam is too low, and the buffering effect is poor. When it is higher than 3 parts, the foaming ratio of the polymer is too large, and the strength of the foam is too low, and it is easy to break when subjected to impact force.

[0031] According to another aspect of the present invention, a method for preparing an acrylic foam tape is provided, including the following steps: Weigh polyacrylate resin, modified resin, curing agent, antioxidant, foaming microspheres, color paste, and solvent by weight parts, mix them evenly, coat the mixed resin on a release film, and dry it through an oven. This is one layer. Repeat this operation to obtain other layers, then laminate them together, and then carry out foaming and winding for storage.

[0032] As a further improvement in the preparation process, the highest temperature of the drying temperature range in the oven is lower than the initial foaming temperature of the foaming microspheres; the highest temperature of the foaming temperature range in the oven is higher than the initial foaming temperature of the foaming microspheres and lower than the rupture temperature of the foaming microspheres.

[0033] Generally speaking, compared with the prior art through the above technical solutions conceived by the present invention, the following beneficial effects are achieved:

[0034] (1) In the polyacrylate used in the present invention, an acrylic monomer with a fluorine atom-containing side chain is introduced. Due to the strong polarity of the fluorine atom, it can form hydrogen bonds with the hydroxyl or carboxyl groups in adjacent polymer chains, enhancing the interaction between polymer chains, thereby improving the high-temperature resistance of the polymer. On the other hand, the introduction of fluorine atoms reduces the surface energy of the polymer, increases the water contact angle of the polymer, greatly improves the waterproof performance, and further improves the high-temperature and high-humidity resistance of the polymer, solving the problem of high-temperature and high-humidity resistance of existing acrylic foam tapes.

[0035] (2) In the preparation method of the polyacrylate foam tape of the present invention, the synthesized polyacrylate resin, modified resin, curing agent, antioxidant, foaming microspheres, color paste, and solvent are mixed evenly. The mixed resin is coated on a release film and dried in an oven. This is one layer. Repeat this operation to obtain other layers, and then laminate them together, and then carry out foaming and winding for storage. By coating in different layers, the VOC content of the foam tape is reduced during high-temperature baking, thereby reducing the VOC release during later use, reducing the entry of water vapor, and further improving the high-temperature and high-humidity performance of the foam tape. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic structural diagram of the high-temperature and high-humidity acrylic foam tape according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] Example 1

[0039] (1) Preparation of polyacrylate:

[0040] The weight parts of each component raw material are as follows: ethyl acrylate (EA) 34 parts; styrene (St) 7 parts; acrylic acid (AA) 2 parts; 2-hydroxyethyl acrylate (HEA) 3 parts; trifluoroethyl acrylate (TFEA) 4 parts; ethyl acetate (EAC) 50 parts; benzoyl peroxide (BPO) 0.3 parts.

[0041] Weigh 34 parts of ethyl acrylate and 40 parts of ethyl acetate. Under nitrogen protection, at 78 - 82 °C, add dropwise 0.2 parts of benzoyl peroxide, 5 parts of ethyl acetate, 7 parts of styrene, 2 parts of acrylic acid, 3 parts of 2-hydroxyethyl acrylate, and 4 parts of trifluoroethyl acrylate. The dropping reaction lasts for 2 h, and then keep the temperature for 1 h. Then add dropwise the remaining 0.1 part of benzoyl peroxide and 5 parts of ethyl acetate, and keep the temperature at 76 - 80 °C for 3 h to obtain the polyacrylate.

[0042] (2) Preparation of acrylic foam tape

[0043] The weight parts of each component raw material are as follows: 70 parts of synthetic polyacrylate; 7 parts of terpene phenol resin; 0.6 part of isocyanate curing agent; 0.7 part of silane coupling agent; 0.5 part of UV928 antioxidant; 30 parts of ethyl acetate; 0.4 part of unexpanded foaming microspheres; 1.4 parts of black paste.

[0044] Specific steps of the preparation method:

[0045] 1) First, add the polyacrylate and the modified resin, and after stirring evenly, add the antioxidant, black paste, foaming microspheres, coupling agent, and curing agent in sequence. After stirring evenly, filter to obtain the coating liquid;

[0046] 2) Coating the obtained coating liquid onto the PET release film through a coater;

[0047] 3) Then dry it in an oven, the drying temperature is 60 - 130 °C. After drying, laminate a release film to obtain a 0.05 mm thick adhesive film;

[0048] 4) Repeat step 2) twice to obtain two or three layers of adhesive film;

[0049] 5) Laminate the obtained three - layer adhesive film, and then foam the obtained adhesive film in the oven, the foaming temperature is 150 - 170 °C, the thickness is 0.2 mm, wind it up and store to obtain the high - temperature and high - humidity resistant acrylic foam tape.

[0050] Perform the following performance tests on the obtained foam tape:

[0051] Thickness test, referring to GB / T 7125 - 2014 Test method for thickness of adhesive tapes;

[0052] Density test, referring to GB / T 6343 - 2009 Determination of apparent density of cellular plastics and rubbers;

[0053] Compression stress - strain test, referring to GB / T 18942.1 - 2003 Determination of compression stress - strain characteristics of porous elastic materials of polymers;

[0054] Peel strength test, referring to GB / T 2792 - 2014 Test method for peel strength of adhesive tapes;

[0055] Peeling force aging rate test, the aging rate of peeling strength X = (T1 - T2) / T1, where T1 is the peeling strength at room temperature before aging and T2 is the peeling strength after aging;

[0056] Water contact angle test, which is carried out using a water contact angle measuring instrument;

[0057] VOC content test, referring to the test method of GB 33372-2020 Limits of volatile organic compounds in adhesives;

[0058] 85°C / 85% humidity holding power test, referring to the test method of GB / T 4851-2014 Adhesion of pressure-sensitive tapes;

[0059] Point impact absorption, 9.08g ball / 30cm height point impact absorption;

[0060] Water absorption test, soaking for 24h to test the absorbed water weight, referring to GB / T 8810-2005 Determination of water absorption of rigid cellular plastics.

[0061] Examples 2 to 19

[0062] Preparation of polyacrylate: The formulation composition of polyacrylate is shown in Tables 11 and 12, and the polymerization process is carried out in the same manner as in Example 1.

[0063] Preparation of acrylic foam tape: The composition of each component of the acrylic foam tape is shown in Tables 11 and 12, and the specific steps are carried out in the same manner as in Example 1.

[0064] The obtained foam tape is tested according to the same performance test method as in Example 1.

[0065] The performance test results of each example are shown in Tables 11 and 12.

[0066] Table 11 Performance test results of Examples 1 to 10

[0067]

[0068]

[0069] Table 12 Performance test results of Examples 11 to 19

[0070]

[0071]

[0072] Comparative Examples 1 to 8

[0073] Preparation of polyacrylate: The composition of the polyacrylate formulation is as shown in Table 2, and the polymerization process is carried out in the same manner as in Example 1.

[0074] Preparation of acrylic foam tape: The composition of each component of the acrylic foam tape is as shown in Table 2. The specific steps are carried out in the same manner as described in Example 1. It should be particularly noted that in Comparative Example 8, instead of multiple coatings, a single coating is used and then foaming is carried out.

[0075] The obtained foam tape is tested according to the same performance test method as in Example 1.

[0076] In Comparative Example 9, a 0.2 mm thick PE foam tape from New Asia Adhesive Products Co., Ltd. is used.

[0077] In Comparative Example 10, a 0.2 mm thick acrylic foam tape from Crown Adhesive Products Co., Ltd. is used.

[0078] The performance test results of each comparative example are shown in Table 2.

[0079] Table 2 Performance Test Results of Comparative Examples 1 to 10

[0080]

[0081]

[0082] Through the comparative analysis of the above data, it can be seen that for the acrylic foam tape in Comparative Example 5 without trifluoroethyl acrylate added, the water contact angle is only 96°, and the water absorption rate reaches 9.4%. After adding trifluoroethyl acrylate monomer, as the addition amount increases, the water contact angle gradually increases, the peel strength at 85°C / 85% humidity first increases and then decreases, the aging rate of the peel strength decreases, and the holding force at 85°C / 85% humidity increases. In Comparative Example 8, a single coating and foaming are used, and the obtained acrylic foam tape has a higher water absorption rate, a higher VOC content, and a lower holding force at 85°C / 85% humidity compared to Example 1. Therefore, the present invention can obtain a high-temperature and high-humidity resistant acrylic foam tape with a low VOC content, which not only has excellent impact absorption performance and lower water absorption rate, but also has a much better holding force performance in an 85°C / 85% humidity environment than the foam tapes on the market, has better shear resistance performance, and has good peel strength performance without the phenomenon of residual glue and glue peeling.

[0083] It is easy for those skilled in the art to understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. An acrylic foam tape resistant to high temperature and high humidity environments, characterized in that, it comprises two layers of release films and one layer of foam body, and the VOCs content of the foam body is less than 50 g / kg; Mix the raw materials of the foam body and coat them on the release film, then dry them in an oven. This is one layer. Repeat this operation to obtain other layers, and then laminate them together, and then carry out foaming to obtain the acrylic foam tape; The foam body contains the following raw materials in parts by weight: 50-70 parts of polyacrylate resin, 5 parts of modified resin, 0.5-2 parts of curing agent, 0.5-2 parts of coupling agent, 0.3-1 part of antioxidant, 0.3-0.4 parts of foaming microspheres, 0.5-3 parts of color paste, 30-50 parts of solvent; The polyacrylate resin contains the following raw materials in parts by weight: 30-34 parts of soft monomer, 5-20 parts of hard monomer, 4-5 parts of crosslinking monomer; 2-5 parts of functional monomer; 40-60 parts of solvent; 0.1-1 part of free radical initiator; Wherein the functional monomer is a fluorine-containing monomer in the side chain, and its chemical structural formula is shown as the following formula (1) or formula (2): Formula (1) Formula (2) In formula (1) and formula (2), R is an alkyl group containing fluorine atoms, wherein the number of carbon atoms does not exceed 8 and the number of fluorine atoms is 3-12.

2. The acrylic foam tape resistant to high temperature and high humidity environments according to claim 1, characterized in that, the average diameter of the foam cells of the foam body is 0.02-0.07 mm, and the average pore spacing is 0.01-0.05 mm.

3. The acrylic foam tape resistant to high temperature and high humidity environments according to claim 1, characterized in that, the water contact angle of the foam body is greater than 100° and less than 150°.

4. The acrylic foam tape resistant to high temperature and high humidity environments according to claim 1, characterized in that, the Tg of the soft monomer is lower than -20°C; the Tg of the hard monomer is higher than 90°C; the crosslinking monomer is one or more of acrylic acid, methacrylic acid, N-hydroxymethylacrylamide, and hydroxyethyl acrylate; the solvent is one or more of ethyl acetate, isopropanol, toluene, and heptane; the free radical initiator is one or more of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, diisopropyl peroxydicarbonate, and dicumyl peroxide.

5. The acrylic foam tape resistant to high temperature and high humidity environments according to claim 4, characterized in that, the soft monomer is one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and lauryl acrylate; the hard monomer is one or more of styrene, acrylonitrile, and methyl methacrylate.

6. The acrylic foam tape resistant to high temperature and high humidity environments according to any one of claims 1-5, characterized in that, the preparation method of the polyacrylate resin comprises the following steps: Weigh the corresponding parts by weight of the soft monomer and 4 / 5 of the solvent, introduce nitrogen protection, and at 78-82°C, dropwise add 2 / 3 of the free radical initiator, 1 / 10 of the solvent, and the corresponding parts by weight of the hard monomer and functional monomer, and carry out dropwise addition reaction for 2-2.5 h, and keep warm for 1-1.5 h; Add the remaining 1 / 3 of the free radical initiator and 1 / 10 of the solvent, and then keep the temperature at 76 - 80 °C for 3 - 4 h to obtain the polyacrylate.

7. The acrylic foam tape resistant to high temperature and high humidity environment according to any one of claims 1 - 5, characterized in that the modified resin is one or more of rosin resin, terpene resin, and terpene phenol resin, and the softening point of the resin is 120 - 150 °C; the curing agent is one or more of isocyanate curing agent, epoxy curing agent, and pyridine - type curing agent; the coupling agent is a silane coupling agent; the antioxidant is one or more of 1010, 1076, 168, 618, DLTDP, and 412S; the solvent is one or more of ethyl acetate, isopropyl alcohol, toluene, and heptane; the foaming microspheres are unexpanded foaming microspheres, and the initial foaming temperature is higher than the highest temperature in the drying temperature range.

8. The preparation method of the acrylic foam tape resistant to high temperature and high humidity environment according to any one of claims 1 - 7, characterized in that it includes the following steps: Weigh the polyacrylate resin, modified resin, curing agent, coupling agent, antioxidant, foaming microspheres, color paste, and solvent by weight parts, mix them evenly, coat the mixed resin on the release film, and dry it through an oven. This is one layer. Repeat this operation to obtain other layers, then laminate them together, and then carry out foaming.

9. The preparation method of the acrylic foam tape resistant to high temperature and high humidity environment according to claim 8, characterized in that the highest temperature in the oven drying temperature range is lower than the initial foaming temperature of the foaming microspheres; the highest temperature in the oven foaming temperature range is higher than the initial foaming temperature of the foaming microspheres and lower than the rupture temperature of the foaming microspheres.

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