Radiation-crosslinkable pressure-sensitive adhesive as well as preparation method and application thereof

Abstract

The invention relates to a radiation-crosslinkable pressure-sensitive adhesive as well as a preparation method and application thereof. The preparation method comprises the following steps: polymerizing an alkyl (meth) acrylate monomer, an olefinic unsaturated polar monomer, a photoinitiator monomer and other monomers in the presence of an initiator to obtain radiation-crosslinkable poly (meth) acrylate; and then mixing with oligomeric (meth) acrylate prepared by copolymerization of alkyl (meth) acrylate and (meth) acrylic acid-N, N-dimethylamino methyl ester (or (meth) acrylic acid-N, N-dimethylamino ethyl ester) to obtain the pressure-sensitive adhesive. The adhesive disclosed by the invention is not influenced by migration of small molecules in the base material, so that stable viscosity is kept on the base material, and particularly, the adhesive disclosed by the invention is transparent and air-permeable, and is suitable for transparent adhesive materials such as medical labels.

Description

Technical Field

[0001] The present invention belongs to new materials and relates to an adhesive, specifically to a radiation cross-linkable pressure-sensitive adhesive and a preparation method and application thereof, especially the use of preparing transparent and breathable adhesive materials such as adhesive labels, adhesive tapes, plasters, bandages and self-adhesive sheets. Background Art

[0002] Soft polyvinyl chloride (PVC) film is cheap, and the polyvinyl chloride tape obtained by coating pressure-sensitive adhesive can be widely used for decoration of doors, windows, walls, furniture and outdoor advertisements. The prior art discloses a high-adhesion and high-strength peeling tape, comprising: a base film and an adhesive layer, one side of the base film is coated with an adhesive layer, and the other side is coated with a silicone oil release agent; the base film is a fiber-reinforced high-density polyethylene film; the adhesive layer is a pressure-sensitive adhesive prepared by acrylic resin, silicone rubber and nitrile rubber in a ratio of 32:44:34; the peel strength at 180°C is 350N / m, that is, 8.75N / 25mm, which is relatively low. The prior art discloses a plasticizer-resistant hot melt pressure-sensitive adhesive and a preparation method thereof; raw materials: 80-120 parts of acrylic copolymer, 7-12 parts of polyvinyl chloride, 10-15 parts of nitrile rubber, 1-6 parts of tackifier, 18-28 parts of polypropylene, 13-23 parts of silane coupling agent, 1-3 parts of bamboo fiber, 10-18 parts of kaolin, 20-30 parts of starch adhesive; the formula is too complicated. The preparation of soft polyvinyl chloride film requires the addition of small molecule plasticizers to polyvinyl chloride resin. For example, diisooctyl phthalate (DOP) is often used as a plasticizer in the manufacture of soft advertising cloth in China. If a decorative film is bonded to such an advertising cloth by a pressure-sensitive adhesive, the performance of the pressure-sensitive adhesive will be greatly deteriorated due to the migration of the small molecule plasticizer to the surface of the soft advertising cloth.

[0003] Therefore, it is necessary to develop new bonding systems to solve the problem of migration of small molecule plasticizers in adhesives. Summary of the invention

[0004] The purpose of the present invention is to provide a radiation-crosslinkable pressure-sensitive adhesive, which can effectively inhibit the migration of small molecule plasticizers in the adhesive and effectively provide the product's use stability. In particular, the adhesive of the present invention is transparent and breathable and is suitable for transparent adhesive materials, such as medical labels.

[0005] The present invention adopts the following technical scheme.

[0006] A radiation-crosslinkable pressure-sensitive adhesive comprises oligomeric (meth)acrylate and radiation-crosslinkable poly(meth)acrylate. Preferably, the weight ratio of the oligomeric (meth)acrylate to the radiation-crosslinkable poly(meth)acrylate is (0.1-0.5):1.

[0007] The invention discloses a method for preparing the radiation-crosslinkable pressure-sensitive adhesive, comprising the following steps: mixing oligomeric (meth)acrylate with radiation-crosslinkable poly(meth)acrylate to obtain the radiation-crosslinkable pressure-sensitive adhesive.

[0008] Preferably, in the oligomeric (meth)acrylate: the nitrogen atom content is greater than 4% by weight; the raw materials for preparing the oligomeric (meth)acrylate include one or more of (meth)acrylate alkyl esters, (meth)acrylate-N,N-dimethylaminomethyl ester, and (meth)acrylate-N,N-dimethylaminoethyl ester. Preferably, the raw materials for preparing the oligomeric (meth)acrylate include (meth)acrylate alkyl esters and (meth)acrylate-N,N-dimethylaminomethyl ester, or the raw materials for preparing the oligomeric (meth)acrylate include (meth)acrylate alkyl esters and (meth)acrylate-N,N-dimethylaminoethyl ester.

[0009] Preferably, the raw materials for preparing the radiation crosslinkable poly(meth)acrylate include alkyl(meth)acrylate monomers, ethylenically unsaturated polar monomers, photoinitiator monomers, and other monomers. Preferably, the weight percentage of the alkyl(meth)acrylate monomers is greater than 50%; the weight percentage of the ethylenically unsaturated polar monomers is 5% to 25%; and the weight percentage of the photoinitiator monomers is 0.1% to 5%.

[0010] In the present invention, the alkyl group of the (meth)acrylate monomer has 4 to 18 carbon atoms; the polar group of the ethylenically unsaturated polar monomer includes one or more of a carboxylic acid group, a carbonamide group, a pyrrolidone group, a carbamate group, and a urea group; the photoinitiator monomer is an ethylenically unsaturated copolymerizable photoinitiator; and the other monomers are monomers different from the (meth)acrylate monomer, the ethylenically unsaturated polar monomer, and the photoinitiator monomer.

[0011] The invention discloses the application of the radiation cross-linkable pressure-sensitive adhesive in the preparation of bonding materials.

[0012] The invention discloses the application of the radiation cross-linkable pressure-sensitive adhesive in the preparation of transparent bonding materials.

[0013] The invention discloses an adhesive material, comprising the radiation-crosslinkable pressure-sensitive adhesive.

[0014] Furthermore, the bonding material also includes a substrate.

[0015] Further, adhesive materials include adhesive labels, adhesive tapes, plasters, bandages and self-adhesive sheets.

[0016] The pressure-sensitive adhesive disclosed in the present invention may contain conventional additives, representative examples of which include resins, plasticizers, antioxidants, crosslinking agents, etc. In order to prepare the coating, the hot melt PSA is applied in the form of a melt to the material to be coated, an example being a substrate for adhesive tapes and labels, the surface of which is at least partially coated with the adhesive of the present invention. The hot melt PSA can be used in the form of a melt, i.e., usually at a temperature of 50 to 160° C., preferably 80 to 150° C. or greater than 100° C.

[0017] The substrate of the present invention is generally a polymer film, which is made of, for example, polyester, polyolefin (more specifically polyethylene or polypropylene), PVC, cellulose or polyacetate. Plasticizers are preferably able to physically interact with substances of high polymerization degree to form a homogeneous system with them through their solubility and swelling ability. For example, in plasticized PVC, preferred aromatic plasticizers are dioctyl phthalate, diisononyl phthalate, diisodecyl phthalate, etc.; non-cyclic aliphatic dicarboxylates, such as dioctyl adipate, diisodecyl adipate, dibutyl sebacate, dioctyl sebacate; alicyclic dicarboxylates, such as diisononyl cyclohexanedicarboxylate; phosphates, such as triphenyl phosphate, etc. The substrate containing plasticizer is preferably a material made of polyvinyl chloride. The content of plasticizer in the substrate is, for example, 10% to 70% by weight, preferably 25% to 50% by weight.

[0018] The invention uses (meth) acrylate alkyl ester monomers, ethylenically unsaturated polar monomers, photoinitiator monomers and other monomers to polymerize in the presence of an initiator to obtain radiation-crosslinkable poly (meth) acrylate, and then mixes with oligo (meth) acrylate prepared by copolymerization of (meth) acrylate alkyl ester and (meth) acrylate-N,N-dimethylaminomethyl ester (or (meth) acrylate-N,N-dimethylaminoethyl ester) to obtain a pressure-sensitive adhesive. The pressure-sensitive adhesive can effectively inhibit the migration of small molecule plasticizers in the adhesive and effectively improve the use stability of the product. In particular, the adhesive of the invention is transparent and breathable, suitable for transparent adhesive materials, and preferably used for preparing adhesive labels, adhesive tapes, plasters, bandages and self-adhesive sheets. DETAILED DESCRIPTION

[0019] As an example, according to the present invention, a radiation-crosslinkable pressure-sensitive adhesive comprises the following components: a) at least one radiation-crosslinkable poly(meth)acrylate formed from the following monomers: i. at least 50% by weight of at least one alkyl (meth)acrylate A1 having 4 to 18 carbon atoms in the alkyl group, selected from n-butyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, propylheptyl (meth)acrylate and mixtures thereof; ii. 5 to 23% by weight of at least one ethylenically unsaturated polar monomer A2, preferably selected from acrylic acid, N-vinyl pyrrolidone; iii. 0.1 to 5% by weight of at least one ethylenically unsaturated copolymerizable photoinitiator monomer A3 having the general structure AXB, wherein: A is an organic group containing a benzophenone structure; X is an ester group selected from -OC(=O)-, -(C=O)-O and -O-(C=O)-O-, B is a free radical polymerizable group containing ethylenic unsaturation.

[0020] iv. optionally at least one further monomer A4 different from monomers (i) to (iii); and b) at least one oligomeric (meth)acrylate, wherein the nitrogen atom content is greater than 4% by weight, preferably greater than 6% by weight, more preferably greater than 8% by weight; preferably selected from copolymers of monomer A1 and N,N-dimethylaminomethyl (meth)acrylate and N,N-dimethylaminoethyl (meth)acrylate.

[0021] The pressure-sensitive adhesive composition formed by combining a) and b) above has a zero shear viscosity at 130° C. of less than 80 Pa·s, preferably less than 75 Pa·s, more preferably not more than 70 Pa·s, such as less than 65 Pa·s.

[0022] Unless expressly stated otherwise, the quantitative values ​​for the monomers of a polymer are based on 100 parts by weight of the sum of all monomers.

[0023] The raw material for preparing the radiation-crosslinkable poly(meth)acrylate comprises at least 55% by weight, preferably at least 58% by weight, and more preferably at least 60% by weight of C4 to C18 alkyl (meth)acrylate (monomer A1). Preference is given to C4 to C10 alkyl (meth)acrylates, especially C4 to C8 alkyl (meth)acrylates, such as n-butyl acrylate, n-hexyl acrylate, 2-propylhexyl acrylate and 2-ethylhexyl acrylate and mixtures thereof. Particular preference is given to n-butyl acrylate and 2-ethylhexyl acrylate.

[0024] The raw material for preparing the radiation-crosslinkable poly(meth)acrylate contains preferably at least 5% to 23% by weight, preferably 6% to 22% by weight, and more preferably 7% to 21% by weight of monomer A2, such as 10%, 15%, or 20% by weight. Monomer A2 is a monomer having a polar group, wherein the polar group is selected from the group consisting of a carboxylic acid group, a carboxylic anhydride group, a hydroxyl group, an amide group, a carbamate group, a urea group, a piperidinyl group, a piperazinyl group, a morpholinyl group, an imidazole group, and a combination of two or more of the groups. The preferred monomer having a carboxylic acid group is acrylic acid.

[0025] At least one ethylenically unsaturated copolymerizable photoinitiator monomer A3 has the general structural formula AXB and is used in an amount of 0.05 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.5 to 2% by weight, and further preferably 0.7 to 1% by weight.

[0026] The raw material for preparing the radiation-crosslinkable poly(meth)acrylate contains, in addition to the monomers A1, A2, A3, other monomers, such as (meth)acrylamide and monomers containing hydroxyl groups, more specifically C1-C10 hydroxyalkyl (meth)acrylates. Preferred monomers containing hydroxyl groups are C1-C10 hydroxyalkyl (meth)acrylates, especially methyl (meth)acrylate, hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate.

[0027] Using monomer A1 and (meth) acrylic acid-N,N-dimethylamino ester as raw materials, polymerization is performed to prepare oligomeric (meth) acrylic acid ester, wherein (meth) acrylic acid-N,N-dimethylamino ester is a copolymer of (meth) acrylic acid-N,N-dimethylamino methyl ester or (meth) acrylic acid-N,N-dimethylamino ethyl ester; wherein the weight ratio of monomer A1 to (meth) acrylic acid-N,N-dimethylamino ester is 1 (0.5-8), preferably, the weight ratio of monomer A1 to (meth) acrylic acid-N,N-dimethylamino ester is 1 (1-6), such as 1:1, 1:1.5, 1:2, etc.

[0028] The radiation-crosslinkable poly(meth)acrylates and oligo(meth)acrylates can be prepared by copolymerizing the monomer components (optionally including copolymerizable photoinitiators) using conventional polymerization initiators and optional chain transfer agents (CTA), wherein the polymerization is carried out at conventional temperatures in bulk, emulsion (e.g. in water or liquid hydrocarbons) or solution. Preferably, the polymer is prepared by solution polymerization or bulk polymerization at a temperature of 70 to 120° C. and at a pressure of 0.3 to 10 bar, in the presence of 0.01 to 10% by weight of a peroxide or azo initiator as a polymerization initiator, based on the monomer, and in the presence of 0 to 200% by weight, preferably 5 to 25% by weight, of an inert solvent based on the monomer. Preferably, the reaction is carried out in an increased vacuum, for example by reducing the pressure from atmospheric pressure (1 bar) to 500 mbar (absolute). The solvent is, for example, a hydrocarbon; an alcohol, such as methanol, ethanol, propanol, butanol, isobutanol; a ketone, such as acetone, methyl ethyl ketone, methyl isobutyl ketone; ethyl acetate; a nitrile, such as acetonitrile and benzonitrile; or a mixture of the solvents. In a preferred embodiment, the solvent used for the polymerization is one or more ketones having a boiling point below 150° C. at atmospheric pressure (1 bar).

[0029] Examples of polymerization initiators under consideration include azo compounds, ketone peroxides and alkyl peroxides; examples are acyl peroxides such as benzoyl peroxide, dilauroyl peroxide, didecanoyl peroxide, isononanoyl peroxide, alkyl esters such as tert-butyl perpivalate, tert-butyl per-2-ethylhexanoate, tert-butyl permaleate, tert-butyl perisononanoate, tert-butyl perbenzoate, tert-amyl per-2-ethylhexanoate, dialkyl peroxides such as dicumyl peroxide, tert-butyl cumyl peroxide, di-tert-butyl peroxide, and peroxydicarbonates. As initiators, it is also possible to use azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(methyl isobutyrate) or 2,2'-azobis(2,4-dimethylvaleronitrile).

[0030] After the polymerization in solution, the solvent can optionally be separated off under reduced pressure, this operation being carried out at elevated temperatures, for example 100 to 150° C. The polymer can then be used in the solvent-free state (solvent content preferably less than 2% by weight, based on all components), ie in the form of a melt.

[0031] Preferably, the zero shear viscosity of the component a) of the present invention at 130° C. is preferably greater than 80 Pa·s and less than 160 Pa·s. It is used in a solvent-free, meltable form.

[0032] After the pressure-sensitive adhesive has been applied to the substrate, the radiation-crosslinkable pressure-sensitive adhesive of the invention is irradiated with high-energy radiation, preferably UV light, more particularly UV-C radiation (200-280 nm) to produce crosslinks. To this end, in general, the coated substrate is placed on a conveyor belt and the belt is conveyed past the radiation source, such as a UV lamp. The degree of crosslinking of the polymer depends on the duration and intensity of the radiation.

[0033] The following is an explanation of the technical progress of the present invention through specific experiments. The raw materials used are existing products, and the specific preparation operations and performance tests are all conventional techniques.

[0034] Zero shear viscosity is the limiting value of the viscosity function at infinitely low shear rates. The measurements are carried out using an Anton Paar rheometer in plate / plate geometry. The samples are measured in oscillatory shear at a low shear amplitude of 10%. The temperature is 130°C.

[0035] Performance Testing: The pressure sensitive adhesive (PSA) was coated with 60 g / m 2 The PSA-coated substrate was knife coated onto a siliconized PET film at an application rate of 1.50 and 1.50 mm and irradiated with UV-C light. The applied film was then transferred onto a tough PVC test plate plasticized with 38 wt % DOP (based on 100 parts of PVC weight). The PSA-coated substrate was cut into 25 mm wide test strips.

[0036] 180 degree peel strength The above test strips are placed at 23 degrees and 50% relative humidity for at least 4 hours. Remove the release paper from the test sample, put the test tape on the clean test board with the adhesive side facing down, and press it with a test roller twice in each direction at a speed of about 10mm / s to make the adhesive surface closely contact with the surface of the test board. After the test sample is attached to the test board, place it for the required time and then test it with a tensile machine.

[0037] The test conditions are: the peeling angle is 180 degrees, and the clamp separation speed is set to 300mm / min. Read the data every 10mm in the middle of the test sample, and take the average value after reading at least 5 data points. The peeling force is expressed in N / 25mm, and the adhesive residue rate on the test board is observed.

[0038] Plasticizer migration resistance test The samples prepared above were attached to the test board, and after being aged at 70 degrees for several hours, their 180-degree peel strength was measured. Example 1

[0039] Component synthesis

[0040] Under nitrogen flow, 180 g of methyl ethyl ketone (MEK) was charged into a polymerization apparatus consisting of a glass reactor, a reflux condenser, a stirrer and a nitrogen inlet, and 610 g of 2-ethylhexyl acrylate, 225 g of methyl methacrylate, 150 g of acrylic acid and 30 g of Visiomer were added at 80°C. 50 g of a monomer mixture consisting of 6976 photoinitiator (containing 30% of benzophenone methacrylate); then 2.65 g of an initiator solution containing 8 g of tert-butyl pivalate (75% in mineral oil) and 45 g of MEK was added, and initial polymerization was carried out for 3 minutes; then the remaining monomer mixture and 50.3 g of the initiator solution were added over 3 hours; then at 90°C, a solution of 2.67 g of tert-butyl pivalate (75% in mineral oil) dissolved in 21.7 g of MEK was added over 30 minutes; then reduced pressure was carried out, and the solvent was distilled off at a temperature of up to 135°C at less than 50 mbar, and radiation-crosslinkable poly(meth)acrylate was obtained by degassing at 135°C for 1 hour under reduced pressure.

[0041] b) Component synthesis Under nitrogen flow, 280 g of isopropanol was charged into a polymerization apparatus consisting of a glass reactor, a reflux condenser, a stirrer and a nitrogen inlet, 55 g of a monomer mixture consisting of 500 g of ethylhexyl acrylate, 500 g of N,N-dimethylaminomethyl methacrylate and 220.00 g of isopropanol at 80°C; then 8.57 g of an initiator solution containing 21.33 g of tert-butyl pivalate (75% in mineral oil) and 180.00 g of isopropanol was added, and initial polymerization was carried out for 3 minutes; then the remaining monomer mixture and the initiator solution were added over 3 hours; then at 90°C, a solution of 2.67 g of tert-butyl pivalate (75% in mineral oil) dissolved in 24 g of isopropanol was added over 30 minutes; then reduced pressure was applied and the solvent was distilled off at a temperature of up to 135°C at less than 50 mbar, and oligomeric (meth)acrylate was obtained by degassing at 135°C under reduced pressure for 1 hour.

[0042] Preparation of a) + b) mixture: 60 g of component a) radiation-crosslinkable poly(meth)acrylate and 40 g of component b) oligo(meth)acrylate were stirred at 135° C. for 30 min to obtain a radiation-crosslinkable pressure-sensitive adhesive, which was a transparent product.

[0043] The samples were then coated on a siliconized PET release film and irradiated with UV-C light. The applied film was then transferred to a toughened PVC test plate plasticized with 38 wt% DOP.

[0044] In Examples 2 to 6 and Comparative Examples 1 to 5, except for the changes in the types and amounts of the materials, the rest are the same as in Example 1, as shown in Table 1. In Comparative Example 6, except for the change of the polymerization solvent isopropanol to methyl ethyl ketone during the synthesis of component b), the rest are the same as in Comparative Example 1.

[0045] Table 1 Examples 1 to 6, Comparative Examples 1 to 7 ;

[0046] The present invention adds component b) to component a), and the initial peel strength of the test sample is high, and the peel strength does not decrease or decreases slightly with the extension of aging time, indicating that it has good resistance to migration of small molecule plasticizers. Comparing the examples with Comparative Example 1, it can be found that when the content of A2 monomer in component a) is high, but there is no component b), the zero shear viscosity of the sample is high and cannot be evenly coated on the surface of the substrate. Comparing the examples with Comparative Example 2, it can be found that when there is no component b), the peel strength decreases significantly with the extension of aging time. Comparing the examples with Comparative Examples 3 and 4, it can be found that when the nitrogen atom content in component b) is low, its initial peel strength is low, and the peel strength decreases significantly with the extension of aging time. Comparing the examples with Comparative Example 5, it can be found that when the proportion of component b) is high, its initial peel strength is low.

[0047] The term "pressure sensitive adhesive" (PSA) is a viscoelastic adhesive in the dry state at room temperature (20°C) whose cured film at room temperature is permanently tacky and remains adhesive. Bonding to the substrate is accomplished instantly by gently applied pressure.

[0048] The term "radiation-crosslinkable" means that the hot melt adhesive contains at least one compound having at least one radiation-sensitive group and initiates a crosslinking reaction upon irradiation. The irradiation for crosslinking is preferably carried out using actinic radiation, preferably UV light, more particularly UV-C radiation. The radiation-crosslinkable hot melt adhesive preferably contains at least one photoinitiator. The photoinitiator is copolymerized into the poly(meth)acrylate.

Claims

1. A radiation-crosslinkable pressure-sensitive adhesive, characterized in that: Includes oligomeric (meth)acrylates and radiation-crosslinkable poly(meth)acrylates.

2. The radiation-crosslinkable pressure-sensitive adhesive according to claim 1, characterized in that The weight ratio of the oligomeric (meth)acrylate to the radiation-crosslinkable poly(meth)acrylate is (0.1-0.5):

1.

3. The radiation-crosslinkable pressure-sensitive adhesive according to claim 1, characterized in that: In the oligomeric (meth)acrylate: the nitrogen atom content is greater than 4% by weight; the raw materials for preparing the oligomeric (meth)acrylate include one or more of (meth)acrylate alkyl ester, (meth)acrylate-N,N-dimethylaminomethyl ester, and (meth)acrylate-N,N-dimethylaminoethyl ester.

4. The radiation-crosslinkable pressure-sensitive adhesive according to claim 1, characterized in that: The raw materials for preparing the radiation crosslinkable poly(meth)acrylate include (meth)acrylate alkyl ester monomers, ethylenically unsaturated polar monomers, photoinitiator monomers and other monomers.

5. The radiation-crosslinkable pressure-sensitive adhesive according to claim 4, characterized in that The alkyl group of the (meth) alkyl acrylate monomer has 4 to 18 carbon atoms; the polar group of the ethylenically unsaturated polar monomer includes one or more of a carboxylic acid group, a carbonamide group, a pyrrolidone group, a carbamate group, and a urea group; and the photoinitiator monomer is an ethylenically unsaturated copolymerizable photoinitiator.

6. The radiation-crosslinkable pressure-sensitive adhesive according to claim 4, characterized in that: The weight percentage of the (meth) alkyl acrylate monomer is greater than 50%; the weight percentage of the ethylenically unsaturated polar monomer is 5% to 25%; and the weight percentage of the photoinitiator monomer is 0.1% to 5%.

7. The method for preparing the radiation-crosslinkable pressure-sensitive adhesive according to claim 1, characterized in that: Oligomeric (meth)acrylates are mixed with radiation-crosslinkable poly(meth)acrylates to give radiation-crosslinkable pressure-sensitive adhesives.

8. Use of the radiation-crosslinkable pressure-sensitive adhesive according to claim 1 in the preparation of bonding materials.

9. Use of the radiation-crosslinkable pressure-sensitive adhesive according to claim 1 in the preparation of transparent adhesive materials.

10. An adhesive material comprising the radiation-crosslinkable pressure-sensitive adhesive according to claim 1.

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