WO2013082222A1

WO2013082222A1 - A pressure sensitive adhesive

Info

Publication number: WO2013082222A1
Application number: PCT/US2012/066956
Authority: WO
Inventors: Weinan Wang; Jessie MA; Junfeng Cao; Jestine HUANG
Original assignee: 3M Innovative Properties Company
Priority date: 2011-11-29
Filing date: 2012-11-29
Publication date: 2013-06-06
Also published as: CN102719205A; CN102719205B

Abstract

The disclosed acrylate pressure sensitive adhesive is formed by a free radical polymerization of the following monomers: (a) a hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group, the amount of the hydrophilic acrylic acid ester monomer being 10 to 30% of the total weight of all monomers; (b) a short-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOOR₁, where R₁is an alkyl group having 1 to 5 carbon atoms, the amount of the short-chain hydrophobic acrylic acid ester monomer being 50 to 70% of the total weight of all monomers; (c) a long-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOOR2, where R₂ is an alkyl group having 6 to 14 carbon atoms, the amount of the long-chain hydrophobic acrylic acid ester monomer being 10 to 35% of the total weight of all monomers; and (d) an acryl monomer having a polar group copolymerizable with the monomers (a) to (c), the amount of the acryl monomer being 0.5 to 5% of the total weight of all monomers.

Description

A PRESSURE SENSITIVE ADHESIVE

Technical Field

The invention relates to a pressure sensitive adhesive and the application thereof, and specifically, to an acrylate pressure sensitive adhesive and the application of the acrylate pressure sensitive adhesive for a pressure sensitive adhesive tape and a medical dressing tape.

Background Art

Acrylate pressure sensitive adhesive has been widely used for various pressure sensitive adhesive tapes and medical dressing tapes such as wound dressing tapes. The wound dressing tape is a product for bandaging a wound or a material for covering a sore, a scar or other lesion. The wound dressing tape has a typical structure comprising a layer of pressure sensitive adhesive applied on a backing and a release film attached on the adhesive side of the pressure sensitive adhesive tape, such as shown in Figure 1. Some wound dressing tapes are waterproof and impermeable to a moisture vapor, and some wound dressing tapes are both waterproof and permeable to a moisture vapor. In recent years, with the development of technology and the improvement of people's living standard, the wound dressing tapes which are both waterproof and permeable to a moisture vapor are attracting more and more attention.

WO 84/03837 discloses a solvent-based acrylate pressure sensitive adhesive having a good adhesion to both of dry and moist skins. This pressure sensitive adhesive contains a number of hydrophilic monomers as the components and thus has a good adhesive power under the high humidity environment. However, this patent document does not relate to the moisture vapor transmission rate of the acrylate pressure sensitive adhesive.

US 6,680,1 13 discloses a pressure sensitive adhesive for a dressing tape, which has higher moisture vapor transmission rate and better adhesion value. This pressure sensitive adhesive has a multilayer structure comprising one or more films having high moisture vapor transmission and a pressure sensitive adhesive layer having high adhesion, and exhibits an overall moisture vapor transmission rate of 1200g/m²/24hrs/37°C and an adhesion value of 15g/inch. The high moisture vapor transmission of the pressure sensitive adhesive for a dressing tape is accomplished mainly by the one or more films having high moisture vapor transmission. However, the effect of the pressure sensitive adhesive used on the moisture vapor transmission is not discussed.

Disclosure of the Invention

The present disclosure relates to an acrylate pressure sensitive adhesive which has high moisture vapor transmission, high hydrophilicity and good adhesion.

Specifically, the disclosure relates to an acrylate pressure sensitive adhesive comprising a polymer formed by a free radical polymerization of the following monomers:

(a) a hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group, the amount of the hydrophilic acrylic acid ester monomer being 10 to 30% of the total weight of all monomers; (b) a short-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOORi, where Ri is an alkyl group having 1 to 5 carbon atoms, the amount of the short-chain hydrophobic acrylic acid ester monomer being 50 to 70% of the total weight of all monomers;

(c) a long-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOOR₂, where R₂ is an alkyl group having 6 to 14 carbon atoms, the amount of the long-chain hydrophobic acrylic acid ester monomer being 10 to 35% of the total weight of all monomers; and

(d) an acryl monomer having a polar group copolymerizable with the monomers (a) to (c), the amount of the acryl monomer being 0.5 to 5% of the total weight of all monomers.

By combining one or more monomers selected from each of the above four type monomers and performing the free radical copolymerization reaction, an acrylate pressure sensitive adhesive which has not only good moisture vapor transmission rate but also good adhesion to both of dry and moist skins and exhibits properties such as low irritation and no adhesive residue can be obtained.

The disclosure further relates to a pressure sensitive adhesive tape having a high Moisture Vapor Transmission Rate (MVTR) property, comprising a layer of the disclosed acrylate pressure sensitive adhesive applied on a backing, wherein the pressure sensitive adhesive tape can have a MVTR (upright) of 1900g/m²/24hrs/37°C, measured after applying a 25 μηι thick dry adhesive film on a 25 μηι thick polyurethane film.

The disclosure further relates to a method of preparing the pressure sensitive adhesive tape, comprising: applying a layer of the disclosed acrylate pressure sensitive adhesive on a backing, and curing the acrylate pressure sensitive adhesive by a cross-linking reaction.

In addition, the disclosure further relates to a medical dressing tape comprising the disclosed pressure sensitive adhesive tape and a release film attached on the adhesive side of the pressure sensitive adhesive tape. The medical dressing tape exhibits an initial dry skin adhesion value of -lOOg/inch and an initial moist skin adhesion value of ~45g/inch, and exhibits a dry/moist skin adhesion value after 72 hours of ~170g/inch, and a dry/moist skin adhesion value after 168 hours of ~1 10g/inch (as used in the invention, "~" represents an average; since different peoples have much different skins, the adhesion to the skin is represented by an average).

The disclosed acrylate pressure sensitive adhesive and medical dressing tape has high moisture vapor transmission, good adhesion and superior hydrophilicity as well as low cost, and further exhibits advantages of high adhesion, little adhesive residue and low irritation to the skin and the like, and can maintain very high adhesive power even under a high humidity environment.

Description of the Drawings

Fig. 1 is a cross section view of the structure of an exemplified wound dressing tape.

Fig. 2 shows the relationships between intrinsic viscosity (I.V.) / moisture vapor transmission rate (MVTR) and the ratio of 2-(2-ethoxyethoxy) ethyl acrylate (EEEA) monomer.

Fig. 3 shows the internal clinical test results of the adhesion of the pressure sensitive adhesive of the invention.

Fig. 4 is a schematic view of the measuring method of the moisture vapor transmission rate (MVTR). While the above-identified drawings and figures set forth embodiments of the invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of this invention. The figures may not be drawn to scale.

Detailed Description

The disclosed acrylate pressure sensitive adhesive comprises a polymer formed by copolymerization of the following four monomers:

(a) a hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group;

(b) a short-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOORi, where Ri is an alkyl group having 1 to 5 carbon atoms;

(c) a long-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOOR₂, where R₂ is an alkyl group having 6 to 14 carbon atoms;

(d) an acryl monomer having a polar group copolymerizable with the monomers (a) to (c).

The copolymerization method may be a conventional free radical polymerization method.

In a specific embodiment, the specific conditions of the polymerization are as follows:

All monomers and solvents are successively added to a 1000-gallon reaction kettle at the ratios of monomer to solvent as shown in Table 2 and stirred at a rate of 70 revolutions/min. for 0.5 h. Nitrogen gas is introduced for about 15-30 min. so as to remove oxygen. The temperature of the materials (monomers, solvents and initiators) in the reaction kettle is then increased to 59 °C. An initiator (for example, AIBN) is dissolved in ethyl acetate at a ratio of 1 : 10 and added to the materials (see Table II). After about 10-15 min., the reaction is initiated and at this time, the temperature of the materials will be significantly increased by 1 -2 °C. The temperature is controlled at 60 °C, the stirring rate is controlled at 70 revolutions/min. and the reaction time is controlled at 24 hrs so that the conversion rate is 99 % or more. After the reaction is complete, the materials are finally cooled to 43 °C and discharged. The final resulting polymer has an I.V. between 0.9 and l . ldl/g and a weight average molecular weight Mw between 500,000 and 900,000.

The method for measuring the conversion rate is as follows:

3 g of the materials are taken out, and placed in an oven at 105 °C. After 2 hrs, the materials are removed from the oven and placed on a drying ware for 15 min. and then weighted. The conversion rate is calculated by the following equation:

Conversion rate = (weight of materials after baking/weight of materials before baking) / (weight of all monomers/weight of all materials before reaction) ^χ 100%

Some chemicals used in the disclosed adhesive are represented by abbreviations, and the details are shown in the following Table I. Table I Representative chemicals used and suppliers thereof

Table II. Ratios of the monomers, solvents and initiators (the ratios in the Table are weight ratios)

: EtOAc herein comprises EtOAc for dissolving AIBN.

The monomers for the acrylate pressure sensitive adhesive of the invention are described in detail below.

a) Hydrophilic acrylic acid ester monomer

In 1984, it was proposed by William R. Snyder and co-workers in WO 84/03837 that if a monomer having good hydrophilicity is polymerized with other monomers and even with hydrophobic monomers, the resulting polymer will also have good hydrophilicity so that adhesion to moist skin can be greatly improved. They proposed a weight percent of this monomer of 5 % to 30 % in the total monomers of the polymers. It is found by the present inventors that, among this type of hydrophilic monomer, the hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group can effectively enhance not only the hydrophilicity but also the moisture vapor transmission of the polymer.

The hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group of the invention includes, but is not limited to, trimethylolpropane diacrylate, pentaerythritol triacrylate, trimethylolpropane triacrylate, 2-hydroxyethyl acrylate (2-HEA), 4-hydroxybenzyl acrylate (4-HBA), 2- (2-ethoxyethoxy)ethyl acrylate (EEEA). EEEA, 2-HEA and 4-HBA are most preferable.

In addition, the effects of different types of hydrophilic monomers on the moisture vapor transmission are different from each other. As shown in Table III, in the case where the weight percents of monomers are same, EEEA containing an ethoxy group provides better effect of improving MVTR as compared with 2-HEA and 4-HBA containing a hydroxyl group. However, in view of the effect on other properties of the adhesive, for example, the decrease of persistent adhesion due to the increase of glass transition temperature, it is undesirable that the amount of this type of hydrophilic monomer is too high. Taking EEEA as an example, as can be seen from Fig.2, when the ratio of EEEA is increased from 5 % to 10 % of the total content of monomers, MVTR is increased by 56 g/m²/24hrs. However, when the ratio of EEEA is increased from 15 % to 22 %, MVTR is only increased by 5 g/m²/24hrs. On the other hand, when the concentration of EEEA is increased, the intrinsic viscosity (I.V.) is also greatly increased. However, too high intrinsic viscosity is found to decrease the adhesion to the surface of the skin, including initial adhesion and persistent adhesion. Taking the balance between the high moisture vapor transmission and other properties into comprehensive consideration, the ratio of the hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group is preferably 10% to 30%, and more preferably 15 % to 25 % of the total weight of all monomers.

Table III Effects of different hydrophilic monomers on the moisture vapor transmission rate (MVTR) (the ratios in the Table are weight ratios.)

Fig.4 shows an apparatus for measuring MVTR and a method for mounting the sample to be measured. The MVTR measurement is performed at a temperature of 37°C, according to TMS0759. The PU film used is a PU film supplied by Bayer. The specific steps and conditions are as follows:

1. Charge about 50 ml of water to a glass bottle.

2. Attach a sample on an adhesive side of an aluminum foil ring 5. Note that the sample should be placed in the center of an elliptical hole of the aluminum foil ring.

3. Place the first aluminum foil ring 5 (with the adhesive side upwards) on a planar surface so as to ensure that it is aligned with a second aluminum foil ring. Align the sample 3 with the center and attach it on the first aluminum foil ring. Then attach the second aluminum foil ring 2 (with the adhesive side downwards) on the sample 3 such that the elliptical holes of the two aluminum foil rings are overlapped. Press the aluminum foil/sample/aluminum foil with a finger so that they are leveled. Note that no wrinkle or gap is produced.

4. Place a rubber gasket 4 on a bottle mouth (see Fig.4) and then place the aluminum foil/sample/aluminum foil assembly on the gasket 4, with the adhesive side of the sample downwards if the sample is coated with adhesive, or the film side downwards if the sample has a film at a side and a fabric or unwoven fabric at the other side.

5. Screw a cover 1 of a bottle gently, place the bottle on a metal rack and put it into an aging box. Set the conditions of the aging box as follows: 4 hrs, 40°C ± 1°C (104°F ± 1.8°F), and a relative humidity of 20% ± 2%.

6. Screw down the cover 1 of the bottle in the aging box (place forefinger on the cover of the bottle and the sample so that the sample is leveled with the cover of the bottle and the production of the expansion is avoided), to place the rubber gasket 4 at an exact position.

7. Remove the sample from the aging box and weight it (initial weight Wl) immediately with an analytic balance having a precision of 0.01 g.

8. Put the bottle back to the aging box and leave it for at least 18 hrs.

9. Remove the sample from the aging box and weight it (final weight W2) immediately with an analytic balance having a precision of 0.01 g.

10. Calculate the moisture vapor transmission rate in g/m²/24hrs as follows.

MVTR = (Wl - W2) / S / T x 24 hrs

wherein

Wl = initial weight (g)

W2 = final weight (g)

S = test area of the sample (m²)

T = test time (hrs), which is greater than 18 hrs. b) Short-chain hydrophobic acrylic acid ester monomer and c) long-chain hydrophobic acrylic acid ester monomer

In addition to the above hydrophilic monomers, the present inventors has further studied the effects of a hydrophobic acrylic acid ester monomer on the moisture vapor transmission and adhesion of the pressure sensitive adhesive, and found that a good balance between the MVTR and adhesion can be achieved by classifying the hydrophobic acrylic acid ester monomer into a short-chain hydrophobic acrylic acid ester monomer and a long-chain hydrophobic acrylic acid ester monomer and properly controlling the ratio between the two monomers.

The short-chain hydrophobic acrylic acid ester monomer of the invention means an acrylic acid ester monomer represented by the structural formula CH₂=CHCOORi, wherein Ri is an alkyl group having 1 to 5 carbon atoms. The specific examples thereof includes, but is not limited to, methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and the like, preferably methyl acrylate, ethyl acrylate, butyl acrylate, and most preferably butyl acrylate (BA).

The long-chain hydrophobic acrylic acid ester monomer of the invention means an acrylic acid ester monomer represented by the structural formula CH₂=CHCOOR₂, wherein R₂ is an alkyl group having 6 to 14 carbon atoms. The specific examples thereof includes, but is not limited to, 2-ethyl-hexyl acrylate, isooctyl acrylate, octyl acrylate, decyl acrylate, dodecyl acrylate, tridecyl acrylate and the like, and preferably 2-ethyl-hexyl acrylate (2-EHA) and isooctyl acrylate. The ratio between b) short-chain hydrophobic acrylic acid ester monomer and c) long-chain hydrophobic acrylic acid ester monomer of the invention has a significant influence on the MVTR and adhesion of the pressure sensitive adhesive. As shown in Table IV, if the content of EEEA is kept unchanged, the ratio of BA is increased and the ratio of 2-EHA is decreased, the MVTR is greatly improved. When the weight percent of BA in all monomers is increased from 0 to 75 parts, the MVTR is improved from ~1500g/m²/24hrs to ~2200g/m²/24hrs, while the adhesion is significantly decreased. Therefore, the ratios of monomers must be kept within suitable ranges in order to achieve a good balance between the MVTR and adhesion. In the invention, the ratio of the short-chain hydrophobic acrylic acid ester monomer is preferably 50% to 70% and most preferably 55% to 65% by weight of the total monomers and the ratio of the long-chain hydrophobic acrylic acid ester monomer is preferably 10% to 35% and most preferably 20% to 30% by weight of the total monomers.

Table IV Effects of BA and 2-EH on MVTR and adhesion

The substrate for adhesion test: stainless steel plate

Method for measuring viscosity: 180° peeling-off, ASTMD3330

I.V.: intrinsic viscosity, measured according to TM0148

PU film: polyurethane film supplied by Vix Co., Korea, a 20.3 μηι PU blank film with a MVTR of 3000g/m²/24hrs

Method for measuring MVTR: TMS0759, at a temperature of 37°C

A specific method for measuring l.V. is as follows:

Measuring apparatus: LAUDA Proline PV24

1. Dissolve small amounts of samples in ethyl acetate to prepare a solution of about 0.25g of dry adhesive in 100 ml of ethyl acetate.

2. Put 25 mL of the solution prepared in the above 1 to an aluminum ware having a known weight, and bake it in an oven at 105°C for 2 hrs. Remove it from the oven and weight it. The actual weight wl of the dry adhesive in 25 mL of the solution is obtained by subtracting the weight of the aluminum ware from the total weight. 3. Flow 9.00 g of analytically pure ethyl acetate as a standard liquid through a capillary of the apparatus, and record the time tl required for the liquid to flow through the capillary. Then flow 9.00 g of the solution prepared in 1 through the same capillary and record the time t2.

4. Input the actual solid content wl of the solution, the time tl required for the standard liquid to flow through the capillary and the time t2 required for the sample to flow through the capillary into the corresponding software so as to obtain an intrinsic viscosity I.V. of the pressure sensitive adhesive.

Method for measuring viscosity: 180° peeling-off, ASTMD3330, measuring apparatus: IMASS SP-2000

1. Prepare a 4 inch x 10 inch steel plate.

2. Cut a 1 inch x l2 inch sample.

3. Firstly wipe a surface of the steel plate with isopropanol so as to remove dust and dirt.

4. Peel off the release paper from the sample, attach it on the surface of the steel plate with the adhesive side downwards and level it down with a scraper. Since the sample is longer than the steel plate, one end of the sample is exposed outside the steel plate.

5. Allow it to stand for 20min.

6. Fix the steel plate horizontally on a sample table of the apparatus, bend the end of the sample exposed outside the steel plate at 180° in a direction of the steel plate and fix it in a clamp of the apparatus. The parameters of the apparatus are set as:

Rate: 12 feet/min.

Measuring mode: peeling power

Delay time: 2 seconds

Measuring time: 5 seconds

7. Press the button "start" and start the test. Record the data upon stopping automatically. d) Acryl monomer having a polar group copolymerizable with the above monomers (a) to (c) The acryl monomer having a polar group copolymerizable with the above monomers (a) to (c) of the invention is preferably an acryl monomer having a high glass transition temperature, and more preferably an acryl monomer having a carboxyl group or amide group. The specific examples thereof include, but are not limited to, acrylamide, acrylic acid, methacrylamide, and methacrylic acid; preferably acrylamide and acrylic acid due to their stronger polarity; and more preferably acrylamide because it has no irritation. The weight ratio of the acryl monomer having a polar group copolymerizable with the above monomers (a) to (c) in all monomers is preferably 0.5% to 5% and more preferably 1% to 3%.

The present inventors have found that, in order to synthesize an acrylate pressure sensitive adhesive having high moisture vapor transmission rate, high adhesion and low adhesive residue, the monomers are mainly consisting of four types of monomers. The first type is a hydrophilic monomer having a hydroxyl group or an ethoxy group at a ratio of 10 to 30% of all monomers, which can mainly provide a certain moisture vapor transmission and further improve the adhesive power to the moist skin. The second type is a short-chain hydrophobic acrylic acid ester monomer represented by CH₂=CHCOORi, where Ri is an alkyl group having 1 to 5 carbon atoms, comprising 50 to 70% of the total weight of all monomers, such as methyl acrylate, ethyl acrylate, butyl acrylate and the like. Although this type of monomers are generally considered to be hydrophobic, they have better moisture vapor transmission as compared with the long-chain acrylic acid ester monomer (see Table IV), and can adjust the balance between the adhesion and the moisture vapor transmission and provide a certain cohesion strength. The third type is a long-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOOR₂, where R₂ is an alkyl group having 6 to 14 carbon atoms, the long-chain hydrophobic acrylic acid ester monomer comprising 10 to 35% of the total weight of all monomers. These long-chain monomers have good flexibility and can enhance the wettability of the adhesive and improve the initial adhesion and peeling power so as to improve the adhesion of the adhesive as a whole. The fourth type is a polar monomer such as acrylamide, acrylic acid, methacrylamide, methacrylic acid and the like, which generally has a polar group such as a carboxyl group or an amide group and can impart good cohesion strength to the adhesive, is easy to be crosslinked and can form firm hydrogen bonds with the bonded substrate. This type of monomer comprises 0.5 to 5% of the total weight of all monomers.

The acrylate adhesive, which is formed by combining one or more monomers selected from each of the above four type monomers and performing the free radical copolymerization reaction, can have not only good moisture vapor transmission rate but also good adhesion to both of dry and moist skins and further exhibit properties such as little irritation and no adhesive residue. The formulations as shown in Table V are several combinations which are preferable in the invention.

Table V Four optimal formulations of the invention and the measured results thereof

controlled by changing the polymerization reaction conditions such that l.V. is decreased. I.V.: intrinsic viscosity, measured according to TM0148

PU film: polyurethane film, supplied by Vix Co., Korea, a 20.3 μηι PU blank film with a MVTR of 3000g/m²/24hrs

Method for measuring MVTR: TMS0759, at a temperature of 37°C

Tegaderm std is Tegaderm Film, product 1626, available from 3M Company

Tegaderm HP is Tegaderm HP Transparent Dressing, product 9546, available from 3M Company MMD is Tegaderm Diamond Film, product 1686, available from 3M Company.

IV-3000 is a product of Smith & Nephew.

As can be seen from Table V, the MVTR of 1837 g/m²/24hrs for HPA-14/14-L and the MVTR of 1900 g/m²/24hrs for HPA-12/12-L are greatly higher than 900g/m²/24hrs for Tegadem std and 1 100 g/m²/24hrs for Tegaderm HP, and slightly higher than 1700 g/m²/24hrs for MMD, but lower than 2700 g/m²/24hrs for IV-3000. Lower than IV-3000 mainly due to the different thicknesses of substrate and adhesive. The thickness of the adhesive layer of IV-3000 is only 12μηι, which is a half of those of HPA- 14/14-L and HPA-12/12-L, and the moisture vapor transmission of the substrate is also higher than that of the substrate supplied by the supplier Vix Co. MMD is prepared by using a dot coating process, where the dry adhesive has a dot distribution on the PU film, so there are very great gaps permeable to the moisture vapor between the dots, which allows the MVTR of the adhesive tape to be greatly improved as compared with conventional continuous coating in the case of using the same pressure sensitive adhesive. In spite of this, it is somewhat inferior as compared with HPA-14/14-L or HPA-12/12-L which uses a pressure sensitive adhesive having high moisture vapor transmission and is prepared by a conventional continuous coating process. In addition, HPA-14/14-L and HPA- 12/12-L have a significant advantage in terms of the MVTR over Tegaderm std and Tegaderm HP with similar thicknesses of the substrate and adhesive layer and coating process. Pressure sensitive adhesive tape and medical dressing tape:

The disclosed acrylate pressure sensitive adhesive can be widely applied for various adhesive fields requiring high moisture vapor transmission rate, including industrial, medical and household adhesives.

As the most common mode of application, the disclosed acrylate pressure sensitive adhesive can be applied on a backing to form a pressure sensitive adhesive tape.

The backing may be a known and conventional backing, such as woven fabric, nonwoven fabric, paper or synthetic material. In order to provide a pressure sensitive adhesive tape having high moisture vapor transmission, the backing would have high moisture vapor transmission in addition to the provision of supporting function. Such backing can be made of a material with high moisture vapor transmission, such as a polyurethane film.

After the acrylate pressure sensitive adhesive is applied on a backing, the acrylate pressure sensitive adhesive is crosslinked and cured. The crosslinking may be carried out by the irradiation with a ray or by the addition of a cross-linking agent. The ray may be γ-ray or electron beam. The cross-linking agent may be one or more selected from the group consisting of a metal ion cross-linking agent, an aziridine crosslinking agent, and an isocyanate cross-linking agent, and the amount of the cross-linking agent is 0.01 to 5% of the total weight of all monomers. The disclosed acrylate pressure sensitive adhesive is particularly suitable for a medical dressing tape. When the pressure sensitive adhesive tape is used for a medical dressing tape, a release film may be attached on an adhesive side of the pressure sensitive adhesive tape so as to exhibit a very low and stable release force to the pressure sensitive adhesive.

The release film includes, but is not limited to, a release film made of a substrate having a coating layer. The substrate includes, but is not limited to, paper-based substrate, film-based substrate, aluminum foil-based substrate and polyolefin-based substrate. The above-mentioned release films each have a coating layer with a low surface energy on at least one surface thereof, and the coating layer comprises one or more of the following compounds: organosilicons, fluorides, fluorosilicon copolymers and compounds with a polyolefin long side chain. The release film is preferably a paper-based release film with a basic weight of 80 to 120g/m² available from Baoyan, loparex, etc.

As seen from Fig.1 , the medical dressing tape has a typical structure comprising a polyurethane film 1 , a pressure sensitive adhesive 2 and a release film 3 in this order from up to down. In one embodiment, the polyurethane film 1 is supplied from supplier, Vix Co., Korea and has a thickness of 20.3μηι. The pressure sensitive adhesive 2 is the acrylate pressure sensitive adhesive of the invention having an adhesive layer thickness of 25μηι and coated by transfer coating method. The release paper 3 is 80 g onesided release paper supplied from Baoyan, Shanghai. The crosslinking/curing and sterilization are carried out by γ-ray irradiation using a cobalt source from Jin Pengyuan radiation technology limited company, Shanghai, at a dose range of 25-50 kGy.

Internal clinical test

The internal clinical test is performed so as to further verify the properties of preferable examples of the invention in the application, that is, to evaluate the application of the samples of the examples on a healthy person and observe the MVTR, adhesion, adhesive residue, edge curling and skin response of the dressing tapes. Commercially available samples Tegaderm std, Tegaderm HP, IV-3000 and MMD are used as references. The process of preparing the samples is as follows:

The four formulations, HPA- 12, HPA- 12L, HPA- 14 and HPA- 14L, of the invention are selected and coated by the coating method: the adhesive is firstly applied on a release paper and a PU film is then applied on the adhesive side. The PU film has a film thickness of 20.3 μηι, the coating amount of the adhesive is 20g/m² and the dry adhesive film has a thickness of 25μηι. The above samples are generally sterilized and crosslinked by γ-ray, then cut into 2.5x8 cm specimens, and attached on backsides of volunteers for clinical test. 12 volunteers are selected and the attached samples are randomly distributed. The adhesion, adhesive residue, edge curling and skin response of the samples at the time of initial 0 h (TO), 72 h (T72) or 168 h (T168) are evaluated. The measuring method is as follows:

Steps:

1. A clinical research engineer firstly cleans the skin of backside of the subject with a diluted aqueous soap solution.

2. The clinical research engineer attaches 8 dressing tapes (dry) (one per sample) at left side of the backside of the subject. Small amounts of warm water is sprayed at right side of the backside of the subject and further 8 dressing tapes (wet) (one per sample) are attached. After 5 min., these samples are measured according to ASTMD3330 method and the results are recorded as TO. The samples have a size of 2.5x8 cm².

3. The clinical research engineer attaches the same dressing tapes in the same positions of the backside of the subject.

4. The subject is required by the clinical research engineer to return back to IHP testing room after 72 hrs so as to evaluate the floating rate and skin response of all samples. A half of samples are torn off so as to evaluate the adhesion and a ratio of adhesive residue (T72).

5. The subject is required by the clinical research engineer to return back to IHP testing room after 168 hrs so as to evaluate the samples. The remaining half of samples are torn off so as to evaluate the floating ratio, adhesion, ratio of adhesive residue and skin response (T168).

Fig. 3 shows the internal clinical test results of the adhesion of the pressure sensitive adhesive. The method for measuring the adhesion is similar to ASTMD3330, except for the change of the steel plate to the backside of a human body, 180° peeling-off and 12 inch/min. In Fig. 3, TO (Dry) represents an initial adhesion of the measured sample to the dry skin, TO (wet) represents an initial adhesion of the measured sample to the moist skin, T72 represents an adhesion of the measured sample to the dry or moist skin after 72 hrs and T168 represents an adhesion of the measured sample to the dry or moist skin after 168 hrs.

As can be seen from Fig.3, at TO, the adhesion values of the above measured samples to the skin are all greater than 40 g/inch. HPA- 12/12L or HPA- 14/14L have an initial adhesion value of 90 to 1 10 g/inch and preferably -l OOg/inch to the dry skin, an initial adhesion value of 30 to 50 g/inch and preferably ~45g/inch to the moist skin, an adhesion value of 160 to 190 g/inch and preferably -170 g/inch after 72 hrs to the dry or moist skin and an adhesion value of 100 to 120 g/inch and preferably ~1 l Og/inch after 168 hrs to the dry or moist skin. At T72 and T168, HPA- 12L and HPA- 14L have similar adhesion as compared with those of commercially available samples Tegaderm std, Tegaderm HP and IV-3000, and the adhesion values thereof are higher than that of the reference sample MMD, showing that the above two formulations have good persistent adhesion. HPA- 12 and HPA- 14 have an adhesion similar to that of MMD, but their adhesion values at T72 and T168 are lower than those of commercially available samples Tegaderm std, Tegaderm HP and IV-3000.

In addition to the adhesion, the adhesive residue and edge curling are also important factors affecting the properties of the dressing tape in the application. The rating of 0-5 is used to evaluate the adhesive residue and edge curling of the dressing tape, wherein 0 represents no adhesive residue or edge curling, 2- 4 represent incremental adhesive residue or edge curling, and 5 represents whole adhesive residue or sample peeling-off.

The adhesive residue and edge curling of the evaluated samples at T72 are shown in Table VI. As can be seen from the results for evaluating adhesive residue in the Table VI, the formulations HPA- 12L, HPA- 14L, HPA- 12 and HPA- 14 of the invention are observed to have no adhesive residue in the internal clinical test and thus have significant advantage as compared with the commercially available products, Tegaderm HP and IV-3000. As can be seen from the results for evaluating edge curling in the Table VI, the evaluated samples do not peel off within 72 h for the evaluation. At T72, HPA- 12L and HPA- 14L are observed to have no or slight edge curling, which are same as the commercially available products, Tegaderm HP, Tegaderm Std and rV-3000. HPA- 12 and HPA- 14 have an edge curling which is severer than the above samples, but still better than MMD.

The results for evaluating adhesive residue and edge curling of the evaluated samples at T 168 are shown in Table VII. As can be seen from the results for evaluating adhesive residue in the Table VII, the formulations HPA- 12L, HPA- 14L, HPA- 12 and HPA- 14 of the invention are observed to have no adhesive residue in the long-term internal clinical test of 168 h (that is, 7 days) and thus have significant advantage as compared with the commercially available products, Tegaderm HP and IV-3000.

As can be seen from the results for evaluating edge curling in the Table VII, HPA- 12L and HPA- 14L have an edge curling property similar to that of the commercially available products, Tegaderm HP and IV-3000 in the long-term test of 7 days (T168), wherein one or two samples peel off. HPA- 12 and HPA- 14 have an edge curling or peeling-off severer than the above samples, wherein 3-4 samples are peeled off.

Table VI Results of the adhesive residue and edge curling at T72 in the internal clinical test

Scores of edge HPA- HPA- 12- HPA- 14- IV

MMD HPA- 14 HP Std

curling at T72 12 L L 3000

0 9 7 10 12 1 1 12 12 1 1

1 1 4 1 1 1

2 2 1

3

4

5 1

Total number of

the samples 12 12 12 12 12 12 12 12 Table VII Results of the adhesive residue and edge curling at T 168 in the internal clinical test

By performing the comprehensive evaluation of the properties of the formulations of the invention at various time points, it can be seen that HPA- 12L and HPA-14L have better adhesion, fewer adhesion residues and better edge curling as compared with HPA-12 and HPA- 14. Furthermore, HPA-12L and HPA-14L have higher MVTR than HPA-12 and HPA-14. Therefore, they are desirably used as the new generation of dressing tape and adhesive tape products having higher moisture vapor transmission and fewer adhesive residues.

As described above, the invention discloses a pressure sensitive adhesive having high moisture transmission (MVTR~1900g/m²/24hrs), high adhesion (no peel-off for 7 days, no edge curling and a peeling power of 1 OOg/inch) and low irritation at the same time. It mainly consists of the four types of monomers, that is, the hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group, the soft short-chain and long-chain hydrophobic acrylic acid ester monomers, and the hard acryl monomer having a polar group. As compared with the similar commercially available products, the pressure sensitive adhesive of the present invention exhibits a great advantage in terms of the properties in the human body test, so it is the first choice of the next generation of medical dressing tapes, and has also wide application prospect in the other industrial adhesive fields such as electronic industry requiring high moisture vapor transmission rate.

Claims

Claims WHAT IS CLAIMED IS:

1 . An acrylate pressure sensitive adhesive comprising a polymer formed by a free radical polymerization of the following monomers:

(a) a hydrophilic acrylic acid ester monomer which has a hydroxyl group or an ethoxy group, the amount of the hydrophilic acrylic acid ester monomer being 10 to 30% of the total weight of all monomers;

(b) a short-chain hydrophobic acrylic acid ester monomer represented by formula CH₂=CHCOORi, where Ri is an alkyl group having 1 to 5 carbon atoms, the amount of the short-chain hydrophobic acrylic acid ester monomer being 50 to 70% of the total weight of all monomers;

2. The acrylate pressure sensitive adhesive according to claim 1, wherein the amount of the hydrophilic acrylic acid ester monomer (a) is 15 to 25% of the total weight of all monomers.

3. The acrylate pressure sensitive adhesive according to claim 1, wherein the amount of the short- chain hydrophobic acrylic acid ester monomer (b) is 55 to 65% of the total weight of all monomers.

4. The acrylate pressure sensitive adhesive according to claim 1, wherein the amount of the long- chain hydrophobic acrylic acid ester monomer (c) is 20 to 30% of the total weight of all monomers.

5. The acrylate pressure sensitive adhesive according to claim 1, wherein the amount of the acryl monomer (d) is 1 to 3% of the total weight of all monomers.

6. The acrylate pressure sensitive adhesive according to claim 1, wherein the hydrophilic acrylic acid ester monomer (a) is one or more selected from the group consisting of 2-(2-Ethoxyethoxy)ethyl acrylate, 2-Hydroxyethyl acrylate, and 4-Hydroxybenzoic acrylate.

7. The acrylate pressure sensitive adhesive according to claim 1, wherein the short-chain hydrophobic acrylic acid ester monomer (b) is one or more selected from the group consisting of methyl acrylate, ethyl acrylate, and butyl acrylate.

8. The acrylate pressure sensitive adhesive according to claim 1 , wherein the long-chain hydrophobic acrylic acid ester monomer (c) is one or more selected from the group consisting of 2-ethylhexyl acrylate and isooctyl acrylate.

9. The acrylate pressure sensitive adhesive according to claim 1 , wherein the acryl monomer (d) is an acryl monomer having a carboxyl group or an amide group.

10. The acrylate pressure sensitive adhesive according to claim 9, wherein the acryl monomer having a carboxyl group or an amide group is one or more selected from the group consisting of acrylamide, acrylic acid, methacrylamide, and methacrylic acid.

1 1. A pressure sensitive adhesive tape, comprising a layer of the acrylate pressure sensitive adhesive according to claim 1 applied on a backing, wherein the pressure sensitive adhesive tape has a MVTR (upright) of 1900g/m²/24hrs/37°C, measured after applying a 25 μηι thick dry adhesive film on a 20.3 μηι thick polyurethane film.

12. The tape according to claim 1 1 , comprising an initial dry skin adhesion value of 90- l l Og/inch and an initial moist skin adhesion value of 30-50g/inch, and a dry/moist skin adhesion value after 72 hours of 160- 190g/inch, and a dry/moist skin adhesion value after 168 hours of 100- 120g/inch.

13. The tape according to claim 12, comprising an initial dry skin adhesion value of -l OOg/inch and an initial moist skin adhesion value of ~45g/inch, and a dry/moist skin adhesion value after 72 hours of ~170g/inch, and a dry/moist skin adhesion value after 168 hours of ~1 l Og/inch.