CH644147A5 - COMPOSITION USEFUL AS A PRESSURE SENSITIVE ADHESIVE AND ADHESIVE SHEET CONTAINING THE SAME. - Google Patents

Description

The present invention relates to a composition useful as a pressure-sensitive adhesive, which is a mixture of a poly (vinyllactam) and of a copolymer of: 1) an acrylic or methacrylic ester or a mixture of esters , and 2) an ethylenically unsaturated acid, the mixture having a unique combination of properties and characteristics.

Pressure sensitive adhesive compositions are commonly applied to a flexible backing or tape where they are supported during use, coating them in the form of a solution or dispersion in a suitable vehicle such as an organic solvent or water, or by coating them in the form of a thermoplastic product without a vehicle. In order to be useful, pressure sensitive adhesive compositions must have not only good adhesiveness, but also good consistency strength and the desired high degree of adhesion. All these properties are generally interdependent, a change in one of them usually causing a change in the others. Although various low molecular weight homopolymers of alkyl acrylates have long been known to be tacky or adhesive materials, they have insufficient coherence strength to be useful in themselves as adhesives sensitive to pressure, and in particular those of the type used on tapes or supports intended to adhere to the skin, and it is necessary to co-polymerize them with other selected monomers to obtain the desired combination of properties, as described for example in US Patent No. 3299010 to Samur.

It has generally been common practice for a long time to formulate pressure sensitive adhesive compositions by mixing together compatible components, each of which, by itself, lacks one or more of the required properties, but which combine to meet to requirements, as in the case of blends of two different water-insoluble and hydrophobic copolymers, as described in US Patent No. 4,045,517 to Guerin et al. It has also been proposed to react water-soluble poly (N-vinyllactams) with poly-carboxylic acids (including copolymers) to form water-insoluble compositions useful for a wide variety of purposes, such as this is described in US Patent No. 2901457 to Stoner et al. As Stoner and others point out, in column 4, lines 56-73, the reaction product described always has substantially the same properties and it contains the two polymer components in the same proportions, regardless of the proportions of the two used to form the product. The compositions of the invention, moreover, vary in properties and in proportions of the components according to the proportions of the raw materials. In US Patent No. 3,975,570 to Ono et al., It has been proposed to improve the moisture permeability of traditional pressure sensitive adhesives, which are copolymers of alkyl acrylates with acrylic acid or methacrylic, by mixing them hydroxyethylcellulose, and it has been reported that mixtures of such adhesives with poly (vinylpyrrolidone) do not exhibit improved moisture permeability.

It has now been found that it is possible to form pressure-sensitive and water-insoluble adhesive compositions having excellent adhesiveness, excellent consistency and excellent adhesion, and which can be applied to a support by coating equipment. of a traditional thermoplastic product, by preparing an optically clear mixture comprising a water-soluble poly (N-vinyllactam) and a water-insoluble copolymer of: A) an ester or a mixture of esters having the structure:

h2c = c-c = o

If where R 'represents hydrogen or methyl and Rx represents an alkyl having from 1 to 14 carbon atoms, and B) from 1 to 12%, preferably from 4 to 7% by weight of the copolymer of a monomer ethylene containing an acid group, the copolymer being viscous, having a glass transition temperature of less than 0 ° Cs having a viscosity of less than 50 Pa - s at 176.7 ° C, and being soluble in organic solvents (it is that is to say substantially free of reticula-

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644,147

tion); it therefore has, in itself, an insufficient coherent force to be useful as a pressure-sensitive adhesive.

The N-vinyllactams, the polymers of which can be used in the present invention, include those having the structure:

\

ch = ch2

where X represents an alkylene bridge having 3 to 5 carbon atoms, such as an l-vinyl-2-pyrrolidone, an l-vinyl-5-methyl-2-pyrroli-done, an l-vinyl-2-piperidone, and a N-vinyl-s-caprolactam; the polymers can have molecular weights between 10,000 and 1,000,000 or more. Preferred are 1-vinyl-2-pyrroli-done polymers. The amount of polymeric N-vinyllactam in the mixture can vary between 1 and 30% by weight of the mixture, depending on the precise copolymer present and the precise properties desired in the mixture.

The amount of the copolymer present in the mixture can be varied from 70 to 99% by weight of the mixture. Preferably, the pressure sensitive adhesive composition contains only the mixture of polymeric N-vinyllactam and the specified copolymer, although small amounts of conventional additives, such as stabilizers, may also be present to prevent deterioration of the mixture during treatment at elevated temperatures. Other traditional additives such as pigments, coloring agents and the like may also be present.

The acid-containing ethylenic monomer, which is co-polymerizable with the ester, may contain a carboxylic acid group or a sulfonic or phosphonic acid, such as acrylic or methacrylic acid, crotonic acid, l maleic acid, 2-sulfoethyl methacrylate and 1-phenylvinylphosphonic acid. Preferably, the acid group in the ethylenic monomer is carboxylic, acrylic acid being the monomer of choice. The ester with which the ethylenically unsaturated monomeric acid is copolymerized can, for example, be butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate and corresponding methacrylates or mixtures thereof. Esters of acrylic acid with mixtures of different alcohols having from 1 to 14 carbon atoms are preferred; alkyl acrylates are particularly preferred, where the alkyl groups have from 4 to 8 carbon atoms. The copolymer need not be a copolymer consisting only of the monomer of the specified ester and an ethylenic monomer containing an acid group, but it may contain up to 20% by weight of the total copolymer of another ethylenically unsaturated copolymerizable monomer. such as vinyl acetate, styrene or acrylonitrile. In general, the presence of such a third comonomer in the copolymer does not adversely affect the properties of the pressure sensitive adhesive and may be desirable in some cases to reduce the price or to increase the strength of consistency.

The mixing can be carried out by mixing together solutions or dispersions of polymeric N-vinyllactam and of the copolymer in any desired vehicles or solvents miscible with them, then removing the vehicle or solvent for example by evaporation. It is also possible to mix the polymer or the copolymer in traditional mixing equipment such as a two-cylinder mill or a Sigma paddle mixer.

In the case of mixtures containing quantities of polymeric N-vinyllactam close to the upper end of the specific range of proportions, i.e. from 10 to 30% by weight of the mixture, the pressure-sensitive adhesive composition exhibits increased moisture vapor permeability compared to compositions containing lower amounts of the polymer. This is an advantageous characteristic in the case of adhesive tapes or adhesive sheets having porous supports or reinforcements intended to be applied to the skin.

Although different polymers and copolymers are normally considered to be incompatible with each other when they are mixed, and incapable of forming a homogeneous mixture having the different properties of each of the components, the mixtures according to the invention are optically clear or, at the more, slightly cloudy in appearance, which highlights the fact that the mixtures are homogeneous at least to the point that there are no separate particles of the components exceeding 4000 Å in diameter. Thanks to this homogeneity, the low consistency force of the viscous copolymer is increased and the high fluidity is reduced by the presence,

in the mixture, polymeric N-vinyllactam which serves as a reinforcing agent.

The mixtures according to the invention can be applied to any traditional flexible support or reinforcement used in the manufacture of sheets and adhesive tapes either by spreading, coating or pouring a mixed solution or dispersing the mixture on the support, then removing the solvent or the liquid vehicle, for example by evaporation; however, the blends have the unique ability to be applied in the melt condition using conventional thermoplastic coating equipment, because the viscosities in this state are less than 100 Pa • s at 176.7 ° C; no hardening or crosslinking of the mixture is required. Traditional pressure-sensitive adhesives containing copolymers of alkyl acrylates and acrylic or methacrylic acid having a viscosity high enough to have an appropriate consistency force have a melt viscosity greater than 100 Pa • s at 176 , 7 ° C, and cannot be applied to a support in melted condition using traditional equipment.

In order to obtain maximum stability and shelf life of the mixture, it may be desirable to include in the pressure-sensitive adhesive composition, in addition to the polymeric N-vinyllactam and the copolymer, a small amount of a traditional stabilizer like 1% by weight of tetrakis- [2,4-ditert.-butylphenyl] -4,4'-biphenylenediphosphonite.

The specific examples which follow are intended to better illustrate the nature of the present invention without in any way limiting its scope. The molecular weights shown here are the peak molecular weights determined by gel permeation chromatography.

Example 1 to 15:

A series of copolymers of alkyl acrylates with varying proportions of acrylic acid have been prepared by conventional solution polymerization processes by dissolving the desired proportions of the monomers in a suitable solvent such as benzene or acetate. ethyl and using, as the polymerization initiator, a small amount (0.1% by weight of the monomers) of a free radical generator such as benzoyl peroxide or 2-t-butylazo-2-cyanopropane. Polymerization was carried out at 85-95 ° C to a high degree of conversion, on the order of 97%, to produce copolymers with insufficient coherence strength to be useful, in themselves, as sensitive adhesives at pressure having molecular weights between 62,000 and 566,000. These copolymers, after removal of the solvent by heating under vacuum, were of an aggressive viscous nature, but lacked a force of coherence sufficient to be pressure-sensitive adhesives satisfying in themselves. A table of the copolymers and their molecular weight is given below:

Weight report

Weight

No.

Acrylic ester of molecular acrylic ester

with acid

(103)

1

n-butyl

98: 2

82

2

n-butyl

97: 3

127

3

n-butyl

97: 3

200

4

n-butyl

95: 5

58

5

2-ethylhexyl

98: 2

566

6

2-ethylhexyl

97: 3

128

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10

15

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30

35

40

45

50

55

60

65

644,147

4

io

A series of homopolymers of l-vinyl-2-pyrrolidone, all soluble in water, but having different indicated molecular weights, were obtained from commercial sources as follows:

No

Polyvinylpyrrolidone Molecular Weight (103)

1

10

2

40

3

360

Mixtures of the two above series were then prepared in variable weight proportions, as indicated in Table I. In some cases, the acrylate copolymer, still in solution in the solvent where it had been polymerized, was mixed. to a solution of the poly (vinylpyrrolidone) in a compatible solvent such as chloroform, and the two solvents were then removed by volatilization at reduced pressure. In other cases, the solvent was first removed from the solution of the acrylate copolymer by heating at reduced pressure and the solvent-free copolymer was then mixed with the solvent-free polyvinylpyrrolidone by grinding on a water mill. two heated cylinders. The mixture was then applied to a standard support consisting of a film of polyethylene terephthalate (Mylar) of 0.038 mm, the mixtures formed in solution being applied by spreading the solution on the film before evaporation of the solvent and the mixtures formed by grinding. being applied by ca-landrage. The product, in each case, was a pressure sensitive adhesive tape having an adhesive layer of 0.025 to 0.076 mm thick.

The adhesive properties of the tape were then determined with "the results indicated in the table below. The stickiness of a probe was determined using a Polyken tester, as described in US Patent No. 3214971 having the following four functional parts: 1) a cylindrical steel probe attached to the spring loaded by compression of 2) a Hunter L series mechanical force gauge (Hunter Spring Company, brochure 750 / FG, revised in February 1961), 3) a ring having an opening slightly larger than the diameter of the probe, and 4) a ring support descending to bring the ring around the probe, then rising to remove the ring. The support moves at a speed of 0.254 cm / s. At the start of the test, the support is at its highest point and the ring rests on the support; thus, the opening in the ring is aligned with the probe placed below. For the implementation of the test, a strip of tape is placed on the ring, adhesive side facing down, and covering the opening of the ring. While the support is lowered by a synchronous motor, the adhesive surface exposed through the opening is brought into contact with the flat surface of the probe; thus, the ribbon and the ring attached to it are suspended on the probe, while the support continues its descent. The support then reverses its movement to raise the ring, thus separating the ribbon from the surface of the probe. The separation begins after a contact of 1 s between the probe and the adhesive. The force required to separate the tape from the probe is recorded on a measuring device. The value recorded is the value of the stickiness of the probe. The measurements were made using a load of 100 g / cm2.

The values of adhesion to flaking represent the forces required to remove a 2.54 cm wide adhesive tape from a stainless steel surface after contact with it for 2 min at a temperature of about 23.9 ° C. The tape is torn from the surface at an angle of 180 ° and at a speed of 30.5 cm / min.

The sliding resistance values are determined by providing a polished stainless steel tube, 2.54 mm in external diameter, mounted horizontally in a constant temperature chamber maintained at 40 + 1.1 ° C. The tube is provided with a slit 0.159 cm wide, which extends along its upper face parallel to its axis. An adhesive tape to be examined is wound on the tube 15.24 cm in length, its adhesive surface being in contact with the tube, and its free ends extend downwards approximately the same distance on the opposite sides. of the tube, the ribbon extending through the slit, perpendicular to it. Each length of the ribbon does not exceed 2.54 cm in width and at each of its lower ends a weight of 179 g / cm of ribbon width is attached. When the ribbon provided with the weights has been kept in the chamber for 15 min, it is broken transversely along the space in the slot and the time required, in hours, for the descent of each end over a distance of 1 is measured. , 27 cm. Slip resistance is expressed in hours.

The melt viscosity at 176.7 ° C is measured as Thermosel Brookfield viscosity (viscometer model RTV), using an SC4-27 spindle at 2.5 rpm.

The results are as follows:

Weight report

Weight

No.

Acrylic ester of molecular acrylic ester

with acid

(10 *)

7

2-ethylhexyl

97: 3

207

8

2-ethylhexyl

96.5: 3.5

304

9

2-ethylhexyl

96: 4

62

10

2-ethylhexyl

96: 4

84

11

2-ethylhexyl

96: 4

112

12

2-ethylhexyl

95.3: 4.7

105

13

2-ethylhexyl

94.5: 5.5

85

14

2-ethylhexyl

94.5: 5.5

105

15

2-ethylhexyl

93: 7

105

Table I

Acrylic copolymer No

Polyvinylpyrrolidone) No.

Copolymer weight ratio: PVP

Viscosity at 176.7 ° C (Pa-sxlO "3)

Suitability for stickiness of a 100 g / cm2 probe

Adhesion to steel (g / cm wide)

Sliding (h) round bar at 37.8 ° C

1

3

90:10

<0.1

404

5.55

100+

1

2

90:10

<0.1

930

53.3

0.3

3

2

87:13

<0.1

228

47.7

100+

4

2

93: 7

<0.1

336

49.4

1.1

4

2

90:10

<0.1

166

37.19

1.3

5

2

95: 5

<0.1

398

44.4

10.0

5

1

90:10

<0.1

300

36.63

100+

5

2

90:10

<0.1

262

35

100+

5

3

90:10

<0.1

238

20

100+

7

2

90:10

<0.1

140

-

100+

7

2

85:15

<0.1

152

-

100+

5 644147

Table I (continued)

Acrylic copolymer No

Poly (vinyl-pyrrolidone) N °

Copolymer weight ratio: PVP

Viscosity at 176.7e C (Pa-s x 10'3)

Suitability for stickiness of a 100 g / cm2 probe

Adhesion to steel (g / cm wide)

Sliding (h) round bar at 37.8 'C

8

2

90:10

<0.1

308

-

100+

8

2

85:15

<0.1

216

-

100+

9

1

94: 6

0.004

944

52.17

0.2

9

2

94: 6

0.0063

260

58.83

7.0

9

2

92: 8

0.015

250

38.85

11.4

9

3

98: 2

0.025

518

31.08

2.6

10

1

94: 6

0.007

972

82.14

0.2

10

2

96: 4

0.015

332

29.97

4.2

10

3

98: 2

0.058

684

51.06

3.8

11

1

94: 6

0.024

460

55.5

11.2

11

2

96: 4

0.038

262

28.86

16.6

12

2

96: 4

0.044

218

23.31

40.0

13

2

96: 4

0.022

296

33.3

22.0

14

2

96: 4

0.060

190

25.53

100+

15

2

96: 4

0.098

144

19.98

100+

Certain compositions of mixtures of alkyl acrylate copolymers containing higher proportions of PVP (poylvinyl-pyrrolidone) have water permeabilities twice or more superior (Table II) to those of adhesives sensitive to pressure to

unmixed acrylate base. The permeability to water of an adhesive is a desirable characteristic, in particular for adhesive care tapes for application to the skin. It is measured by the American standard ASTM E96 process E.

Table II

Acrylic copolymer No

Poly (vinyl-pyrrolidone) N °

Copolymer weight ratio: PVP

Suitability for stickiness of a 100 g / cm2 probe

Adhesion to steel (g / cm wide)

Sliding (h) round bar at 37.8 ° C

Water vapor transmission rate (g of water / cm2 / 24 h)

3

2

87:13

252

29.53

7.9

17

6

2

75:25

187

22.2

100+

14

6

3

75:25

143

18.44

100+

14.7

The mixture in each of the examples is an optically clear mixture and, as can be seen from the above, all of the mixtures form pressure sensitive adhesive tapes which are usable. Reading the table above, the effect produced by variations in the amount of acrylic acid present in the copolymer, the molecular weight of the copolymer, the relative proportion between the copolymer and the poly (vinylpyrrolidone) and the 45 weight The molecular nature of poly (vinylpyrrolidone) is also clear. The properties of the other mixtures according to the invention can easily be determined by extrapolation or interpolation from the results indicated above, bearing in mind that in general lesser amounts of the acid comonomers are required when a 50

sulfonic acid or phosphonic acid group is present, to achieve the same effect as if a carboxylic acid group is used.

Similar results can be obtained by using copolymers of acrylic acid with other alkyl acrylates or mixtures thereof and by using other water-soluble polyvinyllactams in place of poly (vinylpyrrolidone).

Of course, the invention is in no way limited to the embodiments described which have been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are executed according to the spirit and implemented in the context of protection as claimed.

R

Claims (10)

644,147 1. Composition useful as pressure-sensitive adhesive, characterized in that it consists of an optically clear mixture of: 1) a water-soluble polymer of a vinyllactam having the structure: I ch = ch2 where X represents an alkylene bridge having 3 to 5 carbon atoms, and 2) a viscous and water-insoluble copolymer comprising: A) an ester or a mixture of esters having the structure: h2c = c-c = 0? R1 where R 'represents hydrogen or methyl and Rj represents an alkyl having from 1 to 14 carbon atoms, and B) from 1 to 12% by weight, based on said copolymer (2), of a monomer ethylene containing an acid group, said polymer (1) being present in an amount between 1 and 30% by weight of said mixture, said copolymer (2) being present in an amount of 70 to 99% by weight of said mixture, having a glass transition temperature of less than 0 ° C, and being substantially free of crosslinking with a viscosity of less than 50 Pa • s at 176.7 ° C, thus possessing, in itself, a force of coherence insufficient to be useful as a pressure sensitive adhesive. 2. Composition according to claim 1, characterized in that X represents - CH2 - CH2 - CH2—. 2 3. Composition according to one of claims 1 or 2, characterized in that R 'represents hydrogen. 4. Composition according to one of the preceding claims, characterized in that Ri represents an alkyl having from 4 to 8 carbon atoms. 5. Composition according to claim 4, characterized in that Ri represents n-butyl. 6. Composition according to claim 4, characterized in that Ri represents 2-ethylhexyl. 7. Composition according to one of the preceding claims, characterized in that the above-mentioned monomer (B) contains a carboxyl group. 8. Composition according to one of the preceding claims, characterized in that the above-mentioned monomer (B) is acrylic acid. 9. Composition according to one of claims 2 to 8, characterized in that the quantity of the above-mentioned polymer is from 1 to 8% by weight of the above-mentioned mixture. 10. Adhesive sheet, characterized in that it consists of a flexible support with an adhesive layer sensitive to pressure formed by a mixture according to one of the preceding claims.