MXPA98006737A - Sensitive adhesive to improved pressure for etique - Google Patents

Abstract

A pressure sensitive adhesive, which exhibits improved adhesive characteristics and improved convertibility. This adhesive is obtained by combining a typical styrenic block copolymer, mixed with adhesive resins, either natural or hydrocarbon based, and including a two-block copolymer of styrene and isoprene. The effect of this use of the two-block copolymer of styrene and isoprene, in addition to the expected result of reducing the tendency of conventional plasticizers to migrate from the adhesive and cause the staining of the label material or release liner therefrom, also has the unexpected results of substantially improving the operation with the temperature and a very substantial improvement in the capacity to be die

Description

ADHESIVE SENSITIVE TO IMPROVED PRESSURE, FOR. LABEL Technical Field This invention relates to novel compositions of pressure sensitive adhesive, and in particular to those pressure sensitive adhesives, which are more suitable for the manufacture of pressure sensitive labels.

BACKGROUND OF THE INVENTION Pressure sensitive adhesives are materials which have adherent properties at room temperature. The family of pressure sensitive adhesives adheres to a variety of different surfaces without the need of more than the pressure of a finger or hand. During the manufacture of the label, a sheet, formed of a front part, a layer of pressure sensitive adhesive, and a release liner, is passed through an apparatus which converts the sheet, to obtain labels and material for commercially useful labels. The process involved in the conversion operation includes, for example, printing, punching, and separating dies to leave the labels on a release liner, butt-cutting the labels on the release liner, marginal punching, drilling, bending, guillotine and the like. Die-cutting and butt cutting involve cutting the sheet at the front of the peel-off reverberant Other methods involve cutting through the label sheet completely, and include, for example, punching and punching, and guillotining. converting a sheet into a finished product is a function of the speed at which the different operations of the process can be carried out, although the nature of all the layers of the sheet can have -impact on the cost of the conversion capacity, historically the adhesive layer has been the main limiting factor in the ease and cost of the conversion operation.This is true due to the viscoelastic nature of the adhesive.The fact that the adhesive is viscoelastic prevents the precise and clear penetration of a die in the punching operations , and promotes adhesion to cutting blades and the like in any type of cutting operation.The fact that the adhesives can be viscous, also has an impact on matrix separation operations, which are often carried out after the punching operations. To date, achieving a good conversion capacity has not automatically coincided with the achievement of excellent adhesive performance. They must be formulated adhesives that fit predetermined needs. Important properties include film adhesion, tackiness, shear properties, viscosity at various temperatures and the like. Good general purpose adhesives can exhibit poor conversion capacity simply because the adhesive is difficult to cut cleanly. Such an adhesive can be attached to a die or blade. In the manufacture of labels, the die-cutting and matrix separation operations by necessity occur at a variety of speeds that fluctuate up to 300 meters per minute (1000 feet per minute) or more. Within that range, the adhesive can provide regions where a matrix will break despite the fact that successful matrix separation can occur at those speeds, on either side of the region. One goal is to provide adhesive systems wherein the adhesive can be neatly cut and the matrix separated at any substantially practical operating speed. Sasaki et al., U.S. Patent No. 5,290,842 shows a combination wherein the styrene-butadiene block copolymer was combined with a styrene-isoprene-styrene block copolymer, to show two separate and distinct vitreous transition temperature peaks, which is said to improve the conversion capacity. Other patents of interest are Do ney, US Patent No. 3,880,953; Tmdall, U.S. Patent No. 3,509,239; Feeney, U.S. Patent No. 4,060,503; and Korpman, U.S. Patent No. 3,932,328. This invention relates to improvements to the products described above and to solutions to some of the problems caused by them.

Brief Description of the Invention This invention provides a pressure sensitive adhesive, which exhibits an improved conversion capacity, i.e., the ability to achieve cutting of the adhesive in processing operations involving cutting through a material for labeling and adhesive to at least the release liner of the sheet, and at the same time, provide superior adhesive performance. These results can be obtained by combining a typical styrenic block copolymer, mixed with adhesive resins, either natural or hydrocarbon based, and including, in place of some or all of the plasticizers, a two-block copolymer of styrene and isoprene. Both styrene block copolymers and styrene-isoprene two-block copolymer are miscible together with the tackifier to produce a pressure-sensitive adhesive exhibiting a single glass transition temperature (Tv) value. The expected result of this partial replacement or of the plasticizer, is mainly the reduction of the tendency of the plasticizer to migrate from the adhesive and cause staining of the label material, the release liner, or both Also, however, this partial or complete replacement of the plasticizer results in unexpected results of a substantially higher temperature performance, and a very substantial improvement in the ability of the adhesive to be die-cut. Previous attempts to improve the die-cutting of the hot-melt pressure-sensitive adhesives have deleterious effects on other characteristics. For example, the increase in the content of the ream increases the delta value of the tangent of the pressure sensitive adhesive, compared to the value of the delta of the tangent, measured in the absence of an increase in the content of ream, thus increasing the ease of die cutting, but also significantly increasing the vitreous transition temperature, Tv The Tv can be increased to a point where the adhesive no longer maintains its pressure sensitivity characteristics. In addition, the application and service temperature ranges are condensed. The incorporation of or increase in the level of typical process oils will improve the processing capacity, but will decrease the capacity of the adhesive to be die cut, and decrease the performance to high temperature. The addition of a copolymer of two blocks of styrene-isoprene of low molecular weight improves the processability and improves the values of the delta of the tangent at 20 ° C, maintaining at the same time an acceptably low T. This improvement in the ability to be die-cut and the improvement in high-temperature operation are unexpected benefits. A preferred plasticizer is composed of a two-block copolymer of styrene and isoprene and a process oil in a weight ratio of about 1: 2 to 1: 0.5. Other objects and advantages of the invention will be apparent hereinafter.

Detailed Description of the Invention The present invention is generally directed to a pressure sensitive adhesive, formed from a mixture of basic polymers, in particular styrenic block copolymers, and an adherent. As is conventional in general, the styrenic block copolymers can be selected from any of several types, including, but not limited to styrene-isoprene-styrene block copolymers, such as Vector 4111 available from Dexco, styrene-isoprene-styrene / styrene-isoprene block copolymers, such as Kraton D1107 or Kraton D1112, manufactured and sold by Shell, copolymers of styrene-butadiene-styrene blocks such as Vector 6241D available from Dexco, styrene-butadiene-styrene / styrene-butadiene block copolymers, such as Kraton DI102 also from Shell, and styrene-butadiene block copolymers such as the Solprene 1205, manufactured and sold by Housmex, Inc. The above examples are unsaturated half block copolymers. The saturated half block copolymers are also useful, including but not limited to styrene-ethylene-butylene-styrene block copolymers, such as Kraton G1652, available from Shell, styrene-ethylene-butylene-styrene / block copolymers. styrene-ethylene-butylene, such as Kraton G1657, also from Shell, and styrene-ethylene-propylene-styrene / styrene-ethylene-propylene block copolymers, such as Septon 2063, manufactured by Kurarary, a Japanese company , and distributed in the United States by Arakawa Chemical Ind., Ltd. Conventional adhesive systems can generally include, as an example of many available selections, a normally solid adherent such as Wingtack 95, an aliphatic petroleum resin, manufactured by Goodyear. , or Escorez 1310 LC, an aliphatic petroleum resin, manufactured by Exxon, along with a plasticizer system, which usually includes a plasticizing oil such as Shell Flex 371, from Shell, or a normally liquid adherent, such as Wingtack 10, an oil aliphatic resin, available from Goodyear, or some combination of both. The invention calls for the addition of a two-block copolymer of styrene and isoprene having a low viscosity, preferably, a viscosity such that the two-block copolymer of styrene and isoprene is a liquid at 25 ° C. This two-block copolymer of styrene and isoprene used in the adhesive composition of the present invention has the configuration of A-B, wherein "A" is a block of styrene polymer and "B" is a polymer block of isoprene. These "two block" copolymers used in the present invention differ significantly from the "three block" polymers, which have an A-B-A configuration, with "A" and "B" each representing separate, distinct polymers. The two-block copolymers are also distinguished from the "radial polymers" (ABX), which consist of a central block "A" of a polymer with numerous arms or branches of a block "B" of a different polymer, extending from the block of the central polymer A. Preferred two-block copolymers of styrene and Isoprene of the present invention have an absolute molecular weight of less than 70,000, with the copolymers of two blocks of styrene and isoprene plus preferred having an absolute molecular weight of less than 50,000, or a polystyrene equivalent molecular weight of less than 70,000. Preferred two-block copolymers of styrene and isoprene AB of the present invention will have an A block of styrene that contributes from about 5% to about 50% of the mass of the copolymer molecule, more preferably about 5% until about 25 ?. In particular, LVCI-101 is one such commercially available two-block styrene and isoprene co-polymer from Shell, and the LIR-310 is another, available from Kuraray through Arakawa, for this purpose. The plasticizers referred to above and particularly the oils, have tended to be subject to migration, causing adverse effects on the performance of the substrate and the adhesive. Since the two-block copolymer of styrene and isoprene is substantially less migratory than these plasticizers, the addition of the styrene-isoprene copolymer copolymer in place of some or all of the normally liquid adhesive agents and / or plasticizing oils was expected had an effect of reducing staining or staining. What was not expected, however, was that the inclusion of the two-block copolymer of styrene and isoprene will provide wide ranges of end-use temperature, and at the same time a substantial improvement in the performance of die cutting.

To demonstrate and verify these effects, several formulations were prepared, generally using standard preparation methods and methods, according to the Examples 1 through 4 shown in the following tables, and certain test procedures were employed. Dynamic Mechanical Analysis or AMD was used to measure how a material responds to an imposed effort or deformation. This response will be a viscous, elastic or viscoelastic response. AMD was used to model and predict how a material will respond to real-world phenomena, such as coating, die cutting, aging, or other conditions. AMD is also used to predict the performance of the adhesive. The AMD test used to profile these pressure sensitive adhesives was carried out on 25 mm parallel plates, using a frequency of 10 radians per second and an effort of 1 or 5 percent, as indicated. The temperature scans were performed from 140 ° to -40 ° C, with an initial separation of 1.6 mm. The "tangent delta" is the ratio of the viscous response (G ") to the elastic response (G ') of a particular AMD curve.The vitreous transition temperature (T) is measured by a peak on the tangent curve. delta of the temperature sweep The operation of the die cut for the formulations referred to here, you can approximate by comparing the tan delta values at 20 ° C for the different formulations. A large delta tangent value at a given temperature indicates that a material will respond more viscously. The more viscous the response, the more likely a material will flow when subjected to an external force. Consequently, materials with larger values of the delta tangent at a temperature of interest will tend to be cut better with a die. They flow and separate when subjected to shear forces, compared to materials with low tan delta values, which rm and then recover. Consequently, the larger the value of the delta tangent at 20 ° C, the better the die cutting operation. The value of the delta tangent and the Tv of a formulation, together with various performance tests, will determine the suitability of a product for a pressure sensitive application, the addition of the styrene and isoprene two-block copolymer in the present invention, results in a pressure sensitive adhesive having an increased delta tangent value of 5% or greater, when compared to a similar pressure sensitive adhesive, which is identical, except that it lacks the addition of the copolymer of two blocks of styrene and isoprene.

The pressure sensitive adhesive compositions of the present invention can be formulated using any of the techniques well known in the art. A representative example of a prior art process involves placing all oily substances and any optional stabilizing substances in a jacketed mixing kettle, and preferably in a high-performance blender type Baker-Perkins or Day, equipped with rotors. The materials are mixed and the temperature of the mixture is raised to a range of about 121.1 ° C (250 ° F) to about 176.7 ° C (350 ° F). It should be understood that the precise temperature that must be used in this step will depend on the melting point of the particular ingredients. When the initial mixture has been heated, the mixture is purged with C02 at a low flow rate and the required adhesive agents, or resins, described above, are added slowly. When all the ingredients are melted at the desired temperature, the copolymers are added to the mixture. The mixture of the resulting pressure sensitive adhesive composition is stirred until the polymers are completely dissolved. Then vacuum is applied to remove any trapped air. The preparation of the coated material for the pressure sensitive adhesive test, ee describes how follow. The adhesive is coated on a release liner (SBL 42 SC F1U of Akrosil or equivalent), so that a continuous pattern of 5.52 centimeters (2.25 inches) wide is applied to 0.025 ± 0.0001 μm (1.0 ± 0.05 mils) ( dry weight of the adhesive). A polyester film of 0.005 μm (two thousandths of an inch) is laminated to the adhesive within 5 to 5.5 seconds (fabric speed of about 3 meters / min (10 feet / min)), to use a 180-inch peel test. ° and EFAC. One type of test, the detachment test 180 °, was designed to measure the strength of an adhesive bond to a standard stainless steel surface of 5.08 centimeters by 12.7 centimeters (2 inches by 5 inches). The strength of the joint was determined by measuring the force required to peel a strip of polyester material coated with adhesive from a test panel, at an angle of 180 ° after a drying time. The material was conditioned in a controlled environment (22.2 ± 2 ° C (72 ± 2 ° F) / relative humidity of 50 ± 3%), for a minimum of 12 hours before strips were cut from 2.54 centimeters by 25.4 centimeters ( 1 inch by 10 inches) of this one. Each strip was applied to the required stainless steel panel, with the adhesive side down, with a mechanical downward movement machine that used do-s passes of a roller 2 kilogram rubber (4.5 pounds), moving at 30.5 centimeters / in (12 inches / mm). Each sample was allowed to dry for 15 minutes, before being separated at a speed of 30.5 centimeters / min (12 inches / min) on a tensile tester. The detachment angle must be maintained at 180 °. The resulting detachment force was measured and reported in kilograms per linear centimeter (pounds per linear inch). A minimum of three trials had to be carried out and then the average was taken. Another type of test is the Cutting Adhesion Failure Temperature (TFAC) test. This is a measure of the internal resistance of an adhesive at elevated temperatures. A sample of polyester material coated with adhesive was applied to a standard stainless steel panel of 6.4 centimeters by 6.4 centimeters (2.5 inches by 2.5 inches). A constant load was applied and the temperature rose 1.56 ° C (3 ° F) per minute, until the sample came off the panel. The material was conditioned in a controlled environment (22.2 ± 2 ° C (72 ± 2 ° F) / relative humidity of 50 ± 3%) for a minimum of 12 hours, before cutting strips of 2.54 centimeters by 7.6 centimeters (1 inch) by 3 inches) of this one. Each strip was applied to the required stainless steel panel using sufficient pressure, so that a cohesive failure would result when the sample failed.

Each sample was allowed to dry for 1 hour before being placed in an oven capable of raising the temperature at a constant rate of 1.56 ° C (3 ° F) per minute. The test panels were hung vertically in the oven. A weight of 1000 grams (unless otherwise specified) was attached to each sample and allowed to hang until it failed. The oven must be conditioned at a constant temperature of 32.2 ° C (90 ° F) and kept so for 1 minute before raising the temperature. The test was carried out until all the samples were detached from their respective panels. The temperature at which the fault occurs was recorded. All faults must have a cohesive nature. A cohesive failure results when residual adhesive exists both on the surface of the test panel and on the coated substrate. An adhesive failure, indicates the delamination of either the coated substrate or the test panel, without residues, will not result in a representative value. This indicates the temperature at which the adhesive was peeled off from the test panel or substrate, and is not an indication of the internal strength of an adhesive. A minimum of 3 trials had to be carried out and then the average was taken. The pressure sensitive adhesive of the present invention preferably demonstrates a minimal increase or decrease in the TFAC. This preferable minimum decrease corresponds to a decrease of 2.78 ° C (5 ° F) or less for an adhesive pressure sensitive of the present invention, when compared to a similar pressure sensitive adhesive, which is identical except for the lack of addition of the styrene and isoprene two-block copolymer. As for each exemplary formulation, 180 ° peel tests and shear bond failure temperature tests were conducted. The results of those tests on the improved adhesives provided by this invention were compared with the results of those tests conducted on prior art adhesives as controls, and the results tabulated. The glass transition temperature T "and the delta tangent were also calculated and presented in the same tables. The pressure sensitive adhesives of the present invention preferably demonstrate a minimal increase in Tv. This minimum increase in Tv corresponds to an increase of 3 ° C or less for a preferred pressure sensitive adhesive of the present invention, when compared to a similar pressure sensitive adhesive, which is identical except for the lack of addition of the copolymer of two blocks of styrene and isoprene. Table 1 shows controls wherein, in addition to the use of Kraton 1107 as basic polymer, and Piccotac -95, of Hercules, as a normally solid adhesive agent, the mixture includes 15% by weight of conventional plasticizers.

Shellflex 371, a hydrocarbon process oil, was used as the conventional plasticizer in Control 1, while Wingtack 10, a normally liquid adhesive agent, was used as the conventional plasticizer in Control 2. In Example 1, LVSI-101 is the only ingredient used as a plasticizer. Example 2 includes the use of a combination of two thirds of LVSI-101 and one third of Shellflex 371 as a plasticizer, while Example 3 includes the use of a combination of one third of LVSI-101 and two thirds of Shellflex 371 as plasticizer. In each of these formulations, Irganox 1010, a phenol antioxidant, was added to reduce oxidative degradation during processing and to improve shelf life performance. The AMD test for each of the formulations shown in Table 1 was carried out at a tension of 5! .. As can be seen below, each of the examples has an adhesion of the film, equal to or greater than Control 2, which has the liquid adhesive agent as a plasticizer, and clearly superior to Control 1, which has the process oil as a plasticizer. In addition, as indicated by the Adhesion Failure Temperature figures due to the Shear Stress, the examples show a significantly higher high temperature resistance over conventional adhesives.

Also, although Control 2 does not have the highest delta tangent value at 20 ° C, its T "is also much larger than any of the examples. This fact indicates that the operation at ba temperature of this formulation, has been compromised to achieve this high value of the delta tangent. In fact, because the T »is higher than 15 ° C, while the T" of each of the examples is lower than 10 ° C, the adhesive or pressure sensitivity properties of the Control 2 formulation, They will be generally acceptable for most conventional applications. All the examples have T values comparable to those of Control 1, and all the examples show significant increases in delta tangent values at 20 ° C over Control 1. The pressure sensitive adhesives of the present invention exhibit a Only TV value. This unique value of T "is the result of the copolymer of two blocks of styrene and isoprene and the remaining elastomers that are miscible with the adhesive agent. Accordingly, the examples have wider temperature ranges than the controls and the improved delta tangent values indicate a substantial improvement in the ease of conversion.

Table 1 Table 2 compares Example 17 of Sasaki et al., U.S. Patent No. 5,290,842, herein "Control marked as 3, with a formulation provided by the invention, indicated as Example 4 The difference between the two formulations is the replacement of half the process oil, Shellflex 371, with the two-block copolymer of styrene and isoprene LVSI-101. The AMD test for each of the formulations shown in Table 2 was carried out at a tension of 1Sj. Again, as can be seen, the 180 ° peel test and the adhesion failure temperature tests due to shear stress gave much improved characteristics for Example 4, compared to Control 3, indicating a substantial improvement in properties adhesives on the formulation described in the Sasaki patent, which is said to have "excellent adhesive properties". In addition, the characteristics of the delta tangent indicate a much easier conversion, again on the formulation described by Sasaki, which is said to exhibit an "excellent conversion capacity".

Table 2 Table 2 (continued) Control 3 Example 4 Kraton D-1112 16.8 16.8 Escorez 1310 LC 38 Shellflex 371 24 12 Etilo 330"0.7 0.7 Cyanox LTDPb 0.7 0.7 Detachment at 180 ° in Steel 2.8 3.9 Stainless Failure Temperature of Adhesion 54.4 67.8 Due to Shear Stress ° C (° F) (130) (154) (° C) -7.12 -4.9 Tangent Delta at 20 ° C 0.556 0.696 "phenolic antioxidant; propionic acid antioxidant Finally, the effect of other low molecular weight polymers not containing styrene was compared, comparing the formulation of Example 1 above, with formulations using those polymers. In particular, they were selected low molecular weight isoprene rubber polymers LIR-30 and LIR-50, from Kuraray, through Arakawa, for Controls 4 and 5. Here again, the AMD test for each of the formulations shown in Table 3, they were carried out at a tension of 5%. Here the control formulations do not provide film adhesion or high temperature operation of a low molecular weight styrene-isoprene copolymer.

Table 3 Table 3 (continued) Although the adhesives described hereinbefore are effectively adapted to satisfy the above-mentioned objects, it should be understood that the invention is not intended to be limited to the specific preferred embodiments of the pressure-sensitive adhesives for labeling discussed above. In particular, without limitation, it should be understood that the formulations discussed herein, may include oils, fillers, diluents, pigments, dyes, indicators, stabilizers and other such additional ingredients as may be desired, to achieve certain desirable or desired properties, or to avoid certain undesirable or unwanted properties. Additionally, the formulations discussed herein may be free of organic solvents. The invention claimed herein, however, should be treated as including all reasonable equivalents of the subject matter of the appended claims.

Claims (10)

CHAPTER CLAIMEDICATORÍO Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following: CLAIMS:

1. A pressure sensitive adhesive, characterized in that it comprises: an elastomer selected from the group consisting of a block copolymer of styrene-isoprene-styrene, a block copolymer of styrene-isoprene-styrene / styrene-isoprene, a block copolymer of styrene-butadiene-styrene, a styrene-butadiene-styrene / styrene-butadiene block copolymer, a styrene-butadiene block copolymer, a styrene-ethylene-butylene-styrene block copolymer, a styrene-block copolymer ethylene-butylene-styrene / styrene-ethylene-butylene, and a styrene-ethylene-propylene-styrene / styrene-ethylene-propylene block copolymer, and mixtures thereof; an adhesive agent; and a two-block copolymer of styrene and isoprene.

2. The composition according to claim 1, characterized in that the pressure sensitive adhesive has a single glass transition temperature value.

3. The composition according to claim 2, characterized in that the pressure sensitive adhesive has a delta tangent value at 20 ° C, which was increased by at least 5% compared to the value of the delta tangent. measured in the absence of the two-block copolymer of styrene and isoprene, and wherein the vitreous transition temperature is not greater than 15 ° C, and where the failure temperature of the adhesion due to shear stress, did not decrease more than 2.78 ° C (5 ° F) compared to the failure temperature of the adhesion due to the shear stress measured in the absence of the copolymer of two blocks of styrene and isoprene.

4. The composition according to claim 2, characterized in that the pressure-sensitive adhesive has a delta tangent value at 20 ° C, which was increased by at least 10% compared to the value of the delta tangent measured in absence of the two-block copolymer of styrene and isoprene, and wherein the vitreous transition temperature is not greater than 15 ° C, and wherein the failure temperature of the adhesion due to shear stress did not decrease more than 2.78 ° C (5). ° F) compared with the adhesion failure temperature due to shear stress, measured in the absence of the two-block copolymer of styrene and isoprene. The composition according to claim 1, characterized in that the styrene-isoprene two-block copolymer has an absolute molecular weight less than 70,000. The composition according to any of claims 1 to 5, characterized in that the adhesive agent is present in an amount of about 5% to 70% by weight, and the two-block copolymer of styrene and isoprene is present in an amount from about 3% to 40% by weight. The composition according to claims 1 to 6, characterized in that the composition further contains a plasticizer, the plasticizer is composed of a dibrene styrene-isoprene copolymer and a normally liquid adhesive agent. The composition according to claim 7, characterized in that the plasticizer is composed of a two-block copolymer of styrene and isoprene and a process oil, in a weight ratio of about 1: 2 to 1: 0.0

5. 9. The composition according to claim 7, characterized in that the elastomer is present in an amount of about 10% to 55% by weight, the adhesive agent is present in an amount of about 5% to 70% by weight, the plasticizer is present in an amount of about 3% to 40% by weight, and the copolymer of two blocks of. Styrene and isoprene and the process oil are present in a ratio of approximately 1: 2 to 1: 0.5. 10. A sheet suitable for use as a label, characterized in that it comprises a front part, a layer of pressure sensitive adhesive, and a release liner, wherein the layer of pressure sensitive adhesive consists essentially of the composition of claims 1. to 9.