INTRINSICALLY NON-BLOCKING SHRINK SLEEVE MATERIAL

Abstract

Polymer compositions comprising stiff and tough star shaped styrene butadiene block-copolymers A1 and A2 can be used for making shrink films. Block copolymer A2 preferably has the structure

##STR00001##

with hard blocks S.sub.e and S.sub.i, hard random copolymer blocks (B/S).sub.Ae, soft random copolymer blocks (B/S).sub.B coupled by a coupling agent X.

Claims

1-17. (canceled)

18. A polymer composition comprising components (a), (b), and (c): a) 45 to 100 wt.-% of component a) consisting of: a1) 20 to 80 wt.-% of at least one star-shaped block copolymer A1 having: two short branches consisting of a single copolymer block (B/S).sub.Ai made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and having a glass transition temperature Tg.sub.A in the range from 40 to 90° C., and two long branches of the structure S.sub.t—[(B/S).sub.A].sub.n-(B/S).sub.Ai or [(B/S).sub.A].sub.n-(B/S).sub.Ai, linked (to one another via a coupling agent) by way of the inner blocks (B/S).sub.Ai, where the block S.sub.t is made from 95 to 100 wt.-% of vinylaromatic monomers and 0 to 5 wt.-% of dienes; the block [(B/S).sub.A].sub.n consists of one or more different or identical copolymer blocks (B/S).sub.A, each made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and have a glass transition temperature Tg.sub.Ain the range from 40 to 90° C.; n is a regular number of at least 1, and the block (B/S).sub.Ai is as defined above, wherein the block (B/S).sub.Ai has a number average molar mass Mn in the range of from 5000 to 15000 g/mol and the entire block [(B/S).sub.A].sub.n has a number average molar mass Mn of 50000 to 150000 g/mol; and a2) 80 to 20 wt.-% of at least one star-shaped block copolymer A2, which has two short branches of structure S.sub.e—(B/S).sub.B and two long branches of structure (B/S).sub.Ae-S.sub.i—(B/S).sub.B, linked (to one another via a coupling agent) by way of the blocks (B/S).sub.B, wherein the polymer blocks S.sub.e and S.sub.i are identical; the polymer blocks S.sub.e and S.sub.i are made from 95 to 100 wt.-% of vinylaromatic monomers and of from 0 to 5 wt.-% of dienes; the copolymer block (B/S).sub.Ae is made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and has a glass transition temperature Tg.sub.A in the range from 40 to 90° C.; and the homo- or copolymer blocks (B/S).sub.B are each made from 0 to 25 wt.-%, vinylaromatic monomers, and 100 to 75 wt.-%, dienes and have a glass transition temperature Tg.sub.B in the range from −90° to −60° C.; b) 0 to 55 wt.-% of at least one further thermoplastic polymer TP other than block copolymers A1 and A2; and c) 0 to 5 wt.-% of at least one additive or processing aid; where the total amount of components (a) and, if appropriate, (b) and/or (c) is 100% by weight, based on the entire polymer composition, and the glass transition temperature Tg is determined by DSC based on DIN EN ISO 11357-2:2014-07.

19. The polymer composition according to claim 18, wherein component a) consists of a1) 25 to 50 wt.-%, block copolymer A1 and a2) 50 to 75 wt.-%, block copolymer A2.

20. The polymer composition according to claim 18, wherein block copolymer A2 has a melt mass flow index (measured on a polymer melt at 220° C. and 5 kg load according to ISO 1133-1:2011) in the range of from 8 to 15 ml/10 min.

21. The polymer composition according to claim 18, wherein the proportion of the entirety of all of the blocks (B/S).sub.B (=soft phase) of block copolymer A2 is from 30 to 37 wt.-%.

22. The polymer composition according to claim 18, wherein the block (B/S).sub.B of block copolymer A2 is a copolymer block made from 1 to 25 wt.-%, vinylaromatic monomers and 99 to 75 wt. % dienes.

23. The polymer composition according to claim 18, wherein in block copolymer A2 the number average molar mass Mn of the block (B/S).sub.B is 5000 to 50000 g/mol; Mn of the block (B/S).sub.Ae is 30000 to 100000 g/mol; and Mn of the polymer blocks S.sub.e or S.sub.i is in the range from 5000 to 30000 g/mol.

24. The polymer composition according to claim 18, wherein star shaped block copolymer A2 has the following structure: ##STR00004## where S.sub.e, S.sub.i, (B/S).sub.Ae and (B/S).sub.B are as defined above and X is a coupling center, which is formed by reaction of the living anionic polymer chain ends with a polyfunctional coupling agent.

25. The polymer composition according to claim 18, wherein the copolymer blocks (B/S).sub.A, (B/S).sub.Ai, (B/S).sub.Ae and (B/S).sub.B of block copolymers A1 and A2 are composed of polymerized vinylaromatic monomers and of dienes with random distribution.

26. The polymer composition according to claim 18, wherein the number-average molar mass Mn of the block S.sub.t of block copolymer A1 is in the range from 3000 to 8000 g/mol.

27. The polymer composition according to claim 18, wherein the block [(B/S).sub.A].sub.n of block copolymer A1 consists of 2 to 10 different copolymer blocks (B/S).sub.A, where the blocks (B/S).sub.A differ in their molar masses and/or in their vinylaromatic/diene ratio.

28. The polymer composition according to claim 18, wherein the copolymer blocks (B/S).sub.A, and/or (B/S).sub.Ai of block copolymer A1 are made from 85 to 93 wt.-% of a vinylaromatic monomer and from 7 to 15 wt.-% of a diene.

29. The polymer composition according to claim 18, wherein star shaped block copolymer A1 has the following structure: ##STR00005## where S.sub.t, and (B/S).sub.Ai are as defined above, (B/S).sub.A1 and (B/S).sub.A2 are two different copolymer blocks (B/S).sub.A as defined above, and X is a coupling center, which is formed by reaction of the living anionic polymer chain with a polyfunctional coupling agent.

30. A process for the preparation of the polymer composition according to claim 18, comprising the step of melt mixing of component a) and optional components b) and/or c) by aid of a mixing apparatus at a temperature in the range of from 160° C. to 300° C.

31. A method of using the polymer composition according to claim 18 for the production of films.

32. Shrink film, produced from the polymer composition according to claim 18.

33. Star-shaped block copolymer A2 according to claim 18, wherein the star shaped block copolymer A2 has the following structure: ##STR00006## where S.sub.e, S.sub.i, (B/S).sub.Ae and (B/S).sub.B are as defined above and X is a coupling center, which is formed by reaction of the living anionic polymer chain ends with a polyfunctional coupling agent, and the proportion of the entirety of all of the blocks (B/S).sub.B (=soft phase) of block copolymer A2 is from 31 to 35 wt.-%.

34. A process for the preparation of block copolymer A2 according to claim 33 characterized by: a) a double initiation, b) a coupling step after the addition and polymerization of a diene and optionally a vinylaromatic monomer used for the preparation of homo- or copolymer block (B/S).sub.B, and c) the second initiation process placed before the addition and polymerization of the vinylaromatic monomer used for the preparation blocks S.sub.i and S.sub.e, wherein the molar ratio of the first and the second initiation is from 0.9:1 to 1.5:1.

Description

FIGURES

[0152] FIGS. 1 to 5 show TEM pictures which show the morphology of blends of stiff and tough SBC block copolymers according to the prior art and blends according to the invention.

[0153] For the preparation of the films shown in FIGS. 1 to 3, 100 nm slices taken from compression molded plates (5 min, 200° C., 40 bar+1d annealing at 25° C.) of the blends were stained with OSO.sub.4 (-> the butadiene rich phases are black, the styrene phases are white). The voltage of the equipment was 200 kV.

[0154] For the preparation of the films shown in FIGS. 4 and 5, the components used for the blends were pre-compounded on a counter-rotating twin-screw extruder at from 200° C. to 220° C. and subsequently casted as a 225 μm thick film using a single screw extruder.

[0155] Then, the films were stretched on a tentering frame by fivefold at 90° C. Next, the films were stained with OSO.sub.4 and cut in form of slices of 100 nm thickness and investigated in TEM at 200 kV.

[0156] FIG. 1 shows a TEM picture of a film made from a blend according to current state of the art (US 2011/098401 A1), 70 wt.-% tough star-shaped SBC block copolymer B 16 mixed with 30 wt.-% of stiff linear SBC block copolymer A.

[0157] The morphology of this prior art blend is lamellar.

[0158] FIG. 2 (opposite to extrusion direction) and 3 (parallel to extrusion direction) show TEM pictures of a cross-section of a film made from a blend according to the invention, tough SBC A2-1 mixed with 40 wt.-% stiff SBC A1. The TEM pictures according to FIGS. 2 and 3 show a cylinder morphology, which is worm-like distorted due to the matrix dilution effect of the added stiff component (block copolymer A1) preventing regular packing of the domains.

[0159] FIG. 4 shows a TEM picture of a film made from a blend according to US 2011/098401 A1 (70 wt.-% tough star-shaped SBC block copolymer A2-4 mixed with 30 wt.-% of stiff linear SBC block copolymer A). The TEM picture shows a clear laminar morphology with chances for the butadiene-rich soft phases (dark regions) to be on the surface and to cause stickiness.

[0160] FIG. 5 shows a TEM picture of a film made from a further blend according to the invention (70 wt.-% tough star-shaped SBC block copolymer A2-1 mixed with 30 wt.-% of stiff SBC block copolymer A1). The TEM picture shows a different morphology with a more continuous styrene-rich hard phase and the butadiene-rich soft phases dispersed in that, resulting in a surface dominated by styrene-rich hard phases with less stickiness because of the higher T.sub.g. Due to the OSO.sub.4, the styrene appears white and the butadiene appears black in the TEM picture. The darker the phase, the more butadiene is present in the phase.

[0161] Determination of the Coefficient of Friction (COF)

[0162] The tough SBC block copolymers A2-1, A2-3 and A2-4 were separately blended with 10, 20, 30 and 40 wt.-% of the stiff SBC block copolymer A1 on a counter-rotating twin-screw extruder at from 200° C. to 220° C. and extruded to films of 50±20 μm thickness.

[0163] Next, the coefficient of friction (COF) of the films was determined by using standard ISO 8295 in which a 200 g part is wrapped with the film and pulled by a force measurement machine over a surface covered with the same type of film in a horizontal direction at a speed of 100 mm/min. The frictional force needed to pull this part forward is measured and summarized in Table 6 below. The static COF (= at the start) and dynamic COF (=once in motion) are measured. The topside of the film is pulled over the backside of the film (COF.sub.IN-OUT), as this method simulates the unwinding force from a roll. Indeed, during winding of a roll at production, the backside is rolled on the topside of previous layer. An average value of 5 repetitions was calculated as final value. The lower the COF, the lower the stickiness.

TABLE-US-00006 TABLE 6 Coefficient of friction of tested Films Dynamic COF.sub.IN-OUT Static COF COF 90% A2-4-10% A1 0.72 0.66 80% A2-4-20% A1 0.64 0.58 70% A2-4-30% A1 0.30 0.32 60% A2-4-40% A1 0.48 0.49 90% A2-3-10% A1 0.16 0.22 80% A2-3-20% A1 0.23 0.24 70% A2-3-30% A1 0.17 0.16 60% A2-3-40% A1 0.17 0.15 90% A2-1-10% A1 0.31 0.29 80% A2-1-20% A1 0.23 0.24 70% A2-1-30% A1 0.14 0.17 60% A2-1-40% A1 0.22 0.25

[0164] The test results show that the copolymer blends according to the invention (A2-1/A1 and A2-3/A1) have a significantly lower stickiness in comparison to blends comprising a block copolymer (A2-4) according to the state of the art.