Intrinsically non-blocking shrink sleeve material
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 with hard blocks S e and S i , hard random copolymer blocks (B/S) Ae , soft random copolymer blocks (B/S) B coupled by a coupling agent X.
1. 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) Ai made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and having a glass transition temperature Tg A in the range from 40 to 90° C., and two long branches of the structure S t —[(B/S) A ] n -(B/S) Ai or [(B/S) A ] n -(B/S) Ai , linked (to one another via a coupling agent) by way of the inner blocks (B/S) Ai , where the block S t is made from 95 to 100 wt.-% of vinylaromatic monomers and 0 to 5 wt.-% of dienes; the block [(B/S) A ] n , consists of one or more different or identical copolymer blocks (B/S) A , each made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and have a glass transition temperature Tg A in the range from 40 to 90° C.; n is a regular number of at least 1, and the block (B/S) Ai is as defined above, wherein the block (B/S) Ai has a number average molar mass M n in the range of from 5000 to 15000 g/mol and the entire block [(B/S) A ] n has a number average molar mass M n of 50000 to 150000 g/mol; and
a2) 80 to 20 wt.-% of at least one star-shaped block copolymer A2, which has in essence two short branches of structure S e —(B/S) B and two long branches of structure (B/S) Ae —S i —(B/S) B , linked (to one another via a coupling agent) by way of the blocks (B/S) B ,
wherein the polymer blocks S e and S i are identical; the polymer blocks S e and S 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) Ae is made from 65 to 95 wt.-% vinylaromatic monomers and 35 to 5 wt.-% dienes and has a glass transition temperature Tg A in the range from 40 to 90° C.; and the homo- or copolymer blocks (B/S) B are each made from 0 to 25 wt.-%, vinylaromatic monomers, and 100 to 75 wt.-%, dienes and have a glass transition temperature Tg 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 present, (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.
2. The polymer composition according to claim 1 , wherein component a) consists of a1) 25 to 50 wt.-%, block copolymer A1 and a2) 50 to 75 wt.-%, block copolymer A2.
3. The polymer composition according to claim 1 , 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.
4. The polymer composition according to claim 1 , wherein the proportion of the entirety of all of the blocks (B/S) B (=soft phase) of block copolymer A2 is from 30 to 37 wt.-%.
5. The polymer composition according to claim 1 , wherein the block (B/S) B of block copolymer A2 is a copolymer block made from 1 to 25 wt.-%, vinylaromatic monomers and 99 to 75 wt.-% dienes.
6. The polymer composition according to claim 1 , wherein in block copolymer A2 the number average molar mass Mn of the block (B/S) B is 5000 to 50000 g/mol; Mn of the block (B/S) Ae is 30000 to 100000 g/mol; and Mn of the polymer blocks S e or S i is in the range from 5000 to 30000 g/mol.
7. The polymer composition according to claim 1 , wherein star shaped block copolymer A2 has the following structure:
where S e , S i , (B/S) Ae and (B/S) 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.
8. The polymer composition according to claim 1 , wherein the copolymer blocks (B/S) A , (B/S) Ai , (B/S) Ae and (B/S) B of block copolymers A1 and A2 are composed of polymerized vinylaromatic monomers and of dienes with random distribution.
9. The polymer composition according to claim 1 , wherein the number-average molar mass Mn of the block S t of block copolymer A1 is in the range from 3000 to 8000 g/mol.
10. The polymer composition according to claim 1 , wherein the block [(B/S) A ] n of block copolymer A1 consists of 2 to 10 different copolymer blocks (B/S) A , where the blocks (B/S) A differ in their molar masses and/or in their vinylaromatic/diene ratio.
11. The polymer composition according to claim 1 , wherein the copolymer blocks (B/S) A , and/or (B/S) 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.
12. The polymer composition according to claim 1 , wherein star shaped block copolymer A1 has the following structure:
where S t , and (B/S) Ai are as defined in claim 1 , (B/S) A1 and (B/S) A2 are two different copolymer blocks (B/S) A as defined in claim 1 , and X is a coupling center, which is formed by reaction of the living anionic polymer chain with a polyfunctional coupling agent.
13. A process for the preparation of the polymer composition according to claim 1 , 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.
14. A method of using the polymer composition according to claim 1 for the production of films.
15. Shrink film, produced from the polymer composition according to claim 1 .
16. Star-shaped block copolymer A2 according to claim 1 , wherein the star shaped block copolymer A2 has the following structure:
where S e , S i , (B/S) Ae and (B/S) B are as defined in claim 1 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) B (=soft phase) of block copolymer A2 is from 31 to 35 wt.-%.
17. A process for the preparation of block copolymer A2 according to claim 16 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) B , and
c) the second initiation process placed before the addition and polymerization of the vinylaromatic monomer used for the preparation blocks S i and S e , wherein the molar ratio of the first and the second initiation is from 0.9:1 to 1.5:1.