Thermoplastic block copolymers, their preparation and use in pressure sensitive adhesives for labels

Abstract

The application belongs to the field of polymers and specifically discloses a thermoplastic block copolymer, which comprises a block copolymer A1 shown in formula I ((A-D)n-X) and a block copolymer A2 shown in formula II (A-D). In formula I and formula II, A is a vinyl aromatic polymer block, D is two kinds of conjugated diene copolymers, n is an integer greater than 2, and X is a residue of a coupling agent; the random structure content in D is 85-95%; in A-D, the weight of polyisoprene is above 58% by weight, the polybutadiene content is below 27% by weight; the balance is polystyrene; the number average molecular weight of the block copolymer A1 is 250-300 thousand; the number average molecular weight of the block copolymer A2 is 80-90 thousand; in the thermoplastic block copolymer, the content of the block copolymer A1 is 15-30% by weight. The application also comprises a preparation method of the polymer and an application of the polymer in pressure-sensitive adhesive. The application can have excellent initial adhesion, die cutting and low-temperature performance based on the combination of the structure and parameters of the polymer.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hot melt pressure sensitive adhesive, and particularly relates to a thermoplastic block copolymer for label hot melt pressure sensitive adhesive and a preparation method and application thereof. BACKGROUND

[0002] Hot melt pressure sensitive adhesive is a kind of adhesive with the characteristics of hot melt adhesive and pressure sensitive adhesive, which is solvent-free, pollution-free and convenient to use. The adhesive is coated in a molten state, and after hardening, it can be quickly bonded by applying light pressure, and it can be easily peeled off without polluting the surface of the adherend. The main application industries of domestic hot melt pressure sensitive adhesive include labels, tapes, sanitary products, packaging, surface protection films, wood processing, wallpaper and shoemaking, among which the label adhesive is the fastest growing field.

[0003] Hot melt pressure sensitive adhesive label, also known as self-adhesive label, is a composite material with paper, film or special material as the surface material, adhesive coated on the back, and silicon-coated paper as the protective paper. After printing, die cutting and other processes, it becomes a finished label. When used, it only needs to be peeled off from the backing paper and lightly pressed onto the surface of various substrates, or it can be automatically applied on the production line using a labeling machine.

[0004] The main components of the basic structure of hot melt pressure sensitive adhesive label are surface material, adhesive, silicon-coated layer and backing paper. The adhesive is a very important component of hot melt adhesive label, and the die cutting, coating and bonding properties of the label are related to the performance and quality of the adhesive. Hot melt pressure sensitive adhesive for labels is most widely used. Hot melt pressure sensitive adhesive is an adhesive with ABA type block copolymer thermoplastic elastomer as the main component. The representative thermoplastic elastomers are styrene-butadiene-styrene (SBS) block copolymer and styrene-isoprene-styrene (SIS) block copolymer. These elastomers not only impart sufficient elasticity and cohesive strength to the pressure sensitive adhesive like other rubber elastomers, but also have the characteristics of melting after heating and making the pressure sensitive adhesive have hot melt coating properties. Although these block copolymers have thermoplasticity and rubber elasticity, good creep performance and are suitable for preparing pressure sensitive adhesive, the important properties of label pressure sensitive adhesive include initial adhesion, peel strength, viscosity, die cutting performance, bonding at various temperatures, etc. It is difficult to meet all these comprehensive properties at the same time with a single block copolymer.

[0005] The Chinese patent document with publication number CN102504735A discloses a preparation method of hot melt pressure sensitive adhesive: weigh dioctyl phthalate and naphthenic oil and put them into a reaction kettle for heating, then put tetra(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) and tris(2,4-di-tert-butylphenyl) phosphite into the reaction kettle, wait until the temperature reaches 120-130℃, crush SBR rubber in a crusher, slowly add SIS and SBR rubber, then add tackifying resin three times, heat to 130-170℃, keep stirring for 60-100 minutes, and filter and cool to obtain the finished product. The hot melt pressure sensitive adhesive prepared by the method has complex preparation process, low finished product peeling strength and poor low temperature resistance. The Chinese patent document with publication number CN109679529A discloses a preparation method of label adhesive capable of high-speed die cutting, wherein citric acid ester, antioxidant, SBR rubber, hydrogenated C5 / C9 copolymer petroleum resin, rosin modified phenolic resin and functional additives are sequentially added into a stainless steel reaction kettle, the temperature is controlled within 200℃, stirring is performed for 30-60 minutes, vacuum is extracted to-0.085MPa, and the hot melt pressure sensitive adhesive is obtained by discharging and cooling, but the hot melt pressure sensitive adhesive prepared by the method still has problems of low initial tack, low die cutting rate and the like. SUMMARY

[0006] In view of the problems of the existing hot melt pressure sensitive adhesive, such as unsatisfactory initial tack, die cutting and low temperature performance, the first object of the present application is to provide a thermoplastic block copolymer, which aims to improve the initial tack, die cutting and low temperature performance.

[0007] The second object of the present application is to provide the preparation of the thermoplastic block copolymer and the application of the thermoplastic block copolymer in hot melt pressure sensitive adhesive.

[0008] The third object of the present application is to provide hot melt pressure sensitive adhesive containing the thermoplastic block copolymer and labels thereof.

[0009] The existing hot melt pressure sensitive adhesive cannot well balance the adhesion (initial tack), die cutting and low temperature performance. For example, the hot melt pressure sensitive adhesive with good viscoelasticity and high cohesion has high peeling strength, but poor initial tack, large melt viscosity, poor processability, and easy die cutting. The hot melt pressure sensitive adhesive with small elasticity, low cohesion and high flowability has good initial tack, coating and die cutting performance, but poor shear resistance and poor peeling strength. In view of the problems, the present application provides the following improved scheme:

[0010] A thermoplastic block copolymer, comprising a block copolymer A1 shown in formula I and a block copolymer A2 shown in formula II:

[0011] (A-D)n-X (I)

[0012] A-D (II)

[0013] In formula I and formula II, A is a vinyl aromatic polymer block, D is two kinds of conjugated diene copolymers, n is an integer greater than 2, and X is a residue of a coupling agent; the random structure content in D is 85-95%; and the weight content of polyisoprene in A-D is 58% or more, the polybutadiene content is 27% or less, and the balance is polystyrene.

[0014] In A-D, the weight content of polyisoprene is 58% or more, the polybutadiene content is 27% or less, and the balance is polystyrene.

[0015] The number average molecular weight of the block copolymer A1 is 250-300 thousand.

[0016] The number average molecular weight of the block copolymer A2 is 80-90 thousand.

[0017] In the thermoplastic block copolymer, the content of the block copolymer A1 is 15-30% by weight.

[0018] The present application provides a polymer composition with a completely new structure and parameters, and further finds that based on the combination of the structure and parameters of the polymer, synergistic effect can be achieved, and excellent initial adhesion, die cutting and low temperature performance can be achieved.

[0019] In the present application, the combined control of the block structure of the polyaryl ethylene-random two conjugated olefins in the polymer A1 and the polymer A2 and the proportion of the polymer parameters is the key to synergistically improving the initial adhesion, die cutting and low temperature performance of the polymer.

[0020] In the present application, the vinyl aromatic polymer block of A can be a block formed by polymerization of styrene or styrene monomers with substituents on the benzene ring. Further, A can be a polystyrene block.

[0021] In the present application, D can be a random block formed by polymerization of two or more conjugated diene monomers; preferably, D is a random copolymer of butadiene and isoprene (B / I random block).

[0022] In A-D, the weight content of polyisoprene is 59-65 wt.%, the polybutadiene content is 15-26%, and the balance is polystyrene.

[0023] Preferably, the tensile strength of the block copolymer A2 is less than 1 MPa.

[0024] In the present application, in the block copolymer A1, n is 3 or 4.

[0025] Preferably, the tensile strength of the block copolymer A1 is 15-25 MPa.

[0026] In the present application, in the thermoplastic block copolymer, the content of the block copolymer A1 is 20-25% by weight.

[0027] In the present application, the viscosity of the thermoplastic block copolymer in 25% toluene solution at 25℃ is not more than 400 mPa.s;

[0028] Preferably, the melt flow rate of the thermoplastic block copolymer is greater than or equal to 20 g / 10 min, preferably 22-26 g / 10 min;

[0029] Preferably, the tensile strength of the thermoplastic block copolymer is 2-4 MPa;

[0030] Preferably, the elongation at break of the thermoplastic block copolymer is 1000-1300%, and the tensile stress at 300% elongation is 0.2-0.5 MPa.

[0031] The present application also provides a preparation method of the thermoplastic block copolymer, which is obtained by compounding block copolymer A1 and block copolymer A2;

[0032] Preferably, the preparation step of the block copolymer A2 is:

[0033] The vinyl aromatic hydrocarbon, polymerization solvent, alkyl lithium initiator, and regulator are pre-polymerized to obtain A-Li; then the temperature of the polymerization system is controlled at 65-80℃, and two kinds of mixed monomers of conjugated dienes are continuously added to carry out the second stage polymerization to obtain A-D-Li; then the polymerization is terminated to obtain the block copolymer A2 of A-D;

[0034] Preferably, the preparation step of the block copolymer A1 is:

[0035] The A-D-Li obtained by the second stage polymerization of the block copolymer A2 is mixed with a coupling agent to carry out a coupling reaction to obtain the block copolymer A1 of the expression (A-D)n-X.

[0036] Another preparation idea of the present application is: A-D-Li is prepared in advance, and then mixed with a coupling agent to couple part of A-D-Li, and then terminated together to obtain the thermoplastic block copolymer containing the block copolymer A1 and the block copolymer A2.

[0037] The present application also provides an application of the thermoplastic block copolymer, which is used to prepare hot melt pressure sensitive adhesive.

[0038] In the present application, the thermoplastic block copolymer can be used to prepare the required hot melt pressure sensitive adhesive based on the existing means.

[0039] The present application also provides a hot melt pressure sensitive adhesive containing the thermoplastic block copolymer.

[0040] Preferably, the hot melt pressure sensitive adhesive further comprises a tackifying resin and a plasticizer.

[0041] In the present application, the tackifying resin can be a conventional tackifying polymer in the industry, for example, can include at least one of rosin resin and its derivatives, terpene resin and its derivatives, aliphatic petroleum resin, hydrogenated aliphatic petroleum resin, aromatic petroleum resin, hydrogenated aromatic petroleum resin, aliphatic / aromatic copolymer petroleum resin and its hydrogenated derivatives.

[0042] In the present application, the plasticizer can be a conventional plasticizing component in the industry, for example, can be one of naphthenic oil, paraffin oil and aromatic oil.

[0043] In the present application, the content of each component in the hot melt pressure sensitive adhesive can be adjusted as needed, for example, the content of the thermoplastic block copolymer is 20-30 wt.%.

[0044] The content of the tackifying resin is 40-60 wt.%.

[0045] The balance is the plasticizer.

[0046] The present application also provides a hot melt pressure sensitive adhesive label comprising at least the hot melt pressure sensitive adhesive of the present application.

[0047] In the present application, in addition to using the hot melt pressure sensitive adhesive of the present application as the adhesive, other components and structures in the hot melt pressure sensitive adhesive label can be conventional.

[0048] Advantages

[0049] The present application provides a brand new thermoplastic block copolymer, which can realize synergy based on the structure and parameters of polymer A1 and polymer A2 such as molecular weight, randomness, tensile strength and other parameters, so that the hot melt adhesive containing the polymer can have excellent initial adhesion, die cutting and low temperature performance.

[0050] The hot melt adhesive of the present application added with the thermoplastic block copolymer can be coated and die cut at high speed, and can be used at low temperature (-10℃), and further has good initial adhesion and peel strength. DETAILED DESCRIPTION

[0051] The following examples are intended to illustrate the present application, but in no way limit the present application.

[0052] The present application provides a kind of thermoplastic block copolymer (also called thermoplastic block copolymer A), it is the copolymer of vinyl aromatic and mixed conjugated diene compound, in the following case, the vinyl aromatic with typical styrene as example, the mixed conjugated diene compound with butadiene and isoprene as example is further described, specifically:

[0053] The thermoplastic block copolymer A includes block copolymer A1 represented by general formula I and block copolymer A2 represented by general formula II:

[0054] (S-B / I)n-X (I)

[0055] S-B / I (II)

[0056] In formula I and formula II, S is a styrene polymer block, B / I is a butadiene and isoprene random copolymer, n is an integer greater than 2, and X is a residue of a coupling agent;

[0057] Block copolymer A1 is a star-shaped styrene block copolymer having a number average molecular weight of 250,000 to 300,000. The tensile strength of block copolymer A1 is 15 to 25 MPa; further preferably 20 to 25 MPa. In block copolymer A1, n is 3 or 4, more preferably 3 to 3.5.

[0058] Block copolymer A2 is a polystyrene-polybutadiene isoprene random copolymer having a number average molecular weight of 80,000 to 90,000; the polybutadiene / isoprene chain segment random structure content is 85 to 95%; the tensile strength is less than 1 MPa. Further, block copolymer A2 has at least 58% by weight of isoprene; further preferably 59 to 65 wt.%. The proportion of butadiene in block copolymer A2 is 27% by weight or less; further preferably 15 to 26%, the balance being polystyrene.

[0059] The isoprene butadiene in block copolymer A2 under the preferred parameters has a suitable matching ratio, a high content of random copolymer structure, and block copolymer A1, which can exhibit better synergy, helping to improve the initial adhesion and flowability of the label pressure-sensitive adhesive; on the other hand, the random structure helps to further improve the low temperature resistance of the hot melt pressure-sensitive adhesive.

[0060] The thermoplastic block copolymer A is composed of A1 and A2, and the matching ratio of block copolymer A1 in the thermoplastic block copolymer A is 15 to 30% by weight, preferably 20 to 25% by weight. It is found that when the proportion of block copolymer A1 is less than 15% by weight, the holding adhesion of the label pressure-sensitive adhesive decreases rapidly; when the proportion of block copolymer A1 is higher than 30% by weight, the melt viscosity increases when preparing the hot melt pressure-sensitive adhesive, in addition, the bonding strength of the label pressure-sensitive adhesive decreases.

[0061] The thermoplastic block copolymer A has a viscosity of not more than 400 mPa.s as a 25% toluene solution at 25°C.

[0062] The thermoplastic block copolymer A has a melt flow rate (MFR) of greater than or equal to about 20 g / 10 min, preferably 22-26 g / 10 min, when measured at 200°C with a 5 kg weight according to ASTM D-1238.

[0063] The thermoplastic block copolymer A has a tensile strength of 2-4 MPa.

[0064] The thermoplastic block copolymer A has an elongation at break of 1000-1300%, and a tensile stress at 300% elongation of 0.2-0.5 MPa.

[0065] In the present application, the parameters of the block copolymer are adjusted by science, and the combination of the two makes the thermoplastic block copolymer have a high melt flow rate, while having a balanced initial adhesion and peel strength, showing the advantages of good initial adhesion and stable peel strength. On the other hand, the thermoplastic block copolymer A with preferred parameters has suitable cohesion and elasticity, which ensures the appropriate adhesion of the label pressure-sensitive adhesive. At the same time, the thermoplastic block copolymer has a low tensile stress at 300% elongation, corresponding to the hot melt pressure-sensitive adhesive, which has the characteristics of slow elastic recovery and is not easy to flow back. The preparation of hot melt pressure-sensitive adhesive label shows the characteristics of no sticking, no stringing, and no residual glue in peeling.

[0066] The present application also provides a preparation method of the thermoplastic block copolymer, which is synthesized by coupling method, or copolymer A1 and copolymer A2 are synthesized respectively, and then mixed in proportion.

[0067] In the present application, copolymer A1 and copolymer A2 can be prepared by existing methods.

[0068] For example, the process for synthesizing the thermoplastic block copolymer by coupling method is as follows:

[0069] Step (1):

[0070] Styrene, polymerization solvent, alkyl lithium initiator, and regulator are pre-polymerized to obtain S-Li;

[0071] Step (2):

[0072] After the completion of step (1) polymerization, the temperature of the polymerization system is controlled at 65-80°C, and butadiene and isoprene are continuously and slowly input through a mass flow meter, and the butadiene and isoprene feeding time is controlled to be not less than 30 min. S-(B / I)-Li is obtained after the second stage polymerization.

[0073] Step (3):

[0074] A coupling agent is added to the polymerization system of step (2) to carry out a coupling reaction, thereby preparing the thermoplastic block copolymer. The coupling agent is chlorosilane, preferably silicon tetrachloride. The molar ratio of the coupling agent to the active lithium is 0.037-0.094.

[0075] For example, the preparation process of copolymer A1 is as follows:

[0076] Step (A):

[0077] Styrene, a polymerization solvent, an alkyl lithium initiator, and a regulator are pre-polymerized to obtain S-Li.

[0078] Step B):

[0079] After the polymerization of step (A) is completed, the temperature of the polymerization system is controlled at 65-80°C, and butadiene and isoprene are continuously and slowly input through a mass flow meter, and the butadiene and isoprene feeding time is controlled to be not less than 30 min. S-(B / I)-Li is obtained after the second-stage polymerization.

[0080] Step (C):

[0081] A coupling agent is added to the polymerization system of step (B) to carry out a coupling reaction, thereby preparing the copolymer A1. The molar ratio of the coupling agent to the active lithium is 0.23-0.31.

[0082] For example, the preparation process of copolymer A2 is as follows:

[0083] S-(B / I)-Li is prepared by the same method of steps (A) and (B) above.

[0084] For example, the rubber solution of copolymer A1 and the rubber solution of copolymer A2 are mixed uniformly, and then coagulation, swelling drying, and pelletizing are carried out, thereby obtaining the thermoplastic block copolymer.

[0085] In another preparation idea of the present application, S-(B / I)-Li is directly prepared, and then a coupling agent is adjusted according to the content of polymer A1, so that part of the S-(B / I)-Li is coupled, and then terminated, thereby preparing a mixed copolymer containing polymer A1 and polymer A2.

[0086] According to the present application, a hot melt pressure-sensitive adhesive for labels can be provided, which is characterized by containing the above thermoplastic block copolymer A, a tackifying resin B, and a plasticizer C.

[0087] The tackifying resin B can include at least one of rosin resin and derivatives thereof, terpene resin and derivatives thereof, aliphatic petroleum resin, hydrogenated aliphatic petroleum resin, aromatic petroleum resin, hydrogenated aromatic petroleum resin, aliphatic / aromatic copolymer petroleum resin and hydrogenated derivatives thereof. Further, the terpene resin is preferred.

[0088] The plasticizer C can be one of naphthenic oil, paraffin oil, aromatic oil. Further, the naphthenic oil is preferred.

[0089] As preferred, the hot melt pressure sensitive adhesive has a content of 20-30 parts by weight of A based on 100 parts by weight of the total weight of A to C.

[0090] The melt viscosity of the label hot melt pressure sensitive adhesive at 160°C is not more than 5000 mPa.s, more preferably not more than 4500 mPa.s; the melt viscosity at 175°C is not more than 3300 mPa.s, more preferably not more than 2800 mPa.s.

[0091] In the following case, the melt flow rate of the thermoplastic block copolymer is determined by using a BMF-001 melt flow rate tester.

[0092] The initial tack of the hot melt pressure sensitive adhesive is determined by using a KJ-6031 computerized ring type initial tack tester.

[0093] The peel strength of the hot melt pressure sensitive adhesive is determined by using a KJ-1065B adhesive tape peel strength tester.

[0094] The viscosity of the hot melt pressure sensitive adhesive is determined by using a NDJ-IC Brookfield rotational viscometer.

[0095] Tensile strength, elongation at break and 300% modulus: according to GB / T 528-2009 standard.

[0096] Low temperature performance: the hot melt pressure sensitive adhesive is made into label paper, which is pasted on a stainless steel sheet, rolled by a 1 kg weight for 3 times, stored in a special container for 1 hour, then the frozen liquid (calcium chloride aqueous solution) at different temperatures is poured into the container, and the temperature at which the label paper floats on the water surface is taken as the low temperature resistance basis.

[0097] Die cutting rate: the prepared hot melt adhesive is coated on the label paper, the cutting tool is installed on the rolling bearing, and the tool is rotated to realize the cutting of the label paper, and the cutting length of the cutting tool on the label paper per minute is tested.

[0098] In the following case, the parts refer to parts by weight, unless otherwise specified.

[0099] Examples 1-5 (synthesis of block copolymer [S-(B / I)]n-X+S-(B / I) by coupling method)

[0100] In a 5 liter polymerizer, 2500 ml of anhydrous cyclohexane and 0.1 ml of tetrahydrofuran were added, stirred and heated to about 55°C, styrene was added, n-butyllithium was broken, then a calculated amount of n-butyllithium (see Table 1; designed molecular weight about 280,000) was added to initiate styrene, after the complete polymerization of styrene, the butadiene and isoprene were mixed uniformly in a mixer, then the mixed monomers were continuously and slowly added to the polymerizer, the temperature of the polymer was controlled at 65-80°C, the flow rate of the mixed monomers was 0.18-0.42 kg / h, after the addition was completed, the reaction was continued for 5-20 min, after the polymerization was completed, then a calculated amount of silicon tetrachloride (design coupling efficiency 15-30%) was added for coupling reaction, the coupling time was 15-20 min, then 1 g of primary antioxidant 1076 and 1 g of secondary antioxidant 168 were added, the solvent was removed by water vapor condensation and drying, thereby obtaining a thermoplastic block copolymer A (containing A1 and A2) sample, which was tested (results are shown in Table 2).

[0101] The dried sample was subjected to standard mixing and curing to produce a sample sheet, which was tested for MFR, 300% modulus, tensile strength and elongation at break.

[0102] The material ratios are shown in Table 1, and the test data are shown in Table 2.

[0103] Table 1

[0104]

[0105] Table 2

[0106]

[0107] Example 6

[0108] The thermoplastic block copolymer A obtained in Examples 1-5 was each 30 parts, which was placed in a 500 ml beaker, 20 parts of naphthenic oil (naphthenic oil 4010, produced by Nanjing Honghan Petroleum Chemical Co., Ltd.) was added to each of the five beakers, stirred uniformly and soaked for 15 min; the beakers were placed in a temperature-controlled electric heating furnace and heated and stirred, the system temperature was controlled at 150-180°C, and stirred and melted for 20 min; then 50 parts of terpene resin (T100, produced by Jining Sanshi Biological Technology Co., Ltd.) was added to each beaker, and the stirring was continued for 5 min, and the system was completely melted into a uniform viscous melt, which was a hot melt pressure sensitive adhesive. Stop stirring, and evenly coat the melt on the substrate while hot as an analysis sample.

[0109] The test results of each hot melt pressure sensitive adhesive are shown in Table 3.

[0110]

[0111] Comparative Example 1 (synthesis of linear block copolymer S-B / I-S)

[0112] The difference between Example 2 and this example is that the structure of the polymer is changed to S-B / I-S, and the difference is that:

[0113] Into a 5 liter polymerizer, 2500 ml of anhydrous cyclohexane and 0.1 ml of tetrahydrofuran were added, stirred and heated to about 55°C, 22.5 g of styrene was added, then 2.23 ml of 0.4 mol / L n-butyllithium was added to initiate the styrene, after the first stage reaction was completed, 41 g of butadiene and 164 g of isoprene were mixed uniformly in a mixer, then the mixed monomers were continuously and slowly added into the polymerizer, the temperature of the polymer was controlled at 65-80°C, the flow rate of the mixed monomers was controlled at 0.24-0.30 kg / h, the second stage polymerization was carried out, after the polymerization was completed, 22.5 g of styrene was added for the third stage reaction, after 20-25 min, 0.1 g of methanol was added to terminate the reaction, thus a linear block copolymer S-B / I-S was obtained, and the molecular weight was measured to be 282,000.

[0114] Comparative Example 2 (synthesis of two block copolymer S-B / I)

[0115] The difference between Example 2 and this example is that the structure of the polymer is changed to S-B / I-S, and the difference is that:

[0116] Into a 5 liter polymerizer, 2500 ml of anhydrous cyclohexane and 0.1 ml of tetrahydrofuran were added, stirred and heated to about 55°C, 22.5 g of styrene was added, then 2.23 ml of 0.4 mol / L n-butyllithium was added to initiate the styrene, after the first stage reaction was completed, 41 g of butadiene and 164 g of isoprene were mixed uniformly in a mixer, then the mixed monomers were continuously and slowly added into the polymerizer, the temperature of the polymer was controlled at 65-80°C, the flow rate of the mixed monomers was controlled at 0.24-0.30 kg / h, the second stage polymerization was carried out, after the polymerization was completed, 22.5 g of styrene was added for the third stage reaction, after 20-25 min, 0.1 g of methanol was added to terminate the reaction, thus a linear block copolymer S-B / I-S was obtained, and the molecular weight was measured to be 282,000.

[0117] Comparative Example 3 (synthesis of (SB)nSi+SB)

[0118] The difference between Example 2 and this example is that the structure of the polymer is changed to S-B / I-S, and the difference is that:

[0119] Comparative Example 4 (synthesis of (SI)nSi+SI)

[0120] The difference between Example 2 and this example is that the structure of the polymer is changed to S-B / I-S, and the difference is that:

[0121] Comparative Example 5

[0122] Compared with Example 2, the only difference is that the coupling efficiency is designed to be 100%, and the resulting polymer is a single polymer A1. Other operations and parameters are the same as in Example 2.

[0123] Comparative Example 6

[0124] Compared with Example 2, the only difference is that the content of isoprene monomer in the total monomers is 45 wt.%, the content of butadiene is 35 wt%, and the balance is styrene. Other operations and parameters are the same as in Example 2.

[0125] Application of comparative examples

[0126] Compared with the experiments in Example 2 of Example 6, the only difference was that the composition and ratio of the copolymer were changed. The experimental groups were as follows:

[0127] Group A: The copolymer A was replaced in equal amounts with a single polymer A1 (prepared in Comparative Example 5);

[0128] Group B: The copolymer A was replaced in equal amounts with a single polymer A2 (prepared in Comparative Example 2);

[0129] Group C: The copolymer A was replaced in equal amounts with the polymer prepared in Comparative Example 3;

[0130] Group D: The copolymer A was replaced in equal amounts with the polymer prepared in Comparative Example 4;

[0131] Group E: The polymer prepared in Comparative Example 1 is used to replace A1 in copolymer A in equal amounts;

[0132] Group F: The content of Al in copolymer A is 10 wt.%.

[0133] Group G: The content of Al in copolymer A is 35 wt.%.

[0134] Group H: The copolymer A was replaced by an equal weight of the polymer obtained in Comparative Example 6;

[0135] The test results of the comparative hot melt pressure-sensitive adhesive are shown in Table 4.

[0136] Table 4

[0137]

[0138] In summary, the hot melt pressure-sensitive adhesive prepared by the thermoplastic block copolymer described in this invention has low melt viscosity, low operating temperature, good initial tack and peel strength, and improves die-cutting speed when used to prepare pressure-sensitive adhesive labels.

Claims

1. A thermoplastic block copolymer, characterized in that, Including block copolymer A1 represented by Formula I and block copolymer A2 represented by Formula II: (AD)nX (Ⅰ) AD (II) In Formulas I and II, A is a vinyl aromatic polymer block, D is a copolymer of two conjugated dienes, n is an integer greater than 2, and X are residues of the coupling agent; the random structure content in D is 85-95%; In AD, polyisoprene accounts for more than 58% by weight, polybutadiene accounts for less than 27% by weight, and the balance is polystyrene. The number-average molecular weight of the block copolymer A1 is 250,000 to 300,000. The number-average molecular weight of the block copolymer A2 is 80,000 to 90,000. In thermoplastic block copolymers, the content of block copolymer A1 is 15~30% by weight.

2. The thermoplastic block copolymer according to claim 1, characterized in that, A refers to a polystyrene block.

3. The thermoplastic block copolymer according to claim 1, characterized in that, D is a random copolymer of butadiene and isoprene.

4. The thermoplastic block copolymer according to claim 3, characterized in that, In the AD, the weight of polyisoprene is 59~65 wt.%; the content of polybutadiene is 15~26 wt.%; and the balance is polystyrene.

5. The thermoplastic block copolymer according to claim 1, characterized in that, In block copolymer A1, n is 3 or 4.

6. The thermoplastic block copolymer as described in claim 5, characterized in that, The tensile strength of the block copolymer A1 is 15~25 MPa.

7. The thermoplastic block copolymer according to any one of claims 1 to 6, characterized in that, In thermoplastic block copolymers, the content of block copolymer A1 is 20-25% by weight.

8. The thermoplastic block copolymer according to any one of claims 1 to 6, characterized in that, The viscosity of the thermoplastic block copolymer in a 25% toluene solution at 25°C is not greater than 400 mPa·s; The melt flow rate of the thermoplastic block copolymer is 22~26 g / 10min; The tensile strength of the thermoplastic block copolymer is 2~4 MPa; The thermoplastic block copolymer has an elongation at break of 1000-1300% and a tensile stress of 0.2-0.5 MPa at 300% elongation.

9. A method for preparing the thermoplastic block copolymer according to any one of claims 1 to 8, characterized in that, The block copolymer A1 and block copolymer A2 are combined to obtain the following: The preparation steps of the block copolymer A2 are as follows: Vinyl aromatic hydrocarbons, polymerization solvents, alkyl lithium initiators, and regulators are pre-polymerized to obtain A-Li; then, the temperature of the polymerization system is controlled at 65~80℃, and a mixture of two conjugated dienes is continuously added to carry out a second-stage polymerization to obtain AD-Li; then, a termination polymerization is carried out to obtain the block copolymer A2 of AD. The preparation steps of the block copolymer A1 are as follows: The AD-Li obtained by the second-stage polymerization of block copolymer A2 was mixed with a coupling agent and subjected to a coupling reaction to obtain block copolymer A1 with the expression (AD)nX; Alternatively, AD-Li can be prepared in advance, then mixed with a coupling agent to partially couple the AD-Li, and then the coupling can be terminated to obtain a thermoplastic block copolymer containing block copolymer A1 and block copolymer A2.

10. The application of the thermoplastic block copolymer according to any one of claims 1 to 8, characterized in that, It was prepared into a hot melt pressure-sensitive adhesive.

11. A hot melt pressure-sensitive adhesive, characterized in that, It includes the thermoplastic block copolymer according to any one of claims 1 to 8.

12. The hot melt pressure-sensitive adhesive as described in claim 11, characterized in that, It also contains tackifying resins and plasticizers.

13. The hot melt pressure-sensitive adhesive as described in claim 12, characterized in that, The tackifying resin includes at least one of rosin resin and its derivatives, terpene resin and its derivatives, aliphatic petroleum resin, hydrogenated aliphatic petroleum resin, aromatic petroleum resin, hydrogenated aromatic petroleum resin, aliphatic / aromatic copolymer petroleum resin and its hydrogenated derivatives.

14. The hot melt pressure-sensitive adhesive as described in claim 13, characterized in that, The plasticizer is one of naphthenic oil, paraffin oil, or aromatic oil.

15. The hot melt pressure-sensitive adhesive according to any one of claims 11 to 14, characterized in that, In the hot melt pressure-sensitive adhesive, the content of the thermoplastic block copolymer is 20~30 wt.%; The content of tackifying resin is 40~60 wt.%; The remainder is plasticizer.

16. A hot melt pressure-sensitive adhesive label, characterized in that, It includes the hot melt pressure-sensitive adhesive as described in any one of claims 11 to 15.

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