CN115505362A

CN115505362A - Solvent-free polyurethane adhesive for composite low-surface-energy film and preparation method thereof

Info

Publication number: CN115505362A
Application number: CN202211346292.5A
Authority: CN
Inventors: 李曾照; 杜海; 隋学斌; 赫长生; 曹学
Original assignee: Beijing Comens New Materials Co Ltd
Current assignee: Beijing Comens New Materials Co Ltd
Priority date: 2022-10-31
Filing date: 2022-10-31
Publication date: 2022-12-23
Anticipated expiration: 2042-10-31
Also published as: CN115505362B

Abstract

The invention discloses a solvent-free polyurethane adhesive of a composite low surface energy film and a preparation method thereof, wherein the adhesive consists of a component A and a component B; the component A is isocyanate-terminated prepolymer obtained by reacting isocyanate mixture with polyether polyol mixture, and the isocyanate mixture is 4,4 ^， Diphenylmethane diisocyanate and 2,4 ^， The diphenylmethane diisocyanate is mixed according to the weight ratio of 1 to 2:1; the polyether polyol mixture is prepared from polyether polyol with average molecular weight of 300-500, 800-1500 and 1800-2500Mixing according to the weight ratio of 1-2:3-4:1-2; the component B is formed by uniformly mixing polyester polyol and polyether polyol with low molecular weight; the molar ratio of isocyanate functional groups in component A to hydroxyl functional groups in component B is 1.3 to 1.5. The adhesive can be used for compounding an OPP/CPP film, the T-shaped peeling strength after curing is 1.6-1.8N/15mm, and the peeling strength attenuation after 14 days is 1.2-1.4N/15mm.

Description

Solvent-free polyurethane adhesive for composite low-surface-energy film and preparation method thereof

Technical Field

The invention relates to the field of polyurethane adhesives for composite flexible packages, in particular to a double-component solvent-free polyurethane adhesive with high peel strength for compositing an OPP/CPP film structure and a preparation method thereof.

Background

With the vigorous development of economy, people need to use a large amount of composite flexible packaging products in daily life. The flexible package composite process is to adhere plastic films, metal films, paper and the like with different functions by an adhesive to form two or more layers of films with composite structures. The composite structure film can simultaneously have the aesthetic property, the barrier property, the heat sealing property and other special properties which cannot be achieved by a single-layer film, so that the composite structure film can meet the packaging requirements of various products and plays an increasingly important role in numerous fields.

The composite film of the biaxially oriented polypropylene film (BOPP) and the cast polypropylene film (CPP) is widely used in light packages of foods, daily chemical products and the like because of its characteristics of high transparency, high gloss, good moisture resistance, oil resistance, excellent food hygiene and the like. However, unlike polar materials such as PET and nylon, polypropylene (PP) film, which is a non-polar material, has a low surface free energy. The polyurethane resin adhesive has high activity due to containing a large amount of polar groups, and cannot be well wetted and attached to the surface of a polypropylene film. Therefore, PP films are usually subjected to corona treatment in the market, so as to increase the surface free energy thereof, thereby improving the adhesion capability of the composite film. However, due to the reasons of uneven corona effect, poor corona effect along with time extension and the like, the composite strength of the composite film is low, the peeling strength of the composite film after being compounded for 1-3 days can meet the national standard requirement (the normal temperature T-shaped peeling strength of the composite dry and light packaging film of the polyurethane adhesive is more than 0.6N/15 mm), the peeling strength can be attenuated along with the time extension, the peeling strength is attenuated to 0.1-0.3N/15 mm after 7 days, and the low peeling strength has great potential safety hazard for the long-term storage of subsequent products.

Chinese patent application CN 110835513A discloses a solvent-free bi-component polyurethane adhesive and a preparation method thereof, and the technology adopts polyoxypropylene polyol and bisphenol A initiated polyether polyol to be matched with organic isocyanate to prepare an adhesive with good comprehensive performance, and particularly has excellent adhesion to a BOPP/CPP composite structure. However, it is not optimistic that the peel strength of the cured product is about 0.8-0.9N/mm, and whether the peel strength of the cured product after being placed for 7 days or 14 days until 60 days can reach the national standard.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a solvent-free polyurethane adhesive for compounding a low-surface-energy film and a preparation method thereof, and aims to solve the technical problems in the prior art. The adhesive can be used for compounding a printed OPP film with the thickness of 20-30 mu m and a CPP film, the T-shaped peel strength after curing is 1.6-1.8N/15mm, and the peel strength attenuation after 14 days is 1.2-1.4N/15mm. In addition, the product can still reach the national standard after being placed for 60 days.

The purpose of the invention is realized by the following technical scheme:

a solvent-free polyurethane adhesive for a composite low surface energy film is composed of a component A and a component B;

the component A is an isocyanate-terminated prepolymer obtained by reacting an isocyanate mixture with a polyether polyol mixture, wherein in the prepolymer, the isocyanate mixture is formed by mixing 4,4 '-diphenylmethane diisocyanate and 2,4' -diphenylmethane diisocyanate according to the weight ratio of 1-2:1; the polyether polyol mixture is prepared by mixing polyether polyols with the average molecular weights of 300-500, 800-1500 and 1800-2500 according to the weight ratio of 1-2:3-4:1-2;

the component B is formed by uniformly mixing polyester polyol and polyether polyol with low molecular weight;

the molar ratio of isocyanate functional groups in the A component to hydroxyl functional groups in the B component is 1.3-1.5.

The invention relates to a preparation method of a solvent-free polyurethane adhesive for a composite low-surface-energy film, which comprises the following steps:

respectively preparing a component A and a component B:

preparing a component A: adding the isocyanate mixture and the polyether polyol mixture into a container according to a predetermined weight ratio, heating to 80-90 ℃, reacting for 3-4 hours, cooling, and discharging to obtain an isocyanate-terminated prepolymer serving as a component A; the isocyanate mixture is prepared by mixing 4,4 '-diphenylmethane diisocyanate and 2,4' -diphenylmethane diisocyanate according to the weight ratio of 1-2:1; the polyether polyol mixture is prepared by mixing polyether polyols with the average molecular weights of 300-500, 800-1500 and 1800-2500 according to the weight ratio of 1-2:3-4:1-2;

preparation of polyester polyol of component B: adding micromolecular polybasic acid and micromolecular polyalcohol into a polyester kettle according to a preset weight proportion, then adding an antioxidant and a catalyst, and reacting according to a conventional esterification condensation method to obtain the required polyester polyol;

preparing a component B: physically stirring the prepared polyester polyol and polyether polyol with the molecular weight of 500-1000 in proportion to obtain a transparent and uniform component B;

preparing a solvent-free polyurethane adhesive: mixing the prepared component A and the component B according to the molar ratio of isocyanate to hydroxyl of 1.3-1.5.

Compared with the prior art, the invention has at least the following beneficial effects:

(1) In the component A, polyether polyols with average molecular weights of 300-500, 800-1500 and 1800-2500 are respectively mixed according to the weight ratio of 1-2:3-4:1-2 to serve as a polyether polyol mixture of an isocyanate prepolymer, so that a cured adhesive film has strong cohesive force and good flexibility, and the adhesive has good viscoelasticity while the peel strength is improved. Therefore, by adjusting the proportion of polyether polyols with different average molecular weights, different high molecular chain segments can be generated by the isocyanate prepolymer in the component A and hydroxyl in the component B during curing reaction, when the content of polyether polyol with the molecular weight of 300-500 is high, the number of urethane bonds in the high molecular chain segments is increased, the number of hard segments is increased, the acting force of hydrogen bonds and polar bonds in molecules is increased, the system viscosity is increased, the coating performance is influenced, when the content of polyether polyol with the molecular weight of 1800-2500 is high, the content of soft segments is increased, the acting force of hydrogen bonds is reduced, the adhesive force of an adhesive and a base material is reduced, and the peeling strength is reduced.

(2) In the component A, an isocyanate mixture is prepared by mixing 4,4, diphenylmethane diisocyanate, 2,4 and diphenylmethane diisocyanate according to the proportion of 1-2:1, and the NCO group in 4,4 and diphenylmethane diisocyanate has high activity and can generate a self-polymerization phenomenon in the reaction process, so that the viscosity of a system is increased; the prepolymer is white solid at normal temperature, and when the content is higher, the prepolymer is slightly whitened, so that the transparency of the glue solution is poor; while 4,4-diphenylmethane diisocyanate content is low, which affects the reactivity, the present invention can improve the transparency of the A component and improve the reaction efficiency by controlling the ratio of the A component to 2,4-diphenylmethane diisocyanate.

(3) The molar ratio of isocyanate group and hydroxyl group in the component A and the component B is 1.3-1.5, so that the hydroxyl group content is higher than that of the common solvent-free bi-component adhesive, the high molecular chain segment of the A, B component after reaction and solidification is long enough and soft, and after the adhesive is placed for a period of time and completely solidified, the peeling strength attenuation rate of OPP and CPP is smaller and higher than the national standard.

The adhesive disclosed by the invention is solvent-free, environment-friendly and low in viscosity, and is beneficial to coating operation. Has excellent adhesive property aiming at an OPP/CPP composite structure, and has great prospect in the field of light packaging laminating adhesives.

Detailed Description

The technical scheme in the embodiment of the invention is clearly and completely described below; it is to be understood that the described embodiments are merely exemplary of the invention, and are not intended to limit the invention to the particular forms disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.

The terms that may be used herein are first described as follows:

the term "and/or" means that either or both can be achieved, for example, X and/or Y means that both cases include "X" or "Y" as well as three cases including "X and Y".

The terms "comprising," "including," "containing," "having," or other similar terms of meaning should be construed as non-exclusive inclusions. For example: including a feature (e.g., material, component, ingredient, carrier, formulation, material, dimension, part, component, mechanism, device, process, procedure, method, reaction condition, processing condition, parameter, algorithm, signal, data, product, or article of manufacture), is to be construed as including not only the particular feature explicitly listed but also other features not explicitly listed as such which are known in the art.

The term "parts by weight" is intended to indicate the relationship of mass proportions between the various components, for example: if the X component is described as X parts by weight and the Y component is described as Y parts by weight, the mass ratio of the X component to the Y component is represented as X: Y;1 part by weight may represent any mass, for example: 1 part by weight may be 1kg or 3.1415926 kg. The sum of the parts by weight of all components is not necessarily 100 parts and may be greater than 100 parts, less than 100 parts or equal to 100 parts. Parts, ratios and percentages described herein are by mass unless otherwise indicated.

When concentrations, temperatures, pressures, dimensions, or other parameters are expressed as ranges of values, the ranges are to be understood as specifically disclosing all ranges formed from any pair of upper, lower, and preferred values within the range, regardless of whether ranges are explicitly recited; for example, if a numerical range of "2 to 8" is recited, then that numerical range should be interpreted to include ranges such as "2 to 7," "2 to 6," "5 to 7," "3 to 4 and 6 to 7," "3 to 5 and 7," "2 and 5 to 7," and the like. Unless otherwise indicated, the numerical ranges recited herein include both the endpoints thereof and all integers and fractions within the numerical range.

The solvent-free polyurethane adhesive for the composite low surface energy film and the preparation method thereof provided by the present invention are described in detail below. Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to a person skilled in the art. The examples of the present invention, in which specific conditions are not specified, were carried out according to the conventional conditions in the art or conditions suggested by the manufacturer. The reagents and instruments used in the examples of the present invention are not specified by manufacturers, and are conventional products commercially available.

(one) solvent-free polyurethane adhesive compounded with low surface energy film

The invention provides a solvent-free polyurethane adhesive for a composite low-surface-energy film, which consists of a component A and a component B;

The isocyanate-terminated prepolymer obtained by reacting the isocyanate mixture of the component A with the polyether polyol mixture is obtained by carrying out polymerization reaction on the isocyanate mixture and the polyether polyol mixture at the temperature of 80 ℃ according to the weight ratio of 5-6:4-5, and the NCO of the prepolymer is 12-15%.

The component B is prepared by physically mixing polyester polyol and low-molecular-weight polyether polyol according to the weight ratio of 1:1-3, is transparent and uniform liquid, and has the viscosity of 2000-4000mpa.s at 25 ℃. Lower viscosity is beneficial for uniform coating.

The average molecular weight of the polyester polyol in the component B is 800-1200. In a preferred embodiment, the polyester polyol is prepared by taking small molecular polybasic acid, small molecular polyhydric alcohol, 500ppm antioxidant and 50ppm catalyst as raw materials, wherein the small molecular polyhydric alcohol and the small molecular polybasic acid are fed according to the alkyd ratio ranging from 1.3 to 1.6, and the polyester polyol is prepared by a conventional esterification condensation method. In a preferred embodiment, the small molecule polybasic acid is preferably one or more of adipic acid and isophthalic acid;

the micromolecular polyalcohol is one or more of 2-methyl-1,3-propylene glycol, diethylene glycol, ethylene glycol, 1,4-butanediol, glycerol and the like; 2-methyl-1,3-propylene glycol is preferably used, which has a similar molecular structure to polypropylene and is beneficial to increasing the acting force between the adhesive and the polypropylene molecules. In addition, a proper amount of glycerol is added into the polyester polyol, so that the interior of the polyester polyol can be properly crosslinked, and the viscosity of the polyester polyol can be favorably increased.

The antioxidant is preferably triphenyl phosphite;

the catalyst is preferably tetra-n-butyl titanate.

Preferably, the polyether polyol in the component B has a molecular weight of 500 to 1000 and a hydroxyl value of 112 to 224mgKOH/g.

After the polyester polyol and the polyether polyol with the small molecular weight are physically mixed and react with the isocyanate prepolymer in the component A, the curing speed is slow, the adhesive layer after curing for one day is sticky, and the ink layer on the OPP cannot be immediately transferred to the CPP, so that the peeling strength of the film immediately after curing is higher.

(II) preparation method of solvent-free polyurethane adhesive of composite low-surface-energy film

The invention provides a preparation method of a solvent-free polyurethane adhesive for preparing a composite low-surface-energy film, which comprises the following steps:

respectively preparing a component A and a component B:

in a preferred embodiment, the desired polyester polyol for the B component is prepared in the following manner: one or more of adipic acid or isophthalic acid and one or more of 2-methyl-1,3-propylene glycol, diethylene glycol, ethylene glycol, 1,4-butanediol and glycerol are added into a polyester kettle, and then 500ppm of antioxidant triphenyl phosphite and 50ppm of catalyst tetra-n-butyl titanate are added, so as to obtain the polyester by an esterification polycondensation method commonly used in the field;

preparing a solvent-free polyurethane adhesive: and mixing the prepared component A and the component B according to the molar ratio of isocyanate to hydroxyl of 1.3-1.5.

In the component A of the method, the proportion of the isocyanate mixture to the polyether polyol mixture is 5-6:4-5 by weight, and the NCO of the prepolymer is 12-15%;

in the polyester polyol of the component B, the weight ratio of micromolecular polybasic acid to micromolecular polyol is X: Y;

in the component B, the weight ratio of the polyester polyol to the polyether polyol with low molecular weight is 1:1-3.

(III) advantageous effects of the invention

Compared with the prior art, the solvent-free polyurethane adhesive for the composite low-surface-energy film and the preparation method thereof provided by the invention have the following advantages:

(1) According to the invention, different high molecular chain segments can be generated by adjusting the proportion of polyether polyols with different average molecular weights in the component A during the curing reaction of the isocyanate prepolymer in the component A and the hydroxyl in the component B. When the content of the polyether polyol with the molecular weight of 300-500 is high, the urethane bonds in the high molecular chain segment are increased, the hard segment is increased, and the acting force of hydrogen bonds and polar bonds in the molecule is increased, so that the system viscosity is increased, and the coating performance is influenced. When the polyether polyol with the molecular weight of 1800-2500 is high, the content of the soft segment is high, the hydrogen bond acting force is reduced, the adhesive force of the adhesive and the base material is reduced, and the peeling strength is reduced. Therefore, polyether polyols with the average molecular weights of 300-500, 800-1500 and 1800-2500 are respectively mixed according to the weight ratio of (1-2) to (3-4) to (1-2), so that the cured adhesive film has stronger cohesive force and better flexibility, and the adhesive has better viscoelasticity while the peel strength is improved.

(2) The isocyanate in the component A is 4,4, the diphenylmethane diisocyanate is mixed with 2,4 and the diphenylmethane diisocyanate according to the proportion of (1-2): 1, and because the NCO group in the 4,4 and the diphenylmethane diisocyanate has high activity, a self-polymerization phenomenon can occur in the reaction process, so that the viscosity of the system is increased. And the prepolymer is white solid at normal temperature, and when the content is higher, the prepolymer is slightly whitened, so that the transparency of the glue solution is poor. While 4,4, the lower content of diphenylmethane diisocyanate affects the reactivity, so the ratio of the component A to 2,4-diphenylmethane diisocyanate can be controlled to improve the transparency of the component A and improve the reaction efficiency.

(3) In order to improve the bonding force of the adhesive between the OPP and the CPP, 2-methyl-1,3-propylene glycol is preferably selected as the small molecular diol in the 800-1200 polyester polyol, and the small molecular diol has a similar structure with a polypropylene molecule and is beneficial to increasing the acting force between the adhesive and the polypropylene molecule. In addition, a proper amount of glycerin is added into the polyester diol, so that the interior of the polyester polyol can be properly crosslinked, and the viscosity of the polyester polyol can be favorably increased.

(4) For the printed OPP film, the viscosity of the adhesive between the ink layer of the OPP and the CPP film is increased, and the bonding strength is required to be reduced, so that the phenomenon that the OPP is separated from the ink layer due to too high bonding strength is avoided, and the tested peel strength is actually the adhesive force of the ink layer and the OPP, so that the measured actual peel strength is lower. After the prepared polyester polyol and the polyether polyol with the small molecular weight are physically mixed and react with the isocyanate prepolymer in the component A, the curing speed is slow, the adhesive layer after curing for one day is sticky, and the ink layer on the OPP cannot be immediately transferred to the CPP, so that the peeling strength of the film immediately after curing is high.

(5) The molar ratio of isocyanate group to hydroxyl group in the component A and the component B is adjusted to be (1.3-1.5): 1, the content of hydroxyl group is designed to be higher than that of the common solvent-free bi-component adhesive, and the polymer chain segment after the reaction and curing of the component AB is long enough and soft. After the adhesive is placed for a period of time and is completely cured, the peeling strength attenuation rate of the OPP and the CPP is smaller and higher than the national standard.

(6) The adhesive disclosed by the invention is solvent-free, environment-friendly and low in viscosity, and is beneficial to coating operation. Has excellent adhesive property aiming at an OPP/CPP composite structure, and has great prospect in the field of light packaging laminating adhesives.

As can be seen, the adhesive of the examples of the present invention can be used for laminating a CPP film and a printed OPP film having a thickness of 20 to 30 μm, and has a T-peel strength of 1.6 to 1.8N/15mm after curing and a peel strength decay of 1.2 to 1.4N/15mm after 14 days. In addition, the product can still reach the national standard after being placed for 60 days.

In order to more clearly show the technical scheme and the technical effects provided by the present invention, the following detailed description is provided for the solvent-free polyurethane adhesive for a composite low surface energy film and the preparation method thereof.

Example 1

Preparing a component A: firstly adding 1.5 parts of polyether polyol with the molecular weight of 300-500, 3.5 parts of polyether polyol with the molecular weight of 800-1500 and 1 part of polyether polyol with the molecular weight of 1800-2500 into a four-mouth bottle, then adding 5 parts of 4,4, -diphenylmethane diisocyanate and 2.5 parts of 2,4, -diphenylmethane diisocyanate, heating to 80 ℃, and stirring for 3 hours to obtain the component A with the NCO mass fraction of 12-15%.

Preparation of the polyester polyol required for the component B: adding 3 parts of isophthalic acid, 5 parts of adipic acid, 3 parts of 2-methyl-1,3-propylene glycol, 5 parts of diethylene glycol, 1 part of glycerol, 500ppm of antioxidant triphenyl phosphite and 50ppm of catalyst tetra-n-butyl titanate into a polyester kettle, and carrying out condensation polymerization to obtain the polyester polyol with the hydroxyl value of 90-140 mgKOH/g.

Preparing a component B: the polyester polyol prepared above and polyether polyol with molecular weight of 500-1000 are physically stirred according to the proportion of 1:3, so that the polyester polyol and the polyether polyol are uniformly mixed and are in a transparent state, and the viscosity is 2000-4000mpa.s at 25 ℃.

Preparing a solvent-free polyurethane adhesive: and (3) measuring the NCO mass fraction of the component A and the hydroxyl value of the component B, and then uniformly mixing the component A and the component B according to the NCO to hydroxyl molar ratio of 1.4.

Example 2

Preparing a component A: adding 1 part of polyether polyol with the molecular weight of 300-500, 3 parts of polyether polyol with the molecular weight of 800-1500 and 1.5 parts of polyether polyol with the molecular weight of 1800-2500 into a four-mouth bottle, adding 4 parts of 4,4, -diphenylmethane diisocyanate and 4 parts of 2,4, -diphenylmethane diisocyanate, heating to 80 ℃, and stirring for 3 hours to obtain the component A with the NCO mass fraction of 12-15%.

Preparation of the component B the required polyester polyol: adding 3 parts of isophthalic acid, 5 parts of adipic acid, 10 parts of diethylene glycol, 1 part of glycerol, 500ppm of antioxidant triphenyl phosphite and 50ppm of catalyst tetra-n-butyl titanate into a polyester kettle, and carrying out condensation polymerization to obtain the polyester polyol with the hydroxyl value of 90-140 mgKOH/g.

Example 3

Preparing a component A: firstly, adding 1.5 parts of polyether polyol with the molecular weight of 300-500, 3.5 parts of polyether polyol with the molecular weight of 800-1500 and 1 part of polyether polyol with the molecular weight of 1800-2500 into a four-mouth bottle, then adding 5 parts of 4,4, -diphenylmethane diisocyanate and 2.5 parts of 2,4, -diphenylmethane diisocyanate, heating to 80 ℃, and stirring for 3 hours to obtain the component A with the NCO mass fraction of 12-15%.

Preparation of the polyester polyol required for the component B: adding 20 parts of adipic acid, 7 parts of ethylene glycol, 8 parts of 2-methyl-1,3-propylene glycol, 1 part of 1,4-butanediol, 500ppm of antioxidant triphenyl phosphite and 50ppm of catalyst tetra-n-butyl titanate into a polyester kettle, and carrying out condensation polymerization to obtain the polyester polyol with the hydroxyl value of 90-140 mgKOH/g.

Comparative example 1:

preparing a solvent-free polyurethane adhesive: the component B is obtained by uniformly mixing the polyester polyol prepared in the example 1 and polyether polyol with the molecular weight of 500-1000 according to 3:1. Then, through actual measurement and calculation, the component A and the component B prepared in the example 1 are uniformly mixed according to the ratio of NCO to hydroxyl 1.4.

Comparative example 2:

preparing a solvent-free polyurethane adhesive: the component B is obtained by uniformly mixing the polyester polyol prepared in the example 1 and polyether polyol with the molecular weight of 500-1000 according to 1:3. Then, the component A and the component B prepared in the example 1 are mixed uniformly according to the ratio of NCO to hydroxyl 1.1.

Comparative example 3:

preparing a solvent-free polyurethane adhesive: the component B is obtained by uniformly mixing the polyester polyol prepared in the example 1 and polyether polyol with the molecular weight of 500-1000 according to 1:3. Then, through actual measurement and calculation, the component A and the component B prepared in the example 1 are uniformly mixed according to the ratio of NCO to hydroxyl 1.7.

Comparative example 4:

a common solvent-free adhesive YH752A/B for a plastic-plastic structure on the market is used, and the component A and the component B are uniformly mixed according to the given proportion of 100.

Comparative example 5:

the solvent-free double-component polyurethane laminating adhesive prepared in Chinese patent application CN 110734732A is used for solving the problems of low strength and the like of a BOPP/CPP composite film.

Comparative example 6:

the two-component polyurethane adhesive prepared in the Chinese patent application CN 110835513A has excellent adhesion to a BOPP/CPP composite structure.

The two-component solvent-free polyurethane adhesives prepared in examples 1 to 3 and comparative examples 1 to 4 were compounded with 28 μm thick printed OPP and 25 μm thick CPP, respectively, and the T-peel strength of the OPP/CPP composite film after curing at 40 ℃ for 24 hours and the T-peel strength after leaving for 7 days and 14 days after curing were measured according to the Standard of BB/T0039-2013 "retail bags for commercial products". Comparative examples 5 to 6 refer to the chinese patent application, in which the composite curing process and the test method are the same as those of the present invention, and have reference meanings, and the specific data results are shown in table 1.

Table 1:

table 1 the results show that: in examples 1 to 3, the printed OPP and CPP films with the thickness of 20 to 30 μm were compounded by the two-component solvent-free polyurethane adhesive provided by the invention, and after curing at 40 ℃ for 24 hours, the peel strength could reach 1.6 to 1.8N/15mm, at this time, after peeling the films, the adhesive was anti-sticky, but had no influence on transparency and processing. After being placed for 7 days, the peeling strength is increased, the glue is slightly sticky, and the printing layer on the OPP is not transferred. After being placed for 14 days, the composite film is peeled off, the glue is completely cured, and the peel strength attenuation is 1.2-1.4N/15mm, which is far higher than that of the common solvent-free bi-component polyurethane adhesive composite OPP/CPP.

It can be seen that comparative examples 1-3 are not prior art, but are provided by the present invention for the effect of different combinations of the components of reaction A, B on performance, and that comparative example 1 has a ratio of polyester polyol to polyether polyol of 3:1 relative to component B of example 1, resulting in less film tack after curing, more complete curing, and greater peel strength, but more decay in peel strength after 14 days of standing. Comparative example 2 compared to the AB component of example 1, which has an NCO to hydroxyl ratio of 1.1, the hydroxyl component is higher, resulting in incomplete curing of the adhesive film, and after 14 days of standing, although the peel strength is improved, it is still tacky. Comparative example 3 is a ratio of ordinary solvent-free two-component polyurethane adhesive, compared with the AB component in example 1, in which the ratio of NCO to hydroxyl is 1.7, and the curing is sufficient immediately after curing, the adhesive film is slightly sticky, the peel strength is high, but the peel strength decays to below the national standard after being left for 14 days. Comparative example 4 is a solvent-free adhesive on the market for a common plastic structure, and the peel strength of the adhesive cannot meet the national standard after 14 days of attenuation. Comparative examples 5 to 6 refer to peel strength test data of the adhesives for the BOPP/CPP composite films in the cited chinese patent application.

The examples 1-3 and the comparative examples 1-6 show that the solvent-free bi-component polyurethane adhesive is provided aiming at the problems that the bonding strength of OPP and CPP in the flexible packaging market is low, and the peel strength is attenuated to be below the national standard after the OPP/CPP structure is compounded and placed for 7 days, and when the solvent-free bi-component polyurethane adhesive is used for compounding the OPP/CPP structure, the peel strength is high after curing, and after 14 days of complete curing, the peel strength is attenuated to 1.2-1.4N/15mm, which is higher than the T-shaped peel strength of a compound packaging bag specified in the industrial standard BB/T0039-2013 and is more than or equal to 0.6N/15 mm.

In summary, the solvent-free polyurethane adhesive of the present invention has excellent adhesion to low surface energy films, such as OPP/CPP films, and is composed of A, B, wherein the component A is an isocyanate prepolymer obtained by reacting isocyanate with several polyether polyols with different molecular weights. The component B is a homogeneous mixture of polyester polyol and polyether polyol, and the cured adhesive film has both strength and flexibility by adjusting the proportion of the polyether polyols with different molecular weights in the component A; secondly, a small molecular weight polyether polyol is doped into the component B, so that the adhesive film just cured keeps a viscosity, the peeling strength between the OPP and the CPP film is increased, and finally, the molecular chain of the cured adhesive film is longer and soft by adjusting the molar ratio of NCO to hydroxyl of the component A to the component B, so that the decay rate of the peeling strength is reduced. The adhesive can be used for compounding an OPP/CPP film, the T-shaped peeling strength after curing is 1.6-1.8N/15mm, and the peeling strength attenuation after 14 days is 1.2-1.4N/15mm.

The above description is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are also within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims. The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

Claims

1. A solvent-free polyurethane adhesive for a composite low surface energy film is characterized in that the adhesive consists of a component A and a component B;

2. The solvent-free polyurethane adhesive for composite low surface energy films as claimed in claim 1, wherein the isocyanate-terminated prepolymer obtained by reacting the isocyanate mixture of the component A with the polyether polyol mixture is obtained by reacting the isocyanate mixture with the polyether polyol mixture according to the weight ratio of 5-6:4-5 at 80 ℃, the NCO of the prepolymer is 12-15%, and the viscosity of the prepolymer is 6000-8000mpa.s at 25 ℃.

3. The solvent-free polyurethane adhesive for the composite low surface energy film according to claim 1 or 2, wherein the component B is prepared by physically mixing polyester polyol and polyether polyol with low molecular weight according to the weight ratio of 1:1-3.

4. The solvent-free polyurethane adhesive for composite low surface energy films according to claim 3, wherein the average molecular weight of the polyester polyol in the B component is 800-1200.

5. The solvent-free polyurethane adhesive for composite low-surface-energy films as claimed in claim 4, wherein the polyester polyol in the component B is prepared from small molecular polybasic acid, small molecular polyol, 300ppm antioxidant and 50ppm catalyst, wherein the small molecular polyol and the small molecular polybasic acid are fed according to an alkyd ratio ranging from 1.3 to 1.6, and are obtained by a conventional esterification condensation method.

6. The solvent-free polyurethane adhesive of claim 5, wherein the small molecule polyacid is one or more combinations of adipic acid and isophthalic acid;

the micromolecular polyalcohol is one or more of 2-methyl-1,3-propylene glycol, diethylene glycol, ethylene glycol, 1,4-butanediol, glycerol and the like;

the antioxidant is triphenyl phosphite;

the catalyst is tetrabutyl titanate.

7. The solvent-free polyurethane adhesive of claim 3, wherein the polyether polyol in the component B has a molecular weight of 500-1000 and a hydroxyl value of 112-224 mgKOH/g.

8. The solvent-free polyurethane adhesive for composite low surface energy films as claimed in claim 1 or 2, wherein the component B is a transparent uniform liquid with a viscosity of 2000-4000mpa.s at 25 ℃.

9. A method for preparing the solvent-free polyurethane adhesive for the composite low surface energy film of any one of claims 1 to 8, comprising:

respectively preparing a component A and a component B:

10. The method for preparing the solvent-free polyurethane adhesive for the composite low-surface-energy film according to claim 9, wherein in the component A, the ratio of the isocyanate mixture to the polyether polyol mixture is 5-6:4-5 by weight, and the NCO of the prepolymer is 12-15%;

in the component B, the weight ratio of the polyester polyol to the low molecular weight polyether polyol is 1:1-3.