JPH0625264B2 - Method for producing adhesive polyethylene film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an adhesive polyethylene film.

Specifically, the present invention is (a) linear low density polyethylene, (b) low polymerization degree polybutene or low polymerization degree polyisobutylene, and
(c) A method for producing an adhesive polyethylene film from a composition comprising a glyceride having an acyl group having 2 to 6 carbon atoms and an acyl group having 8 to 22 carbon atoms.

Adhesive films are used as supermarket films, department stores, grocery stores or homes as wrapping films and stretch films, and produce fresh food products such as vegetables, fruits, meat and fish,
It is also widely used as a film for simple packaging of these processed products and various containers containing them, and also as a so-called masking film for decorative plates, steel plates and the like.

[Conventional technology]

As materials for the conventional adhesive film, vinyl chloride resins such as polyvinyl chloride and polyvinylidene chloride and polyolefin resins such as low density polyethylene are mainly used.

[Problems to be solved by the invention]

When a vinyl chloride resin is used as the above-mentioned adhesive film, the resin contains chlorine in its molecule and accordingly releases harmful gas when incinerated after use, which causes pollution. . Further, since these adhesive films contain a large amount of plasticizers and stabilizers, when used, these plasticizers and stabilizers may be transferred to foods, etc. with which the plasticizers and stabilizers come into contact, which may have harmful effects, or may cause unpleasant odors. To give.

On the other hand, when polyolefin resin, especially low density polyethylene is used, it has an advantage that no harmful gas is generated at the time of burning, but since the rigidity of the film is small, when the film is lapped into the container, it is easy for the film to stick to each other. It is not easy to remove, and the film does not have a good cut property.
When the film is pulled out from the film winding or the like and cut by a saw-toothed cutter, there is a problem that it is obliquely cut or the cut shape is uneven.

[Means for solving problems]

The present inventors have conducted extensive studies in order to improve the above problems of low density polyethylene film, and as a result, linear low density polyethylene has low polymerization degree polybutene or low polymerization degree polyisobutylene, and a carbon number of 2 to 6 A tacky film obtained by forming a film from a polyethylene resin composition containing a small amount of a glyceride having an acyl group and an acyl group having 8 to 22 carbon atoms as a raw material, and then stretching the film under specific conditions. Has found that the rigidity and cuttability are remarkably excellent, and has completed the present invention.

That is, the gist of the present invention is: (a) linear low density polyethylene (b) low polymerization degree polybutene or low polymerization degree polyisobutylene, and (c) an acyl group having 2 to 6 carbon atoms and 8 to 8 carbon atoms. A method for producing an adhesive polyethylene film, which comprises forming a film using a polyolefin resin composition comprising 22 glycerides having an acyl group, and then stretching the film in one direction at an area ratio of 1.2 times or more. Exist.

The present invention will be described in more detail below.

The linear low-density polyethylene (a) used as the main component of the polyethylene resin composition of the present invention is a copolymer of ethylene and another α-olefin, and is a branched low-density polyethylene produced by a conventional high-pressure method. Different from density polyethylene resin. Linear low-density polyethylene includes, for example, ethylene and other α-olefins such as butene, hexene, octene,
It is a copolymer of decene, 4 methylpentene-1 and the like in an amount of about 4 to 17% by weight, preferably about 5 to 15% by weight. It is a manufactured product, which has a conventional branched structure made of high-density polyethylene with a short branched structure by a copolymerization component, and the density is appropriately reduced to 0.91 to 0.95 g / cm ² by utilizing the short chain branching. It is a polyethylene having a structure that is more linear than conventional branched low-density polyethylene and more branched than high-density polyethylene.

The above-mentioned linear low-density polyethylene has a melt index
0.5 to 10 g / 10 minutes or less, especially 1 to 2 g / 10 minutes, density 0.918 to 0.935 g / cm ² , especially 0.920 to 0.930 g
It is desirable to use the one in the range of / cm ² . If the melt index is less than the above range, high speed processing becomes difficult, and if the melt index is more than the above range, drawdown property is poor and high speed processing becomes difficult, which is not desirable. Further, if the density is less than the above range, the melting point is too low, so that the heat resistance is somewhat insufficient, and if it is more than the above range, the tackiness and transparency are deteriorated, which is not desirable.

In the method of the present invention, the melt index is JIS K6.
The value is a value measured at 190 ° C. according to 760, and the density is a value measured according to JIS K6760.

On the other hand, the (b) low-polymerization degree polybutene or low-polymerization degree polyisobutylene (hereinafter simply referred to as “low-polymerization degree polybutenes”) used in the present invention usually has a number average molecular weight of 45.
0-3000, preferably 550-2500, especially 10
It is preferable to use one having a size of about 00 to 2500. Of course, low polymerization degree polybutene and low polymerization degree polyisobutylene,
Alternatively, two or more kinds having different molecular weight distributions may be used in combination.

Further, (c) an acyl group having 2 to 6 carbon atoms and 8 to 22 carbon atoms
The glyceride having an acyl group means that one of three hydroxyl groups of the glyceride is a lower fatty acid having 2 to 6 carbon atoms and the other one is esterified with a higher fatty acid having 8 to 22 carbon atoms. Is required, and the other one is a hydroxyl group or a lower fatty acid having 2 to 6 carbon atoms or 8 to 2 carbon atoms.
It is a diacetin or triacetin compound esterified with the higher fatty acid of 2 (hereinafter referred to as "mixed glyceride"). The acyl groups of the triacetin compound may, of course, be different. The higher fatty acid may be saturated or unsaturated as long as it has 8 to 22 carbon atoms, and usually has 10 to 1 carbon atoms.
8 fatty acids are preferred. Further, the low fatty acid may be any as long as it has 2 to 6 carbon atoms.

Specifically, for example, diacetyl monolauryl glycerin, diacetyl monopalmityl glycerin, diacetyl monooleyl glycerin, monoacetyl dilauryl glycerin, monoacetyl monopalmityl glycerin, monoacetyl dioleyl glycerin, monoacetyl monolauryl glycerin, monoacetyl monoglycerin. Oleyl glycerin, dipropionyl monolauryl glycerin, dicaproyl monolauryl glycerin, dicaproyl monopalmityl glycerin, monoacetyl monocapryl glycerin, monoacetyl monobrassyl glycerin, monopropyl monobrassyl glycerin, monoacetyl monoelyl glycerin And so on.

Of course, two or more kinds of these mixed glycerides may be used together.

In addition, the composition used in the method of the present invention may be added as necessary.
(d) Add an antifog agent. The antifogging agent is used to prevent water droplets from adhering to the inner surface of the film when packaging foods containing water such as vegetables. As the antifogging agent, many are usually used as a surfactant, for example, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, sodium dialkylsulfosuccinate,
Examples thereof include higher fatty acid esters of glycerin having an acyl group having 8 to 22 carbon atoms, and these may be used alone or in combination. Among these, higher fatty acid esters (mono- or diesters) of glycerin such as lauric acid, palmitic acid, behenic acid, oleic acid, linoleic acid, ricinoleic acid, and stearic acid, or 2 to 2 of glycerin
The higher fatty acid ester of a pentamer, that is, polyglycerin is preferable, and the higher fatty acid ester of polyglycerin is particularly preferable in view of maintaining the antifogging property for a long time. When the polyglycerin is, for example, diglycerin, the esterification of the polyglycerin higher fatty acid ester preferably includes about 50% of the monoester, and other ester may be diester or triester.

The polyethylene resin composition used in the present invention is as described above.
(a) linear low-density polyethylene, (b) low polymerization degree polybutenes, (c) mixed glycerides, and further (e) is an antifogging agent, if necessary, the mixing ratio is , Linear low density polyethylene 87-98.6% by weight, preferably 92-
It is optimal to select from the range of 97.5% by weight, low polymerization degree polybutenes 1 to 7% by weight, preferably 2 to 5% by weight, and mixed glyceride 0.4 to 6% by weight, preferably 0.5 to 3% by weight. Further, (e) the antifogging agent is 2% by weight or less, particularly 0.1 to 1
A weight% range is preferred.

Further, when the blending ratio of the mixed glyceride is 1% by weight or more within the above range, it is preferable to use the low-polymerization degree polybutenes to be blended with the mixed glyceride having a number average molecular weight of 1000 to 2500. is there.

If the low-polymerization degree polybutenes are more than the above range, the melt index of the composition becomes large, and for example, when the film is formed by the inflation method, the tension is insufficient, and the bubbles (extruded from the die and the air inside the (The tube expanded by being blown into the film) wobbles laterally, so that a uniform thickness cannot be obtained and the strength of the film itself is lowered. Further, the 180 ° peel strength of the obtained film becomes too large, resulting in poor packaging workability.

Further, even if the mixed glyceride is used in an amount larger than the above range, notable improvement of the effect cannot be expected, which is not only economically disadvantageous but also film-forming property is deteriorated.

Further, when a low-polymerization degree polybutenes and a mixed glyceride are formed into a thick film at the same concentration, low-polymerization degree polybutenes bleeding on the surface of the film and mixed glycerides are increased, so when a thick film is produced, both The concentration can be reduced to some extent. In any case, it is desirable to select and determine the concentration as appropriate according to the application.

The antifogging agent has a function of a lubricant on one side, and even if a large amount of the antifogging agent is added, the antifogging property is not extremely improved. Not only is it economically disadvantageous, but the tackiness of the produced film is also increased. Sex is slightly impaired. However, in order to prevent fogging of the film, it is desirable to add an appropriate amount within the above range. The antifogging agent migrates to the surface of the film similarly to the low polymerization degree polybutenes and the mixed glyceride, and exhibits the antifogging property for a long period of time.

The above-mentioned linear low-density polyethylene, a polyethylene resin composition comprising a low degree of polymerization polybutene and a mixed glyceride includes a UV absorber, a heat stabilizer, a slip agent, an anti-blocking agent, and an antistatic agent that are usually used. Alternatively, a non-dropping agent or the like may be added.

The composition used in the present invention is a linear low density polyethylene,
The low-polymerization degree polybutenes and the mixed glyceride may be simply blended with an antifogging agent if necessary, but usually, they are kneaded and blended with an arbitrary device such as a Banbury mixer, a continuous mixer, a kneading extruder or the like. Used in the state.

The low-polymerization degree polybutenes in the composition, the concentration of the mixed glyceride and the antifogging agent do not necessarily have to be set within the above range from the beginning, and a high concentration low-polymerization degree polybutenes and the mixed glyceride are adopted by using a so-called master batch method. Alternatively, a master batch containing an antifogging agent may be produced, and this may be set within the above range at the time of film forming.

However, if the master batch has an extremely high concentration, kneading before film forming may not be performed well.

The present invention forms an unstretched film using the composition obtained by mixing as described above, and then stretches the unstretched film in at least one direction to an area ratio of 1.2 times or more to produce an adhesive film. To do.

The unstretched film is formed by using a normal film forming apparatus and a forming method such as an inflation forming method using a circular die and a T die forming method using a T die.

To describe the conditions for inflation molding,
The conditions for forming a normal film can be applied as they are. For example, it is carried out under conditions of a resin temperature of 150 to 250 ° C., a blow up ratio of 1.5 to 3 and a draft ratio of 10 to 50. Especially when strength is required, it is desirable that the blow-up ratio is set to 3 or more, preferably 4 to 7.

The unstretched film obtained as described above is then stretched. Stretching in the present invention means reducing the film thickness before and after stretching and stretching the film in at least one direction so that the surface area becomes 1.2 times or more. The stretching is uniaxially stretched in the machine direction of the film (the film take-up direction of the film forming machine) or in the transverse direction (direction orthogonal to the film take-up direction), or biaxially stretched in the machine direction and the transverse direction. It is done by

In the case of uniaxial stretching, the unstretched film obtained by the T-die method or the inflation method is heated as it is or after being slit into a predetermined width, for example, by changing the peripheral speed of the stretching roll. It is carried out by a method of stretching in the take-up direction, that is, a longitudinal direction, or a method of heating an unstretched film with its end portions fixed and stretching it in the transverse direction by widening this interval.

In the case of biaxial stretching, an unstretched film obtained by the T-die method or the inflation method as it is or slit into a predetermined width is successively biaxially stretched or simultaneously stretched.
It is carried out by axial stretching. Sequential biaxial stretching is carried out either in the longitudinal direction and then in the transverse direction, or vice versa. In the simultaneous biaxial stretching, the time distribution of the stretching in the machine direction and the stretching in the transverse direction is arbitrary. For example, the stretching is gradually continued in the machine direction until the stretching in the machine direction is completed, or the stretching is started in the machine direction. You can make the horizontal direction at the same time,
It is done by a method such as completing the vertical direction first.

When biaxial stretching is carried out, a tenter method, a sequential biaxial stretching method, and a Cheubler method simultaneous biaxial stretching method are preferably adopted. The stretching temperature is the melting point of the polyethylene resin composition −20 ° C.
To melting point -5 ° C, especially melting point -20 ° C to melting point -15 ° C
It is desirable that the range is. At a temperature below the melting point of −20 ° C., the mobility of the molecular chain is poor, so that it is easy to cut during stretching, and even if it can be stretched, the stretching ratio does not increase, and it is difficult to obtain a stretched film with excellent physical properties. At a high temperature, the resin partly melts and cannot be stretched and oriented, which makes it difficult to obtain a stretched film having excellent physical properties, which is not desirable.

The stretching ratio is 1.2 times or more, preferably 1.2 to 8 times, and more preferably 1.5 to 5 times in area at least in one direction. If the stretching ratio is less than 1.2 times, the effect of improving the rigidity and cuttability of the film is small, which is not preferable.

The thick film of the adhesive film obtained by the method of the present invention,
100 μm or less, preferably 10 to 50 μm, and particularly 10 to 30 μm, particularly 12 to 20 μm when the application is a lap film or stretch film.

[Action]

In the method of the present invention, a low-polymerization degree polybutene or a low-polymerization degree polyisobutylene and a hybrid resin composition are used for linear low-density polyethylene, and an unstretched film obtained by film forming has almost improved rigidity and cuttability. However, by further subjecting this to a stretching treatment, the above-mentioned rigidity and cuttability are remarkably improved, and further transparency is remarkably improved.

Therefore, the adhesive film produced by the method of the present invention has various effects as described above, and since it does not contain harmful additives, it is suitable as a stretch film or a wrap film for food packaging. used. Also,
Further, a film produced from a polyethylene resin composition containing an antifogging agent as a raw material has a very high antifogging property, and therefore is very suitable as a packaging film for perishable foods and the like which requires antifogging property. There is.

〔Example〕

Next, an example in which an adhesive polyethylene film is produced by the method of the present invention will be specifically described, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

In addition, the physical-property test method of the adhesive polyethylene film in an Example is as follows.

(1) Transparency According to ASTM D1003-52T, haze was measured and evaluated. There is a correlation between the haze and transparency, and the smaller the haze, the better the transparency.

(2) A 25 mm-wide rigid film test piece was evaluated by the tensile strength [g] when stretched by 1%.

(3) The cut film was evaluated by five-level level (best, good, fair, moderately bad, and poor) on the saw tooth cutting property by a tactile test by hand tearing using saw teeth for a lap film. As a standard for evaluation, the cuttability level of a commercially available polyethylene wrap film was evaluated as normal.

(4) (Adhesive strength); Shear peeling strength, 180 ° peeling strength Two films are lightly stacked in a thermostatic chamber at 20 ° C, and the linear pressure is 0.3 kg / with a roll of 25 mmφ and a width of 150 mm on the film.
Pressure is applied 3 times in cm, and the force required for shear peeling of two films and peeling in 180 ° direction within 5 minutes is measured by an Instron type tensile tester.

(5) Anti-fogging property 1 Put 300 ml of water at 20 ℃ in a glass beaker, cover the beaker with the film to be tested, put in a low temperature tank at 3 ℃, and check the transparency of the film after 10 minutes. It was evaluated with the naked eye. The evaluation criteria are as follows.

Excellent: The water droplets spread well, the entire surface is evenly wet, and the inside can be completely seen through.

Good; Water droplets that have grown to a size of 3 mm or more adhere to the film, and the inside can be seen through almost completely.

No; very fine water droplets adhere to the entire surface of the film and the inside cannot be seen.

Examples 1 to 8 Linear low density polyethylene (L-LDPE) (melt index: 2 g / 10 minutes, density: 0.920 g / cm ² , flow ratio: 8, copolymerization component: butene-1, copolymerization amount: 10% by weight), low-polymerization degree polybutene (TAC) having a number average molecular weight of 1260, and diacetyl monolauryl glycerin (trade name: PL002, manufactured by Riken Vitamin Oil Co., Ltd.) as a mixed glyceride (KG) at the ratios shown in Table 1. By blending, a polyethylene resin composition was obtained.

Using a 40 mmφ extruder equipped with a T-die, the composition was heated at a resin temperature (die temperature) of 180 ° C. and a cooling roll temperature of 2
An unstretched film original film having a film thickness of 15 μm was formed at 0 ° C. and a winding speed of 30 m / min.

1 roll of this film stock was rolled using a uniaxial stretching machine
On rolls heated to 00 ° C and having different peripheral speeds,
The stretched film was produced by uniaxially stretching in the machine direction under the conditions shown in Table 1. The stretched film thus obtained was tested for physical properties of the film by the methods described above, and the results shown in Table 1 were obtained.

Example 9 In Example 1, diglycerin monooleate (trade name: Rikemar o-71D, manufactured by Riken Vitamin Oil Co., Ltd.) was further added to the polyethylene resin composition as an antifogging agent (SA).
The same procedure as in Example 1 was carried out except that the addition was made in the ratio shown in. The results are shown in Table 1.

Example 10 In Example 1, the unstretched film was molded by an inflation molding method (resin temperature: 18) instead of the T-die molding method.
The same procedure as in Example 1 was carried out except that the procedure was carried out at 0 ° C., blow-up ratio: 2.0, draft ratio: 67). The results are shown in Table 1.

Comparative Example 1 The procedure of Example 1 was repeated, except that the stretching ratio was outside the conditions of the present invention, that is, the stretching ratio was 1.1 times. The results are shown in Table 1.

Comparative Examples 2 to 3 In Example 1, high pressure low density polyethylene (LDPE) (melt index: 4 g / 10 g, density: 0.926 g / cm ² ) was used in place of the linear low density polyethylene in Table 1.
After the inflation molding (Comparative Example 2) or the T-die molding (Comparative Example 3) was used in the proportions shown in (1), the same procedure as in Example 1 was carried out except that no stretching treatment was carried out. The results are shown in Table 1.

Comparative Examples 4 to 5 In Example 1, as the polyethylene resin composition, high pressure low density polyethylene (melt index: 4 g / 1
0 minutes, density: 0.926 g / cm ² ) was used, except that after inflation molding (Comparative Example 4) or T-die molding (Comparative Example 5), no stretching treatment was performed. Performed in the same manner as 1. The results are shown in Table 1.

Examples 11 to 17 In Examples 1 to 17, except that the unstretched film was stretched by biaxial stretching under the conditions shown in Table 1 instead of uniaxial stretching (using a batch type biaxial stretching machine). Performed in the same manner as 1. The results are shown in Table 2.

Example 18 Example 1 was repeated except that the unstretched film was formed by an inflation molding method.
Performed in the same manner as 1. The results are shown in Table 2.

[Advantages of the Invention] According to the present invention, an adhesive film having good blocking resistance and excellent cuttability can be obtained, and a lap film such as a fresh food product, a stretch film or the like, or a mask for a decorative plate, a steel plate or the like. It is very suitably used as a film or the like.

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Claims (2)

[Claims] 1. A linear low density polyethylene, (b) a low-polymerization polybutene or a low-polymerization degree polyisobutylene,
And (c) a film is formed using a polyethylene resin composition comprising a glyceride having an acyl group having 2 to 6 carbon atoms and an acyl group having 8 to 22 carbon atoms, and then the film has an area ratio of 1.2 at least in one direction. A method for producing an adhesive polyethylene film, which comprises stretching the film twice or more. 2. A linear low-density polyethylene (b) a low degree of polymerization polybutene or a low degree of polymerization polyisobutylene, (c) a glyceride having an acyl group having 2 to 6 carbon atoms and an acyl group having 8 to 22 carbon atoms. And (d) a polyethylene resin composition comprising an antifogging agent is used to form a film, and the film is then stretched in at least one direction to an area ratio of 1.2 times or more. The method for producing the adhesive polyethylene film according to the item.