JP4252122B2 - Method for producing easy-adhesive biaxially stretched polyamide film - Google Patents

Description

【００４１】
【発明の効果】
本発明によれば、逐次二軸延伸法により、耐溶剤性及び基材フィルムとの密着性に優れた塗膜を有する易接着性二軸延伸ポリアミドフィルムが提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an easy-adhesive sequential biaxially stretched polyamide film.
[0002]
[Prior art]
Biaxially stretched polyamide film is excellent in mechanical properties, optical properties, thermal properties, barrier properties, wear resistance, impact resistance, pinhole resistance, etc. Widely used as an industrial film.
[0003]
When the polyamide film is used for food packaging, it is used by laminating it with a sealant film. However, if the adhesive strength between the two films is weak, the base film is used for boiling and retorting for sterilization. There is a problem that a so-called delamination phenomenon occurs in which the film peels off from the sealant film.
[0004]
When laminating, it is common to use an adhesive diluted with an organic solvent such as ethyl acetate or methyl ethyl ketone. In this case, in the laminating process of the film, if the solvent resistance of the coating film is poor, the coating film is peeled off by the organic solvent on the roll, and the performance is extremely lowered.
Furthermore, the polyamide film is often used after printing, and also requires adhesion with printing ink.
[0005]
Conventionally, surface treatment for imparting easy adhesion to a polyamide film has been performed. For example, in Japanese Patent Publication No. 3-55302, when producing an easily adhesive polyamide film, an aqueous emulsion containing a polyurethane resin and a melamine-based crosslinking agent is applied to an unstretched film, dried, and simultaneously biaxial A method of stretching and heat setting is disclosed.
However, when an aqueous emulsion having the composition disclosed in this publication is used, the cross-linking reaction does not proceed smoothly unless it is treated at a high temperature. After the longitudinal stretching, the aqueous emulsion is applied, dried, preheated, and then stretched laterally. It could not be applied to the stretching method. That is, in the sequential biaxial stretching method, if the film after longitudinal stretching is processed at a high temperature, it becomes difficult to perform transverse stretching. Therefore, it is necessary to dry and preheat at a low temperature. There was a problem with sex.
[0006]
[Problems to be solved by the invention]
The present invention is intended to provide an easy-adhesive biaxially stretched polyamide film having excellent solvent resistance by a sequential biaxial stretching method.
[0007]
[Means for Solving the Problems]
In view of the above circumstances, the present inventors have intensively studied a method for obtaining an easy-adhesive polyamide film by a sequential biaxial stretching method, and as a result, by appropriately selecting the property and preheating of the easy-adhesive resin and the stretching temperature, preheating is possible. The present invention was completed by finding that a biaxially stretched polyamide film having excellent adhesiveness of the easy-adhesive layer was obtained even at low temperatures, and further having excellent solvent resistance.
[0008]
That is, the gist of the present invention is as follows.
A substantially amorphous, non-oriented unstretched polyamide film is longitudinally stretched by a longitudinal stretching machine comprising a series of roll groups, and an aqueous polyurethane emulsion (A) and a melamine crosslinking agent (on at least one side of the longitudinally stretched film ( After coating the mixed solution of B), the following formulas (1) to (2) are satisfied in the method of producing an easy-adhesive type sequential biaxially stretched polyamide film by preheating and transverse stretching with a tenter type transverse stretching machine. The preadhesive biaxially stretched polyamide is characterized in that moisture is dried together with preheating under the conditions of the above, transversely stretched under the conditions satisfying the following formula (3), and heat-set under the conditions satisfying the following formula (4): A method for producing a film.
T ₁ ≧ Tmf (A) (1)
_{Tg ≦ T 1 ≦ Tg + 20} ℃ (2)
Tsf (A) ≦ T ₂ ≦ Tg + 60 ° C. (3)
T ₃ ≧ Tts (B) (4)
Here, T ₁ is the preheating temperature, T ₂ is the transverse stretching temperature, T ₃ is the heat setting temperature, Tmf (A) is the minimum film forming temperature of A, Tg is the glass transition temperature of polyamide, and Tsf (A) is the softening of A. The onset temperature, Tts (B), indicates the onset temperature of the B crosslinking reaction.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
In the present invention, the polyamide means a thermoplastic polyamide having oriented crystallinity. Specific examples of such polyamides include nylon 6 and nylon 66.
Nylon 610, nylon 11, nylon 12, nylon MXD6 (polymetaxylylene adipamide) and copolymers and mixtures based on these. Particularly preferred is nylon 6 which is excellent in cost performance.
These polyamides may contain various additives such as a lubricant, an antistatic agent, an antiblocking agent, and inorganic fine particles as long as they do not adversely affect the performance of the film.
[0010]
In the present invention, first, a substantially amorphous and non-oriented unstretched polyamide film is obtained according to a conventional method. For example, polyamide chips are heated and melted with an extruder and extruded from a T-die into a film shape, which is cooled and solidified on a cooling drum that rotates by a known casting method such as an air knife casting method or an electrostatic application casting method, and then rapidly cooled. Form a film.
[0011]
Next, the unstretched film is supplied to a roller-type longitudinal stretching machine composed of a group of heating rollers having different peripheral speeds, preheated for stretching, and then stretched to a temperature equal to or higher than the glass transition point of the unstretched film. A longitudinally stretched film is formed by stretching 2.7 to 3.6 times between the roll and the cooling roll.
[0012]
Next, at least one side of the above-mentioned longitudinally stretched film is coated with a mixed solution of an aqueous polyurethane emulsion (A) and a melamine crosslinking agent (B) so that the thickness after transverse stretching is 0.03 to 0.1 μm. Then, it leads to a tenter preheating part and performs preheating for drying of moisture and film transverse stretching.
[0013]
In the present invention, it is necessary to manufacture the preheating temperature (T ₁ ) under the conditions shown in the following formulas 1 and 2.
T ₁ ≧ Tmf (A) (1)
_{Tg ≦ T 1 ≦ Tg + 20} ℃ (2)
Here, Tmf (A) is the minimum film forming temperature of A, and Tg is the glass transition temperature of polyamide.
[0014]
The preheating temperature is made to satisfy the condition of the formula (1) in order to appropriately form the polyurethane resin film before transverse stretching. When the formula (1) is not satisfied, the polyurethane resin film is not formed on the film after transverse stretching.
In addition, the preheating temperature is made to satisfy the condition of the formula (2) in order to perform the horizontal stretching uniformly. When the preheating temperature is lower than Tg, the film is broken at the initial stage of transverse stretching, and when it is higher than Tg + 20 ° C., the crystallization of the longitudinally stretched film proceeds excessively, and the film is broken or even stretched during transverse stretching. Even so, a neck occurs in the length direction of the film, and the value as a product is lowered.
[0015]
Next, in the present invention, the preheated longitudinally stretched film is stretched 3.0 to 5.0 times in the transverse direction at a stretching temperature (T ₂ ) that satisfies the following formula (3).
Tsf (A) ≦ T ₂ ≦ Tg + 60 ° C. (3)
Here, Tsf (A) represents the softening start temperature of A.
[0016]
The reason why the transverse stretching temperature satisfies the condition of the formula (3) is to form a uniform film after the transverse stretching.
When the transverse stretching temperature is lower than the softening start temperature of A, the film is cracked during transverse stretching, so that the solvent resistance and adhesiveness of the film are lowered. On the other hand, when the temperature is higher than Tg + 60 ° C., the film frequently breaks during transverse stretching, or the stretching becomes uneven and the thickness unevenness increases.
[0017]
The biaxially stretched film thus obtained is heat-set under a temperature condition that satisfies the following formula (4) in order to impart dimensional stability.
T ₃ ≧ Tts (B)
Here, T ₃ represents a heat set temperature, and Tts (B) represents a crosslinking reaction initiation temperature of B.
[0018]
When the heat setting temperature is lower than the crosslinking reaction start temperature of B, the reaction between the polyurethane and the crosslinking agent does not occur, so that the solvent resistance and adhesion of the film cannot be obtained.
T ₃ may be appropriately selected as long as it is not lower than the crosslinking reaction initiation temperature of B and does not affect the strength of the film.
In addition, as a kind of B, in order to obtain a high shrink film, since a low temperature setting is normally performed, the thing with low crosslinking reaction temperature is used.
[0019]
Examples of the aqueous polyurethane emulsion (A) used in the present invention include an ionomer type self-emulsifying polyurethane resin and an ionomer type self-emulsifying polyurethane-polyurea resin.
In order to improve the solvent resistance, it is preferable to use an aromatic component for at least one of both components. Moreover, in order to improve adhesiveness, it is preferable to use what introduce | transduced the hydroxyl group, the carboxyl group, and the amino group into the polymer principal chain or the terminal.
[0020]
As the melamine-based cross-linking agent (B), a melamine methylolated one is used, and a methylol group alkoxylated one is generally used in order to provide reactivity control and storage stability. Examples of the alkoxyl group include a methoxy group, an ethoxy group, a propoxy group, and a butoxy group. Moreover, you may add a crosslinking catalyst as needed. Examples of the crosslinking catalyst include p-toluenesulfonic acid.
[0021]
As for the addition amount of a melamine type crosslinking agent (B), 5-7 weight part is preferable with respect to A for 90-100 weight part.
If the addition amount of (B) is less than 5 parts by weight, the solvent resistance becomes insufficient, and if it is more than 7 parts by weight, the solvent resistance is saturated, which is not economical. Moreover, a crosslinking reaction can be accelerated | stimulated by adding 5 to 7weight% of a crosslinking catalyst with respect to the quantity of a crosslinking agent as needed.
[0022]
Various known additives such as an antistatic agent and a slip agent can be added to the easy-adhesion coating solution in the present invention, as necessary, within a range that does not affect the adhesiveness. Further, an antifoaming agent and a surfactant can be added in order to improve coatability.
[0023]
In addition, as a storage method of the aqueous emulsion mixed solution, a low temperature is preferable as long as it is not frozen in order to suppress a crosslinking reaction during storage, for example, a method of flowing cooling water of about 10 to 20 ° C. over the surface of the storage tank. May be used.
[0024]
The thickness of the film after stretching the film is preferably 0.03 to 0.1 μm, more preferably 0.05 to 0.08 μm. When the thickness of the film is less than 0.03 μm, sufficient adhesiveness cannot be obtained, and even when the thickness is more than 0.1 μm, the performance is saturated, so it is not economical to apply a thickness larger than that.
[0025]
In the present invention, the coating method of the film is not particularly limited, for example, gravure roll method, reverse roll method, air knife method, reverse gravure method, Mayer bar method, inverse roll method, or various coating methods by a combination thereof. In addition, various spraying methods can be employed.
Moreover, a corona treatment apparatus etc. can be installed between a longitudinal stretch machine and a coater, and the wet tension of the film after longitudinal stretch can be adjusted.
[0026]
The biaxially stretched polyamide film thus obtained is subjected to a relaxation treatment as necessary in order to impart dimensional stability of the film.
The film is then released from the clip, the unstretched remainder at the end is trimmed, and the remainder is wound up as a product.
[0027]
Next, the present invention will be specifically described based on examples.
The evaluation method in the present invention is as follows.
[0028]
(1) A solvent-resistant coated film (biaxially stretched film) was immersed in ethyl acetate at 20 ° C. for 3 minutes, air-dried, the amount of coating was quantified, the rate of decrease in coating amount was determined, and the following four stages were evaluated. .
A: Less than 30% by weight B: 30-40% by weight
Δ: 40% by weight to less than 60% by weight x: 60% by weight or more The coating amount was determined as follows.
The easy adhesion treatment film has a melamine ring derived from a cross-linking agent and exhibits a characteristic ultraviolet absorption at 260 to 300 nm. For this reason, if the difference spectrum (area) of the ultraviolet absorption spectrum of the base film that has not been subjected to the easy adhesion treatment and the easy adhesion treatment film is obtained, the amount of coating can be quantified.
Therefore, a coating amount calibration curve was prepared in advance using a coat film with a known coating amount, and the coating amount of the coating film was quantified.
(2) Laminate strong easy-adhesion treated film and unstretched polypropylene film: (Toray Synthetic Co., Ltd. “Trephan”, thickness 60 μm) was dry laminated using a polyurethane adhesive.
A test piece having a width of 15 mm was taken from this laminate film and tested in an atmosphere of 20 ° C. and 65% RH using a tensile tester AGS-100B manufactured by Shimadzu Corporation at a tensile rate of 300 mm / min by the T peel method. The film interface was peeled off from the edge of the piece and the strength was measured.
(3) A polyurethane-based ink was applied to the ink adhesive coat film, and after drying, the cellophane tape made by Nichiban was applied to the ink surface so that air did not enter, and it was peeled off in a direction of 180 ° at once, and the ink was peeled off. The evaluation was made according to the following four stages according to the area ratio.
A: Less than 30% B: 30-40%
Δ: 40% to less than 60% ×: 60% or more
(4) Minimum film formation temperature Measured by temperature gradient plate method (TF Protzman, GL Brown, J. Appl.
Polymer Sci., 4, 81 (1960)).
(5) Softening point Measured according to JIS-K-7196.
[0029]
Example 1
Nylon 6 (melting point: 220 ° C., Tg 45 ° C.) was melt-extruded into a sheet form from a 600 mm wide T-die at a temperature of 260 ° C., and then closely cooled to a rotating drum at a temperature of 25 ° C. by an air knife casting method. An unstretched polyamide film having a thickness of 155 μm and substantially amorphous and not oriented was obtained.
Next, this unstretched film was stretched longitudinally at a temperature of 55 to 62 ° C. and a stretching ratio of 2.8 times by a longitudinal stretching machine composed of a group of heating rollers having different peripheral speeds to obtain a longitudinally stretched film.
Then, the longitudinally stretched film is adjusted to a solid concentration of 6 weight% pH 9.0 The aqueous polyurethane-based emulsion (A) (manufactured by Dainippon Ink and Chemicals, Inc. ^" Hydran ^“ ) (Tmf = about 0 ° C., Tsf = 80 ° C.) 100 parts by weight of tri (methoxymethyl) melamine resin (B) (Tts = 150 ° C.) 7 parts by weight was mixed using a Meyer bar coater Then, coating was performed so that the thickness after transverse stretching was 0.07 μm.
Next, it is led to a tenter and dried at a temperature of 60 ° C. in the preheated part to form a coating film. The film is stretched 3.7 times at a temperature of 90 ° C. and then heat-treated at 215 ° C. A biaxially stretched polyamide film was obtained.
The performance of the obtained film is shown in Table 1.
[0030]
Example 2
A biaxially stretched polyamide film with a surface coating of 15 μm in thickness was used in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) with Tmf = 62 ° C. and Tsf = 80 ° C. was used and the preheating temperature was 65 ° C. Got.
The performance of the obtained film is shown in Table 1.
[0031]
Example 3
A surface-coated biaxially stretched polyamide having a thickness of 15 μm in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) having Tmf = 40 ° C. and Tsf = 90 ° C. was used and the transverse stretching temperature was 100 ° C. A film was obtained.
The performance of the obtained film is shown in Table 1.
[0032]
Example 4
A heat-shrinkable biaxially stretched polyamide film having a surface coating thickness of 15 μm was obtained in the same manner as in Example 1 except that a melamine-based crosslinking agent having Tts = 120 ° C. was used and the heat setting temperature was 130 ° C.
The performance of the obtained film is shown in Table 1.
[0033]
Example 5
The thickness is the same as in Example 2 except that polymetaxylylene adipamide (MXD6, Tg 75 ° C.) is used as the polyamide, the longitudinal stretching temperature is 85 ° C., the preheating temperature is 90 ° C., and the transverse stretching temperature is 95 ° C. A biaxially stretched polyamide film having a thickness of 15 μm was obtained.
The performance of the obtained film is shown in Table 1.
[0034]
Comparative Example 1
A surface-coated biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 2 except that the preheating temperature was 60 ° C.
The performance of the obtained film is shown in Table 1.
In this case, the film was inferior in solvent resistance and adhesion because it was stretched in the preheated portion without being formed into a film.
[0035]
Comparative Example 2
A surface-coated biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) having Tmf = about 0 ° C. and Tsf = 100 ° C. was used.
Manufacturing conditions and characteristic values are shown in Table 1.
The performance of the obtained film is shown in Table 1.
The film obtained was a film with poor solvent resistance and adhesiveness because the film did not follow during transverse stretching.
[0036]
Comparative Example 3
A biaxially stretched polyamide film with a surface coating of 15 μm in thickness was used in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) with Tmf = 70 ° C. and Tsf = 80 ° C. was used and the preheating temperature was 75 ° C. Obtained.
In this case, since the preheating temperature was too high, crystallization of the base film progressed, and the film was frequently cut.
[0037]
Comparative Example 4
A surface-coated biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) having Tmf = 62 ° C. and Tsf = 100 ° C. was used.
The performance of the obtained film is shown in Table 1.
In this case, no film was formed in the preheated part, and the film had poor solvent resistance and adhesion.
[0038]
Comparative Example 5
A surface-coated biaxially stretched polyamide film having a thickness of 15 μm was obtained in the same manner as in Example 1 except that the aqueous polyurethane emulsion (A) with Tsf = 120 ° C. was used and the transverse stretching temperature was 125 ° C.
The performance of the obtained film is shown in Table 1.
In this production method, since the transverse stretching temperature was too high, orientational crystallization in the transverse stretching process proceeded excessively, a neck was partially generated, and the film had a large thickness unevenness.
[0039]
Comparative Example 6
A heat-shrinkable biaxially stretched polyamide film having a surface coating thickness of 15 μm was obtained in the same manner as in Example 4 except that the melamine-based crosslinking agent (B) at Tts = 150 ° C. was used.
The performance of the obtained film is shown in Table 1.
In this case, the crosslinking in the heat setting part did not proceed, and the film had poor solvent resistance and adhesion.
[0040]
[Table 1]

[0041]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the easy-adhesion biaxially stretched polyamide film which has a coating film excellent in solvent resistance and adhesiveness with a base film is provided by the sequential biaxial stretching method.

Claims (1)

A substantially amorphous, non-oriented unstretched polyamide film is longitudinally stretched by a longitudinal stretching machine comprising a series of roll groups, and an aqueous polyurethane emulsion (A) and a melamine crosslinking agent (on at least one side of the longitudinally stretched film ( After coating the mixed solution of B), the following formulas (1) to (2) are satisfied in the method of producing an easy-adhesive type sequential biaxially stretched polyamide film by preheating and transverse stretching with a tenter type transverse stretching machine. The preadhesive biaxially stretched polyamide is characterized in that moisture is dried together with preheating under the conditions of the above, transversely stretched under the conditions satisfying the following formula (3), and heat-set under the conditions satisfying the following formula (4): A method for producing a film.
T ₁ ≧ Tmf (A) (1)
_{Tg ≦ T 1 ≦ Tg + 20} ℃ (2)
Tsf (A) ≦ T ₂ ≦ Tg + 60 ° C. (3)
T ₃ ≧ Tts (B) (4)
Here, T ₁ is the preheating temperature, T ₂ is the transverse stretching temperature, T ₃ is the heat setting temperature, Tmf (A) is the minimum film forming temperature of A, Tg is the glass transition temperature of polyamide, and Tsf (A) is the softening of A. The onset temperature, Tts (B), indicates the onset temperature of the B crosslinking reaction.