JPH07676B2 - Polypropylene film for adhesive tape - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polypropylene film for adhesive tape.

[Conventional technology]

BACKGROUND ART Conventionally, an adhesive tape in which an adhesive layer is provided on one surface of a tape-shaped support is widely known and used in large numbers.

Polypropylene film is no exception, because of its excellent properties, a polypropylene film support with an adhesive layer on one side and a release agent layer on the opposite side (for example,
Dumplon tape, intertape, vegetable binding tape, etc.) are used.

For example, JP-A-60-88049 discloses that the intrinsic viscosity [η]
And a biaxially oriented polypropylene film in which a nucleating agent and a silicon compound are contained in crystalline polypropylene having a specified isotacticity, and it is disclosed that it can be used as an adhesive tape.

[Problems to be Solved by the Invention]

However, the conventional biaxially oriented polypropylene film has the following problems. That is, there is a problem in that the dimensional change of the film in the step of applying the pressure-sensitive adhesive layer and the release agent layer and the subsequent drying step, and "worse" defects due to air entrainment in the pressure-sensitive adhesive layer in the winding step are likely to occur.

The "worm-like" defect means that when a polypropylene film coated with a release agent on one side and an adhesive on the other side is taken up as a wide tape through a hot-air drying oven, the solvent resistance of the film Part of the film becomes rippled due to factors such as heat resistance, thermal dimensional change, slippage, and winding tension, and is wound into a tape with a width of 5 to 10 mm and a length of about 10 cm. This is a defect that looks like "a worm" when viewed from the surface.

The present invention solves the above problems, a polypropylene film for pressure-sensitive adhesive tapes, in which the dimensional change of the film in the pressure-sensitive adhesive layer, the release agent coating and the subsequent drying step is small, and there is almost no possibility of occurrence of "worm" -like defects. The purpose is to provide.

[Means for Solving the Problems]

MEANS TO SOLVE THE PROBLEM This invention WHEREIN: In order to achieve the above objectives, distortion amount Y (%) of a film longitudinal direction is -3 <Y <= {(W-80) / 220} exp {0.035 (T-80)} However, T is the measured temperature in the range of 40 to 140 ° C, W is the applied load in the range of 80 to 1000 g / mm ² , and the widthwise heat shrinkage stress start temperature is 116 ° C or higher, and the widthwise heat shrinkage stress maximum value. Of 100 to 500 g / mm ² for adhesive tape polypropylene film.

The polypropylene for pressure-sensitive adhesive tape of the present invention is a homopolymer of polypropylene and propylene in which a monomer such as ethylene or butene is copolymerized within 2% by weight, for example, an ethylene-propylene copolymer or a propylene butene copolymer. In the case of the invention, homopolypropylene is preferred. Among them, the stereoregularity with excellent crystallinity (isotacticity, hereinafter abbreviated as "II") is high (II: 98-9
Homopolymers (about 9.5%) are particularly preferred. The intrinsic viscosity “η” of polypropylene is not particularly limited, but film-forming property,
From the viewpoint of solvent resistance, 1.6 to 2.4 is desirable. Polypropylene, if necessary an amphoteric or nonionic antistatic agent or an antistatic agent obtained by mixing both in the range of 0.1 to 1.0 wt%, further antioxidant, heat stabilizer, lubricant, crystal nucleating agent,
An ultraviolet absorber, a pigment or the like may be added within a range that does not impair the effects of the present invention.

Incidentally, the film applied to the adhesive tape of the present invention,
The film made of the above polypropylene is preferably uniaxially stretched, and particularly preferably biaxially stretched from the viewpoint of rigidity, transparency, strength and elongation.

Strain amount Y in the longitudinal direction of the polypropylene film of the present invention
(%) Must satisfy the following expression (1).

-3 <Y≤ {(W-80) / 220} exp {0.035 (T-80)}
(1) However, T is the measurement temperature (° C) and W is the applied load (g / mm ² ).
Is.

Here, the longitudinal strain amount Y (%) is the temperature from 40 ° C to 140 ° C at 5 ° C when the load W (g / mm ² ) is applied to the sample with the trial length l _0.
When the expansion / contraction length Δl at each temperature T (° C.) is measured by increasing the temperature at a temperature increase rate of 1 / min, it is defined by the following formula.

Y = 100 (Δl / l ₀ ) However, the load W shall be 80g / mm ² or more and 1000g / mm ² or less. That is, Y is a value given for each load W and each temperature T, the load W being 80 to 1000 g / mm ² and the temperature T being 40 to 140 ° C. ) Should satisfy the formula. When the load W is less than 80 g / mm ² , heat shrinkage stress causes heat shrinkage stress, and when the load W exceeds 1000 g / mm ² , the polypropylene has a significant plastic deformation region at high temperature and the measured value fluctuation becomes large. Therefore, Y must satisfy the above formula (1). There is no.

The measured temperature T is near the melting point of polypropylene (about 15
Above 0 ℃, viscous flow occurs, so the measurement temperature range is 4
0 to 140 ° C, and outside this temperature range, Y is the above (1).
It is not necessary to satisfy the formula.

When the longitudinal strain amount Y is less than -3, the dimensional change (elongation) of the film is remarkable in the drying step after the application of the pressure-sensitive adhesive or the release agent, and further the air inclusion in the pressure-sensitive adhesive layer in the winding step causes " Worm-like defects are likely to occur. On the other hand, when the strain amount Y becomes larger than the value on the right side of the above formula (1), the film is tensioned against tension in the drying step and winding step after coating the adhesive, or a slight fluctuation in the tension. At the same time as extending in the direction (longitudinal direction), width variation (dimensional change) occurs in the direction perpendicular to the tension direction, and induces "worm" -like defects.

The polypropylene film of the present invention needs to have a heat shrinkage stress initiation temperature in the width direction of 116 ° C. or higher, preferably 120 ° C. or higher.

Here, the width-direction heat shrinkage stress start temperature is the sample 100 mm,
A film with a width of 10 mm is fixed with a load of 50 g / mm ² , the temperature is raised from 25 ° C at a rate of 3 ° C / min, temperature is plotted on the horizontal axis and heat shrinkage stress in the width direction is plotted on the vertical axis. When drawing a stress curve, it is the temperature at which the heat shrinkage stress in the width direction starts to increase rapidly. An example of the temperature-width direction heat shrinkage stress curve is shown in FIG. _1, where T ₁ is the width direction heat shrinkage stress start temperature.

Width direction heat shrinkage stress start temperature T ₁ is less than 116 ° C, preferably 1
If the temperature is lower than 20 ° C, a dimensional change (width shrinkage) occurs in the step of drying the pressure-sensitive adhesive and the release agent, and "worm" -like defects due to air entrapment occur. The upper limit of the heat shrinkage initiation temperature T ₁ is not particularly limited, but may be about 150 ° C. due to the melting point of polypropylene and the like.

Next, the polypropylene film of the present invention must have a widthwise heat shrinkage stress maximum value S _max of 100 to 500 g / mm ² .

Here, the maximum value of the heat shrinkage stress in the width direction means the heat shrinkage stress in the width direction at the peak point in the above temperature-width shrinkage stress curve. In FIG. 1, S _max is the maximum value of the heat shrinkage stress in the width direction.

When the maximum value of the heat shrinkage stress in the width direction S _max is less than 100 g / mm ² , the film stretches or sags during the coating of the adhesive layer and the release layer and during the drying process, and "worm" -like defects occur. Wavy wrinkles. Conversely, S _max is 500 g / mm ²
If it exceeds the above range, the film shrinks during the application of the pressure-sensitive adhesive and the release agent and the drying process, and at the same time, "worm" defects occur.

As a polypropylene film for adhesive tapes, one with a small temperature dependence of the heat shrinkage ratio in the width direction is preferable. Specifically, if the heat shrinkage ratio at 130 ° C is set to ± 1.0%, dimensional changes and "worm-like" defects occur. Is particularly preferable because it can be largely prevented.

The static friction coefficient of polypropylene film at 80 ℃ is 1.
When the coefficient of kinetic friction is 0 or less and 0.8 or less, the slipperiness in the drying process is improved and the occurrence of "worm" -like defects can be prevented, which is preferable.

Furthermore, the Young's modulus of the film (especially in the longitudinal direction) is 250 kg / mm
^{It is} more preferable to set it to ² or more, preferably 275 Kg / mm ² or more, since it is possible to prevent the generation of "worm" -like defects and to improve the handleability.

The thickness of the polypropylene film of the present invention is not particularly limited, but 30 to 60 μm is preferably used.

Further, it is apparent that the film of the present invention may be subjected to corona discharge treatment in the presence of air, carbon dioxide gas, nitrogen gas or the like alone or in a mixed gas to improve the adhesive of the pressure-sensitive adhesive or the release agent.

Next, the method for producing the polypropylene film for an adhesive tape of the present invention will be described, but the method is not necessarily limited to this. As polypropylene, polypropylene having an intrinsic viscosity [η] of 1.6 to 2.4 was used, the polymer was supplied to an extruder and melted at 220 to 280 ° C, and then the melt was extruded from a die and cooled to 13 to 50 ° C. It is cooled and solidified on the cooling drum by a known adhesion method such as an air knife method or a press roll method. The cast film is preheated by a preheating roll group heated to 115 to 145 ° C. and then stretched in the longitudinal direction by 4 to 10 times, preferably 5.0 to 8 times,
Subsequently, it is stretched 6 to 12 times in the width direction with a stenter in an atmosphere of 154 to 169 ° C., and then heat treated at 150 to 166 ° C. while being relaxed by 3 to 15% in the width direction. In the case of the present invention,
The stretching temperature and the stretching ratio in the longitudinal direction and the width direction are set to be higher (for example, the temperature in the longitudinal direction is 130 to 145 ° C, and the stretching ratio is 5.0 to 10).
Double, and 9 to 12 times at the width direction temperature of 158 to 169 ° C), and subsequently subjected to the width direction relaxation heat treatment at a sufficiently high temperature, and the stress in stretching,
It is important to relax the strain sufficiently. Here, the stretching ratio in the longitudinal direction is increased, but the orientation in the longitudinal direction is low (for example, from the refractive index n _{MD in the} longitudinal direction to the refractive index n _{TD in the} width direction).
Is suitable for the polypropylene film of the present invention.

The polypropylene film of the present invention thus obtained,
Used to make adhesive tape. To form an adhesive tape, for example, the polypropylene of the present invention is used as a tape-like support, and an adhesive layer is provided on one side and a release agent layer is provided on the opposite side.

The method of measuring the characteristic value and the method of evaluating the effect of the present invention are as follows.

(1) Strain amount Y (%) Using a balance-type automatic recording creep tester manufactured by Toyo Sokki Co., Ltd., a sample with a sample length l ₀ of 130 mm and a width of 15 mm was set in an oven at 40 ° C. While the temperature is rising at a heating rate of 5 ° C / min, the DC differential transformer automatically records the expansion and contraction of the sample.
The amount of expansion / contraction Δl is shown as a percentage (%) with respect to the effective test length.
The load W applied at this time was calculated in g per mm ² of the sample cross-sectional area.

(2) Thermal shrinkage stress onset temperature, thermal shrinkage stress maximum value Fixed to a predetermined film with a test length of 100 mm and a width of 10 mm at 25 ° C. with a load of 50 g / mm ² and a temperature increase of 3 ° C./min. The stress temperature (T 1 in FIG. ₁ ) was taken as the heat shrinkage stress onset temperature. Moreover, the maximum value point (T _{2 in} FIG. 1) of the heat shrinkage stress was taken as the peak temperature.

The stress at the maximum point of thermal shrinkage stress (T ₂ ) is shown in terms of stress per unit area (g / mm ² ).

(3) Intrinsic viscosity [η] It was obtained by measuring the relative viscosity in a 135 ° C. tetralin solution and extrapolating to determine the limiting value.

(4) Isotacticity (II) 5 g of a sample was extracted with n-heptane at 120 ° C. for 12 hours (n-heptane dropping number: 80 drops / min), and then dried under an atmosphere of 100 mmHg, 80 ° C. for 2 hours. , Calculated from the weight before and after extraction by

II (%) = (b / a) x 100 where a: sample weight before extraction (g) b: sample weight after extraction (g) (5) Coefficient of friction 24 hours in a room at 20 ° C and 65% RH Humidified 100 mm (MD) x 75 m
Overlap opposite surfaces of a sample of size m (TD) and
Place on a metal plate heated to ℃, put a load of 200 g (bottom size 65 mm × 65 mm) on it, and after 15 seconds, move one sample at a speed of 162 mm / min, The resistance value was read and the calculated resistance value (g) / 200 g was shown. Note that μ _s
Is the coefficient of static friction, and μ _d is the coefficient of dynamic friction.

(6) Thermal shrinkage Based on JIS K 6782, the shrinkage was measured at 130 ° C. for 15 minutes in a Kia oven. The values in the table indicate the values in the film width direction.

(7) Worm-like defects ⊚ indicates that there are no "worm-like" defects, ◯ indicates that there are almost no "worm-like" defects, and x indicates that there are "worm-like" defects.

(8) Dimensional change ⊚ indicates that the width variation with respect to the entire width is less than 0.05%, ∘ is less than 0.1, and x is 0.1% or more.

(9) Appearance of tape Good is good, and bad is bad winding shape or uneven thickness.

[Action]

Since the polypropylene film for pressure-sensitive adhesive tape according to the present invention has specified the longitudinal strain amount Y (%) as -3 <Y≤ {(W-80) / 220} exp {0.035 (T-80)}, Prevents dimensional changes due to tension during the application of pressure sensitive adhesives and release agents, as well as during the drying and winding processes, and has a thermal shrinkage stress starting temperature in the width direction of 116 ° C or higher and a shrinkage stress peak peak value of 100. Since it is ~ 500 g / mm ² ,
It was possible to obtain a polypropylene film for an adhesive tape, which has a small width shrinkage in the drying step and is unlikely to cause "worm" -shaped defects.

〔Example〕

 Next, embodiments of the present invention will be described based on examples.

Examples 1 to 3 Crystalline homopolypropylene having the composition shown in Table 1 was supplied to an extruder, extruded from a T-die at 280 ° C and cast on a casting drum at 20 ° C to obtain an unstretched sheet. The sheet is stretched 5 times in the longitudinal direction while being heated to 135 ° C. by a roll group, cooled, introduced into a tenter heated to 165 ° C. and stretched in the width direction to about 10 times, and further a relaxation rate of 8% is applied in the width direction. A biaxially oriented polypropylene film having a thickness of 40 μm was prepared in an atmosphere of 157 ° C. A rubber adhesive (using solvent toluene) is applied to one side of this film at 30 μm, and a silicone type release agent (using solvent toluene) is applied at 0.1 μm to the other side, and dried at 130 ° C for 40 seconds with a hot air dryer. As a polypropylene adhesive tape. The physical properties of the film and the adhesive tape properties are summarized in Table 1. When the strain amount Y of the film, the heat shrinkage stress starting temperature in the width direction, and the heat shrinkage stress value are within the specific ranges of the present invention, the adhesive tape has a "worm-like" defect and an excellent appearance without dimensional change. I understand.

Comparative Examples 1 to 4 The crystalline polypropylene of Example 2 was fed to an extruder,
It was extruded from a T-die at 0 ° C and cast on a casting drum at 25 ° C to obtain an unstretched sheet. The unstretched sheet is heated to 120 to 130 ° C. with a preheating roll, stretched 5 times in the longitudinal direction, cooled, and stretched about 10 times in the width direction with a tenter heated to 158 to 164 ° C., further 150 to 158 ° C., width Heat treatment was appropriately changed at a directional relaxation rate of 6 to 13% to obtain a film having the physical properties shown in Table 1. The polypropylene film was used as an adhesive tape in the same manner as in the examples. The adhesive tape properties are shown in Table 1, but when the shrinkage stress onset temperature is less than 116 ° C or the shrinkage stress at the peak value is not within the specified range, "worm" -like defects and dimensional change It becomes a big thing.

Comparative Example 5 An adhesive tape was prepared in the same manner as in Example 1 except that the stretching ratio in the longitudinal direction was 3.7 times. If the strain amount Y was not within the specific range, the tape had a large dimensional change, resulting in a poor appearance.

Comparative Example 6 An adhesive tape was prepared in the same manner as in Example 2 except that stretching in the width direction and heat treatment were not performed (film thickness 40 μm).
m). The physical properties of the film and the tape properties are shown in Table 1. However, if the shrinkage stress value at the peak value of shrinkage stress is not within the specified range, the film may sag, resulting in "worm-like" defects and poor appearance. Recognize.

[Effects of the Invention] The polypropylene film of the present invention has a strain value, a heat shrinkage stress start temperature and a shrinkage stress value at a shrinkage stress peak as specific values, so that the appearance as a pressure-sensitive adhesive tape is good, and a dimensional change and "worm "There is almost no possibility of occurrence of defects.

[Brief description of drawings]

FIG. 1 shows an example of a temperature-width direction heat shrinkage stress curve. T ₁ …… Temperature temperature of heat shrinkage stress in width direction T ₂ …… Peak temperature of heat shrinkage stress S _max …… Maximum value of heat shrinkage stress in width direction

Claims (1)

[Claims] 1. The amount of strain Y (%) in the longitudinal direction of the film is -3 <Y≤ {(W-80) / 220} exp {0.035 (T-80)}, where T is 40 to 140 at the measurement temperature. When the applied load is 80 to 1000 g / mm ² , the transverse heat shrinkage stress start temperature is 116 ℃ or more, and the transverse heat shrinkage stress maximum value is 100 to 500 g / mm ² . A polypropylene film for adhesive tape, which is characterized by