JPH0249214B2 - SUCHIRENKEIJUSHIFUIRUMU - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement of a polystyrene resin film modified with rubber particles, and more specifically, an improvement that exhibits particularly useful features in the field of handkerchief packaging and twist packaging in which the ends of the film are fixed by twisting. The present invention relates to a modified polystyrene resin film. Modified polystyrene resin films containing rubber components have been known for a long time. These rubber components are intended to improve the impact resistance and blocking resistance of the styrene resin without impairing the transparency of the styrene resin as much as possible, and to impart toughness to the styrene resin film. Rubber-like substances such as butadiene rubber, styrene-butadiene block copolymer, and styrene-butadiene graft copolymer are mainly used for these rubber components, and islands of the above-mentioned rubber-like substances are scattered in a sea of polystyrene resin. It is used in a dispersed manner. On the other hand, in the modified polystyrene film market, the required quality has become more sophisticated over the years, and in order to meet the required quality in fields such as handkerchief packaging and twist packaging, it is felt that it is necessary to fundamentally change the quality design. There is something that makes me One example of the reason for this is the handkerchief packaging for fruits and vegetables such as lettuce. Originally, this material had the water vapor permeability (preventing stuffiness) of polystyrene film,
It has been adopted with an emphasis on transparent glossiness (maintaining appearance quality), and the packaging is done by hand.As long as the above two characteristics are met, other It has been put into practical use as long as it has the quality to withstand handkerchief packaging. However, in this handkerchief packaging, the lettuce is placed on top of several sheets of film that have been stacked and cut into squares, and one piece of film is cut from the surface of the stacked film.
Peel off the square ends of each sheet of film, fold them up along the long axis of the lettuce, overlap the two opposing ends on the top of the lettuce, and fold the other two opposing ends together. Because it requires operations such as twisting or tying the film together and locking it, for example, it has the ability to peel off the film one by one accurately, the slipperiness that allows the film to be easily handled, and the film's smoothness. The tear strength and elongation that prevent tearing, the flexibility (tensile elasticity modulus) that prevents twisting of the film, and the toughness (drop weight impact strength), etc., make a huge difference in the work efficiency and packaging quality of manual handkerchief packaging. Therefore, from the standpoint of the consumer, it is a natural quality requirement that these characteristics should be combined at a high level with glossy transparency. However, on the other hand, styrenic films originally have
It is highly rigid, and when it is made into a thin film and swayed in the wind, it makes a metallic sound called ``Siyarisiyari'', and the bends quickly turn white and wrinkle, and when twisted, it can easily tear and tear. It is a film that has Therefore, even if an appropriate amount of rubber material is dispersed and modified, there is a limit to the modification of the characteristics of the styrene film, and even more so, there is a limit to the modification of the characteristics of the styrene film, and even more so, it does not leave behind glossy transparency or a metallic sound. This is because satisfying the above quality requirements means simultaneously satisfying contradictory requirements, which is expected to be extremely difficult. As for the current level of these technologies, for example,
The films disclosed in Japanese Patent Publication No. 50-74649 and Japanese Patent Publication No. 53-35585 are modified films that have poor flexibility and are difficult to twist and fix at the ends of the film. In addition, in particular, JP-A-50-74649 describes that the blocking problem of the film was solved without applying a surface treatment agent, but this is referred to in the present application as slipperiness and peeling. When evaluated in terms of strength, only a low evaluation value is achieved, and therefore, the film is difficult to be used in applications where the film is peeled off one by one. That is, in JP-A-50-74649, the quality of the evaluation of a single surface characteristic, usually called the slip angle, is covered in a wide range of contents without conducting sufficient technical examination. This is because the concept is expressed in place of the term "anti-blocking." Furthermore, the modified films represented by the above two publications are
If an attempt is made to improve the flexibility and toughness of the film by increasing the amount of rubber substances added, the glossy transparency (HAZE) will deteriorate significantly, making it difficult to achieve the goal. I have a problem where I can't. As a method for improving the flexibility of the above technique, there are modified films disclosed in, for example, JP-A-53-87893 and JP-A-53-110688. This film has the flexibility to allow handkerchief packaging and twist packaging, and also has water vapor permeability and glossy transparency, so it was put to practical use in the field of handkerchief packaging and twist packaging prior to the filing of this application. Although it has been developed as a conventional technology and has achieved sufficient results, it has come to a point where it no longer satisfies the above-mentioned increasing quality demands of the market. One of the reasons for this is that properties (e.g. releasability, tear strength, tensile strength and elongation) that cannot be satisfied by modification through the addition of rubber substances, can be achieved by improving lubricity due to special surface treatments and by improving handling. I regret that I have compensated for this by sacrificing my efficiency level. The present invention has been made in view of the current state of modified films, and its purpose is to improve rubber-modified styrene resin films, which have been thought to be virtually impossible to improve any further. ,
It retains the characteristics unique to styrene resins, such as a metallic sound, sufficient water vapor permeability, and glossy transparency, while also providing excellent removability and smoothness without applying a surface treatment agent. It has a high level of mechanical properties such as elasticity, tear strength, tensile strength and elongation, tensile modulus, and drop weight impact strength.
As a result, when applied to handkerchief packaging, for example, an improved modified styrene film is provided that does not cause peeling defects, tear defects, untwisting, etc., and enables highly efficient and high quality packaging. It's about doing. The above object of the present invention is to provide a modified styrenic resin film in which particles of a rubber substance are dispersed in a styrene resin, wherein the particles of the rubber substance are
Particles with an average diameter [Db] of 0.3 to 2μ, which have an occluded structure in which small groups mainly composed of styrene are surrounded by skins mainly composed of butadiene, and particles containing 35 to 80% by weight of styrene and butadiene. is 65~
A 20% by weight styrene-butadiene block copolymer with particles having an average diameter [Ds] of 0.04μ or less and mainly consisting of a butadiene component obtained by dispersing the styrene-butadiene block copolymer in a styrene resin. There are two types, each of which has a butadiene content (wt%) based on the total amount of the film.
[Wb], [Ws], [Wb] = 0.1 to 1.4/[Db],
[Ws] has a value in the range of 0.9 to 9 and is almost homogeneously covaried, and furthermore, the film has an ORS [ASTM・D1504] value of 3 to 25 in two orthogonal axes directions.
The film has an orientation index of [Kg/cm ² ], haze [ASTM・D1003] of 5% or less, tensile modulus [ASTM・D882] of 210 to 265Kg/mm ^{2 , and slip property [ASTM・D1003] of 210 to 265Kg/mm 2} . D1894] and a value of less than 0.7. Hereinafter, the content of the present invention will be explained in detail using drawings and the like. FIG. 1 shows the results of FIGS. 2 and 3 of the film of the present invention.
The figures are micrographs (25,000x magnification) of cross-sections parallel to the surfaces of films for comparison. FIG. 4 is a cross-sectional micrograph (magnification: 25,000 times) of the film shown in FIG. 1 taken in the thickness direction to clearly show the grain structure of the film shown in FIG. In the film of the present invention, an important requirement is that the rubber particles have a structure (i.e., an occluded structure) in which small groups mainly composed of styrene components are surrounded by a skin mainly composed of butadiene components (i.e., particles with a large diameter). ), the styrene component is 35-80% by weight, and the butadiene component is
65 to 20% by weight of a styrene-butadiene block copolymer, the styrene-butadiene copolymer is dispersed in a styrene resin, and the butadiene component is the main component (i.e., small diameter particles). are co-distributed and co-existing in the styrene film. The advantages are shown in Table 1 of the main text (Example/Comparative Example 1)
As shown in , the film of the present invention has flexibility, (tensile modulus), toughness (falling weight impact strength),
This is to achieve a high level of slipperiness and releasability while maintaining glossy transparency. For example, this uses particles with a large diameter or particles with a small diameter, respectively. The film has a level that cannot be achieved by simply increasing the concentration of each of these. What is even more surprising is that the coexistence of these particles is effective in terms of drop weight impact strength, slipperiness, releasability, etc., exceeding the levels that can be achieved by each particle alone. . The cause of this synergistic effect has not yet been fully analyzed, but according to the experiments of the present inventors, for example, by leaving small diameter particles as they are and replacing them with large diameter particles, If other types of rubber material particles are used, or if other types of rubber material particles are used for the small diameter particles while leaving the larger diameter particles as they are, the former will have glossy transparency, It has been observed that peelability, falling weight impact strength, etc. are reduced, and in the latter case, tensile modulus, falling weight impact strength, etc. are reduced, and the same effects as the film of the present invention cannot be obtained. In addition to these phenomena, since the large-diameter particles of the present invention are polymer particles obtained by graft polymerizing styrene-butadiene rubber, butadiene rubber, isoprene rubber, etc. to styrene, they have an occluded structure as shown in Figure 4. On the other hand, the small-diameter particles of are obtained by dispersing them in polystyrene, and the combination of particles in the present invention is are dispersed in such a way that no difference in refractive index occurs in the particles themselves or at the interface between the particles and the styrene resin, so the glossy transparency of the styrene resin is not easily impaired, and It is presumed that the unique flexibility modification ability, shock absorption ability, and surface properties that coexist with the rubber particles have come to be recognized. In order to more objectively confirm the effect of the above-mentioned mixed particles, the present inventors conducted a comparison with techniques in known documents. Known documents include JP-A-50-74649 and JP-A-Sho 53, in which the name or structure of the rubber substance used is relatively similar to the individual particles of the present invention.
I chose Publication No. 110688. However, these documents do not necessarily include particle size,
Since the conditions such as presence or absence of ORS surface treatment are not met,
All of these were adjusted to the conditions of the present invention, and a method was used to compare the property level of the film shown in the rubber substance concentration range referred to in each literature with the film of the present invention. Table 8 (Example/Comparative Example 7) shows the 9th
The table (Example/Comparative Example 8) shows the evaluation results of each film when the concentration of the rubber substance was fixed and the ORS was varied. As is clear from Tables 7 and 8, it can be seen that the film of the present invention exhibits a synergistic effect that cannot be predicted from the characteristics of the films in each document. Moreover, this phenomenon is particularly noticeable in tensile modulus, falling weight impact strength, and surface properties, which supports the above discussion. In particular, in terms of surface properties (without surface treatment), it has been clarified that there is no correlation between slip angle, slipperiness, and releasability. Next, an important requirement of the present invention is the relationship between the particle diameters of the two types of particles and their dispersion concentration, as shown by . This necessity is explained by the fact that even when the particles of the present invention are used together, there are limits to the particle size and dispersion concentration of each of the particles, and beyond this limit the purpose of the present invention cannot be achieved. This is because it will no longer be done. That is, according to Table 2 (Example/Comparative Example 2) and Table 3 (Example/Comparative Example 3) showing this relationship, the larger rubber particle side has an average particle diameter [Db]
is in the range of 0.3 to 2μ, and the relationship between the butadiene content [Wb] and the weight% of the particles relative to the total weight of the film [Db×Wb] is in the range of 0.1 to 1.4, that is, [Wb] = (0.1 to 1.4/ [Db]), and the other smaller rubber particle side has an average diameter [Ds] of 0.04μ.
Below, it is shown that the butadiene content [Ws] of the particles must be in the range of 0.9 to 9 in weight % based on the total weight of the film. The above average particle diameters [Db] and [Ds] are calculated based on the weight average particle diameter. The weight average particle diameter is determined by heating the film at 150℃ for 30 minutes or more to shrink it, making it into a sheet, taking an electron micrograph using an ultrathin section method, and measuring the particle diameter of 500 rubber particles in the photo. It could have been done. [Wb] is expressed as the butadiene content (% by weight) based on the total weight of the film of rubber particles having a structure in which small groups mainly composed of styrene are surrounded by a shell mainly composed of butadiene. [Ws] is expressed as the butadiene content (% by weight) based on the total weight of the film of rubber particles of styrene-butadiene-block copolymer. The value of [Db x Wb] = 0.1 to 1.4 was set in consideration of the optical-physical phenomenon that it is possible and necessary to mix a large amount of butadiene with small diameter particles. Based on the results of Experiment No. 2 and Experiments No. 10 to 19 of Example/Comparative Example 2, which will be described later, this is determined from a range that simultaneously satisfies haze of less than 5% and slipperiness of 0.7 or less. When the weight average particle diameter of the graft copolymer exceeds 2μ, the film becomes hazy and gloss is difficult to obtain (see Experiment No. 16). Moreover, if it is less than 0.3μ, it is difficult to obtain slipperiness. In the case of block copolymer rubber particles, Examples
From Experiment No. 27 of Comparative Example 3, when the weight average particle diameter [Ds] μ of the rubber particles exceeds 0.04 μ, transparency deteriorates (haze increases). In addition, the butadiene content (wt%) of the rubber particles of the butadiene copolymer relative to the total weight of the film.
are Experiment No. 1 of Example/Comparative Example 3 and Experiment No.
24. From the results of experiment No. 26, the tensile modulus is 265Kg/
It is determined from the range of less than mm ² and excellent releasability. Next, an important requirement for the present invention is ASTM
It is necessary that the film be biaxially oriented so as to exhibit an ORS value of 3 to 25 [Kg/cm ² ] according to D1504. ORS (Orientation Release Stress) is defined as the stress that occurs when molecules try to return to their original well-oriented state, and is one indicator of the orientation state of a film. Table 4 (Example/Comparative Example 4) shows the necessity of setting the above-mentioned orientation index within a certain range. content, even if the film is co-dispersed, for example, the ORS is less than 3 [Kg/cm ² ], and 25
If the orientation exceeds [Kg/cm ² ],
This indicates that it is no longer possible to harmoniously combine elongation, drop weight impact, and tear strength to high values. The film of the present invention has the following three main requirements.
Through the integrated combination of the requirements explained in the following sections, the essence of styrene resin, such as a smooth feel, glossy transparency, and excellent water vapor transmission rate, can be maintained, and the surface can be treated. This is a new, unprecedented rubber that satisfies slip angle, slipperiness, and peelability even when not applied, and also has a high level of mechanical properties such as tensile modulus, drop weight impact strength, tear strength, and elongation. It embodies a modified styrene film. In particular, it is considered new that a styrene film with a HAZE (transparency) of 5 or less and a tensile modulus of less than 265 kg/mm ² can be obtained with a slip property of less than 0.7. We have decided to include the characteristics of these three parties in the claims as requirements for distinguishing them from the prior art. Table 5, (Example/Comparative Example 5), and Table 6 (Example/Comparative Example 6) show the results showing the practical performance evaluation when the film of the present invention is put into practical use. On the front, vegetables and fruits such as lettuce are wrapped in handkerchiefs,
It is shown in the case where it is used for twist packaging of confectionery and the like. In addition, Tables 5 and 6 recognize the validity of the evaluation criteria and evaluation scales used to evaluate the film of the present invention, and also show the evaluation results of the film of the present invention using all evaluation criteria. It is. According to the results in Tables 5 and 6, it can be seen that the film of the present invention exhibits excellent practical performance and satisfies all market requirements. In addition, the film of the present invention may be wrinkled, diagonally cut, or rolled into rolls during the slitting process of cutting it to a certain width, the cutting process of cutting it to a certain width and a certain length, and the printing process of printing characters, symbols, patterns, etc. It has also been confirmed that there are advantages in that sticking and the like are less likely to occur, and cut ends are less likely to be fused. The film of the present invention can be produced by mixing a styrene-based resin with a specific rubber substance to be described later, forming the mixture into a film using a known extrusion-stretch film-forming method, and subjecting it to biaxial stretching. There is nothing special to mention about the stretching film forming method, and a desired ORS value can be obtained by adjusting known stretching conditions. As described above, the film of the present invention has sufficient surface properties even without surface treatment, but depending on the application, necessary surface treatment can be applied. The thickness of the film used in practical use is approximately 10μ to 120μ.
This film is mainly suitable for packaging applications, but this film is laminated on one side of another sheet, such as a flowable sheet of HI polystyrene resin, and the resulting laminated sheet is subjected to vacuum forming, pressure forming, etc.
It can also be applied to containers for dairy products and food and drink products. The particles referred to in the present invention are copolymer particles obtained by block and/or random copolymerization of styrene and butadiene, copolymer particles obtained by graft polymerization of styrene-butadiene rubber to styrene, or particles of imprene, butadiene, etc. These are copolymer particles obtained by graft polymerizing a rubber substance with styrene.
Both of these exhibit an occluded structure as shown in FIG. 4, and the particle size is preferably adjusted to be in the range of 0.3 to 2 .mu.m so that the substantial particle size distribution is narrow. The rubber substance content of the graft copolymer (single substance) is preferably in the range of 2 to 20% by weight from the viewpoint of production. Next, the particles of the present invention have a particle size of 0.04 μm when a block copolymer of styrene and butadiene is dispersed in polystyrene, and the particle size is 0.04μ.
The particles are adjusted to have a small particle size as shown below, but at present it does not seem necessary to make this extremely small (for example, 0.002μ). In order to obtain a uniform film thickness, the styrene resin of the present invention is
It is best to choose a solution with a solution viscosity (according to a Canon Fuenske viscometer) of 10 to 30 poise at 25°C. Next, the evaluation method and evaluation scale for evaluating the physical properties and practicality of the film used in the present invention are as follows. Film properties Based on ORS ASTM D1504. Parallel to the film extrusion direction (vertical) and perpendicular to it (horizontal)
Measure the directions and write each direction. Tensile Modulus According to ASTM D882. Measurements are made in the vertical and horizontal directions of the film, and the arithmetic mean value of the two is taken as a geometric mean. Elongation According to ASTM D882. Measurements are made in the vertical and horizontal directions of the film, and the arithmetic mean value of the two is taken as a geometric mean. Falling weight impact strength According to ASTM D1709. Tear strength per ASTM D1922. The film is measured in both the vertical and horizontal directions, and evaluated using the smaller of the arithmetic mean values of the two. Haze (HAZE) According to ASTM D1003. Glossiness According to ASTM D2457 angle of incidence 45°. Slip property According to ASTM D1894. Slip angle per ASTM F254. However, the length of the sliding steel rider is 50.8mm.
A rectangular parallelepiped with a width of 50.8 mm and a height of 9.9 mm and a weight of 200 g was used. Measure the sliding angle between films without surface treatment. Film removability Film cut into 400mm x 400mm squares
Stack 1000 sheets and apply a load of 0.05Kg/ ^cm2 at 38℃
After leaving the film under 90% RH for one week, a test was performed to peel off each film, and up to 50 films were removed.The results are written as follows. [Evaluation scale] ◎: All pieces (50 pieces), each piece peels off. ○: Occasionally, two pieces will peel off when pecked, but there is no practical problem. Δ: Two or more sheets are often peeled off by being pinched, which is a practical problem. ×: Three or more pieces are often peeled off by being pecked at, and it is difficult to peel them off one by one. Method for evaluating practicality of film 1 Lettuce packaging test A film cut into a 400mm x 400mm square was
Stack 500 sheets and apply a load of 0.05Kg/ ^cm2 at 38℃.
Leave it for one week under 90%RH. Next, 8 people each tested the packaging of 50 pieces of lettuce. Packaging testing is performed using the following process. Stacked film (400mm square)
Place the lettuce in the center of the stack. Peel off the square end of one film from the surface of the stack and roll it up along the long axis of the lettuce. The two opposing ends are twisted and locked together. The above tests were conducted and the following items were evaluated. (1) Flexibility Judgment was made based on the results of a lettuce packaging test in which the panel packaging was asked how it felt, and was expressed as follows. ◎: None of the participants felt pain in their fingers during packaging. ○: The majority of people did not feel pain in the middle finger of the packaging. △: More than half of the people complained that their fingers hurt when twisting the film. ×: All of them complained that their fingers hurt when twisting the film. (2) Tear rate The number of films torn during the film packaging test was counted and the tear rate (=
The number of torn sheets/total number of films is calculated and expressed as follows. ◎: Tear rate 0 to less than 0.5% 〃: 〃 0.5% or more and less than 2% △: 〃 2% or more but less than 4% ×: 〃 4% or more (3) Packaging speed Required for 8 people to wrap 50 pieces each Expressed as an average value over time. ◎: Average time required 13 minutes or less 〇: 〃 13 minutes or more, less than 16 minutes △: 〃 16 minutes or more, less than 21 minutes ×: 〃 21 minutes or more (4) Appearance Visually inspect the contents immediately after the packaging test. The evaluation results are expressed as follows. ◎: Lettuce looks very clear. 〇: Lettuce does not look cloudy, and there is no problem in practical use. △: Lettuce looks white and dusty. ×: The film is white and the contents cannot be clearly seen. The overall evaluation was displayed as follows. The evaluation results of flexibility, tear rate, packaging speed, and appearance were treated equally and displayed as follows. Overall evaluation ◎: All items are ◎ 〇: If there is one or more 〇, there is no △ or × △: If there is one or more △, there is no × ×: If there is one or more × 2 Twist packaging test Film Slit into 110mm width and 1000mm length. This film is fed to a horizontal twist wrapping machine (CD company (Italy)) and the wrapping speed is 500.
Pack 1000 pieces each at the condition of 1000 pieces per minute. The contents are biscuits approximately 30 mm x 50 mm. Evaluate the following items. (1) Twist fixity Twist each biscuit twice and visually judge the degree of untwisting. The evaluation results are expressed as follows. ◎: 800 sweets with more than one twist remaining
There are more than one. 〇: 500 sweets with more than one twist remaining
There are more than one. △: More than 500 sweets have more than 3/4 twist and less than 1 twist remaining. ×: More than 800 sweets have more than 3/4 twists and less than 1 twist remaining. (2) Breakage rate Expressed as the defective rate where breakage occurred out of 1000 pieces. ◎: Defect rate 0% 〇: Defect rate over 0% but not more than 0.3% △: Defect rate more than 0.3% and not more than 0.6% If the slipperiness is poor, when the film is fed out from the film roll in the film feed section, the film will be drawn to the film roll, which will eventually make it difficult to cut to the specified length and the length of the film will not be uniform. , there are cases where the contents spill out. The evaluation results are expressed as follows. ◎: The cut length of the film is accurately expressed. ○: The cut length of the film is approximately the same, and there are no cases of the contents spilling out. △: There are occasional film cut mistakes. ×: The cut length of the film often changes. (4) Appearance Visually inspect the contents immediately after the packaging test. The evaluation results are expressed as follows. ◎: Contents are clearly visible. 〇: Contents are visible without clouding and there is no problem in practical use. △: The film feels a little dusty. ×: The film is white and the contents cannot be clearly seen. The display method for the overall evaluation was the same as that for lettuce packaging. Preparation of resins used Graft copolymers of SBR and styrene (A to F) (hereinafter abbreviated as graft copolymers) were produced in the following manner. Resin A, B SBR rubber (manufactured by Asahi Kasei Corporation, product name: Tuffden)
2000, Mooney viscosity 45.5% styrene solution viscosity
(45 cps, styrene content 25%) was dissolved in styrene monomer and bulk polymerization was performed. Polymerization takes place at 130℃ 5
The mixture was heated at 150° C. for 4 hours and at 180° C. for 2 hours with stirring, and polymerization was carried out until the weight ratio of SBR rubber to polystyrene was 8:92. During the process, the rubber particle size was changed by changing the stirring number of the reactor.
Two types of resins, 2.5μ (resin A) and 2.0μ (resin B), were obtained. Residual monomers were removed from these polymers under vacuum at 230° C. for 2 hours, and the resulting pellets were pelletized using a 40 mm extrusion pelletizer. Resin C: Mix 84 parts by weight of styrene monomer, 8 parts by weight of ethylbenzene, and 8 parts by weight of SBR rubber (manufactured by Asahi Kasei Corporation, product name: Tuffden 2000, Mooney viscosity 45, 5% styrene solution viscosity 45 cps, styrene content 25%) Dissolved and prepared a rubber solution. Add a polymerization initiator to 100 parts by weight of the above rubber solution.
0.03 parts by weight was added to prepare a polymerization raw material liquid. This polymerization raw material liquid was continuously fed into a continuous three-stage reactor to perform polymerization. The stirring number of the first stage reactor is
The speed was maintained at 50 rpm, and the polymerization rate of styrene monomer in the first stage reactor was maintained at 30%. The average polymerization rate in the first stage reactor was 10.2%/HR. Subsequently, the polymerization liquid was continuously sent to the second stage reactor and the third reactor, and then sent to a devolatilization device to remove unreacted components. The weight average particle diameter was 1.0μ. Resin D Polymerization was carried out under the same conditions as Resin C, except that the reaction temperature in the first stage reactor was increased and the average polymerization rate in the first stage reactor was set to 13.0. The weight average particle size in the obtained polymer was 0.3μ. Resin E 0.05 parts by weight of t-butyl perbenzoate was added to 100 parts by weight of the rubber solution of Resin A, and the first
Polymerization was carried out under the same conditions as Resin A, except that the stirring speed of the stage reactor was 100 rpm and the average polymerization rate in the first stage reactor was 16.7%. The weight average particle diameter in the obtained polymer was 0.1μ. Styrene of each (G to I) is prepared by the following method.
A butadiene-block copolymer (hereinafter abbreviated as block copolymer) was produced. Resin G Under a nitrogen gas atmosphere, (a) 0.126 mol of n-butyllithium as an active lithium compound was added to a toluene solution containing 15% by weight of styrene.
Polymerization was carried out at ℃ for 7 hours, and after 99% of the added styrene was polymerized, (b) a toluene solution containing 10% by weight of 1,3-butadiene was added in an amount 0.64 times the amount of (a) above, and polymerization was carried out at 50℃ for 5 hours. After more than 99% of the added 1,3-butadiene was polymerized, 0.032 mol of silicon tetrachloride was added to carry out a coupling reaction without losing activity. After adding 0.5 parts by weight of a heat stabilizer per 100 parts by weight of the block copolymer to the obtained solution of the block copolymer, the copolymer was precipitated in methanol. The weight average molecular weight of the obtained block copolymer was about 150,000, and the ratio of styrene to butadiene was about 7:3. Resin H For the method of manufacturing resin G, (a) styrene was added to 15
Change the polymerization time of the wt% toluene solution to 5 hours, and (b) change the amount of the 10 wt% toluene solution of 1,3-butadiene to 2.25 times that of (a) and change the polymerization time to 7 hours. Polymerization was carried out under the same conditions as Resin G except for the following. The ratio of styrene to butadiene in the obtained block copolymer was 4:6. Resin I For the method by which Resin G was manufactured (a) 15 of styrene
Except that the polymerization time for the wt% toluene solution was changed to 4 hours, the amount of the 10 wt% toluene solution of 1,3-butadiene was increased 3.5 times that of (a), and the polymerization time was changed to 8 hours. Polymerization was carried out under the same conditions as Resin G. The ratio of styrene to butadiene in the obtained block copolymer was 3:7. Examples, Comparative Example 1 The raw material resins used were general polystyrene [trade name: Styron 685, manufactured by Asahi Dow Co., Ltd.] and resin C.
(graft copolymer) and resin G (block copolymer) were used. The above resins are mixed in the formulation shown in Table 1, Section A,
Extruded with a 50mm extruder and stretched 8 times in length and width using the inflation method at a resin temperature of 180℃.
A 16 μ film with an ORS of 9 to 16 Kg/cm ² was obtained. The tensile modulus, falling weight impact strength, slipperiness, and cloudiness of this film were evaluated using the method and evaluation scale described in the text, and the results are listed in Table 1 (D). Experiments No. 1 to 3 in Table 1 use graft copolymers,
The film is a mixture of block polymer rubber particles, and it can be seen that it satisfies each evaluation item at a high level. FIG. 1 is an electron micrograph of a cross section of the film (parallel to the film surface) of Experiment No. 2 of the present invention. From FIG. 1, it can be clearly seen that in the film of the present invention, a small number of large rubber particles of the graft copolymer are mixed with a large number of fine rubber particles of the block copolymer. On the other hand, from Table 1, the films of Experiment Nos. 4 to 6 used only the graft copolymer and varied the amount of the graft copolymer, but it was difficult to achieve high standards for each evaluation item. I understand. Figure 2 is an electron micrograph of a cross section (parallel to the film surface) of the film of Experiment No. 5. It can be seen that only large rubber particles of the graft copolymer are present. In addition, although the films of Experiment Nos. 7 to 9 in Table 1 used only block copolymers and varied the amount of the block copolymer mixed, it was found that it was still difficult to achieve high standards for each evaluation item. Ru. FIG. 3 is an electron micrograph of a cross section of the film (parallel to the film surface) of Experiment No. 8. It can be seen that only minute rubber particles of the block copolymer are present.

[Table] Example; Comparative Example 2 The same experiment as in Example and Comparative Example 1 was repeated except that the mixing ratio of the raw materials was changed as shown in Table 2 (A).
The graft copolymers used were resins A, B, C,
D and E. Item (B) in Table 2 shows the content of large rubber particles. The film of Experiment No. 2 was added to the obtained film, and the slip properties, cloudiness, gloss, and releasability were evaluated using the method and evaluation scale described in the text. The results are shown in Table 2 (D). The films of Experiment No. 2 and Experiment Nos. 10 to 15 had good slip properties, haze, gloss, and peelability. In Experiment No. 16 of Comparative Example 2, the gloss was somewhat unsatisfactory. Experiments No. 17, 19, and 21 had a high degree of cloudiness. Rubber particle diameter [Db] μ of graft copolymer of these films and base resin of rubber particles (film)
When looking at the relationship between the butadiene content [W] and the weight percentage of [Db] x [Wb], it can be seen that all of these films exceed the value of 1.4. On the other hand, Experiment Nos. 18, 20, and 22 had poor slip properties. If we look at the values of [Db] x [Wb] in the same way as above, we can see that they are all less than 0.1. Even if the value of [Db] x [Wb] satisfies the value of 0.1 to 1.4, if the weight average rubber particle diameter [D] exceeds 2.0 μ as in Experiment No. 16, the gloss will decrease,
Also, as in Experiment 23, the weight average rubber particle diameter [Db]
If it becomes smaller than 0.3μ, the slipperiness will deteriorate. From the above, in order to simultaneously obtain the desired slipperiness, cloudiness, and gloss releasability, the weight average rubber particle diameter [D]μ of the graft copolymer must be 0.3μ or more, 2.0μ
The butadiene content [Wb] of the large rubber particles based on the base resin (film) is as follows:
It can be seen that the relationship between [Db] x [Wb] should be between 0.1 and 1.4.

[Table] Example, Comparative Example 3 The same experiment as in Example and Comparative Example 1 was repeated except that the composition of the resin was changed as shown in Table 3 (A). The block copolymers used were Resins G, H, and I. The films of Experiment Nos. 1 and 2 were added to the obtained films, and the tensile modulus, cloudiness, and peelability were evaluated using the method and evaluation scale described in the text. The results are shown in Table 3 (D). Experiments Nos. 1 and 2 and Experiment No. 24 had excellent tensile modulus haze and peelability. In Experiment No. 25, the film had a high tensile modulus and poor flexibility, and in Experiment No. 26, the tensile modulus of the film was too low, inhibiting peelability. In order to obtain an appropriate tensile modulus, pay attention to item (B) in Table 3, and compare Experiment No. 1 and Experiment No. 25, Experiment No. 24 and Experiment
From the results of No. 24, the butadiene content (wt%) of the block copolymer relative to the base resin (film)
It can be seen that the ratio should be between 0.9% and 9%. Furthermore, in Experiment No. 27, even if the butadiene content (% by weight) of the block copolymer was within the above range, the rubber particle diameter was large, so the degree of haze was increased. Experiment No.
A comparison between Experiment No. 27 and Experiment No. 24 shows that the weight average rubber particle diameter of the block copolymer should be 0.04μ or less.

[Table] Example, Comparative Example 4 Six types of films with different ORS were produced by changing the stretching conditions using the raw material blending ratio used in Experiment No. 2 (general polystyrene 80%, resin C 5%, resin G 15%). I got it. The stretching conditions were appropriately selected such that the stretching ratio was 4 to 15 times and the resin temperature during stretching was 140 to 190°C. The ORS of the obtained film is shown in Table 4 (C). The film of Experiment No. 2 was added to the obtained film, and the degree of cloudiness and slipperiness were evaluated using the method and evaluation scale described in the text. The results are shown in Table 4 (D). The films of Experiment No. 2 and Experiments No. 28 to 30 had excellent elongation, falling weight impact strength, and tear strength. Experiment No. 31 had a film that was easy to tear. Experiment No. 32 had a brittle film. From the results in Table 4, even if the dispersion state of the rubber particles shown in Examples and Comparative Examples 1, 2, and 3 is appropriate, if you pay attention to item (C) in Table 4, it is possible to obtain excellent mechanical properties.
It is found that the ORS should be between 3 and 25 Kg/ ^cm2 .

[Table] Example 5, Comparative Example 5 Since the evaluation of the films of Example and Comparative Examples 1 to 4 was a partial evaluation, just to be sure, Experiment No. 1, 2,
A lettuce packaging test was conducted on films Nos. 11, 12, 23, 25, 6, 7, 22, 26, and 27 using the method and evaluation scale described in the text. The results are shown in Table 5. The films of Experiment Nos. 1, 2, 13, 12, 28, and 30 met all required performances. Experiment No. 6 had a high degree of haze and had a poor appearance. In Experiment No. 22, the packaging speed was unsatisfactory due to lack of slipperiness. Experiment No. 23 had a high tensile modulus and was unsatisfied with its flexibility. Experiment No. 31 has a high ORS, so the tear strength is low and the tearing rate (due to tearing) is high. Experiment No. 32 had a low ORS, low elongation drop impact strength, and a high breakage rate (due to brittleness). From Table 5, it can be seen that the lettuce packaging film must have the following physical property values. (1) Tensile modulus 210-265Kg/mm ² (2) Elongation 40% or more (3) Fall weight impact strength 3Kg・cm or more (4) Tear strength 1.4g or more (5) Slip property 0.7 or less (6) ) Haze 5.0% or less Furthermore, since the evaluation symbols for the film's physical properties correspond to the evaluation symbols for the practical characteristics, it can be seen that the evaluation symbols for the film's physical properties are appropriate evaluations.

【table】

[Table] Example 6, Comparative Example 6 Experiment No. 1, 2, 13, 12, 28, 30, 6, 22, 25,
A twist wrapping test was conducted on films 31 and 32. The test method and evaluation scale used were those described in the text. The films of Experiment Nos. 1, 2, 13, 12, 28, and 30 met all required performances. Experiment No. 6 had a high degree of haze and had a poor appearance. In Experiment No. 22, the cutting performance was unsatisfactory due to the lack of slipperiness. Experiment No. 25 had a high tensile modulus and was unsatisfied with twist fixation. Experiment No. 31 had a high ORS and a high rate of tearing. In Experiment No. 32, the film was brittle and had a high tearing rate. From this, it can be seen that even in twist packaging, it is necessary to have the physical property values described above (lettuce packaging test). It can also be seen that the film evaluation display is appropriate.

【table】

[Table] Example, Comparative Example 7 Next, in order to further clarify the characteristics of the present invention, a comparison with the prior art was made. As the known literature, we selected JP-A-50-74649 and JP-A-53-110688, in which the names and compositions of the rubber substances used are described in the examples. Film performance varies depending on the raw materials used, ORS, film thickness, and surface treatment, so for example, when evaluating only the differences due to the raw materials used,
It is necessary to make a judgment after aligning the ORS, film thickness, and surface treatment conditions. The above literature does not necessarily include ORS, film thickness,
Since the conditions for surface treatment were not available, only the raw materials used were adjusted to the conditions described in the literature and within the range of practicable conditions. In other words, the graft copolymer of styrene and butadiene contains a high-impact polymer containing about 94.1% by weight of polystyrene and about 5.9% by weight of rubber, as described in Example 1 of JP-A-50-74649. The rubber was polymerized with polystyrene so that the polystyrene was grafted and occluded (interpreted as an occluded structure) at a ratio of 2.5 parts of polystyrene per part of rubber, and the diameter of the dispersed weight-average particles was approximately 2.2μ. Manufactured under selected conditions. The rubber used was Tuffden 2000 (properties described above) used in the present invention. The obtained resin was named F resin. Next, the block copolymer was disclosed in Japanese Patent Application Laid-Open No. 53-110688.
Tuffprene used in "Example 1 and Comparative Example 1" was used. Further, the ORS was manufactured to have a length of 108 Kg/cm ² and a width of 8.8 Kg/cm ² as described in Japanese Patent Application Laid-Open No. 74649/1982. However, the method was the same as in Example 1 except that only the stretching ratio and stretching temperature were changed. Further, the film thickness was 16μ and no surface treatment was applied. The results are listed in Table 7. Experiment Nos. 33 to 36 were films in which rubber particles of a graft copolymer having a polymerization average particle diameter of 2.2 μm, which is a requirement of the present invention, and rubber particles of a block copolymer were mixed. The weight average particle diameter of the block copolymer (Tuffprene) was 0.035μ. Experiment Nos. 37 to 40 are films manufactured based on the assumption of JP-A-53-110688, in which only minute rubber particles (weight average particle diameter 0.035 μ) of styrene-butadiene-block copolymer are present. According to Table 7, the films corresponding to JP-A No. 110688/1988 are the films of the present invention (Experiment Nos. 33 to 36).
It can be seen that not only the slip property and the slip width by the slip angle method are improved, but also the falling weight impact strength is improved. Next, Experiment Nos. 41 to 44 are films manufactured based on the assumption of JP-A-50-74649, in which only large (weight average particle diameter 2.2 μ) rubber particles of the graft copolymer are present. From Table 7, Tokukaisho
Compared to the film of the present invention (Experiment Nos. 33 to 36), the film corresponding to Publication No. 50-74649 showed not only the tensile modulus but also the drop weight impact strength, the slip angle measured by the slip angle method, and especially the film 1. It can be seen that the releasability of peeling off one sheet at a time has been greatly improved. It is also clear that the slippage by the slip angle method and the peelability of peeling off the film one by one do not necessarily have the same tendency. It is presumed that the reason for the improved releasability of the present invention is the synergistic effect of slipperiness, typified by slip angle or the like, and tensile modulus (flexibility).

[Table] Example, Comparative Example 8 Next, Example, except for changing the ORS of the film.
The same experiment as Comparative Example 7 was repeated. In the present invention, the blending ratio of raw materials is Experiment No. 34, JP-A-53
-Experiment No. 39 corresponding to Publication No. 110688, JP-A-1983-
In the case equivalent to Publication No. 74649, it was adjusted to Experiment No. 42. The film's ORS is 5 as shown in Table 8 (B).
It was evaluated based on the level. From Table 8, it is clear that the performance of the film changes depending on the ORS. Among them, the film of the present invention (Example 8) has different characteristics compared to the film of Comparative Example 8.
When comparing ORS, it is clearly seen that each evaluation item is met at a high level. This tendency is particularly noticeable in peelability, falling weight impact strength, etc. Experiment No.53-56
In the evaluation based on the slip angle, although relatively good performance was obtained, it was found that the releasability of peeling off one sheet at a time was unsatisfactory.

【table】 [Brief explanation of drawings]

Figures 1, 2, and 3 are photographs taken with a transmission electron microscope at a magnification of 25,000 times of cross sections parallel to the surface of the film. Figure 1 shows experiment No. 2,
The figure is a photograph of the film of Experiment No. 5, and Figure 3 is a photograph of the film of Experiment No. 8. Figure 4 is a photograph of a cross section parallel to the thickness direction of Experiment No. 2 film taken with a transmission electron microscope at a magnification of 25,000 times, and is an enlarged view of the side occluded portion of Figure 1. Figure 5 shows Experiment No. 2.
The graph shows the relationship between the weight average rubber particle diameter of the graft copolymer and the butadiene content (wt%) in Experiment Nos. 10 to 19.
The mark is a comparative example. )

Claims (1)

[Scope of Claims] 1. A modified styrenic resin film in which particles of a rubber substance are dispersed in a styrene resin, wherein the particles of the rubber substance are composed of small groups mainly composed of a styrene component and small groups mainly composed of a butadiene component. Average diameter of the occluded structure [Db]
A styrene-butadiene block copolymer containing particles of 0.3 to 2μ, a styrene component of 35 to 80% by weight, and a butadiene component of 65 to 20% by weight, the styrene-butadiene block copolymer being dispersed in a styrene resin. There are two types of particles with an average diameter [Ds] of 0.04μ or less, which are mainly composed of butadiene components.
[Wb] = 0.1 to 1.4/[Db] and [Ws] have values in the range of 0.9 to 9 and are almost homogeneously covaried, and furthermore, the film is subjected to ORS [ASTM・
D1504] has an orientation index of 3 to 25 [Kg/cm ² ], and the film has a haze value [ASTM・D1003]
5% or less, tensile modulus [ASTM・D882]
210~265Kg/mm ² , sliding property [ASTM・D1894]
A styrene resin film having a value of less than 0.7.