CN112111237B

CN112111237B - Film for display back shell and protection thereof

Info

Publication number: CN112111237B
Application number: CN201910530048.6A
Authority: CN
Inventors: 万倍祯; 贯井启介; 真锅功; 荒井崇
Original assignee: Toray Advanced Materials Research Laboratories China Co Ltd
Current assignee: Toray Advanced Materials Research Laboratories China Co Ltd
Priority date: 2019-06-19
Filing date: 2019-06-19
Publication date: 2023-03-31
Anticipated expiration: 2039-06-19
Also published as: CN112111237A

Abstract

The invention provides a film and a shell made of the film, which can be used as a back shell and shell protection of an electronic product display. The film provided by the invention does not warp in the gluing and printing processes, does not have the problem of inter-film adsorption or positioning sliding, and does not influence the subsequent processing and production efficiency. The film has the advantages of less foreign matters in the film, low haze and high full light transmittance, and does not influence the appearance decorative effect. The molding performance and the bonding performance of the composite material are excellent, the composite material can meet the requirements of curved surface molding or bonding, the appearance does not have the bad phenomena of folds or deformation and the like before and after molding or bonding, the composite material can be suitable for protecting a plane and a curved surface shell and a shell, and the appearance quality is high. The shell made of the film provided by the invention can be subjected to UV photoetching and is suitable for high-end machine types and overseas brand machine types.

Description

Film for display back shell and protection thereof

Technical Field

The invention relates to a film and a shell made of the film, in particular to a film for protecting a display back shell and a shell.

Background

With the rapid development of the consumer electronics industry, various manufacturers have not only continuously innovated the functions of electronic products, but also continuously promoted new products in the appearance design. Many electronic products on the market become glass dorsal scale from original metal dorsal scale, in order to prevent that glass dorsal scale is cracked to splash, can use film and glass dorsal scale laminating. And a plurality of decorative layers are added on the surface of the film for more beautiful design effect.

However, the adhesive films on the market today have many disadvantages in terms of conformability or appearance decorative properties. In addition, more and more curved screen electronic equipment appears in the market at present, and not only the camber of its casing is littleer and littleer, the curved surface casing of four sides has still appeared. This places higher demands on the curved surface processability and conformability of the film. How to make an adhesive film have both appearance decorativeness, conformability and formability is a great problem in the industry.

Disclosure of Invention

In view of the shortcomings of the prior art, the present invention provides a film and a housing made therefrom, which can be used as a back housing and housing protection for electronic product displays.

In practical use, at least one side of the film is coated with an adhesive layer, the adhesive is generally coated at high temperature, and the film is subjected to high-temperature treatment and then has different degrees of thermal shrinkage in the length direction and the width direction, so that the coated adhesive film is warped or deformed, and the subsequent processing technology and the production efficiency are directly influenced. After the film is subjected to heat treatment at 150 ℃ for 30 minutes, the thermal shrinkage rate Hm in the length direction and the thermal shrinkage rate Ht in the width direction of the film meet the following formula 1:

0% to | Hm-Ht | to 0.3% to formula 1.

Within this range, it is possible to ensure that the film does not warp or deform after coating.

The display back cover and cover protection are directly visible to the human eye, so that foreign matter, if any, in the film applied thereto is easily found. Moreover, for the decoration effect, the surface of the film is generally provided with a decoration layer, and meanwhile, the transparency of the film directly influences the decoration effect. Therefore, the film of the present invention is preferred to have a number of foreign matters having a particle diameter of 10 μm or more of 1 per mm ² The film has a total light transmittance of 88% or more and a haze of 2.0% or less, and thus appearance problems due to transparency of the film can be avoided.

When the film is used for protecting the shell, the film can be attached to the shell, and if the film is thermally deformed in the attaching process, the film can be wrinkled during attaching. In order to avoid wrinkles and deformation during the lamination process, it is preferable that the film of the present invention satisfies the following formula 2-formula 3 at a thermal expansion coefficient Ca of 30-50 ℃ and a thermal expansion coefficient Cb of 75-100 ℃:

1.0╳10 ^-5 mm/℃≦Ca≦2.0╳10 ^-5 mm/DEG C formula 2;

0.5╳10 ^-5 mm/℃≦Cb≦1.5╳10 ^-5 mm/. Degree.C.formula 3.

The film needs to be carried for many times in the process of being processed and made into the decorative explosion-proof film for many times, and the film surface needs to have a certain friction coefficient in the processing process, so that the film can be prevented from sliding to cause positioning error or being adhered to adsorb to cause non-continuous processing in the carrying process. Therefore, the film of the present invention is preferred to have a dynamic friction coefficient μ s and a static friction coefficient μ k satisfying the following formula 4 to formula 5:

0.4. Mu.s. Is 0.6. Mu.s.4. Mu.s.0.6 formula 4.

0.2 ≦ μ k ≦ 0.4 formula 5.

To prevent the glass from shattering and splashing, a certain adhesion between the film and the glass is required, but too high an adhesion results in difficulty in tearing the film and rework operations in case of problems with the application. Meanwhile, if reworking operation is needed, the film is required to have certain rigidity and is not easy to break in the tearing process. And the film has certain rigidity, which is also beneficial to the jointing operation. Therefore, the film of the present invention preferably has an adhesive layer on at least one side, and can be bonded to glass, the adhesive layer has an adhesive strength of 10N/inch to 30N/inch, and the film has a Young's modulus of 3.5GPa to 5.5 GPa.

From the processing technology of the decorative film, the adhesive layer of the film is processed first, and then the decorative coating is processed. Since the above two steps are separately performed, a release film is attached to the adhesive surface after the adhesive layer is processed, so as to facilitate the subsequent processing. The decorative coating is generally processed by a printing process, and the printing process has a drying process, so that the adhesive film attached with the release film cannot have large thermal shrinkage in the drying process, thereby generating warping deformation and further influencing the subsequent processing process and the production efficiency. Therefore, it is preferable that the film of the present invention further includes a release film between the adhesive layer and the film, and after the heat treatment at 75 ℃ for 60 minutes, the film has a thermal shrinkage Tm in the longitudinal direction and a thermal shrinkage Tt in the width direction after the heat treatment at 75 ℃ for 60 minutes, which satisfy the following formula 6 to formula 7:

0% Tm < 0.5% formula 6;

0% ≦ Tt ≦ 0.3% equation 7.

In addition, as a decorative explosion-proof film, a film is required to have a decorative property and not to affect a decorative effect due to molding and bonding with a housing. It is therefore preferred that the film of the present invention has one or more decorative layers on at least one side, and that the haze when the film is stretched at a stretch ratio of 10% HZa and the haze before stretching HZb satisfy the following formula 8:

Hza-Hzb ≦ 0.5% for formula 8. Within this range, it is possible to ensure that the decorative effect before and after molding is not affected by the moldability of the film.

At present, each consumer electronics manufacturer uses UV light to etch patterns such as brands and trademarks inside the housing, especially high-end models or overseas brands. Therefore, the invention also discloses a shell, and the transmittance of light under the wavelength of 355nm is more than 10% and less than 40% after the decorative explosion-proof film is attached. Within the range, the UV photoetching condition can be met, and other performances cannot be influenced. In order to satisfy this requirement, it is more preferable that the case to which the decorative explosion-proof film of the present invention is attached has a light transmittance of from 20% to 30% at a wavelength of 355 nm.

In order to better conform to curved screens, good film formability must be ensured. It is preferable to use the decoration film thickness Aa at the corner R of the curved surface of the case and the decoration film thickness Ab of the flat portion of the case according to the present invention satisfying the following formula 9 to formula 11:

25um ≦ Aa ≦ 100um formula 9;

25um ≦ Ab ≦ 100um formula 10;

(Ab-Aa)/Ab 100 ≦ 15 formula 11. When the adhesive is applied within this range, wrinkles are not easily generated.

Drawings

FIG. 1 is a view showing the attachment of a film to a housing; wherein, 1 shell, 2 adhesive layers, 3 films and 4 decorative layers.

FIG. 2 is a flow chart of a general curved surface decoration explosion-proof membrane process.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the following describes embodiments of the present invention in further detail with reference to the accompanying drawings and tables.

The films, adhesives, release films, inks, and cases used in the examples and comparative examples were as follows (specific physical properties are shown in table 1):

< film >

A: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched at that temperature by a factor of 3.0 in the direction of rotation of the roll (MD direction) by the rotation of the roll. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.5 times in the width direction (TD direction) at 120 degrees, and heat-treated at 220 ℃ to shrink 2% in the MD direction with the film interposed. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film were 150 ℃ 30min heat shrinkage to length direction Hm0.3%, width direction Ht0.3%, total light transmittance 91.0%, haze 0.4%, coefficient of dynamic friction 0.4, coefficient of static friction 0.3, young's modulus 4.2GPa.

B, a polyethylene terephthalate raw material containing a filler was melt-extruded at 280 ℃ onto a casting roll at 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched 3.0 times in the roll rotation direction (MD direction) by the rotation of the roll at that temperature. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.5 times at 120 degrees in the width direction (TD direction), heat-treated at 230 ℃ so as not to shrink in the MD direction while sandwiching the film, and finally, a biaxially stretched polyester film having an easy-adhesion layer was obtained. The film had physical properties of 50 ℃ 30min heat shrinkage of Hm0.9% in the length direction, ht0.6% in the width direction, a total light transmittance of 87.0%, a haze of 2.1%, a coefficient of dynamic friction of 0.5, a coefficient of static friction of 0.4, and a Young's modulus of 4.1GPa.

Melt-extruding a polyethylene terephthalate raw material containing no filler at 280 ℃ onto a casting roll of 20 ℃ to which static electricity is applied to prepare a cast film, heating to 100 ℃ and stretching the film by a factor of 3.0 in the roll rotating direction (MD direction) by the rotation of a roll shaft at that temperature. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.5 times at 120 degrees in the width direction (TD direction), and heat-treated at 235 ℃ to shrink 1% in the MD direction with the film interposed, to obtain a biaxially stretched polyester film having an easy-adhesion layer. Finally, a coating material capable of improving the adhesion property is coated on the surface of the polyester film, and the polyester film is dried at 80 ℃ and cured by UV irradiation to form a coating film. The physical properties of the film were 150 ℃ 30min heat shrinkage to length direction Hm0.6%, width direction Ht0.4%, total light transmittance 91.0%, haze 1.0%, coefficient of dynamic friction 0.8, coefficient of static friction 0.6, young's modulus 4.2GPa.

D: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched at that temperature by a factor of 3.0 in the direction of rotation of the roll (MD direction) by the rotation of the roll. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.5 times in the width direction (TD direction) at 120 degrees, and heat-treated at 220 ℃ to shrink 1% in the MD direction with the film interposed. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film were 150 ℃ 30min heat shrinkage to length direction Hm0.6%, width direction Ht0.4%, total light transmittance 90.0%, haze 1.0%, coefficient of dynamic friction 0.4, coefficient of static friction 0.3, young's modulus 4.3GPa.

E: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched at that temperature by a factor of 3.0 in the direction of rotation of the roll (MD direction) by the rotation of the roll. In the running state of the film, the easy-to-adhere coating material whose dynamic surface tension is measured in advance is coated on both sides of the film by a wire bar. Then, the film was stretched 3.5 times at 120 degrees in the width direction (TD direction) and heat-treated at 220 ℃ to sandwich the film without shrinkage in the MD direction. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film were 150 ℃ C. For 30min, heat shrinkage was Hm0.8% in the length direction, ht0.5% in the width direction, total light transmittance 91.0%, haze 1.1%, coefficient of dynamic friction 0.4, coefficient of static friction 0.3, and Young's modulus 4.1GPa.

F: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched at that temperature by a factor of 3.0 in the direction of rotation of the roll (MD direction) by the rotation of the roll. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.5 times at 120 degrees in the width direction (TD direction), and heat-treated at 220 ℃ to shrink 2% in the MD direction while sandwiching the film. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film were 150 ℃ 30min heat shrinkage to length direction Hm0.4%, width direction Ht0.3%, total light transmittance 89.0%, haze 0.8%, coefficient of dynamic friction 0.5, coefficient of static friction 0.3, young's modulus 4.4GPa.

G: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched 2.9 times in the roll rotation direction (MD direction) by the rotation of the roll at that temperature. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.4 times at 120 degrees in the width direction (TD direction) and heat-treated at 220 ℃ to sandwich the film without shrinkage in the MD direction. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film were 150 ℃ 30min heat shrinkage to length direction Hm1.0%, width direction Ht0.6%, total light transmittance 90.0%, haze 1.3%, coefficient of dynamic friction 0.5, coefficient of static friction 0.4, young's modulus 3.8GPa.

H: a polyethylene terephthalate raw material containing a filler was melt-extruded at 280 ℃ onto a casting roll at 20 ℃ to which static electricity was applied to produce a cast film, which was then heated to 100 ℃ and stretched at that temperature by 3.0 times in the roll rotation direction (MD direction) by the rotation of the roll. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.6 times at 120 degrees in the width direction (TD direction), and heat-treated at 235 ℃ to sandwich the film so as not to shrink in the MD direction, thereby obtaining a biaxially stretched polyester film having an easy-adhesion layer. Finally, a coating material capable of improving the adhesion property is coated on the surface of the polyester film, and the polyester film is dried at 80 ℃ and cured by UV irradiation to form a coating film. The physical properties of the film are that the film is subjected to thermal shrinkage at 150 ℃ for 30min to Hm0.7% in the length direction, ht0.2% in the width direction, 87.1% of total light transmittance, 2.2% of haze, 0.8 of dynamic friction coefficient, 0.6 of static friction coefficient and 4.2GPa of Young modulus.

I: a polyethylene terephthalate raw material containing no filler was melt-extruded at 280 ℃ onto a casting roll of 20 ℃ to which static electricity was applied to prepare a cast film, which was then heated to 100 ℃ and stretched 2.8 times in the roll rotation direction (MD direction) by the rotation of the roll at that temperature. In the film running state, an easy-to-adhere coating material having a dynamic surface tension measured in advance was applied to both sides of the film by a wire bar. Then, the film was stretched 3.3 times at 120 degrees in the width direction (TD direction) and heat-treated at 220 ℃ to sandwich the film without shrinkage in the MD direction. Finally, a biaxially stretched polyester film having an easy adhesion layer was obtained. The physical properties of the film are that the film is subjected to thermal shrinkage at 150 ℃ for 30min to obtain Hm1.0% in the length direction, ht0.5% in the width direction, 90.0% of total light transmittance, 1.0% of haze, 0.4 of dynamic friction coefficient, 0.3 of static friction coefficient and 3.3GPa of Young modulus.

< Adhesives >

Polymethyl methacrylate, and glass has an adhesion of 18N/inch.

< Release film >

I: a silicon-based release film.

< ink >

I: a color royal black ink.

< housing >

1: the curved glass of the blue Cisco technology company has an arc chamfer of R6mm on the long side.

Tables 1 and 2 show the films and release films used in examples and comparative examples, respectively. Table 3 shows the basic properties of the film and the curved casing in the examples and comparative examples after bonding. Table 4 shows the results of examples and comparative examples. The invention relates to a process flow of a curved surface decoration explosion-proof membrane (figure 2), so the embodiment and the comparative example are mainly explained by a processing process. As can be seen from Table 4, the film had no warpage from the application of the adhesive to the printing, and the film was considered to have processability. The film has no cracking, whitening and wrinkling problems in the curved surface forming and attaching process, and is considered to be suitable for attaching the shell with a plane and a curved surface; the appearance of the adhered shell does not show abnormal conditions such as white spots, foreign matters and the like, and the film is considered to have high-quality appearance and not influence the decorative effect. The attached shell can be subjected to UV photoetching processing, and the shell can be used for etching icons and can be used as a shell on a display of a high-end or overseas brand.

The following examples and comparative examples were used to conduct tests. The test methods used in the examples and comparative examples are as follows.

1. Thermal shrinkage: the test was performed with a projector, and the dimensional change before and after the heat treatment was calculated. Two points with a mark interval of about 100mm in the longitudinal direction and the width direction of the film were measured accurately by a projector, and the distance between the two points was recorded as Xm in the longitudinal direction and as Xt in the width direction. And then putting the sample into an oven with a specified temperature for heat treatment, taking out the sample after the test time is up, and accurately measuring the distance between the two points by using a projector again, wherein the distance in the length direction is recorded as Xm ', and the distance in the width direction is recorded as Xt'. Then, the heat shrinkage Hm and Ht in both directions were calculated according to the formula H = (X-Y)/X × 100.

2. Number of foreign matters: the test was observed with a microscope. After printing black ink on the back surface of the film, the number of foreign matters having a particle diameter of 10 μm or more within 1mm2 was counted by observing and measuring with a microscope.

3. Haze and total light transmittance: and testing by using a haze meter. Cutting the film into proper size, putting the film into a haze meter, and testing by using a C light source transmission method.

4. Coefficient of thermal expansion: and tested by TMA. The film was cut into strips 20mm long by 3mm wide in the longitudinal direction and the width direction, respectively, and tested in the TMA tensile mode. Wherein the testing temperature range is 25 ℃ to 120 ℃, the heating rate is 10 ℃/min, and the load is 98mN. From the results of the TMA test, the arithmetic mean of the thermal expansion coefficients in two directions of 30 to 50 ℃ was selected as the thermal expansion coefficient Ca, and the arithmetic mean of the thermal expansion coefficients in two directions of 75 to 100 ℃ was selected as the thermal expansion coefficient Cb.

5. Coefficient of friction: the test was performed with a surface property tester. A50 mm long by 50mm wide coupon was mounted on the rubbing pair with the test side facing down. A sample piece 200mm in length and 80mm in width was mounted on the test platform with the test side facing up. The two test surfaces are in contact with each other, and the platform is pulled at a speed of 100mm/min under a load of 200g to test the dynamic friction coefficient and the static friction coefficient of the platform.

6. Adhesive strength: and testing by using a tensile testing machine. A1 inch bonded product of a film and glass was taken, a part of the film on the side of the bonded product was peeled, and then the peeled film and glass were sandwiched by a stretcher, and peeled at a speed of 300mm/min to test the adhesive strength.

7. Young's modulus: and testing by using a tensile testing machine. The film was cut into strips 150mm long and 10mm wide along the length and width directions, respectively. The two ends of the sample strip are clamped by a stretching machine, the middle 100mm is taken as a testing distance, and stretching is carried out at the speed of 200mm/min until the sample strip is broken. The Young's modulus is the arithmetic average of the three moduli in two directions, i.e., the modulus at 0.7% to 0.8%, the modulus at 0.8% to 0.9%, and the modulus at 0.9% to 1.0%, respectively.

8. Spectral transmittance: and testing by using a spectrophotometer. Cutting the sample into proper size, placing into a spectrophotometer, testing by a transmission method, and taking the transmittance at the wavelength of 355 nm.

9. Film thickness: measured after observation with a scanning electron microscope SEM. And observing the section of the processed curved shell containing the film, and measuring the thickness of the R corner of the curved surface of the decorative film and the thickness of the plane part.

Example 1

After coating the adhesive a on one side of the film A, drying at 120 ℃ for 2 minutes, attaching the release film I, and drying and curing the printing ink i at 75 ℃ for 60 minutes on the other side. And (3) thermoforming the film A at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing off the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Example 2

After coating the adhesive a on one side of the film B, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film B at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Example 3

After coating the adhesive a on one side of the film C, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film C at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Example 4

After coating an adhesive a on one side of the film D, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i printing on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film D at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, and tearing the release film I after cutting off, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Example 5

After coating the adhesive a on one side of the film E, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film E at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Example 6

After coating the adhesive a on one side of the film F, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film F at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing off the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Comparative example 1

After coating the adhesive a on one side of the film G, drying at 120 ℃ for 2 minutes, attaching a release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film G at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, and tearing the release film I after cutting off, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Comparative example 2

After coating the adhesive a on one side of the film H, drying at 120 ℃ for 2 minutes, attaching the release film I, and carrying out printing ink i on the other side, drying at 75 ℃ for 60 minutes and curing. And (3) thermoforming the film H at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, cutting off, tearing the release film I, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

Comparative example 3

After coating the adhesive a on one side of the film I, drying at 120 ℃ for 2 minutes, attaching the release film I, and drying and curing the printing ink I at 75 ℃ for 60 minutes on the other side. And (3) thermoforming the film I at 120 ℃ for 15s to prepare a curved decorative explosion-proof film with a long edge provided with an R6mm arc chamfer, and tearing the release film I after cutting off, and attaching the release film I to the inner side of the cover plate 1. After the completion of the bonding, pattern etching was performed from the case side with 355nm UV light. And observing the appearance of the attached product after finishing.

As can be seen from the above examples 1-6, the film of the present invention has no warpage during the coating process, and the subsequent process flow and production efficiency are not affected. The film a described in example 1, which did not have any warpage problem during the gumming process and the printing process, was considered to have processability. And can satisfy bending forming and laminating processes, and is considered to be suitable for plane and curved surface shells or shell protection. It also has no effect on appearance and UV photo-etching properties, and it is considered that the film has a high-quality appearance, has no effect on decorative effect, and is suitable for high-end models and overseas brands. The film B described in example 2 was considered to be unsuitable for a case or a case protection which is required to have a high appearance decoration requirement or a high attachment requirement because wrinkles occur after attachment and white spots are visible. The film C described in example 3, which had a whitish appearance on the curved surface after the curved surface was formed and had wrinkles after the lamination, was not considered suitable for the protection of the curved surface or the case with a high lamination requirement. The film D of example 4, which was not subjected to the UV photo-etching process, was considered to be unsuitable for use in high-end models or overseas brands requiring UV photo-etching patterns, although it could be used for flat and curved housings or housing protection and had a high quality appearance with decorativeness. The film E described in example 5 is warped during printing, and in actual production or mass production, the subsequent process and production efficiency are directly affected. The film F described in example 6 had a whitening phenomenon at the curved surface portion after the curved surface molding, and was considered to be unsuitable for the curved surface case or the case protection.

TABLE 1 film samples and base Properties

TABLE 2 basic Properties of Release film-attached adhesive film samples

TABLE 3 basic Properties of the bonded film and curved surface case

Table 4 comparison of the results of the examples with those of the comparative examples

Claims

1. A display back shell, characterized in that: the film is attached to the shell, and after the film is subjected to heat treatment at 150 ℃ for 30 minutes, the thermal shrinkage rate Hm in the length direction and the thermal shrinkage rate Ht in the width direction of the film satisfy the following formula 1:

| Hm-Ht | < 0% to 0.3% of formula 1,

the film has a coefficient of thermal expansion Ca at 30-50 ℃ and a coefficient of thermal expansion Cb at 75-100 ℃ that satisfy the following formula 2-formula 3:

1.0╳10 ^-5 mm/℃≦Ca≦2.0╳10 ^-5 mm/DEG C formula 2;

0.5╳10 ^-5 mm/℃≦Cb≦1.5╳10 ^-5 mm/DEG C formula 3,

the Young's modulus of the film is 3.5GPa to 4.3GPa.

2. The display back housing of claim 1, wherein: the number of foreign matters with particle size of more than 10 μm in the film is 1/mm ² The total light transmittance is 88% or more, and the haze is 2.0% or less.

3. The display back housing of claim 1, wherein: the dynamic friction coefficient mu s and the static friction coefficient mu k of the film satisfy the following formula 4-formula 5:

0.4 ≦ μ s ≦ 0.6 formula 4;

0.2. Mu. K. Ltoreq.0.4 formula 5.

4. The display back housing of claim 1, wherein: the film has an adhesive layer on at least one side, and the adhesive strength between the adhesive layer and glass is 10N/inch to 30N/inch.

5. The display back housing of claim 4, wherein: and a release film is further arranged between the adhesive layer and the film, and after the film is subjected to heat treatment at 75 ℃ for 60 minutes, the thermal shrinkage ratio Tm in the length direction and the thermal shrinkage ratio Tt in the width direction of the film satisfy the following formulas 6 to 7:

tm < 0% < 0.5% formula 6;

0% ≦ Tt ≦ 0.3% equation 7.

6. The display back housing of claim 1, wherein: the film has one or more decorative layers on at least one side, and the haze Hza when the film is stretched at a stretch ratio of 10% and the haze HZb before stretching satisfy the following formula 8:

Hza-Hzb ≦ 0.5% for formula 8.

7. The display back cover according to claim 1, wherein the film has a transmittance of 10% to 40% at a wavelength of 355 nm.

8. The display back housing of claim 1, wherein: the decorative film thickness Aa at the corner R of the curved surface of the case and the decorative film thickness Ab of the planar portion of the case satisfy the following formula 9-formula 11:

25um ≦ Aa ≦ 100um formula 9;

25um ≦ Ab ≦ 100um formula 10;

(Ab-Aa)/Ab 100 ≦ 15 formula 11.