阅读说明：本技术 具备冰凉透气性的人造革及其制备方法与应用 (Artificial leather with ice-cold air permeability and preparation method and application thereof ) 是由 李彬 熊芬 张旭 付丹 谢德钰 于 2020-05-25 设计创作，主要内容包括：本发明公开了一种具备冰凉透气性的人造革及其制备方法与应用,属于汽车内饰材料技术领域。该人造革包括由下至上依次设置的基布层、PVC粘结层、PVC密实层及表处层；其中,PVC密实层包括如下质量份的各原料：聚氯乙烯:100份、增塑剂:50～70份、红外线反射助剂:4～14份、稳定剂:1～7份、色浆:2～8份,该人造革材料不仅提供足够打孔自由度,保证打孔后的较高强度,而且还具备红外线反射功能,将其应用到汽车内饰产品中,在炎热夏天使用时不至于使其表面升温过快。(The invention discloses artificial leather with ice-cold air permeability and a preparation method and application thereof, and belongs to the technical field of automotive interior materials. The artificial leather comprises a base cloth layer, a PVC bonding layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top; the PVC compact layer comprises the following raw materials in parts by mass: 100 parts of polyvinyl chloride, 50-70 parts of plasticizer, 4-14 parts of infrared reflection auxiliary agent, 1-7 parts of stabilizer and 2-8 parts of color paste, the artificial leather material not only provides enough punching freedom degree and ensures higher strength after punching, but also has an infrared reflection function, and when the artificial leather material is applied to automobile interior products, the surface of the artificial leather is not heated too fast when the artificial leather material is used in hot summer.)

1. An artificial leather having cool air permeability, characterized in that: the PVC fabric comprises a base cloth layer, a PVC bonding layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top;

the PVC dense layer comprises the following raw materials in parts by mass:

100 parts of polyvinyl chloride, 50-70 parts of plasticizer, 4-14 parts of infrared reflection auxiliary agent, 1-7 parts of stabilizer and 2-8 parts of color paste.

2. The artificial leather having cool air permeability according to claim 1, wherein: the artificial leather further comprises a PVC foaming layer positioned between the PVC bonding layer and the PVC compact layer, wherein the PVC foaming layer comprises the following raw materials in parts by mass:

100 parts of polyvinyl chloride, 60-80 parts of plasticizer, 4.8-16 parts of infrared reflection auxiliary agent, 0.5-4 parts of stabilizer, 1-10 parts of color paste, 10-20 parts of calcium carbonate filler, 5-20 parts of glass bead filler and 1-5 parts of AC foaming agent.

3. The artificial leather having cool air permeability according to claim 2, wherein: the infrared reflection auxiliary agent in the PVC foaming layer and the infrared reflection auxiliary agent in the PVC compact layer are the same and are formed by dispersing infrared reflection particles in a plasticizer DOA, and the particle size of the infrared reflection particles is 1000-1500 nm.

4. The artificial leather having cold air permeability according to claim 2 or 3, wherein: the density of the glass bead filler is 0.25-0.6 g/cm³The grain size is 2-125 μm, the compressive strength is 5-80 Mpa, and the heat conductivity coefficient is 0.0534-0.10W/m.

5. Artificial leather with cooling breathability according to claim 1, 2 or 3, characterized in that: the adhesive in the PVC bonding layer is polyvinyl chloride paste or polyurethane paste, the viscosity of the polyvinyl chloride paste is 12000-25000 cps, and the viscosity of the polyurethane paste is 8000-15000 cps.

6. The artificial leather having cool air permeability according to claim 5, wherein: the polyvinyl chloride paste is prepared by mixing polyvinyl chloride, a plasticizer and other auxiliary agents, and the polyurethane paste is prepared by mixing polyurethane resin and a solvent.

7. Artificial leather with cold air permeability according to claim 1 or 2 or 3 or 6, characterized in that: the base cloth layer is a suede-like suede layer, the suede-like suede layer is one of suede-like woven fabric, knitted fabric or non-woven fabric, and the surface density is more than or equal to 250g/m²；

The mass percent of the polyester resin in the base cloth layer is 50-70%, the mass percent of the carbamate is 30-50%, and the mass percent of the flame retardant is 2-8%.

8. A preparation method of artificial leather with ice-cold air permeability is characterized by comprising the following steps: the artificial leather comprises a base cloth layer, a PVC bonding layer, a PVC foaming layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top;

the method specifically comprises the following steps:

1) preparing PVC compact layer slurry, PVC foaming layer slurry, PVC bonding layer slurry and surface layer slurry according to a formula, and selecting base cloth and release paper;

2) coating the PVC compact layer slurry obtained in the step 1) on release paper at one time or multiple times, and controlling the drying temperature to be 165-205 ℃;

3) coating the PVC foaming layer slurry obtained in the step 1) on the surface of the product obtained in the step 2), and controlling the drying temperature to be 170-200 ℃;

4) coating the PVC bonding layer slurry obtained in the step 1) on the surface of the product obtained in the step 3), and then attaching a base fabric, wherein the drying temperature is controlled to be 190-205 ℃; then removing the release paper to obtain a semi-finished product of the artificial leather coating;

5) coating the surface layer slurry on the surface of the artificial leather coating semi-finished product obtained in the step 4) twice, and controlling the drying temperature to be 80-120 ℃; obtaining a semi-finished product of the artificial leather surface;

6) embossing and punching the semi-finished product on the surface of the artificial leather obtained in the step 5) to obtain the artificial leather with ice-cold air permeability.

9. The method for preparing artificial leather having cool air permeability according to claim 8, wherein: the PVC compact layer slurry and/or the PVC foaming layer slurry contain an infrared reflection auxiliary agent, the infrared reflection auxiliary agent is formed by dispersing infrared reflection particles in a plasticizer DOA, and the particle size of the infrared reflection particles is 1000-1500 nm.

10. An application of artificial leather with ice-cold air permeability in automobile interior decoration.

Technical Field

The invention relates to artificial leather, belongs to the technical field of automotive interior materials, and particularly relates to artificial leather with ice-cold air permeability and a preparation method and application thereof.

Background

At present, with economic development, automobile requirements are further expanded, and meanwhile, the requirements of most consumers on automobile quality and cost performance are further improved. Therefore, the competition of various large main engine plants is more and more intense, the cost reduction pressure is higher and higher, and the application of the high-performance PVC leather for replacing leather and microfiber materials on the A surface of the seat and reducing the cost becomes a trend. The PVC artificial leather material coated on the automobile seat is taken as an important visual part of an automobile, and the mechanical property, the environmental protection property and the durability of the PVC artificial leather material are widely concerned by consumers.

For automotive interior materials, it is required to have good performance indexes: mechanical property, high and low temperature aging resistance, illumination resistance, wear resistance, environmental protection, atomization property, relevant regulations and the like, wherein the wear resistance, the environmental protection property and the mechanical property residue after punching of the PVC leather for the seat surface A are currently concerned. In the existing automobile interior material market, the PVC artificial leather is widely applied to the surface of the auxiliary material area of the seat due to poor wear resistance and air permeability, and the main material area is easy to wear and break due to frequent contact with body clothes, so that the use amount is small.

Chinese invention patent application (application publication No. CN110373912A, application publication date: 2019-10-25) discloses PVC artificial leather, a preparation method thereof and an automobile seat containing the PVC artificial leather. The PVC artificial leather comprises a base cloth layer, a PVC bonding layer, a PVC foaming layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top; the PVC bonding layer is prepared from the following raw materials in parts by weight: 100 parts of polyvinyl chloride, 55-90 parts of plasticizer, 1-5 parts of calcium-zinc stabilizer and 1-3 parts of AC foaming agent. The PVC artificial leather provided by the invention not only meets the technical standard of common PVC leather, but also has the advantages of high wear resistance, environmental friendliness, high strength residue after punching and the like, and meets the increasingly strict requirements of industry environmental protection regulations.

Chinese invention patent application (application publication No. CN101624783A, application publication date: 2010-1-13) discloses highly infrared-reflective polyvinyl chloride artificial leather, and in particular relates to highly infrared-reflective polyvinyl chloride artificial leather comprising a surface layer comprising a black pigment mixture of a flower black pigment and a carbon black pigment, a foam layer comprising a white titanium dioxide pigment and a polyvinyl chloride resin, and a base layer comprising polyester fibers comprising a white titanium dioxide pigment. The surface layer of the artificial leather designed by the invention projects infrared rays, and the foam layer and the base layer reflect the infrared rays, thereby reducing the temperature rise of the artificial leather of the invention.

Chinese invention patent application (application publication No. CN107237163A, application publication date: 2017-10-10) discloses a heat-reflecting artificial leather. It comprises a surface layer, a middle layer and a bottom layer which are arranged in sequence. The surface layer is prepared from the following raw materials in parts by weight; 95-105 parts of polyurethane resin, 95-105 parts of solvent, 5-10 parts of color paste and 5-15 parts of heat reflection additive, wherein the middle layer is prepared from the following raw materials in parts by weight: 95-105 parts of polyvinyl chloride resin, 5-10 parts of color paste and 5-15 parts of heat reflection additive, wherein the bottom layer is prepared from the following raw materials in parts by weight: 95-105 parts of polyvinyl chloride resin, 135-145 parts of filler, 4-6 parts of foaming agent, 5-10 parts of color paste and 5-15 parts of heat reflection additive. The heat reflection artificial leather designed by the invention can effectively reflect infrared light in sunlight, effectively control the temperature rise speed of the leather surface and reduce the leather surface temperature.

However, the above-mentioned application documents do not disclose an artificial leather material having both an infrared reflection function and an air-permeable effect even when used in summer after being perforated. Especially in hot summer, the surface temperature rise of the existing materials such as genuine leather, artificial leather and the like is obvious after a period of sunshine irradiation. In summer, the vehicle is stopped outdoors and exposed for a period of time, the temperature in the vehicle can almost reach about 65 ℃, the leather material on the seat can almost reach the same temperature, and in order to ensure the driving comfort, the vehicle often needs to be driven to start an air conditioner for cooling for a period of time, so that the energy and the time waste are caused.

Disclosure of Invention

In order to solve the technical problems, the invention discloses artificial leather with ice-cold air permeability and a preparation method and application thereof. Wherein, this synthetic leather material not only provides enough degree of freedom that punches, guarantees the higher intensity after punching, but also possesses the infrared reflection function, uses it to the automotive interior product, is unlikely to make its surface heating up too fast when using in hot summer, uses in winter and still possesses the heat preservation effect.

In order to achieve the purpose, the invention discloses artificial leather with ice-cold air permeability, which comprises a base cloth layer, a PVC bonding layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top;

the PVC dense layer comprises the following raw materials in parts by mass:

100 parts of polyvinyl chloride, 50-70 parts of plasticizer, 4-14 parts of infrared reflection auxiliary agent, 1-7 parts of stabilizer and 2-8 parts of color paste.

Further, the synthetic leather still including being located the PVC tie coat with the PVC foaming layer between the closely knit layer of PVC, the PVC foaming layer includes each raw materials of following parts by mass:

100 parts of polyvinyl chloride, 60-80 parts of plasticizer, 4.8-16 parts of infrared reflection auxiliary agent, 0.5-4 parts of stabilizer, 1-10 parts of color paste, 10-20 parts of calcium carbonate filler, 5-20 parts of glass bead filler and 1-5 parts of AC foaming agent.

Furthermore, the infrared reflection auxiliary agent in the PVC foaming layer and the infrared reflection auxiliary agent in the PVC compact layer are the same and are formed by dispersing infrared reflection particles in a plasticizer DOA, and the particle size of the infrared reflection particles is 1000-1500 nm. The material of the infrared reflection particles is preferably titanium dioxide.

Further, the density of the glass bead filler is 0.25-0.6 g/cm³The grain size is 2-125 μm, the compressive strength is 5-80 Mpa, and the heat conductivity coefficient is 0.0534-0.10W/m.

Furthermore, the adhesive in the PVC bonding layer is polyvinyl chloride paste or polyurethane paste, the viscosity of the polyvinyl chloride paste is 12000-25000 cps, and the viscosity of the polyurethane paste is 8000-15000 cps.

Further, the polyvinyl chloride paste is prepared by mixing polyvinyl chloride, a plasticizer and other auxiliary agents, and the polyurethane paste is prepared by mixing polyurethane resin and a solvent.

Further, the base cloth layer is a suede nap layer, the suede nap layer is one of suede woven fabric, knitted fabric or non-woven fabric, and the surface density is more than or equal to 250g/m²；

The mass percent of the polyester resin in the base cloth layer is 50-70%, the mass percent of the carbamate is 30-50%, and the mass percent of the flame retardant is 2-8%.

In order to better realize the technical purpose of the invention, the invention also discloses a preparation method of the artificial leather with ice-cold air permeability, which is characterized by comprising the following steps: the artificial leather comprises a base cloth layer, a PVC bonding layer, a PVC foaming layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top;

the method specifically comprises the following steps:

1) preparing PVC compact layer slurry, PVC foaming layer slurry, PVC bonding layer slurry and surface layer slurry according to a formula, and selecting base cloth and release paper;

2) coating the PVC compact layer slurry obtained in the step 1) on release paper at one time or multiple times, and controlling the drying temperature to be 165-205 ℃;

3) coating the PVC foaming layer slurry obtained in the step 1) on the surface of the product obtained in the step 2), and controlling the drying temperature to be 170-200 ℃;

4) coating the PVC bonding layer slurry obtained in the step 1) on the surface of the product obtained in the step 3), and then attaching a base fabric, wherein the drying temperature is controlled to be 190-205 ℃; then removing the release paper to obtain a semi-finished product of the artificial leather coating;

5) coating the surface layer slurry on the surface of the artificial leather coating semi-finished product obtained in the step 4) twice, and controlling the drying temperature to be 80-120 ℃; obtaining a semi-finished product of the artificial leather surface;

6) embossing and punching the semi-finished product on the surface of the artificial leather obtained in the step 5) to obtain the artificial leather with ice-cold air permeability.

Further, the PVC compact layer slurry and/or the PVC foaming layer slurry contain an infrared reflection aid, the infrared reflection aid is formed by dispersing infrared reflection particles in a plasticizer DOA, and the particle size of the infrared reflection particles is 1000-1500 nm. In addition, the invention also discloses application of the artificial leather with ice-cold air permeability in automobile interior ornaments. In particular for applications such as car seats.

Has the advantages that:

1. the artificial leather material designed by the invention has the advantages that the base cloth layer adopts the suede nap layer, the suede nap layer has high punching freedom degree, high strength and good ventilation effect after punching can be ensured, and meanwhile, the suede nap layer also has acid resistance, alkali resistance, wear resistance and certain flame retardant property.

2. The artificial leather material designed by the invention has the infrared reflection function due to the synergistic effect of the infrared reflection auxiliary agent and the glass bead filler, cannot cause quick temperature rise when used in summer, has a certain heat preservation effect when used in winter, is applied to automotive interior products, and is favorable for ensuring the driving comfort.

3. The preparation method designed by the invention has simple process and is convenient to popularize.

Drawings

FIG. 1 is a schematic structural diagram of an artificial leather material designed according to an embodiment of the present invention;

FIG. 2 is a flow chart of the manufacturing process of the present invention.

FIG. 3 is a distribution diagram of each sample piece in a surface temperature rise test according to an embodiment of the present invention.

Wherein the reference numbers in the above figures are as follows:

the PVC base fabric comprises a base fabric layer 1, a PVC bonding layer 2, a PVC foaming layer 3, a PVC dense layer 4 and a surface layer 5.

Detailed Description

The invention discloses artificial leather with ice-cold air permeability, which structurally comprises a base cloth layer, a PVC bonding layer, a PVC compact layer and a surface layer which are sequentially arranged from bottom to top; or as shown in the attached figure 1 of the specification, the artificial leather structure can further comprise a base cloth layer 1, a PVC bonding layer 2, a PVC foaming layer 3, a PVC compact layer 4 and a surface layer 5 which are sequentially arranged from bottom to top.

The thickness of each layer is not particularly limited, and the invention only needs to ensure the smooth proceeding of the preparation process and the performance of the product.

The raw materials and the formula composition of each layer are as follows:

the base cloth layer is suede layer, which can be suede woven fabric, knitted fabric or non-woven fabric, and has surface density of 250g/m or more²The suede nap layer comprises the following components in percentage by mass: 50-70% of carbamate: 30-50%, flame retardant: 2-8%; this imitative chamois leather fine hair layer not only possesses the high degree of freedom that punches, still possesses higher intensity and better ventilation effect after can guaranteeing to punch, and this imitative chamois leather fine hair layer still possesses acidproof, alkali-proof, wear-resisting and certain flame retardant property simultaneously.

The PVC compact layer comprises the following raw materials in parts by mass:

100 parts of polyvinyl chloride, 50-70 parts of plasticizer, 4-14 parts of infrared reflection auxiliary agent, 1-7 parts of stabilizer and 2-8 parts of color paste. The infrared reflection auxiliary agent has good compatibility with polyvinyl chloride, and the compatibility among the components in the infrared reflection auxiliary agent is also good, so that the stability is good even after long-term use, and the infrared reflection auxiliary agent can not be influenced to play the infrared reflection function.

Meanwhile, the polyvinyl chloride is preferably polyvinyl chloride powder, and the K value of the polyvinyl chloride powder is 65-80.

The plasticizer is o-benzene plasticizer, and specifically comprises one or more of DINP, DPHP, DOA, 911 and 124.

The stabilizer is calcium-zinc stabilizer.

The color paste is a common color paste, and the invention is not specially limited for explanation.

The PVC foaming layer comprises the following raw materials in parts by mass:

100 parts of polyvinyl chloride, 60-80 parts of plasticizer, 4.8-16 parts of infrared reflection auxiliary agent, 0.5-4 parts of stabilizer, 1-10 parts of color paste, 10-20 parts of calcium carbonate filler, 5-20 parts of glass bead filler and 1-5 parts of AC foaming agent;

the infrared reflection auxiliary agent and the polyvinyl chloride have good compatibility. And because the PVC foaming layer and the PVC compact layer are added with different amounts of infrared reflection aids, when sunlight irradiates the surface of the material, infrared rays in light are reflected by the PVC compact layer and the PVC foaming layer in sequence, so that the temperature rising effect of the material is not obvious, and the material can still show a cool effect when being used in summer.

Furthermore, the infrared reflection auxiliary agent in the PVC foaming layer and the infrared reflection auxiliary agent in the PVC compact layer are the same and are formed by dispersing infrared reflection particles in a plasticizer DOA, and the particle size of the infrared reflection particles is 1000-1500 nm. The material of the infrared reflection particles is preferably titanium dioxide. The titanium dioxide with the granularity forms a stably dispersed auxiliary agent in the plasticizer, and the auxiliary agent can be stably dispersed in the polyvinyl chloride, so that the infrared reflection function of the polyvinyl chloride is well exerted.

Meanwhile, the K value of the polyvinyl chloride is 55-70.

The plasticizer is o-benzene plasticizer, and specifically comprises one or more of DINP, DPHP, DOA, 911 and 124.

The stabilizer is calcium-zinc stabilizer.

The color paste is a common color paste, and the invention is not specially limited for explanation.

The density of the glass bead filler is 0.25-0.6 g/cm³The grain size is 2-125 μm, the compressive strength is 5-80 Mpa, and the heat conductivity coefficient is 0.0534-0.10W/m. According to the invention, a certain amount of glass beads with the physicochemical characteristics are used as fillers instead of calcium carbonate, so that the strength of the material is ensured, and meanwhile, as the glass beads are internally provided with hollow layers and externally provided with spherical shapes, the glass beads not only have a certain infrared ray reflection function together with an infrared ray reflection auxiliary agent, but also have extremely low heat conductivity, can reflect infrared rays in summer, and can have a certain heat preservation effect in winter.

In addition, the PVC tie layer consists essentially of an adhesive, which may be a polyvinyl chloride paste or a polyurethane-based paste; the polyvinyl chloride paste consists of the following components in parts by mass: 100 parts of polyvinyl chloride, 55-90 parts of plasticizer and 1-8 parts of other additives, wherein the K value of the polyvinyl chloride is 55-75; mixing the components, stirring for 10-15 minutes, and controlling the viscosity to be 12000-25000 cps to obtain the polyvinyl chloride paste.

The polyurethane paste comprises the following components in parts by mass:

100 parts of polyurethane resin and 20-70 parts of solvent, wherein the solvent is preferably toluene, the components are uniformly mixed and stirred for 30 minutes, and the viscosity is controlled to be 8000-15000 cps.

For the surface treatment layer, the surface treatment layer comprises the following raw materials in parts by mass:

100 parts of waterborne polyurethane polyester, 6-12 parts of a bridging agent and 1-10 parts of other auxiliary agents, wherein the waterborne polyurethane polyester is polycarbonate, the solid content is 20-35%, and the bridging agent is polycarbodiimide PCDI; the other auxiliary agents comprise a thickening agent, a defoaming agent, a leveling agent, a slipping agent and the like, and the thickening agent, the defoaming agent, the leveling agent and the slipping agent are all commonly used in the field, and the invention is not particularly limited.

In addition, the invention also discloses a preparation method of the artificial leather with ice-cold air permeability, wherein the artificial leather comprises a base cloth layer 1, a PVC bonding layer 2, a PVC foaming layer 3, a PVC compact layer 4 and a surface layer 5 which are sequentially arranged from bottom to top as shown in figure 1; the whole process is shown in figure 2;

the method specifically comprises the following steps:

1) preparing PVC compact layer slurry, PVC foaming layer slurry, PVC bonding layer slurry and surface layer slurry according to a formula, and selecting base cloth and release paper;

the PVC compact layer slurry is prepared by mixing the above components in proportion, then conveying the mixture to an internal mixer for mixing and plasticizing, and conveying the mixture to a coating and scraping station for later use after open mixing and filtering.

The PVC foaming layer slurry is prepared by mixing the above formula in proportion, then conveying the mixture to an internal mixer for mixing and plasticizing, and conveying the mixture to a coating and scraping station for later use through open mixing and filtering.

The PVC bonding layer slurry is prepared by mixing the components according to the formula proportion.

The surface layer slurry is prepared by mixing the components according to the formula proportion.

2) Coating the PVC compact layer slurry obtained in the step 1) on release paper at one time or multiple times, and controlling the drying temperature to be 165-205 ℃;

specifically, when one-time coating is adopted, the baking temperature is controlled to be 180-205 ℃, and compared with a multiple-time coating mode, the baking time is properly prolonged.

When the second coating is adopted, the baking temperature is controlled to be 165-195 ℃ after the first coating, the polyvinyl chloride surface layer I is formed after drying, the surface of the polyvinyl chloride surface layer I is continuously coated, the baking temperature is controlled to be 165-195 ℃, and the polyvinyl chloride surface layer II is formed after drying.

The coating method has the advantages of being convenient to operate by adopting one-time coating, and the coating method is favorable for ensuring the uniformity of the coating layer and exerting the synergistic effect of each component by adopting secondary coating.

3) Coating the PVC foaming layer slurry obtained in the step 1) on the surface of the product obtained in the step 2), and controlling the drying temperature to be 170-200 ℃; and preparing the PVC foaming layer.

4) Coating the PVC bonding layer slurry obtained in the step 1) on the surface of the product obtained in the step 3), and then attaching a base fabric, wherein the drying temperature is controlled to be 190-205 ℃; then removing the release paper to obtain a semi-finished product of the artificial leather coating;

5) coating the surface layer slurry on the surface of the artificial leather coating semi-finished product obtained in the step 4) twice, and controlling the drying temperature to be 80-120 ℃; obtaining a semi-finished product of the artificial leather surface; specifically, roller coating the surface layer slurry on the surface of the artificial leather coating semi-finished product obtained in the step 4) by using a roller, controlling the temperature to be 80-120 ℃, and drying for 30 seconds to form a water-based adhesive layer on the surface of the semi-finished product; and (3) continuously and uniformly coating the surface layer slurry on the surface of the water-based adhesive layer by adopting a roller, controlling the temperature to be 80-120 ℃, and drying for 2 minutes to obtain the semi-finished product of the artificial leather surface.

6) Embossing and punching the semi-finished product on the surface of the artificial leather obtained in the step 5) to obtain the artificial leather with ice-cold air permeability. Specifically, the color, pattern and hand feeling requirements of the finished product need to be met during embossing. When punching, the holes are punched according to the hole diameter of 0.8mm or 1.0mm or 1.1mm or 1.2mm and the pitch of the holes is 5mm multiplied by 5mm or 6mm multiplied by 6mm or 7mm multiplied by 7 mm.

In order to better explain the present invention, the following detailed description is given in conjunction with specific examples.