Air permeability refers to the effect of gas on polymer materials such as films, coatings and fabricsPermeability。Is important for polymersphysical property one of.Air permeability isleather clothing, leather shoes and other leather products for wearingFasciculusDegree of dispersion, leatherPorosityAnd oiling, filling and coating performance.
suedeThe leather with heavy filling or thick coating has poor air permeability.The air permeability can be measured with an instrument, which is expressed by the amount of air that the leather sample penetrates per unit area under a certain pressure and within a certain time.
And polymer structurePhase stateandMolecular motionThe situation is relevant.for examplepolyester fibermoleculePolarityStrong, withRigid chainTherefore, its permeability is less than that of small polarityFlexible chainPolyethylene;butyl rubber Each structure contains two methyl groups,Chain segmentIt can not move freely, so its permeability ratioNatural rubberIt is dozens of times lower and is the rubber with the best air tightness.The study of polymer permeability has important practical value.It has been widely used in the preservation of fruits, vegetables, food, heat preservation and ripening of crops, packaging and storage of food and drugs, and preparation of medical materials and separation membranes.[1]
Actual application scope
It refers to the speed at which water vapor molecules penetrate the clothing layer.This movement depends on the difference in water vapor concentration (or humidity) between the skin surface and the air outside the clothing, and is also affected by the physical resistance of the fabric.The difference of moisture also depends on your exercise intensity (the greater the exercise intensity, the more sweat you will produce) and the climate environment you are in.Fabric resistance is a kind of performance of materials used in clothing and their thickness.The thicker the clothes, the stronger the resistance and the worse the permeability.[1]
Air permeability measurement method
Textile materials、textileAir permeability.It is generally expressed by the amount of air passing through the unit area of the sample in unit time under certain pressure difference conditions.
Applied knowledge in textile industry
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Breathable and waterprooftextileIt is the goal that people have been striving for. It is more necessary for modern social life. It has the ability to release sweat from the human body through the fabric to the surrounding environment, also known as excellent breathability, waterproof and wearabilityTextile materials。In the past, this kind of fabric could only be used in places with special purposes, such as flight suits, life jackets for shipwrecksProtective clothingAnd other occasions.But attention is paid to waterproofWater resistanceThe ventilation and comfort can only be reduced.With the development of modern technology, people's requirements are getting higher and higher. All kinds of sports are widely popular. They hope to have high-performance outdoorAthletic Wear、Ski shirt, fishing clothes, beautiful raincoats and rain and shine jackets, which promoted the development of breathable and waterproof fabrics, and launched various new breathable and waterproof fabrics.[1]
Development history of breathable and waterproof fabrics
Long ago, in order to prevent rain, people usedtung oil, linseed oil and other natural products, coated on cloth or paper, made of airtight oilcloth, oilpaper, waterproof, but very hard, poor durability.When rubber is found, it is made into rubberCoated fabricAlthough it is softer, it is still airtight and uncomfortable to wear.In order to solve the problem of permeability, many hydrophobic treatment agents have been invented, such as the earlyAluminium soapWaterproof agent,Paraffin emulsionWait, ordinary raincoat is usedHydrophobic agentProcessedorganosilicon , organic fluorine and other hydrophobic agents, with better performance and more extensive use.This kind of waterproof fabric is made by finishing ordinary fabric with hydrophobic agent, which is called the first type of waterproof fabric
1960shigh polymerThe emergence of industrial synthetic materials has produced many polymer coatings, such asNeoprene、Vinyl resin、polyacrylic acidCheese resin, polyamineformic acidAt the same time, the development of synthetic fiber industry also provides high strength and light weight purenylonAs the base cloth, the coated waterproof fabric is light, thin and soft. This kind of product was very popular in the market more than ten years ago.As the coating formula varies with the polymer, various additives can be added, so many varieties can give various advantages such as low temperature resistance, oil resistance, mold resistance, etcHydrophilicityMaterial and air permeability are also increased, further improving the practical performance.in recent years,high polymerGreat progress has been made in theory and synthesis technology, and ultrathin films with micropores can be madePolymer membrane, use bonding or laminating technology to combine with fabric, such asteflonThe microporous film and nylon fabric are laminated into a composite material to keep the fabric soft and light, and the fork can be breathable and waterproof. These are called the second type of waterproof fabrics.
In the early 1980s, a breathable and waterproof fabric made of high-density fabric appeared in the market. It completely keeps the natural style of fiber fabric, withoutHydrophobic agentFinishing and processing, there is no coating or film covering, so it has good hand feel, soft style and excellent wearing performance.The principle and performance of this high-density waterproof breathable fabric, which is called the third type of waterproof fabric, will be introduced in detail below.[1]
Breathable and waterproof principle
The first type is that the fabric undergoes variousHydrophobic agentEmulsion or solution impregnation, dryingpost-cure After that, a layer of hydrophobic water is formed on the surface of the fabricgene, to achieve the purpose of waterproof, which is well known.The air permeability varies slightly with different hydrophobic agents, but the water resistance is not ideal, the water resistance is low, and the washing resistance is not good.
The second type mainly uses coatings and filmsmicroporeProperties, used to be added in the coatingHydrophilicityMicro particles, porous fillers, foaming agents and other methods can generate channels for sweat and water vapor emission in the coating, but the pores generated by these methods are uneven and cannot completely block the immersion of water droplets.From polymersMicrostructureIn terms of morphology, it is found that some polymers can form row and column thin sheet structures composed of raw fibers under specific process conditions. After uniaxial tension, they can deform and form micropores between rows and columns. After heat treatment, the structure is fixed, and these micropores have a diameter of 0.2~10micron，porosityMore than 80%, which is equivalent to more than one billion micropores on a square centimeter. Since the diameter of micropores is 1/5000~1/20000 of the diameter of water droplets and about 700 times of the diameter of water vapor molecules, it can prevent water droplets from passing through, allowing water vapor molecules to pass through freely. Sweat vapor is discharged to the outside by using the temperature difference and humidity difference between the temperature inside the cloth and the outside environment.
The third type isMicrofiberProducts combined with ultra-high shrinkage technology, usingDanielOr finerSuperfine denier fiber, textileMeridional directionMore than 10000 per inchRoot fibreThere are 50000 to 60000 fibers per inch in the weft direction. The density of this kind of fabric is about 20 times that of ordinary fabric. After shrinking, the fabric isgrey60% of the area, so the ground is tightly woven, as ifSynthetic leatherThere are micro hairs on the surface, and the pores are only about 7 microns, which can play the role of air permeability and water resistance. This microfiber can bepolyester fiber, nylon and other synthetic fibers, orCotton fibreDevelopment trend of waterproof and breathable fabrics
Waterproof and breathability are a pair of mutually contradictory indicators, and we cannot absolutely put forward strict requirements for excellent waterproof and breathability.[1]
The matching and application of rigid breathable corneal contact lens
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Rigid Gas Permeable Contact Lens (RGP) is referred to as rigid lens for short. Compared with frame glasses, the corneal contact lens is used as an optical instrument to correct refractive errors. The magnification of the corneal contact lens changes less than that of the frame glasses, especially at a high degree;The field of vision of wearing contact lenses is the same as that of emmetropic eyes. There is no field of vision limitationFrame glassesCircular blind spot and circular diplopia.The aberration of corneal contact lens is less than that of frame glasses, avoiding imaging distortion. 90% corneal astigmatism can be corrected through tear lens.
Overview of RGP
1) Material properties of RGP
RGP materials are developed on the basis of PMMA (polymethyl methacrylate)Cellulose acetate butyrate, siloxane methacrylate, fluorosilicone acrylate, fluoropolymer, etc.The oxygen permeability coefficient DK of modern high oxygen permeability RGP can reach 80~140, which is enough to meet the demand of cornea for oxygen. The water content of RGP is less than 3%, and the low water content can resist sediment.The refractive index of RGP ranges from 1.40 to 1.47, and the light transmittance is more than 90%. It has good optical properties.RGP has high hardness, strong scratch resistance, and is easy to process and not easy to break.
2) RGP design
RGP design includes super polygon arc, double aspherical surface, astigmatic RGP, Rose-k design, etc.The multi arc design is suitable for patients with corneal conformal astigmatism of 2.50D and anti conformal astigmatism of 1.50D.The double aspheric design is suitable for patients with corneal astigmatism 1.00D~3.75D, and the astigmatism is mainly corneal astigmatism.The astigmatic RGP is suitable for patients with corneal astigmatism of more than 2.00D and total astigmatism of less than 10.00D. The Rose-k design is suitable for patients with corneal astigmatism of more than 2.00D and total astigmatism of less than 10.00DKeratoconuspatient.[2]
RGP matching
1) Inspection before fitting
Pre fitting inspection includes: ① consultation: understanding the wearer's wearing history, wearing purpose, general health, work nature and environment. ②Eye health examination: check the health of eyelid, cornea, conjunctiva, anterior chamber, lens, etc.
2) Refractometry
Through computer optometry or retinoscopy optometry, combined with subjective optometry test, the refractive power of the wearer can be obtained, which is helpful to the reasonable selection of RGP type and the determination of the power of RGP lenses.
3) Optometry related inspection
Optometry related examination is used to better understand the eye structure and corneal morphology of the wearer, evaluate whether the patient is suitable for wearing RGP lenses, and guide the selection of RGP diagnostic test lenses.Optometry related examinations include: corneal curvature examination, corneal diameter measurement, eye axis examination, tear film examination, corneal endothelium examination, intraocular pressure examination, etc.
4) Selection of diagnostic test pieces
Use a complete set of trial lenses, select diagnostic trial lenses with appropriate base arc and diameter according to the K value of corneal curvature, corneal astigmatism, corneal diameter and other factors of the wearer, and try them on for the wearer. After 15-20 minutes, when the lenses are in a stable state, the lens will be evaluated for fit.
5) Fitness assessment
The adaptation assessment of diagnostic test pieces includes dynamic assessment and static assessment. ①Dynamic evaluation: after wearing glasses, the lens moves up and down smoothly for 1~2mm, and the lens always completely covers the pupil, with the center positioning deviation ≤ 0.5mm. ②Static evaluation: After wearing the glasses, fluorescein staining was used, and the slit lamp cobalt blue light was used to irradiate, and the static adaptation of the lenses was observed.The ideal fit is that the lenses in the central area and the paracentral area match well with the corneal surface, the staining is uniform, there is no obvious dark area and effusion area, the marginal area is slightly raised, the staining band is about 0.4 mm wide, and the tear gap is 60 μ m~70 μ m.According to the fitting result of the test piece, adjust the parameters of the test piece to achieve the ideal fitting.
6) On film optometry
After wearing RGP, the refractive state is affected by the tear lens, so optometry on the film must be carried out to guide the determination of the final prescription focus.[2]
Clinical application of RGP
1) High myopia
Wear for high myopiaFrame glassesIt is often difficult to achieve the best visual correction effect, and RGP can also achieve satisfactory visual correction effect for these patients due to its superior optical characteristics.Li Yungeng et al. investigated and counted the results of RGP wearing in 40 cases of 74 eyes with ultra-high myopia whose equivalent spherical lens value was ≥ -10.00D, and found that 64.86% of them had the best corrected visual acuity ≥ 5.0, and 85.14% had the best corrected visual acuity ≥ 4.9 after wearing RGP.The above results prove that RGP can achieve the best visual correction effect for high and ultrahigh myopia.
2) High astigmatism
Due to the problem of the magnification of the optical lens itself, special optical defects such as enlargement or reduction of the retinal image and small field of vision are often caused. The higher the degree, the spherical aberration, cometary aberration, chromatic aberration, image distortion, etc. will be significantly increased, affecting corrected vision or comfortable visual perception.RGP forms a new optical system through tears and cornea, and plays the tear lens effect to compensate for the irregularity of the corneal surface, making the optical interface of the cornea smooth, correcting corneal astigmatism, including asymmetric astigmatism and irregular astigmatism, significantly reducing the prism effect, so as to obtain better corrected vision and contrast sensitivity, and eliminate aberrations,Improve visual quality.Liu Guohua wore RGP on 25 patients (46 eyes) with astigmatism ≥ 2.0D, aged 8-14 years old. The results showed that the correction effect of RGP was better than that of high astigmatismFrame glasses。
Clinically, keratoconus is characterized by progressive thinning of the central corneaIrregular astigmatismAnd high myopia.RGP is one of the most important treatment methods for keratoconus patients.The RGP lens with common design is suitable for patients with mild to moderate keratoconus and can control the development of the disease to a certain extent.Xie Peiying et al. observed 27 cases (54 eyes) of mild, moderate and severe keratoconus patients aged from 12 to 35 years old with computer-assisted corneal topography, subjective wavefront aberration meter and contrast sensitivity meterFrame glassesThe changes of corneal morphology and visual quality during and RGP correction.It is believed that wearing appropriate RGP can effectively eliminate corneal astigmatism, reduce aberrations, improve visual acuity and contrast sensitivity curve, and significantly improve visual quality by effectively bridging and reshaping the tear lens into a new central optical interface.[2]
